diff --git a/README b/README index 9d74139..d95f459 100644 --- a/README +++ b/README @@ -11,736 +11,746 @@ https://github.com/LibVNC/libvncserver/commit/498d222976975f53dea885cfe43ef0f805 Copyright (C) 2002-2010 Karl J. Runge All rights reserved. -x11vnc README file Date: Mon Dec 27 20:58:57 EST 2010 - -The following information is taken from these URLs: - - http://www.karlrunge.com/x11vnc/index.html - http://www.karlrunge.com/x11vnc/x11vnc_opts.html - ... - -they contain the most up to date info. - - -http://www.karlrunge.com/x11vnc/index.html: - # x11vnc: a VNC server for real X displays - x11vnc allows one to view remotely and interact with real X displays - (i.e. a display corresponding to a physical monitor, keyboard, and - mouse) with any VNC viewer. In this way it plays the role for Unix/X11 - that WinVNC plays for Windows. - - It has built-in SSL/TLS encryption and 2048 bit RSA authentication, - including VeNCrypt support; UNIX account and password login support; - server-side scaling; single port HTTPS/HTTP+VNC; Zeroconf service - advertising; and TightVNC and UltraVNC file-transfer. It has also been - extended to work with non-X devices: natively on Mac OS X Aqua/Quartz, - webcams and TV tuner capture devices, and embedded Linux systems such - as Qtopia Core. Full IPv6 support is provided. More features are - described here. - - It also provides an encrypted Terminal Services mode (-create, -svc, - or -xdmsvc options) based on Unix usernames and Unix passwords where - the user does not need to memorize his VNC display/port number. - Normally a virtual X session (Xvfb) is created for each user, but it - also works with X sessions on physical hardware. See the tsvnc - terminal services mode of the SSVNC viewer for one way to take - advantage of this mode. - - I wrote x11vnc back in 2002 because x0rfbserver was basically - impossible to build on Solaris and had poor performance. The primary - x0rfbserver build problems centered around esoteric C++ toolkits. - x11vnc is written in plain C and needs only standard libraries and so - should work on nearly all Unixes, even very old ones. I also created - enhancements to improve the interactive response, added many features, - and etc. - - This page including the FAQ contains much information [*]; solutions - to many problems; and interesting applications, but nevertheless - please feel free to contact me if you have problems or questions (and - if I save you time or expense by giving you some of my time, please - consider a PayPal Donation.) Do check the FAQ and this page first; I - realize the pages are massive, but you can often use your browser's - find-in-page search action using a keyword to find the answer to your - problem or question. - - SSVNC: An x11vnc side-project provides an Enhanced TightVNC Viewer - package (SSVNC) for Unix, Windows, and Mac OS X with automatic SSL - and/or SSH tunnelling support, SSL Certificate creation, Saved - connection profiles, Zeroconf, VeNCrypt, and built-in Proxy support. - Added features for the TightVNC Unix viewer: NewFBSize, ZRLE encoding, - Viewer-side Scaling, cursor alphablending, low color modes, and - enhanced popup menu; UltraVNC extensions support for: File Transfer, - Text Chat, Single Window, Server Input, and 1/n Scaling extensions, - and UltraVNC DSM encryption. The SSVNC bundle could be placed on, say, - a USB memory stick for SSL/SSH VNC viewing from nearly any networked - computer. - - -# Announcements: - - Important: If you created any permanent SSL certificates (e.g. via - "x11vnc -ssl SAVE ...") on a Debian or Ubuntu system from Sept. 2006 - through May 2008, then those keys are likely extremely weak and can be - easily cracked. The certificate files should be deleted and recreated - on a non-Debian system or an updated one. See - http://www.debian.org/security/2008/dsa-1571 for details. The same - applies to SSH keys (not used by x11vnc directly, but many people use - SSH tunnels for VNC access.) - - FAQ moved: The huge FAQ has finally been moved to its own page. If you - are trying to follow someone's link to an FAQ once on this page it is - now a broken link. Try inserting the string "faq.html", e.g.: -from: http://www.karlrunge.com/x11vnc/#faq-singleclick -to: http://www.karlrunge.com/x11vnc/faq.html#faq-singleclick - - Apologies for the inconvenience, unfortunately it is not possible to - automatically redirect to the new page since the '#' anchor is not - sent to the webserver. - - -# Background: - - VNC (Virtual Network Computing) is a very useful network graphics - protocol (applications running on one computer but displaying their - windows on another) in the spirit of X, however, unlike X, the - viewing-end is very simple and maintains no state. It is a remote - framebuffer (RFB) protocol. - - Some VNC links: - - * http://www.realvnc.com - * http://www.tightvnc.com - * http://www.ultravnc.com/ - * http://www.testplant.com/products/vine_server/OS_X - - For Unix, the traditional VNC implementation includes a "virtual" X11 - server Xvnc (usually launched via the vncserver command) that is not - associated with a physical display, but provides a "fake" one X11 - clients (xterm, firefox, etc.) can attach to. A remote user then - connects to Xvnc via the VNC client vncviewer from anywhere on the - network to view and interact with the whole virtual X11 desktop. - - The VNC protocol is in most cases better suited for remote connections - with low bandwidth and high latency than is the X11 protocol because - it involves far fewer "roundtrips" (an exception is the cached pixmap - data on the viewing-end provided by X.) Also, with no state maintained - the viewing-end can crash, be rebooted, or relocated and the - applications and desktop continue running. Not so with X11. - - So the standard Xvnc/vncserver program is very useful, I use it for - things like: - - * Desktop conferencing with other users (e.g. code reviews.) - * Long running apps/tasks I want to be able to view from many places - (e.g. from home and work.) - * Motif, GNOME, and similar applications that would yield very poor - performance over a high latency link. - - However, sometimes one wants to connect to a real X11 display (i.e. - one attached to a physical monitor, keyboard, and mouse: a Workstation - or a SunRay session) from far away. Maybe you want to close down an - application cleanly rather than using kill, or want to work a bit in - an already running application, or would like to help a distant - colleague solve a problem with their desktop, or would just like to - work out on the deck for a while. This is where x11vnc is useful. - -# How to use x11vnc: - - In this basic example let's assume the remote machine with the X - display you wish to view is "far-away.east:0" and the workstation you - are presently working at is "sitting-here.west". - - Step 0. Download x11vnc (see below) and have it available to run on - far-away.east (on some linux distros it is as easy as "apt-get install - x11vnc", "emerge x11vnc", etc.) Similarly, have a VNC viewer (e.g. - vncviewer) ready to run on sitting-here.west. We recommend TightVNC - Viewers (see also our SSVNC viewer.) - - Step 1. By some means log in to far-away.east and get a command shell - running there. You can use ssh, or even rlogin, telnet, or any other - method to do this. We do this because the x11vnc process needs to be - run on the same machine the X server process is running on (otherwise - things would be extremely slow.) - - Step 2. In that far-away.east shell (with command prompt "far-away>" - in this example) run x11vnc directed at the far-away.east X session - display: - - ``` - far-away> x11vnc -display :0 - ``` - - You could have also set the environment variable DISPLAY=:0 instead of - using "-display :0". This step attaches x11vnc to the far-away.east:0 - X display (i.e. no viewer clients yet.) - - Common Gotcha: To get X11 permissions right, you may also need to set - the XAUTHORITY environment variable (or use the -auth option) to point - to the correct MIT-MAGIC-COOKIE file (e.g. /home/joe/.Xauthority.) If - x11vnc does not have the authority to connect to the display it exits - immediately. More on how to fix this below. - - If you suspect an X11 permissions problem do this simple test: while - sitting at the physical X display open a terminal window - (gnome-terminal, xterm, etc.) You should be able to run x11vnc - successfully in that terminal without any need for command line - options. If that works OK then you know X11 permissions are the only - thing preventing it from working when you try to start x11vnc via a - remote shell. Then fix this with the tips below. - - Note as of Feb/2007 you can also try the -find option instead of - "-display ..." and see if that finds your display and Xauthority. Note - as of Dec/2009 the -findauth and "-auth guess" options may be helpful - as well. - (End of Common Gotcha) - - When x11vnc starts up there will then be much chatter printed out (use - "-q" to quiet it), until it finally says something like: - - ``` - . - . - 13/05/2004 14:59:54 Autoprobing selected port 5900 - 13/05/2004 14:59:54 screen setup finished. - 13/05/2004 14:59:54 - 13/05/2004 14:59:54 The VNC desktop is far-away:0 - PORT=5900 - ``` - - which means all is OK, and we are ready for the final step. - - Step 3. At the place where you are sitting (sitting-here.west in this - example) you now want to run a VNC viewer program. There are VNC - viewers for Unix, Windows, MacOS, Java-enabled web browsers, and even - for PDA's like the Palm Pilot and Cell Phones! You can use any of them - to connect to x11vnc (see the above VNC links under "Background:" on - how to obtain a viewer for your platform or see this FAQ. For Solaris, - vncviewer is available in the Companion CD package SFWvnc.) - - In this example we'll use the Unix vncviewer program on sitting-here - by typing the following command in a second terminal window: - - ``` - sitting-here> vncviewer far-away.east:0 - ``` - - That should pop up a viewer window on sitting-here.west showing and - allowing interaction with the far-away.east:0 X11 desktop. Pretty - nifty! When finished, exit the viewer: the remote x11vnc process will - shutdown automatically (or you can use the -forever option to have it - wait for additional viewer connections.) - - Common Gotcha: Nowadays there will likely be a host-level firewall on - the x11vnc side that is blocking remote access to the VNC port (e.g. - 5900.) You will either have to open up that port (or a range of ports) - in your firewall administration tool, or try the SSH tunnelling method - below (even still the firewall must allow in the SSH port, 22.) - - - Shortcut: Of course if you left x11vnc running on far-away.east:0 in a - terminal window with the -forever option or as a service, you'd only - have to do Step 3 as you moved around. Be sure to use a VNC Password - or other measures if you do that. - - - Super Shortcut: Here is a potentially very easy way to get all of it - working. - - * Have x11vnc (0.9.3 or later) available to run on the remote host - (i.e. in $PATH.) - * Download and unpack a SSVNC bundle (1.0.19 or later, e.g. - ssvnc_no_windows-1.0.28.tar.gz) on the Viewer-side machine. - * Start the SSVNC Terminal Services mode GUI: ./ssvnc/bin/tsvnc - * Enter your remote username@hostname (e.g. fred@far-away.east) in - the "VNC Terminal Server" entry. - * Click "Connect". - - That will do an SSH to username@hostname and start up x11vnc and then - connect a VNC Viewer through the SSH encrypted tunnel. - - There are a number of things assumed here, first that you are able to - SSH into the remote host; i.e. that you have a Unix account there and - the SSH server is running. On Unix and MacOS X it is assumed that the - ssh client command is available on the local machine (on Windows a - plink binary is included in the SSVNC bundle.) Finally, it is assumed - that you are already logged into an X session on the remote machine, - e.g. your workstation (otherwise, a virtual X server, e.g. Xvfb, will - be started for you.) - - In some cases the remote SSH server will not run commands with the - same $PATH that you normally have in your shell there. In this case - click on Options -> Advanced -> X11VNC Options, and type in the - location of the x11vnc binary under "Full Path". (End of Super - Shortcut) - - - Desktop Sharing: The above more or less assumed nobody was sitting at - the workstation display "far-away.east:0". This is often the case: a - user wants to access her workstation remotely. Another usage pattern - has the user sitting at "far-away.east:0" and invites one or more - other people to view and interact with his desktop. Perhaps the user - gives a demo or presentation this way (using the telephone for vocal - communication.) A "Remote Help Desk" mode would be similar: a - technician connects remotely to the user's desktop to interactively - solve a problem the user is having. - - For these cases it should be obvious how it is done. The above steps - will work, but more easily the user sitting at far-away.east:0 simply - starts up x11vnc from a terminal window, after which the guests would - start their VNC viewers. For this usage mode the "-connect - host1,host2" option may be of use to automatically connect to the - vncviewers in "-listen" mode on the list of hosts. - -# Tunnelling x11vnc via SSH: - - The above example had no security or privacy at all. When logging into - remote machines (certainly when going over the internet) it is best to - use ssh, or use a VPN (for a VPN, Virtual Private Network, the above - example should be pretty safe.) - - For x11vnc one can tunnel the VNC protocol through an encrypted ssh - channel. It would look something like running the following commands: - - ``` - sitting-here> ssh -t -L 5900:localhost:5900 far-away.east 'x11vnc -localhost --display :0' - ``` - - (you will likely have to provide passwords/passphrases to login from - sitting-here into your far-away.east Unix account; we assume you have - a login account on far-away.east and it is running the SSH server) - - And then in another terminal window on sitting-here run the command: - - ``` - sitting-here> vncviewer -encodings "copyrect tight zrle hextile" localhost:0 - ``` - - Note: The -encodings option is very important: vncviewer will often - default to "raw" encoding if it thinks the connection is to the local - machine, and so vncviewer gets tricked this way by the ssh - redirection. "raw" encoding will be extremely slow over a networked - link, so you need to force the issue with -encodings "copyrect tight - ...". Nowadays, not all viewers use the -encodings option, try - "-PreferredEncoding=ZRLE" (although the newer viewers seem to - autodetect well when to use raw or not.) - - Note that "x11vnc -localhost ..." limits incoming vncviewer - connections to only those from the same machine. This is very natural - for ssh tunnelling (the redirection appears to come from the same - machine.) Use of a VNC password is also strongly recommended. - - Note also the -t we used above (force allocate pseudoterminal), it - actually seems to improve interactive typing response via VNC! - - You may want to add the -C option to ssh to enable compression. The - VNC compression is not perfect, and so this may help a bit. However, - over a fast LAN you probably don't want to enable SSH compression - because it can slow things down. Try both and see which is faster. - - If your username is different on the remote machine use something - like: "fred@far-away.east" in the above ssh command line. - - Some VNC viewers will do the ssh tunnelling for you automatically, the - TightVNC Unix vncviewer does this when the "-via far-away.east" option - is supplied to it (this requires x11vnc to be already running on - far-away.east or having it started by inetd(8).) See the 3rd script - example below for more info. - - SSVNC: You may also want to look at the Enhanced TightVNC Viewer - (ssvnc) bundles because they contain scripts and GUIs to automatically - set up SSH tunnels (e.g. the GUI, "ssvnc", does it automatically and - so does this command: "ssvnc_cmd -ssh user@far-away.east:0") and can - even start up x11vnc as well. - - The Terminal Services mode of SSVNC is perhaps the easiest way to use - x11vnc. You just need to have x11vnc available in $PATH on the remote - side (and can SSH to the host), and then on the viewer-side you type - something like: - - ``` - tsvnc fred@far-away.east - ``` - - everything else is done automatically for you. Normally this will - start a virtual Terminal Services X session (RAM-only), but if you - already have a real X session up on the physical hardware it will find - that one for you. - - Gateways: If the machine you SSH into is not the same machine with - the X display you wish to view (e.g. your company provides incoming - SSH access to a gateway machine), then you need to change the above - to, e.g.: "-L 5900:OtherHost:5900": - - ``` - sitting-here> ssh -t -L 5900:OtherHost:5900 gateway.east - ``` - - Where gateway.east is the internet hostname (or IP) of the gateway - machine (SSH server.) 'OtherHost' might be, e.g., freds-pc or - 192.168.2.33 (it is OK for these to be private hostnames or private IP - addresses, the host in -L is relative to the remote server side.) - - Once logged in, you'll need to do a second login (ssh, rsh, etc.) to - the workstation machine 'OtherHost' and then start up x11vnc on it (if - it isn't already running.) (The "-connect gateway:59xx" option may be - another alternative here with the viewer already in -listen mode.) For - an automatic way to use a gateway and have all the network traffic - encrypted (including inside the firewall) see Chaining SSH's. - - These gateway access modes also can be done automatically for you via - the "Proxy/Gateway" setting in SSVNC (including the Chaining SSH's - case, "Double Proxy".) - - Firewalls/Routers: - - A lot of people have inexpensive devices for home or office that act - as a Firewall and Router to the machines inside on a private LAN. One - can usually configure the Firewall/Router from inside the LAN via a - web browser. - - Often having a Firewall/Router sitting between the vncviewer and - x11vnc will make it impossible for the viewer to connect to x11vnc. - - One thing that can be done is to redirect a port on the - Firewall/Router to, say, the SSH port (22) on an inside machine (how - to do this depends on your particular Firewall/Router, often the - router config URL is http://192.168.100.1 See www.portforward.com for - more info.) This way you reach these computers from anywhere on the - Internet and use x11vnc to view X sessions running on them. - - Suppose you configured the Firewall/Router to redirect these ports to - two internal machines: - - ``` - Port 12300 -> 192.168.1.3, Port 22 (SSH) - Port 12301 -> 192.168.1.4, Port 22 (SSH) - - (where 192.168.1.3 is "jills-pc" and 192.168.1.4 is "freds-pc".) Then - the ssh's would look something like: - sitting-here> ssh -t -p 12300 -L 5900:localhost:5900 jill@far-away.east 'x11v -nc -localhost -display :0' - sitting-here> ssh -t -p 12301 -L 5900:localhost:5900 fred@far-away.east 'x11v -nc -localhost -display :0' - ``` - - Where far-away.east means the hostname (or IP) that the - Router/Firewall is using (for home setups this is usually the IP - gotten from your ISP via DHCP, the site http://www.whatismyip.com/ is - a convenient way to determine what it is.) - - It is a good idea to add some obscurity to accessing your system via - SSH by using some high random port (e.g. 12300 in the above example.) - If you can't remember it, or are otherwise not worried about port - scanners detecting the presence of your SSH server and there is just - one internal PC involved you could map 22: - - ``` - Port 22 -> 192.168.1.3, Port 22 (SSH) - ``` - - Again, this SSH gateway access can be done automatically for you via - the "Proxy/Gateway" setting in SSVNC. And under the "Remote SSH - Command" setting you can enter the x11vnc -localhost -display :0. - - Host-Level-Firewalls: even with the hardware Firewall/Router problem - solved via a port redirection, most PC systems have their own Host - level "firewalls" enabled to protect users from themselves. I.e. the - system itself blocks all incoming connections. So you will need to see - what is needed to configure it to allow in the port (e.g. 22) that you - desire. E.g. Yast, Firestarter, iptables(1), etc.. - - VNC Ports and Firewalls: The above discussion was for configuring the - Firewall/Router to let in port 22 (SSH), but the same thing can be - done for the default VNC port 5900: - - ``` - Port 5900 -> 192.168.1.3, Port 5900 (VNC) - Port 5901 -> 192.168.1.4, Port 5900 (VNC) - ``` - - (where 192.168.1.3 is "jills-pc" and 192.168.1.4 is "freds-pc".) This - could be used for normal, unencrypted connections and also for SSL - encrypted ones. - - The VNC displays to enter in the VNC viewer would be, say, - "far-away.east:0" to reach jills-pc and "far-away.east:1" to reach - freds-pc. We assume above that x11vnc is using port 5900 (and any - Host-Level-firewalls on jills-pc has been configured to let that port - in.) Use the "-rfbport" option to tell which port x11vnc should listen - on. - - For a home system one likely does not have a hostname and would have - to use the IP address, say, "24.56.78.93:0". E.g.: - - ``` - vncviewer 24.56.78.93:0 - ``` - - You may want to choose a more obscure port on the router side, e.g. - 5944, to avoid a lot of port scans finding your VNC server. For 5944 - you would tell the viewer to use: - - ``` - vncviewer 24.56.78.93:44 - ``` - - The IP address would need to be communicated to the person running the - VNC Viewer. The site http://www.whatismyip.com/ can help here. - - - Scripts to automate ssh tunneling: As discussed below, there may be - some problems with port 5900 being available. If that happens, the - above port and display numbers may change a bit (e.g. -> 5901 and :1). - However, if you "know" port 5900 will be free on the local and remote - machines, you can easily automate the above two steps by using the - x11vnc option -bg (forks into background after connection to the - display is set up) or using the -f option of ssh. Some example scripts - are shown below. Feel free to try the ssh -C to enable its compression - and see if that speeds things up noticeably. - - #1. A simple example script, assuming no problems with port 5900 being - taken on the local or remote sides, looks like: - ``` +x11vnc allows one to view remotely and interact with real X displays +(i.e. a display corresponding to a physical monitor, keyboard, and +mouse) with any VNC viewer. In this way it plays the role for Unix/X11 +that WinVNC plays for Windows. + +It has built-in SSL/TLS encryption and 2048 bit RSA authentication, +including VeNCrypt support; UNIX account and password login support; +server-side scaling; single port HTTPS/HTTP+VNC; Zeroconf service +advertising; and TightVNC and UltraVNC file-transfer. It has also been +extended to work with non-X devices: natively on Mac OS X Aqua/Quartz, +webcams and TV tuner capture devices, and embedded Linux systems such +as Qtopia Core. Full IPv6 support is provided. More features are +described here. + +It also provides an encrypted Terminal Services mode (-create, -svc, +or -xdmsvc options) based on Unix usernames and Unix passwords where +the user does not need to memorize his VNC display/port number. +Normally a virtual X session (Xvfb) is created for each user, but it +also works with X sessions on physical hardware. See the tsvnc +terminal services mode of the SSVNC viewer for one way to take +advantage of this mode. + +I wrote x11vnc back in 2002 because x0rfbserver was basically +impossible to build on Solaris and had poor performance. The primary +x0rfbserver build problems centered around esoteric C++ toolkits. +x11vnc is written in plain C and needs only standard libraries and so +should work on nearly all Unixes, even very old ones. I also created +enhancements to improve the interactive response, added many features, +and etc. + +This page including the FAQ contains much information [*]; solutions +to many problems; and interesting applications, but nevertheless +please feel free to contact me if you have problems or questions (and +if I save you time or expense by giving you some of my time, please +consider a PayPal Donation.) Do check the FAQ and this page first; I +realize the pages are massive, but you can often use your browser's +find-in-page search action using a keyword to find the answer to your +problem or question. + +SSVNC: An x11vnc side-project provides an Enhanced TightVNC Viewer +package (SSVNC) for Unix, Windows, and Mac OS X with automatic SSL +and/or SSH tunnelling support, SSL Certificate creation, Saved +connection profiles, Zeroconf, VeNCrypt, and built-in Proxy support. +Added features for the TightVNC Unix viewer: NewFBSize, ZRLE encoding, +Viewer-side Scaling, cursor alphablending, low color modes, and +enhanced popup menu; UltraVNC extensions support for: File Transfer, +Text Chat, Single Window, Server Input, and 1/n Scaling extensions, +and UltraVNC DSM encryption. The SSVNC bundle could be placed on, say, +a USB memory stick for SSL/SSH VNC viewing from nearly any networked +computer. + + +# Announcements + +Important: If you created any permanent SSL certificates (e.g. via +"x11vnc -ssl SAVE ...") on a Debian or Ubuntu system from Sept. 2006 +through May 2008, then those keys are likely extremely weak and can be +easily cracked. The certificate files should be deleted and recreated +on a non-Debian system or an updated one. See +http://www.debian.org/security/2008/dsa-1571 for details. The same +applies to SSH keys (not used by x11vnc directly, but many people use +SSH tunnels for VNC access.) + +# News + +See [NEWS](NEWS) + +# Frequently Asked Questions (FAQs) + +See [FAQ.md](doc/FAQ.md) + + +# Background + +VNC (Virtual Network Computing) is a very useful network graphics +protocol (applications running on one computer but displaying their +windows on another) in the spirit of X, however, unlike X, the +viewing-end is very simple and maintains no state. It is a remote +framebuffer (RFB) protocol. + +Some VNC links: + +* http://www.realvnc.com +* http://www.tightvnc.com +* http://www.ultravnc.com/ +* http://www.testplant.com/products/vine_server/OS_X + +For Unix, the traditional VNC implementation includes a "virtual" X11 +server Xvnc (usually launched via the vncserver command) that is not +associated with a physical display, but provides a "fake" one X11 +clients (xterm, firefox, etc.) can attach to. A remote user then +connects to Xvnc via the VNC client vncviewer from anywhere on the +network to view and interact with the whole virtual X11 desktop. + +The VNC protocol is in most cases better suited for remote connections +with low bandwidth and high latency than is the X11 protocol because +it involves far fewer "roundtrips" (an exception is the cached pixmap +data on the viewing-end provided by X.) Also, with no state maintained +the viewing-end can crash, be rebooted, or relocated and the +applications and desktop continue running. Not so with X11. + +So the standard Xvnc/vncserver program is very useful, I use it for +things like: + +* Desktop conferencing with other users (e.g. code reviews.) +* Long running apps/tasks I want to be able to view from many places + (e.g. from home and work.) +* Motif, GNOME, and similar applications that would yield very poor + performance over a high latency link. + +However, sometimes one wants to connect to a real X11 display (i.e. +one attached to a physical monitor, keyboard, and mouse: a Workstation +or a SunRay session) from far away. Maybe you want to close down an +application cleanly rather than using kill, or want to work a bit in +an already running application, or would like to help a distant +colleague solve a problem with their desktop, or would just like to +work out on the deck for a while. This is where x11vnc is useful. + +# How to use x11vnc + +In this basic example let's assume the remote machine with the X +display you wish to view is "far-away.east:0" and the workstation you +are presently working at is "sitting-here.west". + +Step 0. Download x11vnc (see below) and have it available to run on +far-away.east (on some linux distros it is as easy as "apt-get install +x11vnc", "emerge x11vnc", etc.) Similarly, have a VNC viewer (e.g. +vncviewer) ready to run on sitting-here.west. We recommend TightVNC +Viewers (see also our SSVNC viewer.) + +Step 1. By some means log in to far-away.east and get a command shell +running there. You can use ssh, or even rlogin, telnet, or any other +method to do this. We do this because the x11vnc process needs to be +run on the same machine the X server process is running on (otherwise +things would be extremely slow.) + +Step 2. In that far-away.east shell (with command prompt "far-away>" +in this example) run x11vnc directed at the far-away.east X session +display: + +``` +far-away> x11vnc -display :0 +``` + +You could have also set the environment variable DISPLAY=:0 instead of +using "-display :0". This step attaches x11vnc to the far-away.east:0 +X display (i.e. no viewer clients yet.) + +Common Gotcha: To get X11 permissions right, you may also need to set +the XAUTHORITY environment variable (or use the -auth option) to point +to the correct MIT-MAGIC-COOKIE file (e.g. /home/joe/.Xauthority.) If +x11vnc does not have the authority to connect to the display it exits +immediately. More on how to fix this below. + +If you suspect an X11 permissions problem do this simple test: while +sitting at the physical X display open a terminal window +(gnome-terminal, xterm, etc.) You should be able to run x11vnc +successfully in that terminal without any need for command line +options. If that works OK then you know X11 permissions are the only +thing preventing it from working when you try to start x11vnc via a +remote shell. Then fix this with the tips below. + +Note as of Feb/2007 you can also try the -find option instead of +"-display ..." and see if that finds your display and Xauthority. Note +as of Dec/2009 the -findauth and "-auth guess" options may be helpful +as well. +(End of Common Gotcha) + +When x11vnc starts up there will then be much chatter printed out (use +"-q" to quiet it), until it finally says something like: + +``` +. +. +13/05/2004 14:59:54 Autoprobing selected port 5900 +13/05/2004 14:59:54 screen setup finished. +13/05/2004 14:59:54 +13/05/2004 14:59:54 The VNC desktop is far-away:0 +PORT=5900 +``` + +which means all is OK, and we are ready for the final step. + +Step 3. At the place where you are sitting (sitting-here.west in this +example) you now want to run a VNC viewer program. There are VNC +viewers for Unix, Windows, MacOS, Java-enabled web browsers, and even +for PDA's like the Palm Pilot and Cell Phones! You can use any of them +to connect to x11vnc (see the above VNC links under "Background:" on +how to obtain a viewer for your platform or see this FAQ. For Solaris, +vncviewer is available in the Companion CD package SFWvnc.) + +In this example we'll use the Unix vncviewer program on sitting-here +by typing the following command in a second terminal window: + +``` +sitting-here> vncviewer far-away.east:0 +``` + +That should pop up a viewer window on sitting-here.west showing and +allowing interaction with the far-away.east:0 X11 desktop. Pretty +nifty! When finished, exit the viewer: the remote x11vnc process will +shutdown automatically (or you can use the -forever option to have it +wait for additional viewer connections.) + +Common Gotcha: Nowadays there will likely be a host-level firewall on +the x11vnc side that is blocking remote access to the VNC port (e.g. +5900.) You will either have to open up that port (or a range of ports) +in your firewall administration tool, or try the SSH tunnelling method +below (even still the firewall must allow in the SSH port, 22.) + +Shortcut: Of course if you left x11vnc running on far-away.east:0 in a +terminal window with the -forever option or as a service, you'd only +have to do Step 3 as you moved around. Be sure to use a VNC Password +or other measures if you do that. + +Super Shortcut: Here is a potentially very easy way to get all of it +working. + +* Have x11vnc (0.9.3 or later) available to run on the remote host + (i.e. in $PATH.) +* Download and unpack a SSVNC bundle (1.0.19 or later, e.g. + ssvnc_no_windows-1.0.28.tar.gz) on the Viewer-side machine. +* Start the SSVNC Terminal Services mode GUI: ./ssvnc/bin/tsvnc +* Enter your remote username@hostname (e.g. fred@far-away.east) in + the "VNC Terminal Server" entry. +* Click "Connect". + +That will do an SSH to username@hostname and start up x11vnc and then +connect a VNC Viewer through the SSH encrypted tunnel. + +There are a number of things assumed here, first that you are able to +SSH into the remote host; i.e. that you have a Unix account there and +the SSH server is running. On Unix and MacOS X it is assumed that the +ssh client command is available on the local machine (on Windows a +plink binary is included in the SSVNC bundle.) Finally, it is assumed +that you are already logged into an X session on the remote machine, +e.g. your workstation (otherwise, a virtual X server, e.g. Xvfb, will +be started for you.) + +In some cases the remote SSH server will not run commands with the +same $PATH that you normally have in your shell there. In this case +click on Options -> Advanced -> X11VNC Options, and type in the +location of the x11vnc binary under "Full Path". (End of Super +Shortcut) + +Desktop Sharing: The above more or less assumed nobody was sitting at +the workstation display "far-away.east:0". This is often the case: a +user wants to access her workstation remotely. Another usage pattern +has the user sitting at "far-away.east:0" and invites one or more +other people to view and interact with his desktop. Perhaps the user +gives a demo or presentation this way (using the telephone for vocal +communication.) A "Remote Help Desk" mode would be similar: a +technician connects remotely to the user's desktop to interactively +solve a problem the user is having. + +For these cases it should be obvious how it is done. The above steps +will work, but more easily the user sitting at far-away.east:0 simply +starts up x11vnc from a terminal window, after which the guests would +start their VNC viewers. For this usage mode the "-connect +host1,host2" option may be of use to automatically connect to the +vncviewers in "-listen" mode on the list of hosts. + +## Tunnelling x11vnc via SSH + +The above example had no security or privacy at all. When logging into +remote machines (certainly when going over the internet) it is best to +use ssh, or use a VPN (for a VPN, Virtual Private Network, the above +example should be pretty safe.) + +For x11vnc one can tunnel the VNC protocol through an encrypted ssh +channel. It would look something like running the following commands: + +``` +sitting-here> ssh -t -L 5900:localhost:5900 far-away.east 'x11vnc -localhost -display :0' +``` + +(you will likely have to provide passwords/passphrases to login from +sitting-here into your far-away.east Unix account; we assume you have +a login account on far-away.east and it is running the SSH server) + +And then in another terminal window on sitting-here run the command: + +``` +sitting-here> vncviewer -encodings "copyrect tight zrle hextile" localhost:0 +``` + +Note: The -encodings option is very important: vncviewer will often +default to "raw" encoding if it thinks the connection is to the local +machine, and so vncviewer gets tricked this way by the ssh +redirection. "raw" encoding will be extremely slow over a networked +link, so you need to force the issue with -encodings "copyrect tight +...". Nowadays, not all viewers use the -encodings option, try +"-PreferredEncoding=ZRLE" (although the newer viewers seem to +autodetect well when to use raw or not.) + +Note that "x11vnc -localhost ..." limits incoming vncviewer +connections to only those from the same machine. This is very natural +for ssh tunnelling (the redirection appears to come from the same +machine.) Use of a VNC password is also strongly recommended. + +Note also the -t we used above (force allocate pseudoterminal), it +actually seems to improve interactive typing response via VNC! + +You may want to add the -C option to ssh to enable compression. The +VNC compression is not perfect, and so this may help a bit. However, +over a fast LAN you probably don't want to enable SSH compression +because it can slow things down. Try both and see which is faster. + +If your username is different on the remote machine use something +like: "fred@far-away.east" in the above ssh command line. + +Some VNC viewers will do the ssh tunnelling for you automatically, the +TightVNC Unix vncviewer does this when the "-via far-away.east" option +is supplied to it (this requires x11vnc to be already running on +far-away.east or having it started by inetd(8).) See the 3rd script +example below for more info. + +SSVNC: You may also want to look at the Enhanced TightVNC Viewer +(ssvnc) bundles because they contain scripts and GUIs to automatically +set up SSH tunnels (e.g. the GUI, "ssvnc", does it automatically and +so does this command: "ssvnc_cmd -ssh user@far-away.east:0") and can +even start up x11vnc as well. + +The Terminal Services mode of SSVNC is perhaps the easiest way to use +x11vnc. You just need to have x11vnc available in $PATH on the remote +side (and can SSH to the host), and then on the viewer-side you type +something like: + +``` +tsvnc fred@far-away.east +``` + +everything else is done automatically for you. Normally this will +start a virtual Terminal Services X session (RAM-only), but if you +already have a real X session up on the physical hardware it will find +that one for you. + +Gateways: If the machine you SSH into is not the same machine with +the X display you wish to view (e.g. your company provides incoming +SSH access to a gateway machine), then you need to change the above +to, e.g.: "-L 5900:OtherHost:5900": + +``` +sitting-here> ssh -t -L 5900:OtherHost:5900 gateway.east +``` + +Where gateway.east is the internet hostname (or IP) of the gateway +machine (SSH server.) 'OtherHost' might be, e.g., freds-pc or +192.168.2.33 (it is OK for these to be private hostnames or private IP +addresses, the host in -L is relative to the remote server side.) + +Once logged in, you'll need to do a second login (ssh, rsh, etc.) to +the workstation machine 'OtherHost' and then start up x11vnc on it (if +it isn't already running.) (The "-connect gateway:59xx" option may be +another alternative here with the viewer already in -listen mode.) For +an automatic way to use a gateway and have all the network traffic +encrypted (including inside the firewall) see Chaining SSH's. + +These gateway access modes also can be done automatically for you via +the "Proxy/Gateway" setting in SSVNC (including the Chaining SSH's +case, "Double Proxy".) + +## Chaining SSH's + +Note that for use of a ssh gateway and -L redirection +to an internal host (e.g. "-L 5900:otherhost:5900") the VNC traffic +inside the firewall is not encrypted and you have to manually log into +otherhost to start x11vnc. Kyle Amon shows a method where you chain +two ssh's together that encrypts all network traffic and also +automatically starts up x11vnc on the internal workstation: + +``` #!/bin/sh -# usage: x11vnc_ssh : -# e.g.: x11vnc_ssh snoopy.peanuts.com:0 -# (user@host:N also works) - -host=`echo $1 | awk -F: '{print $1}'` -disp=`echo $1 | awk -F: '{print $2}'` -if [ "x$disp" = "x" ]; then disp=0; fi - -cmd="x11vnc -display :$disp -localhost -rfbauth .vnc/passwd" -enc="copyrect tight zrle hextile zlib corre rre raw" +# +gateway="example.com" # or "user@example.com" +host="labyrinth" # or "user@hostname" +user="kyle" -ssh -f -t -L 5900:localhost:5900 $host "$cmd" +# Need to sleep long enough for all of the passwords and x11vnc to start up. +# The /dev/null) & -for i in 1 2 3 -do +# Chain the vnc connection thru 2 ssh's, and connect x11vnc to user's display: +# +exec /usr/bin/ssh -t -L 5900:localhost:5900 $gateway \ + /usr/bin/ssh -t -L 5900:localhost:5900 $host \ + sudo /usr/bin/x11vnc -localhost -auth /home/$user/.Xauthority \ + -rfbauth .vnc/passwd -display :0 +``` + +Also note the use of sudo(1) to switch to root so that the different +user's .Xauthority file can be accessed. See the visudo(8) manpage for +details on how to set this up (remove the sudo if you do not want to +do this). One can also chain together ssh's for reverse connections +with vncviewers using the -listen option. For this case -R would +replace the -L (and 5500 the 5900, see the #2 example script above). +If the gateway machine's sshd is configured with GatewayPorts=no (the +default) then the double chaining of "ssh -R ..." will be required for +reverse connections to work. + +## Firewalls/Routers + +A lot of people have inexpensive devices for home or office that act +as a Firewall and Router to the machines inside on a private LAN. One +can usually configure the Firewall/Router from inside the LAN via a +web browser. + +Often having a Firewall/Router sitting between the vncviewer and +x11vnc will make it impossible for the viewer to connect to x11vnc. + +One thing that can be done is to redirect a port on the +Firewall/Router to, say, the SSH port (22) on an inside machine (how +to do this depends on your particular Firewall/Router, often the +router config URL is http://192.168.100.1 See www.portforward.com for +more info.) This way you reach these computers from anywhere on the +Internet and use x11vnc to view X sessions running on them. + +Suppose you configured the Firewall/Router to redirect these ports to +two internal machines: + +``` +Port 12300 -> 192.168.1.3, Port 22 (SSH) +Port 12301 -> 192.168.1.4, Port 22 (SSH) + +(where 192.168.1.3 is "jills-pc" and 192.168.1.4 is "freds-pc".) Then the ssh's would look something like: +sitting-here> ssh -t -p 12300 -L 5900:localhost:5900 jill@far-away.east 'x11v nc -localhost -display :0' +sitting-here> ssh -t -p 12301 -L 5900:localhost:5900 fred@far-away.east 'x11v nc -localhost -display :0' +``` + +Where far-away.east means the hostname (or IP) that the +Router/Firewall is using (for home setups this is usually the IP +gotten from your ISP via DHCP, the site http://www.whatismyip.com/ is +a convenient way to determine what it is.) + +It is a good idea to add some obscurity to accessing your system via +SSH by using some high random port (e.g. 12300 in the above example.) +If you can't remember it, or are otherwise not worried about port +scanners detecting the presence of your SSH server and there is just +one internal PC involved you could map 22: + +``` +Port 22 -> 192.168.1.3, Port 22 (SSH) +``` + +Again, this SSH gateway access can be done automatically for you via +the "Proxy/Gateway" setting in SSVNC. And under the "Remote SSH +Command" setting you can enter the x11vnc -localhost -display :0. + +Host-Level-Firewalls: even with the hardware Firewall/Router problem +solved via a port redirection, most PC systems have their own Host +level "firewalls" enabled to protect users from themselves. I.e. the +system itself blocks all incoming connections. So you will need to see +what is needed to configure it to allow in the port (e.g. 22) that you +desire. E.g. Yast, Firestarter, iptables(1), etc.. + +VNC Ports and Firewalls: The above discussion was for configuring the +Firewall/Router to let in port 22 (SSH), but the same thing can be +done for the default VNC port 5900: + +``` +Port 5900 -> 192.168.1.3, Port 5900 (VNC) +Port 5901 -> 192.168.1.4, Port 5900 (VNC) +``` + +(where 192.168.1.3 is "jills-pc" and 192.168.1.4 is "freds-pc".) This +could be used for normal, unencrypted connections and also for SSL +encrypted ones. + +The VNC displays to enter in the VNC viewer would be, say, +"far-away.east:0" to reach jills-pc and "far-away.east:1" to reach +freds-pc. We assume above that x11vnc is using port 5900 (and any +Host-Level-firewalls on jills-pc has been configured to let that port +in.) Use the "-rfbport" option to tell which port x11vnc should listen +on. + +For a home system one likely does not have a hostname and would have +to use the IP address, say, "24.56.78.93:0". E.g.: + +``` +vncviewer 24.56.78.93:0 +``` + +You may want to choose a more obscure port on the router side, e.g. +5944, to avoid a lot of port scans finding your VNC server. For 5944 +you would tell the viewer to use: + +``` +vncviewer 24.56.78.93:44 +``` + +The IP address would need to be communicated to the person running the +VNC Viewer. The site http://www.whatismyip.com/ can help here. + +Scripts to automate ssh tunneling: As discussed below, there may be +some problems with port 5900 being available. If that happens, the +above port and display numbers may change a bit (e.g. -> 5901 and :1). +However, if you "know" port 5900 will be free on the local and remote +machines, you can easily automate the above two steps by using the +x11vnc option -bg (forks into background after connection to the +display is set up) or using the -f option of ssh. Some example scripts +are shown below. Feel free to try the ssh -C to enable its compression +and see if that speeds things up noticeably. + +1. A simple example script, assuming no problems with port 5900 being +taken on the local or remote sides, looks like: + + ``` + #!/bin/sh + # usage: x11vnc_ssh : + # e.g.: x11vnc_ssh snoopy.peanuts.com:0 + # (user@host:N also works) + + host=`echo $1 | awk -F: '{print $1}'` + disp=`echo $1 | awk -F: '{print $2}'` + if [ "x$disp" = "x" ]; then disp=0; fi + + cmd="x11vnc -display :$disp -localhost -rfbauth .vnc/passwd" + enc="copyrect tight zrle hextile zlib corre rre raw" + + ssh -f -t -L 5900:localhost:5900 $host "$cmd" + + for i in 1 2 3 + do sleep 2 if vncviewer -encodings "$enc" :0; then break; fi -done - ``` - - See also rx11vnc.pl below. - - #2. Another method is to start the VNC viewer in listen mode - "vncviewer -listen" and have x11vnc initiate a reverse connection - using the -connect option: - - ``` -#!/bin/sh -# usage: x11vnc_ssh : -# e.g.: x11vnc_ssh snoopy.peanuts.com:0 -# (user@host:N also works) - -host=`echo $1 | awk -F: '{print $1}'` -disp=`echo $1 | awk -F: '{print $2}'` -if [ "x$disp" = "x" ]; then disp=0; fi - -cmd="x11vnc -display :$disp -localhost -connect localhost" # <== note new opt -ion -enc="copyrect tight zrle hextile zlib corre rre raw" - -vncviewer -encodings "$enc" -listen & -pid=$! -ssh -t -R 5500:localhost:5500 $host "$cmd" -kill $pid - ``` - - Note the use of the ssh option "-R" instead of "-L" to set up a remote - port redirection. - - #3. A third way is specific to the TightVNC vncviewer special option - -via for gateways. The only tricky part is we need to start up x11vnc - and give it some time (5 seconds in this example) to start listening - for connections (so we cannot use the TightVNC default setting for - VNC_VIA_CMD): - - ``` -#!/bin/sh -# usage: x11vnc_ssh : -# e.g.: x11vnc_ssh snoopy.peanuts.com:0 - -host=`echo $1 | awk -F: '{print $1}'` -disp=`echo $1 | awk -F: '{print $2}'` -if [ "x$disp" = "x" ]; then disp=0; fi - -VNC_VIA_CMD="ssh -f -t -L %L:%H:%R %G x11vnc -localhost -rfbport 5900 -display -:$disp; sleep 5" -export VNC_VIA_CMD - -vncviewer -via $host localhost:0 # must be TightVNC vncviewer. - ``` - - Of course if you already have the x11vnc running waiting for - connections (or have it started out of inetd(8)), you can simply use - the TightVNC "vncviewer -via gateway host:port" in its default mode to - provide secure ssh tunnelling. - - - - VNC password file: Also note in the #1. example script that the option - "-rfbauth .vnc/passwd" provides additional protection by requiring a - VNC password for every VNC viewer that connects. The vncpasswd or - storepasswd programs, or the x11vnc -storepasswd option can be used to - create the password file. x11vnc also has the slightly less secure - -passwdfile and "-passwd XXXXX" options to specify passwords. - - Very Important: It is up to YOU to tell x11vnc to use password - protection (-rfbauth or -passwdfile), it will NOT do it for you - automatically or force you to (use -usepw if you want to be forced - to.) The same goes for encrypting the channel between the viewer and - x11vnc: it is up to you to use ssh, stunnel, -ssl mode, a VPN, etc. - (use the Enhanced TightVNC Viewer (SSVNC) GUI if you want to be forced - to use SSL or SSH.) For additional safety, also look into the -allow - and -localhost options and building x11vnc with tcp_wrappers support - to limit host access. - - -# Tunnelling x11vnc via SSL/TLS: - - One can also encrypt the VNC traffic using an SSL/TLS tunnel such as - stunnel.mirt.net (also stunnel.org) or using the built-in (Mar/2006) - -ssl openssl mode. A SSL-enabled Java applet VNC Viewer is also - provided in the x11vnc package (and https can be used to download it.) - - Although not as ubiquitous as ssh, SSL tunnelling still provides a - useful alternative. See this FAQ on -ssl and -stunnel modes for - details and examples. - - The Enhanced TightVNC Viewer (SSVNC) bundles contain some convenient - utilities to automatically set up an SSL tunnel from the viewer-side - (i.e. to connect to "x11vnc -ssl ...".) And many other enhancements - too. - -# Downloading x11vnc: - - x11vnc is a contributed program to the LibVNCServer project at - SourceForge.net. I use libvncserver for all of the VNC aspects; I - couldn't have done without it. The full source code may be found and - downloaded (either file-release tarball or GIT tree) from the above - link. As of Sep 2010, the x11vnc-0.9.12.tar.gz source package is - released (recommended download). The x11vnc 0.9.12 release notes. - - The x11vnc package is the subset of the libvncserver package needed to - build the x11vnc program. Also, you can get a copy of my latest, - bleeding edge x11vnc-0.9.13-dev.tar.gz tarball to build the most up to - date one. - - Precompiled Binaries/Packages: See the FAQ below for information - about where you might obtain a precompiled x11vnc binary from 3rd - parties and some ones I create. - - VNC Viewers: To obtain VNC viewers for the viewing side (Windows, Mac - OS, or Unix) try these links: - - * http://www.tightvnc.com/download.html - * http://www.realvnc.com/download-free.html - * http://sourceforge.net/projects/cotvnc/ - * http://www.ultravnc.com/ - * Our Enhanced TightVNC Viewer (SSVNC) - - [ssvnc.gif] - - - More tools: Here is a ssh/rsh wrapper script rx11vnc that attempts to - automatically do the above Steps 1-3 for you (provided you have - ssh/rsh login permission on the machine x11vnc is to be run on.) The - above example would be: "rx11vnc far-away.east:0" typed into a shell - on sitting-here.west. Also included is an experimental script - rx11vnc.pl that attempts to tunnel the vnc traffic through an ssh port - redirection (and does not assume port 5900 is free.) Have a look at - them to see what they do and customize as needed: - - * rx11vnc wrapper script - * rx11vnc.pl wrapper script to tunnel traffic thru ssh + done + ``` + + See also rx11vnc.pl below. + +2. Another method is to start the VNC viewer in listen mode +"vncviewer -listen" and have x11vnc initiate a reverse connection +using the -connect option: + + ``` + #!/bin/sh + # usage: x11vnc_ssh : + # e.g.: x11vnc_ssh snoopy.peanuts.com:0 + # (user@host:N also works) + + host=`echo $1 | awk -F: '{print $1}'` + disp=`echo $1 | awk -F: '{print $2}'` + if [ "x$disp" = "x" ]; then disp=0; fi + + cmd="x11vnc -display :$disp -localhost -connect localhost" # <== note new option + enc="copyrect tight zrle hextile zlib corre rre raw" + + vncviewer -encodings "$enc" -listen & + pid=$! + ssh -t -R 5500:localhost:5500 $host "$cmd" + kill $pid + ``` + + Note the use of the ssh option "-R" instead of "-L" to set up a remote + port redirection. + +3. A third way is specific to the TightVNC vncviewer special option +-via for gateways. The only tricky part is we need to start up x11vnc +and give it some time (5 seconds in this example) to start listening +for connections (so we cannot use the TightVNC default setting for +VNC_VIA_CMD): + + ``` + #!/bin/sh + # usage: x11vnc_ssh : + # e.g.: x11vnc_ssh snoopy.peanuts.com:0 + + host=`echo $1 | awk -F: '{print $1}'` + disp=`echo $1 | awk -F: '{print $2}'` + if [ "x$disp" = "x" ]; then disp=0; fi + + VNC_VIA_CMD="ssh -f -t -L %L:%H:%R %G x11vnc -localhost -rfbport 5900 -display + :$disp; sleep 5" + export VNC_VIA_CMD + + vncviewer -via $host localhost:0 # must be TightVNC vncviewer. + ``` + + Of course if you already have the x11vnc running waiting for + connections (or have it started out of inetd(8)), you can simply use + the TightVNC "vncviewer -via gateway host:port" in its default mode to + provide secure ssh tunnelling. + +VNC password file: Also note in the #1. example script that the option +"-rfbauth .vnc/passwd" provides additional protection by requiring a +VNC password for every VNC viewer that connects. The vncpasswd or +storepasswd programs, or the x11vnc -storepasswd option can be used to +create the password file. x11vnc also has the slightly less secure +-passwdfile and "-passwd XXXXX" options to specify passwords. + +Very Important: It is up to YOU to tell x11vnc to use password +protection (-rfbauth or -passwdfile), it will NOT do it for you +automatically or force you to (use -usepw if you want to be forced +to.) The same goes for encrypting the channel between the viewer and +x11vnc: it is up to you to use ssh, stunnel, -ssl mode, a VPN, etc. +(use the Enhanced TightVNC Viewer (SSVNC) GUI if you want to be forced +to use SSL or SSH.) For additional safety, also look into the -allow +and -localhost options and building x11vnc with tcp_wrappers support +to limit host access. + + +## Tunnelling x11vnc via SSL/TLS + +One can also encrypt the VNC traffic using an SSL/TLS tunnel such as +stunnel.mirt.net (also stunnel.org) or using the built-in (Mar/2006) +-ssl openssl mode. A SSL-enabled Java applet VNC Viewer is also +provided in the x11vnc package (and https can be used to download it.) + +Although not as ubiquitous as ssh, SSL tunnelling still provides a +useful alternative. See this FAQ on -ssl and -stunnel modes for +details and examples. + +The Enhanced TightVNC Viewer (SSVNC) bundles contain some convenient +utilities to automatically set up an SSL tunnel from the viewer-side +(i.e. to connect to "x11vnc -ssl ...".) And many other enhancements +too. + +# Downloading x11vnc + +x11vnc is a contributed program to the LibVNCServer project at +SourceForge.net. I use libvncserver for all of the VNC aspects; I +couldn't have done without it. The full source code may be found and +downloaded (either file-release tarball or GIT tree) from the above +link. As of Sep 2010, the x11vnc-0.9.12.tar.gz source package is +released (recommended download). The x11vnc 0.9.12 release notes. + +The x11vnc package is the subset of the libvncserver package needed to +build the x11vnc program. Also, you can get a copy of my latest, +bleeding edge x11vnc-0.9.13-dev.tar.gz tarball to build the most up to +date one. + +Precompiled Binaries/Packages: See the FAQ below for information +about where you might obtain a precompiled x11vnc binary from 3rd +parties and some ones I create. + +VNC Viewers: To obtain VNC viewers for the viewing side (Windows, Mac +OS, or Unix) try these links: + +* http://www.tightvnc.com/download.html +* http://www.realvnc.com/download-free.html +* http://sourceforge.net/projects/cotvnc/ +* http://www.ultravnc.com/ +* Our Enhanced TightVNC Viewer (SSVNC)[ssvnc.gif] +More tools: Here is a ssh/rsh wrapper script rx11vnc that attempts to +automatically do the above Steps 1-3 for you (provided you have +ssh/rsh login permission on the machine x11vnc is to be run on.) The +above example would be: "rx11vnc far-away.east:0" typed into a shell +on sitting-here.west. Also included is an experimental script +rx11vnc.pl that attempts to tunnel the vnc traffic through an ssh port +redirection (and does not assume port 5900 is free.) Have a look at +them to see what they do and customize as needed: -# Building x11vnc: +* rx11vnc wrapper script +* rx11vnc.pl wrapper script to tunnel traffic thru ssh - Make sure you have all the needed build/compile/development packages - installed. On a Debian-based distro you can simply do - ``` - sudo apt-get build-dep x11vnc - ``` +# Building x11vnc + +Make sure you have all the needed build/compile/development packages +installed. On a Debian-based distro you can simply do - to install most of them. +``` +sudo apt-get build-dep x11vnc +``` - To generate the build system, do a +to install most of them. - ``` - autoreconf -fiv - ``` +To generate the build system, do a - After that, it's the usual +``` +autoreconf -fiv +``` - ``` - ./configure - make - ``` +After that, it's the usual - You might want to take a look at the dfferent configure options - provided by `configure --help` to build without X11 or adapt the - build to your needs in other ways. - - Building on Solaris, FreeBSD, etc: Depending on your version of - Solaris or other Unix OS the jpeg and/or zlib libraries may be in - non-standard places (e.g. /usr/local, /usr/sfw, /opt/sfw, etc.) +``` +./configure +make +``` - Note: If configure cannot find these two libraries then TightVNC and - ZRLE encoding support will be disabled, and you don't want that!!! The - TightVNC encoding gives very good compression and performance, it even - makes a noticeable difference over a fast LAN. +You might want to take a look at the dfferent configure options +provided by `configure --help` to build without X11 or adapt the +build to your needs in other ways. +## Building on Solaris, FreeBSD, etc - Shortcuts: On Solaris 10 you can pick up almost everything just by - insuring that your PATH has /usr/sfw/bin (for gcc) and /usr/ccs/bin - (for other build tools), e.g.: +Depending on your version of +Solaris or other Unix OS the jpeg and/or zlib libraries may be in +non-standard places (e.g. /usr/local, /usr/sfw, /opt/sfw, etc.) - ``` - env PATH=/usr/sfw/bin:/usr/ccs/bin:$PATH sh -c './configure; make' - ``` +Note: If configure cannot find these two libraries then TightVNC and +ZRLE encoding support will be disabled, and you don't want that!!! The +TightVNC encoding gives very good compression and performance, it even +makes a noticeable difference over a fast LAN. - (The only thing this misses is /usr/X11/lib/libXrandr.so.2, which is - for the little used -xrandr option, see the script below to pick it up - as well.) +Shortcuts: On Solaris 10 you can pick up almost everything just by +insuring that your PATH has /usr/sfw/bin (for gcc) and /usr/ccs/bin +(for other build tools), e.g.: +``` +env PATH=/usr/sfw/bin:/usr/ccs/bin:$PATH sh -c './configure; make' +``` - libjpeg is included in Solaris 9 and later (/usr/sfw/include and - /usr/sfw/lib), and zlib in Solaris 8 and later (/usr/include and - /usr/lib.) So on Solaris 9 you can pick up everything with something - like this: +(The only thing this misses is /usr/X11/lib/libXrandr.so.2, which is +for the little used -xrandr option, see the script below to pick it up +as well.) - ``` - env PATH=/usr/local/bin:/usr/ccs/bin:$PATH sh -c './configure --with-jpeg=/us -r/sfw; make' - ``` - assuming your gcc is in /usr/local/bin and x11vnc 0.7.1 or later. - These are getting pretty long, see those assignments split up in the - build script below. +libjpeg is included in Solaris 9 and later (/usr/sfw/include and +/usr/sfw/lib), and zlib in Solaris 8 and later (/usr/include and +/usr/lib.) So on Solaris 9 you can pick up everything with something +like this: +``` +env PATH=/usr/local/bin:/usr/ccs/bin:$PATH sh -c './configure --with-jpeg=/usr/sfw; make' +``` - If your system does not have these libraries at all you can get the - source for the libraries to build them: libjpeg is available at - ftp://ftp.uu.net/graphics/jpeg/ and zlib at http://www.gzip.org/zlib/. - See also http://www.sunfreeware.com/ for Solaris binary packages of - these libraries as well as for gcc. Normally they will install into - /usr/local but you can install them anywhere with the - --prefix=/path/to/anywhere, etc. +assuming your gcc is in /usr/local/bin and x11vnc 0.7.1 or later. +These are getting pretty long, see those assignments split up in the +build script below. +If your system does not have these libraries at all you can get the +source for the libraries to build them: libjpeg is available at +ftp://ftp.uu.net/graphics/jpeg/ and zlib at http://www.gzip.org/zlib/. +See also http://www.sunfreeware.com/ for Solaris binary packages of +these libraries as well as for gcc. Normally they will install into +/usr/local but you can install them anywhere with the +--prefix=/path/to/anywhere, etc. - Here is a build script that indicates one way to pass the library - locations information to the libvncserver configuration via the - CPPFLAGS and LDFLAGS environment variables. +Here is a build script that indicates one way to pass the library +locations information to the libvncserver configuration via the +CPPFLAGS and LDFLAGS environment variables. - ``` +``` #!/bin/sh # Build script for Solaris, etc, with gcc, libjpeg and libz in @@ -780,17557 +790,468 @@ export PATH CPPFLAGS LDFLAGS make ls -l ./x11vnc/x11vnc - ``` +``` - Then do make install or copy the x11vnc binary to your desired - destination. +Then do make install or copy the x11vnc binary to your desired +destination. - BTW, To run a shell script, just cut-and-paste the above into a file, - say "myscript", then modify the "/path/to/..." items to correspond to - your system/environment, and then type: "sh myscript" to run it. +BTW, To run a shell script, just cut-and-paste the above into a file, +say "myscript", then modify the "/path/to/..." items to correspond to +your system/environment, and then type: "sh myscript" to run it. - Note that on Solaris make is /usr/ccs/bin/make, so that is why the - above puts /usr/ccs/bin in PATH. Other important build utilities are - there too: ld, ar, etc. Also, it is probably a bad idea to have - /usr/ucb in your PATH while building. +Note that on Solaris make is /usr/ccs/bin/make, so that is why the +above puts /usr/ccs/bin in PATH. Other important build utilities are +there too: ld, ar, etc. Also, it is probably a bad idea to have +/usr/ucb in your PATH while building. - Starting with the 0.7.1 x11vnc release the "configure --with-jpeg=DIR - --with-zlib=DIR" options are handy if you want to avoid making a - script. +Starting with the 0.7.1 x11vnc release the "configure --with-jpeg=DIR +--with-zlib=DIR" options are handy if you want to avoid making a +script. - If you need to link OpenSSL libssl.a on Solaris see this method. +If you need to link OpenSSL libssl.a on Solaris see this method. - If you need to build on Solaris 2.5.1 or earlier or other older Unix - OS's, see this workaround FAQ. +If you need to build on Solaris 2.5.1 or earlier or other older Unix +OS's, see this workaround FAQ. +## Building on FreeBSD, OpenBSD, ... - Building on FreeBSD, OpenBSD, ...: The jpeg libraries seem to be in - /usr/local or /usr/pkg on these OS's. You won't need the openwin stuff - in the above script (but you may need /usr/X11R6/....) Also starting - with the 0.7.1 x11vnc release, this usually works: +The jpeg libraries seem to be in +/usr/local or /usr/pkg on these OS's. You won't need the openwin stuff +in the above script (but you may need /usr/X11R6/....) Also starting +with the 0.7.1 x11vnc release, this usually works: - ``` - ./configure --with-jpeg=/usr/local - make - ``` +``` +./configure --with-jpeg=/usr/local +make +``` - Building on HP-UX: For jpeg and zlib you will need to do the same - sort of thing as described above for Solaris. You set CPPFLAGS and - LDFLAGS to find them (see below for an example.) You do not need to do - any of the above /usr/openwin stuff. Also, HP-UX does not seem to - support -R, so get rid of the -R items in LDFLAGS. Because of this, at - runtime you may need to set LD_LIBRARY_PATH or SHLIB_PATH to indicate - the directory paths so the libraries can be found. It is a good idea - to have static archives, e.g. libz.a and libjpeg.a for the nonstandard - libraries so that they get bolted into the x11vnc binary (and so won't - get "lost".) +## Building on HP-UX - Here is what we recently did to build x11vnc 0.7.2 on HP-UX 11.11 +For jpeg and zlib you will need to do the same +sort of thing as described above for Solaris. You set CPPFLAGS and +LDFLAGS to find them (see below for an example.) You do not need to do +any of the above /usr/openwin stuff. Also, HP-UX does not seem to +support -R, so get rid of the -R items in LDFLAGS. Because of this, at +runtime you may need to set LD_LIBRARY_PATH or SHLIB_PATH to indicate +the directory paths so the libraries can be found. It is a good idea +to have static archives, e.g. libz.a and libjpeg.a for the nonstandard +libraries so that they get bolted into the x11vnc binary (and so won't +get "lost".) - ``` +Here is what we recently did to build x11vnc 0.7.2 on HP-UX 11.11 + +``` ./configure --with-jpeg=$HOME/hpux/jpeg --with-zlib=$HOME/hpux/zlib make - ``` +``` - Where we had static archives (libjpeg.a, libz.a) only and header files - in the $HOME/hpux/... directories as discussed for the build script. +Where we had static archives (libjpeg.a, libz.a) only and header files +in the $HOME/hpux/... directories as discussed for the build script. - On HP-UX 11.23 and 11.31 we have had problems compiling with gcc. - "/usr/include/rpc/auth.h:87: error: field 'syncaddr' has incomplete - type". As a workaround for x11vnc 0.9.4 and later set your CPPFLAGS to - include: +On HP-UX 11.23 and 11.31 we have had problems compiling with gcc. +"/usr/include/rpc/auth.h:87: error: field 'syncaddr' has incomplete +type". As a workaround for x11vnc 0.9.4 and later set your CPPFLAGS to +include: - ``` - CPPFLAGS="-DIGNORE_GETSPNAM" - export CPPFLAGS - ``` +``` +CPPFLAGS="-DIGNORE_GETSPNAM" +export CPPFLAGS +``` - This disables a very rare usage mode for -unixpw_nis by not trying - getspnam(3). +This disables a very rare usage mode for -unixpw_nis by not trying +getspnam(3). - Using HP-UX's C compiler on 11.23 and 11.31 we have some severe - compiler errors that have not been worked around yet. If you need to - do this, contact me and I will give you a drastic recipe that will - produce a working binary. +Using HP-UX's C compiler on 11.23 and 11.31 we have some severe +compiler errors that have not been worked around yet. If you need to +do this, contact me and I will give you a drastic recipe that will +produce a working binary. +## Building on AIX - Building on AIX: AIX: one user had to add the "X11.adt" package to - AIX 4.3.3 and 5.2 to get build header files like XShm.h, etc. You may - also want to make sure that /usr/lpp/X11/include, etc is being picked - up by the configure and make. +AIX: one user had to add the "X11.adt" package to +AIX 4.3.3 and 5.2 to get build header files like XShm.h, etc. You may +also want to make sure that /usr/lpp/X11/include, etc is being picked +up by the configure and make. - For a recent build on AIX 5.3 we needed to add these CFLAGS to be able - to build with gcc: - env CFLAGS='-maix64 -Xlinker -bbigtoc' ./configure ... +For a recent build on AIX 5.3 we needed to add these CFLAGS to be able +to build with gcc: +env CFLAGS='-maix64 -Xlinker -bbigtoc' ./configure ... - we also built our own libjpeg and libz using -maix64. +we also built our own libjpeg and libz using -maix64. - BTW, one way to run an Xvfb-like virtual X server for testing on AIX - is something like "/usr/bin/X11/X -force -vfb -ac :1". +BTW, one way to run an Xvfb-like virtual X server for testing on AIX +is something like "/usr/bin/X11/X -force -vfb -ac :1". +## Building on Mac OS X - Building on Mac OS X: There is now native Mac OS X support for - x11vnc by using the raw framebuffer feature. This mode does not use or - need X11 at all. To build you may need to disable X11: +There is now native Mac OS X support for +x11vnc by using the raw framebuffer feature. This mode does not use or +need X11 at all. To build you may need to disable X11: - ``` +``` ./configure --without-x ... make - ``` - - However, if your system has the Mac OS X build package for X11 apps - you will not need to supply the "--without-x" option (in this case the - resulting x11vnc would be able to export both the native Mac OS X - display and windows displayed in the XDarwin X server.) Be sure to - include the ./configure option to find libjpeg on your system. - - - OpenSSL: Starting with version 0.8.3 x11vnc can now be built with - SSL/TLS support. For this to be enabled the libssl.so library needs to - be available at build time. So you may need to have additional - CPPFLAGS and LDFLAGS items if your libssl.so is in a non-standard - place. As of x11vnc 0.9.4 there is also the --with-ssl=DIR configure - option. - - Note that from OpenSSL 1.1.0 on SSLv2 support has been dropped and - SSLv3 deactivated at build time per default. This means that unless - explicitly enabled, OpenSSL builds only support TLS (any version). - Since there is a reason for dropping SSLv3 (heard of POODLE?), most - distributions do not enable it for their OpenSSL binary. In summary - this means compiling x11vnc against OpenSSL 1.1.0 or newer is no - problem, but using encryption will require a viewer with TLS support. - - On Solaris using static archives libssl.a and libcrypto.a instead of - .so shared libraries (e.g. from www.sunfreeware.com), we found we - needed to also set LDFLAGS as follows to get the configure to work: - - ``` +``` + +However, if your system has the Mac OS X build package for X11 apps +you will not need to supply the "--without-x" option (in this case the +resulting x11vnc would be able to export both the native Mac OS X +display and windows displayed in the XDarwin X server.) Be sure to +include the ./configure option to find libjpeg on your system. + +## OpenSSL + +Starting with version 0.8.3 x11vnc can now be built with +SSL/TLS support. For this to be enabled the libssl.so library needs to +be available at build time. So you may need to have additional +CPPFLAGS and LDFLAGS items if your libssl.so is in a non-standard +place. As of x11vnc 0.9.4 there is also the --with-ssl=DIR configure +option. + +Note that from OpenSSL 1.1.0 on SSLv2 support has been dropped and +SSLv3 deactivated at build time per default. This means that unless +explicitly enabled, OpenSSL builds only support TLS (any version). +Since there is a reason for dropping SSLv3 (heard of POODLE?), most +distributions do not enable it for their OpenSSL binary. In summary +this means compiling x11vnc against OpenSSL 1.1.0 or newer is no +problem, but using encryption will require a viewer with TLS support. + +On Solaris using static archives libssl.a and libcrypto.a instead of +.so shared libraries (e.g. from www.sunfreeware.com), we found we +needed to also set LDFLAGS as follows to get the configure to work: + +``` env LDFLAGS='-lsocket -ldl' ./configure --with-ssl=/path/to/openssl ... make - ``` - -# Beta Testing: - - I don't have any formal beta-testers for the releases of x11vnc, so - I'd appreciate any additional testing very much. - - Thanks to those who suggested features and helped beta test x11vnc - 0.9.12 released in Sep 2010! - - Please help test and debug the 0.9.13 version for release sometime in - Winter 2010. - - The version 0.9.13 beta tarball is kept here: - x11vnc-0.9.13-dev.tar.gz - - There are also some Linux, Solaris, Mac OS X, and other OS test - binaries here. Please kick the tires and report bugs, performance - regressions, undesired behavior, etc. to me. - - To aid testing of the built-in SSL/TLS support for x11vnc, a number of - VNC Viewer packages for Unix, Mac OS X, and Windows have been created - that provide SSL Support for the TightVNC Viewer (this is done by - wrapper scripts and a GUI that starts STUNNEL.) It should be pretty - convenient for automatic SSL and SSH connections. It is described in - detail at and can be downloaded from the Enhanced TightVNC Viewer - (SSVNC) page. The SSVNC Unix viewer also supports x11vnc's symmetric - key encryption ciphers (see the 'UltraVNC DSM Encryption Plugin' - settings panel.) - - - Here are some features that will appear in the 0.9.13 release: - - * Improved support for non-X11 touchscreen devices (e.g. handheld or - cell phone) via Linux uinput input injection. Additional tuning - parameters are added. TSLIB touchscreen calibration is supported. - Tested on Qtmoko Neo Freerunner. A tool, misc/uinput.pl, is - provided to diagnose uinput behavior on new devices. The env. - vars. X11VNC_UINPUT_BUS and X11VNC_UINPUT_VERSION are available if - leaving them unset does not work. - * The Linux uinput non-X11 input injection can now be bypassed: - events can be directly written to the /dev/input/event devices - specified by the user (direct_abs=..., etc.) A -pipeinput input - injection helper script, misc/qt_tslib_inject.pl is provided as a - tweakable non-builtin direct input injection method. - * The list of new uinput parameters for the above two features is: - pressure, tslib_cal, touch_always, dragskip, btn_touch; - direct_rel, direct_abs, direct_btn, direct_key. - * The MacOSX native server can now use OpenGL for the screen - capture. In nearly all cases this is faster than the raw - framebuffer capture method. There are build and run time flags, - X11VNC_MACOSX_NO_DEPRECATED, etc. to disable use of deprecated - input injection and screen access interfaces. Cursor shape now - works for 64bit binaries. - * The included SSL enabled Java VNC Viewers now handle Mouse Wheel - events. - * miscellaneous new features and changes: - * In -reflect mode, the libvncclient connection can now have the - pixel format modified via the environment variables - X11VNC_REFLECT_bitsPerSample, X11VNC_REFLECT_samplesPerPixel, and - X11VNC_REFLECT_bytesPerPixel - * In -create mode the following environment variables are added to - fine tune the behavior: FIND_DISPLAY_NO_LSOF: do not use lsof(1) - to try to determine the Linux VT, FIND_DISPLAY_NO_VT_FIND: do not - try to determine the Linux VT at all, X11VNC_CREATE_LC_ALL_C_OK: - do not bother undoing the setting LC_ALL=C that the create_display - script sets. The performance of the -create script has been - improved for large installations (100's of user sessions on one - machine.) - * In -unixpw mode, one can now Tab from login: to Password. - * An environment variable, X11VNC_SB_FACTOR, allows one to scale the - -sb screenblank sleep time from the default 2 secs. - * An experimental option -unixsock is available for testing. Note, - however, that it requires a manual change to - libvncserver/rfbserver.c for it to work. - * Documented that -grabkbd is no longer working with some/most - window managers (it can prevent resizing and menu posting.) - - - Here are some features that appeared in the 0.9.12 release (Sep/2010): - - * One can now specify the maximum number of displays that can be - created in -create mode via the env. var. - X11VNC_CREATE_MAX_DISPLAYS - * The X11VNC_NO_LIMIT_SHM env. var. is added to skip any automatic - shared memory reduction. - * The kdm display manager is now detected when trying not to get - killed by the display manager. - * A compile time bug is fixed so that configuring using - --with-system-libvncserver pointing to LibVNCServer 0.9.7 works - again. A bug from forced use of Xdefs.h is worked around. - - - Here are some features that appeared in the 0.9.11 release (Aug/2010): - - * The source tree is synchronized with the most recent libvncclient - (this only affects -reflect mode.) Build is fixed for - incompatibilities when using an external LibVNCServer (e.g. - ./configure --with-system-libvncserver...) Please help test these - build and runtime aspects and report back what you find, thanks. - * The SSL enabled Java VNC Viewer Makefile has been modified so that - the jar files that are built are compatible back to Java 1.4. - * In -create/-unixpw mode, the env. var. FD_USERPREFS may be set to - a filename in the user's home directory that includes default - username:options values (so the options do not need to be typed - every time at the login prompt.) - * In -reflect mode cursor position updates are now handled - correctly. - - - Here are some features that appeared in the 0.9.10 release (May/2010): - - * The included SSL enabled Java applet viewer now supports Chained - SSL Certificates. The debugCerts=yes applet parameter aids - troubleshooting certificate validation. The x11vnc -ssl mode has - always supported chained SSL certificates (simply put the - intermediate certificates, in order, after the server certificate - in the pem file.) - * A demo CGI script desktop.cgi shows how to create an SSL - encrypted, multi-user x11vnc web login desktop service. The script - requires x11vnc version 0.9.10. The user logs into a secure web - site and gets his/her own virtual desktop (Xvfb.) x11vnc's SSL - enabled Java Viewer Applet is launched by the web browser for - secure viewing (and so no software needs to be installed on the - viewer-side.) One can use the desktop.cgi script for ideas to - create their own fancier or customized web login desktop service - (e.g. user-creation, PHP, SQL, specialized desktop application, - etc.) More info here. There is also an optional 'port redirection' - mode that allows redirection to other SSL enabled VNC servers - running inside the firewall. - * Built-in support for IPv6 (128 bit internet addresses) is now - provided. See the -6 and -connect options for details. - Additionally, in case there are still problems with built-in IPv6 - support, a transitional tool is provided in inet6to4 that allows - x11vnc (or any other IPv4 application) to receive connections over - IPv6. - * The Xdummy wrapper script for Xorg's dummy driver is updated and - no longer requires being run as root. New service options are - provided to select Xdummy over Xvfb as the virtual X server to be - created. - * The "%" unix password verification tricks for the -unixpw option - are now documented. They have also been extended to run a command - as the user if one sets the environment variable UNIXPW_CMD. The - desktop.cgi demo script takes advantage of this new feature. - * A bug has been fixed that would prevent the Java applet viewer - from being downloaded successfully in single-port HTTPS/VNC inetd - mode. The env. var. X11VNC_HTTPS_DOWNLOAD_WAIT_TIME can be used to - adjust for how many seconds a -inetd or -https httpd download is - waited for (default 15 seconds.) The applet will now autodetect - x11vnc and use GET=1 for faster connecting. Many other - improvements and fixes. - * The TightVNC security type (TightVNC features enabler) now works - for RFB version 3.8. - * The X property X11VNC_TRAP_XRANDR can be set on a desktop to force - x11vnc to use the -xrandr screen size change trapping code. - * New remote control query options: pointer_x, pointer_y, - pointer_same, pointer_root, and pointer_mask. A demo script using - them misc/panner.pl is provided. - * The -sslScripts option prints out the SSL certificate management - scripts. - - - Here are some features that appeared in the 0.9.9 release (Dec/2009): - - * The -unixpw_system_greeter option, when used in combined unixpw - and XDMCP FINDCREATEDISPLAY mode (for example: -xdmsvc), enables - the user to press Escape to jump directly to the XDM/GDM/KDM login - greeter screen. This way the user avoids entering his unix - password twice at X session creation time. Also, the unixpw login - panel now has a short help displayed if the user presses 'F1'. - * x11vnc now tries to be a little bit more aggressive in keeping up - with VNC client's framebuffer update requests. Some broken VNC - clients like Eggplant and JollysFastVNC continuously spray these - requests at VNC servers (regardless of whether they have received - any updates or not.) Under some circumstances this could lead to - x11vnc falling behind. The -extra_fbur option allows one to fine - tune the setting. Additionally, one may also dial down delays: - e.g. "-defer 5" and "-wait 5" (or to 1 or even 0) or -nonap or - -allinput to keep up with these VNC clients at the expense of - increased system load. - * Heuristics are applied to try to determine if the X display is - currently in a Display Manager Greeter Login panel (e.g. GDM) If - so, x11vnc's creation of any windows and use of XFIXES are - delayed. This is to try to avoid x11vnc being killed after the - user logs in if the GDM KillInitClients=true is in effect. So one - does not need to set KillInitClients=false. Note that in recent - GDM the KillInitClients option has been removed. Also delayed is - the use of the XFIXES cursor fetching functionality; this avoids - an Xorg bug that causes Xorg to crash right after the user logs - in. - * A new option -findauth runs the FINDDISPLAY script that applies - heuristics that try to determine the XAUTHORITY file. The use of - '-auth guess' will use the XAUTHORITY that -findauth reveals. This - can be handy in with the lastest GDM where the ability to store - cookies in ~/.Xauthority has been removed. If x11vnc is running as - root (e.g. inetd) and you add -env FD_XDM=1 to the above -findauth - or -auth guess command lines, it will find the correct XAUTHORITY - for the given display (this works for XDM/GDM/KDM if the login - greeter panel is up or if someone has already logged into an X - session.) - * The FINDDISPLAY and FINDCREATEDISPLAY modes (i.e. "-display - WAIT:cmd=...", -find, -create) now work correctly for the - user-supplied login program scheme "-unixpw_cmd ...", as long as - the login program supports running commands specified in the - environment variable "RFB_UNIXPW_CMD_RUN" as the logged-in user. - The mode "-unixpw_nis ..." has also been made more consistent. - * The -stunnel option (like -ssl but uses stunnel as an external - helper program) now works with the -ssl "SAVE" and "TMP" special - certificate names. The -sslverify and -sslCRL options now work - correctly in -stunnel mode. Single port HTTPS connections are also - supported for this mode. - * There is an experimental Application Sharing mode that improves - upon the -id/-sid single window sharing: -appshare (run "x11vnc - -appshare -help" for more info.) It is still very primitive and - approximate, but at least it displays multiple top-level windows. - * The remote control command -R can be used to instruct x11vnc to - resend its most recent copy of the Clipboard, Primary, or - Cutbuffer selections: "x11vnc -R resend_clipboard", "x11vnc -R - resend_primary", and "x11vnc -R resend_cutbuffer". - * The fonts in the GUI (-gui) can now by set via environment - variables, e.g. -env X11VNC_FONT_BOLD='Helvetica -16 bold' and - -env X11VNC_FONT_FIXED='Courier -14'. - * The XDAMAGE mechanism is now automatically disabled for a period - of time if a game or screensaver generates too many XDAMAGE - rectangles per second. This avoids the X11 event queue from - soaking up too much memory. - * There is an experimental workaround: "-env X11VNC_WATCH_DX_DY=1" - that tries to avoid problems with poorly constructed menu themes - that place the initial position of the mouse cursor inside a menu - item's active zone. More information can be found here. - - - Here are some features that appeared in the 0.9.8 release (Jul/2009): - - * Stability improvements to -threads mode. Running x11vnc this way - is more reliable now. Threaded operation sometimes gives better - interactive response and faster updates: try it out. The threaded - mode now supports multiple VNC viewers using the same VNC - encoding. The threaded mode can also yield a performance - enhancement in the many client case (e.g. class-room broadcast.) - We have tested with 30 to 50 simultaneous clients. See also - -reflect. - For simultaneous clients: the ZRLE encoding is thread safe on all - platforms, and the Tight and Zlib encodings are currently only - thread safe on Linux where thread local storage, __thread, is - used. If your non-Linux system and compiler support __thread one - can supply -DTLS=__thread to enable it. When there is only one - connected client, all encodings are safe on all platforms. Note - that some features (e.g. scroll detection and -ncache) may be - disabled or run with reduced functionality in -threads mode. - * Automatically tries to work around an Xorg server and GNOME bug - involving infinitely repeating keys when turning off key - repeating. Use -repeat if the automatic workaround fails. - * Improved reliability of the Single Port SSL VNC and HTTPS java - viewer applet delivery mechanism. - * The -clip mode works under -rawfb. - - - Here are some features that appeared in the 0.9.7 release (Mar/2009): - - * Support for polling Linux Virtual Terminals (also called virtual - consoles) directly instead of using /dev/fb. The option to use is, - for example, "-rawfb vt2" for Virtual Terminal 2, etc. In this - case the special file /dev/vcsa2 is used to retrieve vt2's current - text. Text and colors are shown, but no graphics. - * Support for less than 8 bits per pixel framebuffers (e.g. 4 or 1 - bpp) in the -rawfb mode. - * The SSL enabled UltraVNC Java viewer applet now has a [Home] entry - in the "drives" drop down menu. This menu can be configured with - the ftpDropDown applet parameter. All of the applet parameters are - documented in classes/ssl/README. - * Experimental support for VirtualGL's TurboVNC (an enhanced - TightVNC for fast LAN high framerate usage.) - * The CUPS Terminal Services helper mode has been improved. - * Improvements to the -ncache_cr that allows smooth opaque window - motions using the 'copyrect' encoding when using -ncache mode. - * The -rmflag option enables a way to indicate to other processes - x11vnc has exited. - * Reverse connections using anonymous Diffie Hellman SSL encryption - now work. - - - Here are some features that appeared in the 0.9.6 release (Dec/2008): - - * Support for VeNCrypt SSL/TLS encrypted connections. It is enabled - by default in the -ssl mode. VNC Viewers like vinagre, - gvncviewer/gtk-vnc, the vencrypt package, SSVNC, and others - support this encryption mode. It can also be used with the -unixpw - option to enable Unix username and password authentication - (VeNCrypt's "*Plain" modes.) A similar but older VNC security type - "ANONTLS" (used by vino) is supported as well. See the -vencrypt - and -anontls options for additional control. The difference - between x11vnc's normal -ssl mode and VeNCrypt is that the former - wraps the entire VNC connection in SSL (like HTTPS does for HTTP, - i.e. "vncs://") while VeNCrypt switches on the SSL/TLS at a - certain point during the VNC handshake. Use -sslonly to disable - both VeNCrypt and ANONTLS (vino.) - * The "-ssl ANON" option enables Anonymous Diffie-Hellman (ADH) key - exchange for x11vnc's normal SSL/TLS operation. Note that - Anonymous Diffie-Hellman uses encryption for privacy, but provides - no authentication and so is susceptible to Man-In-The-Middle - attacks (and so we do not recommend it: we prefer you use "-ssl - SAVE", etc. and have the VNC viewer verify the cert.) The ANONTLS - mode (vino) only supports ADH. VeNCrypt mode supports both ADH and - regular X509 SSL certificates modes. For these ADH is enabled by - default. See -vencrypt and -anontls for how to disable ADH. - * For x11vnc's SSL/TLS modes, one can now specify a Certificate - Revocation List (CRL) with the -sslCRL option. This will only be - useful for wide deployments: say a company-wide x11vnc SSL access - deployment using a central Certificate Authority (CA) via - -sslGenCA and -sslGenCert. This way if a user has his laptop lost - or stolen, you only have to revoke his key instead of creating a - new Certificate Authority and redeploying new keys to all users. - * The default SSL/TLS mode, "-ssl" (no pem file parameter supplied), - is now the same as "-ssl SAVE" and will save the generated - self-signed cert in "~/.vnc/certs/server.pem". Previously "-ssl" - would create a temporary self-signed cert that was discarded when - x11vnc exited. The reason for the change is to at least give the - chance for the VNC Viewer side (e.g. SSVNC) to remember the cert - to authenticate subsequent connections to the same x11vnc server. - Use "-ssl TMP" to regain the previous behavior. Use "-ssl - SAVE_NOPROMPT" to avoid being prompted about using passphrase when - the certificate is created. - * The option -http_oneport enables single-port HTTP connections via - the Java VNC Viewer. So, for example, the web browser URL - "http://myhost.org:5900" works the same as - "http://myhost.org:5800", but with the convenience of only - involving one port instead of two. This works for both unencrypted - connections and for SSH tunnels (see -httpsredir if the tunnel - port differs.) Note that HTTPS single-port operation in -ssl SSL - encrypted mode has been available since x11vnc version 0.8.3. - * For the -avahi/-zeroconf Service Advertizing mode, if x11vnc was - not compiled with the avahi-client library, then an external - helper program, either avahi-publish(1) (on Unix) or dns-sd(1) (on - Mac OS X), is used instead. - * The "-rfbport PROMPT" option will prompt the user via the GUI to - select the VNC port (e.g. 5901) to listen on, and a few other - basic settings. This enables a handy GUI mode for naive users: - x11vnc -gui tray=setpass -rfbport PROMPT -logfile $HOME/.x11vnc.log.%VNCDISP -LAY - suitable for putting in a launcher or menu, e.g. x11vnc.desktop. - The -logfile expansion is new too. In the GUI, the tray=setpass - Properties panel has been improved. - * The -solid solid background color option now works for the Mac OS - X console. - * The -reopen option instructs x11vnc to try to reopen the X display - if it is prematurely closed by, say, the display manager (e.g. - GDM.) - - - Here are some features that appeared in the 0.9.5 release (Oct/2008): - - * Symmetric key encryption ciphers. ARC4, AES-128, AES-256, - blowfish, and 3des are supported. Salt and initialization vector - seeding is provided. These compliment the more widely used SSL and - SSH encryption access methods. SSVNC also supports these - encryption modes. - * Scaling differently along the X- and Y-directions. E.g. "-scale - 1280x1024" or "-scale 0.8x0.75" Also, "-geometry WxH" is an - alias for "-scale WxH" - * By having SSVNC version 1.0.21 or later available in your $PATH, - the -chatwindow option allows a UltraVNC Text Chat window to - appear on the local X11 console/display (this way the remote - viewer can chat with the person at the physical display; e.g. - helpdesk mode.) This also works on the Mac OS X console if the - Xquartz X11 server (enabled by default on leopard) is running for - the chatwindow. - * The HTTP Java viewer applet jar, classes/VncViewer.jar, has been - updated with an improved implementation based on the code used by - the classes/ssl applets. - - - Here are some features that appeared in the 0.9.4 release (Sep/2008): - - * Improvements to the -find and -create X session finding or - creating modes: new desktop types and service redirection options. - Personal cupsd daemon and SSH port redirection helper for use with - SSVNC's Terminal Services feature. - * Reverse VNC connections via -connect work in the -find, -create - and related -display WAIT:... modes. - * Reverse VNC connections (either normal or SSL) can use a Web Proxy - or a SOCKS proxy, or a SSH connection, or even a CGI URL to make - the outgoing connection. See: -proxy. Forward connections can also - use: -ssh. - * Reverse VNC connections via the UltraVNC repeater proxy (either - normal or SSL) are supported. Use either the "-connect - repeater=ID:NNNN+host:port" or "-connect - repeater://host:port+ID:NNNN" notation. The SSVNC VNC viewer also - supports the UltraVNC repeater. Also, a perl repeater implemention - is here: ultravnc_repeater.pl - * Support for indexed colormaps (PseudoColor) with depths other than - 8 (from 1 to 16 now work) for non-standard hardware. Option - "-advertise_truecolor" to handle some workaround in this mode. - * Support for the ZYWRLE encoding, this is the RealVNC ZRLE encoding - extended to do motion video and photo regions more efficiently by - way of a Wavelet based transformation. - * The -finddpy and -listdpy utilities help to debug and configure - the -find, -create, and -display WAIT:... modes. - * Some automatic detection of screen resizes are handled even if the - -xrandr option is not supplied. - * The -autoport options gives more control over the VNC port x11vnc - chooses. - * The -ping secs can be used to help keep idle connections alive. - * Pasting of the selection/clipboard into remote applications (e.g. - Java) has been improved. - * Fixed a bug if a client disconnects during the 'speed-estimation' - phase. - * To unset Caps_Lock, Num_Lock and raise all keys in the X server - use -clear_all. - * Usage with dvorak keyboards has been improved. See also: -xkb. - * The Java Viewer applet source code is now included in the - x11vnc-0.9.*.tar.gz tarball. This means you can now build the Java - viewer applet jar files from source. If you stopped shipping the - Java viewer applet jar files due to lack of source code, you can - start again. - - - Here are some features that appeared in the 0.9.3 release (Oct/2007): - - * Viewer-side pixmap caching. A large area of pixels (at least 2-3 - times as big as the framebuffer itself; the bigger the better... - default is 10X) is placed below the framebuffer to act as a - buffer/cache area for pixel data. The VNC CopyRect encoding is - used to move it around, so any viewer can take advantage of it. - Until we start modifying viewers you will be able to see the cache - area if you scroll down (this makes it easier to debug!) For - testing the default is "-ncache 10". The unix Enhanced TightVNC - Viewer ssvnc has a nice -ycrop option to help hide the pixel cache - area from view. - - - Here are some features that appeared in the 0.9.2 release (Jun/2007): - - * Building with no OpenSSL libssl available (or with --without-ssl) - has been fixed. - * One can configure x11vnc via "./configure - --with-system-libvncserver" to use a system installed libvncserver - library instead of the one bundled in the release tarball. - * If UltraVNC file transfer or chat is detected, then VNC clients - are "pinged" more often to prevent these side channels from - becoming serviced too infrequently. - * In -unixpw mode in the username and password dialog no text will - be echoed if the first character sent is "Escape". This enables a - convenience feature in SSVNC to send the username and password - automatically. - - - Here are some features that appeared in the 0.9.1 release (May/2007): - - * The UltraVNC Java viewer has been enhanced to support SSL (as the - TightVNC viewer had been previously.) The UltraVNC Java supports - ultravnc filetransfer, and so can be used as a VNC viewer on Unix - that supports ultravnc filetransfer. It is in the - classes/ssl/UltraViewerSSL.jar file (that is pointed to by - ultra.vnc.) The signed applet SignedUltraViewerSSL.jar version - (pointed to by ultrasigned.vnc) will be needed to access the local - drive if you are using it for file transfer via a Web browser. - Some other bugs in the UltraVNC Java viewer were fixed and a few - improvements to the UI made. - * A new Unix username login mode for VNC Viewers authenticated via a - Client SSL Certificate: "-users sslpeer=". The emailAddress - subject field is inspected for username@hostname and then acts as - though "-users +username" has been supplied. This way the Unix - username is identified by (i.e. simply extracted from) the Client - SSL Certificate. This could be useful with -find, -create and -svc - modes if you are also have set up and use VNC Client SSL - Certificate authentication. - * For external display finding/creating programs (e.g. WAIT:cmd=...) - if the VNC Viewer is authenticated via a Client SSL Certificate, - then that Certificate is available in the environment variable - RFB_SSL_CLIENT_CERT. - - - Here are some features that appeared in the 0.9 release (Apr/2007): - - * VNC Service advertising via mDNS / ZeroConf / BonJour with the - Avahi client library. Enable via "-avahi" or "-zeroconf". - * Implementations of UltraVNC's TextChat, SingleWindow, and - ServerInput extensions (requires ultravnc viewer or ssvnc Unix - viewer.) They toggle the selection of a single window (-id), and - disable (friendly) user input and viewing (monitor blank) at the - VNC server. - * Short aliases "-find", "-create", "-svc", and "-xdmsvc" for - commonly used FINDCREATEDISPLAY usage modes. - * Reverse VNC connections (viewer listening) now work in SSL (-ssl) - mode. - * New options to control the Monitor power state and keyboard/mouse - grabbing: -forcedpms, -clientdpms, -noserverdpms, and -grabalways. - * A simple way to emulate inetd(8) to some degree via the "-loopbg" - option. - * Monitor the accuracy of XDAMAGE and apply "-noxdamage" if it is - not working well. OpenGL applications like like beryl and MythTv - have been shown to make XDAMAGE not work properly. - * For Java SSL connections involving a router/firewall port - redirection, an option -httpsredir to spare the user from needing - to include &PORT=NNN in the browser URL. - - - Here are some features that appeared in the 0.8.4 release (Feb/2007): - - * Native Mac OS X Aqua/Quartz support. (i.e. OSXvnc alternative; - some activities are faster) - * A new login mode: "-display WAIT:cmd=FINDCREATEDISPLAY -unixpw - ..." that will Create a new X session (either virtual or real and - with or without a display manager, e.g. kdm) for the user if it - cannot find the user's X session display via the FINDDISPLAY - method. See the -svc and the -xdmsvc aliases. - * x11vnc can act as a VNC reflector/repeater using the "-reflect - host:N" option. Instead of polling an X display, the remote VNC - Server host:N is connected to and re-exported via VNC. This is - intended for use in broadcasting a display to many (e.g. > 16; - classroom or large demo) VNC viewers where bandwidth and other - resources are conserved by spreading the load over a number of - repeaters. - * Wireframe copyrect detection for local user activity (e.g. someone - sitting at the physical display moving windows) Use - -nowireframelocal to disable. - * The "-N" option couples the VNC Display number to the X Display - number. E.g. if your X DISPLAY is :2 then the VNC display will be - :2 (i.e. using port 5902.) If that port is taken x11vnc will exit. - * Option -nodpms to avoid problems with programs like KDE's - kdesktop_lock that keep restarting the screen saver every few - seconds. - * To automatically fix the common mouse motion problem on XINERAMA - (multi-headed) displays, the -xwarppointer option is enabled by - default when XINERAMA is active. - - If you have a Mac please try out the native Mac OS X support, build - with "./configure --without-x", or download a binary mentioned above, - (even if you don't plan on ever using it in this mode!), and let me - know how it went. Thanks. - - - Here are some features that appeared in the 0.8.3 release (Nov/2006): - - * The -ssl option provides SSL encryption and authentication - natively via the www.openssl.org library. One can use from a - simple self-signed certificate server certificate up to full CA - and client certificate authentication schemes. - * Similar to -ssl, the -stunnel option starts up a SSL tunnel server - stunnel (that must be installed separately on the system: - stunnel.mirt.net ) to allow only encrypted SSL connections from - the network. - * The -sslverify option allows for authenticating VNC clients via - their certificates in either -ssl or -stunnel modes. - * Certificate creation and management tools are provide in the - -sslGenCert, -sslGenCA, and related options. - * An SSL enabled Java applet VNC Viewer applet is provided by x11vnc - in classes/ssl/VncViewer.jar. In addition to normal HTTP, the - applet may be loaded into the web browser via HTTPS (HTTP over - SSL.) (one can use the VNC port, e.g. https://host:5900/, or also - the separate -https port option.) A wrapper shell script - ss_vncviewer is also provided that sets up a stunnel client-side - tunnel on Unix systems. See Enhanced TightVNC Viewer (SSVNC) for - other SSL/SSH viewer possibilities. - * The -unixpw option supports Unix username and password - authentication (a simpler variant is the -unixpw_nis option that - works in environments where the encrypted passwords are readable, - e.g. NIS.) The -ssl or -localhost + -stunnel options are enforced - in this mode to prevent password sniffing. As a convenience, these - requirements are lifted if a SSH tunnel can be deduced (but - -localhost still applies.) - * Coupling -unixpw with "-display WAIT:cmd=FINDDISPLAY" or "-display - WAIT:cmd=FINDCREATEDISPLAY" provides a way to allow a user to - login with their UNIX password and have their display connected to - automatically. See the -svc and the -xdmsvc aliases. - * Hooks are provided in the -unixpw_cmd and "-passwdfile - cmd:,custom:..." options to allow you to supply your own - authentication and password lookup programs. - * x11vnc can be configured and built to not depend on X11 libraries - "./configure --without-x" for -rawfb only operation (e.g. embedded - linux console devices.) - * The -rotate option enables you to rotate or reflect the screen - before exporting via VNC. This is intended for use on handhelds - and other devices where the rotation orientation is not "natural". - * The "-ultrafilexfer" alias is provided and improved UltraVNC - filetransfer rates have been achieved. - * Under the "-connect_or_exit host" option x11vnc will exit - immediately unless the reverse connection to host succeeds. The - "-rfbport 0" option disables TCP listening for connections (useful - for this mode.) - * The "-rawfb rand" and "-rawfb none" options are useful for testing - automation scripts, etc., without requiring a full desktop. - * Reduced spewing of information at startup, use "-verbose" (also - "-v") to turn it back on for debugging or if you are going to send - me a problem report. - -# Here are some Previous Release Notes - -## Some Notes: - - Both a client and a server: It is sometimes confusing to people that - x11vnc is both a client and a server at the same time. It is an X - client because it connects to the running X server to do the screen - polls. Think of it as a rather efficient "screenshot" program running - continuously. It is a server in the sense that it is a VNC server that - VNC viewers on the network can connect to and view the screen - framebuffer it manages. - - When trying to debug problems, remember to think of both roles. E.g. - "how is x11vnc connecting to the X server?", "how is the vncviewer - connecting to x11vnc?", "what permits/restricts the connection?". Both - links may have reachability, permission, and other issues. - - Network performance: Whether you are using Xvnc or x11vnc it is - always a good idea to have a solid background color instead of a - pretty background image. Each and every re-exposure of the background - must be resent over the network: better to have that background be a - solid color that compresses very well compared to a photo image. (This - is one place where the X protocol has an advantage over the VNC - protocol.) I suggest using xsetroot, dtstyle or similar utility to set - a solid background while using x11vnc. You can turn the pretty - background image back on when you are using the display directly. - Update: As of Feb/2005 x11vnc has the -solid [color] option that works - on recent GNOME, KDE, and CDE and also on classic X (background image - is on the root window.) Update: As of Oct/2007 x11vnc has the -ncache - option that does a reasonable job caching the background (and other) - pixmap data on the viewer side. - - I also find the TightVNC encoding gives the best response for my usage - (Unix <-> Unix over cable modem.) One needs a tightvnc-aware vncviewer - to take advantage of this encoding. - - TCP port issues: Notice the lines - - ``` - 18/07/2003 14:36:31 Autoprobing selected port 5900 - PORT=5900 - ``` - - in the output. 5900 is the default VNC listening port (just like 6000 - is X11's default listening port.) Had port 5900 been taken by some - other application, x11vnc would have next tried 5901. That would mean - the viewer command above should be changed to vncviewer - far-away.east:1. You can force the port with the "-rfbport NNNN" - option where NNNN is the desired port number. If that port is already - taken, x11vnc will exit immediately. The "-N" option will try to match - the VNC display number to the X display. (also see the "SunRay - Gotcha" note below) - - Options: x11vnc has (far too) many features that may be activated - via its command line options. Useful options are, e.g., -scale to do - server-side scaling, and -rfbauth passwd-file to use VNC password - protection (the vncpasswd or storepasswd programs, or the x11vnc - -storepasswd option can be used to create the password file.) - - Algorithm: How does x11vnc do it? Rather brute-forcedly: it - continuously polls the X11 framebuffer for changes using - XShmGetImage(). When changes are discovered, it instructs libvncserver - which rectangular regions of the framebuffer have changed, and - libvncserver compresses the changes and sends them off to any - connected VNC viewers. A number of applications do similar things, - such as x0rfbserver, krfb, x0vncserver, vino. x11vnc uses a 32 x 32 - pixel tile model (the desktop is decomposed into roughly 1000 such - tiles), where changed tiles are found by pseudo-randomly polling 1 - pixel tall horizontal scanlines separated vertically by 32 pixels. - This is a surprisingly effective algorithm for finding changed - regions. For keyboard and mouse user input the XTEST extension is used - to pass the input events to the X server. To detect XBell "beeps" the - XKEYBOARD extension is used. If available, the XFIXES extension is - used to retrieve the current mouse cursor shape. Also, if available - the X DAMAGE extension is used to receive hints from the X server - where modified regions on the screen are. This greatly reduces the - system load when not much is changing on the screen and also improves - how quickly the screen is updated. - - Barbershop mirrors effect: What if x11vnc is started up, and - vncviewer is then started up on the same machine and displayed on the - same display x11vnc is polling? One might "accidentally" do this when - first testing out the programs. You get an interesting - recursive/feedback effect where vncviewer images keep popping up each - one contained in the previous one and slightly shifted a bit by the - window manager decorations. There will be an even more interesting - effect if -scale is used. Also, if the XKEYBOARD is supported and the - XBell "beeps" once, you get an infinite loop of beeps going off. - Although all of this is mildly exciting it is not much use: you will - normally run and display the viewer on a different machine! - -## Sun Ray Notes: - - You can run x11vnc on your (connected or disconnected) SunRay session. - Here are some notes on SunRay usage with x11vnc. - - -## Limitations: - - * Due to the polling nature, some activities (opaque window moves, - scrolling), can be pretty choppy/ragged and others (exposures of - large areas) slow. Experiment with interacting a bit differently - than you normally do to minimize the effects (e.g. do fullpage - paging rather than line-by-line scrolling, and move windows in a - single, quick motion.) Recent work has provided the - -scrollcopyrect and -wireframe speedups using the CopyRect VNC - encoding and other things, but they only speed up some activities, - not all. - * A rate limiting factor for x11vnc performance is that graphics - hardware is optimized for writing, not reading (x11vnc reads the - video framebuffer for the screen image data.) The difference can - be a factor of 10 to 1000, and so it usually takes about 0.5-1 sec - to read in the whole video hardware framebuffer (e.g. 5MB for - 1280x1024 at depth 24 with a read rate of 5-10MB/sec.) So whenever - activity changes most of the screen (e.g. moving or iconifying a - large window) there is a delay of 0.5-1 sec while x11vnc reads the - changed regions in. - A slow framebuffer read rate will often be the performance - bottleneck on a fast LAN (whereas on slower links the reduced - network bandwidth becomes the bottleneck.) - Note: A quick way to get a 2X speedup of this for x11vnc is to - switch your X server from depth 24 (32bpp) to depth 16 (16bpp.) - You get a 4X speedup going to 8bpp, but the lack of color cells is - usually unacceptable. - To get a sense of the read and write speeds of your video card, - you can run benchmarks like: "x11perf -getimage500", "x11perf - -putimage500", "x11perf -shmput500" and for XFree86 displays with - direct graphics access the "dga" command (press "b" to run the - benchmark and then after a few seconds press "q" to quit.) Even - this "dd if=/dev/fb0 of=/dev/null" often gives a good estimate. - x11vnc also prints out its estimate: - 28/02/2009 11:11:07 Autoprobing TCP port - 28/02/2009 11:11:07 Autoprobing selected port 5900 - 28/02/2009 11:11:08 fb read rate: 10 MB/sec - 28/02/2009 11:11:08 screen setup finished. - We have seen a few cases where the hardware fb read speed is - greater than 65 MB/sec: on high end graphics workstations from SGI - and Sun, and also from a Linux user using nvidia proprietary - drivers for his nvidia video card. Update 2008: thankfully, these - sped up drivers are becoming more common on Linux and *BSD systems - and that makes x11vnc run somewhat more quickly. Sometimes they - have a read rate of over 400 MB/sec. - On XFree86/Xorg it is actually possible to increase the - framebuffer read speed considerably (10-100 times) by using the - Shadow Framebuffer (a copy of the framebuffer is kept in main - memory and this can be read much more quickly.) To do this one - puts the line Option "ShadowFB" "true" in the Device section of - the /etc/X11/XF86Config or /etc/X11/xorg.conf file. Note that this - disables 2D acceleration at the physical display and so that might - be unacceptable if one plays games, etc. on the machine's local - display. Nevertheless this could be handy in some circumstances, - e.g. if the slower speed while sitting at the physical display was - acceptable (this seems to be true for most video cards these - days.) Unfortunately it does not seem shadowfb can be turned on - and off dynamically... - Another amusing thing one can do is use Xvfb as the X server, e.g. - "xinit $HOME/.xinitrc -- /usr/X11R6/bin/Xvfb :1 -screen 0 - 1024x768x16" x11vnc can poll Xvfb efficiently via main memory. - It's not exactly clear why one would want to do this instead of - using vncserver/Xvnc, (perhaps to take advantage of an x11vnc - feature, such as framebuffer scaling or built-in SSL encryption), - but we mention it because it may be of use for special purpose - applications. You may need to use the "-cc 4" option to force Xvfb - to use a TrueColor visual instead of DirectColor. See also the - description of the -create option that does all of this - automatically for you (be sure to install the Xvfb package, e.g. - apt-get install xvfb.) - Also, a faster and more accurate way is to use the "dummy" - Xorg/XFree86 device driver (or our Xdummy wrapper script.) See - this FAQ for details. - * Somewhat surprisingly, the X11 mouse (cursor) shape is write-only - and cannot be queried from the X server. So traditionally in - x11vnc the cursor shape stays fixed at an arrow. (see the "-cursor - X" and "-cursor some" options, however, for a partial hack for the - root window, etc.) However, on Solaris using the SUN_OVL overlay - extension, x11vnc can show the correct mouse cursor when the - -overlay option is also supplied. A similar thing is done on IRIX - as well when -overlay is supplied. - More generally, as of Dec/2004 x11vnc supports the new XFIXES - extension (in Xorg and Solaris 10) to query the X server for the - exact cursor shape, this works pretty well except that cursors - with transparency (alpha channel) need to approximated to solid - RGB values (some cursors look worse than others.) - * Audio from applications is of course not redirected (separate - redirectors do exist, e.g. esd, see the FAQ on this below.) The - XBell() "beeps" will work if the X server supports the XKEYBOARD - extension. (Note that on Solaris XKEYBOARD is disabled by default. - Passing +kb to Xsun enables it.) - * The scroll detection algorithm for the -scrollcopyrect option can - give choppy or bunched up transient output and occasionally - painting errors. - * Using -threads can expose some bugs/crashes in libvncserver. - - Please feel free to contact me if you have any questions, problems, or - comments about x11vnc, etc. Please be polite, thorough, and not - demanding (sadly, the number of people contacting me that are rude and - demanding is increasing dramatically.) - Also, some people ask if they can make a donation, see this link for - that. - -http://www.karlrunge.com/x11vnc/faq.html: - - -# x11vnc FAQ: - - - [Building and Starting] - - Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed - (null)" or "Xlib: connection to ":0.0" refused by server Xlib: No - protocol specified" and then exits. What do I need to do? - - Q-2: I can't get x11vnc and/or libvncserver to compile. - - Q-3: I just built x11vnc successfully, but when I use it my keystrokes - and mouse button clicks are ignored (I am able to move the mouse - though.) - - Q-4: Help, I need to run x11vnc on Solaris 2.5.1 (or other old - Unix/Linux) and it doesn't compile! - - Q-5: Where can I get a precompiled x11vnc binary for my Operating - System? - - Q-6: Where can I get a VNC Viewer binary (or source code) for the - Operating System I will be viewing from? - - Q-7: How can I see all of x11vnc's command line options and - documentation on how to use them? - - Q-8: I don't like typing arcane command line options every time I - start x11vnc. What can I do? Is there a config file? Or a GUI? - - Q-9: How can I get the GUI to run in the System Tray, or at least be a - smaller, simpler icon? - - Q-10: How can I get x11vnc to listen on a different port besides the - default VNC port (5900)? - - Q-11: My Firewall/Router doesn't allow VNC Viewers to connect to - x11vnc. - - Q-12: Is it possible for a VNC Viewer and a VNC Server to connect to - each other even though both are behind Firewalls that block all - incoming connections? - - Q-13: Can I make x11vnc more quiet and also go into the background - after starting up? - - Q-14: Sometimes when a VNC viewer dies abruptly, x11vnc also dies with - the error message like: "Broken pipe". I'm using the -forever mode and - I want x11vnc to keep running. - - Q-15: The Windows TightVNC 1.3.9 Viewer cannot connect to x11vnc. - - Q-16: KDE's krdc VNC viewer cannot connect to x11vnc. - - Q-17: When I start x11vnc on an Alpha Tru64 workstation the X server - crashes! - - Q-18: When running x11vnc on an IBM AIX workstation after a few - minutes the VNC connection freezes. - - Q-19: Are there any build-time customizations possible, e.g. change - defaults, create a smaller binary, etc? - - [Win2VNC Related] - - Q-20: I have two separate machine displays in front of me, one Windows - the other X11: can I use x11vnc in combination with Win2VNC in - dual-screen mode to pass the keystrokes and mouse motions to the X11 - display? - - Q-21: I am running Win2VNC on my Windows machine and "x11vnc -nofb" on - Unix to pass keyboard and mouse to the Unix monitor. Whenever I start - Win2VNC it quickly disconnects and x11vnc says: - rfbProcessClientNormalMessage: read: Connection reset by peer - - Q-22: Can I run "x11vnc -nofb" on a Mac OS X machine to redirect mouse - and keyboard input to it from Windows and X11 machines via Win2VNC and - x2vnc, respectively? - - [Color Issues] - - Q-23: The X display I run x11vnc on is only 8 bits per pixel (bpp) - PseudoColor (i.e. only 256 distinct colors.) The x11vnc colors may - start out OK, but after a while they are incorrect in certain windows. - - Q-24: Color problems: Why are the colors for some windows incorrect in - x11vnc? BTW, my X display has nice overlay/multi-depth visuals of - different color depths: e.g. there are both depth 8 and 24 visuals - available at the same time. - - Q-25: I am on a high color system (depth >= 24) but I seem to have - colormap problems. They either flash or everything is very dark. - - Q-26: How do I figure out the window id to supply to the -id windowid - option? - - Q-27: Why don't menus or other transient windows come up when I am - using the -id windowid option to view a single application window? - - Q-28: My X display is depth 24 at 24bpp (instead of the normal depth - 24 at 32bpp.) I'm having lots of color and visual problems with x11vnc - and/or vncviewer. What's up? - - [Xterminals] - - Q-29: Can I use x11vnc to view and interact with an Xterminal (e.g. - NCD) that is not running UNIX and so x11vnc cannot be run on it - directly? - - Q-30: How do I get my X permissions (MIT-MAGIC-COOKIE file) correct - for a Unix/Linux machine acting as an Xterminal? - - [Sun Rays] - - Q-31: I'm having trouble using x11vnc with my Sun Ray session. - - [Remote Control] - - Q-32: How do I stop x11vnc once it is running in the background? - - Q-33: Can I change settings in x11vnc without having to restart it? - Can I remote control it? - - [Security and Permissions] - - Q-34: How do I create a VNC password for use with x11vnc? - - Q-35: Can I make it so -storepasswd doesn't show my password on the - screen? +``` - Q-36: Can I have two passwords for VNC viewers, one for full access - and the other for view-only access to the display? +## Misc. Build problems - Q-37: Can I have as many full-access and view-only passwords as I - like? +We collect here rare build problems some users +have reported and the corresponding workarounds. See also the FAQ's on +building. - Q-38: Does x11vnc support Unix usernames and passwords? Can I further - limit the set of Unix usernames who can connect to the VNC desktop? +--- - Q-39: Can I supply an external program to provide my own custom login - method (e.g. Dynamic/One-time passwords or non-Unix (LDAP) usernames - and passwords)? +ENV parameter: One user had a problem where the build script below was +failing because his work environment had the ENV variable set to a +script that was resetting his PATH so that gcc could no longer be +found. Make sure you do not have any ENV or BASH_ENV in your +environment doing things like that. Typing "unset ENV", etc. before +configuring and building should clear it. - Q-40: Why does x11vnc exit as soon as the VNC viewer disconnects? And - why doesn't it allow more than one VNC viewer to connect at the same - time? +--- - Q-41: Can I limit which machines incoming VNC clients can connect - from? +Bash xpg: One user had his bash shell compiled with +--enable-xpg-echo-default that causes some strange behavior with +things like echo "\\1 ..." the configure script executes. In +particular instead of getting "\1" the non-printable character "^A" is +produced, and causes failures at compile time like: - Q-42: How do I build x11vnc/libvncserver with libwrap (tcp_wrappers) - support? +``` +../rfb/rfbconfig.h:9:22: warning: extra tokens at end of #ifndef directive +``` - Q-43: Can I have x11vnc only listen on one network interface (e.g. - internal LAN) rather than having it listen on all network interfaces - and relying on -allow to filter unwanted connections out? +The workaround is to configure like this: - Q-44: Now that -localhost implies listening only on the loopback - interface, how I can occasionally allow in a non-localhost via the -R - allowonce remote control command? +``` +env CONFIG_SHELL=/bin/sh /bin/sh ./configure +``` - Q-45: Can I fine tune what types of user input are allowed? E.g. have - some users just be able to move the mouse, but not click or type - anything? +i.e. avoid using the bash with the misbehavior. A bug has been filed +against autoconf to guard against this. - Q-46: Can I prompt the user at the local X display whether the - incoming VNC client should be accepted or not? Can I decide to make - some clients view-only? How about running an arbitrary program to make - the decisions? +--- - Q-47: I start x11vnc as root because it is launched via inetd(8) or a - display manager like gdm(1). Can I have x11vnc later switch to a - different user? +AIX: one user had to add the "X11.adt" package to AIX to get build +header files like XShm.h, etc. - Q-48: I use a screen-lock when I leave my workstation (e.g. - xscreensaver or xlock.) When I remotely access my workstation desktop - via x11vnc I can unlock the desktop fine, but I am worried people will - see my activities on the physical monitor. What can I do to prevent - this, or at least make it more difficult? +--- - Q-49: Can I have x11vnc automatically lock the screen when I - disconnect the VNC viewer? +Ubuntu Feisty Fawn 7.04: In May/2007 one user said he needed to add +these packages to compile x11vnc on that Linux distro and version: - [Encrypted Connections] +``` +apt-get install build-essential make bin86 libjpeg62-dev libssl-dev libxtst-dev +``` - Q-50: How can I tunnel my connection to x11vnc via an encrypted SSH - channel between two Unix machines? +Note that Ubuntu is based on Debian, so perhaps this is the list +needed on Debian (testing?) as well. To build in Avahi (mDNS service +advertising) support it would appear that libavahi-client-dev is +needed as well. - Q-51: How can I tunnel my connection to x11vnc via an encrypted SSH - channel from Windows using an SSH client like Putty? +--- - Q-52: How can I tunnel my connection to x11vnc via an encrypted SSL - channel using an external tool like stunnel? +Exceedingly slow compilation: x11vnc has a couple of files which +contain very large "case statements" (over 100 cases) that on some +platforms can take a very long time to compile (in extreme cases over +an hour). However on 32bit Linux with intel/amd processor and gcc +these files usually take less than 10 seconds to compile. For 64bit +systems using gcc the problem appears to be much worse. - Q-53: Does x11vnc have built-in SSL tunneling? +The two files with the large number of cases, remote.c and x11vnc.c, +have no real need to be optimized (the code is used only very +infrequently). So it is fine to supply "-O0" (disables optimization) +to CFLAGS when compiling them. However, it is tricky with +autoconf/automake to do this (especially since both the compiler and +make versions have a big effect). - Q-54: How do I use VNC Viewers with built-in SSL tunneling? +So if the compile times are getting too long for you for these two +files you will need to manually change some things. First, run +configure and when it has finished, edit the generated file +x11vnc/Makefile and put these lines at the very top: - Q-55: How do I use the Java applet VNC Viewer with built-in SSL - tunneling when going through a Web Proxy? - - Q-56: Can Apache web server act as a gateway for users to connect via - SSL from the Internet with a Web browser to x11vnc running on their - workstations behind a firewall? - - Q-57: Can I create and use my own SSL Certificate Authority (CA) with - x11vnc? - - [Display Managers and Services] - - Q-58: How can I run x11vnc as a "service" that is always available? - - Q-59: How can I use x11vnc to connect to an X login screen like xdm, - GNOME gdm, KDE kdm, or CDE dtlogin? (i.e. nobody is logged into an X - session yet.) - - Q-60: Can I run x11vnc out of inetd(8)? How about xinetd(8)? - - Q-61: Can I have x11vnc advertise its VNC service and port via mDNS / - Zeroconf (e.g. Avahi) so VNC viewers on the local network can detect - it automatically? - - Q-62: Can I have x11vnc allow a user to log in with her UNIX username - and password and then have it find her X session display on that - machine and then attach to it? How about starting an X session if one - cannot be found? - - Q-63: Can I have x11vnc restart itself after it terminates? - - Q-64: How do I make x11vnc work with the Java VNC viewer applet in a - web browser? - - Q-65: Are reverse connections (i.e. the VNC server connecting to the - VNC viewer) using "vncviewer -listen" and vncconnect(1) supported? - - Q-66: Can reverse connections be made to go through a Web or SOCKS - proxy or SSH? - - Q-67: Can x11vnc provide a multi-user desktop web login service as an - Apache CGI or PHP script? - - Q-68: Can I use x11vnc as a replacement for Xvnc? (i.e. not for a real - display, but for a virtual one I keep around.) - - Q-69: How can I use x11vnc on "headless" machines? Why might I want - to? - - [Resource Usage and Performance] - - Q-70: I have lots of memory, but why does x11vnc fail with shmget: - No space left on device or Minor opcode of failed request: 1 - (X_ShmAttach)? - - Q-71: How can I make x11vnc use less system resources? - - Q-72: How can I make x11vnc use MORE system resources? - - Q-73: I use x11vnc over a slow link with high latency (e.g. dialup - modem or broadband), is there anything I can do to speed things up? - - Q-74: Does x11vnc support the X DAMAGE Xserver extension to find - modified regions of the screen quickly and efficiently? - - Q-75: My OpenGL application shows no screen updates unless I supply - the -noxdamage option to x11vnc. - - Q-76: When I drag windows around with the mouse or scroll up and down - things really bog down (unless I do the drag in a single, quick - motion.) Is there anything to do to improve things? - - Q-77: Why not do something like wireframe animations to avoid the - windows "lurching" when being moved or resized? - - Q-78: Can x11vnc try to apply heuristics to detect when a window is - scrolling its contents and use the CopyRect encoding for a speedup? - - Q-79: Can x11vnc do client-side caching of pixel data? I.e. so when - that pixel data is needed again it does not have to be retransmitted - over the network. - - Q-80: Does x11vnc support TurboVNC? - - [Mouse Cursor Shapes] - - Q-81: Why isn't the mouse cursor shape (the little icon shape where - the mouse pointer is) correct as I move from window to window? - - Q-82: When using XFIXES cursorshape mode, some of the cursors look - really bad with extra black borders around the cursor and other cruft. - How can I improve their appearance? - - Q-83: In XFIXES mode, are there any hacks to handle cursor - transparency ("alpha channel") exactly? - - [Mouse Pointer] - - Q-84: Why does the mouse arrow just stay in one corner in my - vncviewer, whereas my cursor (that does move) is just a dot? - - Q-85: Can I take advantage of the TightVNC extension to the VNC - protocol where Cursor Positions Updates are sent back to all connected - clients (i.e. passive viewers can see the mouse cursor being moved - around by another viewer)? - - Q-86: Is it possible to swap the mouse buttons (e.g. left-handed - operation), or arbitrarily remap them? How about mapping button clicks - to keystrokes, e.g. to partially emulate Mouse wheel scrolling? - - [Keyboard Issues] - - Q-87: How can I get my AltGr and Shift modifiers to work between - keyboards for different languages? - - Q-88: When I try to type a "<" (i.e. less than) instead I get ">" - (i.e. greater than)! Strangely, typing ">" works OK!! - - Q-89: Extra Character Inserted, E.g.: When I try to type a "<" (i.e. - less than) instead I get "<," (i.e. an extra comma.) - - Q-90: I'm using an "international" keyboard (e.g. German "de", or - Danish "dk") and the -modtweak mode works well if the VNC viewer is - run on a Unix/Linux machine with a similar keyboard. But if I run - the VNC viewer on Unix/Linux with a different keyboard (e.g. "us") or - Windows with any keyboard, I can't type some keys like: "@", "$", - "<", ">", etc. How can I fix this? - - Q-91: When typing I sometimes get double, triple, or more of my - keystrokes repeated. I'm sure I only typed them once, what can I do? - - Q-92: The x11vnc -norepeat mode is in effect, but I still get repeated - keystrokes!! +``` +x11vnc-x11vnc.o : CFLAGS += -O0 +x11vnc-remote.o : CFLAGS += -O0 +``` - Q-93: After using x11vnc for a while, I find that I cannot type some - (or any) characters or my mouse clicks and drags no longer have any - effect, or they lead to strange effects. What happened? +Those lines assume gnu make (gmake) is being used. If you are using +another make, say Solaris make, insert these instead: - Q-94: The machine where I run x11vnc has an AltGr key, but the local - machine where I run the VNC viewer does not. Is there a way I can map - a local unused key to send an AltGr? How about a Compose key as well? +``` +x11vnc-x11vnc.o := CFLAGS += -O0 +x11vnc-remote.o := CFLAGS += -O0 +``` - Q-95: I have a Sun machine I run x11vnc on. Its Sun keyboard has just - one Alt key labelled "Alt" and two Meta keys labelled with little - diamonds. The machine where I run the VNC viewer only has Alt keys. - How can I send a Meta keypress? (e.g. emacs needs this) +You could write a build shell script that modified the Makefile this +way before running make. - Q-96: Running x11vnc on HP-UX I cannot type "#" I just get a "3" - instead. +The "-O0" (note it is "capital Oh" followed by "zero") assumes the gcc +compiler. If you are using a different compiler you will need to find +the command line option to disable optimization, or otherwise have the +lines set CFLAGS to the empty string. - Q-97: Can I map a keystroke to a mouse button click on the remote - machine? +--- - Q-98: How can I get Caps_Lock to work between my VNC viewer and - x11vnc? +Broken Thread Local Storage on SuSE 9.2: Starting with x11vnc 0.9.8 +the bundled libvncserver uses the __thread keyword to make some of the +encodings (i.e. tight) thread safe (multiple VNC clients can be using +tight at the same time in x11vnc -threads mode.) Evidently on the old +SuSE 9.2 system the compiler does not support the thread local storage +properly. Here is an example build failure: - [Screen Related Issues and Features] +``` +tight.c:1126: error: unrecognizable insn: +(insn:HI 11 10 13 0 (nil) (set (reg/f:SI 59) + (const:SI (plus:SI (symbol_ref:SI ("%lpalette")) + (const_int 2048 [0x800])))) -1 (nil) + (expr_list:REG_EQUAL (const:SI (plus:SI (symbol_ref:SI ("%lpalette")) + (const_int 2048 [0x800]))) + (nil))) +tight.c:1126: internal compiler error: in extract_insn, at recog.c:2175 +Please submit a full bug report, +with preprocessed source if appropriate. +See URL:http://www.suse.de/feedback for instructions. +``` - Q-99: The remote display is larger (in number of pixels) than the - local display I am running the vncviewer on. I don't like the - vncviewer scrollbars, what I can do? +The workaround is to disable thread local storage at configure time +like this: - Q-100: Does x11vnc support server-side framebuffer scaling? (E.g. to - make the desktop smaller.) +``` +env CPPFLAGS="-DTLS=''" ./configure +``` +and then build it. + + +# Some Notes + +## Both a client and a server + +It is sometimes confusing to people that +x11vnc is both a client and a server at the same time. It is an X +client because it connects to the running X server to do the screen +polls. Think of it as a rather efficient "screenshot" program running +continuously. It is a server in the sense that it is a VNC server that +VNC viewers on the network can connect to and view the screen +framebuffer it manages. + +When trying to debug problems, remember to think of both roles. E.g. +"how is x11vnc connecting to the X server?", "how is the vncviewer +connecting to x11vnc?", "what permits/restricts the connection?". Both +links may have reachability, permission, and other issues. + +## Network performance + +Whether you are using Xvnc or x11vnc it is +always a good idea to have a solid background color instead of a +pretty background image. Each and every re-exposure of the background +must be resent over the network: better to have that background be a +solid color that compresses very well compared to a photo image. (This +is one place where the X protocol has an advantage over the VNC +protocol.) I suggest using xsetroot, dtstyle or similar utility to set +a solid background while using x11vnc. You can turn the pretty +background image back on when you are using the display directly. +Update: As of Feb/2005 x11vnc has the -solid [color] option that works +on recent GNOME, KDE, and CDE and also on classic X (background image +is on the root window.) Update: As of Oct/2007 x11vnc has the -ncache +option that does a reasonable job caching the background (and other) +pixmap data on the viewer side. + +I also find the TightVNC encoding gives the best response for my usage +(Unix <-> Unix over cable modem.) One needs a tightvnc-aware vncviewer +to take advantage of this encoding. + +## TCP port issues + +Notice the lines + +``` +18/07/2003 14:36:31 Autoprobing selected port 5900 +PORT=5900 +``` + +in the output. 5900 is the default VNC listening port (just like 6000 +is X11's default listening port.) Had port 5900 been taken by some +other application, x11vnc would have next tried 5901. That would mean +the viewer command above should be changed to vncviewer +far-away.east:1. You can force the port with the "-rfbport NNNN" +option where NNNN is the desired port number. If that port is already +taken, x11vnc will exit immediately. The "-N" option will try to match +the VNC display number to the X display. (also see the "SunRay +Gotcha" note below) + +## Options + +x11vnc has (far too) many features that may be activated +via its command line options. Useful options are, e.g., -scale to do +server-side scaling, and -rfbauth passwd-file to use VNC password +protection (the vncpasswd or storepasswd programs, or the x11vnc +-storepasswd option can be used to create the password file.) + +## Algorithm + +How does x11vnc do it? Rather brute-forcedly: it +continuously polls the X11 framebuffer for changes using +XShmGetImage(). When changes are discovered, it instructs libvncserver +which rectangular regions of the framebuffer have changed, and +libvncserver compresses the changes and sends them off to any +connected VNC viewers. A number of applications do similar things, +such as x0rfbserver, krfb, x0vncserver, vino. x11vnc uses a 32 x 32 +pixel tile model (the desktop is decomposed into roughly 1000 such +tiles), where changed tiles are found by pseudo-randomly polling 1 +pixel tall horizontal scanlines separated vertically by 32 pixels. +This is a surprisingly effective algorithm for finding changed +regions. For keyboard and mouse user input the XTEST extension is used +to pass the input events to the X server. To detect XBell "beeps" the +XKEYBOARD extension is used. If available, the XFIXES extension is +used to retrieve the current mouse cursor shape. Also, if available +the X DAMAGE extension is used to receive hints from the X server +where modified regions on the screen are. This greatly reduces the +system load when not much is changing on the screen and also improves +how quickly the screen is updated. + +## Barbershop mirrors effect + +What if x11vnc is started up, and +vncviewer is then started up on the same machine and displayed on the +same display x11vnc is polling? One might "accidentally" do this when +first testing out the programs. You get an interesting +recursive/feedback effect where vncviewer images keep popping up each +one contained in the previous one and slightly shifted a bit by the +window manager decorations. There will be an even more interesting +effect if -scale is used. Also, if the XKEYBOARD is supported and the +XBell "beeps" once, you get an infinite loop of beeps going off. +Although all of this is mildly exciting it is not much use: you will +normally run and display the viewer on a different machine! + + +# Limitations + +* Due to the polling nature, some activities (opaque window moves, + scrolling), can be pretty choppy/ragged and others (exposures of + large areas) slow. Experiment with interacting a bit differently + than you normally do to minimize the effects (e.g. do fullpage + paging rather than line-by-line scrolling, and move windows in a + single, quick motion.) Recent work has provided the + -scrollcopyrect and -wireframe speedups using the CopyRect VNC + encoding and other things, but they only speed up some activities, + not all. +* A rate limiting factor for x11vnc performance is that graphics + hardware is optimized for writing, not reading (x11vnc reads the + video framebuffer for the screen image data.) The difference can + be a factor of 10 to 1000, and so it usually takes about 0.5-1 sec + to read in the whole video hardware framebuffer (e.g. 5MB for + 1280x1024 at depth 24 with a read rate of 5-10MB/sec.) So whenever + activity changes most of the screen (e.g. moving or iconifying a + large window) there is a delay of 0.5-1 sec while x11vnc reads the + changed regions in. + A slow framebuffer read rate will often be the performance + bottleneck on a fast LAN (whereas on slower links the reduced + network bandwidth becomes the bottleneck.) + Note: A quick way to get a 2X speedup of this for x11vnc is to + switch your X server from depth 24 (32bpp) to depth 16 (16bpp.) + You get a 4X speedup going to 8bpp, but the lack of color cells is + usually unacceptable. + To get a sense of the read and write speeds of your video card, + you can run benchmarks like: "x11perf -getimage500", "x11perf + -putimage500", "x11perf -shmput500" and for XFree86 displays with + direct graphics access the "dga" command (press "b" to run the + benchmark and then after a few seconds press "q" to quit.) Even + this "dd if=/dev/fb0 of=/dev/null" often gives a good estimate. + x11vnc also prints out its estimate: - Q-101: Does x11vnc work with Xinerama? (i.e. multiple monitors joined - together to form one big, single screen.) + ``` + 28/02/2009 11:11:07 Autoprobing TCP port + 28/02/2009 11:11:07 Autoprobing selected port 5900 + 28/02/2009 11:11:08 fb read rate: 10 MB/sec + 28/02/2009 11:11:08 screen setup finished. + ``` - Q-102: Can I use x11vnc on a multi-headed display that is not Xinerama - (i.e. separate screens :0.0, :0.1, ... for each monitor)? - - Q-103: Can x11vnc show only a portion of the display? (E.g. for a - special purpose application or a very large screen.) - - Q-104: Does x11vnc support the XRANDR (X Resize, Rotate and - Reflection) extension? Whenever I rotate or resize the screen x11vnc - just seems to crash. - - Q-105: Independent of any XRANDR, can I have x11vnc rotate and/or - reflect the screen that the VNC viewers see? (e.g. for a handheld - whose screen is rotated 90 degrees.) - - Q-106: Why is the view in my VNC viewer completely black? Or why is - everything flashing around randomly? - - Q-107: I use Linux Virtual Terminals (VT's) to implement 'Fast User - Switching' between users' sessions (e.g. Betty is on Ctrl-Alt-F7, - Bobby is on Ctrl-Alt-F8, and Sid is on Ctrl-Alt-F1: they use those - keystrokes to switch between their sessions.) How come the view in a - VNC viewer connecting to x11vnc is either completely black or - otherwise all messed up unless the X session x11vnc is attached to is - in the active VT? - - Q-108: I am using x11vnc where my local machine has "popup/hidden - taskbars" and the remote display where x11vnc runs also has - "popup/hidden taskbars" and they interfere and fight with each other. - What can I do? - - Q-109: Help! x11vnc and my KDE screensaver keep switching each other - on and off every few seconds. - - Q-110: I am running the compiz 3D window manager (or beryl, MythTv, - Google Earth, or some other OpenGL app) and I do not get screen - updates in x11vnc. - - Q-111: Can I use x11vnc to view my VMWare session remotely? - - [Exporting non-X11 devices via VNC] - - Q-112: Can non-X devices (e.g. a raw framebuffer) be viewed (and even - controlled) via VNC with x11vnc? - - Q-113: Can I export the Linux Console (Virtual Terminals) via VNC - using x11vnc? - - Q-114: Can I export via VNC a Webcam or TV tuner framebuffer using - x11vnc? - - Q-115: Can I connect via VNC to a Qt-embedded/Qt-enhanced/Qtopia - application running on my handheld, cell phone, or PC using the Linux - console framebuffer (i.e. not X11)? - - Q-116: How do I inject touch screen input into an - Qt-embedded/Qt-enhanced/Qtopia cell phone such as openmoko/qtmoko Neo - Freerunner? - - Q-117: Now that non-X11 devices can be exported via VNC using x11vnc, - can I build it with no dependencies on X11 header files and libraries? - - Q-118: How do I cross compile x11vnc for a different architecture than - my Linux i386 or amd64 PC? - - Q-119: Does x11vnc support Mac OS X Aqua/Quartz displays natively - (i.e. no X11 involved)? - - Q-120: Can x11vnc be used as a VNC reflector/repeater to improve - performance for the case of a large number of simultaneous VNC viewers - (e.g. classroom broadcasting or a large demo)? - - Q-121: Can x11vnc be used during a Linux, Solaris, etc. system - Installation so the Installation can be done remotely? - - [Misc: Clipboard, File Transfer/Sharing, Printing, Sound, Beeps, - Thanks, etc.] - - Q-122: Does the Clipboard/Selection get transferred between the - vncviewer and the X display? - - Q-123: Can I use x11vnc to record a Shock Wave Flash (or other format) - video of my desktop, e.g. to record a tutorial or demo? - - Q-124: Can I transfer files back and forth with x11vnc? - - Q-125: Which UltraVNC extensions are supported? - - Q-126: Can x11vnc emulate UltraVNC's Single Click helpdesk mode for - Unix? I.e. something very simple for a naive user to initiate a - reverse vnc connection from their Unix desktop to a helpdesk - operator's VNC Viewer. - - Q-127: Can I (temporarily) mount my local (viewer-side) Windows/Samba - File share on the machine where x11vnc is running? - - Q-128: Can I redirect CUPS print jobs from the remote desktop where - x11vnc is running to a printer on my local (viewer-side) machine? - - Q-129: How can I hear the sound (audio) from the remote applications - on the desktop I am viewing via x11vnc? - - Q-130: Why don't I hear the "Beeps" in my X session (e.g. when typing - tput bel in an xterm)? - - Q-131: Does x11vnc work with IPv6? - - Q-132: Thanks for your program or for your help! Can I make a - donation? - - Q-133: I am experiencing extreme framebuffer update lags and am - using an Intel graphics card. What to do? - -_________________________________________________________________ - - - [Building and Starting] - - Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed - (null)" or "Xlib: connection to ":0.0" refused by server Xlib: No - protocol specified" and then exits. What do I need to do? - - For the former error, you need to specify the X display to connect to - (it also needs to be on the same machine the x11vnc process is to run - on.) Set your DISPLAY environment variable (or use the -display - option) to specify it. Nearly always the correct value will be ":0" - (in fact, x11vnc will now assume :0 if given no other information.) - - - For the latter error, you need to set up the X11 permissions - correctly. - - To make sure X11 permissions are the problem do this simple test: - while sitting at the physical X display open a terminal window - (gnome-terminal, xterm, etc.) You should be able to run x11vnc - successfully without any need for special steps or command line - options in that terminal (i.e. just type "x11vnc".) If that works OK - then you know X11 permissions are the only thing preventing it from - working when you try to start x11vnc via, say, a remote shell. - - How to Solve: See the xauth(1), Xsecurity(7), and xhost(1) man pages - or this Howto for much info on X11 permissions. For example, you may - need to set your XAUTHORITY environment variable (or use the -auth - option) to point to the correct MIT-MAGIC-COOKIE file (e.g. - /home/joe/.Xauthority or /var/gdm/:0.Xauth or /var/lib/kdm/A:0-crWk72K - or /tmp/.gdmzndVlR, etc, etc.), or simply be sure you run x11vnc as - the correct user (i.e. the user who is logged into the X session you - wish to view.) - - Note: The MIT cookie file contains the secret key that allows x11vnc - to connect to the desired X display. - - If, say, sshd has set XAUTHORITY to point to a random file it has - created for X forwarding that will cause problems. (Under some - circumstances even su(1) and telnet(1) can set XAUTHORITY. See also - the gdm parameter NeverPlaceCookiesOnNFS that sets XAUTHORITY to a - random filename in /tmp for the whole X session.) - - Running x11vnc as root is often not enough: you need to know where the - MIT-MAGIC-COOKIE file for the desired X display is. - - Example solution: - x11vnc -display :0 -auth /var/gdm/:0.Xauth - - (this is for the display manager gdm and requires root permission to - read the gdm cookie file, see this faq for other display manager - cookie file names.) - - Note as of Feb/2007 you can also try the -find option instead of - "-display ..." and see if that finds your display and Xauthority. - - Less safe, but to avoid figuring out where the correct XAUTHORITY file - is, if the person sitting at the physical X session types "xhost - +localhost" then one should be able to attach x11vnc to the session - (from the same machine.) The person could then type "xhost -localhost" - after x11vnc has connected to go back to the default permissions. - Also, for some situations the "-users lurk=" option may soon be of use - (please read the documentation on the -users option.) - - To test out your X11 permissions from a remote shell, set DISPLAY and - possibly XAUTHORITY (see your shell's man page, bash(1), tcsh(1), on - how to set environment variables) and type xdpyinfo in the same place - you will be typing (or otherwise running) x11vnc. If information is - printed out about the X display (screen sizes, supported extensions, - color visuals info) that means the X11 permissions are set up - properly: xdpyinfo successfully connected to DISPLAY! You could also - type xclock and make sure no errors are reported (a clock should - appear on the X display, press Ctrl-C to stop it.) If these work, then - typing "x11vnc" in the same environment should also work. - - Important: if you cannot get your X11 permissions so that the xdpyinfo - or xclock tests work, x11vnc also will not work (all of these X - clients must be allowed to connect to the X server to function - properly.) - - Firewalls: Speaking of permissions, it should go without saying that - the host-level firewall will need to be configured to allow - connections in on a port. E.g. 5900 (default VNC port) or 22 (default - SSH port for tunnelling VNC.) Most systems these days have firewalls - turned on by default, so you will actively have to do something to - poke a hole in the firewall at the desired port number. See your - system administration tool for Firewall settings (Yast, Firestarter, - etc.) - - - Q-2: I can't get x11vnc and/or libvncserver to compile. - - Make sure you have gcc (or other C compiler) and all of the required - libraries and the corresponding -dev/-devel packages installed. These - include Xorg/XFree86, libX11, libjpeg, libz, libssl, ... and don't - forget the devs: libjpeg-dev, libssl-dev ... - - The most common build problem that people encounter is that the - necessary X11 libraries are installed on their system however it does - not have the corresponding -dev/-devel packages installed. These dev - packages include C header files and build-time .so symlink. It is a - shame the current trend in distros is to not install the dev package - by default when the the library runtime package is installed... (it - diminishes the power of open source) - - As of Nov/2006 here is a list of libraries that x11vnc usually likes - to use: -libc.so libX11.so libXtst.so libXext.so -libXfixes.so libXdamage.so libXinerama.so libXrandr.so -libz.so libjpeg.so libpthread.so -libssl.so libcrypto.so libcrypt.so - - although x11vnc will be pretty usable with the subset: libc.so, - libX11.so, libXtst.so, libXext.so, libz.so, and libjpeg.so. - - After running the libvncserver configure, carefully examine the output - and the messages in the config.log file looking for missing - components. For example, if the configure output looks like: - checking how to run the C preprocessor... gcc -E - checking for X... no - checking for XkbSelectEvents in -lX11... no - checking for XineramaQueryScreens in -lXinerama... no - checking for XTestFakeKeyEvent in -lXtst... no - - or even worse: - checking for C compiler default output file name... configure: error: - C compiler cannot create executables - See `config.log' for more details. - - there is quite a bit wrong with the build environment. Hopefully - simply adding -dev packages and/or gcc or make will fix it. - - For Debian the list seems to be: - gcc - make - libc6-dev - libjpeg8-dev (formerly libjpeg62-dev) - libx11-dev - x11proto-core-dev (formerly x-dev) - libxext-dev - libxtst-dev - libxdamage-dev - libxfixes-dev - libxrandr-dev - libxinerama-dev - libxss-dev (formerly xlibs-static-dev) - zlib1g-dev - libssl-dev - libavahi-client-dev - linux-libc-dev (only needed for linux console rawfb support) - - Note that depending on your OS version the above names may have been - changed and/or additional packages may be needed. - - For Redhat the list seems to be: - gcc - make - glibc-devel - libjpeg-devel - libX11-devel - xorg-x11-proto-devel - libXdamage-devel - libXfixes-devel - libXrandr-devel - zlib-devel - openssl-devel - avahi-devel - kernel-headers (only needed for linux console rawfb support) - - For other distros or OS's the package names may not be the same but - will look similar. Also, distros tend to rename packages as well so - the above list may be out of date. So only use the above lists as - hints for the package names that are needed. - - Have a look at Misc. Build Problems for additional fixes. - - Note: there is growing trend in Linux and other distros to slice up - core X11 software into more and smaller packages. So be prepared for - more headaches compiling software... - - - Q-3: I just built x11vnc successfully, but when I use it my keystrokes - and mouse button clicks are ignored (I am able to move the mouse - though.) - - This is most likely due to you not having a working build environment - for the XTEST client library libXtst.so. The library is probably - present on your system, but the package installing the build header - file is missing. - - If you were watching carefully while configure was running you would - have seen: - checking for XTestFakeKeyEvent in -lXtst... no - - The solution is to add the necessary build environment package (and - the library package if that is missing too.) On Debian the build - package is libxtst-dev. Other distros/OS's may have it in another - package. - - x11vnc will build without support for this library (e.g. perhaps one - wants a view-only x11vnc on a stripped down or embedded system...) And - at runtime it will also continue to run even if the X server it - connects to does not support XTEST. In both cases it cannot inject - keystrokes or button clicks since XTEST is needed for that (it can - still move the mouse pointer using the X API XWarpPointer().) - - You will see a warning message something like this at run time: - 20/03/2005 22:33:09 WARNING: XTEST extension not available (either missing fr -om - 20/03/2005 22:33:09 display or client library libXtst missing at build time -.) - 20/03/2005 22:33:09 MOST user input (pointer and keyboard) will be DISCARDE -D. - 20/03/2005 22:33:09 If display does have XTEST, be sure to build x11vnc wit -h - 20/03/2005 22:33:09 a working libXtst build environment (e.g. libxtst-dev, - 20/03/2005 22:33:09 or other packages.) - 20/03/2005 22:33:09 No XTEST extension, switching to -xwarppointer mode for - 20/03/2005 22:33:09 pointer motion input. - - Also, as of Nov/2006 there will be a configure build time warning as - well: - ... - checking for XFixesGetCursorImage in -lXfixes... yes - checking for XDamageQueryExtension in -lXdamage... yes - configure: WARNING: - ========================================================================== - A working build environment for the XTEST extension was not found (libXtst). - An x11vnc built this way will be only barely usable. You will be able to - move the mouse but not click or type. There can also be deadlocks if an - application grabs the X server. - - It is recommended that you install the necessary development packages - for XTEST (perhaps it is named something like libxtst-dev) and run - configure again. - ========================================================================== - - - Q-4: Help, I need to run x11vnc on Solaris 2.5.1 (or other old - Unix/Linux) and it doesn't compile! - - We apologize that x11vnc does not build cleanly on older versions of - Solaris, Linux, etc.: very few users are on these old releases. - - We have heard that since Dec/2004 a Solaris 2.6 built x11vnc will run - on Solaris Solaris 2.5 and 2.5.1 (since a workaround for XConvertCase - is provided.) - - In any event, here is a workaround for Solaris 2.5.1 (and perhaps - earlier and perhaps non-Solaris): - - First use the environment settings (CPPFLAGS, LDFLAGS, etc.) in the - above Solaris build script to run the configure command. That should - succeed without failure. Then you have to hand edit the autogenerated - rfb/rfbconfig.h file in the source tree, and just before the last - #endif at the bottom of that file insert these workaround lines: -struct timeval _tmp_usleep_tv; -#define usleep(x) \ - _tmp_usleep_tv.tv_sec = (x) / 1000000; \ - _tmp_usleep_tv.tv_usec = (x) % 1000000; \ - select(0, NULL, NULL, NULL, &_tmp_usleep_tv); -int gethostname(char *name, int namelen); -long random(); -int srandom(unsigned int seed); -#undef LIBVNCSERVER_HAVE_LIBPTHREAD -#define SHUT_RDWR 2 -typedef unsigned int in_addr_t; -#define snprintf(a, n, args...) sprintf((a), ## args) - - Then run make with the Solaris build script environment, everything - should compile without problems, and the resulting x11vnc binary - should work OK. If some non-x11vnc related programs fail (e.g. test - programs) and the x11vnc binary is not created try "make -k" to have - it keep going. Similar sorts of kludges in rfb/rfbconfig.h can be done - on other older OS (Solaris, Linux, ...) releases. - - Here are some notes for similar steps that need to be done to build on - SunOS 4.x - - Please let us know if you had to use the above workaround (and whether - it worked or not.) If there is enough demand we will try to push clean - compilations back to earlier Solaris, Linux, etc, releases. - - - Q-5: Where can I get a precompiled x11vnc binary for my Operating - System? - - Hopefully the build steps above and FAQ provide enough info for a - painless compile for most environments. Please report problems with - the x11vnc configure, make, etc. on your system (if your system is - known to compile other GNU packages successfully.) - - There are precompiled x11vnc binaries built by other groups that are - available at the following locations: - Slackware: (.tgz) http://www.linuxpackages.net/ - - SuSE: (.rpm) http:/software.opensuse.org/ Gentoo: (info) - http://gentoo-wiki.com/ and http://gentoo-portage.com/ FreeBSD: (.tbz) - http://www.freebsd.org/ http://www.freshports.org/net/x11vnc NetBSD: - (src) http://pkgsrc.se/x11/x11vnc OpenBSD: (.tgz) http://openports.se/ - Arch Linux: (.tgz) http://www.archlinux.org/ Nokia 770 (.deb) - http://mike.saunby.googlepages.com/x11vncfornokia7702 Sharp Zaurus - http://www.focv.com/ Debian: (.deb) http://packages.debian.org/x11vnc - Redhat/Fedora: (.rpm) http://packages.sw.be/x11vnc RPMforge - http://dag.wieers.com/rpm/packages/x11vnc/ (N.B.: unmaintained after - 0.9.3) Solaris: (pkg) http://www.sunfreeware.com/ - - If the above binaries don't work and building x11vnc on your OS fails - (and all else fails!) you can try one of My Collection of x11vnc - Binaries for various OS's and x11vnc releases. - - As a general note, the x11vnc program is simple enough you don't - really need to install a package: the binary will in most cases work - as is and from any location (as long as your system libraries are not - too old, etc.) So, for Linux distributions that are not one of the - above, the x11vnc binary from the above packages has a good chance of - working. You can "install" it by just copying the x11vnc binary to the - desired directory in your PATH. Tip on extracting files from a Debian - package: extract the archive via a command like: "ar x - x11vnc_0.6-2_i386.deb" and then you can find the binary in the - resulting data.tar.gz tar file. Also, rpm2cpio(1) is useful in - extracting files from rpm packages. - - If you use a standalone binary like this and also want x11vnc to serve - up the Java VNC Viewer jar file (either SSL enabled or regular one), - then you will need to extract the classes subdirectory from the source - tarball and point x11vnc to it via the -httpdir option. E.g.: - x11vnc -httpdir /path/to/x11vnc-0.9.9/classes/ssl ... - - Alternatively, you can also go for a more up-to-date approach and use - the very decent noVNC viewer (https://kanaka.github.io/noVNC/) that is - purely HTML5 and does not need any plugins at all. - - - Q-6: Where can I get a VNC Viewer binary (or source code) for the - Operating System I will be viewing from? - - To obtain VNC viewers for the viewing side (Windows, Mac OS, or Unix) - try here: - * http://www.tightvnc.com/download.html - * http://www.realvnc.com/download-free.html - * http://sourceforge.net/projects/cotvnc/ - * http://www.ultravnc.com/ - * Our Enhanced TightVNC Viewer (SSVNC) - - [ssvnc.gif] - - - Q-7: How can I see all of x11vnc's command line options and - documentation on how to use them? - - Run: x11vnc -opts to list just the option names or run: x11vnc - -help for long descriptions about each option. The output is listed - here as well. Yes, x11vnc does have a lot of options, doesn't it... - - - Q-8: I don't like typing arcane command line options every time I - start x11vnc. What can I do? Is there a config file? Or a GUI? - - You could create a shell script that calls x11vnc with your options: -#!/bin/sh -# -# filename: X11vnc (i.e. not "x11vnc") -# It resides in a directory in $PATH. "chmod 755 X11vnc" has been run on it. -# -x11vnc -wait 50 -localhost -rfbauth $HOME/.vnc/passwd -display :0 $* - - a similar thing can be done via aliases in your shell (bash, tcsh, - csh, etc..) - - Or as of Jun/2004 you can use the simple $HOME/.x11vncrc config file - support. If that file exists, each line is taken as a command line - option. E.g. the above would be: -# this is a comment in my ~/.x11vncrc file -wait 50 # this is a comment to the end of the line. --localhost # note: the leading "-" is optional. -rfbauth /home/fred/.vnc/passwd -display :0 - - As of Dec/2004 there is now a simple Tcl/Tk GUI based on the - remote-control functionality ("-R") that was added. The /usr/bin/wish - program is needed for operation. The gui is not particularly - user-friendly, it just provides a point and click mode to set all the - many x11vnc parameters and obtain help on them. It is also very useful - for testing. See the -gui option for more info. Examples: "x11vnc ... - -gui" and "x11vnc ... -gui other:0" in the latter case the gui is - displayed on other:0, not the X display x11vnc is polling. There is - also a "-gui tray" system tray mode. - - [tkx11vnc.gif] - - NOTE: You may need to install the "wish" or "tk" or "tk8.4" package - for the gui mode to work (the package name depends on your OS/distro.) - The tcl/tk "wish" interpreter is used. In debian (and so ubuntu too) - one would run "apt-get install tk" or perhaps "apt-get install tk8.4" - - - Q-9: How can I get the GUI to run in the System Tray, or at least be a - smaller, simpler icon? - - As of Jul/2005 the gui can run in a more friendly small icon mode - "-gui icon" or in the system tray: "-gui tray". It has balloon status, - a simple menu, and a Properities dialog. The full, complicated, gui is - only available under "Advanced". Other improvements were added as - well. Try "Misc -> simple_gui" for a gui with fewer esoteric menu - items. - - If the gui fails to embed itself in the system tray, do a retry via - "Window View -> icon" followed by "Window View -> tray" with the popup - menu. - - For inexperienced users starting up x11vnc and the GUI while sitting - at the physical X display (not remotely), using something like "x11vnc - -display :0 -gui tray=setpass" might be something for them that they - are accustomed to in a Desktop environment (it prompts for an initial - password, etc.) This is a basic "Share My Desktop" usage mode. - - As of Nov/2008 in x11vnc 0.9.6 there is a desktop menu item - (x11vnc.desktop) that runs this command: - x11vnc -gui tray=setpass -rfbport PROMPT -logfile %HOME/.x11vnc.log.%VNCDISP -LAY - - which also prompts for which VNC port to use and a couple other - parameters. - - - Q-10: How can I get x11vnc to listen on a different port besides the - default VNC port (5900)? - - Use something like, e.g., "x11vnc -rfbport 5901" to force it to use - port 5901 (this is VNC display :1.) If something else is using that - port x11vnc will exit immediately. If you do not supply the -rfbport - option, it will autoprobe starting at 5900 and work its way up to 5999 - looking for a free port to listen on. In that case, watch for the - PORT=59xx line to see which port it found, then subtract 5900 from it - for the VNC display number to enter into the VNC Viewer(s). - - The "-N" option will try to match the VNC display number to the X - display (e.g. X11 DISPLAY of :5 (port 6005) will have VNC display :5 - (port 5905).) - - Also see the "-autoport n" option to indicated at which value the auto - probing should start at. - - - Q-11: My Firewall/Router doesn't allow VNC Viewers to connect to - x11vnc. - - See the Firewalls/Routers discussion. - - - Q-12: Is it possible for a VNC Viewer and a VNC Server to connect to - each other even though both are behind Firewalls that block all - incoming connections? - - This is very difficult or impossible to do unless a third machine, - reachable by both, is used as a relay. So we assume a third machine is - somehow being used as a relay. - - (Update: It may be possible to do "NAT-2-NAT" without a relay machine - by using a UDP tunnel such as http://samy.pl/pwnat/. All that is - required is that both NAT firewalls allow in UDP packets from an IP - address to which a UDP packet has recently been sent to. If you try it - out let us know how it went.) - - In the following discussion, we will suppose port 5950 is being used - on the relay machine as the VNC port for the rendezvous. - - A way to rendezvous is to have the VNC Server start a reverse - connection to the relay machine: - x11vnc -connect third-machine.net:5950 ... - - and the VNC viewer forward connects as usual: - vncviewer third-machine.net:50 - - Or maybe two ports would be involved, e.g. the viewer goes to display - :51 (5951.) It depends on the relay software being used. - - What software to run on third-machine? A TCP relay of some sort could - be used... Try a google search on "tcp relay" or "ip relay". However, - note that this isn't a simple redirection because it hooks up two - incoming connections. You can look at our UltraVNC repeater - implementation ultravnc_repeater.pl for ideas and possibly to - customize. - - Also, if you are not the admin of third-machine you'd have to convince - the owner to allow you to install this software (and he would likely - need to open his server's firewall to allow the port through.) - - It is recommended that SSL is used for encryption (e.g. "-ssl SAVE") - when going over the internet. - - We have a prototype for performing a rendezvous via a Web Server - acting as the relay machine. Download the vncxfer CGI script and see - the instructions at the top. - - Once that CGI script is set up on the website, both users go to, say, - http://somesite.com/vncxfer (or maybe a "/cgi-bin" directory or ".cgi" - suffix must be used.) Previously, both have agreed on the same session - name (say by phone or email) , e.g. "5cows", and put that into the - entry form on the vncxfer starting page (hopefully separated by a few - seconds, so the relay helper can fully start up at the first request.) - - The page returned tells them the hostname and port number and possible - command to use for forward (VNC Viewer) and reverse (VNC Server, i.e. - x11vnc) connections as described above. - - Also since Oct/2007, x11vnc can connect directly (no web browser), - like this: - x11vnc ... -connect localhost:0 -proxy 'http://somesite.com/vncxfer?session= -5cows&' - - Unfortunately the prototype requires that the Web server's firewall - allow in the port (e.g. 5950) used for the rendezvous. Most web - servers are not configured to do this, so you would need to ask the - admin to do this for you. Nearly all free webspace sites, e.g. - www.zendurl.com, will not allow your CGI script to be an open relay - like this. (If you find one that does allow this, let me know!) - - Maybe someday a clever trick will be thought up to relax the listening - port requirement (e.g. use HTTP/CGI itself for the transfer... it is - difficult to emulate a full-duplex TCP connection with them.) - - See also the Firewalls/Routers discussion and Reverse Connection Proxy - discussion. - - - SSH method: If both users (i.e. one on Viewer-side and the other on - x11vnc server side) have SSH access to a common machine on the - internet (or otherwise mutually reachable), then SSH plumbing can be - used to solve this problem. The users create SSH tunnels going through - the SSH login machine. - - Instead of assuming port 5900 is free on the SSH machine, we will - assume both users agreed to use 5933. This will illustrate how to use - a different port for the redir. It could be any port, what matters is - that both parties refer to the same one. - - Set up the Tunnel from the VNC Server side: - ssh -t -R 5933:localhost:5900 user@third-machine.net - - Set up the Tunnel from the VNC Viewer side: - ssh -t -L 5900:localhost:5933 user@third-machine.net - - Run Server on the VNC Server side: - x11vnc -rfbport 5900 -localhost ... - - Run Viewer on the VNC Viewer side: - vncviewer -encodings "copyrect tight zrle hextile" localhost:0 - - (we assume the old-style -encodings option needs to be used. See here - for details.) - - If the SSH machine has been configured (see sshd_config(5)) with the - option GatewayPorts=yes, then the tunnel set up by the VNC Server will - be reachable directly by the VNC viewer (as long as the SSH machine's - firewall does not block the port, 5933 in this example.) So in that - case the Viewer side does not need to run any ssh command, but rather - only runs: - vncviewer third-machine.net:33 - - In this case we recommend SSL be used for encryption. - - The creation of both tunnels can be automated. As of Oct/2007 the -ssh - x11vnc option is available and so only this command needs to be run on - the VNC Server side: - x11vnc -ssh user@third-machine.net:33 ... - - (the SSH passphrase may need to be supplied.) - - To automate on the VNC Viewer side, the user can use the Enhanced - TightVNC Viewer (SSVNC) by: - * Clicking on 'Use SSH' - * Entering user@third-machine.net:33 into 'VNC Host:Display' entry - box - * Clicking on 'Connect' - - As above, if the SSH GatewayPorts=yes setting is configured the Viewer - side doesn't need to create a SSH tunnel. In SSVNC the Viewer user - could instead select 'Use SSL' and then, e.g., on the Server side - supply "-ssl SAVE" to x11vnc. Then end-to-end SSL encryption would be - used (in addition to the SSH encryption on the Server-side leg.) - - - Q-13: Can I make x11vnc more quiet and also go into the background - after starting up? - - Use the -q and -bg options, respectively. (also: -quiet is an alias - for -q) - - Note that under -bg the stderr messages will be lost unless you use - the "-o logfile" option. - - - Q-14: Sometimes when a VNC viewer dies abruptly, x11vnc also dies with - the error message like: "Broken pipe". I'm using the -forever mode and - I want x11vnc to keep running. - - As of Jan/2004 the SIGPIPE signal is ignored. So if a viewer client - terminates abruptly, libvncserver will notice on the next I/O - operation and will close the connection and continue on. - - Up until of Apr/2004 the above fix only works for BSD signal systems - (Linux, FreeBSD, ...) For SYSV systems there is a workaround in place - since about Jun/2004. - - - Q-15: The Windows TightVNC 1.3.9 Viewer cannot connect to x11vnc. - - This appears to be fixed in x11vnc version 0.9 and later. If you need - to use an earlier version of x11vnc, try using the "-rfbversion 3.7" - option. In general sometimes one can get a misbehaving viewer to work - by supplying rfb versions 3.7 or 3.3. - - - Q-16: KDE's krdc VNC viewer cannot connect to x11vnc. - - This has been fixed in x11vnc version 0.8.4. More info here, here, and - here. - - - Q-17: When I start x11vnc on an Alpha Tru64 workstation the X server - crashes! - - This is a bug in the X server obviously; an X client should never be - able to crash it. - - The problem seems to be with the RECORD X extension and so a - workaround is to use the "-noxrecord" x11vnc command line option. - - - Q-18: When running x11vnc on an IBM AIX workstation after a few - minutes the VNC connection freezes. - - One user reports when running x11vnc on AIX 5.3 in his CDE session - after a few minutes or seconds x11vnc will "freeze" (no more updates - being sent, etc.) The freezing appeared to be worse for versions later - than 0.9.2. - - The problem seems to be with the RECORD X extension on AIX and so a - workaround is to use the "-noxrecord" x11vnc command line option. The - user found no freezes occurred when using that option. - - - Q-19: Are there any build-time customizations possible, e.g. change - defaults, create a smaller binary, etc? - - There are some options. They are enabled by adding something like - -Dxxxx=1 to the CPPFLAGS environment variable before running configure - (see the build notes for general background.) -/* - * Mar/2006 - * Build-time customization via CPPFLAGS. - * - * Summary of options to include in CPPFLAGS for custom builds: - * - * -DVNCSHARED to have the vnc display shared by default. - * -DFOREVER to have -forever on by default. - * -DNOREPEAT=0 to have -repeat on by default. - * -DADDKEYSYMS=0 to have -noadd_keysyms the default. - * - * -DREMOTE_DEFAULT=0 to disable remote-control on by default (-yesremote.) - * -DREMOTE_CONTROL=0 to disable remote-control mechanism completely. - * -DEXTERNAL_COMMANDS=0 to disable the running of all external commands. - * -DFILEXFER=0 disable filexfer. - * - * -DHARDWIRE_PASSWD=... hardwired passwords, quoting necessary. - * -DHARDWIRE_VIEWPASSWD=... - * -DNOPW=1 make -nopw the default (skip warning) - * -DUSEPW=1 make -usepw the default - * -DPASSWD_REQUIRED=1 exit unless a password is supplied. - * -DPASSWD_UNLESS_NOPW=1 exit unless a password is supplied and no -nopw. - * - * -DWIREFRAME=0 to have -nowireframe as the default. - * -DWIREFRAME_COPYRECT=0 to have -nowirecopyrect as the default. - * -DWIREFRAME_PARMS=... set default -wirecopyrect parameters. - * -DSCROLL_COPYRECT=0 to have -noscrollcopyrect as the default. - * -DSCROLL_COPYRECT_PARMS=... set default -scrollcopyrect parameters. - * -DSCALING_COPYRECT=0 - * -DXDAMAGE=0 to have -noxdamage as the default. - * -DSKIPDUPS=0 to have -noskip_dups as the default or vice versa. - * - * -DPOINTER_MODE_DEFAULT={0,1,2,3,4} set default -pointer_mode. - * -DBOLDLY_CLOSE_DISPLAY=0 to not close X DISPLAY under -rawfb. - * -DSMALL_FOOTPRINT=1 for smaller binary size (no help, no gui, etc) - * use 2 or 3 for even smaller footprint. - * -DNOGUI do not include the gui tkx11vnc. - * -DPOLL_8TO24_DELAY=N - * -DDEBUG_XEVENTS=1 enable printout for X events. - * - * Set these in CPPFLAGS before running configure. E.g.: - * - * % env CPPFLAGS="-DFOREVER -DREMOTE_CONTROL=0" ./configure - * % make - */ - - If other things (e.g. "-I ...") are needed in CPPFLAGS add them as - well. - - On some systems is seems you need to set LC_ALL=C for configure to - work properly... - - Be careful the following two variables: HARDWIRE_PASSWD and - HARDWIRE_VIEWPASSWD. If set (remember to include the double quotes - around the string), they will be used as default values for the - -passwd and -viewpasswd options. Of course the strings will exist - unobscured in the x11vnc binary: it better not be readable by - unintendeds. Perhaps this is of use in remote access for an embedded - application, etc... - - Let us know if more build-time customizations would be useful. - - - [Win2VNC Related] - - Q-20: I have two separate machine displays in front of me, one Windows - the other X11: can I use x11vnc in combination with Win2VNC in - dual-screen mode to pass the keystrokes and mouse motions to the X11 - display? - - Yes, for best response start up x11vnc with the "-nofb" option - (disables framebuffer polling, and does other optimizations) on the - secondary display (X11) machine. Then start up Win2VNC on the primary - display (Windows) referring it to the secondary display. - - This will also work X11 to X11 using x2vnc, however you would probably - just want to avoid VNC and use x2x for that. - - For reference, here are some links to Win2VNC-like programs for - multiple monitor setups: - * Original Win2VNC - * Enhanced Win2VNC (broken?) and sourceforge link - * x2vnc - * x2x - * zvnc (MorphOS) - - All of them will work with x11vnc (except x2x where it is not needed.) - - - Q-21: I am running Win2VNC on my Windows machine and "x11vnc -nofb" on - Unix to pass keyboard and mouse to the Unix monitor. Whenever I start - Win2VNC it quickly disconnects and x11vnc says: - rfbProcessClientNormalMessage: read: Connection reset by peer - - Is the default visual of the X display you run x11vnc on low color - (e.g. 8 bit per pixel PseudoColor)? (you can run xdpyinfo to check, - look in the "screen" section.) There seems to be a bug in Win2VNC in - that it cannot deal correctly with colormaps (PseudoColor is the most - common example of a visual with a colormap.) - - If so, there are a couple options. 1) Can you set the default visual - on your display to be depth 24 TrueColor? Sun machines often have 8+24 - overlay/multi-depth visuals, and you can make the default visual depth - 24 TrueColor (see fbconfig(1) and Xsun(1).) 2) As of Feb/2004 x11vnc - has the -visual option to allow you to force the framebuffer visual to - whatever you want (this usually messes up the colors unless you are - very clever.) In this case, the option provides a convenient - workaround for the Win2VNC bug: - x11vnc -nofb -visual TrueColor -display :0 ... - - So the visual will be set to 8bpp TrueColor and Win2VNC can handle - this. Since Win2VNC does not use the framebuffer data there should be - no problems in doing this. - - Q-22: Can I run "x11vnc -nofb" on a Mac OS X machine to redirect mouse - and keyboard input to it from Windows and X11 machines via Win2VNC and - x2vnc, respectively? - - Yes, as of Nov/2006 you can. There may be a trick or two you'll need - to do to get the Clipboard exchange between the machines to work. - - - - [Color Issues] - - Q-23: The X display I run x11vnc on is only 8 bits per pixel (bpp) - PseudoColor (i.e. only 256 distinct colors.) The x11vnc colors may - start out OK, but after a while they are incorrect in certain windows. - - Use the -flashcmap option to have x11vnc watch for changes in the - colormap, and propagate those changes back to connected clients. This - can be slow (since the whole screen must be updated over the network - whenever the colormap changes.) This flashing colormap behavior often - happens if an application installs its own private colormap when the - mouse is in its window. "netscape -install" is a well-known historical - example of this. Consider reconfiguring the system to 16 bpp or depth - 24 TrueColor if at all possible. - - Also note the option -8to24 (Jan/2006) can often remove the need for - flashing the colormap. Everything is dynamically transformed to depth - 24 at 32 bpp using the colormaps. There may be painting errors however - (see the following FAQ for tips on reducing and correcting them.) - - In some rare cases (SCO unixware) the -notruecolor option has - corrected colors on 8bpp displays. The red, green, and blue masks were - non-zero in 8bpp PseudoColor on an obscure setup, and this option - corrected the problems. - - - Q-24: Color problems: Why are the colors for some windows incorrect in - x11vnc? BTW, my X display has nice overlay/multi-depth visuals of - different color depths: e.g. there are both depth 8 and 24 visuals - available at the same time. - - You may want to review the previous question regarding 8 bpp - PseudoColor. - - On some hardware (Sun/SPARC and SGI), the -overlay option discussed a - couple paragraphs down may solve this for you (you may want to skip to - it directly.) On other hardware the less robust -8to24 option may help - (also discussed below.) - - Run xdpyinfo(1) to see what the default visual is and what the depths - of the other visuals are. Does the default visual have a depth of 8 - but there are other visuals of depth 24? If it does, can you possibly - re-configure your X server to make a depth 24 visual the default? If - you can do it, this will save you a lot of grief WRT colors and x11vnc - (and for general usage too!) Here is how I do this on an old - Sparcstation 20 running Solaris 9 with SX graphics - xinit -- -dev /dev/fb defclass TrueColor defdepth 24 - - and it works nicely (note: to log into console from the dtlogin - window, select "Options -> Command Line Login", then login and enter - the above command.) See the -dev section of the Xsun(1) manpage for a - description of the above arguments. If you have root permission, a - more permanent and convenient thing to do is to record the arguments - in a line like: - :0 Local local_uid@console root /usr/openwin/bin/Xsun -dev /dev/fb defclass -TrueColor defdepth 24 - - in /etc/dt/config/Xservers (copy /usr/dt/config/Xservers.) Also look - at the fbconfig(1) and related manpages (e.g. ffbconfig, m64config, - pgxconfig, SUNWjfb_config, etc ...) for hardware framebuffer settings - that may achieve the same effect. - - In general for non-Sun machines, look at the "-cc class" and related - options in your X server manpage (perhaps Xserver(1)), it may allow - modifying the default visual (e.g. "-cc 4", see for the - visual class numbers.) On XFree86 some video card drivers (e.g. Matrox - mga) have settings like Option "Overlay" "24,8" to support multi-depth - overlays. For these, use the "-cc 4" X server command line option to - get a depth 24 default visual. - - - The -overlay mode: Another option is if the system with overlay - visuals is a Sun system running Solaris or SGI running IRIX you can - use the -overlay x11vnc option (Aug/2004) to have x11vnc use the - Solaris XReadScreen(3X11) function to poll the "true view" of the - whole screen at depth 24 TrueColor. XReadDisplay(3X11) is used on - IRIX. This is useful for Legacy applications (older versions of - Cadence CAD apps are mentioned by x11vnc users) that require the - default depth be 8bpp, or the app will use a 8bpp visual even if depth - 24 visuals are available, and so the default depth workaround - described in the previous paragraph is not sufficient for these apps. - - It seems that Xorg is working toward supporting XReadDisplay(3X11) as - part of the RENDER extension work. When it does support it and - provides a library API x11vnc will be modified to take advantage of - the feature to support -overlay on Linux, *BSD, etc. Until then see - the -8to24 mode below. - - Misc. notes on -overlay mode: An amusing by-product of -overlay mode - is that the mouse cursor shape is correct! (i.e. XFIXES is not - needed.) The -overlay mode may be somewhat slower than normal mode due - to the extra framebuffer manipulations that must be performed. Also, - on Solaris there is a bug in that for some popup menus, the windows - they overlap will have painting errors (flashing colors) while the - popup is up (a workaround is to disable SaveUnders by passing -su to - Xsun, e.g. in your /etc/dt/config/Xservers file.) - - - The -8to24 mode: The -8to24 x11vnc option (Jan/2006) is a kludge to - try to dynamically rewrite the pixel values so that the 8bpp part of - the screen is mapped onto depth 24 TrueColor. This is less robust than - the -overlay mode because it is done by x11vnc outside of the X - server. So only use it on OS's that do not support -overlay. The - -8to24 mode will work if the default visual is depth 24 or depth 8. It - scans for any windows within 3 levels of the root window that are 8bpp - (i.e. legacy application), or in general ones that are not using the - default visual. For the windows it finds it uses XGetSubImage() to - retrieve the pixels values and uses the correct indexed colormap to - create a depth 24 TrueColor view of the whole screen. This depth 24, - 32bpp view is exported via VNC. - - Even on pure 8bpp displays it can be used as an alternative to - -flashcmap to avoid color flashing completely. - - This scheme is approximate and can often lead to painting errors. You - can manually correct most painting errors by pressing 3 Alt_L's in a - row, or by using something like: -fixscreen V=3.0 to automatically - refresh the screen every 3 seconds. Also -fixscreen 8=3.0 has been - added to just refresh the non-default visual parts of the screen. - - In general the scheme uses many resources and may give rise to - sluggish behavior. If multiple windows are using different 8bpp - indexed colormaps all but one window may need to be iconified for the - colors to be correct. There are a number of tunable parameters to try - to adjust performance and painting accuracy. The option -8to24 - nogetimage can give a nice speedup if the default depth 24 X server - supports hiding the 8bpp bits in bits 25-32 of the framebuffer data. - On very slow machines -8to24 poll=0.2,cachewin=5.0 gives an useful - speedup. See the -8to24 help description for information on tunable - parameters, etc. - - - Colors still not working correctly? Run xwininfo on the application - with the incorrect colors to verify that the depth of its visual is - different from the default visual depth (gotten from xdpyinfo.) One - possible workaround in this case is to use the -id option to point - x11vnc at the application window itself. If the application is - complicated (lots of toplevel windows and popup menus) this may not be - acceptable, and may even crash x11vnc (but not the application.) See - also -appshare. - - It is theoretically possible to solve this problem in general (see - xwd(1) for example), but it does not seem trivial or sufficiently fast - for x11vnc to be able to do so in real time. The -8to24 method does - this approximately and is somewhat usable. Fortunately the -overlay - option works for Solaris machines with overlay visuals where most of - this problem occurs. - - - Q-25: I am on a high color system (depth >= 24) but I seem to have - colormap problems. They either flash or everything is very dark. - - This can happen if the default Visual (use xdpyinfo to list them) is - DirectColor instead of TrueColor. These are both usually used in high - color modes, but whereas TrueColor uses static ramps for the Red, - Green, and Blue components, DirectColor has arbitrary colormaps for - the Red, Green, and Blue Components. Currently x11vnc cannot decode - these colormaps and treats them just like TrueColor. - - The only workaround so far is to restart the X server with the "-cc 4" - option to force TrueColor as the default visual (DirectColor is "-cc - 5"; see /usr/include/X11/X.h.) The only place we have seen this is - with the virtual framebuffer server Xvfb on Xorg 7.2. So in that case - you probably should restart it with something like this: "Xvfb :1 -cc - 4 -screen 0 1280x1024x24". It should be possible for x11vnc to handle - DirectColor, but this hasn't been implemented due to its rare usage. - - You may also see this problem on an X display with a TrueColor default - visual where an application chooses a DirectColor visual for its - window(s). It seems the application also needs to install its own - colormap for the visual for the colors to be messed up in x11vnc. One - can make xwud do this for example. - - - Q-26: How do I figure out the window id to supply to the -id windowid - option? - - Run the xwininfo program in a terminal. It will ask you to click on - the desired application window. After clicking, it will print out much - information, including the window id (e.g. 0x6000010.) Also, the - visual and depth of the window printed out is often useful in - debugging x11vnc color problems. - - Also, as of Dec/2004 you can use "-id pick" to have x11vnc run - xwininfo(1) for you and after you click the window it extracts the - windowid. Besides "pick" there is also "id:root" to allow you to go - back to root window when doing remote-control. - - - Q-27: Why don't menus or other transient windows come up when I am - using the -id windowid option to view a single application window? - - This is related to the behavior of the XGetImage(3X11) and - XShmGetImage() interfaces regarding backingstore, saveunders, etc. The - way the image is retrieved depends on some aspects of how the X server - maintains the display image data and whether other windows are - clipping or obscuring it. See the XGetImage(3X11) man page for more - details. If you disable BackingStore and SaveUnders in the X server - you should be able to see these transient windows. - - If things are not working and you still want to do the single window - polling, try the -sid windowid option ("shifted" windowid.) - - Update: as of Nov/2009 in the 0.9.9 x11vnc development tarball, there - is an experimental Application Sharing mode that improves upon the - -id/-sid single window sharing: -appshare (run "x11vnc -appshare - -help" for more info.) It is still very primitive and approximate, but - at least it displays multiple top-level windows. - - - Q-28: My X display is depth 24 at 24bpp (instead of the normal depth - 24 at 32bpp.) I'm having lots of color and visual problems with x11vnc - and/or vncviewer. What's up? - - First off, depth 24 at 24bpp (bpp=bits-per-pixel) is fairly uncommon - and can cause problems in general. It also can be slower than depth 24 - at 32bpp. You might want to switch to 32bpp (for XFree86 see the - "-fbbpp 32", DefaultFbBpp, FbBpp and related options.) Perhaps you - have 24bpp because the video memory of the machine is low and the - screen wouldn't fit in video RAM at 32bpp. For this case depth 16 at - 16bpp might be an acceptable option. - - In any event x11vnc should handle depth 24 at 24bpp (although - performance may be slower, and you may need to use the ZRLE encoding - instead of Tight.) There are some caveats involving the viewer - however: - - The RealVNC Unix viewer cannot handle 24bpp from the server, it will - say: "main: setPF: not 8, 16 or 32 bpp?" and exit. I have not checked - the RealVNC Windows viewer. - - So you need to use the TightVNC Unix viewer. However there are some - problems with that too. It seems libvncserver does not do 24bpp - correctly with the Tight encoding. The colors and screen ultimately - get messed up. So you have to use a different encoding with the - TightVNC vncviewer, try "zlib", "hextile", or one of the other - encodings (e.g. vncviewer -encodings "zlib hextile" ....) I have not - checked the TightVNC or UltraVNC Windows viewers. - - It appears the older RealVNC Unix viewers (e.g. 3.3.3 and 3.3.7) can - handle 24bpp from the server, so you may want to use those. They - evidently request 32 bpp and libvncserver obliges. - - Update: as of Apr/2006 you can use the -24to32 option to have x11vnc - dynamically transform the 24bpp pixel data to 32bpp. This extra - transformation could slow things down further however. - - Now coming the opposite direction if you are running the vncviewer on - the 24bpp display, TightVNC will fail with "Can't cope with 24 - bits-per-pixel. Sorry." and RealVNC will fail with "main: Error: - couldn't find suitable pixmap format" so evidently you cannot use - 24bpp for the vncviewers to work on that X display. - - Note, however, that the Unix viewer in the Enhanced TightVNC Viewer - (SSVNC) project can handle 24bpp X displays. It does this by - requesting a 16bpp pixel format (or 8bpp if the -bgr233 option has - been supplied) from the VNC server, and translates that to 24bpp - locally. - [Xterminals] - - Q-29: Can I use x11vnc to view and interact with an Xterminal (e.g. - NCD) that is not running UNIX and so x11vnc cannot be run on it - directly? - - You can, but it will likely be very wasteful of network bandwidth - since you will be polling the X display over the network as opposed to - over the local hardware. To do this, run x11vnc on a UNIX machine as - close as possible network-wise (e.g. same switch) to the Xterminal - machine. Use the -display option to point the display to that of the - Xterminal (you'll of course need basic X11 permission to do that) and - finally supply the -noshm option (this enables the polling over the - network.) - - If the Xterminal's X display is open to the network for connections, - you might use something like "-display xterm123:0". If you are trying - to do this via an SSH tunnel (assuming you can actually ssh into the - Xterminal) it will be a little tricky (either use the ssh "-R" option - or consider ssh-ing in the other direction.) In all cases the X11 - permissions need to allow the connection. - - The response will likely be sluggish (maybe only one "frame" per - second.) This mode is not recommended except for "quick checks" of - hard to get to X servers. Use something like "-wait 150" to cut down - on the polling rate. You may also need -flipbyteorder if the colors - get messed up due to endian byte order differences. - - Q-30: How do I get my X permissions (MIT-MAGIC-COOKIE file) correct - for a Unix/Linux machine acting as an Xterminal? - - If the X display machine is a traditional Xterminal (where the X - server process runs on the Xterminal box, but all of the X client - applications (firefox, etc) run on a central server (aka "terminal - server")), you will need to log into the Xterminal machine (i.e. get a - shell running there) and then start the x11vnc program. If the - Xterminal Linux/Unix machine is stripped down (e.g. no users besides - root) that may be difficult. - - The next problem is the login Display Manager (e.g. gdm, kdm), and - hence the MIT-MAGIC-COOKIE auth files, are on the central server and - not on the Xterminal box where the X server and x11vnc processes are. - - So unless X permissions are completely turned off (e.g. "xhost +"), to - run the x11vnc process on the Xterminal box the MIT-MAGIC-COOKIE auth - file data (XAUTHORITY or $HOME/.Xauthority) must be accessible by or - copied to the Xterminal. If $HOME/.Xauthority is exported via NFS - (this is insecure of course, but has been going on for decades), then - x11vnc can simply pick it up via NFS (you may need to use the -auth - option to point to the correct file.) Other options include copying - the auth file using scp, or something like: - central-server> xauth nextract - xterm123:0 | ssh xterm123 xauth nmerge - - - and then, say, ssh from central-server to xterm123 to start x11vnc. - Here "xterm123" refers to the computer acting as the Xterminal and - "central-server" is the terminal server. You can use "xauth -f - /path/to/cookie-file list" to examine the contents of the cookie(s) in - a file "/path/to/cookie-file". See the xauth(1) manpage for more - details. - - If the display name in the cookie file needs to be changed between the - two hosts, see this note on the "xauth add ..." command. - - A less secure option is to run something like "xhost +127.0.0.1" while - sitting at the Xterminal box to allow cookie-free local access for - x11vnc. You can run "xhost -127.0.0.1" after x11vnc connects if you - want to go back to the original permissions. - - If the Xterminal is really stripped down and doesn't have any user - accounts, NFS, etc. you'll need to contact your system administrator - to set something up. It can be done!!! Some Xterminal projects have - actually enabled "run locally" facilities for the running of an - occasional app more efficiently locally on the Xterminal box (e.g. - realplayer.) - - Not recommended, but as a last resort, you could have x11vnc poll the - Xterminal Display over the network. For this you would run a "x11vnc - -noshm ..." process on the central-server (and hope the network admin - doesn't get angry...) - - Note: use of Display Manager (gdm, kdm, ...) auth cookie files (i.e. - from /var/..., /tmp/..., or elsewhere) may require modification via - xauth(1) to correctly include the display x11vnc refers to (e.g. - "xauth -f cookie-file add :0 . 45be51ae2ce9dfbacd882ab3ef8e96b1", - where the "45be51..." cookie value was found from an "xauth -f - /path/to/original/cookie-file list") or other reasons. See xauth(1) - manpage for full details on how to transfer an MIT-MAGIC-COOKIE - between machines and displays. - - VNCviewer performance on Xterminals: This isn't related to x11vnc on - Xterminals, but we mention it here anyway because of the similar - issues. If you are on an Xterminal and want to use vncviewer to - connect to a VNC server somewhere, then performance would be best if - you ran the viewer on the Xterminal box. Otherwise, (i.e. running the - viewer process on the central-server) all of the vncviewer screen - drawing is done more inefficiently over the network. Something to - consider, especially on a busy network. (BTW, this has all of the - above permission, etc, problems: both vncviewer and x11vnc are X - client apps desired to be run on the Xterminal box.) - - [Sun Rays] - - Q-31: I'm having trouble using x11vnc with my Sun Ray session. - - The Sun Ray technology is a bit like "VNC done in hardware" (the Sun - Ray terminal device, DTU, playing the role of the vncviewer.) - Completely independent of that, the SunRay user's session is still an - X server that speaks the X11 protocol and so x11vnc simply talks to - the X server part to export the SunRay desktop to any place in the - world (i.e. not only to a Sun Ray terminal device), creating a sort of - "Soft Ray". Please see this discussion of Sun Ray issues for solutions - to problems. - - Also see the Sun Ray Remote Control Toolkit that uses x11vnc. - - [Remote Control] - - Q-32: How do I stop x11vnc once it is running in the background? - - As of Dec/2004 there is a remote control feature. It can change a huge - number of parameters on the fly: see the -remote and -query options. - To shut down the running x11vnc server just type "x11vnc -R stop". To - disconnect all clients do "x11vnc -R disconnect:all", etc. - - If the -forever option has not been supplied, x11vnc will - automatically exit after the first client disconnects. In general if - you cannot use the remote control, then you will have to kill the - x11vnc process This can be done via: "kill NNNNN" (where NNNNN is the - x11vnc process id number found from ps(1)), or "pkill x11vnc", or - "killall x11vnc" (Linux only.) - - If you have not put x11vnc in the background via the -bg option or - shell & operator, then simply press Ctrl-C in the shell where x11vnc - is running to stop it. - - Potential Gotcha: If somehow your Keypress of Ctrl-C went through - x11vnc to the Xserver that then delivered it to x11vnc it is possible - one or both of the Ctrl or C keys will be left stuck in the pressed - down state in the Xserver. Tapping the stuck key (either via a new - x11vnc or at the physical console) will release it from the stuck - state. If the keyboard seems to be acting strangely it is often fixed - by tapping Ctrl, Shift, and Alt. Alternatively, the -clear_mods option - and -clear_keys option can be used to release pressed keys at startup - and exit. The option -clear_all will also try to unset Caps_Lock, - Num_Lock, etc. - - - Q-33: Can I change settings in x11vnc without having to restart it? - Can I remote control it? - - Look at the -remote (an alias is -R) and -query (an alias is -Q) - options added in Dec/2004. They allow nearly everything to be changed - dynamically and settings to be queried. Examples: "x11vnc -R shared", - "x11vnc -R forever", "x11vnc -R scale:3/4", "x11vnc -Q modtweak", - "x11vnc -R stop", "x11vnc -R disconnect:all", etc.. - - These commands do not start a x11vnc server, but rather communicate - with one that is already running. The X display (X11VNC_REMOTE - property) is used as the communication channel, so the X permissions - and DISPLAY must be set up correctly for communication to be possible. - - There is also a simple Tcl/Tk gui based on this remote control - mechanism. See the -gui option for more info. You will need to have - Tcl/Tk (i.e. /usr/bin/wish) installed for it to work. It can also run - in the system tray: "-gui tray" or as a standalone small icon window: - "-gui icon". Use "-gui tray=setpass" for a naive user "Share My - Desktop" mode. - - [Security and Permissions] - - Q-34: How do I create a VNC password for use with x11vnc? - - You may already have one in $HOME/.vnc/passwd if you have used, say, - the vncserver program from the regular RealVNC or TightVNC packages - (i.e. launching the Xvnc server.) Otherwise, you could use the - vncpasswd(1) program from those packages. - - As of Jun/2004 x11vnc supports the -storepasswd "pass" "file" option, - which is the same functionality of storepasswd. Be sure to quote the - "pass" if it contains shell meta characters, spaces, etc. Example: - x11vnc -storepasswd 'sword*fish' $HOME/myvncpasswd - - You then use the password via the x11vnc option: "-rfbauth - $HOME/myvncpasswd" - - As of Jan/2006 if you do not supply any arguments: - x11vnc -storepasswd - - you will be prompted for a password to save to ~/.vnc/passwd (your - keystrokes when entering the password will not be echoed to the - screen.) If you supply one argument, e.g. "x11vnc -storepasswd - ~/.mypass", the password you are prompted for will be stored in that - file. - - x11vnc also has the -passwdfile and -passwd/-viewpasswd plain text - (i.e. not obscured like the -rfbauth VNC passwords) password options. - - You can use the -usepw option to automatically use any password file - you have in ~/.vnc/passwd or ~/.vnc/passwdfile (the latter is used - with the -passwdfile option.) - - x11vnc -usepw -display :0 ... - - If neither file exists you are prompted to store a password in - ~/.vnc/passwd. If a password file cannot be found or created x11vnc - exits immediately. An admin may want to set it up this way for users - who do not know better. - - - Q-35: Can I make it so -storepasswd doesn't show my password on the - screen? - - You can use the vncpasswd program from RealVNC or TightVNC mentioned - above. As of Jan/2006 the -storepasswd option without any arguments - will not echo your password as you type it and save the file to - ~/.vnc/passwd: - # x11vnc -storepasswd - Enter VNC password: - Verify password: - Write password to /home/myname/.vnc/passwd? [y]/n - Password written to: /home/myname/.vnc/passwd - - You can also give it an alternate filename, e.g. "x11vnc -storepasswd - ~/.mypass" - - - Q-36: Can I have two passwords for VNC viewers, one for full access - and the other for view-only access to the display? - - Yes, as of May/2004 there is the -viewpasswd option to supply the - view-only password. Note the full-access password option -passwd must - be supplied at the same time. E.g.: -passwd sword -viewpasswd fish. - - To avoid specifying the passwords on the command line (where they - could be observed via the ps(1) command by any user) you can use the - -passwdfile option to specify a file containing plain text passwords. - Presumably this file is readable only by you, and ideally it is - located on the machine x11vnc is run on (to avoid being snooped on - over the network.) The first line of this file is the full-access - password. If there is a second line in the file and it is non-blank, - it is taken as the view-only password. (use "__EMPTY__" to supply an - empty one.) - - View-only passwords currently do not work for the -rfbauth password - option (standard VNC password storing mechanism.) FWIW, note that - although the output (usually placed in $HOME/.vnc/passwd) by the - vncpasswd or storepasswd programs (or from x11vnc -storepasswd) looks - encrypted they are really just obscured to avoid "casual" password - stealing. It takes almost no skill to figure out how to extract the - plain text passwords from $HOME/.vnc/passwd since it is very - straight-forward to work out what to do from the VNC source code. - - - Q-37: Can I have as many full-access and view-only passwords as I - like? - - Yes, as of Jan/2006 in the libvncserver CVS the -passwdfile option has - been extended to handle as many passwords as you like. You put the - view-only passwords after a line __BEGIN_VIEWONLY__. - - You can also easily annotate and comment out passwords in the file. - You can have x11vnc re-read the file dynamically when it is modified. - - - Q-38: Does x11vnc support Unix usernames and passwords? Can I further - limit the set of Unix usernames who can connect to the VNC desktop? - Update: as of Feb/2006 x11vnc has the -unixpw option that does this - outside of the VNC protocol and libvncserver. The standard su(1) - program is used to validate the user's password. A familiar "login:" - and "Password:" dialog is presented to the user on a black screen - inside the vncviewer. The connection is dropped if the user fails to - supply the correct password in 3 tries or does not send one before a - 25 second timeout. Existing clients are view-only during this period. - A list of allowed Unix usernames may also be supplied along with - per-user settings. - - There is also the -unixpw_nis option for non-shadow-password - (typically NIS environments, hence the name) systems where the - traditional getpwnam() and crypt() functions are used instead of - su(1). The encrypted user passwords must be accessible to the user - running x11vnc in -unixpw_nis mode, otherwise the logins will always - fail even when the correct password is supplied. See ypcat(1) and - shadow(5). - - Two settings are enforced in the -unixpw and -unixpw_nis modes to - provide extra security: the 1) -localhost and 2) -stunnel or -ssl - options. Without these one might send the Unix username and password - data in clear text over the network which is a very bad idea. They can - be relaxed if you want to provide encryption other than stunnel or - -ssl (the constraint is automatically relaxed if SSH_CONNECTION is set - and indicates you have ssh-ed in, however the -localhost requirement - is still enforced.) - - The two -unixpw modes have been tested on Linux, Solaris, Mac OS X, - HP-UX, AIX, Tru64, FreeBSD, OpenBSD, and NetBSD. Additional testing is - appreciated. For the last 4 it appears that su(1) will not prompt for - a password if su-ing to oneself. Since x11vnc requires a password - prompt from su, x11vnc forces those logins to fail even when the - correct password is supplied. On *BSD it appears this can be corrected - by removing the pam_self.so entry in /etc/pam.d/su. - - - Previous older discussion (prior to the -unixpw option): - - Until the VNC protocol and libvncserver support this things will be - approximate at best. - - One approximate method involves starting x11vnc with the -localhost - option. This basically requires the viewer user to log into the - workstation where x11vnc is running via their Unix username and - password, and then somehow set up a port redirection of his vncviewer - connection to make it appear to emanate from the local machine. As - discussed above, ssh is useful for this: "ssh -L 5900:localhost:5900 - user@hostname ..." See the ssh wrapper scripts mentioned elsewhere on - this page. stunnel does this as well. - - Of course a malicious user could allow other users to get in through - his channel, but that is a problem with every method. Another thing to - watch out for is a malicious user on the viewer side (where ssh is - running) trying to sneak in through the ssh port redirection there. - - Regarding limiting the set of Unix usernames who can connect, the - traditional way would be to further require a VNC password to supplied - (-rfbauth, -passwd, etc) and only tell the people allowed in what the - VNC password is. A scheme that avoids a second password involves using - the -accept option that runs a program to examine the connection - information to determine which user is connecting from the local - machine. That may be difficult to do, but, for example, the program - could use the ident service on the local machine (normally ident - should not be trusted over the network, but on the local machine it - should be accurate: otherwise root has been compromised and so there - are more serious problems! Unfortunately recent Linux distros seem to - provide a random string (MD5 hash?) instead of the username.) An - example script passed in via -accept scriptname that deduces the Unix - username and limits who can be accepted might look something like - this: -#!/bin/sh -if [ "$RFB_CLIENT_IP" != "127.0.0.1" -o "$RFB_SERVER_IP" != "127.0.0.1" ]; then - exit 1 # something fishy... reject it. -fi -user=`echo "$RFB_CLIENT_PORT, $RFB_SERVER_PORT" | nc -w 1 $RFB_CLIENT_IP 113 \ - | grep 'USERID.*UNIX' | head -n 1 | sed -e 's/[\r ]//g' | awk -F: '{pri -nt $4}'` - -for okuser in fred barney wilma betty -do - if [ "X$user" = "X$okuser" ]; then - exit 0 # accept it - fi -done -exit 1 # reject it - - For this to work with ssh port redirection, the ssh option - UsePrivilegeSeparation must be enabled otherwise the userid will - always be "root". - - Here is a similar example based on Linux netstat(1) output: -#!/bin/sh -# -# accept_local_netstat: x11vnc -accept command to accept a local -# vncviewer connection from acceptable users. Linux netstat -nte is used. - -PATH=/bin:/usr/bin:$PATH; export PATH; # set to get system utils - -allowed="`id -u fred`"; # add more user numbers if desired. - -# check required settings -ok=1 -if [ "X$allowed" = "X" ]; then - ok=0; # something wrong with allowed list -fi -if [ "X$RFB_CLIENT_IP" != "X127.0.0.1" -o "X$RFB_SERVER_IP" != "X127.0.0.1" ]; -then - ok=0; # connection not over localhost -fi -if [ "$RFB_CLIENT_PORT" -le 0 -o "$RFB_SERVER_PORT" -le 0 ]; then - ok=0; # something wrong with tcp port numbers -fi -if [ "$ok" = 0 ]; then - echo "$0: invalid setting:" 1>&2 - env | grep ^RFB | sort 1>&2 - exit 1 -fi - -# Linux netstat -nte: -# Proto Recv-Q Send-Q Local Address Foreign Address State - User Inode -# 0 0 0 RFB_CLIENT RFB_SERVER ESTABLISHED - nnnn .... -# -user=`netstat -nte | grep ESTABLISHED \ - | grep " $RFB_CLIENT_IP:$RFB_CLIENT_PORT *$RFB_SERVER_IP:$RFB_SERVER_P -ORT "` - -echo "netstat match: $user" 1>&2 -user=`echo "$user" | head -n 1 | sed -e 's/^.*ESTABLISHED/ /' | awk '{print $1} -'` - -ok=0 -for u in $allowed -do - if [ "X$user" = "X$u" ]; then - ok=1 - break - fi -done - -if [ "X$ok" = "X1" ]; then - echo "$0: user accepted: '$user'" 1>&2 - exit 0 -else - echo "$0: user '$user' invalid:" 1>&2 - echo "$0: allowed: $allowed" 1>&2 - env | grep ^RFB | sort 1>&2 - exit 1 -fi - - - Q-39: Can I supply an external program to provide my own custom login - method (e.g. Dynamic/One-time passwords or non-Unix (LDAP) usernames - and passwords)? - Yes, there are several possibilities. For background see the FAQ on - the -accept where an external program may be run to decide if a VNC - client should be allowed to try to connect and log in. If the program - (or local user prompted by a popup) answers "yes", then -accept - proceeds to the normal VNC and x11vnc authentication methods, - otherwise the connection is dropped. - - To provide more direct coupling to the VNC client's username and/or - supplied password the following options were added in Sep/2006: - * -unixpw_cmd command - * -passwdfile cmd:command - * -passwdfile custom:command - - In each case "command" is an external command run by x11vnc. You - supply it. For example, it may couple to your LDAP system or other - servers you set up. - - For -unixpw_cmd the normal -unixpw Login: and Password: prompts are - supplied to the VNC viewer and the strings the client returns are then - piped into "command" as the first two lines of its standard input. If - the command returns success, i.e. exit(0), the VNC client is accepted, - otherwise it is rejected. - - For "-passwdfile cmd:command" the command is run and it returns a - password list (like a password file, see the -passwdfile read:filename - mode.) Perhaps a dynamic, one-time password is retrieved from a server - this way. - - For "-passwdfile custom:command" one gets complete control over the - VNC challenge-response dialog with the VNC client. x11vnc sends out a - string of random bytes (16 by the VNC spec) and the client returns the - same number of bytes in a way the server can verify only the - authorized user could have created. The VNC protocol specifies DES - encryption with a password. If you are willing to modify the VNC - viewers, you can have it be anything you want, perhaps a less - crackable MD5 hash scheme or one-time pad. Your program will read from - its standard input the size of the challenge-response followed by a - newline, then the challenge bytes followed by the response bytes. If - your command then returns success, i.e. exit(0), the VNC client is - accepted, otherwise it is rejected. - - In all cases the "RFB_*" environment variables are set as under - -accept. These variables can provide useful information for the - externally supplied program to use. - - - Q-40: Why does x11vnc exit as soon as the VNC viewer disconnects? And - why doesn't it allow more than one VNC viewer to connect at the same - time? - - These defaults are simple safety measures to avoid someone unknowingly - leaving his X11 desktop exposed (to the internet, say) for long - periods of time. Use the -forever option (aka -many) to have x11vnc - wait for more connections after the first client disconnects. Use the - -shared option to have x11vnc allow multiple clients to connect - simultaneously. - - Recommended additional safety measures include using ssh (see above), - stunnel, -ssl, or a VPN to authenticate and encrypt the viewer - connections or to at least use the -rfbauth passwd-file option to use - VNC password protection (or -passwdfile) It is up to YOU to apply - these security measures, they will not be done for you automatically. - - - Q-41: Can I limit which machines incoming VNC clients can connect - from? - - Yes, look at the -allow and -localhost options to limit connections by - hostname or IP address. E.g. - x11vnc -allow 192.168.0.1,192.168.0.2 - - for those two hosts or - x11vnc -allow 192.168.0. - - for a subnet. For individual hosts you can use the hostname instead of - the IP number, e.g.: "-allow snoopy", and "-allow darkstar,wombat". - Note that -localhost achieves the same thing as "-allow 127.0.0.1" - - For more control, build libvncserver with libwrap support - (tcp_wrappers) and then use /etc/hosts.allow See hosts_access(5) for - complete details. - - - Q-42: How do I build x11vnc/libvncserver with libwrap (tcp_wrappers) - support? - - Here is one way to pass this information to the configure script: - env CPPFLAGS=-DUSE_LIBWRAP LDFLAGS=-lwrap ./configure - - then run make as usual. This requires libwrap and its development - package (tcpd.h) to be installed on the build machine. If additional - CPPFLAGS or LDFLAGS options are needed supply them as well using - quotes. - - The resulting x11vnc then uses libwrap/tcp_wrappers for connections. - The service name you will use in /etc/hosts.allow and /etc/hosts.deny - is "vnc", e.g.: - vnc: 192.168.100.3 .example.com - - Note that if you run x11vnc out of inetd you do not need to build - x11vnc with libwrap support because the /usr/sbin/tcpd reference in - /etc/inetd.conf handles the tcp_wrappers stuff. - - - Q-43: Can I have x11vnc only listen on one network interface (e.g. - internal LAN) rather than having it listen on all network interfaces - and relying on -allow to filter unwanted connections out? - - As of Mar/2005 there is the "-listen ipaddr" option that enables this. - For ipaddr either supply the desired network interface's IP address - (or use a hostname that resolves to it) or use the string "localhost". - For additional filtering simultaneously use the "-allow host1,..." - option to allow only specific hosts in. - - This option is useful if you want to insure that no one can even begin - a dialog with x11vnc from untrusted network interfaces (e.g. ppp0.) - The option -localhost now implies "-listen localhost" since that is - what most people expect it to do. - - - Q-44: Now that -localhost implies listening only on the loopback - interface, how I can occasionally allow in a non-localhost via the -R - allowonce remote control command? - - To do this specify "-allow localhost". Unlike -localhost this will - leave x11vnc listening on all interfaces (but of course only allowing - in local connections, e.g. ssh redirs.) Then you can later run "x11vnc - -R allowonce:somehost" or use to gui to permit a one-shot connection - from a remote host. - - - Q-45: Can I fine tune what types of user input are allowed? E.g. have - some users just be able to move the mouse, but not click or type - anything? - - As of Feb/2005, the -input option allows you to do this. "K", "M", - "B", "C", and "F" stand for Keystroke, Mouse-motion, Button-clicks, - Clipboard, and File-Transfer, respectively. The setting: "-input M" - makes attached viewers only able to move the mouse. "-input KMBC,M" - lets normal clients do everything and enables view-only clients to - move the mouse. - - These settings can also be applied on a per-viewer basis via the - remote control mechanism or the GUI. E.g. x11vnc -R input:hostname:M - - - Q-46: Can I prompt the user at the local X display whether the - incoming VNC client should be accepted or not? Can I decide to make - some clients view-only? How about running an arbitrary program to make - the decisions? - - Yes, look at the "-accept command" option, it allows you to specify an - external command that is run for each new client. (use quotes around - the command if it contains spaces, etc.) If the external command - returns 0 (success) the client is accepted, otherwise with any other - return code the client is rejected. See below how to also accept - clients view-only. - - The external command will have the RFB_CLIENT_IP environment variable - set to the client's numerical IP address, RFB_CLIENT_PORT its port - number. Similarly for RFB_SERVER_IP and RFB_SERVER_PORT to allow - identification of the tcp virtual circuit. DISPLAY will be set to that - of the X11 display being polled. Also, RFB_X11VNC_PID is set to the - x11vnc process id (e.g. in case you decided to kill it), RFB_CLIENT_ID - will be an id number, and RFB_CLIENT_COUNT the number of other clients - currently connected. RFB_MODE will be "accept". - - Built-in Popup Window: As a special case, "-accept popup" will - instruct x11vnc to create its own simple popup window. To accept the - client press "y" or click mouse on the "Yes" button. To reject the - client press "n" or click mouse on the "No" button. To accept the - client View-only, press "v" or click mouse on the "View" button. If - the -viewonly option has been supplied, the "View" action will not be - present: the whole display is view only in that case. - - The popup window times out after 120 seconds, to change this behavior - use "-accept popup:N" where N is the number of seconds (use 0 for no - timeout.) More tricks: "-accept popupmouse" will only take mouse click - responses, while "-accept popupkey" will only take keystroke responses - (popup takes both.) After any of the 3 popup keywords you can supply a - position of the window: +N+M, (the default is to center the window) - e.g. -accept popupmouse+10+10. - - Also as a special case "-accept xmessage" will run the xmessage(1) - program to prompt the user whether the client should be accepted or - not. This requires that you have xmessage installed and available via - PATH. In case it is not already on your system, the xmessage program - is available at ftp://ftp.x.org/ - (End of Built-in Popup Window:) - - To include view-only decisions for the external commands, prefix the - command something like this: "yes:0,no:*,view:3 mycommand ..." This - associates the three actions: yes(accept), no(reject), and - view(accept-view-only), with the numerical return (i.e. exit()) codes. - Use "*" instead of a number to set the default action (e.g. in case - the external command returns an unexpected return code.) - - Here is an example -accept script called accept_or_lock. It uses - xmessage and xlock (replace with your screen lock command, maybe it is - "xscreensaver-command -lock", or kdesktop_lock, or "dtaction - LockDisplay".) It will prompt the user at the X display whether to - accept, reject, or accept view-only the client, but if the prompt - times out after 60 seconds the screen is locked and the VNC client is - accepted. This allows the remote access when no one is at the display. -#!/bin/sh -# -# accept_or_lock: prompt user at X display whether to accept an incoming -# VNC connection. If timeout expires, screen is locked -# and the VNC viewer is accepted (allows remote access -# when no one is sitting at the display.) -# -# usage: x11vnc ... -forever -accept 'yes:0,no:*,view:4 accept_or_lock' -# -xmessage -buttons yes:2,no:3,view-only:4 -center \ - -timeout 60 "x11vnc: accept connection from $RFB_CLIENT_IP?" -rc=$? -if [ $rc = 0 ]; then - xlock & # or "xlock -mode blank" for no animations. - sleep 5 - exit 0 -elif [ $rc = 2 ]; then - exit 0 -elif [ $rc = 4 ]; then - exit 4 -fi -exit 1 - - Stefan Radman has written a nice dtksh script dtVncPopup for use in - CDE environments to do the same sort of thing. Information on how to - use it is found at the top of the file. He encourages you to provide - feedback to him to help improve the script. - - Note that in all cases x11vnc will block while the external command or - popup is being run, so attached clients will not receive screen - updates, etc during this period. - - To run a command when a client disconnects, use the "-gone command" - option. This is for the user's convenience only: the return code of - the command is not interpreted by x11vnc. The same environment - variables are set as in "-accept command" (except that RFB_MODE will - be "gone".) - - As of Jan/2006 the "-afteraccept command" option will run the command - only after the VNC client has been accepted and authenticated. Like - -gone the return code is not interpreted. RFB_MODE will be - "afteraccept".) - - - Q-47: I start x11vnc as root because it is launched via inetd(8) or a - display manager like gdm(1). Can I have x11vnc later switch to a - different user? - - As of Feb/2005 x11vnc has the -users option that allows things like - this. Please read the documentation on it (also in the x11vnc -help - output) carefully for features and caveats. It's use can often - decrease security unless care is taken. - - BTW, a nice use of it is "-users +nobody" that switches to the Unix - user nobody right after connections to the X display are established. - - In any event, while running x11vnc as root, remember it comes with no - warranty ;-). - - - Q-48: I use a screen-lock when I leave my workstation (e.g. - xscreensaver or xlock.) When I remotely access my workstation desktop - via x11vnc I can unlock the desktop fine, but I am worried people will - see my activities on the physical monitor. What can I do to prevent - this, or at least make it more difficult? - - Probably most work environments would respect your privacy if you - powered off the monitor. Also remember if people have physical access - to your workstation they basically can do anything they want with it - (e.g. install a backdoor for later use, etc.) - - In any event, as of Jun/2004 there is an experimental utility to make - it more difficult for nosey people to see your x11vnc activities. The - source for it is blockdpy.c The idea behind it is simple (but - obviously not bulletproof): when a VNC client attaches to x11vnc put - the display monitor in the DPMS "off" state, if the DPMS state ever - changes immediately start up the screen-lock program. The x11vnc user - will notice something is happening and think about what to do next - (while the screen is in a locked state.) - - This works (or at least has a chance of working) because if the - intruder moves the mouse or presses a key on the keyboard, the monitor - wakes up out of the DPMS off state, and this induces the screen lock - program to activate as soon as possible. Of course there are cracks in - this, the eavesdropper could detach your monitor and insert a non-DPMS - one, and there are race conditions. As mentioned above this is not - bulletproof. A really robust solution would likely require X server - and perhaps even video hardware support. - - The blockdpy utility is launched by the -accept option and told to - exit via the -gone option (the vnc client user should obviously - re-lock the screen before disconnecting!) Instructions can be found in - the source code for the utility at the above link. Roughly it is - something like this: - x11vnc ... -accept "blockdpy -bg -f $HOME/.bdpy" -gone "touch $HOME/.bdpy" - - but please read the top of the file. - - Update: As of Feb/2007 there is some builtin support for this: - -forcedpms and -clientdpms however, they are probably less robust than - the above blockdpy.c scheme, since if the person floods the physical - machine with mouse or pointer input he can usually see flashes of the - screen before the monitor is powered off again. See also the -grabkbd, - -grabptr, and -grabalways options. - - - Q-49: Can I have x11vnc automatically lock the screen when I - disconnect the VNC viewer? - - Yes, a user mentions he uses the -gone option under CDE to run a - screen lock program: - x11vnc -display :0 -forever -gone 'dtaction LockDisplay' - - Other possibilities are: - x11vnc -display :0 -forever -gone 'xscreensaver-command -lock' - x11vnc -display :0 -forever -gone 'kdesktop_lock' - x11vnc -display :0 -forever -gone 'xlock &' - x11vnc -display :0 -forever -gone 'xlock -mode blank &' - - Here is a scheme using the -afteraccept option (in version 0.8) to - unlock the screen after the first valid VNC login and to lock the - screen after the last valid VNC login disconnects: - x11vnc -display :0 -forever -shared -afteraccept ./myxlocker -gone ./myxlocke -r - - Where the script ./myxlocker is: -#!/bin/sh - -#/usr/bin/env | grep RFB_ | sort # for viewing RFB_* settings. - -if [ "X$RFB_MODE" = "Xafteraccept" ]; then - if [ "X$RFB_STATE" = "XNORMAL" ]; then # require valid login - if [ "X$RFB_CLIENT_COUNT" = "X1" ]; then - killall xlock # Linux only. - fi - fi -elif [ "X$RFB_MODE" = "Xgone" ]; then - if [ "X$RFB_STATE" = "XNORMAL" ]; then # require valid login - if [ "X$RFB_CLIENT_COUNT" = "X0" ]; then - xlock -mode blank & - fi - fi -fi - - Note the xlock option "-mode blank" to avoid animations. - - There is a problem if you have x11vnc running this way in -forever - mode and you hit Ctrl-C to stop it. The xlock (or other program) will - get killed too. To work around this make a little script called - setpgrp that looks like: -#!/usr/bin/perl -setpgrp(0, 0); -exec @ARGV; - - then use -gone "setpgrp xlock &", etc. - [Encrypted Connections] - - Q-50: How can I tunnel my connection to x11vnc via an encrypted SSH - channel between two Unix machines? - - See the description earlier on this page on how to tunnel VNC via SSH - from Unix to Unix. A number of ways are described along with some - issues you may encounter. - - Other secure encrypted methods exists, e.g. stunnel, IPSEC, various - VPNs, etc. - - See also the Enhanced TightVNC Viewer (SSVNC) page where much of this - is now automated. - - - Q-51: How can I tunnel my connection to x11vnc via an encrypted SSH - channel from Windows using an SSH client like Putty? - - Above we described how to tunnel VNC via SSH from Unix to Unix, you - may want to review it. To do this from Windows using Putty it would go - something like this: - * In the Putty dialog window under 'Session' enter the hostname or - IP number of the Unix machine with display to be viewed. - * Make sure the SSH protocol is selected and the server port is - correct. - * Under 'Connections/SSH/Tunnels' Add a Local connection with - 'Source port: 5900' and 'Destination: localhost:5900' - * Log into the remote machine by pressing 'Open' and supplying - username, password, etc. - * In that SSH shell, start up x11vnc by typing the command: x11vnc - -display :0 plus any other desired options (e.g. -localhost.) - * Finally, start up your VNC Viewer in Windows and enter - 'localhost:0' as the VNC server. - - You can keep all of the settings in a Putty 'Saved Session'. Also, - once everything is working, you can consider putting x11vnc -display - :0 (plus other cmdline options) in the 'Remote command' Putty setting - under 'Connections/SSH'. - - See also the Enhanced TightVNC Viewer (SSVNC) page where much of this - is now automated via the Putty plink utility. - - For extra protection feel free to run x11vnc with the -localhost and - -rfbauth/-passwdfile options. - - If the machine you SSH into via Putty is not the same machine with the - X display you wish to view (e.g. your company provides incoming SSH - access to a gateway machine), then you need to change the above Putty - dialog setting to: 'Destination: otherhost:5900', Once logged in, - you'll need to do a second login (ssh or rsh) to the workstation - machine 'otherhost' and then start up x11vnc on it. This can also be - automated by Chaining SSH's. - - As discussed above another option is to first start the VNC viewer in - "listen" mode, and then launch x11vnc with the "-connect localhost" - option to establish the reverse connection. In this case a Remote port - redirection (not Local) is needed for port 5500 instead of 5900 (i.e. - 'Source port: 5500' and 'Destination: localhost:5500' for a Remote - connection.) - - - Q-52: How can I tunnel my connection to x11vnc via an encrypted SSL - channel using an external tool like stunnel? - - It is possible to use a "lighter weight" encryption setup than SSH or - IPSEC. SSL tunnels such as stunnel (also stunnel.org) provide an - encrypted channel without the need for Unix users, passwords, and key - passphrases required for ssh (and at the other extreme SSL can also - provide a complete signed certificate chain of trust.) On the other - hand, since SSH is usually installed everywhere and firewalls often - let its port through, ssh is frequently the path of least resistance - (it also nicely manages public keys for you.) - - Update: As of Feb/2006 x11vnc has the options -ssl, -stunnel, and - -sslverify to provide integrated SSL schemes. They are discussed in - the Next FAQ (you probably want to skip to it now.) - - We include these non-built-in method descriptions below for historical - reference. They are handy because can be used to create SSL tunnels to - any VNC (or other type of) server. - - - Here are some basic examples using stunnel but the general idea for - any SSL tunnel utility is the same: - * Start up x11vnc and constrain it to listen on localhost. - * Then start up the SSL tunnel running on the same machine to - forward incoming connections to that x11vnc. - * Set up and run a similar SSL tunnel for the outgoing connection on - the VNC viewer machine pointing it to the SSL/x11vnc server. - * Optionally, set up server (or even client) public/private keys for - use in authenticating one side to the other. - * Finally, start the VNC Viewer and tell it to connect to the local - port (e.g. a vnc display localhost:0) where its outgoing SSL - tunnel is listening. - - We'll first use the stunnel version 3 syntax since it is the most - concise and Unixy. - - Start up x11vnc listening on port 5900: - x11vnc -display :0 -rfbport 5900 -localhost -bg -passwdfile ~/mypass - - Then start stunnel (version 3, not 4) with this command: - stunnel -d 5901 -r 5900 -p /path/to/stunnel.pem - - The above two commands are run on host "far-away.east". The - stunnel.pem is the self-signed PEM file certificate created when - stunnel is built. One can also create certificates signed by - Certificate Authorities or self-signed if desired using the x11vnc - utilities described there. - - SSL Viewers: Next, on the VNC viewer side we need an SSL tunnel to - encrypt the outgoing connection. The nice thing is any SSL tunnel can - be used because the protocol is a standard. For this example we'll - also use stunnel on the viewer side on Unix. First start up the - client-side stunnel (version 3, not 4): - stunnel -c -d localhost:5902 -r far-away.east:5901 - - Then point the viewer to the local tunnel on port 5902: - vncviewer -encodings "copyrect tight zrle hextile" localhost:2 - - That's it. Note that the ss_vncviewer script can automate this - easily, and so can the Enhanced TightVNC Viewer (SSVNC) package. - - Be sure to use a VNC password because unlike ssh by default the - encrypted SSL channel provides no authentication (only privacy.) With - some extra configuration one could also set up certificates to provide - authentication of either or both sides as well (and hence avoid - man-in-the-middle attacks.) See the stunnel and openssl documentation - and also the key management section for details. - - stunnel has also been ported to Windows, and there are likely others - to choose from for that OS. Much info for using it on Windows can be - found at the stunnel site and in this article The article also shows - the detailed steps to set up all the authentication certificates. (for - both server and clients, see also the x11vnc utilities that do this.) - The default Windows client setup (no certs) is simpler and only 4 - files are needed in a folder: stunnel.exe, stunnel.conf, libssl32.dll, - libeay32.dll. We used an stunnel.conf containing: -# stunnel.conf: -client = yes -options = ALL -[myvncssl] -accept = localhost:5902 -connect = far-away.east:5901 - - then double click on the stunnel.exe icon to launch it (followed by - pointing the VNC viewer to localhost:2). - - - stunnel inetd-like mode: - - As an aside, if you don't like the little "gap" of unencrypted TCP - traffic (and a localhost listening socket) on the local machine - between stunnel and x11vnc it can actually be closed by having stunnel - start up x11vnc in -inetd mode: - stunnel -p /path/to/stunnel.pem -P none -d 5900 -l ./x11vnc_sh - - Where the script x11vnc_sh starts up x11vnc: -#!/bin/sh -x11vnc -q -inetd -display :0 -passwdfile ~/mypass - - Note that this creates a separate x11vnc process for each incoming - connection (as any inetd x11vnc usage would), but for the case of - normally just one viewer at a time it should not be a big problem. - - - stunnel 4 syntax: - - Somewhat sadly, the stunnel version 4 syntax is not so amenable to the - command line or scripts. You need to create a config file with the - parameters. E.g.: - stunnel x11vnc.cfg - - Where the file x11vnc.cfg contains: -foreground = yes -pid = -cert = /path/to/stunnel.pem -[x11vnc_stunnel] -accept = 5901 -connect = 5900 - - One nice thing about version 4 is often the PEM file does not need to - be specified because stunnel finds it in its installed area. One other - gotcha the PEM file is usually only readable by root (it has the - private key afterall), so you'll need to relax the permissions or make - a copy that the user running x11vnc/stunnel can read. - - - SSL VNC Viewers: - - Regarding VNC viewers that "natively" do SSL unfortunately there do - not seem to be many. The SingleClick UltraVNC Java Viewer is SSL and - is compatible with x11vnc's -ssl option and stunnel.) Commercial - versions of VNC seem to have some SSL-like encryption built in, but we - haven't tried those either and they probably wouldn't work since their - (proprietary) SSL-like negotiation is likely embedded in the VNC - protocol unlike our case where it is external. - - Note: as of Mar/2006 libvncserver/x11vnc provides a SSL-enabled Java - applet that can be served up via the -httpdir or -http options when - -ssl is enabled. It will also be served via HTTPS via either the VNC - port (e.g. https://host:5900/) or a 2nd port via the -https option. - - In general current SSL VNC solutions are not particularly "seemless". - But it can be done, and with a wrapper script on the viewer side and - the -stunnel or -ssl option on the server side it works well and is - convenient. Here is a simple script ss_vncviewer that automates - running stunnel on the VNC viewer side on Unix a little more carefully - than the commands printed above. (One could probably do a similar - thing with a .BAT file on Windows in the stunnel folder.) - - Update Jul/2006: we now provide an Enhanced TightVNC Viewer (SSVNC) - package that starts up STUNNEL automatically along with some other - features. All binaries (stunnel, vncviewer, and some utilities) are - provided in the package. It works on Unix, Mac OS X, and Windows. - - - Q-53: Does x11vnc have built-in SSL tunneling? - - You can read about non-built-in methods in the Previous FAQ for - background. - - SSL tunnels provide an encrypted channel without the need for Unix - users, passwords, and key passphrases required for ssh (and at the - other extreme SSL can also provide a complete signed certificate chain - of trust.) On the other hand, since SSH is usually installed - everywhere and firewalls often let its port through, ssh is frequently - the path of least resistance. - - Built-in SSL x11vnc options: - - As of Feb/2006 the x11vnc -ssl option automates the SSL tunnel - creation on the x11vnc server side. An SSL-enabled Java Viewer applet - is also provided that can be served via HTTP or HTTPS to automate SSL - on the client side. - - The -ssl mode uses the www.openssl.org library if available at build - time. - - The mode requires an SSL certificate and key (i.e. .pem file.) These - are usually created via the openssl(1) program (in fact in for "-ssl" - (same as "-ssl SAVE") it will run openssl for you automatically.) So - the SSL is not completely "built-in" since this external tool needs to - be installed, but at least x11vnc runs it for you automatically. - - An -ssl example: - x11vnc -display :0 -ssl -passwdfile ~/mypass - - You'll get output like this: - 09/04/2006 19:27:35 Creating a self-signed PEM certificate... - 09/04/2006 19:27:35 - ... - - The SSL VNC desktop is: far-away.east:0 - PORT=5900 - SSLPORT=5900 - - In this case openssl(1) was used to create a PEM automatically. It - will prompt you if you want to protect it with with a passphrase. Use - "-ssl SAVE_NOPROMPT" to not be prompted. Use "-ssl TMP" to create a - temporary self-signed cert that will be discarded when x11vnc exits. - - Update: As of Nov/2008 x11vnc also supports the VeNCrypt SSL/TLS - tunnel extension to the VNC protocol. The older ANONTLS method (vino) - is also supported. This support is on by default when the -ssl option - is in use and can be fine-tuned using these options: -vencrypt, - -anontls, and -sslonly. - - The normal x11vnc -ssl operation is somewhat like a URL method - vncs://hostname if vnc://hostname indicates a standard unencrypted VNC - connection. Just as https://hostname is an SSL encrypted version of - http://hostname. The entire VNC session goes through the SSL tunnel. - VeNCrypt, on the other hand, switches to SSL/TLS early in the VNC - protocol handshake. x11vnc 0.9.6 supports both simultaneously when - -ssl is active. - - Note: With the advent of OpenSSL 1.1.0, SSLv2 is dropped and SSLv3 - deactivated per default. A couple broken ciphers have also gone, most - importantly though is that clients trying to connect to x11vnc will - now have to support TLS if encryption is to be used. You can of - course always cook up your own build and run time OpenSSL 1.1.x if - SSLv3 is absolutely required, but it isn't wise from a security point - of view. - - - SSL VNC Viewers:. Viewer-side will need to use SSL as well. See the - next FAQ and here for SSL enabled VNC Viewers, including SSVNC, to - connect to the above x11vnc via SSL. - - - As seen above, the PEM (privacy enhanced mail) file does not need to - be supplied if the openssl(1) command is available in PATH, in that - case a self-signed, certificate good the current and subsequent x11vnc - sessions is created (this may take a while on very slow machines.) - - In general, the PEM file contains both the Certificate (i.e. public - key) and the Private Key. Because of the latter, the file should be - protected from being read by untrusted users. The best way to do this - is to encrypt the key with a passphrase (note however this requires - supplying the passphrase each time x11vnc is started up.) - - See the discussion on x11vnc Key Management for some utilities - provided for creating and managing certificates and keys and even for - creating your own Certificate Authority (CA) for signing VNC server - and client certificates. This may be done by importing the certificate - into Web Browser or Java plugin keystores, or pointing stunnel to it. - The wrapper script ss_vncviewer provides an example on unix (see the - -verify option.) - - Here are some notes on the simpler default (non-CA) operation. To have - x11vnc save the generated certificate and key, use the "SAVE" keyword - like this: - x11vnc -ssl SAVE -display :0 ... - - (this is the same as the default: "-ssl".) This way it will be saved - in the default directory ~/.vnc/certs/ as server.crt (the certificate - only) and server.pem (both certificate and private key.) This opens up - the possibility of copying the server.crt to machines where the VNC - Viewer will be run to enable authenticating the x11vnc SSL VNC server - to the clients. When authentication takes place this way (or via the - more sophisticated CA signing described here), then - Man-In-The-Middle-Attacks are prevented. Otherwise, the SSL encryption - only provides protection against passive network traffic "sniffing" - (i.e. you are not protected against M-I-T-M attacks.) Nowadays, most - people seem mostly concerned mainly about passive sniffing (and the - default x11vnc SSL mode protects against it.) Note that there are - hacker tools like dsniff/webmitm and cain that implement SSL - Man-In-The-Middle attacks. They rely on the client not bothering to - check the cert. - - - One can test to some degree that SSL is working after starting x11vnc - with the -stunnel or -ssl option. From another machine one can use the - openssl command something like this: - openssl s_client -debug -msg -showcerts -connect far-away.east:5900 - - After all of the debugging output and informational messages you'll - see the string "RFB 003.008" that came from x11vnc. Pointing a web - browser connecting to: https://far-away.east:5900/ and then viewing - the SSL certificate information about the connection in the panels - will also work. - - Note: If you serve up the SSL enabled Java VNC Viewer via something - like: - x11vnc -ssl -httpdir /usr/local/share/x11vnc/classes/ssl - - (or just the -http option), you can test it out completely using that, - including using https to download it into the browser and connect to - x11vnc. - - - The older -stunnel option: Before the -ssl option there was a - convenience option -stunnel that would start an external SSL tunnel - for you using stunnel. The -ssl method is the preferred way, but for - historical reference we keep the -stunnel info here. - - The -stunnel mode requires the stunnel.mirt.net command stunnel(8) to - be installed on the system. - - Some -stunnel examples: - x11vnc -display :0 -stunnel /path/to/stunnel.pem -passwdfile ~/mypass - - x11vnc -display :0 -stunnel SAVE ... - - You'll get output like this: - The VNC desktop is: localhost:50 - The SSL VNC desktop is: far-away.east:0 - PORT=5950 - SSLPORT=5900 - - That indicates stunnel is listening on port 5900 for incoming - SSL-wrapped VNC connections from viewers. x11vnc is listening for - local connections on port 5950 in this case (remote viewers cannot - connect to it directly.) For -stunnel to work the stunnel command must - be installed on the machine and available in PATH (note stunnel is - often installed in sbin directories rather than bin.) Note that the - default "-stunnel" by itself creates a temporary cert (as in "-ssl - TMP".) - - - Q-54: How do I use VNC Viewers with built-in SSL tunneling? - - Notes on using "native" VNC Viewers with SSL: - - There aren't any native VNC Viewers that do SSL (ask your VNC viewer - developer to add the feature.) So a tunnel must be setup that you - point the VNC Viewer to. This is often STUNNEL. You can do this - manually, or use the ss_vncviewer script on Unix, or our Enhanced - TightVNC Viewer (SSVNC) package on Unix, Windows, or MacOSX. See the - next section for Java Web browser SSL VNC Viewers (you only need a - Java-enabled Web browser for it to work.) - - Notes on the SSL enabled Java VNC Viewer provided in x11vnc - classes/ssl/VncViewer.jar: - - A Java applet VNC Viewer allows you to connect to a VNC Server from a - Java-enabled Web browser. - - The SSL enabled Java VNC Viewer (VncViewer.jar) in the x11vnc package - supports only SSL based connections by default. As mentioned above the - -httpdir can be used to specify the path to .../classes/ssl. A typical - location might be /usr/local/share/x11vnc/classes/ssl. Or -http can be - used to try to have it find the directory automatically. - - Also note that the SingleClick UltraVNC Java Viewer is compatible with - x11vnc's -ssl SSL mode. (We tested it this way: "java -cp - ./VncViewer.jar VncViewer HOST far-away.east PORT 5900 USESSL 1 - TRUSTALL 1") - - The Java viewer uses SSL to communicate securely with x11vnc. Note - that the applet can optionally also be downloaded into your web - browser via HTTPS (which is HTTP over SSL.) This way the HTML page and - the Java applet itself are also delivered securely with SSL (as - opposed to only the VNC traffic being encrypted with SSL.) - - For this case the output will be something like this: - x11vnc -ssl SAVE -http - ... - The SSL VNC desktop is: far-away.east:0 - Java SSL viewer URL: https://far-away.east:5900/ - Java SSL viewer URL: http://far-away.east:5800/ - PORT=5900 - SSLPORT=5900 - - Indicating the two URLs (the first one encrypted, the second not) one - could point the web browser at to get the VNC viewer applet. E.g. put - this - http://far-away.east:5800/ - - or: - https://far-away.east:5900/ - - into your Java-enabled Web browser. - - Note that KDE's Konqueror web browser seems to have problems with - https Java applets, so you'll have to use the http/5800 with it (if - you get https/5900 working let us know how you did it.) - - If you are using a router/firewall with port-redirection, and you are - redirecting ports other than the default ones (5800, 5900) listed - above see here. - - The https service provided thru the actual VNC port (5900 in the above - example) can occasionally be slow or unreliable (it has to read some - input and try to guess if the connection is VNC or HTTP.) If it is - unreliable for you and you still want to serve the Java applet via - https, use the -https option to get an additional port dedicated to - https (its URL will also be printed in the output.) - - Another possibility is to add the GET applet parameter: - https://far-away.east:5900/?GET=1 - - This will have the VNC Viewer send a special HTTP GET string "GET - /request.https.vnc.connection HTTP/1.0" that x11vnc will notice more - quickly as a request for a VNC connection. Otherwise it must wait for - a timeout to expire before it assumes a VNC connection. - - You may also use "urlPrefix=somestring" to have /somestring prepended - to /request.https.vnc.connection". Perhaps you are using a web server - proxy scheme to enter a firewall or otherwise have rules applied to - the URL. If you need to have any slashes "/" in "somestring" use - "_2F_" (a deficiency in libvncserver prevents using the more natural - "%2F".) - - You apply multiple applet parameters in the regular URL way, e.g.: - https://far-away.east:5900/?GET=1&urlPrefix=mysubdir&... - - All of the x11vnc Java Viewer applet parameters are described in the - file classes/ssl/README - - - Tips on Getting the SSL Java Applet Working the First Time: - Unfortunately, it can be a little tricky getting the SSL VNC Java - Viewer working with x11vnc. Here are some tips to getting working the - first time (afterwards you can incrementally customize with more - complex settings.) - * First try it on the LAN: Do NOT try to have it work the first time - going through firewalls, Web proxies, home router port - redirections, or Apache portal. Just try a direct connection over - your LAN first (if you only have 1 machine and no LAN, just do a - direct connection to the same machine: localhost.) If the LAN - machine you run x11vnc on has its own host-level firewall (most - linux machine come with that on by default), disable it or at - least let tcp ports 5800-6000 through. - * First try HTTP to download the Java Applet: x11vnc can serve both - the Java Applet jar file and VNC out of the same port (both - tunneled through SSL, see below.) But it can lead to timing and - other problems. So first try HTTP instead of HTTPS to download the - Applet jar file (VncViewer.jar.) That is to say try - http://hostname:5800 in your web browser first before trying - https://hostname:5900. x11vnc will print out the ports and URLs it - is using, so use the HTTP one it prints out. - * Always Restart the Browser: If you are having failures and have to - repeatedly retry things ALWAYS restart the browser (i.e. - completely exit it and then start a new browser process) each - time. Otherwise as you are changing things the browser may - "remember" failed applet downloads, etc. and just add to the - confusion and irreproducibility. If you see it trying to download - VncViewer.class (instead of VncViewer.jar) you know it is really - confused and needs to be restarted. - * Step Lively: If you get Browser or Java VM or VNC Viewer applet - dialog boxes saying things like "Do you want to trust this - certificate?" or "The hostname does not match the one on the - certificate", etc. just go through them as quickly as possible. - x11vnc cannot wait forever for each SSL connection, and so if you - dawdle too long inspecting the certs, etc it can lead to problems. - Get it working first before taking your time to read the details - in the dialogs, etc. - * No inetd, Please: Even if you intend to deploy via inetd or xinetd - eventually, get that working later (and remember do not use - something like "-ssl TMP" that creates a new temporary SSL - certificate for every new socket connection.) - * Nothing Fancy: Do not try fancy stuff like -svc, -create, -unixpw, - "-users unixpw=", "-users sslpeer=", -sslverify, etc. Just get the - simplest connection working first and then incrementally add what - you need. - - So the recommended test command lines are: - x11vnc -ssl SAVE -http - x11vnc -ssl SAVE -httpdir /path/to/x11vnc/classes/ssl - - Use the latter if x11vnc cannot automatically find the classes/ssl - directory (this what the -http option instructs it to do.) Then point - your browser to the HTTP (not HTTPS) URL it prints out. - - Following the above guidelines, did it work? If so, Congratulations!! - you created an SSL encrypted connection between the SSL Java applet - running in your web browser and x11vnc. The fact that you used HTTP - instead of HTTPS to download the applet is not the end of the world - (some users do it this way), the main thing is that the VNC traffic is - encrypted with SSL. If you are having trouble even with the above - baseline test case feel free to contact me (please send the Full - x11vnc output, not just part of it; the complete x11vnc command line; - the URL(s) entered in the browser; the full Java Console output; and - anything else you can think of.) - - Next, you can add the features you want one by one testing it still - works each time. I suggest first turning on the HTTPS applet download - (https://hostname:5900) if that is what you intend to use. That one - gives the most trouble because of the ambiguity of passing two - different protocols (HTTP and VNC) through the same SSL service port. - - Next, turn on inetd if you intend to use that (this can be tricky too, - be sure to use -oa logfile and inspect it carefully if there are - problems.) If you are going to use non-standard ports (e.g. "-rfbport - 443" as root), work on that next. Then enable the firewall, router - port redirection channel (you will somehow need to be outside to do - that, maybe test that through another VNC session.) - - Then, if you plan to use them, enable "fancy stuff" like "-svc" or - "-unixpw", etc, etc. Be sure to add a password either "-rfbauth" or - "-unixpw" or both. If you need to have the web browser use a corporate - Web Proxy (i.e. it cannot connect directly) work on that last. Ditto - for the Apache portal. - - - Router/Firewall port redirs: If you are doing port redirection at - your router to an internal machine running x11vnc AND the internet - facing port is different from the internal machine's VNC port, you - will need to apply the PORT applet parameter to indicate to the applet - the Internet facing port number (otherwise by default the internal - machine's port, say 5900, is sent and that of course is rejected at - the firewall/router.) For example: - https://far-away.east:443/?GET=1&PORT=443 - - So in this example the user configures his router to redirect - connections to port 443 on his Internet side to, say, port 5900 on the - internal machine running x11vnc. See also the -httpsredir option that - will try to automate this for you. - - To configure your router to do port redirection, see its instructions. - Typically, from the inside you point a web browser to a special URL - (e.g. http://192.168.1.1) and you get a web interface to configure it. - Look for something like "Port Redirection" or "Port Forwarding", - probably under "Advanced" or something like that. If you have a Linux - or Unix system acting as your firewall/router, see its firewall - configuration. - - You can also use x11vnc options -rfbport NNNNN and -httpport NNNNN to - match the ports that your firewall will be redirecting to the machine - where x11vnc is run. - - - Tedious Dialogs: If you do serve the SSL enabled Java viewer via https - be prepared for quite a number of "are you sure you trust this site?" - dialogs: - * First from the Web browser that cannot verify the self-signed - certificate when it downloads index.vnc. - * From the Web browser again noting that the common name on the - certificate does not match the hostname of the remote machine. - * Next from the Java VM that cannot verify the self-signed - certificate when it downloads VncViewer.jar. - * And also from the Java VM again noting that the common name on the - certificate does not match the hostname of the remote machine. - * Finally from the Java VncViewer applet itself saying it cannot - verify the certificate! (or a popup asking you if you want to see - the certificate.) - - Note that sometimes if you pause too long at one of the above dialogs - then x11vnc may exceed a timeout and assume the current socket - connection is VNC instead of the HTTPS it actually is (but since you - have paused too long at the dialog the GET request comes too late.) - Often hitting Reload and going through the dialogs more quickly will - let you connect. The Java VM dialogs are the most important ones to - NOT linger at. If you see in the x11vnc output a request for - VncViewer.class instead of VncViewer.jar it is too late... you will - need to completely restart the Web browser to get it to try for the - jar again. You can use the -https option if you want a dedicated port - for HTTPS connections instead of sharing the VNC port. - - To see example x11vnc output for a successful https://host:5900/ - connection with the Java Applet see This Page. And here is a newer - example including the Java Console output. - - All of the x11vnc Java Viewer applet parameters are described in the - file classes/ssl/README - - - Notes on the VNC Viewer ss_vncviewer wrapper script: - - If you want to use a native VNC Viewer with the SSL enabled x11vnc you - will need to run an external SSL tunnel on the Viewer side. There do - not seem to be any native SSL VNC Viewers outside of our x11vnc and - SSVNC packages. The basic ideas of doing this were discussed for - external tunnel utilities here. - - The ss_vncviewer script provided with x11vnc and SSVNC can set up the - stunnel tunnel automatically on unix as long as the stunnel command is - installed on the Viewer machine and available in PATH (and vncviewer - too of course.) Note that on a Debian based system you will need to - install the package stunnel4 not stunnel. You can set the environment - variables STUNNEL and VNCVIEWERCMD to point to the correct programs if - you want to override the defaults. - - Here are some examples: - 1) ss_vncviewer far-away.east:0 - - 2) ss_vncviewer far-away.east:0 -encodings "copyrect tight zrle hextile" - - 3) ss_vncviewer -verify ./server.crt far-away.east:0 - - 4) ss_vncviewer -mycert ./client.pem far-away.east:0 - - 5) ss_vncviewer -proxy far-away.east:8080 myworkstation:0 - - The first one is the default mode and accepts the x11vnc certificate - without question. The second one is as the first, but adds the - -encodings options to the vncviewer command line. - - The third one requires that the x11vnc server authenticate itself to - the client against the certificate in the file ./server.crt (e.g. one - created by "x11vnc -ssl SAVE" and safely copied to the VNC viewer - machine.) - - The fourth one is for VNC Viewer authentication, it uses ./client.pem - to authenticate itself to x11vnc. One can supply both -verify and - -mycert simultaneously. - - The fifth one shows that Web proxies can be used if that is the only - way to get out of the firewall. If the "double proxy" situation arises - separate the two by commas. See this page for more information on how - Web proxies come into play. - - If one uses a Certificate Authority (CA) scheme described here, the - wrapper script would use the CA cert instead of the server cert: - 3') ss_vncviewer -verify ./cacert.crt far-away.east:0 - - Update Jul/2006: we now provide an Enhanced TightVNC Viewer (SSVNC) - package that starts up STUNNEL automatically along with some other - features. All binaries (stunnel, vncviewer, and some utilities) are - provided in the package. It works on Unix, Mac OS X, and Windows. - - - Q-55: How do I use the Java applet VNC Viewer with built-in SSL - tunneling when going through a Web Proxy? - The SSL enabled Java VNC Viewer and firewall Proxies: - - SSL and HTTPS aside, there is a general problem with Firewall Proxies - and Java Applets that open sockets. The applet is downloaded - successfully (through the browser) using HTTP and the proxy, but when - the applet tries to reconnect to the originating host (the only one - allowed by security) it does not use the proxy channel. So it cannot - reconnect to the server the applet came from! - - We have found a convenient workaround: in the directory where - VncViewer.jar resides there is a digitally signed version of the same - applet called SignedVncViewer.jar. Since the applet is digitally - signed, there will be an additional dialog from the Java VM plugin - asking you if you want to trust the applet fully. - - You should say "Yes". If you do, the applet will be run in a mode - where it can try to determine the firewall proxy host name and port - (it will ask you for them if it cannot find them.) This way it can - connect directly to the Proxy and then request the CONNECT method to - be redirected to the originating host (the x11vnc VNC Server.) SSL is - then layered over this socket. - - To do this you should use the proxy.vnc HTML file like via this URL in - your browser: - https://yourmachine.com:5900/proxy.vnc - - (instead of the unsigned one in https://yourmachine.com:5900/ that - gives the default index.vnc) - - Proxies that limit CONNECT to ports 443 and 563: - - Things become trickier if the Web proxy restricts which CONNECT ports - can be redirected to. For security, some (most?) proxies only allow - port 443 (HTTPS) and 563 (SNEWS) by default. In this case, the only - thing to do is run x11vnc on that low port, e.g. "-rfbport 443", (or - use a port redirection on, say, a firewall or router port 443 to the - internal machine.) - - If you do such a redirection to an internal machine and x11vnc is not - listening on port 443, you will probably need to edit proxy.vnc. - Suppose the SSL x11vnc server was listening on port 5901. You should - change the line in proxy.vnc from: - - - to: - - - Since otherwise $PORT will be expanded to 5901 by x11vnc and the - viewer applet will fail to connect to that port on the firewall. - - Another way to achieve the same thing is to use the applet PORT - parameter: - https://yourmachine.com/proxy.vnc?PORT=443 - - this is cleaner because it avoids editing the file, but requires more - parameters in the URL. See also the -httpsredir x11vnc option that - will try to automate this for you. To use the GET trick discussed - above, do: - https://yourmachine.com/proxy.vnc?GET=1&PORT=443 - - All of the x11vnc Java Viewer applet parameters are described in the - file classes/ssl/README - - Here is an example of Java Console and x11vnc output for the Web proxy - case. - - - Note that both the ss_vncviewer stunnel Unix wrapper script and - Enhanced TightVNC Viewer (SSVNC) can use Web proxies as well even - though they do not involve a Web browser. - - - Q-56: Can Apache web server act as a gateway for users to connect via - SSL from the Internet with a Web browser to x11vnc running on their - workstations behind a firewall? - Yes. You will need to configure apache to forward these connections. - It is discussed here. This SSL VNC portal provides a clean alternative - to the traditional method where the user uses SSH to log in through - the gateway to create the encrypted port redirection to x11vnc running - on her desktop. - - Also see the desktop.cgi CGI script method that achieves much of what - this Apache VNC SSL portal method does (as long as desktop.cgi's 'port - redirection' mode is enabled.) - - - Q-57: Can I create and use my own SSL Certificate Authority (CA) with - x11vnc? - Yes, see this page for how to do this and the utility commands x11vnc - provides to create and manage many types of certificates and private - keys. - - - - [Display Managers and Services] - - Q-58: How can I run x11vnc as a "service" that is always available? - - There are a number of ways to do this. The primary thing you need to - decide is whether you want x11vnc to connect to the X session on the - machine 1) regardless of who (or if anyone) has the X session, or 2) - only if a certain user has the X session. Because X sessions are - protected by X permissions (MIT-MAGIC-COOKIE files XAUTHORITY and - $HOME/.Xauthority) the automatically started x11vnc will of course - need to have sufficient permissions to connect to the X display. - - Here are some ideas: - * Use the description under "Continuously" in the FAQ on x11vnc and - Display Managers - * Use the description in the FAQ on x11vnc and inetd(8) - * Use the description in the FAQ on Unix user logins and inetd(8) - * Start x11vnc from your $HOME/.xsession (or $HOME/.xinitrc or - autostart script or ...) - * Although less reliable, see the x11vnc_loop rc.local hack below. - - The display manager scheme will not be specific to which user has the - X session unless a test is specifically put into the display startup - script (often named Xsetup.) The inetd(8) scheme may or may not be - specific to which user has the X session (and it may not be able to do - all users via the XAUTHORITY permission issues.) - - The .xsession/.xinitrc scheme is obviously is specific to a particular - user and only when they are logged into X. If you do not know what a - $HOME/.xsession script is or how to use one, perhaps your desktop has - a "session startup commands" configuration option. The command to be - run in the .xsession or .xinitrc file may look like this: -x11vnc -logfile $HOME/.x11vnc.log -rfbauth $HOME/.vnc/passwd -forever -bg - - plus any other options you desire. - - Depending on your desktop and/or OS/distribution the automatically run - X startup scripts (traditionally .xsession/.xinitrc) may have to be in - a different directory or have a different basename. One user - recommends the description under 'Running Scripts Automatically' at - this link. - - Firewalls: note all methods will require the host-level firewall to be - configured to allow connections in on a port. E.g. 5900 (default VNC - port) or 22 (default SSH port for tunnelling VNC.) Most systems these - days have firewalls turned on by default, so you will actively have to - do something to poke a hole in the firewall at the desired port - number. See your system administration tool for Firewall settings - (Yast, Firestarter, etc.) - - - Q-59: How can I use x11vnc to connect to an X login screen like xdm, - GNOME gdm, KDE kdm, or CDE dtlogin? (i.e. nobody is logged into an X - session yet.) - - We describe two scenarios here. The first is called 'One time only' - meaning you just need to do it quickly once and don't want to repeat; - and the second is called 'Continuously' meaning you want the access to - be available after every reboot and after every desktop logout. - _________________________________________________________________ - - One time only: If the X login screen is running and you just want to - connect to it once (i.e. a one-shot): - - It is usually possible to do this by just adjusting the XAUTHORITY - environment variable to point to the correct MIT-COOKIE auth file - while running x11vnc as root, e.g. for the gnome display manager, GDM: - x11vnc -auth /var/gdm/:0.Xauth -display :0 - - (the -auth option sets the XAUTHORITY variable for you.) - - There will be a similar thing to do for xdm using however a different - auth directory path (perhaps something like - /var/lib/xdm/authdir/authfiles/A:0-XQvaJk) for the xdm greeter or - /var/lib/kdm/A:0-crWk72 (or /var/run/xauth/A:0-qQPftr, etc. etc) for - the kdm greeter. Of course, the random characters in the file basename - will vary and you will need to use the actual filename on your system. - Read your system docs to find out where the display manager cookie - files are kept. - - Trick: sometimes ps(1) can reveal the X server process -auth argument - (e.g. "ps wwaux | grep auth") and hence the path to the auth file. - - x11vnc must be run as root for this because the /var/gdm/:0.Xauth, - /var/lib/kdm/A:0-crWk72, etc. auth files are only readable by root. If - you do not want to run x11vnc as root, you can copy (as root or sudo) - the auth file to some location and make it readable by your userid. - Then run x11vnc as your userid with -auth pointed to the copied file. - - Update Dec/2009: use "-auth guess" to have x11vnc try to guess the - location of the auth file for you. - - You next connect to x11vnc with a VNC viewer, give your username and - password to the X login prompt to start your session. - - Note: GDM: gdm seems to have an annoying setting that causes x11vnc - (and any other X clients) to be killed after the user logs in. Setting - KillInitClients=false in the [daemon] section of /etc/X11/gdm/gdm.conf - (or /etc/gdm/gdm.conf, etc.) avoids this. Otherwise, just restart - x11vnc and then reconnect your viewer. Other display managers (kdm, - etc) may also have a similar problem. One user reports having to alter - "gdm.conf-custom" as well. - - Note: Solaris: For dtlogin in addition to the above sort of trick - (BTW, the auth file should be in /var/dt), you'll also need to add - something like Dtlogin*grabServer:False to the Xconfig file - (/etc/dt/config/Xconfig or /usr/dt/config/Xconfig on Solaris, see the - example at the end of this FAQ.) Then restart dtlogin, e.g.: - /etc/init.d/dtlogin stop; /etc/init.d/dtlogin start or reboot. - - Update Nov/2008: Regarding GDM KillInitClients: see the -reopen option - for another possible workaround. - - Update Oct/2009: Regarding GDM KillInitClients: starting with x11vnc - 0.9.9 it will try to apply heuristics to detect if a window manager is - not running (i.e. whether the Display Manager Greeter Login panel is - still up.) If it thinks the display manager login is still up it will - delay creating windows or using XFIXES. The former is what GDM uses to - kill the initial clients, use of the latter can cause a different - problem: an Xorg server crash. So with 0.9.9 and later it should all - work without needing to set KillInitClients=false (which is a good - because recent GDM, v2.24, has removed this option) or use -noxfixes. - To disable the heuristics and delaying set X11VNC_AVOID_WINDOWS=never; - to set the delay time explicitly use, e.g., X11VNC_AVOID_WINDOWS=120 - (delays for 120 seconds after the VNC connection; you have that long - to log in.) - _________________________________________________________________ - - Continuously: Have x11vnc reattach each time the X server is - restarted (i.e. after each logout and reboot): - - To make x11vnc always attached to the X server including the login - screen you will need to add a command to a display manager startup - script. - - Please consider the security implications of this! The VNC display for - the X session always accessible (but hopefully password protected.) - Add -localhost if you only plan to access via a SSH tunnel. - - The name of the display manager startup script file depends on desktop - used and seem to be: - GDM (GNOME) /etc/X11/gdm/Init/Default - /etc/gdm/Init/Default - KDM (KDE) /etc/kde*/kdm/Xsetup - XDM /etc/X11/xdm/Xsetup (or sometimes xdm/Xsetup_0) - CDE /etc/dt/config/Xsetup - - although the exact location can be operating system, distribution, and - time dependent. See the documentation for your display manager: - gdm(1), kdm(1), xdm(1), dtlogin(1) for additional details. There may - also be display number specific scripts: e.g. Xsetup_0 vs. Xsetup, you - need to watch out for. - - Note: You should read and understand all of the Note's and Update's - in the 'One time only' section above. All of the GDM topics apply here - as well: - - Note: GDM: The above (in 'One time only') gdm setting of - KillInitClients=false in /etc/X11/gdm/gdm.conf (or /etc/gdm/gdm.conf, - etc.) for GDM is needed here as well. Other display managers (KDM, - etc) may also have a similar problem. - - Also see the Update Oct/2009 above where x11vnc 0.9.9 and later - automatically avoids being killed. - - Note: DtLogin: The above (in 'One time only') - Dtlogin*grabServer:False step for Solaris will be needed for dtlogin - here as well. - - In any event, the line you will add to the display manager script - (Xsetup, Default, or whatever) will look something like: - /usr/local/bin/x11vnc -rfbauth /path/to/the/vnc/passwd -o /var/log/x11vnc.log - -forever -bg - - where you should customize the exact command to your needs (e.g. - -localhost for SSH tunnel-only access; -ssl SAVE for SSL access; etc.) - - Happy, happy, joy, joy: Note that we do not need to specify -display - or -auth because happily they are already set for us in the DISPLAY - and XAUTHORITY environment variables for the Xsetup script!!! - - You may also want to force the VNC port with something like "-rfbport - 5900" (or -N) to avoid autoselecting one if 5900 is already taken. - _________________________________________________________________ - - Fedora/gdm: Here is an example of what we did on a vanilla install of - Fedora-C3 (seems to use gdm by default.) Add a line like this to - /etc/X11/gdm/Init/:0 - /usr/local/bin/x11vnc -rfbauth /etc/x11vnc.passwd -forever -bg -o /var/log/x1 -1vnc.log - - And then add this line to /etc/X11/gdm/gdm.conf (or /etc/gdm/gdm.conf, - etc.) in the [daemon] section: - KillInitClients=false - - Then restart: /usr/sbin/gdm-restart (or reboot.) The - KillInitClients=false setting is important: without it x11vnc will be - killed immediately after the user logs in. Here are full details on - how to configure gdm - _________________________________________________________________ - - Solaris/dtlogin: Here is an example of what we did on a vanilla - install of Solaris: - Make the directory /etc/dt/config: - mkdir -p /etc/dt/config - - Copy over the Xconfig file for customization: - cp /usr/dt/config/Xconfig /etc/dt/config/Xconfig - - Edit /etc/dt/config/Xconfig and uncomment the line: - Dtlogin*grabServer: False - - Next, copy over Xsetup for customization: - cp /usr/dt/config/Xsetup /etc/dt/config/Xsetup - - Edit /etc/dt/config/Xsetup and at the bottom put a line like: - /usr/local/bin/x11vnc -forever -o /var/log/x11vnc.log -bg - - (tweaked to your local setup and preferences, a password via -rfbauth, - etc. would be a very good idea.) - - Restart the X server and dtlogin: - /etc/init.d/dtlogin stop - /etc/init.d/dtlogin start - - (or reboot or maybe just restart the X session.) - _________________________________________________________________ - - KDM: One user running the kdm display manager reports putting this - line: - x11vnc -forever -rfbauth /home/xyz/.vnc/passwd -bg -o /var/log/x11vnc.log - - in /etc/kde/kdm/Xsetup. After rebooting the system it all seemed to - work fine. - _________________________________________________________________ - - - If you do not want to deal with any display manager startup scripts, - here is a kludgey script that can be run manually or out of a boot - file like rc.local: x11vnc_loop It will need some local customization - before running. Because the XAUTHORITY auth file must be guessed by - this script, use of the display manager script method described above - is greatly preferred. There is also the -loop option that does - something similar. - - If the machine is a traditional Xterminal you may want to read this - FAQ. - - Firewalls: note all methods will require the host-level firewall to be - configured to allow connections in on a port. E.g. 5900 (default VNC - port) or 22 (default SSH port for tunnelling VNC.) Most systems these - days have firewalls turned on by default, so you will actively have to - do something to poke a hole in the firewall at the desired port - number. See your system administration tool for Firewall settings - (Yast, Firestarter, etc.) - - - Q-60: Can I run x11vnc out of inetd(8)? How about xinetd(8)? - - Yes, perhaps a line something like this in /etc/inetd.conf will do it - for you: - - 5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc_sh - - where the shell script /usr/local/bin/x11vnc_sh uses the -inetd option - and looks something like (you'll need to customize to your settings.) -#!/bin/sh -/usr/local/bin/x11vnc -inetd -display :0 -auth /home/fred/.Xauthority \ - -rfbauth /home/fred/.vnc/passwd -o /var/log/x11vnc_sh.log - - Important: Note that you must redirect the standard error output to a - log file (e.g. -o logfile) or "2>/dev/null" for proper operation via - inetd (otherwise the standard error also goes to the VNC vncviewer, - and that confuses it greatly, causing it to abort.) If you do not use - a wrapper script as above but rather call x11vnc directly in - /etc/inetd.conf and do not redirect stderr to a file, then you must - specify the -q (aka -quiet) option: "/usr/local/bin/x11vnc -q -inetd - ...". When you supply both -q and -inet and no "-o logfile" then - stderr will automatically be closed (to prevent, e.g. library stderr - messages leaking out to the viewer.) The recommended practice is to - use "-o logfile" to collect the output in a file or wrapper script - with "2>logfile" redirection because the errors and warnings printed - out are very useful in troubleshooting problems. - - Note also the need to set XAUTHORITY via -auth to point to the - MIT-COOKIE auth file to get permission to connect to the X display - (setting and exporting the XAUTHORITY variable accomplishes the same - thing.) See the x11vnc_loop file in the previous question for more - ideas on what that auth file may be, etc. The scheme described in the - FAQ on Unix user logins and inetd(8) works around the XAUTHORITY issue - nicely. - - Note: On Solaris you cannot have the bare number 5900 in - /etc/inetd.conf, you'll need to replace it with a word like x11vnc an - then put something like "x11vnc 5900/tcp" in /etc/services. - - Since the process runs as root, it might be a bad idea to have the - logfile in a world-writable area like /tmp if there are untrustworthy - users on the machine. Perhaps /var/log is a better place. - - Be sure to look at your /etc/hosts.allow and /etc/hosts.deny settings - to limit the machines that can connect to this service (your desktop!) - For the above example with /etc/hosts.allow: - x11vnc_sh : 123.45.67.89 - - A really safe way to do things is to limit the above inetd to - localhost only (via /etc/hosts.allow) and use ssh to tunnel the - incoming connection. Using inetd for this prevents there being a tiny - window of opportunity between x11vnc starting up and your vncviewer - connecting to it. Always use a VNC password to further protect against - unwanted access. - - For xinetd(8), one user reports he created the file - /etc/xinetd.d/x11vncservice containing the following: -# default: off -# description: -service x11vncservice -{ - flags = REUSE NAMEINARGS - port = 5900 - type = UNLISTED - socket_type = stream - protocol = tcp - wait = no - user = root - server = /usr/sbin/tcpd - server_args = /usr/local/bin/x11vnc_sh - disable = no -} - - With the contents of /usr/local/bin/x11vnc_sh similar to the example - given above. One user reports this works with avoiding the wrapper - script: -service x11vncservice -{ - port = 5900 - type = UNLISTED - socket_type = stream - protocol = tcp - wait = no - user = root - server = /usr/local/bin/x11vnc - server_args = -inetd -q -display :0 -auth /var/gdm/:0.Xauth - disable = no -} - - (or one can replace the -q with say "-o /var/log/x11vnc.log" to - capture a log) - - The above works nicely for GDM because the -auth file is a fixed name. - For KDM or XDM the filename varies. Here is one idea for a x11vnc_sh - wrapper to try to guess the name: -#!/bin/sh -COLUMNS=256 -export COLUMNS -authfile=`ps wwaux | grep '/X.*-auth' | grep -v grep | sed -e 's/^.*-auth *//' --e 's/ .*$//' | head -n 1` - -if [ -r "$authfile" ]; then - exec /usr/local/bin/x11vnc -inetd -o /var/log/x11vnc.log -display :0 -a -uth "$authfile" -fi -exit 1 - - Starting with x11vnc 0.9.3 this can be automated by: -#!/bin/sh -exec /usr/local/bin/x11vnc -inetd -o /var/log/x11vnc.log -find -env FD_XDM=1 - - - Q-61: Can I have x11vnc advertise its VNC service and port via mDNS / - Zeroconf (e.g. Avahi) so VNC viewers on the local network can detect - it automatically? - - Yes, as of Feb/2007 x11vnc supports mDNS / Zeroconf advertising of its - service via the Avahi client library. Use the option -avahi (same as - -mdns or -zeroconf) to enable it. Depending on your setup you may need - to install Avahi (including the development/build packages), enable - the server: avahi-daemon and avahi-dnsconfd, and possibly open up UDP - port 5353 on your firewall. - - If the Avahi client library or build environment is not available at - build-time, then at run-time x11vnc will try to look for external - helper programs, avahi-browse(1) or dns-sd(1), to do the work. - - The service was tested with Chicken of the VNC ("Use Bonjour" - selected) on a Mac on the same network and the service was noted and - listed in the servers list. Clicking on it and then "Connect" - connected automatically w/o having to enter any hostnames or port - numbers. - - It appears SuSE 10.1 comes with avahi (or you can add packages, e.g. - avahi-0.6.5-27) but not the development package (you can use the - OpenSuSE avahi-devel rpm.) Unfortunately, you may need to disable - another Zeroconf daemon "/etc/init.d/mdnsd stop", before doing - "/etc/init.d/avahi-daemon start" and "/etc/init.d/avahi-dnsconfd - start". We also had to comment out the browse-domains line in - /etc/avahi/avahi-daemon.conf. Hopefully there is "LessConf" to do on - other distros/OS's... - - - Q-62: Can I have x11vnc allow a user to log in with her UNIX username - and password and then have it find her X session display on that - machine and then attach to it? How about starting an X session if one - cannot be found? - - The easiest way to do this is via inetd(8) using the -unixpw and - -display WAIT options. The reason inetd(8) makes this easier is that - it starts a new x11vnc process for each new user connection. Otherwise - a wrapper would have to listen for connections and spawn new x11vnc's - (see this example and also the -loopbg option.) inetd(8) is not - required for this, but it makes some aspects more general. - - Also with inetd(8) users always connect to a fixed VNC display, say - hostname:0, and do not need to memorize a special VNC display number - just for their personal use, etc. - - Update: Use the -find, -create, -svc, and -xdmsvc options that are - shorthand for common FINDCREATEDISPLAY usage modes (e.g. terminal - services) described below. (i.e. simply use "-svc" instead of the - cumbersome "-display WAIT:cmd=FINDCREATEDISPLAY-Xvfb -unixpw -users - unixpw= -ssl SAVE") - - The -display WAIT option makes x11vnc wait until a VNC viewer is - connected before attaching to the X display. - - Additionally it can be used to run an external command that returns - the DISPLAY and XAUTHORITY data. We provide some useful builtin ones - (FINDDISPLAY and FINDCREATEDISPLAY below), but in principle one could - supply his own script: "-display WAIT:cmd=/path/to/find_display" where - the script find_display might look something like this. - - A default script somewhat like the above is used under "-display - WAIT:cmd=FINDDISPLAY" (same as -find) The format for any such command - is that it returns DISPLAY=:disp as the first line and any remaining - lines are either XAUTHORITY=file or raw xauth data (the above example - does the latter.) If applicable (-unixpw mode), the program is run as - the Unix user name who logged in. - - On Linux if the virtual terminal is known the program appends ",VT=n" - to the DISPLAY line; a chvt n will be attempted automatically. Or if - only the X server process ID is known it appends ",XPID=n" (a chvt - will be attempted by x11vnc.) - - Tip: Note that the -find option is an alias for "-display - WAIT:cmd=FINDDISPLAY". Use it! - - The -unixpw option allows UNIX password logins. It conveniently knows - the Unix username whose X display should be found. Here are a couple - /etc/inetd.conf examples of this usage: -5900 stream tcp nowait nobody /usr/sbin/tcpd /usr/local/bin/x11vnc -inetd --unixpw \ - -find -o /var/log/x11vnc.log -ssl SAVE -ssldir /usr/local/certs -5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc -inetd --unixpw \ - -find -o /var/log/x11vnc.log -ssl SAVE -users unixpw= - - Note we have used the -find alias and the very long lines have been - split. An alternative is to use a wrapper script, e.g. - /usr/local/bin/x11vnc.sh that has all of the options. (see also the - -svc alias.) - - In the first inetd line x11vnc is run as user "nobody" and stays user - nobody during the whole session. The permissions of the log files and - certs directory will need to be set up to allow "nobody" to use them. - - In the second one x11vnc is run as root and switches to the user that - logs in due to the "-users unixpw=" option. - - Note that SSL is required for this mode because otherwise the Unix - password would be passed in clear text over the network. In general - -unixpw is not required for this sort of scheme, but it is convenient - because it determines exactly who the Unix user is whose display - should be sought. Otherwise the find_display script would have to use - some method to work out DISPLAY, XAUTHORITY, etc (perhaps you use - multiple inetd ports and hardwire usernames for different ports.) - - If you really want to disable the SSL or SSH -localhost constraints - (this is not recommended unless you really know what you are doing: - Unix passwords sent in clear text is a very bad idea...) read the - -unixpw documentation. - - A inetd(8) scheme for a fixed user that doesn't use SSL or unix - passwds could be: - /usr/local/bin/x11vnc -inetd -users =fred -find -rfbauth /home/fred/.vnc/pass -wd -o /var/log/x11vnc.log - - The "-users =fred" option will cause x11vnc to switch to user fred and - then find his X display. The VNC password (-rfbauth) as opposed to - Unix password (-unixpw) is used to authenticate the VNC client. - - Similar looking commands to the above examples can be run directly and - do not use inetd (just remove the -inetd option and run from the - cmdline, etc.) - - - X Session Creation: An added (Nov/2006) extension to FINDDISPLAY is - FINDCREATEDISPLAY where if it does not find an X display via the - FINDDISPLAY method it will create an X server session for the user - (i.e. desktop/terminal server.) This is the only time x11vnc actually - tries to start up an X server (normally it just attaches to an - existing one.) - - For virtual sessions you will need to install the Xvfb program (e.g. - apt-get install xvfb) or our Xdummy program (see below.) - - By default it will only try to start up virtual (non-hardware) X - servers: first Xvfb and if that is not available then Xdummy (included - in the x11vnc source code.) Note that Xdummy only works on Linux - whereas Xvfb works just about everywhere (and in some situations - Xdummy must be run as root.) An advantage of Xdummy over Xvfb is that - Xdummy supports RANDR dynamic screen resizing, which can be handy if - the user accesses the desktop from different sized screens (e.g. - workstation and laptop.) - - So an inetd(8) example might look like: -5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc -inetd \ - -o /var/log/x11vnc.log -http -prog /usr/local/bin/x11vnc \ - -ssl SAVE -unixpw -users unixpw= -display WAIT:cmd=FINDCREATEDISPLAY - - Where the very long lines have been split. See below where that long - and cumbersome last line is replaced by the -svc alias. - - The above mode will allow direct SSL (e.g. ss_vncviewer or SSVNC) - access and also Java Web browers access via: https://hostname:5900/. - - Tip: Note that the -create option is an alias for "-display - WAIT:cmd=FINDCREATEDISPLAY-Xvfb". - - Tip: Note that -svc is a short hand for the long "-ssl SAVE -unixpw - -users unixpw= -display WAIT:cmd=FINDCREATEDISPLAY" part. Unlike - -create, this alias also sets up SSL encryption and Unix password - login. - - The above inetd example then simplifies to: -5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc -inetd \ - -o /var/log/x11vnc.log -http -prog /usr/local/bin/x11vnc \ - -svc - - Tip: In addition to the usual unixpw parameters, inside the VNC viewer - the user can specify after his username (following a ":" see -display - WAIT for details) for FINDCREATEDISPLAY they can add "geom=WxH" or - "geom=WxHxD" to specify the width, height, and optionally the color - depth. E.g. "fred:geom=800x600" at the login: prompt. Also if the env. - var X11VNC_CREATE_GEOM is set to the desired WxH or WxHxD that will be - used by x11vnc. - - You can set the env. var X11VNC_SKIP_DISPLAY to a comma separated list - of displays to ignore in the FINDDISPLAY process (to force creation of - new displays in some cases.) The user logging in via the vncviewer can - also set this via username:nodisplay=...) - - If you do not plan on using the Java Web browser applet you can remove - the -http (and -prog) option since this will speed up logging-in by a - few seconds (x11vnc will not have to wait to see if a connection is - HTTPS or VNC.) - - For reference, xinetd format in the file, say, /etc/xinetd.d/x11vnc: -service x11vnc -{ - type = UNLISTED - port = 5900 - socket_type = stream - protocol = tcp - wait = no - user = root - server = /usr/local/bin/x11vnc - server_args = -inetd -o /var/log/x11vnc.log -http -prog /usr/local/ -bin/x11vnc -svc - disable = no -} - - To print out the script in this case use "-display - WAIT:cmd=FINDCREATEDISPLAY-print". To change the preference of - Xservers and which to try list them, e.g.: "-display - WAIT:cmd=FINDCREATEDISPLAY-X,Xvfb,Xdummy" or use "-create_xsrv - X,Xvfb,Xdummy". The "X" one means to try to start up a real, hardware - X server, e.g. startx(1) (if there is already a real X server running - this may only work on Linux and the chvt program may need to be run to - switch to the correct Linux virtual terminal.) x11vnc will try to run - chvt automatically if it can determine which VT should be switched to. - - XDM/GDM/KDM Login Greeter Panel: If you want to present the user with - a xdm/gdm/kdm display manager "greeter" login you can use Xvfb.xdmcp - instead of Xvfb, etc in the above list. However, you need to configure - xdm/gdm/kdm to accept localhost XDMCP messages, this can be done by - (from -help output): - If you want the FINDCREATEDISPLAY session to contact an XDMCP login - manager (xdm/gdm/kdm) on the same machine, then use "Xvfb.xdmcp" - instead of "Xvfb", etc. The user will have to supply his username - and password one more time (but he gets to select his desktop - type so that can be useful.) For this to work, you will need to - enable localhost XDMCP (udp port 177) for the display manager. - This seems to be: - - for gdm in gdm.conf: Enable=true in section [xdmcp] - for kdm in kdmrc: Enable=true in section [Xdmcp] - for xdm in xdm-config: DisplayManager.requestPort: 177 - - Unless you are also providing XDMCP service to xterminals or other - machines, make sure that the host access list only allows local - connections (the name of this file is often Xaccess and it is usually - setup by default to do just that.) Nowadays, host level firewalling - will also typically block UDP (port 177 for XDMCP) by default - effectively limiting the UDP connections to localhost. - - Tip: Note that -xdmsvc is a short hand alias for the long "-ssl SAVE - -unixpw -users unixpw= -display - WAIT:cmd=FINDCREATEDISPLAY-Xvfb.xdmcp". So we simply use: -service x11vnc -{ - type = UNLISTED - port = 5900 - socket_type = stream - protocol = tcp - wait = no - user = root - server = /usr/local/bin/x11vnc - server_args = -inetd -o /var/log/x11vnc.log -xdmsvc - disable = no -} - - (Note: use "-svc" instead of "-xdmsvc" for no XDMCP login greeter.) - - - Local access (VNC Server and VNC Viewer on the same machine): To - access your virtual X display session locally (i.e. while sitting at - the same machine it is running on) one can perhaps have something like - this in their $HOME/.xinitrc -#!/bin/sh -x11vnc -create -rfbport 5905 -env WAITBG=1 -vncviewer -geometry +0+0 -encodings raw -passwd $HOME/.vnc/passwd localhost:5 - - You may not need the -passwd. Recent RealVNC viewers might be this: -#!/bin/sh -x11vnc -create -rfbport 5905 -env WAITBG=1 -vncviewer -FullScreen -PreferredEncoding raw -passwd $HOME/.vnc/passwd localhos -t:5 - - This way a bare X server is run with no window manager or desktop; it - simply runs only the VNC Viewer on the real X server. The Viewer then - draws the virtual X session on to the real one. On your system it - might not be $HOME/.xinitrc, but rather .xsession, .Xclients, or - something else. You will need to figure out what it is for your system - and configuration. - - There may be a problem if the resolution (WxH) of the virtual X - display does not match that of the physical X display. - - If you do not want to or cannot figure out the X startup script name - (.xinitrc, etc) you could save the above commands to a shell script, - say "vnclocal", and the log in via the normal KDM or GDM greeter - program using the "Failsafe" option. Then in the lone xterm that comes - up type "vnclocal" to connect to your virtual X display via x11vnc and - vncviewer. - - _________________________________________________________________ - - Summary: The "-display WAIT:cmd=FINDCREATEDISPLAY" scheme can be used - to provide a "desktop service" (i.e. terminal service) on the server - machine: you always get some desktop there, either a real hardware X - server or a virtual one (depending on how you set things up.) - - So it provides simple "terminal services" based on Unix username and - password. The created X server sessions (virtual or real hardware) - will remain running after you disconnect the VNC viewer and will be - found again on reconnecting via VNC and logging in. To terminate them - use the normal way to Exit/LogOut from inside your X session. The user - does not have to memorize which VNC display number is his. They all go - the same one (e.g. hostname:0) and it switches based on username. - - - Q-63: Can I have x11vnc restart itself after it terminates? - - One could do this in a shell script, but now there is an option -loop - that makes it easier. Of course when x11vnc restarts it needs to have - permissions to connect to the (potentially new) X display. This mode - could be useful if the X server restarts often. Use e.g. "-loop5000" - to sleep 5000 ms between restarts. Also "-loop2000,5" to sleep 2000 ms - and only restart 5 times. - - One can also use the -loopbg to emulate inetd(8) to some degree, where - each connected process runs in the background. It could be combined, - say, with the -svc option to provide simple terminal services without - using inetd(8). - - - Q-64: How do I make x11vnc work with the Java VNC viewer applet in a - web browser? - - To have x11vnc serve up a Java VNC viewer applet to any web browsers - that connect to it, run x11vnc with this option: - -httpdir /path/to/the/java/classes/dir - - (this directory will contain the files index.vnc and, for example, - VncViewer.jar) Note that libvncserver contains the TightVNC Java - classes jar file for your convenience. (it is the file - classes/VncViewer.jar in the source tree.) - - You will see output something like this: - 14/05/2004 11:13:56 Autoprobing selected port 5900 - 14/05/2004 11:13:56 Listening for HTTP connections on TCP port 5800 - 14/05/2004 11:13:56 URL http://walnut:5800 - 14/05/2004 11:13:56 screen setup finished. - 14/05/2004 11:13:56 The VNC desktop is walnut:0 - PORT=5900 - - then you can connect to that URL with any Java enabled browser. Feel - free to customize the default index.vnc file in the classes directory. - - As of May/2005 the -http option will try to guess where the Java - classes jar file is by looking in expected locations and ones relative - to the x11vnc binary. - - Also note that if you wanted to, you could also start the Java viewer - entirely from the viewer-side by having the jar file there and using - either the java or appletviewer commands to run the program. - java -cp ./VncViewer.jar VncViewer HOST far-away.east PORT 5900 - - Proxies: See the discussion here if the web browser must use a web - proxy to connect to the internet. It is tricky to get Java applets to - work in this case: a signed applet must be used so it can connect to - the proxy and ask for the redirection to the VNC server. One way to do - this is to use the signed SSL one referred to in classes/ssl/proxy.vnc - and set disableSSL=yes (note that this has no encryption; please use - SSL or SSH as discuss elsewhere on this page) in the URL or the file. - - - Q-65: Are reverse connections (i.e. the VNC server connecting to the - VNC viewer) using "vncviewer -listen" and vncconnect(1) supported? - - As of Mar/2004 x11vnc supports reverse connections. On Unix one starts - the VNC viewer in listen mode: "vncviewer -listen" (see your - documentation for Windows, etc), and then starts up x11vnc with the - -connect option. To connect immediately at x11vnc startup time use the - "-connect host:port" option (use commas for a list of hosts to connect - to.) The ":port" is optional (default is VNC listening port is 5500.) - - If a file is specified instead: -connect /path/to/some/file then that - file is checked periodically (about once a second) for new hosts to - connect to. - - The -remote control option (aka -R) can also be used to do this during - an active x11vnc session, e.g.: -x11vnc -display :0 -R connect:hostname.domain - - Use the "-connect_or_exit" option to have x11vnc exit if the reverse - connection fails. Also, note the "-rfbport 0" option disables TCP - listening for connections (potentially useful for reverse connection - mode, assuming you do not want any "forward" connections.) - - Note that as of Mar/2006 x11vnc requires password authentication for - reverse connections as well as for forward ones (assuming password - auth has been enabled, e.g. via -rfbauth, -passwdfile, etc.) Many VNC - servers do not require any password for reverse connections. To regain - the old behavior supply this option "-env - X11VNC_REVERSE_CONNECTION_NO_AUTH=1" to x11vnc. - - Vncconnect command: To use the vncconnect(1) program (from the core - VNC package at www.realvnc.com) specify the -vncconnect option to - x11vnc (Note: as of Dec/2004 -vncconnect is now the default.) - vncconnect(1) must be pointed to the same X11 DISPLAY as x11vnc (since - it uses X properties to communicate with x11vnc.) If you do not have - or do not want to get the vncconnect(1) program, the following script - (named "Vncconnect") may work if your xprop(1) supports the -set - option: -#!/bin/sh -# usage: Vncconnect -# Vncconnect -# note: not all xprop(1) support -set. -# -xprop -root -f VNC_CONNECT 8s -set VNC_CONNECT "$1" - - - Q-66: Can reverse connections be made to go through a Web or SOCKS - proxy or SSH? - - Yes, as of Oct/2007 x11vnc supports reverse connections through - proxies: use the "-proxy host:port" option. The default is to assume - the proxy is a Web proxy. Note that most Web proxies only allow proxy - destination connections to ports 443 (HTTPS) and 563 (SNEWS) and so - this might not be too useful unless the proxy has been modified - (AllowCONNECT apache setting) or the VNC viewer listens on one of - those ports (or the router does a port redir.) A web proxy may also be - specified via "-proxy http://host:port" - - For SOCKS4 and SOCKS4a proxies use this format "-proxy - socks://host:port". If the reverse connection hostname is a numerical - IP or "localhost" then SOCKS4 (no host lookup) is used, otherwise - SOCKS4a will be used. For SOCKS5 (proxy will do lookup and many other - things) use "-proxy socks5://host:port". Note that the SSH builtin - SOCKS proxy "ssh -D port" only does SOCKS4 or SOCKS5, so use socks5:// - for a ssh -D proxy. - - The proxying works for both SSL encrypted and normal reverse - connections. - - An experimental mode is "-proxy http://host:port/..." where the URL - (e.g. a CGI script) is retrieved via the GET method. See -proxy for - more info. - - Another experimental mode is "-proxy ssh://user@host" in which case a - SSH tunnel is used for the proxying. See -proxy for more info. - - Up to 3 proxies may be chained together by listing them by commas - e.g.: "-proxy http://host1:port1,socks5://host2:port2" in case one - needs to ricochet off of several machines to ultimately reach the - listening viewer. - - - Q-67: Can x11vnc provide a multi-user desktop web login service as an - Apache CGI or PHP script? - Yes. See the example script desktop.cgi for ideas. It is in the source - tree in the directory x11vnc/misc. It serves x11vnc's SSL enabled Java - Applet to the web browser with the correct connection information for - the user's virtual desktop (an Xvfb session via -create; be sure to - add the Xvfb package.) HTTPS/SSL enabled Apache should be used to - serve the script to avoid unix and vnc passwords from being sent in - cleartext and sniffed. - - By default it uses a separate VNC port for each user desktop (either - by autoprobing in a range of ports or using a port based on the userid - number.) The web server's firewall must allow incoming connections to - these ports. - - It is somewhat difficult to do all of this with x11vnc listening on a - single port, however there is also a 'fixed port' scheme described in - the script based on -loopbg that works fairly well (but more - experience is needed to see what problems contention for the same port - causes; however at worst one user may need to re-login.) - - There is also an optional 'port redirection' mode for desktop.cgi that - allows redirection to other machines inside the firewall already - running SSL enabled VNC servers. This provides much of the - functionality as the SSL Portal and is easier to set up. - - - Q-68: Can I use x11vnc as a replacement for Xvnc? (i.e. not for a real - display, but for a virtual one I keep around.) - - You can, but you would not be doing this for performance reasons (for - virtual X sessions via VNC, Xvnc should give the fastest response.) - You may want to do this because Xvnc is buggy and crashes, does not - support an X server extension you desire, or you want to take - advantage of one of x11vnc's unending number of options and features. - - One way to achieve this is to have a Xvfb(1) virtual framebuffer X - server running in the background and have x11vnc attached to it. - Another method, faster and more accurate, is to use the "dummy" Device - Driver in XFree86/Xorg (see below.) - - For these virtual sessions you will need to install the Xvfb program - (e.g. apt-get install xvfb) or our Xdummy program (see below.) - - In either case, one can view this desktop both remotely and also - locally using vncviewer. Make sure vncviewer's "-encodings raw" is in - effect for local viewing (compression seems to slow things down - locally.) For local viewing you set up a "bare" window manager that - just starts up vncviewer and nothing else (See how below.) - - Here is one way to start up Xvfb: - xinit -- /usr/bin/Xvfb :1 -cc 4 -screen 0 1024x768x16 - - This starts up a 16bpp virtual display. To export it via VNC use - x11vnc -display :1 ... - - Then have the remote vncviewer attach to x11vnc's VNC display (e.g. :0 - which is port 5900.) - - The "-cc 4" Xvfb option is to force it to use a TrueColor visual - instead of DirectColor (this works around a recent bug in the Xorg - Xvfb server.) - - One good thing about Xvfb is that the virtual framebuffer exists in - main memory (rather than in the video hardware), and so x11vnc can - "screen scrape" it very efficiently (more than, say, 100X faster than - normal video hardware.) - - Update Nov/2006: See the FINDCREATEDISPLAY discussion of the "-display - WAIT:cmd=FINDDISPLAY" option where virtual (Xvfb or Xdummy, or even - real ones by changing an option) X servers are started automatically - for new users connecting. This provides a "desktop service" for the - machine. You either get your real X session or your virtual - (Xvfb/Xdummy) one whenever you connect to the machine (inetd(8) is a - nice way to provide this service.) The -find, -create, -svc, and - -xdmsvc aliases can also come in handy here. - - There are some annoyances WRT Xvfb however. The default keyboard - mapping seems to be very poor. One should run x11vnc with -add_keysyms - option to have keysyms added automatically. Also, to add the Shift_R - and Control_R modifiers something like this is needed: -#!/bin/sh -xmodmap -e "keycode any = Shift_R" -xmodmap -e "add Shift = Shift_L Shift_R" -xmodmap -e "keycode any = Control_R" -xmodmap -e "add Control = Control_L Control_R" -xmodmap -e "keycode any = Alt_L" -xmodmap -e "keycode any = Alt_R" -xmodmap -e "keycode any = Meta_L" -xmodmap -e "add Mod1 = Alt_L Alt_R Meta_L" - - (note: these are applied automatically in the FINDCREATEDISPLAY mode - of x11vnc.) Perhaps the Xvfb options -xkbdb or -xkbmap could be used - to get a better default keyboard mapping... - - Dummy Driver: A user points out a faster and more accurate method is - to use the "dummy" Device Driver of XFree86/Xorg instead of Xvfb. He - uses this to create a persistent and resizable desktop accessible from - anywhere. In the Device Section of the config file set Driver "dummy". - You may also need to set VideoRam NNN to be large enough to hold the - framebuffer. The framebuffer is kept in main memory like Xvfb except - that the server code is closely correlated with the real XFree86/Xorg - Xserver unlike Xvfb. - - The main drawback to this method (besides requiring extra - configuration and possibly root permission) is that it also does the - Linux Virtual Console/Terminal (VC/VT) switching even though it does - not need to (since it doesn't use a real framebuffer.) There are some - "dual headed" (actually multi-headed/multi-user) patches to the X - server that turn off the VT usage in the X server. Update: As of - Jul/2005 we have an LD_PRELOAD script Xdummy that allows you to use a - stock (i.e. unpatched) Xorg or XFree86 server with the "dummy" driver - and not have any VT switching problems! An advantage of Xdummy over - Xvfb is that Xdummy supports RANDR dynamic screen resizing. - - The standard way to start the "dummy" driver would be: -startx -- :1 -config /etc/X11/xorg.conf.dummy - - where the file /etc/X11/xorg.conf.dummy has its Device Section - modified as described above. To use the LD_PRELOAD wrapper script: -startx -- /path/to/Xdummy :1 - - An xdm(1) example is also provided. - - In general, one can use these sorts of schemes to use x11vnc to export - other virtual X sessions, say Xnest or even Xvnc itself (useful for - testing x11vnc.) - - Local access (VNC Server and VNC Viewer on the same machine): You use - a VNC viewer to access the display remotely; to access your virtual X - display locally (i.e. while sitting at the same machine it is running - on) one can perhaps have something like this in their $HOME/.xinitrc -#!/bin/sh -x11vnc -display :5 -rfbport 5905 -bg -vncviewer -geometry +0+0 -encodings raw -passwd $HOME/.vnc/passwd localhost:5 - - The display numbers (VNC and X) will likely be different (you could - also try -find), and you may not need the -passwd. Recent RealVNC - viewers might be this: -#!/bin/sh -x11vnc -display :5 -rfbport 5905 -bg -vncviewer -FullScreen -PreferredEncoding raw -passwd $HOME/.vnc/passwd localhos -t:5 - - This way a bare X server is run with no window manager or desktop; it - simply runs only the VNC Viewer on the real X server. The Viewer then - draws the virtual X session on to the real one. On your system it - might not be $HOME/.xinitrc, but rather .xsession, .Xclients, or - something else. You will need to figure out what it is for your system - and configuration. - - - XDM/GDM/KDM One-Shot X sessions: For the general replacement of Xvnc - by Xvfb+x11vnc, one user describes a similar setup he created where - the X sessions are one-shot's (destroyed after the vncviewer - disconnects) and it uses the XDM/GDM/KDM login greeter here. - - - Q-69: How can I use x11vnc on "headless" machines? Why might I want - to? - - An interesting application of x11vnc is to let it export displays of - "headless" machines. For example, you may have some lab or server - machines with no keyboard, mouse, or monitor, but each one still has a - video card. One can use x11vnc to provide a simple "desktop service" - from these server machines. - - An X server can be started on the headless machine (sometimes this - requires configuring the X server to not fail if it cannot detect a - keyboard or mouse, see the next paragraph.) Then you can export that X - display via x11vnc (e.g. see this FAQ) and access it from anywhere on - the network via a VNC viewer. - - Some tips on getting X servers to start on machines without keyboard - or mouse: For XFree86/Xorg the Option "AllowMouseOpenFail" "true" - "ServerFlags" config file option is useful. On Solaris Xsun the - +nkeyboard and +nmouse options are useful (put them in the server - command line args in /etc/dt/config/Xservers.) There are patches - available for Xsun at lease back to Solaris 8 that support this. See - Xserver(1) for more info. - - Although this usage may sound strange it can be quite useful for a GUI - (or other) testing or QA setups: the engineers do not need to walk to - lab machines running different hardware, OS's, versions, etc (or have - many different machines in their office.) They just connect to the - various test machines over the network via VNC. The advantage to - testing this way instead of using Xvnc or even Xvfb is that the test - is done using the real X server, fonts, video hardware, etc. that will - be used in the field. - - One can imagine a single server machine crammed with as many video - cards as it can hold to provide multiple simultaneous access or - testing on different kinds of video hardware. - - See also the FINDCREATEDISPLAY discussion of the "-display - WAIT:cmd=FINDDISPLAY" option where virtual Xvfb or Xdummy, or real X - servers are started automatically for new users connecting. The -find, - -create, -svc, and -xdmsvc aliases can also come in handy here. - - [Resource Usage and Performance] - - Q-70: I have lots of memory, but why does x11vnc fail with shmget: - No space left on device or Minor opcode of failed request: 1 - (X_ShmAttach)? - - It is not a matter of free memory, but rather free shared memory (shm) - slots, also known as shm segments. This often occurs on a public - Solaris machine using the default of only 100 slots. You (or the owner - or root) can clean them out with ipcrm(1). x11vnc tries hard to - release its slots, but it, and other programs, are not always able to - (e.g. if kill -9'd.) - - Sometimes x11vnc will notice the problem with shm segments and tries - to get by with fewer, only giving a warning like this: - 19/03/2004 10:10:58 shmat(tile_row) failed. - shmat: Too many open files - 19/03/2004 10:10:58 error creating tile-row shm for len=4 - 19/03/2004 10:10:58 reverting to single_copytile mode - - Here is a shell script shm_clear to list and prompt for removal of - your unattached shm segments (attached ones are skipped.) I use it - while debugging x11vnc (I use "shm_clear -y" to assume "yes" for each - prompt.) If x11vnc is regularly not cleaning up its shm segments, - please contact me so we can work to improve the situation. - - Longer term, on Solaris you can put something like this in - /etc/system: - set shmsys:shminfo_shmmax = 0x2000000 - set shmsys:shminfo_shmmni = 0x1000 - - to sweep the problem under the rug (4096 slots.) On Linux, examine - /proc/sys/kernel/shmmni; you can modify the value by writing to that - file. - - Things are even more tight on Solaris 8 and earlier, there is a - default maximum number of shm segments per process of 6. The error is - the X server (not x11vnc) being unable to attach to the segments, and - looks something like this: - 30/04/2004 14:04:26 Got connection from client 192.168.1.23 - 30/04/2004 14:04:26 other clients: - X Error of failed request: BadAccess (attempt to access private resource den -ied) - Major opcode of failed request: 131 (MIT-SHM) - Minor opcode of failed request: 1 (X_ShmAttach) - Serial number of failed request: 14 - Current serial number in output stream: 17 - - This tight limit on Solaris 8 can be increased via: - set shmsys:shminfo_shmseg = 100 - - in /etc/system. See the next paragraph for more workarounds. - - To minimize the number of shm segments used by x11vnc try using the - -onetile option (corresponds to only 3 shm segments used, and adding - -fs 1.0 knocks it down to 2.) If you are having much trouble with shm - segments, consider disabling shm completely via the -noshm option. - Performance will be somewhat degraded but when done over local machine - sockets it should be acceptable (see an earlier question discussing - -noshm.) - - - Q-71: How can I make x11vnc use less system resources? - - The -nap (now on by default; use -nonap to disable) and "-wait n" - (where n is the sleep between polls in milliseconds, the default is 30 - or so) option are good places to start. In addition, something like - "-sb 15" will cause x11vnc to go into a deep-sleep mode after 15 - seconds of no activity (instead of the default 60.) - - Reducing the X server bits per pixel depth (e.g. to 16bpp or even - 8bpp) will further decrease memory I/O and network I/O. The ShadowFB X - server setting will make x11vnc's screen polling less severe. Using - the -onetile option will use less memory and use fewer shared memory - slots (add -fs 1.0 for one less slot.) - - - Q-72: How can I make x11vnc use MORE system resources? - - You can try -threads (note this mode can be unstable and/or crash; and - as of May/2008 is strongly discouraged, see the option description) or - dial down the wait time (e.g. -wait 1) and possibly dial down -defer - as well. Note that if you try to increase the "frame rate" too much - you can bog down the server end with the extra work it needs to do - compressing the framebuffer data, etc. - - That said, it is possible to "stream" video via x11vnc if the video - window is small enough. E.g. a 256x192 xawtv TV capture window (using - the x11vnc -id option) can be streamed over a LAN or wireless at a - reasonable frame rate. If the graphics card's framebuffer read rate is - faster than normal then the video window size and frame rate can be - much higher. The use of TurboVNC and/or TurboJPEG can make the frame - rate somewhat higher still (but most of this hinges on the graphics - card's read rate.) - - - Q-73: I use x11vnc over a slow link with high latency (e.g. dialup - modem or broadband), is there anything I can do to speed things up? - - Some things you might want to experiment with (many of which will help - performance on faster links as well): - - X server/session parameters: - * Configure the X server bits per pixel to be 16bpp or even 8bpp. - (reduces amount of data needed to be polled, compressed, and sent) - * Use a smaller desktop size (e.g. 1024x768 instead of 1280x1024) - * Make sure the desktop background is a solid color (the background - is resent every time it is re-exposed.) Consider using the -solid - [color] option to try to do this automatically. - * Configure your window manager or desktop "theme" to not use fancy - images, shading, and gradients for the window decorations, etc. - Disable window animations, etc. Maybe your desktop has a "low - bandwidth" theme you can easily switch into and out of. Also in - Firefox disable eye-candy, e.g.: Edit -> Preferences -> Advanced - -> Use Smooth Scrolling (deselect it.) - * Avoid small scrolls of large windows using the Arrow keys or - scrollbar. Try to use PageUp/PageDown instead. (not so much of a - problem in x11vnc 0.7.2 if -scrollcopyrect is active and detecting - scrolls for the application.) - * If the -wireframe option is not available (earlier than x11vnc - 0.7.2 or you have disabled it via -nowireframe) then Disable - Opaque Moves and Resizes in the window manager/desktop. - * However if -wireframe is active (on by default in x11vnc 0.7.2) - then you should Enable Opaque Moves and Resizes in the window - manager! This seems counter-intuitive, but because x11vnc detects - the move/resize events early there is a huge speedup over a slow - link when Opaque Moves and Resizes are enabled. (e.g. CopyRect - encoding will be used.) - * Turn off Anti-aliased fonts on your system, web browser, terminal - windows, etc. AA fonts do not compress as well as traditional - fonts (sometimes 10X less.) - * On Firefox/Mozilla (and anything else) turn off "Smooth Scroll" - animations. In Firefox put in the URL "about:config" and set - general.smoothScroll to false. - * On Xorg/XFree86 turn on the Shadow Framebuffer to speed up - reading. (Option "ShadowFB" "true" in the Device section of - /etc/X11/XF86Config) This disables 2D acceleration on the physical - display and so may not be worth it (if you play games, etc), but - could be of use in some situations. Note: If the network link is - very slow, this speedup may not be noticed. - - VNC viewer parameters: - * Use a TightVNC enabled viewer! (Actually, RealVNC 4.x viewer with - ZRLE encoding is not too bad either; some claim it is faster.) - * Make sure the tight (or zrle) encoding is being used (look at - vncviewer and x11vnc outputs) - * Request 8 bits per pixel using -bgr233 (up to 4X speedup over - depth 24 TrueColor (32bpp), but colors will be off) - * RealVNC 4.x viewer has some extremely low color modes (only 64 and - even 8 colors.) SSVNC does too. The colors are poor, but it is - usually noticeably faster than bgr233 (256 colors.) - * Try increasing the TightVNC -compresslevel (compresses more on - server side before sending, but uses more CPU) - * Try reducing the TightVNC -quality (increases JPEG compression, - but is lossy with painting artifacts) - * Try other VNC encodings via -encodings (tight may be the fastest, - but you should compare it to zrle and maybe some of the others) - * On the machine where vncviewer is run, make sure Backing Store is - enabled (Xorg/XFree86 disables it by default causing re-exposures - of vncviewer to be very slow) Option "backingstore" in config - file. - - x11vnc parameters: - * Make sure the -wireframe option is active (it should be on by - default) and you have Opaque Moves/Resizes Enabled in the window - manager. - * Make sure the -scrollcopyrect option is active (it should be on by - default.) This detects scrolls in many (but not all) applications - an applies the CopyRect encoding for a big speedup. - * Enforce a solid background when VNC viewers are connected via - -solid - * Try x11vnc's client-side caching client-side caching scheme: - -ncache - * Specify -speeds modem to force the wireframe and scrollcopyrect - heuristic parameters (and any future ones) to those of a dialup - modem connection (or supply the rd,bw,lat numerical values that - characterize your link.) - * If wireframe and scrollcopyrect aren't working, try using the more - drastic -nodragging (no screen updates when dragging mouse, but - sometimes you miss visual feedback) - * Set -fs 1.0 (disables fullscreen updates) - * Try increasing -wait or -defer (reduces the maximum "frame rate", - but won't help much for large screen changes) - * Try the -progressive pixelheight mode with the block pixelheight - 100 or so (delays sending vertical blocks since they may change - while viewer is receiving earlier ones) - * If you just want to watch one (simple) window use -id or -appshare - (cuts down extraneous polling and updates, but can be buggy or - insufficient) - * Set -nosel (disables all clipboard selection exchange) - * Use -nocursor and -nocursorpos (repainting the remote cursor - position and shape takes resources and round trips) - * On very slow links (e.g. <= 28.8) you may need to increase the - -readtimeout n setting if it sometimes takes more than 20sec to - paint the full screen, etc. - * Do not use -fixscreen to automatically refresh the whole screen, - tap three Alt_L's then the screen has painting errors (rare - problem.) - - - Example for the KDE desktop: - - Launch the "KDE Control Center" utility. Sometimes this is called - "Personal Settings". - - Select "Desktop". - - Then Select "Window Behavior". In the "Moving" Tab set these: - * YES - Display content in moving windows - * YES - Display content in resizing windows - * NO - Display window geometry when moving or resizing - * NO - Animate minimize and restore - - In the "Translucency" Tab set: - * NO - Use translucency/shadows - - Next hit "Back" and then select "Panels". - - In the "Appearance" Tab set: - * NO - Enable icon mouseover effects - * NO - Enable transparency - - Now go all the way back up to the top and Select "Appearance & - Themes". - - Select "Background" and set: - * YES - No picture - * Colors: Single Color - - Select "Fonts" and disable anti-aliased fonts if you are bold enough. - - Select "Launch Feedback" and set: - * Busy Cursor: No Busy Cursor - * NO - Enable taskbar notification - - Select "Screen Saver" and set: - * Screen Saver: Blank Screen - - Select "Style" and in the "Effects" Tab set: - * NO - Enable GUI effects - - - Example for the GNOME desktop: - * TBD. - - - Q-74: Does x11vnc support the X DAMAGE Xserver extension to find - modified regions of the screen quickly and efficiently? - - Yes, as of Mar/2005 x11vnc will use the X DAMAGE extension by default - if it is available on the display. This requires libXdamage to be - available in the build environment as well (recent Linux distros and - Solaris 10 have it.) - - The DAMAGE extension enables the X server to report changed regions of - the screen back to x11vnc. So x11vnc doesn't have to guess where the - changes are (by polling every pixel of the entire screen every 2-4 - seconds.) The use of X DAMAGE dramatically reduces the load when the - screen is not changing very much (i.e. most of the time.) It also - noticeably improves updates, especially for very small changed areas - (e.g. clock ticking, cursor flashing, typing, etc.) - - Note that the DAMAGE extension does not speed up the actual reading of - pixels from the video card framebuffer memory, by, say, mirroring them - in main memory. So reading the fb is still painfully slow (e.g. - 5MB/sec), and so even using X DAMAGE when large changes occur on the - screen the bulk of the time is still spent retrieving them. Not ideal, - but use of the ShadowFB XFree86/Xorg option speeds up the reading - considerably (at the cost of h/w acceleration.) - - Unfortunately the current Xorg DAMAGE extension implementation can at - times be overly conservative and report very large rectangles as - "damaged" even though only a small portion of the pixels have actually - been modified. This behavior is often the fault of the window manager - (e.g. it redraws the entire, unseen, frame window underneath the - application window when it gains focus), or the application itself - (e.g. does large, unnecessary repaints.) - - To work around this deficiency, x11vnc currently only trusts small - DAMAGE rectangles to contain real damage. The larger rectangles are - only used as hints to focus the traditional scanline polling (i.e. if - a scanline doesn't intersect a recent DAMAGE rectangle, the scan is - skipped.) You can use the "-xd_area A" option to adjust the size of - the trusted DAMAGE rectangles. The default is 20000 pixels (e.g. a - 140x140 square, etc.) Use "-xd_area 0" to disable the cutoff and trust - all DAMAGE rectangles. - - The option "-xd_mem f" may also be of use in tuning the algorithm. To - disable using DAMAGE entirely use "-noxdamage". - - - Q-75: My OpenGL application shows no screen updates unless I supply - the -noxdamage option to x11vnc. - One user reports in his environment (MythTV using the NVIDIA OpenGL - drivers) he gets no updates after the initial screen is drawn unless - he uses the "-noxdamage" option. - - This seems to be a bug in the X DAMAGE implementation of that driver. - You may have to use -noxdamage as well. A way to autodetect this will - be tried, probably the best it will do is automatically stop using X - DAMAGE. - - A developer for MiniMyth reports that the 'alphapulse' tag of the - theme G.A.N.T. can also cause problems, and should be avoided when - using VNC. - - Update: see this FAQ too. - - - Q-76: When I drag windows around with the mouse or scroll up and down - things really bog down (unless I do the drag in a single, quick - motion.) Is there anything to do to improve things? - - This problem is primarily due to slow hardware read rates from video - cards: as you scroll or move a large window around the screen changes - are much too rapid for x11vnc to keep up them (it can usually only - read the video card at about 5-10 MB/sec, so it can take a good - fraction of a second to read the changes induce from moving a large - window, if this to be done a number of times in succession the window - or scroll appears to "lurch" forward.) See the description in the - -pointer_mode option for more info. The next bottleneck is compressing - all of these changes and sending them out to connected viewers, - however the VNC protocol is pretty much self-adapting with respect to - that (updates are only packaged and sent when viewers ask for them.) - - As of Jan/2004 there are some improvements to libvncserver. The - default should now be much better than before and dragging small - windows around should no longer be a huge pain. If for some reason - these changes make matters worse, you can go back to the old way via - the "-pointer_mode 1" option. - - Also added was the -nodragging option that disables all screen updates - while dragging with the mouse (i.e. mouse motion with a button held - down.) This gives the snappiest response, but might be undesired in - some circumstances when you want to see the visual feedback while - dragging (e.g. menu traversal or text selection.) - - As of Dec/2004 the -pointer_mode n option was introduced. n=1 is the - original mode, n=2 an improvement, etc.. See the -pointer_mode n help - for more info. - - Also, in some circumstances the -threads option can improve response - considerably. Be forewarned that if more than one vncviewer is - connected at the same time then libvncserver may not be thread safe - (try to get the viewers to use different VNC encodings, e.g. tight and - ZRLE.) This option can be unstable and so as of Feb/2008 it is - disabled by default. Set env. X11VNC_THREADED=1 to re-enable. - - As of Apr/2005 two new options (see the wireframe FAQ and - scrollcopyrect FAQ below) provide schemes to sweep this problem under - the rug for window moves or resizes and for some (but not all) window - scrolls. These are the preferred way of avoiding the "lurching" - problem, contact me if they are not working. Note on SuSE and some - other distros the RECORD X extension used by scrollcopyrect is not - enabled by default, turn it on in xorg.conf: -Section "Module" - ... - Load "record" - ... -EndSection - - - Q-77: Why not do something like wireframe animations to avoid the - windows "lurching" when being moved or resized? - - Nice idea for a hack! As of Apr/2005 x11vnc by default will apply - heuristics to try to guess if a window is being (opaquely) moved or - resized. If such a change is detected framebuffer polling and updates - will be suspended and only an animated "wireframe" (a rectangle - outline drawn where the moved/resized window would be) is shown. When - the window move/resize stops, it returns to normal processing: you - should only see the window appear in the new position. This spares you - from interacting with a "lurching" window between all of the - intermediate steps. BTW the lurching is due to slow video card read - rates (see here too.) A displacement, even a small one, of a large - window requires a non-negligible amount of time, a good fraction of a - second, to read in from the hardware framebuffer. - - Note that Opaque Moves/Resizes must be Enabled by your window manager - for -wireframe to do any good. - - The mode is currently on by default because most people are afflicted - with the problem. It can be disabled with the -nowireframe option (aka - -nowf.) Why might one want to turn off the wireframing? Since x11vnc - is merely guessing when windows are being moved/resized, it may guess - poorly for your window-manager or desktop, or even for the way you - move the pointer. If your window-manager or desktop already does its - own wireframing then this mode is a waste of time and could do the - wrong thing occasionally. There may be other reasons the new mode - feels unnatural. If you have very expensive video hardware (SGI, well - now even proprietary Xorg drivers are fast at reading) or are using an - in-RAM video framebuffer (SunRay, ShadowFB, Xvfb), the read rate from - that framebuffer may be very fast (100's of MB/sec) and so you don't - really see much lurching (at least over a fast LAN): opaque moves look - smooth in x11vnc. Note: ShadowFB is often turned on when you are using - the vesafb or fbdev XFree86 video driver instead of a native one so - you might be using it already and not know. - - The heuristics used to guess window motion or resizing are simple, but - are not fool proof: x11vnc is sometimes tricked and so you'll - occasionally see the lurching opaque move and rarely something even - worse. - - First it assumes that the move/resize will occur with a mouse button - pressed, held down and dragged (of course this is only mostly true.) - Next it will only consider a window for wireframing if the mouse - pointer is initially "close enough" to the edges of the window frame, - e.g. you have grabbed the title bar or a resizer edge (this - requirement can be disabled and it also not applied if a modifier key, - e.g. Alt, is pressed.) If these are true, it will wait an amount of - time to see if the window starts moving or resizing. If it does, it - starts drawing the wireframe "outline" of where the window would be. - When the mouse button is released, or a timeout occurs, it goes back - to the standard mode to allow the actual framebuffer changes to - propagate to the viewers. - - These parameters can be tweaked: - * Color/Shade of the wireframe. - * Linewidth of the outline frame. - * Cutoff size of windows to not apply wireframing to. - * Cutoffs for closeness to Top, Bottom, Left, and Right edges of - window. - * Modifier keys to enable interior window grabbing. - * Maximum time to wait for dragging pointer events. - * Maximum time to wait for the window to start moving/resizing. - * Maximum time to show a wireframe animation. - * Minimum time between sending wireframe outlines. - - See the "-wireframe tweaks" option for more details. On a slow link, - e.g. dialup modem, the parameters may be automatically adjusted for - better response. - - - CopyRect encoding: In addition to the above there is the - "-wirecopyrect mode" option. It is also on by default. This instructs - x11vnc to not only show the wireframe animation, but to also instruct - all connected VNC viewers to locally translate the window image data - from the original position to the new position on the screen when the - animation is done. This speedup is the VNC CopyRect encoding: the - framebuffer update doesn't need to send the actual new image data. - This is nice in general, and very convenient over a slow link, but - since it is based on heuristics you may need to disable it with the - -nowirecopyrect option (aka -nowcr) if it works incorrectly or - unnaturally for you. - - The -wirecopyrect modes are: "never" (same as -nowirecopyrect); "top", - only apply the CopyRect if the window is appears to be on the top of - the window stack and is not obstructed by other windows; and "always" - to always try to apply the CopyRect (obstructed regions are usually - clipped off and not translated.) - - Note that some desktops (KDE and xfce) appear to mess with the window - stacking in ways that are not yet clear. In these cases x11vnc works - around the problem by applying the CopyRect even if obscuring windows' - data is translated! Use -nowirecopyrect if this yields undesirable - effects for your desktop. - - Also, the CopyRect encoding may give incorrect results under -scale - (depending on the scale factor the CopyRect operation is often only - approximate: the correctly scaled framebuffer will be slightly - different from the translated one.) x11vnc will try to push a - "cleanup" update after the CopyRect if -scale is in effect. Use - -nowirecopyrect if this or other painting errors are unacceptable. - - - Q-78: Can x11vnc try to apply heuristics to detect when a window is - scrolling its contents and use the CopyRect encoding for a speedup? - - Another nice idea for a hack! As of May/2005 x11vnc will by default - apply heuristics to try to detect if the window that has the input - focus is scrolling its contents (but only when x11vnc is feeding user - input, keystroke or pointer, to the X server.) So, when detected, - scrolls induced by dragging on a scrollbar or by typing (e.g. Up or - Down arrows, hitting Return in a terminal window, etc), will show up - much more quickly than via the standard x11vnc screen polling update - mechanism. - - There will be a speedup for both slow and fast links to viewers. For - slow links the speedup is mostly due to the CopyRect encoding not - requiring the image data to be transmitted over the network. For fast - links the speedup is primarily due to x11vnc not having to read the - scrolled framebuffer data from the X server (recall that reading from - the hardware framebuffer is slow.) - - To do this x11vnc uses the RECORD X extension to snoop the X11 - protocol between the X client with the focus window and the X server. - This extension is usually present on most X servers (but SuSE disables - it for some reason.) On XFree86/Xorg it can be enabled via Load - "record" in the Module section of the config file if it isn't already: -Section "Module" - ... - Load "record" - ... -EndSection - - Currently the RECORD extension is used as little as possible so as to - not slow down regular use. Only simple heuristics are applied to - detect XCopyArea and XConfigureWindow calls from the application. - These catch a lot of scrolls, e.g. in mozilla/firefox and in terminal - windows like gnome-terminal and xterm. Unfortunately the toolkits KDE - applications use make scroll detection less effective (only rarely are - they detected: i.e. Konqueror and Konsole don't work.) An interesting - project, that may be the direction x11vnc takes, is to record all of - the X11 protocol from all clients and try to "tee" the stream into a - modified Xvfb watching for CopyRect and other VNC speedups. A - potential issue is the RECORD stream is delayed from actual view on - the X server display: if one falls too far behind it could become a - mess... - - The initial implementation of -scrollcopyrect option is useful in that - it detects many scrolls and thus gives a much nicer working - environment (especially when combined with the -wireframe - -wirecopyrect options, which are also on by default; and if you are - willing to enable the ShadowFB things are very fast.) The fact that - there aren't long delays or lurches during scrolling is the primary - improvement. - - But there are some drawbacks: - * Not all scrolls are detected. Some apps scroll windows in ways - that cannot currently be detected, and other times x11vnc "misses" - the scroll due to timeouts, etc. Sometimes it is more distracting - that a speedup occasionally doesn't work as opposed to being - consistently slow! - * For rapid scrolling (i.e. sequence of many scrolls over a short - period) there can be painting errors (tearing, bunching up, etc.) - during the scroll. These will repair themselves after the scroll - is over, but when they are severe it can be distracting. Try to - think of the approximate window contents as a quicker and more - useful "animation" compared to the slower polling scheme... - * Scrolling inside shells in terminal windows (gnome-terminal, - xterm), can lead to odd painting errors. This is because x11vnc - did not have time to detect a screen change just before the scroll - (most common is the terminal undraws the block cursor before - scrolling the text up: in the viewer you temporarily see multiple - block cursors.) Another issue is with things like more(1): scroll - detection for 5-6 lines happens nicely, but then it can't keep up - and so there is a long pause for the standard polling method to - deliver the remaining updates. - * More rarely sometimes painting errors are not repaired after the - scroll is over. This may be a bug in x11vnc or libvncserver, or it - may be an inescapable fact of the CopyRect encoding and the delay - between RECORD callbacks and what is actually on the X display. - One can tap the Alt_L key (Left "Alt" key) 3 times in a row to - signal x11vnc to refresh the screen to all viewers. Your - VNC-viewer may have its own screen refresh hot-key or button. See - also: -fixscreen - * Some applications, notably OpenOffice, do XCopyArea scrolls in - weird ways that assume ancestor window clipping is taking place. - See the -scr_skip option for ways to tweak this on a - per-application basis. - * Selecting text while dragging the mouse may be slower, especially - if the Button-down event happens near the window's edge. This is - because the scrollcopyrect scheme is watching for scrolls via - RECORD and has to wait for a timeout to occur before it does the - update. - * For reasons not yet understood the RECORD extension can stop - responding (and hence scrolls are missed.) As a workaround x11vnc - attempts to reset the RECORD connection every 60 seconds or so. - Another workaround is to type 4 Super_L (Left Super/Windows-Flag - key) in a row to reset RECORD. Work is in progress to try to fix - this bug. - * Sometimes you need to "retrain" x11vnc for a certain window - because it fails to detect scrolls in it. Sometimes clicking - inside the application window or selecting some text in it to - force the focus helps. - * When using the -scale option there will be a quick CopyRect - scroll, but it needs to be followed by a slower "cleanup" update. - This is because for a fixed finite screen resolution (e.g. 75 dpi) - scaling and copyrect-ing are not exactly independent. Scaling - involves a blending of nearby pixels and if you translate a pixel - the neighbor pixel weighting may be different. So you have to wait - a bit for the cleanup update to finish. On slow links x11vnc may - automatically decide to not detect scrolls when -scale is in - effect. In general it will also try to defer the cleanup update if - possible. - - If you find the -scrollcopyrect behavior too approximate or - distracting you can go back to the standard polling-only update method - with the -noscrollcopyrect (or -noscr for short.) If you find some - extremely bad and repeatable behavior for -scrollcopyrect please - report a bug. - - Alternatively, as with -wireframe, there are many tuning parameters to - try to improve the situation. You can also access these parameters - inside the gui under "Tuning". These parameters can be tweaked: - * The minimum pixel area of a rectangle to be watched for scrolls. - * A list if application names to skip scroll detection. - * Which keystrokes should trigger scroll detection. - * Which applications should have a "terminal" tweak applied to them. - * When repeating keys (e.g. Up arrow) should be discarded to - preserve a scroll. - * Cutoffs for closeness to Top, Bottom, Left, and Right edges of - window for mouse induced scrolls. - * Set timeout parameters for keystroke induced scrolls. - * Set timeout parameters for mouse pointer induced scrolls. - * Have the full screen be periodically refreshed to fix painting - errors. - - - Q-79: Can x11vnc do client-side caching of pixel data? I.e. so when - that pixel data is needed again it does not have to be retransmitted - over the network. - - As of Dec/2006 in the 0.9 development tarball there is an experimental - client-side caching implementation enabled by the "-ncache n" option. - In fact, during the test period it was on by default with n set to 10. - To disable it use "-noncache". - - It is a simple scheme where a (very large) lower portion of the - framebuffer (i.e. starting just below the user's actual desktop - display) is used for storing pixel data. CopyRect; a fast, essentially - local viewer-side VNC encoding; is used to swap the pixel data in and - out of the actual display area. It gives an excellent speedup for - iconifying/deiconifying and moving windows and re-posting of menus - (often it doesn't feel like VNC at all: there is no delay waiting for - the pixel data to fill in.) - - This scheme is nice because it does all of this within the existing - VNC protocol, and so it works with all VNC viewers. - - A challenge to doing more sophisticated (e.g. compressed and/or - shared) client-side caching is that one needs to extend the VNC - protocol, modify a viewer and then also convince users to adopt your - modified VNC Viewer (or get the new features to be folded into the - main VNC viewers, patches accepted, etc... likely takes many years - before they might be deployed in the field.) So it is convenient that - the "-ncache n" works with any unaltered VNC viewer. - - A drawback of the "-ncache n" method is that in the VNC Viewer you can - scroll down and actually see the cached pixel data. So it looks like - there is a bug: you can scroll down in your viewer and see a strange - "history" of windows on your desktop. This is working as intended. One - will need to try to adjust the size of his VNC Viewer window so the - cache area cannot be seen. SSVNC (see below) can do this - automatically. - - At some point LibVNCServer may implement a "rfbFBCrop" pseudoencoding - that viewers can use to learn which portion of the framebuffer to - actually show to the users (with the hidden part used for caching, or - perhaps something else, maybe double buffering or other offscreen - rendering...) - - The Enhanced TightVNC Viewer (SSVNC) Unix viewer has a nice -ycrop - option to help hide the pixel cache area from view. It will turn on - automatically if the framebuffer appears to be very tall (height more - than twice the width), or you can supply the actual value for the - height. If the screen is resized by scaling, etc, the ycrop value is - scaled as well. In fullscreen mode you cannot scroll past the end of - the actual screen, and in non-fullscreen mode the window manager frame - is adjusted to fit the actual display (so you don't see the pixel - cache region) and the scrollbars are very thin to avoid distraction - and trouble fitting inside your display. Use the "-sbwidth n" viewer - option to make the scrollbars thicker if you like. - - Another drawback of the scheme is that it is VERY memory intensive, - the n in "-ncache n" is the factor of increase over the base - framebuffer size to use for caching. It is an even integer and should - be fairly large, 6-12, to achieve good response. This usually requires - about 50-100MB of additional RAM on both the client and server sides. - For example with n=6 a 1280x1024 display will use a framebuffer that - is 1280x7168: everything below row 1024 is the pixel buffer cache. If - you are running on low memory machines or memory is tight because of - other running applications you should not use -ncache. - - The reason for so much memory is because the pixel data is not - compressed and so the whole window to be saved must be stored - "offscreen". E.g. for a large web browser window this can be nearly 1 - million pixels, and that is only for a single window! One typically - wants to cycle between 5-10 large active windows. Also because both - backing-store (the window's actual contents) and save-unders (the - pixels covered up by the window) are cached offscreen that introduces - an additional factor of 2 in memory use. - - However, even in the smallest usage mode with n equal 2 and - -ncache_no_rootpixmap set (this requires only 2X additional - framebuffer memory) there is still a noticable improvement for many - activities, although it is not as dramatic as with, say n equal 12 and - rootpixmap (desktop background) caching enabled. - - The large memory consumption of the current implementation can be - thought of as a tradeoff to providing caching and being compatible - with all VNC viewers and also ease of implementing. Hopefully it can - be tuned to use less, or the VNC community will extend the protocol to - allow caching and replaying of compressed blobs of data. - - Another option to experiment with is "-ncache_cr". By specifying it, - x11vnc will try to do smooth opaque window moves instead of its - wireframe. This can give a very nice effect (note: on Unix the realvnc - viewer seems to be smoother than the tightvnc viewer), but can lead to - some painting problems, and can be jerky in some circumstances. - - Surprisingly, for very slow connections, e.g. modem, the -ncache_cr - option can actually improve window drags. This is probably because no - pixel data (only CopyRect instructions) are sent when dragging a - window. Normally, the wireframe must be sent and this involves - compressing and sending the lines that give rise to the moving box - effect (note that real framebuffer data is sent to "erase" the white - lines of the box.) - - If you experience painting errors you can can tap the Alt_L key (Left - "Alt" key) 3 times in a row to signal x11vnc to refresh the screen to - all viewers. You may also need to iconify and then deiconify any - damaged windows to correct their cache data as well. Note that if you - change color viewer depth (e.g. 8bpp to full color) dynamically that - will usually lead to the entire extended framebuffer being resent - which can take a long time over very slow links: it may be better to - reconnect and reset the format right after doing so. x11vnc will try - to detect the format change and clear (make completely black) the - cache region. - - Gotcha for older Unix VNC Viewers: The older Unix VNC viewers (e.g. - current TightVNC Unix Viewer) require X server backingstore to keep - off-viewer screen data local. If the viewer-side X server has - backingstore disabled (sadly, currently the default on Linux, etc), - then to get the offscreen pixels the viewer has to ask for a refresh - over the network, thereby defeating the caching. Use something like - this in your viewer-side /etc/X11/xorg.conf file (or otherwise get - your viewer-side system to do it) -Section "Device" - ... - Option "backingstore" - ... -EndSection - - No problems like this have been observed with Windows VNC Viewers: - they all seem to keep their entire framebuffer in local memory. - - Gotcha for KDE krdc VNC Viewer: One user found that KDE's krdc viewer - has some sort of hardwired limit on the maximum size of the - framebuffer (64MB?). It fails quickly saying "The connection to the - host has been interrupted." The workaround for his 1280x1024 - x11vnc-side display was to run with "-ncache 10", i.e. a smaller value - to be under the krdc threshold. - - Although this scheme is not as quick (nor as compressed) as - nx/nomachine, say, it does provide a good step in the direction of - improving VNC performance by client side caching. - - - Q-80: Does x11vnc support TurboVNC? - - As of Feb/2009 (development tarball) there is an experimental kludge - to let you build x11vnc using TurboVNC's modified TightVNC encoding. - TurboVNC is part of the VirtualGL project. It does two main things to - speed up the TightVNC encoding: - * It eliminates bottlenecks, overheads, wait-times in the TightVNC - encoding implementation and instead only worries about sending - very well (and quickly) compressed JPEG data. - * A fast proprietary JPEG implemention is used (Intel IPP on x86) - instead of the usual libjpeg implementation. TurboJPEG is an - interface library, libturbojpeg, provided by the project that - achieves this. - - TurboVNC works very well over LAN and evidently fast Broadband too. - When using it with x11vnc in such a situation you may want to dial - down the delays, e.g. "-wait 5" and "-defer 5" (or even a smaller - setting) to poll and pump things out more quickly. - - See the instructions in "x11vnc/misc/turbovnc/README" for how to build - x11vnc with TurboVNC support. You will also need to download the - TurboJPEG software. - - In brief, the steps look like this: - cd x11vnc-x.y.z/x11vnc/misc/turbovnc - ./apply_turbovnc - cd ../../.. - env LDFLAGS='-L/DIR -Xlinker --rpath=/DIR' ./configure - make AM_LDFLAGS='-lturbojpeg' - - where you replace "/DIR" with the directory containing libturbojpeg.so - you downloaded separately. If it works out well enough TurboVNC - support will be integrated into x11vnc and more of its tuning features - will be implemented. Support for TurboVNC in SSVNC viewer has been - added as an experiment as well. If you try either one, let us know how - it went. - - There also may be some Linux.i686 and Darwin.i386 x11vnc binaries with - TurboVNC support in the misc. bins directory. For other platforms you - will need to compile yourself. - - On relatively cheap and old hardware (Althon64 X2 5000+ / GeForce - 6200) x11vnc and SSVNC, both TurboVNC enabled, were able to sustain - 13.5 frames/sec (fps) and 15 Megapixels/sec using the VirtualGL - supplied OpenGL benchmark program glxspheres. VirtualGL on higher-end - hardware can sustain 20-30 fps with the glxspheres benchmark. - - Potential Slowdown: As we describe elsewhere, unless you use x11vnc - with an X server using, say, NVidia proprietary drivers (or a virtual - X server like Xvfb or Xdummy, or in ShadowFB mode), then the read rate - from the graphics card can be rather slow (e.g. 10 MB/sec) and becomes - the bottleneck when using x11vnc over fast networks. Note that all of - Xorg's drivers currently (2009) have slow read rates (only proprietary - drivers appear to have optimized reads.) - - So under these (more or less typical) conditions, the speed - improvement provided by TurboVNC may only be marginal. Look for this - output to see your read rate: - 28/02/2009 11:11:07 Autoprobing TCP port - 28/02/2009 11:11:07 Autoprobing selected port 5900 - 28/02/2009 11:11:08 fb read rate: 10 MB/sec - 28/02/2009 11:11:08 screen setup finished. - - A rate of 10 MB/sec means a 1280x1024x24 screen takes 0.5 seconds to - read in. TurboVNC compresses that to JPEG in a much shorter time. On - the other hand, an NVidia driver may have a read rate of 250 MB/sec - and so only takes 0.02 seconds to read the entire screen in. - - - - [Mouse Cursor Shapes] - - Q-81: Why isn't the mouse cursor shape (the little icon shape where - the mouse pointer is) correct as I move from window to window? - - On X servers supporting XFIXES or Solaris/IRIX Overlay extensions it - is possible for x11vnc to do this correctly. See a few paragraphs down - for the answer. - - Historically, the X11 mouse cursor shape (i.e. little picture: an - arrow, X, I-beam, resizer, etc) is one of the few WRITE-only objects - in X11. That is, an application can tell the X server what the cursor - shape should be when the pointer is in a given window, but a program - (like x11vnc) unfortunately cannot read this information. I believe - this is because the cursor shape is often downloaded to the graphics - hardware (video card), but I could be mistaken. - - A simple kludge is provided by the "-cursor X" option that changes the - cursor when the mouse is on the root background (or any window has the - same cursor as the root background.) Note that desktops like GNOME or - KDE often cover up the root background, so this won't work for those - cases. Also see the "-cursor some" option for additional kludges. - - Note that as of Aug/2004 on Solaris using the SUN_OVL overlay - extension and IRIX, x11vnc can show the correct mouse cursor when the - -overlay option is supplied. See this FAQ for more info. - - Also as of Dec/2004 XFIXES X extension support has been added to allow - exact extraction of the mouse cursor shape. XFIXES fixes the problem - of the cursor-shape being write-only: x11vnc can now query the X - server for the current shape and send it back to the connected - viewers. XFIXES is available on recent Linux Xorg based distros and - Solaris 10. - - The only XFIXES issue is the handling of alpha channel transparency in - cursors. If a cursor has any translucency then in general it must be - approximated to opaque RGB values for use in VNC. There are some - situations where the cursor transparency can also handled exactly: - when the VNC Viewer requires the cursor shape be drawn into the VNC - framebuffer or if you apply a patch to your VNC Viewer to extract - hidden alpha channel data under 32bpp. Details can be found here. - - - Q-82: When using XFIXES cursorshape mode, some of the cursors look - really bad with extra black borders around the cursor and other cruft. - How can I improve their appearance? - - This happens for cursors with transparency ("alpha channel"); regular - X cursors (bitmaps) should be correct. Unfortunately x11vnc 0.7 was - released with a very poor algorithm for approximating the - transparency, which led to the ugly black borders. - - The problem is as follows: XFIXES allows x11vnc to retrieve the - current X server cursor shape, including the alpha channel for - transparency. For traditional bitmap cursors the alpha value will be 0 - for completely transparent pixels and 255 for completely opaque - pixels; whereas for modern, eye-candy cursors an alpha value between 0 - and 255 means to blend in the background colors to that degree with - the cursor colors. The pixel color blending formula is something like - this: Red = Red_cursor * a + Red_background * (1 - a), (where here 0 - =< a =< 1), with similar for Green and Blue. The VNC protocol does not - currently support an alpha channel in cursors: it only supports - regular X bitmap cursors and Rich Cursors that have RGB (Red, Green, - Blue) color data, but no "A" = alpha data. So in general x11vnc has to - approximate a cursor with transparency to create a Rich Cursor. This - is easier said than done: some cursor themes have cursors with - complicated drop shadows and other forms of translucency. - - Anyway, for the x11vnc 0.7.1 release the algorithm for approximating - transparency is much improved and hopefully gives decent cursor shapes - for most cursor themes and you don't have to worry about it. - - In case it still looks bad for your cursor theme, there are (of - course!) some tunable parameters. The "-alphacut n" option lets you - set the threshold "n" (between 0 and 255): cursor pixels with alpha - values below n will be considered completely transparent while values - equal to or above n will be completely opaque. The default is 240. The - "-alphafrac f" option tries to correct individual cursors that did not - fare well with the default -alphacut value: if a cursor has less than - fraction f (between 0.0 and 1.0) of its pixels selected by the default - -alphacut, the threshold is lowered until f of its pixels are - selected. The default fraction is 0.33. - - Finally, there is an option -alpharemove that is useful for themes - where many cursors are light colored (e.g. "whiteglass".) XFIXES - returns the cursor data with the RGB values pre-multiplied by the - alpha value. If the white cursors look too grey, specify -alpharemove - to brighten them by having x11vnc divide out the alpha value. - - One user played with these parameters and reported back: - Of the cursor themes present on my system: - - gentoo and gentoo-blue: alphacut:192 - noalpharemove - - gentoo-silver: alphacut:127 and alpharemove - - whiteglass and redglass (presumably also handhelds, which is based - heavily on redglass) look fine with the apparent default of alphacut:255. - - - Q-83: In XFIXES mode, are there any hacks to handle cursor - transparency ("alpha channel") exactly? - - As of Jan/2005 libvncserver has been modified to allow an alpha - channel (i.e. RGBA data) for Rich Cursors. So x11vnc can now send the - alpha channel data to libvncserver. However, this data will only be - used for VNC clients that do not support the CursorShapeUpdates VNC - extension (or have disabled it.) It can be disabled for all clients - with the -nocursorshape x11vnc option. In this case the cursor is - drawn, correctly blended with the background, into the VNC framebuffer - before being sent out to the client. So the alpha blending is done on - the x11vnc side. Use the -noalphablend option to disable this behavior - (always approximate transparent cursors with opaque RGB values.) - - The CursorShapeUpdates VNC extension complicates matters because the - cursor shape is sent to the VNC viewers supporting it, and the viewers - draw the cursor locally. This improves response over slow links. Alpha - channel data for these locally drawn cursors is not supported by the - VNC protocol. - - However, in the libvncserver CVS there is a patch to the TightVNC - viewer to make this work for CursorShapeUpdates under some - circumstances. This hack is outside of the VNC protocol. It requires - the screens on both sides to be depth 24 at 32bpp (it uses the extra 8 - bits to secretly hide the cursor alpha channel data.) Not only does it - require depth 24 at 32bpp, but it also currently requires the client - and server to be of the same endianness (otherwise the hidden alpha - data gets reset to zero by a libvncserver translation function; we can - fix this at some point if there is interest.) The patch is for the - TightVNC 1.3dev5 Unix vncviewer and it enables the TightVNC viewer to - do the cursor alpha blending locally. The patch code should give an - example on how to change the Windows TightVNC viewer to achieve the - same thing (send me the patch if you get that working.) - - This patch is applied to the Enhanced TightVNC Viewer (SSVNC) package - we provide. - - [Mouse Pointer] - - Q-84: Why does the mouse arrow just stay in one corner in my - vncviewer, whereas my cursor (that does move) is just a dot? - - This default takes advantage of a tightvnc extension - (CursorShapeUpdates) that allows specifying a cursor image shape for - the local VNC viewer. You may disable it with the -nocursor option to - x11vnc if your viewer does not have this extension. - - Note: as of Aug/2004 this should be fixed: the default for - non-tightvnc viewers (or ones that do not support CursorShapeUpdates) - will be to draw the moving cursor into the x11vnc framebuffer. This - can also be disabled via -nocursor. - - - Q-85: Can I take advantage of the TightVNC extension to the VNC - protocol where Cursor Positions Updates are sent back to all connected - clients (i.e. passive viewers can see the mouse cursor being moved - around by another viewer)? - - Use the -cursorpos option when starting x11vnc. A VNC viewer must - support the Cursor Positions Updates for the user to see the mouse - motions (the TightVNC viewers support this.) As of Aug/2004 -cursorpos - is the default. See also -nocursorpos and -nocursorshape. - - - Q-86: Is it possible to swap the mouse buttons (e.g. left-handed - operation), or arbitrarily remap them? How about mapping button clicks - to keystrokes, e.g. to partially emulate Mouse wheel scrolling? - - You can remap the mouse buttons via something like: -buttonmap 13-31 - (or perhaps 12-21.) Also, note that xmodmap(1) lets you directly - adjust the X server's button mappings, but in some circumstances it - might be more desirable to have x11vnc do it. - - One user had an X server with only one mouse button(!) and was able to - map all of the VNC client mouse buttons to it via: -buttonmap 123-111. - - Note that the -debug_pointer option prints out much info for every - mouse/pointer event and is handy in solving problems. - - To map mouse button clicks to keystrokes you can use the alternate - format where the keystrokes are enclosed between colons like this - :: in place of the mouse button digit. For a sequence of - keysyms separate them with "+" signs. Look in the include file - , or use xev(1), or -debug_keyboard to find the - keysym names. Button clicks can also be included in the sequence via - the fake keysyms Button1, etc. - - As an example, suppose the VNC viewer machine has a mouse wheel (these - generate button 4 and 5 events), but the machine that x11vnc is run on - only has the 3 regular buttons. In normal operation x11vnc will - discard the button 4 and 5 events. However, either of the following - button maps could possibly be of use emulating the mouse wheel events - in this case: - -buttonmap 12345-123:Prior::Next: - -buttonmap 12345-123:Up+Up+Up::Down+Down+Down: - - Exactly what keystroke "scrolling" events they should be bound to - depends on one's taste. If this method is too approximate, one could - consider not using -buttonmap but rather configuring the X server to - think it has a mouse with 5 buttons even though the physical mouse - does not. (e.g. 'Option "ZAxisMapping" "4 5"'.) - - Note that when a keysym-mapped mouse button is clicked down this - immediately generates the key-press and key-release events (for each - keysym in turn if the mapping has a sequence of keysyms.) When the - mouse button goes back up nothing is generated. - - If you include modifier keys like Shift_L instead of key-press - immediately followed by key-release the state of the modifier key is - toggled (however the initial state of the modifier key is ignored.) So - to map the right button to type my name 'Karl Runge' I could use this: - -buttonmap 3-:Shift_L+k+Shift_L+a+r+l+space+Shift_L+r+Shift_L+u+n+g+e: - - (yes, this is getting a little silly.) - - BTW, Coming the other way around, if the machine you are sitting at - does not have a mouse wheel, but the remote machine does (or at least - has 5 buttons configured), this key remapping can be useful: - -remap Super_R-Button4,Menu-Button5 - - you just tap those two keys to get the mouse wheel scrolls (this is - more useful than the Up and Down arrow keys because a mouse wheel - "click" usually gives a multi-line scroll.) - [Keyboard Issues] - - Q-87: How can I get my AltGr and Shift modifiers to work between - keyboards for different languages? - - The option -modtweak should help here. It is a mode that monitors the - state of the Shift and AltGr Modifiers and tries to deduce the correct - keycode to send, possibly by sending fake modifier key presses and - releases in addition to the actual keystroke. - - Update: As of Jul/2004 -modtweak is now the default (use -nomodtweak - to get the old behavior.) This was done because it was noticed on - newer XFree86 setups even on bland "us" keyboards like "pc104 us" - XFree86 included a "ghost" key with both "<" and ">" it. This key does - not exist on the keyboard (see this FAQ for more info.) Without - -modtweak there was then an ambiguity in the reverse map keysym => - keycode, making it so the "<" symbol could not be typed. - - Also see the FAQ about the -xkb option for a more powerful method of - modifier tweaking for use on X servers with the XKEYBOARD extension. - - When trying to resolve keyboard mapping problems, note that the - -debug_keyboard option prints out much info for every keystroke and so - can be useful debugging things. - - Note that for some users, the solution is to disable all of the above, - and use -nomodtweak. This is the simplest form of keystroke insertion and - it actually solved the problem. Try it if the other options don't help. - - - Q-88: When I try to type a "<" (i.e. less than) instead I get ">" - (i.e. greater than)! Strangely, typing ">" works OK!! - - Does your keyboard have a single key with both "<" and ">" on it? Even - if it doesn't, your X server may think your keyboard has such a key - (e.g. pc105 in the XF86Config file when it should be something else, - say pc104.) - - Short Cut: Try the -xkb or -sloppy_keys options and see if that helps - the situation. The discussion below is a bit outdated (e.g. -modtweak - is now the default) but it is useful reference for various tricks and - so is kept. - - - The problem here is that on the Xserver where x11vnc is run there are - two keycodes that correspond to the "<" keysym. Run something like - this to see: - - xmodmap -pk | egrep -i 'KeyCode|less|greater' - There are 4 KeySyms per KeyCode; KeyCodes range from 8 to 255. - KeyCode Keysym (Keysym) ... - 59 0x002c (comma) 0x003c (less) - 60 0x002e (period) 0x003e (greater) - 94 0x003c (less) 0x003e (greater) - - That keycode 94 is the special key with both "<" and ">". When x11vnc - receives the "<" keysym over the wire from the remote VNC client, it - unfortunately maps it to keycode 94 instead of 59, and sends 94 to the - X server. Since Shift is down (i.e. you are Shifting the comma key), - the X server interprets this as Shifted-94, which is ">". - - A workaround in the X server configuration is to "deaden" that special - key: - - xmodmap -e "keycode 94 = " - - However, one user said he had to do this: - - xmodmap -e "keycode 94 = 0x002c 0x003c" - - (If the numerical values are different for your setup, substitute the - ones that correspond to your display. The above xmodmap scheme can - often be used to work around other ambiguous keysym to keycode - mappings.) - - Alternatively, here are some x11vnc options to try to work around the - problem: - -modtweak - - and - -remap less-comma - - These are convenient in that they do not modify the actual X server - settings. The former (-modtweak) is a mode that monitors the state of - the Shift and AltGr modifiers and tries to deduce the correct keycode - sequence to send. Since Jul/2004 -modtweak is now the default. The - latter (-remap less-comma) is an immediate remapping of the keysym - less to the keysym comma when it comes in from a client (so when Shift - is down the comma press will yield "<".) - - See also the FAQ about the -xkb option as a possible workaround using - the XKEYBOARD extension. - - Note that the -debug_keyboard option prints out much info for every - keystroke to aid debugging keyboard problems. - - - Q-89: Extra Character Inserted, E.g.: When I try to type a "<" (i.e. - less than) instead I get "<," (i.e. an extra comma.) - - This is likely because you press "Shift" then "<" but then released - the Shift key before releasing the "<". Because of a keymapping - ambiguity the last event "< up" is interpreted as "," because that key - unshifted is the comma. - - This extra character insertion will happen for other combinations of - characters: in general it can happen whenever the Shift key is - released early. - - This should not happen in -xkb mode, because it works hard to resolve - the ambiguities. If you do not want to use -xkb, try the option - -sloppy_keys to attempt a similar type of algorithm. - - One user had this problem for Italian and German keyboards with the - key containing ":" and "." When he typed ":" he would get an extra "." - inserted after the ":". The solution was -sloppy_keys. - - - Q-90: I'm using an "international" keyboard (e.g. German "de", or - Danish "dk") and the -modtweak mode works well if the VNC viewer is - run on a Unix/Linux machine with a similar keyboard. But if I run - the VNC viewer on Unix/Linux with a different keyboard (e.g. "us") or - Windows with any keyboard, I can't type some keys like: "@", "$", - "<", ">", etc. How can I fix this? - - The problem with Windows is it does not seem to handle AltGr well. It - seems to fake it up by sending Control_L+Alt_R to applications. The - Windows VNC viewer sends those two down keystrokes out on the wire to - the VNC server, but when the user types the next key to get, e.g., "@" - the Windows VNC viewer sends events bringing the up the - Control_L+Alt_R keys, and then sends the "@" keysym by itself. - - The Unix/Linux VNC viewer on a "us" keyboard does a similar thing - since "@" is the Shift of the "2" key. The keysyms Shift and "@" are - sent to the VNC server. - - In both cases no AltGr is sent to the VNC server, but we know AltGr is - needed on the physical international keyboard to type a "@". - - This all worked fine with x11vnc running with the -modtweak option (it - figures out how to adjust the Modifier keys (Shift or AltGr) to get - the "@".) However it fails under recent versions of XFree86 (and the - X.org fork.) These run the XKEYBOARD extension by default and make - heavy use of it to handle international keyboards. - - To make a long story short, on these newer XFree86 setups the - traditional X keymap lookup x11vnc uses is no longer accurate. x11vnc - can't find the keysym "@" anywhere in the keymapping! (even though it - is in the XKEYBOARD extended keymapping.) - - How to Solve: As of Jul/2004 x11vnc has two changes: - * -modtweak (tweak Modifier keys) is now the default (use - -nomodtweak to go back to the old way) - * there is a new option -xkb to use the XKEYBOARD extension API to - do the Modifier key tweaking. - - The -xkb option seems to fix all of the missing keys: "@", "<", ">", - etc.: it is recommended that you try it if you have this sort of - problem. Let us know if there are any remaining problems (see the next - paragraph for some known problems.) If you specify the -debug_keyboard - (aka -dk) option twice you will get a huge amount of keystroke - debugging output (send it along with any problems you report.) - - Update: as of Jun/2005 x11vnc will try to automatically enable -xkb if - it appears that would be beneficial (e.g. if it sees any of "@", "<", - ">", "[" and similar keys are mapped in a way that needs the -xkb to - access them.) To disable this automatic check use -noxkb. - - Known problems: - * One user had to disable a "ghost" Mode_switch key that was causing - problems under -xkb. His physical AltGr key was bound to - ISO_Level3_Shift (which seems to be the XKEYBOARD way of doing - things), while there was a ghost key Mode_switch (which seems to - be obsolete) in the mapping as well. Both of these keysyms were - bound to Mod5 and x11vnc was unfortunately choosing Mode_switch. - From the x11vnc -xkb -dk -dk output it was noted that Mode_switch - was attached to keycode 93 (no physical key generates this - keycode) while ISO_Level3_Shift was attached to keycode 113. The - keycode skipping option was used to disable the ghost key: - -skip_keycodes 93 - * In implementing -xkb we noticed that some characters were still - not getting through, e.g. "~" and "^". This is not really an - XKEYBOARD problem. What was happening was the VNC viewer was - sending the keysyms asciitilde and asciicircum to x11vnc, but on - the X server with the international keyboard those keysyms were - not mapped to any keys. So x11vnc had to skip them (Note: as of - May/2005 they are added by default see -add_keysyms below.) - The way these characters are typically entered on international - keyboards is by "dead" (aka "mute") keys. E.g. to enter "~" at the - physical display the keysym dead_tilde is pressed and released - (this usually involves holding AltGr down while another key is - pressed) and then space is pressed. (this can also be used get - characters with the "~" symbol on top, e.g. "\E3" by typing "a" - instead of space.) - What to do? In general the VNC protocol has not really solved this - problem: what should be done if the VNC viewer sends a keysym not - recognized by the VNC server side? Workarounds can possibly be - created using the -remap x11vnc option: - -remap asciitilde-dead_tilde,asciicircum-dead_circumflex - etc. Use -remap filename if the list is long. Please send us your - workarounds for this problem on your keyboard. Perhaps we can have - x11vnc adjust automatically at some point. Also see the - -add_keysyms option in the next paragraph. - Update: for convenience "-remap DEAD" does many of these mappings - at once. - * To complement the above workaround using the -remap, an option - -add_keysyms was added. This option instructs x11vnc to bind any - unknown Keysyms coming in from VNC viewers to unused Keycodes in - the X server. This modifies the global state of the X server. When - x11vnc exits it removes the extra keymappings it created. Note - that the -remap mappings are applied first, right when the Keysym - is received from a VNC viewer, and only after that would - -add_keysyms, or anything else, come into play. - Update: -add_keysyms is now on by default. Use -noadd_keysyms to - disable. - - - Q-91: When typing I sometimes get double, triple, or more of my - keystrokes repeated. I'm sure I only typed them once, what can I do? - - This may be due to an interplay between your X server's key autorepeat - delay and the extra time delays caused by x11vnc processing. - - Short answer: disable key autorepeating by running the command "xset r - off" on the Xserver where x11vnc is run (restore via "xset r on") or - use the new (Jul/2004) -norepeat x11vnc option. You will still have - autorepeating because that is taken care of on your VNC viewer side. - - Update: as of Dec/2004 -norepeat is now the default. Use -repeat to - disable it. - - Details: - suppose you press a key DOWN and it generates changes in large regions - of the screen. The CPU and I/O work x11vnc does for the large screen - change could be longer than your X server's key autorepeat delay. - x11vnc may not get to processing the key UP event until after the - screen work is completed. The X server believes the key has been held - down all this time, and applies its autorepeat rules. - - Even without inducing changes in large regions of the screen, this - problem could arise when accessing x11vnc via a dialup modem or - otherwise high latency link (e.g. > 250 ms latency.) - - Look at the output of "xset q" for the "auto repeat delay" setting. Is - it low (e.g. < 300 ms)? If you turn off autorepeat completely: "xset r - off", does the problem go away? - - The workaround is to manually apply "xset r off" and "xset r on" as - needed, or to use the -norepeat (which has since Dec/2004 been made - the default.) Note that with X server autorepeat turned off the VNC - viewer side of the connection will (nearly always) do its own - autorepeating so there is no big loss here, unless someone is also - working at the physical display and misses his autorepeating. - - - Q-92: The x11vnc -norepeat mode is in effect, but I still get repeated - keystrokes!! - - Are you using x11vnc to log in to an X session via display manager? - (as described in this FAQ) If so, x11vnc is starting before your - session and it disables autorepeat when you connect, but then after - you log in your session startup (GNOME, KDE, ...) could be resetting - the autorepeat to be on. Or it could be something inside your desktop - trying to be helpful that decides to turn it back on. - - x11vnc in -norepeat mode will by default reset autorepeat to off 2 - times (to help get thru the session startup problem), but it will not - continue to battle with things turning autorepeat back on. It will - also turn autorepeat off whenever it goes from a state of zero clients - to one client. You can adjust the number of resets via "-norepeat N", - or use "-norepeat -1" to have it keep resetting it whenever autorepeat - gets turned back on when clients are connected. - - In general you can manually turn autorepeating off by typing "xset r - off", or a using desktop utility/menu, or "x11vnc -R norepeat". If - something in your desktop is automatically turning it back on you - should figure out how to disable that somehow. - - - Q-93: After using x11vnc for a while, I find that I cannot type some - (or any) characters or my mouse clicks and drags no longer have any - effect, or they lead to strange effects. What happened? - - Probably a modifier key, e.g. Control or Alt is "stuck" in a pressed - down state. - - This happens for VNC in general by the following mechanism. Suppose on - the Viewer side desktop there is some hot-key to switch - desktops/rooms/spaces, etc. E.g. suppose Alt+LeftArrow moves to the - left desktop/room/space. Or suppose an Alt+hotkey combination - iconifies a window. This can leave the Alt key pressed down on the - remote side. - - Consider the sequence that happens. The Alt_L key and then the - LeftArrow key go down. Since you are inside the viewer the Alt_L key - press is sent to the other side (x11vnc) and so it is pressed down in - the remote desktop as well. (by "Alt_L" we mean the Alt key on the - left-hand side of the keyboard.) Your local desktop (where the VNC - Viewer is running) then warps to the new desktop/room/space: Leaving - the Alt_L key still pressed down in the remote desktop. - - If someone is sitting at the desktop, or when you return in the viewer - it may be very confusing because the Alt_L is still pressed down but - you (or the person sitting at the desktop) do not realize this. - Depending on which remote desktop (x11vnc side) is used, it can act - very strangely. - - A quick workaround when you notice this is to press and release all of - the Alt, Shift, Control, Windows-Flag, modifier keys to free the - pressed one. You need to do this for both the left and right Shift, - Alt, Control, etc. keys to be sure. - - Note that many VNC Viewers try to guard against this when they are - notified by the window system that the viewer app has "lost focus". - When it receives the "lost focus" event, the viewer sends VNC - Key-Release events for all modifier keys that are currently pressed - down. This does not always work, however, since it depends on how the - desktop manages these "warps". If the viewer is not notified it cannot - know it needs to release the modifiers. - - You can also use the -clear_mods option to try to clear all of the - modifier keys at x11vnc startup. You will still have to be careful - that you do not leave the modifier key pressed down during your - session. It is difficult to prevent this problem from occurring (short - of using -remap to prevent sending all of the problem modifier keys, - which would make the destkop pretty unusable.) - - During a session these x11vnc remote control commands can also help: - x11vnc -R clear_mods - x11vnc -R clear_keys - x11vnc -R clear_locks - x11vnc -R clear_all - - A similar problem can occur if you accidentally press the Caps_Lock or - Num_Lock down. When these are locked on the remote side it can - sometimes lead to strange desktop behavior (e.g. cannot drag or click - on windows.) As above you may not notice this because the lock isn't - down on the local (Viewer) side. See this FAQ on lock keys problem. - These options may help avoid the problem: -skip_lockkeys and - -capslock. See also -clear_all. - - - Q-94: The machine where I run x11vnc has an AltGr key, but the local - machine where I run the VNC viewer does not. Is there a way I can map - a local unused key to send an AltGr? How about a Compose key as well? - - Something like "-remap Super_R-Mode_switch" x11vnc option may work. - Note that Super_R is the "Right Windoze(tm) Flaggie" key; you may want - to choose another. The -debug_keyboard option comes in handy in - finding keysym names (so does xev(1).) - - For Compose how about "-remap Menu-Multi_key" (note that Multi_key is - the official name for Compose.) To do both at the same time: "-remap - Super_R-Mode_switch,Menu-Multi_key" or use "-remap filename" to - specify remappings from a file. - - - Q-95: I have a Sun machine I run x11vnc on. Its Sun keyboard has just - one Alt key labelled "Alt" and two Meta keys labelled with little - diamonds. The machine where I run the VNC viewer only has Alt keys. - How can I send a Meta keypress? (e.g. emacs needs this) - - Here are a couple ideas. The first one is to simply use xmodmap(1) to - adjust the Sun X server. Perhaps xmodmap -e "keysym Alt_L = Meta_L - Alt_L" will do the trick. (there are other ways to do it, one user - used: xmodmap -e "keycode 26 = Meta_L" for his setup.) - - Since xmodmap(1) modifies the X server mappings you may not want to do - this (because it affects local work on that machine.) Something like - the -remap Alt_L-Meta_L to x11vnc may be sufficient for ones needs, - and does not modify the X server environment. Note that you cannot - send Alt_L in this case, maybe -remap Super_L-Meta_L would be a better - choice if the Super_L key is typically unused in Unix. - - - Q-96: Running x11vnc on HP-UX I cannot type "#" I just get a "3" - instead. - - One user reports this problem on HP-UX Rel_B.11.23. The problem was - traced to a strange keyboard mapping for the machine (e.g. xmodmap -pk - output) that looked like: - ... - 039 2 at at at - ... - 047 3 numbersign numbersign numbersign - - and similar triple mappings (with two in the AltGr/Mode_switch group) - of a keysum to a single keycode. - - Use the -nomodtweak option as a workaround. You can also use xmodmap - to correct these mappings in the server, e.g.: - xmodmap -e "keycode 47 = 3 numbersign" - - Also, as of Feb/2007, set the environment variable MODTWEAK_LOWEST=1 - (either in your shell or via "-env MODTWEAK_LOWEST=1" option) to - handle these mappings better. - - - Q-97: Can I map a keystroke to a mouse button click on the remote - machine? - - This can be done directly in some X servers using AccessX and - Pointer_EnableKeys, but is a bit awkward. It may be more convenient to - have x11vnc do the remapping. This can be done via the -remap option - using the fake "keysyms" Button1, Button2, etc. as the "to" keys (i.e. - the ones after the "-") - - As an example, consider a laptop where the VNC viewer is run that has - a touchpad with only two buttons. It is difficult to do a middle - button "paste" because (using XFree86/Xorg Emulate3Buttons) you have - to click both buttons on the touch pad at the same time. This - remapping: - -remap Super_R-Button2 - - maps the Super_R "flag" key press to the Button2 click, thereby making - X pasting a bit easier. - - Note that once the key goes down, the button down and button up events - are generated immediately on the x11vnc side. When the key is released - (i.e. goes up) no events are generated. - - Q-98: How can I get Caps_Lock to work between my VNC viewer and - x11vnc? - - This is a little tricky because it is possible to get the Caps_Lock - state out of sync between your viewer-side machine and the x11vnc-side - X server. For best results, we recommend not ever letting the - Caps_Lock keypresses be processed by x11vnc. That way when you press - Caps_Lock in the viewer your local machine goes into the Caps_Lock on - state and sends keysym "A" say when you press "a". x11vnc will then - fake things up so that Shift is held down to generate "A". The - -skip_lockkeys option should help to accomplish this. For finer grain - control use something like: "-remap Caps_Lock-None". - - Also try the -nomodtweak and -capslock options. - - Another useful option that turns off any Lock keys on the remote side - at startup and end is the -clear_all option. During a session you can - run these remote control commands to modify the Lock keys: - x11vnc -R clear_locks - x11vnc -R clear_all - - the former will try to unset any Lock keys, the latter will do same - and also try to make it so no key is pressed down (e.g. "stuck" Alt_L, - etc.) - [Screen Related Issues and Features] - - Q-99: The remote display is larger (in number of pixels) than the - local display I am running the vncviewer on. I don't like the - vncviewer scrollbars, what I can do? - - vncviewer has a option (usually accessible via F8 key or -fullscreen - option) for vncviewer to run in full screen, where it will - automatically scroll when the mouse is near the edge of the current - view. For quick scrolling, also make sure Backing Store is enabled on - the machine vncviewer is run on. (XFree86/Xorg disables it by default - for some reason, add Option "backingstore" to XF86Config on the - vncviewer side.) - - BTW, contact me if you are having problems with vncviewer in - fullscreen mode with your window manager (i.e. no keyboard response.) - I have a workaround for vncviewer using XGrabServer(). - - There may also be scaling viewers out there (e.g. TightVNC or UltraVNC - on Windows) that automatically shrink or expand the remote framebuffer - to fit the local display. Especially for hand-held devices. See also - the next FAQ on x11vnc scaling. - - - Q-100: Does x11vnc support server-side framebuffer scaling? (E.g. to - make the desktop smaller.) - - As of Jun/2004 x11vnc provides basic server-side scaling. It is a - global scaling of the desktop, not a per-client setting. To enable it - use the "-scale fraction" option. "fraction" can either be a floating - point number (e.g. -scale 0.75) or the alternative m/n fraction - notation (e.g. -scale 3/4.) Note that if fraction is greater than one - the display is magnified. - - Extra resources (CPU, memory I/O, and memory) are required to do the - scaling. If the machine is slow where x11vnc is run with scaling - enabled, the interactive response can be unacceptable. OTOH, if run - with scaling on a fast machine the performance degradation is usually - not a big issue or even noticeable. - - It may help to compile x11vnc with compiler option -O3 or -O4 to speed - up the scaling code. Set the CFLAGS env. var. before running - configure. - - Also, if you just want a quick, rough "thumbnail" of the display you - can append ":nb" to the fraction to turn on "no blending" mode. E.g.: - "-scale 1/3:nb" Fonts will be difficult to read, but the larger - features will be recognizable. BTW, "no blending" mode is forced on - when scaling 8bpp PseudoColor displays (because blending an indexed - colormap is a bad idea and leads to random colors, use :fb to force it - on.) - - One can also use the ":nb" with an integer scale factor (say "-scale - 2:nb") to use x11vnc as a screen magnifier for vision impaired - applications. Since with integer scale factors the framebuffers become - huge and scaling operations time consuming, be sure to use ":nb" for - the fastest response. - - In general for a scaled display if you are using a TightVNC viewer you - may want to turn off jpeg encoding (e.g. vncviewer -nojpeg host:0.) - There appears to be a noise enhancement effect, especially for regions - containing font/text: the scaling can introduce some pixel artifacts - that evidently causes the tight encoding algorithm to incorrectly - detect the regions as image data and thereby introduce additional - pixel artifacts due to the lossiness of the jpeg compression - algorithm. Experiment to see if -nojpeg vncviewer option improves the - readability of text when using -scale to shrink the display size. Also - note that scaling may actually slow down the transfer of text regions - because after being scaled they do not compress as well. (this can - often be a significant slowdown, e.g. 10X.) - - Another issue is that it appears VNC viewers require the screen width - to be a multiple of 4. When scaling x11vnc will round the width to the - nearest multiple of 4. To disable this use the ":n4" sub option (like - ":nb" in the previous paragraph; to specify both use a comma: - ":nb,n4", etc.) - - If one desires per-client scaling for something like 1:1 from a - workstation and 1:2 from a smaller device (e.g. handheld), currently - the only option is to run two (or more) x11vnc processes with - different scalings listening on separate ports (-rfbport option, etc.) - - Update: As of May/2006 x11vnc also supports the UltraVNC server-side - scaling. This is a per-client scaling by factors 1/2, 1/3, ... and so - may be useful for PDA's ("-scale 1/2", etc. will give similar results - except that it applies to all clients.) You may need to supply - "-rfbversion 3.6" for this to be recognized by UltraVNC viewers. - - BTW, whenever you run two or more x11vnc's on the same X display and - use the GUI, then to avoid all of the x11vnc's simultaneously - answering the gui you will need to use something like "-connect file1 - -gui ..." with different connect files for each x11vnc you want to - control via the gui (or remote-control.) The "-connect file1" usage - gives separate communication channels between a x11vnc process and the - gui process. Otherwise they all share the same X property channels: - VNC_CONNECT and X11VNC_REMOTE. - - Update: As of Mar/2005 x11vnc now scales the mouse cursor with the - same scale factor as the screen. If you don't want that, use the - "-scale_cursor frac" option to set the cursor scaling to a different - factor (e.g. use "-scale_cursor 1" to keep the cursor at its natural - unscaled size.) - - - Q-101: Does x11vnc work with Xinerama? (i.e. multiple monitors joined - together to form one big, single screen.) - - Yes, it should generally work because it simply polls the big - effective screen. - - If the viewing-end monitor is not as big as the remote Xinerama - display, then the vncviewer scrollbars, etc, will have to be used to - pan across the large area. However one user started two x11vnc's, one - with "-clip 1280x1024+0+0" and the other with "-clip 1280x1024+1280+0" - to split the big screen into two and used two VNC viewers to access - them. - - As of Jun/2008: Use "-clip xinerama0" to clip to the first xinerama - sub-screen (if xinerama is active.) xinerama1 for the 2nd sub-screen, - etc. This way you don't need to figure out the WxH+X+Y of the desired - xinerama sub-screen. screens are sorted in increasing distance from - the (0,0) origin (I.e. not the Xserver's order.) - - There are a couple potential issues with Xinerama however. If the - screen is not rectangular (e.g. 1280x1024 and 1024x768 monitors joined - together), then there will be "non-existent" areas on the screen. The - X server will return "garbage" image data for these areas and so they - may be distracting to the viewer. The -blackout x11vnc option allows - you to blacken-out rectangles by manually specifying their WxH+X+Y - geometries. If your system has the libXinerama library, the -xinerama - x11vnc option can be used to have it automatically determine the - rectangles to be blackened out. (Note on 8bpp PseudoColor displays the - fill color may not be black.) Update: -xinerama is now on by default. - - Some users have reported that the mouse does not behave properly for - their Xinerama display: i.e. the mouse cannot be moved to all regions - of the large display. If this happens try using the -xwarppointer - option. This instructs x11vnc to fake mouse pointer motions using the - XWarpPointer function instead of the XTestFakeMotionEvent XTEST - function. (This may be due to a bug in the X server for XTEST when - Xinerama is enabled.) Update: As of Dec/2006 -xwarppointer will be - applied automatically if Xinerama is detected. To disable use: - -noxwarppointer - - - Q-102: Can I use x11vnc on a multi-headed display that is not Xinerama - (i.e. separate screens :0.0, :0.1, ... for each monitor)? - - You can, but it is a little bit awkward: you must start separate - x11vnc processes for each screen, and on the viewing end start up - separate VNC viewer processes connecting to them. e.g. on the remote - end: - x11vnc -display :0.0 -bg -q -rfbport 5900 - x11vnc -display :0.1 -bg -q -rfbport 5901 - - (this could be automated in the display manager Xsetup for example) - and then on the local machine where you are sitting: - vncviewer somehost:0 & - vncviewer somehost:1 & - - Note: if you are running on Solaris 8 or earlier you can easily hit up - against the maximum of 6 shm segments per process (for Xsun in this - case) from running multiple x11vnc processes. You should modify - /etc/system as mentioned in another FAQ to increase the limit. It is - probably also a good idea to run with the -onetile option in this case - (to limit each x11vnc to 3 shm segments), or even -noshm to use no shm - segments. - - - Q-103: Can x11vnc show only a portion of the display? (E.g. for a - special purpose application or a very large screen.) - - As of Mar/2005 x11vnc has the "-clip WxH+X+Y" option to select a - rectangle of width W, height H and offset (X, Y). Thus the VNC screen - will be the clipped sub-region of the display and be only WxH in size. - One user used -clip to split up a large Xinerama screen into two more - managable smaller screens. - - This also works to view a sub-region of a single application window if - the -id or -sid options are used. The offset is measured from the - upper left corner of the selected window. - - - Q-104: Does x11vnc support the XRANDR (X Resize, Rotate and - Reflection) extension? Whenever I rotate or resize the screen x11vnc - just seems to crash. - - As of Dec/2004 x11vnc supports XRANDR. You enable it with the -xrandr - option to make x11vnc monitor XRANDR events and also trap X server - errors if the screen change occurred in the middle of an X call like - XGetImage. Once it traps the screen change it will create a new - framebuffer using the new screen. - - If the connected vnc viewers support the NewFBSize VNC extension - (Windows TightVNC viewer and RealVNC 4.0 windows and Unix viewers do) - then the viewer will automatically resize. Otherwise, the new - framebuffer is fit as best as possible into the original viewer size - (portions of the screen may be clipped, unused, etc.) For these - viewers you can try the -padgeom option to make the region big enough - to hold all resizes and rotations. We have fixed this problem for the - TightVNC Viewer on Unix: SSVNC - - If you specify "-xrandr newfbsize" then vnc viewers that do not - support NewFBSize will be disconnected before the resize. If you - specify "-xrandr exit" then all will be disconnected and x11vnc will - terminate. - - - Q-105: Independent of any XRANDR, can I have x11vnc rotate and/or - reflect the screen that the VNC viewers see? (e.g. for a handheld - whose screen is rotated 90 degrees.) - - As of Jul/2006 there is the -rotate option allow this. E.g's: "-rotate - +90", "-rotate -90", "-rotate x", etc. - - - Q-106: Why is the view in my VNC viewer completely black? Or why is - everything flashing around randomly? - - See the next FAQ for a possible explanation. - - - Q-107: I use Linux Virtual Terminals (VT's) to implement 'Fast User - Switching' between users' sessions (e.g. Betty is on Ctrl-Alt-F7, - Bobby is on Ctrl-Alt-F8, and Sid is on Ctrl-Alt-F1: they use those - keystrokes to switch between their sessions.) How come the view in a - VNC viewer connecting to x11vnc is either completely black or - otherwise all messed up unless the X session x11vnc is attached to is - in the active VT? - - This seems to have to do with how applications (the X server processes - in this case) must "play nicely" if they are not on the active VT - (sometimes called VC for virtual console.) That is, they should not - read from the keyboard or mouse or manage the video display unless - they have the active VT. Given that it appears the XGetImage() call - must ultimately retrieve the framebuffer data from the video hardware - itself, it would make sense x11vnc's polling wouldn't work unless the - X session had active control of the VT. - - There does not seem to be an easy way to work around this. Even xwd(1) - doesn't work in this case (try it.) Something would need to be done at - a lower level, say in the XFree86/Xorg X server. Also, using the - Shadow Framebuffer (a copy of the video framebuffer is kept in main - memory) does not appear to fix the problem. - - If no one is sitting at the workstation and you just want to remotely - switch the VT over to the one associated with your X session (so - x11vnc can poll it correctly), one can use the chvt(1) command, e.g. - "chvt 7" for VT #7. - - - Q-108: I am using x11vnc where my local machine has "popup/hidden - taskbars" and the remote display where x11vnc runs also has - "popup/hidden taskbars" and they interfere and fight with each other. - What can I do? - - When you move the mouse to the edge of the screen where the popups - happen, the taskbars interfere with each other in strange ways. This - sometimes happens where the local machine is GNOME or Mac OS X and the - remote machine is GNOME. Is there a way to temporarily disable one or - both of these magic desktop taskbars? - - One x11vnc user suggests: it should be straightforward to right mouse - click on the task bar panel, and uncheck "enable auto-hide" from the - panel properties dialog box. This will make the panel always visible. - - Q-109: Help! x11vnc and my KDE screensaver keep switching each other - on and off every few seconds. - - This is a new (Jul/2006) problem seen, say, on the version of KDE that - is shipped with SuSE 10.1. It is not yet clear what is causing this... - If you move the mouse through x11vnc the screensaver shuts off like it - should but then a second or two after you stop moving the mouse the - screensaver snaps back on. - - This may be a bug in kdesktop_lock. For now the only workaround is to - disable the screensaver. You can try using another one such as - straight xscreensaver (see the instructions here for how to disable - kdesktop_lock.) If you have more info on this or see it outside of KDE - please let us know. - - Update: It appears this is due to kdesktop_lock enabling the screen - saver when the Monitor is in DPMS low-power state (e.g. standby, - suspend, or off.) In Nov/2006 the x11vnc -nodpms option was added as a - workaround. Normally it is a good thing that the monitor powers down - (since x11vnc can still poll the framebuffer in this state), but if - you experience the kdesktop_lock problem you can specify the "-nodpms" - option to keep the Monitor out of low power state while VNC clients - are connected. This is basically the same as typing "xset dpms force - on" periodically. (if you don't want to do these things just disable - the screensaver.) Feel free to file a bug against kdesktop_lock with - KDE. - - Q-110: I am running the compiz 3D window manager (or beryl, MythTv, - Google Earth, or some other OpenGL app) and I do not get screen - updates in x11vnc. - - This appears to be because the 3D OpenGL/GLX hardware screen updates - do not get reported via the XDAMAGE mechanism. So this is a bug in - compiz/beryl or XDAMAGE/Xorg or the (possibly 3rd party) video card - driver. - - As a workaround apply the -noxdamage option. As of Feb/2007 x11vnc - will try to autodetect the problem and disable XDAMAGE if is appears - to be missing a lot of updates. But if you know you are using compiz - you might as well always supply -noxdamage. Thanks to this user who - reported the problem and discovered the workaround. - - A developer for MiniMyth reports that the 'alphapulse' tag of the - theme G.A.N.T. can also cause problems, and should be avoided when - using VNC. - - Please report a bug or complaint to Beryl/Compiz and/or Xorg about - this: running x11vnc with -noxdamage disables a nice improvement in - responsiveness (especially for typing) and also leads to unnecessary - CPU and memory I/O load due to the extra polling. - - Update: as of May/2010 NVIDIA may have fixed this problem in their - proprietary drivers. See the NVIDIA Release Notes. (look for - 'x11vnc'.) - - Q-111: Can I use x11vnc to view my VMWare session remotely? - - Yes, since VMWare usually runs as an X application you can view it via - x11vnc in the normal way. - - Note that VMWare has several viewing modes: - * Normal X application window (with window manager frame) - * Quick-Switch mode (with no window manager frame) - * Fullscreen mode - - The way VMWare does Fullscreen mode on Linux is to display the Guest - desktop in a separate Virtual Terminal (e.g. VT 8) (see this FAQ on - VT's for background.) Unfortunately, this Fullscreen VT is not an X - server. So x11vnc cannot access it (however, see this discussion of - -rawfb for a possible workaround.) x11vnc works fine with "Normal X - application window" and "Quick-Switch mode" because these use X. - - Update: It appears the in VMWare 5.x the Fullscreen mode is X, so - x11vnc access does work. - - One user reports he left his machine with VMWare in the Fullscreen - mode, and even though his X session wasn't in the active VT, he could - still connect x11vnc to the X session and pass the keystrokes Ctrl-Alt - (typing "blind") to the VMWare X app. This induced VMWare to switch - out of Fullscreen into Normal X mode and he could continue working in - the Guest desktop remotely. - - - Aside: Sometimes it is convenient (for performance, etc.) to start - VMWare in its own X session using startx(1). This can be used to have - a minimal window manger (e.g. twm or even no window manager), to - improve response. One can also cut the display depth (e.g. to 16bpp) - in this 2nd X session to improve video performance. This 2nd X session - emulates Fullscreen mode to some degree and can be viewed via x11vnc - as long as the VMWare X session is in the active VT. - - Also note that with a little bit of playing with "xwininfo -all - -children" output one can extract the (non-toplevel) window-id of the - of the Guest desktop only when VMWare is running as a normal X - application. Then one can export just the guest desktop (i.e. without - the VMWare menu buttons) by use of the -id windowid option. The - caveats are the X session VMWare is in must be in the active VT and - the window must be fully visible, so this mode is not terribly - convenient, but could be useful in some circumstances (e.g. running - VMWare on a very powerful server machine in a server room that happens - to have a video card, (but need not have a monitor, Keyboard or - mouse).) - - - - [Exporting non-X11 devices via VNC] - - Q-112: Can non-X devices (e.g. a raw framebuffer) be viewed (and even - controlled) via VNC with x11vnc? - - As of Apr/2005 there is support for this. Two options were added: - "-rawfb string" (to indicate the raw frame buffer device, file, etc. - and its parameters) and "-pipeinput command" (to provide an external - program that will inject or otherwise process mouse and keystroke - input.) Some useful -pipeinput schemes, VID, CONSOLE, and UINPUT, have - since been built into x11vnc for convenience. - - This non-X mode for x11vnc is somewhat experimental because it is so - removed in scope from the intended usage of the tool. Incomplete - attempt is made to make all of the other options consistent with non-X - framebuffer polling. So all of the X-related options (e.g. - -add_keysyms, -xkb) are just ignored or may cause an error if used. Be - careful applying such an option via remote control. - - The format for the -rawfb string is: - -rawfb :@xx[-][://][+] - - There are also some useful aliases (e.g. "console".) Some examples: - -rawfb shm:210337933@800x600x32:ff/ff00/ff0000 - - -rawfb map:/dev/fb0@1024x768x16 - - -rawfb map:/tmp/Xvfb_screen0@640x480x8+3232 - - -rawfb file:/tmp/my.pnm@250x200x24+37 - - -rawfb file:/dev/urandom@128x128x8 - - -rawfb snap:/dev/video0@320x240x24 -24to32 - - -rawfb console - - -rawfb vt2 - - -rawfb video - - -rawfb setup:mycmd.sh - - So the type can be "shm" for shared memory objects, and "map" or - "file" for file objects. "map" uses mmap(2) to map the file into - memory and is preferred over "file" (that uses the slower lseek(2) - access method.) Only use file if map isn't working. BTW, "mmap" is an - alias for "map" and if you do not supply a type and the file exists, - map is assumed (see the -help output and below for some exceptions to - this.) The "snap:" setting applies the -snapfb option with "file:" - type reading (this is useful for exporting webcams or TV tuner video; - see the next FAQ for more info.) - - Also, if the string is of the form "setup:cmd" then cmd is run and the - first line of its output retrieved and used as the rawfb string. This - allows initializing the device, determining WxHxB, etc. - - The object will be the numerical shared memory id for the case of shm. - The idea here is some other program has created this shared memory - segment and periodically updates it with new framebuffer data. x11vnc - polls the area for changes. See shmat(2) and ipcs(8) for more info. - The ipcs command will list current shared memory segments on the - system. Sometimes you can snoop on a program's framebuffer it did not - expect you would be polling! - - The object will be the path to the regular or character special file - for the cases of map and file. The idea here is that in the case of a - regular file some other program is writing/updating framebuffer image - data to it. In the case of a character special (e.g. /dev/fb0) it is - the kernel that is "updating" the framebuffer data. - - In most cases x11vnc needs to be told the width, height, and number of - bits per pixel (bpp) of the framebuffer. This is the @WxHxB field. For - the case of the Linux framebuffer device, /dev/fb0, the fbset(8) may - be of use (but may not always be accurate for what is currently - viewable.) In general some guessing may be required, especially for - the bpp. Update: in "-rawfb console" mode x11vnc will use the linuxfb - API to try to guess (it is still not always accurate.) Also try - "-rawfb vtN" (on x11vnc 0.9.7 and later) for the N-th Linux text - console (aka virtual terminal.) If the number of Bytes Per Line is not - WxHxB/8 (i.e. the framebuffer lines are padded) you can specify this - information after WxHxB via "-BPL", e.g. @800x600x16-2048 - - Based on the bpp x11vnc will try to guess the red, green, and blue - masks (these indicate which bits correspond to each color.) It if gets - it wrong you can specify them manually via the optional ":R/G/B" - field. E.g. ":0xff0000/0x00ff00/0x0000ff" (this is the default for - 32bpp.) - - Finally, the framebuffer may not begin at the beginning of the memory - object, so use the optional "+offset" parameter to indicate where the - framebuffer information starts. So as an example, the Xvfb virtual - framebuffer has options -shmem and -fbdir for exporting its virtual - screen to either shm or a mapped file. The format of these is XWD and - so the initial header should be skipped. BTW, since XWD is not - strictly RGB the view will only be approximate, but usable. Of course - for the case of Xvfb x11vnc can poll it much better via the X API, but - you get the idea. - - By default in -rawfb mode x11vnc will actually close any X display it - happened to open. This is basically to shake out bugs (e.g it will - crash rather than mysteriously interacting with the X display.) If you - want x11vnc to keep the X display open while polling the raw - framebuffer prefix a "+" sign at the beginning of the string (e.g. - +file:/dev/urandom@64x64x8) This could be convenient for keeping the - remote control channel active (it uses X properties.) The "-connect - /path/to/file" mechanism could also be used for remote control to - avoid the X property channel. Rare usage, but if you also supply - -noviewonly in this "+" mode then the mouse and keyboard input are - still sent to the X display, presumably for doing something amusing - with /dev/fb... - - Interesting Devices:. Here are some aliases for interesting device - files that can be polled via -rawfb: - -rawfb console /dev/fb0 Linux Console - -rawfb vt2 /dev/vcsa2 Linux Console (e.g. virtual ter -minal #2) - -rawfb video /dev/video0 Video4Linux Capture device - -rawfb rand /dev/urandom Random Bytes - -rawfb null /dev/zero Zero Bytes (black screen) - - The Linux console, /dev/fb0, etc needs to have its driver enabled in - the kernel. Some of the drivers are video card specific and - accelerated. The console is either the Text consoles (usually - tty1-tty6), or X graphical display (usually starting at tty7.) In - addition to the text console other graphical ones may be viewed and - interacted with as well, e.g. DirectFB or SVGAlib apps, VMWare non-X - fullscreen, or Qt-embedded apps (PDAs/Handhelds.) By default the - pipeinput mechanisms UINPUT and CONSOLE (keystrokes only) are - automatically attempted in this mode under "-rawfb console". - - The Video4Linux Capture device, /dev/video0, etc is either a Webcam or - a TV capture device and needs to have its driver enabled in the - kernel. See this FAQ for details. If specified via "-rawfb Video" then - the pipeinput method "VID" is applied (it lets you change video - parameters dynamically via keystrokes.) - - The last two, /dev/urandom and /dev/zero are just for fun, but are - also useful in testing. - - - All of the above -rawfb options are just for viewing the raw - framebuffer (although some of the aliases do imply keystroke and mouse - pipeinput methods.) That may be enough for certain applications of - this feature (e.g. suppose a video camera mapped its framebuffer into - memory and you just wanted to look at it via VNC.) - To handle the pointer and keyboard input from the viewer users the - "-pipeinput cmd" option was added to indicate a helper program to - process the user input. The input is streamed to it and looks - something like this: - Pointer 1 205 257 0 None - Pointer 1 198 253 0 None - Pointer 1 198 253 1 ButtonPress-1 - Pointer 1 198 253 0 ButtonRelease-1 - Pointer 1 198 252 0 None - Keysym 1 1 119 w KeyPress - Keysym 1 0 119 w KeyRelease - Keysym 1 1 65288 BackSpace KeyPress - Keysym 1 0 65288 BackSpace KeyRelease - Keysym 1 1 112 p KeyPress - Keysym 1 0 112 p KeyRelease - - Run "-pipeinput tee:/bin/cat" to get a description of the format. Note - that the -pipeinput option is independent of -rawfb mode and so may - have some other interesting uses. The "tee:" prefix means x11vnc will - both process the user input and pipe it to the command. The default is - to just pipe it to the -pipeinput command. - - Note the -pipeinput helper program could actually control the raw - framebuffer. In the libvncserver CVS a simple example program - x11vnc/misc/slide.pl is provided that demonstrates a simple jpeg - "slideshow" application. Also the builtin "-pipeinput VID" mode does - this for webcams and TV capture devices (/dev/video0.) - - The -pipeinput program is run with these environment variables set: - X11VNC_PID, X11VNC_PROG, X11VNC_CMDLINE, X11VNC_RAWFB_STR to aid its - knowing what is up. - - Another example provided in libvncserver CVS is a script to inject - keystrokes into the Linux console (e.g. the virtual consoles: - /dev/tty1, /dev/tty2, etc) in x11vnc/misc/vcinject.pl. It is based on - the vncterm/LinuxVNC.c program also in the libvncserver CVS. So to - view and interact with VT #2 (assuming it is the active VT) one can - run something like: - x11vnc -rawfb map:/dev/fb0@1024x768x16 -pipeinput './vcinject.pl 2' - - This assumes your Linux framebuffer device (/dev/fb0) is properly - configured. See fbset(8) and other documentation. Try - "file:/dev/fb0@WxHxB" as a last resort. Starting with x11vnc 0.8.1, - the above VT injection is built in, as well as WxHxB determination. - Just use something like: - x11vnc -rawfb console - - this will try to guess the active virtual console (via /dev/tty0) and - also the /dev/fb0 WxHxB and rgb masks automatically. Use, e.g., - "-rawfb console3" to force the VT number. This input method can be - used generally via "-pipeinput CONSOLE". Also starting with x11vnc - 0.8.2 the "-pipeinput UINPUT" mode is tried first (it does both - keyboard and mouse input) and then falls back to CONSOLE mode if it is - not available. Here is the -help output for this mode: - - If the rawfb string begins with "console" the framebuffer device - /dev/fb0 is opened (this requires the appropriate kernel modules to - be installed) and so is /dev/tty0. The latter is used to inject - keystrokes (not all are supported, but the basic ones are.) You - will need to be root to inject keystrokes. /dev/tty0 refers to the - active VT, to indicate one explicitly, use "console2", etc. using - the VT number. - - If the Linux version seems to be 2.6 or later and the "uinput" - module appears to be present, then the uinput method will be used - instead of /dev/ttyN. uinput allows insertion of BOTH keystrokes - and mouse input and so it preferred when accessing graphical (e.g. - Qt-embedded) linux console apps. See -pipeinput UINPUT below for - more information on this mode (you may want to also use the - -nodragging and -cursor none options.) Use "console0", etc or - -pipeinput CONSOLE to force the /dev/ttyN method. - - Note you can change VT remotely using the chvt(1) command. - Sometimes switching out and back corrects the framebuffer state. - - To skip input injecting entirely use "consolex". - - The string "/dev/fb0" (1, etc) can be used instead of "console". - This can be used to specify a different framebuffer device, e.g. - /dev/fb1. As a shortcut the "/dev/" can be dropped. If the name is - something nonstandard, use "console:/dev/foofb" - - If you do not want x11vnc to guess the framebuffer's WxHxB and - masks automatically (sometimes the kernel gives inaccurate - information), specify them with a @WxHxB at the end of the string. - - The above is just an example of what can be done. Note that if you - really want to view and interact with the Linux Text console it is - better to use the more accurate and faster LinuxVNC program. The - advantage x11vnc -rawfb might have is that it can allow interaction - with a non-text application, e.g. one based on SVGAlib or Qt-embedded - Also, for example the VMWare Fullscreen mode is actually viewable - under -rawfb and can be interacted with if uinput is enabled. - - If the Linux uinput driver is available then full keystroke and mouse - input into the Linux console can be performed. You may be able to - enable uinput via commands like these: - modprobe uinput - mknod /dev/input/uinput c 10 223 - - The -rawfb and -pipeinput features are intended to help one creatively - "get out of a jam" (say on a legacy or embedded device) where X is - absent or doesn't work properly. Feedback and bug reports are welcome. - For more control and less overhead use libvncserver in your own C - program that passes the framebuffer to libvncserver. - - - Q-113: Can I export the Linux Console (Virtual Terminals) via VNC - using x11vnc? - - Yes, you may need to be root to access the devices that make up the - linux console. - - To access the active Linux console via the computer's framebuffer try - something like: - x11vnc -rawfb console - x11vnc -rawfb console2 - - These will try to access the framebuffer through /dev/fb (or /dev/fb0, - etc.) and if it succeeds it will show any text or graphics that is - currently displayed. Keystrokes will be injected via the device - /dev/tty0 (to force an explicit virtual terminal append a number, e.g. - "console2" to select /dev/tty2.) - - If your Linux system does not have a framebuffer device (/dev/fb) you - can get one by adding, e.g., vga=0x31B boot parameter. This enables - the VGA framebuffer device at 1280x1024x24. 0x317 gives 1024x768x16, - etc. You can also enable a Linux framebuffer device by modprobing a - framebuffer driver specific to your video card. - - Note that this "-rawfb console" mode shows the contents of the - hardware framebuffer, and so will show whatever is on the screen. It - has no concept of Virtual Terminals WRT what there is to view, it - always shows the active virtual terminal. - - Another mode is specific to the Linux text Virtual Terminals, it shows - their text and colors (but no graphics) regardless of whether it is - the active VT or not. It is available on x11vnc 0.9.7 and later. - Enable this mode like this: - x11vnc -rawfb vt - x11vnc -rawfb vt2 - - The former will select the active one, the latter the 2nd VT. x11vnc - implements this mode by opening the current console text file - "/dev/vcsa2" instead of "/dev/fb". In this way it provides the basic - functionality of the LibVNCServer LinuxVNC program. - - The vt mode can be a useful way to try to get a machine's X server - working remotely, e.g. you edit /etc/X11/xorg.conf and then type - startx (or similar, e.g. gdm) in the virtual terminal. A 2nd x11vnc - could be used to see if the X server is now working correctly. - - Q-114: Can I export via VNC a Webcam or TV tuner framebuffer using - x11vnc? - - Yes, this is possible to some degree with the -rawfb option. There is - no X11 involved: snapshots from the video capture device are used for - the screen image data. See the previous FAQ on -rawfb for background. - For best results, use x11vnc version 0.8.1 or later. - - Roughly, one would do something like this: - x11vnc -rawfb snap:/dev/video@320x240x32 - - This requires that the system allows simple read(2) access to the - video device. This is true for video4Linux on Linux kernel 2.6 and - later (it won't work for 2.4, you'll need a separate program to - snapshot to a file that you point -rawfb to; ask me if it is not clear - what to do.) - - The "snap:" enforces -snapfb mode which appears to be necessary. The - read pointer for video capture devices cannot be repositioned (which - would be needed for scanline polling), but you can read a full frame - of data from the device. - - On Linux, if the Video4Linux API is present or the v4l-info(1) program - (related to xawtv) exists in in PATH, then x11vnc can be instructed to - try it to determine the -rawfb WxHxB parameters for you automatically. - In this case one would just type: - x11vnc -rawfb video - - or "-rawfb video1" for the 2nd video device, etc. - - x11vnc has also been extended to use the Video4Linux API over v4l-info - if it is available at build time. This enables setting parameters - (e.g. size and brightness) via x11vnc. See the description below. - Without Video4Linux you will need to initialize the settings of the - video device using something like xawtv or spcaview (and then hope the - settings persist until x11vnc reopens the device.) - - Many video4linux drivers tend to set the framebuffer to be 24bpp (as - opposed to 32bpp.) Since this can cause problems with VNC viewers, - etc, the -24to32 option will be automatically imposed when in 24bpp. - - Note that by its very nature, video capture involves rapid change in - the framebuffer. This is especially true for cameras where slight - wavering in brightness is always happening. This can lead to much - network bandwidth consumption for the VNC traffic and also local CPU - and I/O resource usage. You may want to experiment with "dialing down" - the framerate via the -wait, -slow_fb, or -defer options. Decreasing - the window size and bpp also helps. - - - Setting Camera/Tuner parameters via x11vnc: - - There is also some support for setting parameters of the capture - device. This is done via "-rawfb video:". This could be - useful for unattended startup at boottime, etc. Here is the -help - description: - - A more sophisticated video device scheme allows initializing the - device's settings using: - - -rawfb video: - - The prefix could also be, as above, e.g. "video1:" to specify the - device file. The v4l API must be available for this to work. - Otherwise, you will need to try to initialize the device with an - external program, e.g. xawtv, spcaview, and hope they persist when - x11vnc re-opens the device. - - is a comma separated list of key=value pairs. The - device's brightness, color, contrast, and hue can be set to - percentages, e.g. br=80,co=50,cn=44,hu=60. - - The device filename can be set too if needed (if it does not start - with "video"), e.g. fn=/dev/qcam. - - The width, height and bpp of the framebuffer can be set via, e.g., - w=160,h=120,bpp=16. - - Related to the bpp above, the pixel format can be set via the - fmt=XXX, where XXX can be one of: GREY, HI240, RGB555, RGB565, - RGB24, and RGB32 (with bpp 8, 8, 16, 16, 24, and 32 respectively.) - See http://www.linuxtv.org for more info (V4L api.) - - For TV/rf tuner cards one can set the tuning mode via tun=XXX where - XXX can be one of PAL, NTSC, SECAM, or AUTO. - - One can switch the input channel by the inp=XXX setting, where XXX - is the name of the input channel (Television, Composite1, S-Video, - etc.) Use the name that is in the information about the device that - is printed at startup. - - For input channels with tuners (e.g. Television) one can change - which station is selected by the sta=XXX setting. XXX is the - station number. Currently only the ntsc-cable-us (US cable) - channels are built into x11vnc. See the -freqtab option below to - supply one from xawtv. If XXX is greater than 500, then it is - interpreted as a raw frequency in KHz. - - Example: - - -rawfb video:br=80,w=320,h=240,fmt=RGB32,tun=NTSC,sta=47 - - one might need to add inp=Television too for the input channel to - be TV if the card doesn't come up by default in that one. - - Note that not all video capture devices will support all of the - above settings. - - See the -pipeinput VID option below for a way to control the - settings through the VNC Viewer via keystrokes. - - As above, if you specify a "@WxHxB..." after the string - they are used verbatim: the device is not queried for the current - values. Otherwise the device will be queried. - - Also, if you supply the "-pipeinput VID" (or use "-rawfb Video") - option you can control the settings to some degree via keystroke - mappings, e.g. B to increase the brightness or Up arrow to change the - TV station: - - For "-pipeinput VID" and you are using the -rawfb for a video - capture device, then an internal list of keyboard mappings is used - to set parameters of the video. The mappings are: - - "B" and "b" adjust the brightness up and down. - "H" and "h" adjust the hue. - "C" and "c" adjust the colour. - "N" and "n" adjust the contrast. - "S" and "s" adjust the size of the capture screen. - "I" and "i" cycle through input channels. - Up and Down arrows adjust the station (if a tuner) - F1, F2, ..., F6 will switch the video capture pixel - format to HI240, RGB565, RGB24, RGB32, RGB555, and - GREY respectively. See -rawfb video for details. - - See also the -freqtab option to supply your own xawtv channel to - frequency mappings for your country (only ntsc-cable-us is built into - x11vnc.) - - - Q-115: Can I connect via VNC to a Qt-embedded/Qt-enhanced/Qtopia - application running on my handheld, cell phone, or PC using the Linux - console framebuffer (i.e. not X11)? - - Yes, the basic method for this is the -rawfb scheme where the Linux - console framebuffer (usually /dev/fb0) is polled and the uinput driver - is used to inject keystrokes and mouse input. Often you will just have - to type: - x11vnc -rawfb console - - (you may need to enable the uinput driver on the system via "modprobe - uinput; mknod /dev/input/uinput c 10 223") If this does not find the - correct frame buffer properties figure them out or guess them and use - something like: - x11vnc -rawfb /dev/fb0@640x480x16 - - Also, to force usage of the uinput injection method use "-pipeinput - UINPUT". See the -pipeinput description for tunable parameters, etc. - - One problem with the x11vnc uinput scheme is that it cannot guess the - mouse motion "acceleration" used by the windowing application (e.g. - QWS or X11.) For X11 and Qt-embedded the acceleration is usually 2 - (i.e. a dx of 1 from the mouse yields a 2 pixel displacement of the - mouse cursor.) The default x11vnc uses is 2, since that is often used. - However for one Qt-embedded system we needed to do: - x11vnc -rawfb console -pipeinput UINPUT:accel=4.0 - - to get reasonable positioning of the mouse. - - Even with the correct acceleration setting there is still some drift - (probably because of the mouse threshold where the acceleration kicks - in) and so x11vnc needs to reposition the cursor from 0,0 about 5 - times a second. See the -pipeinput UINPUT option for tuning parameters - that can be set (there are some experimental thresh=N tuning - parameters as well) - - Currently, one can expect mouse input to be a little flakey. All in - all, the Linux framebuffer input mechanism for Qt-embedded framebuffer - apps is not perfect, but it is usable. - - If you need to create a smaller x11vnc binary for a handheld - environment be sure to run strip(1) on it and also consider - configuring with, e.g. "env CPPFLAGS='-DSMALL_FOOTPRINT=1' ./configure - ..." to remove rarely used features and large texts (use 2 or 3 - instead of 1 to remove more.) Currently (Jul/2006) this can lower the - size of the x11vnc from 1.1MB to 0.6-0.7MB. - - The x11vnc uinput method applies to nearly anything on the Linux - framebuffer console, not just Qt-embedded/Qtopia. DirectFB, SDL using - fbcon driver, SVGAlib applications can also be viewed and interacted - with. Even a Linux X session can be viewed and interacted with without - using X11 (and x11vnc does not have to terminate when the X server - restarts!) The Linux Text consoles (F1-F6) also work. - - Note that Qt-embedded supplies its own VNC graphics driver, but it - cannot do both the Linux console framebuffer and VNC at the same time, - which is often what is desired from VNC. - - Update: We are finding some setups like Qtopia on the IPAQ do not - allow mouse input via uinput. Please help us debug this problem by - trying x11vnc on your device and letting us know what does and does - not work. See the next FAQ for a possible workaround for touchscreens. - - - Q-116: How do I inject touch screen input into an - Qt-embedded/Qt-enhanced/Qtopia cell phone such as openmoko/qtmoko Neo - Freerunner? - - The qtmoko project does not use X11 for the graphical display. - Unfortunately the Linux uinput method described in the previous FAQ - does not work because Qt is using TSLIB (touch screen library) to - process the input and it only reads from one device (often - /dev/input/event1) and not from the new UINPUT device that x11vnc - creates (under -pipeinput UINPUT) - - So something else needs to be done. It was discovered that by simply - writing the touchscreen events directly to /dev/input/event1 then - input can be injected into the system. There is no x11vnc builtin mode - for this yet (until we understand it better), but there is a working - script provided in x11vnc/misc/qt_tslib_inject.pl. So one could use it - this way for example: - x11vnc ... -rawfb console -pipeinput path/to/qt_tslib_inject.pl -env INJECT_O -PTIONS=clickonly,cal=/etc/pointercal - - Read the script for how to enable other options and what the above - options mean (e.g. /etc/pointercal contains TSLIB's calibration - parameters and are necessary to achieve accurate pointing.) - - The x11vnc/misc/qt_tslib_inject.pl script can potentially be modified - to handle other devices where the uinput method fails. It could also - be modified to create 'hot keys', etc. - - Please let us know how things go if you try this out; there is much to - learn about synthetic input injection in handhelds and cell phones. As - we learn more we can develop a builtin x11vnc mode for this sort of - injection. - - Update Dec/2010: There is experimental built-in UINPUT support in the - x11vnc development tarball for qtmoko with touchpad managed by tslib. - See -pipeinput UINPUT for more info. Here is an example: - x11vnc -rawfb console -pipeinput UINPUT:touch,tslib_cal=/etc/pointercal,dire -ct_abs=/dev/input/event1,nouinput,dragskip=3 - - - Q-117: Now that non-X11 devices can be exported via VNC using x11vnc, - can I build it with no dependencies on X11 header files and libraries? - - Yes, as of Jul/2006 x11vnc enables building for -rawfb only support. - Just do something like when building: - ./configure --without-x (plus any other flags) - make - - You can then test via "ldd x11vnc" that the binary does not depend on - libX11.so, etc. See the previous FAQ's for non-X11 framebuffer usage. - If you use this for an interesting non-X11 application please let us - know what you did. - - - Q-118: How do I cross compile x11vnc for a different architecture than - my Linux i386 or amd64 PC? - - You will need a cross-compiling toolchain. Perhaps your distro - provides these or you can find a HOWTO for your distro. We found a - nice one at qtmoko.org for building armel binaries on Debian Linux - i386 machines. It includes most of the libraries that x11vnc needs. We - use that example here. - - We ran this script to set PATH, configure, and build: -#!/bin/sh - -# toolchain from: qtmoko-debian-toolchain-armv4t-eabi.tar.gz - -export PATH=/opt/toolchains/arm920t-eabi/bin:$PATH - -env CC=arm-linux-gcc ./configure --host=arm-linux --without-avahi - -make - -arm-linux-strip ./x11vnc/x11vnc -ls -l ./x11vnc/x11vnc - - Note we had to include --without-avahi due to lack of - libavahi-client.so.3 supplied by the toolchain we used. One would need - to add it if it was desired on the target machine. We also stripped - the binary to make it smaller. - - For an embedded system one may also want to add --without-x if the - embedded system does not use X11 and the -rawfb mechanism must be - used. - - - Q-119: Does x11vnc support Mac OS X Aqua/Quartz displays natively - (i.e. no X11 involved)? - - Yes, since Nov/2006 in the development tree (x11vnc-0.8.4 tarball) - there is support for native Mac OS X Aqua/Quartz displays using the - -rawfb mechanism described above. The mouse and keyboard input is - achieved via Mac OS X API's. - - So you can use x11vnc as an alternative to OSXvnc (aka Vine Server), - or Apple Remote Desktop (ARD). Perhaps there is some x11vnc feature - you'd like to use on Mac OS X, etc. For a number of activities (e.g. - window drags) it seems to be faster than OSXvnc. - - Notes: - - X11: x11vnc will also work (as it has for years) with a X11 server - (XDarwin) running on Mac OS X (people often install this software to - display remote X11 apps on their Mac OS X system, or use some old - favorites locally such as xterm.) However in this case x11vnc will - only work reasonably in single window -id windowid mode (and the - window may need to have mouse focus.) - - If you do not have the DISPLAY env. variable set, x11vnc will assume - native Aqua/Quartz on Mac OS X, however if DISPLAY is set it will - assume an X11 connection. Use "-rawfb console" to force the native - display (or unset DISPLAY.) - - Update: Leopard sets DISPLAY by default in all sessions. Since it - starts with the string "/tmp/" x11vnc will use that to know if it - should ignore it. Use "-display :0.0" to force it. - - Building: If you don't have the X11 build and runtime packages - installed you will need to build it like this: - (cd to the e.g. x11vnc-0.9, source directory) - ./configure --without-x - make - - Win2VNC/x2vnc: One handy use is to use the -nofb mode to redirect - mouse and keyboard input to a nearby Mac (i.e. one to the side of your - desk) via x2vnc or Win2VNC. See this FAQ for more info. - - Options: Here are the Mac OS X specific x11vnc options: - -macnodim For the native Mac OS X server, disable dimming. - -macnosleep For the native Mac OS X server, disable display sleep -. - -macnosaver For the native Mac OS X server, disable screensaver. - -macnowait For the native Mac OS X server, do not wait for the - user to switch back to his display. - -macwheel n For the native Mac OS X server, set the mouse wheel - speed to n (default 5.) - -macnoswap For the native Mac OS X server, do not swap mouse - buttons 2 and 3. - -macnoresize For the native Mac OS X server, do not resize or rese -t - the framebuffer even if it is detected that the scree -n - resolution or depth has changed. - -maciconanim n For the native Mac OS X server, set n to the number - of milliseconds that the window iconify/deiconify - animation takes. In -ncache mode this value will be - used to skip the animation if possible. (default 400) - -macmenu For the native Mac OS X server, in -ncache client-sid -e - caching mode, try to cache pull down menus (not perfe -ct - because they have animated fades, etc.) - - PasteBoard/Clipboard: There is a bug that the Clipboard (called - PasteBoard on Mac it appears) exchange will not take place unless - x11vnc was started from inside the Aqua display (e.g. started inside a - Terminal app window.) Otherwise it cannot connect to the PasteBoard - server. So Clipboard exchange won't work for our standard "ssh in" - startup scheme. - - Hopefully this deficiency can be removed, but until then for Clipboard - exchange to work you will need to start x11vnc inside the desktop - session (i.e. either start it running before you leave, or start up a - 2nd x11vnc inside from a 1st one started outside, or use the apple - script below) - - Here also is a osascript trick that seems to work (it opens the - Terminal app and instructs it to start x11vnc): - -#!/bin/sh -# -# start_x11vnc: start x11vnc in a Terminal window -# (this will allow Clipboard/Pasteboard exchange to work) - -tmp=/tmp/start_x11vnc.$$ - -cat > $tmp < vncviewer -listen - client2> vncviewer -listen - client3> vncviewer -listen - ... - client64> vncviewer -listen - - (e.g. client1> is the cmdline prompt on machine client1 ... etc) and - all the repeaters R are started like this: - repeater1> x11vnc -reflect listen -connect client1,client2,...client8 - repeater2> x11vnc -reflect listen -connect client9,client10,...client16 - ... - repeater8> x11vnc -reflect listen -connect client57,client58,...client64 - - and finally the main server is started to kick the whole thing into - motion: - vncserver> x11vnc -display :0 -connect repeater1,repeater2,...repeater8 - - (or instruct a non-x11vnc VNC server to reverse connect to the - repeaters.) For a classroom broadcasting setup one might have the - first two sets of commands start automatically at bootup or when - someone logs in, and then start everything up with the S server. One - may even be able to script the forward connection bootstrap case, let - us know what you did. A really nice thing would be some sort of - auto-discovery of your repeater, etc... - - Q-121: Can x11vnc be used during a Linux, Solaris, etc. system - Installation so the Installation can be done remotely? - - This can be done, but it doesn't always work because it depends on how - the OS does its install. We have to "sneak in" somehow. Note that some - OS's have a remote install (ssh etc.) built in and so you might want - to use that instead. - - Usually the OS install will have to be a network-install in order to - have networking up during the install. Otherwise, you may have a - (slim) chance to configure the networking manually (ifconfig(8) and - route(8).) - - To avoid library dependencies problems in the typical minimal (e.g. - busybox) installation OS it is a good idea to build a statically - linked x11vnc binary. A way that often works is to do a normal build - and then paste the final x11vnc link line into a shell script. Then - change the "gcc" to "gcc -static" and run the shell script. You may - need to disable features (e.g. "--without-xfixes") if there is not a - static library for the feature available. You may also need to add - extra link options (e.g. "-lXrender") to complete library dependencies - manually. - - Let's call the binary x11vnc.static. Place it on a webserver - somewhere. It may be possible to retrieve it via scp(1) too. - - During the install you need to get a shell to retreive x11vnc.static - and run it. - - If the Solaris install is an older X-based one, there will be a menu - for you to get a terminal window. From that window you might be able - to retrieve x11vnc.static via wget, scp, or ftp. Remember to do "chmod - 755 ./x11vnc.static" and then find the -auth file as in this FAQ. - - If it is a Linux install that uses an X server (e.g. SuSE and probably - Fedora), then you can often get a shell by pressing Ctrl-Alt-F2 or - similar. Then get the x11vnc binary via something like this: - cd /tmp - wget http://192.168.0.22/x11vnc.static - chmod 755 ./x11vnc.static - - Find the name of the auth file as in this FAQ. (maybe run "ps wwaux | - grep auth".) Then run it like this: - ./x11vnc.static -forever -nopw -display :0 -auth /tmp/wherever/the/authfile - - then press Alt-F7 to go back to the X install. You should now be able - to connect via a vnc viewer and continue the install. Watch out for - the display being :1, etc. - - If there is a firewall blocking incoming connections during the - install, use the "-connect hostname" option option for a reverse - connection to the hostname running the VNC viewer in listen mode. - - Debian based installs are either console-text or console-framebuffer - based. These are install (or expert) and installgui (or expertgui) - boot lines, respectively. For the console-text based installs you - probably need to add a boot cmd line option like vga=0x314 (which is - 800x600x16) to get the console-text to use the linux framebuffer - device properly. - - For a Debian console-text based install after the network is - configured press Ctrl-Alt-F2 to get a shell. Retrieve the binary via - wget as above and chmod 755 it. Then run it something like this: - sleep 10; ./x11vnc.static -forever -nopw -rawfb console - - then before the sleep is over press Alt-F1 to get back to the install - virtual console. You should be able to connect via a VNC viewer and - continue with the install. - - For a recent (2009) Debian install we booted with "expert vga=0x301" - and "expert vga=0x311" to get console text based installs at 640x480x8 - and 640x480x16, respectively (replace "expert" with "install" if you - like.) Otherwise it was giving a 16 color 640x480x4 (4 bit per pixel) - display which x11vnc could not handle. - - For Debian console-framebuffer GUI based installs (installgui or - expertgui) we have not be able to enter keystrokes or mouse motions. - This may be resolved if the install had the Linux kernel module - uinput, but it doesn't; one can wget uinput.ko and then run insmod on - it, but the module must match the installation kernel. So, failing - that, you can only do the GUI view-only, which can be handy to watch a - long network install from your desk instead of in front of the machine - being installed. For these, after the network is configured press - Ctrl-Alt-F2 to get a shell. Retrieve the binary via wget as above and - chmod 755 it. Then run it something like this: - sleep 10; ./x11vnc.static -forever -nopw -rawfb console - - then before the sleep is over press Alt-F5 to get back to the GUI - install console. You should be able to connect via a VNC viewer and - watch the install. - [Misc: Clipboard, File Transfer/Sharing, Printing, Sound, Beeps, - Thanks, etc.] - - Q-122: Does the Clipboard/Selection get transferred between the - vncviewer and the X display? - - As of Jan/2004 x11vnc supports the "CutText" part of the RFB (aka VNC) - protocol. When text is selected/copied in the X session that x11vnc is - polling it will be sent to connected VNC viewers. And when CutText is - received from a VNC viewer then x11vnc will set the X11 selections - PRIMARY, CLIPBOARD, and CUTBUFFER0 to it. x11vnc is able to hold the - PRIMARY and CLIPBOARD selections (Xvnc does not seem to do this.) - - The X11 selections can be confusing, especially to those coming from - Windows or MacOSX where there is just a single 'Clipboard'. The X11 - CLIPBOARD selection is a lot like that of Windows and MacOSX, e.g. - highlighted text is sent to the clipboard when the user activates - "Edit -> Copy" or presses "Control+C" (and pasting it via "Edit -> - Paste" or "Control+V".) The X11 PRIMARY selection has been described - as 'for power users' or 'an Easter Egg'. As soon as text is - highlighted it is set to the PRIMARY selection and so it is - immediately ready for pasting, usually via the Middle Mouse Button or - "Shift+Insert". See this jwz link for more information. - - x11vnc's default behavior is to watch both CLIPBOARD and PRIMARY and - whenever one of them changes, it sends the new text to connected - viewers. Note that since the RFB protocol only has a single "CutText" - then both selections are "merged" to some degree (and this can lead to - confusing results.) One user was confused why x11vnc was "forgetting" - his CLIPBOARD selection and the reason was he also changed PRIMARY - some time after he copied text to the clipboard. Usually an app will - set PRIMARY as soon as any text is highlighted so it easy to see how - CLIPBOARD was forgotten. Use the -noprimary described below as a - workaround. Similarly, by default when x11vnc receives CutText it sets - both CLIPBOARD and PRIMARY to it (this is probably less confusing, but - could possibly lead to some failure modes as well.) - - You may not like these defaults. Here are ways to change the behavior: - * If you don't want the Clipboard/Selection exchanged at all use the - -nosel option. - * If you want changes in PRIMARY to be ignored use the -noprimary - option. - * If you want changes in CLIPBOARD to be ignored use the - -noclipboard option. - * If you don't want x11vnc to set PRIMARY to the "CutText" received - from viewers use the -nosetprimary option. - * If you don't want x11vnc to set CLIPBOARD to the "CutText" - received from viewers use the -nosetclipboard option. - - You can also fine-tune it a bit with the -seldir dir option and also - -input. - - You may need to watch out for desktop utilities such as KDE's - "Klipper" that do odd things with the selection, clipboard, and - cutbuffers. - - - Q-123: Can I use x11vnc to record a Shock Wave Flash (or other format) - video of my desktop, e.g. to record a tutorial or demo? - - Yes, it is possible with a number of tools that record VNC and - transform it to swf format or others. One such popular tool is - pyvnc2swf. There are a number of tutorials (broken link?) on how to do - this. Another option is to use the vnc2mpg that comes in the - LibVNCServer package. - An important thing to remember when doing this is that tuning - parameters should be applied to x11vnc to speed up its polling for - this sort of application, e.g. "-wait 10 -defer 10". - - Q-124: Can I transfer files back and forth with x11vnc? - - As of Oct/2005 and May/2006 x11vnc enables, respectively, the TightVNC - and UltraVNC file transfer implementations that were added to - libvncserver. This currently works with TightVNC and UltraVNC viewers - (and Windows viewers only support filetransfer it appears... but they - do work to some degree under Wine on Linux.) - - The SSVNC Unix VNC viewer supports UltraVNC file transfer by use of a - Java helper program. - - TightVNC file transfer is off by default, if you want to enable it use - the -tightfilexfer option. - - UltraVNC file transfer is off by default, to enable it use something - like "-rfbversion 3.6 -permitfiletransfer" - options (UltraVNC incorrectly uses the RFB protocol version to - determine if its features are available, so x11vnc has to pretend to - be version 3.6.) As of Sep/2006 "-ultrafilexfer" is an alias for these - two options. Note that running as RFB version 3.6 may confuse other - VNC Viewers. - - Sadly you cannot do both -tightfilexfer and -ultrafilexfer at the same - time because the latter requires setting the version to 3.6 and - tightvnc will not do filetransfer when it sees that version number. - - Also, because of the way the LibVNCServer TightVNC file transfer is - implemented, you cannot do Tightvnc file transfer in -unixpw mode. - However, UltraVNC file transfer does work in -unixpw (but if a client - tries it do a filetransfer during the login process it will be - disconnected.) - - IMPORTANT: please understand if -ultrafilexfer or -tightfilexfer is - specified and you run x11vnc as root for, say, inetd or display - manager (gdm, kdm, ...) access and you do not have it switch users via - the -users option, then VNC Viewers that connect are able to do - filetransfer reads and writes as *root*. - - The UltraVNC and TightVNC settings can be toggled on and off inside - the gui or by -R remote control. However for TightVNC the changed - setting only applies for NEW clients, current clients retain their - TightVNC file transfer ability. For UltraVNC it works better, however - if an UltraVNC client has initiated a file transfer dialog it will - remain in effect until the dialog is closed. If you want to switch - between UltraVNC and TightVNC file transfer in the gui or by remote - control you will probably be foiled by the "-rfbversion 3.6" issue. - - - Q-125: Which UltraVNC extensions are supported? - - Some of them are supported. To get UltraVNC Viewers to attempt to use - these extensions you will need to supply this option to x11vnc: - -rfbversion 3.6 - - Or use -ultrafilexfer which is an alias for the above option and - "-permitfiletransfer". UltraVNC evidently treats any other RFB version - number as non-UltraVNC. - - Here are a list of the UltraVNC extensions supported by x11vnc: - * ServerInput: "Toggle Remote Input and Remote Blank Monitor" - * FileTransfer: "Open File Transfer..." - * SingleWindow: "Select Single Window..." - * TextChat: "Open Chat..." - * 1/n Server Scaling - - The SSVNC Unix VNC viewer supports these UltraVNC extensions. - - To disable SingleWindow and ServerInput use -noultraext (the others - are managed by LibVNCServer.) See this option too: -noserverdpms. - - Also, the UltraVNC repeater proxy is supported for use with reverse - connections: "-connect repeater://host:port+ID:NNNN". Use it for both - plaintext and SSL connections. This mode can send any string before - switching to the VNC protocol, and so could be used with other - proxy/gateway tools. Also, a perl repeater implemention is here: - ultravnc_repeater.pl - - - Q-126: Can x11vnc emulate UltraVNC's Single Click helpdesk mode for - Unix? I.e. something very simple for a naive user to initiate a - reverse vnc connection from their Unix desktop to a helpdesk - operator's VNC Viewer. - - Yes, UltraVNC's Single Click (SC) mode can be emulated fairly well on - Unix. - - We use the term "helpdesk" below, but it could be any sort of remote - assistance you want to set up, e.g. something for Unix-using friends - or family to use. This includes Mac OS X. - - Assume you create a helpdesk directory "hd" on your website: - http://www.mysite.com/hd (any website that you can upload files to - should work, although remember the user will be running the programs - you place there.) - - In that "hd" subdirectory copy an x11vnc binary to be run on the Unix - user's machine (e.g. Linux, etc) and also create a file named "vnc" - containing the following: -#!/bin/sh - -webhost="http://www.mysite.com/hd" # Your helpdesk dir URL. - -vnchost="ip.someplace.net" # Your host running 'vncviewer -listen' - # It could also be your IP number. If it is - # a router/firewall, you will need to - # configure it to redirect port 5500 to you -r - # workstation running 'vncviewer -listen' - -dir=/tmp/vnc_helpdesk.$$ # Make a temporary working dir. -mkdir $dir || exit 1 -cd $dir || exit 1 - -trap "cd /tmp; rm -rf $dir" 0 2 15 # Cleans up on exit. - -wget $webhost/x11vnc # Fetch x11vnc binary. If multi- -chmod 755 ./x11vnc # platform, use $webhost/`uname`/x11vnc - # or similar. - -./x11vnc -connect_or_exit $vnchost -rfbport 0 -nopw - - with the hostnames / IP addresses customized to your case. - - On the helpdesk VNC viewer machine (ip.someplace.net in this example) - you have the helpdesk operator running VNC viewer in listen mode: - vncviewer -listen - - or if on Windows, etc. somehow have the VNC viewer be in "listen" - mode. - - Then, when the naive user needs assistance you instruct him to open up - a terminal window on his Unix desktop and paste the following into the - shell: - wget -qO - http://www.mysite.com/hd/vnc | sh - - - and then press Enter. You could have this instruction on a web page or - in an email you send him, etc. This requires that the wget is - installed on the user's Unix machine (he might only have curl or lynx, - see below for more info.) - - - So I guess this is about 3-4 clicks (start a terminal and paste) and - pressing "Enter" instead of "single click"... - - See this page for some variations on this method, e.g. how to add a - password, SSL Certificates, etc. - - - If you don't have a website (there are many free ones) or don't want - to use one you will have to email him all of the ingredients (x11vnc - binary and a launcher script) and tell him how to run it. This could - be easy or challenging depending on the skill of the naive unix - user... - - A bit of obscurity security could be put in with a -passwd, -rfbauth - options, etc. (note that x11vnc will require a password even for - reverse connections.) More info here. - - - Firewalls: If the helpdesk (you) with the vncviewer is behind a - NAT/Firewall/Router the router will have to be configured to redirect - a port (i.e. 5500 or maybe different one if you like) to the vncviewer - machine. If the vncviewer machine also has its own host-level - firewall, you will have to open up the port there as well. - - NAT-2-NAT: There is currently no way to go "NAT-2-NAT", i.e. both User - and Helpdesk workstations behind NAT'ing Firewall/Routers without - configuring a router to do a port redirection (i.e. on your side, the - HelpDesk.) To avoid modifying either firewall/router, one would need - some public (IP address reachable on the internet) redirection/proxy - service. Perhaps such a thing exists. http://sc.uvnc.com provides this - service for their UltraVNC Single Click users. - - Update: It may be possible to do "NAT-2-NAT" with a UDP tunnel such as - http://samy.pl/pwnat/. All that is required is that both NAT firewalls - allow in UDP packets from an IP address to which a UDP packet has - recently been sent to. If you try it out let us know how it went. - - - Very Naive Users: - - If it is beyond the user how to open a terminal window and paste in a - command (you have my condolences...) you would have to somehow setup - his Web browser to download the "vnc" file (or a script containing the - above wget line) and prompt the user if he wants to run it. This may - be tricky to set up (which is probably a good thing to not have the - web browser readily run arbitrary programs downloaded from the - internet...) - - One command-line free way, tested with KDE, is to name the file vnc.sh - and then instruct the user to right-click on the link and do "Save - Link As" to his Desktop. It will appear as an icon, probably one that - looks like a terminal or a command line prompt. He next should - right-click on the icon and select "Properties" and go to the - "Permissions" tab. Then in that dialog select the checkbox "Is - executable". He should then be able to click on the icon to launch it. - Another option is to right-click on the icon and select "Open With -> - Other ..." and for the name of the application type in "/bin/sh". - Unfortunately in both cases the command output is lost and so errors - cannot be debugged as easily. A similar thing appears to work in GNOME - if under "Properties -> Permissions" they click on "Execute" checkbox - for "Owner". Then when they click on the icon, they will get a dialog - where they can select "Run in Terminal". In general for such cases, if - it is feasible, it might be easier to ssh to his machine and set - things up yourself... - - - SSL Encrypted Helpdesk Connections: - - As of Apr/2007 x11vnc supports reverse connections in SSL and so we - can do this. On the Helpdesk side (Viewer) you will need STUNNEL or - better use the Enhanced TightVNC Viewer (SSVNC) package we provide - that automates all of the SSL for you. - - To do this create a file named "vncs" in the website "hd" directory - containing the following: -#!/bin/sh - -webhost="http://www.mysite.com/hd" # Your helpdesk dir URL. - -vnchost="ip.someplace.net" # Your host running 'vncviewer -listen' - # It could also be your IP number. If it is - # a router/firewall, you will need to - # configure it to redirect port 5500 to you -r - # workstation running 'vncviewer -listen' - -dir=/tmp/vnc_helpdesk.$$ # Make a temporary working dir. -mkdir $dir || exit 1 -cd $dir || exit 1 - -trap "cd /tmp; rm -rf $dir" 0 2 15 # Cleans up on exit. - -wget $webhost/x11vnc # Fetch x11vnc binary. If multi- -chmod 755 ./x11vnc # platform, use $webhost/`uname`/x11vnc - # or similar. - -./x11vnc -connect_or_exit $vnchost -rfbport 0 -nopw -ssl # Note -ssl option. - - with the hostnames or IP addresses customized to your case. - - The only change from the "vnc" above is the addition of the -ssl - option to x11vnc. This will create a temporary SSL cert: openssl(1) - will need to be installed on the user's end. A fixed SSL cert file - could be used to avoid this (and provide some authentication; more - info here.) - - The naive user will be doing this: - wget -qO - http://www.mysite.com/hd/vncs | sh - - - (or perhaps even use https:// if available.) - - But before that, the helpdesk operator needs to have "vncviewer - -listen" running as before, however he needs an SSL tunnel at his end. - The easiest way to do this is use Enhanced TightVNC Viewer (SSVNC). - Start it, and select Options -> 'Reverse VNC Connection (-listen)'. - Then UN-select 'Verify All Certs' (this can be enabled later if you - want; you'll need the x11vnc SSL certificate), and click 'Listen'. - - If you don't want to use SSVNC for the viewer, but rather set up - STUNNEL manually instead, make a file "stunnel.cfg" containing: -foreground = yes -pid = - -[vnc] -accept = 5500 -connect = localhost:5501 - - and run: - stunnel ./stunnel.cfg - - and then start the "vncviewer -listen 1" (i.e. 1 to correspond to the - 5501 port.) Note that this assumes the stunnel install created a - Server SSL cert+key, usually /etc/stunnel/stunnel.pem (not all distros - will do this.) Also, that file is by default only readable by root, so - stunnel needs to be run as root. If your system does not have a key - installed or you do not want to run stunnel as root (or change the - permissions on the file), you can use x11vnc to create one for you for - example: - x11vnc -sslGenCert server self:mystunnel - - answer the prompts with whatever you want; you can take the default - for all of them if you like. The openssl(1) package must be installed. - See this link and this one too for more info on SSL certs. This - creates $HOME/.vnc/certs/server-self:mystunnel.pem, then you would - change the "stunnel.cfg" to look something like: -foreground = yes -pid = -cert = /home/myusername/.vnc/certs/server-self:mystunnel.pem - -[vnc] -accept = 5500 -connect = localhost:5501 - - In any event, with stunnel having been setup, the naive user is - instructed to paste in and run: - wget -qO - http://www.mysite.com/hd/vncs | sh - - - to pick up the vncs script this time. - - Of course if a man-in-the-middle can alter what the user downloads - then all bets are off!. - - More SSL variations and info about certificates can be found here. - - - OpenSSL libssl.so.0.9.7 problems: - - If you build your own stunnel or x11vnc for deployment, you may want - to statically link libssl.a and libcrypto.a into it because Linux - distros are currently a bit of a mess regarding which version of - libssl is installed. - - You will find the details here. - - - Q-127: Can I (temporarily) mount my local (viewer-side) Windows/Samba - File share on the machine where x11vnc is running? - - You will have to use an external network redirection for this. - Filesystem mounting is not part of the VNC protocol. - - We show a simple Samba example here. - - First you will need a tunnel to redirect the SMB requests from the - remote machine to the one you sitting at. We use an ssh tunnel: - sitting-here> ssh -C -R 1139:localhost:139 far-away.east - - Or one could combine this with the VNC tunnel at the same time, e.g.: - sitting-here> ssh -C -R 1139:localhost:139 -t -L 5900:localhost:5900 far-away -.east 'x11vnc -localhost -display :0' - - Port 139 is the Windows Service port. For Windows systems instead of - Samba, you may need to use the actual IP address of the Window machine - instead of "localhost" in the -R option (since the Windows service - does not listen on localhost by default.) - - Note that we use 1139 instead of 139 on the remote side because 139 - would require root permission to listen on (and you may have a samba - server running on it already.) - - The ssh -C is to enable compression, which might speed up the data - transfers. - - Depending on the remote system side configuration, it may or may not - be possible to mount the SMB share as a non-root user. Try it first as - a non-root user and if that fails you will have to become root. - - We will assume the user name is "fred" and we will try to mount the - viewer-side Windows SMB share "//haystack/pub" in - /home/fred/smb-haystack-pub. - far-away> mkdir -p /home/fred/smb-haystack-pub - far-away> smbmount //haystack/pub /home/fred/smb-haystack-pub -o username=fre -d,ip=127.0.0.1,port=1139 - - (The 2nd command may need to be run as root.) Then run "df" or "ls -l - /home/fred/smb-haystack-pub" to see if it is mounted properly. Consult - the smbmount(8) and related documentation (it may require some - fiddling to get write permissions correct, etc.) To unmount: - far-away> smbumount /home/fred/smb-haystack-pub - - At some point we hope to fold some automation for SMB ssh redir setup - into the Enhanced TightVNC Viewer (SSVNC) package we provide (as of - Sep 2006 it is there for testing.) - - - Q-128: Can I redirect CUPS print jobs from the remote desktop where - x11vnc is running to a printer on my local (viewer-side) machine? - - You will have to use an external network redirection for this. - Printing is not part of the VNC protocol. - - We show a simple Unix to Unix CUPS example here. Non-CUPS port - redirections (e.g. LPD) should also be possible, but may be a bit more - tricky. If you are viewing on Windows SMB and don't have a local cups - server it may be trickier still (see below.) - - First you will need a tunnel to redirect the print requests from the - remote machine to the one you sitting at. We use an ssh tunnel: - sitting-here> ssh -C -R 6631:localhost:631 far-away.east - - Or one could combine this with the VNC tunnel at the same time, e.g.: - sitting-here> ssh -C -R 6631:localhost:631 -t -L 5900:localhost:5900 far-away -.east 'x11vnc -localhost -display :0' - - Port 631 is the default CUPS port. The above assumes you have a Cups - server running on your viewer machine (localhost:631), if not, use - something like my-cups-srv:631 (the viewer-side Cups server) in the -R - instead. - - Note that we use 6631 instead of 631 on the remote side because 631 - would require root permission to listen on (and you likely have a cups - server running on it already.) - - Now the tricky part: to get applications to notice your cups - server/printer on localhost:6631. - - If you have administrative privilege (i.e. root password) on the - x11vnc side where the desktop is running, it should be easy to add the - printer through some configuration utility (e.g. in KDE: Utilities -> - Printing -> Printing Manager, and then supply admin password, and then - Add Printer/Class, and then fill in the inquisitive wizard. Most - important is the "Remote IPP server" panel where you put in localhost - for Host and 6631 for Port.) The main setting you want to convey is - the host is localhost and the port is non-standard (e.g. 6631.) Some - configuration utilities will take an Internet Printing Protocol (IPP) - URI, e.g. http://localhost:6631/printers/, - ipp://localhost:6631/printers/printer-name, - ipp://localhost:6631/ipp/printer-name, etc. Check your CUPS - documentation and admin interfaces to find what the syntax is and what - the "printer name" is. - - If you do not have root or print admin privileges, but are running a - recent (version 1.2 or greater) of the Cups client software, then an - easy way to temporarily switch Cups servers is to create the directory - and file: $HOME/.cups/client.conf on the remote side with a line like: - ServerName localhost:6631 - - When not using x11vnc for remote access you can comment the above line - out with a '#' (or rename the client.conf file), to have normal cups - operation. - - Unfortunately, running applications may need to be restarted to notice - the new printers (libcups does not track changes in client.conf.) - Depending on circumstances, a running application may actually notice - the new printers without restarting (e.g. no print dialog has taken - place yet, or there are no CUPS printers configured on the remote - side.) - - Cups client software that is older (1.1) does not support appending - the port number, and for newer ones there is a bug preventing it from - always working (fixed in 1.2.3.) Kludges like these at the command - line will work: - far-away> env CUPS_SERVER=localhost IPP_PORT=6631 lpstat -p -d - far-away> env CUPS_SERVER=localhost IPP_PORT=6631 lpr -P myprinter file.ps - far-away> env CUPS_SERVER=localhost IPP_PORT=6631 firefox - - but are somewhat awkward since you have to retroactively set the env. - var IPP_PORT. Its value cannot be broadcast to already running apps - (like the $HOME/.cups/client.conf trick sometimes does.) A common - workaround for an already running app is to somehow get it to "Print - To File", e.g. file.ps and then use something like the lpr example - above. Also, the option "-h host:port" works with CUPS lp(1) and - lpr(1). - - You can also print to Windows shares printers in principle. You may do - this with the smbspool(8) command, or configure the remote CUPS via - lpadmin(8), etc, to use a printer URI something like - smb://machine:port/printer (this may have some name resolution - problems WRT localhost.) Also, as with SMB mounting, the port redir - (-R) to the Windows machine must use the actual IP address instead of - "localhost". - - At some point we hope to fold some automation for CUPS ssh redir setup - into the Enhanced TightVNC Viewer (SSVNC) package we provide (as of - Sep 2006 it is there for testing.) - - - Q-129: How can I hear the sound (audio) from the remote applications - on the desktop I am viewing via x11vnc? - - You will have to use an external network audio mechanism for this. - Audio is not part of the VNC protocol. - - We show a simple Unix to Unix esd example here (artsd should be - possible too, we have also verified the esd Windows port works for the - method described below.) - - First you will need a tunnel to redirect the audio from the remote - machine to the one you sitting at. We use an ssh tunnel: - sitting-here> ssh -C -R 16001:localhost:16001 far-away.east - - Or one could combine this with the VNC tunnel at the same time, e.g.: - sitting-here> ssh -C -R 16001:localhost:16001 -t -L 5900:localhost:5900 far-a -way.east 'x11vnc -localhost -display :0' - - Port 16001 is the default ESD uses. So when an application on the - remote desktop makes a sound it will connect to this tunnel and be - redirected to port 16001 on the local machine (sitting-here in this - example.) The -C option is an attempt to compress the audio a little - bit. - - So we next need a local (sitting-here) esd daemon running that will - receive those requests and play them on the local sound device: - sitting-here> esd -promiscuous -port 16001 -tcp -bind 127.0.0.1 - - See the esd(1) man page for the meaning of the options (the above are - not very secure.) (This method also works with the EsounD windows port - esd.exe) - - To test this sound tunnel, we use the esdplay program to play a simple - .wav file: - far-away> esdplay -s localhost:16001 im_so_happy.wav - - If you hear the sound (Captain Kirk in this example), that means you - are in great shape. - - To run individual audio applications you can use the esddsp(1) - command: - far-away> esddsp -s localhost:16001 xmms - - Then you could try playing some sounds inside xmms. You could also set - the environment variable ESPEAKER=localhost:16001 to not need to - supply the -s option all the time. (for reasons not clear, sometimes - esddsp can figure it out on its own.) All the script esddsp does is to - set ESPEAKER and LD_PRELOAD for you so that when the application opens - the sound device (usually /dev/dsp) its interactions with the device - will be intercepted and sent to the esd daemon running on sitting-here - (that in turn writes them to the real, local /dev/dsp.) - - Redirecting All sound: - - It does not seem to be possible to switch all of the sound of the - remote machine from its sound device to the above esd+ssh tunnel - without some preparation. But it can be done reasonably well if you - prepare (i.e. restart) the desktop with this in mind. - - Here is one way to redirect all sound. The idea is we run the entire - desktop with sound directed to localhost:16001. When we are sitting at - far-away.east we run "esd -promiscuous -port 16001 -tcp -bind - 127.0.0.1" on far-away.east (to be able to hear the sound.) However, - when we are sitting at sitting-here.west we kill that esd process and - run that same esd command on sitting-here.west and start up the above - ssh tunnel. This is a little awkward, but with some scripts one would - probably kill and restart the esd processes automatically when x11vnc - is used. - - So next we have to run the whole desktop pointing toward our esd. Here - is a simple way to test. Log in to the machine via the "FailSafe" - desktop. Then in the lone terminal type something like: - esddsp -s localhost:16001 gnome-session -or: - esddsp -s localhost:16001 startkde - - where the last part is whatever command starts your desktop (even - fvwm2.) This causes the environment variables ESPEAKER and LD_PRELOAD - to be set appropriately and every application (processes with the - desktop as an ancestor) will use them. If this scheme works well you - can make it less klunky by adding the command to your ~/.xsession, - etc. file that starts your default desktop. Or you may be able to - configure your desktop to use localhost:16001, or whatever is needed, - via a gui configuration panel. Some Notes: - * Not all audio applications are compatible with the esd and artsd - mechanisms, but many are. - * The audio is not compressed so you probably need a broadband or - faster connection. Listening to music may not be very pleasant... - (Although we found streaming music from across the US over cable - modem worked OK, but took 200 KB/sec, to use less bandwidth - consider something like "ssh far-away.east 'cat favorite.mp3' | - mpg123 -b 4000 -") - * Linux does not seem to have the concept of LD_PRELOAD_64 so if you - run on a mixed 64- and 32-bit ABI system (e.g. AMD x86_64) some of - the applications will fail to run because LD_PRELOAD will point to - libraries of the wrong wordsize. - * At some point we hope to fold some automation for esd or artsd ssh - redir setup into the Enhanced TightVNC Viewer (SSVNC) package we - provide (as of Sep/2006 it is there for testing.) - - - Q-130: Why don't I hear the "Beeps" in my X session (e.g. when typing - tput bel in an xterm)? - - As of Dec/2003 "Beep" XBell events are tracked by default. The X - server must support the XKEYBOARD extension (this is not on by default - in Solaris, see Xserver(1) for how to turn it on via +kb), and so you - won't hear them if the extension is not present. - - If you don't want to hear the beeps use the -nobell option. If you - want to hear the audio from the remote applications, consider trying a - redirector such as esd. - - - Q-131: Does x11vnc work with IPv6? - - Update: as of Apr/2010 in the 0.9.10 x11vnc development tarball, there - is now built-in support for IPv6 (128 bit internet addresses.) See the - -6 and -connect options for details. - - The remainder of this FAQ entry shows how to do with this with pre - 0.9.10 x11vnc using IPv6 helper tools. - _________________________________________________________________ - - Using an external IPv6 helper: - A way to do this is via a separate helper program such as inetd (or - for encrypted connections: ssh or stunnel.) For example, you configure - x11vnc to be run from inetd or xinetd and instruct it to listen on an - IPv6 address. For xinetd the setting "flags = IPv6" will be needed. - For inetd.conf, an example is: - 5900 stream tcp6 nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc_wrapper.sh - - We also provide a transitional tool in "x11vnc/misc/inet6to4" that - acts as a relay for any IPv4 application to allow connections over - IPv6. For example: - inet6to4 5900 localhost:5900 - - where x11vnc is listening on IPv4 port 5900. - - Also note that not all VNC Viewers are IPv6 enabled, so a redirector - may also be needed for them. The tool "inet6to4 -r ..." can do this as - well. SSVNC (see below) supports IPv6 without need for the helper. - - # ./inet6to4 -help - - inet6to4: Act as an ipv6-to-ipv4 relay for tcp applications that - do not support ipv6. - - Usage: inet6to4 - inet6to4 -r - - Examples: inet6to4 5900 localhost:5900 - inet6to4 8080 web1:80 - inet6to4 -r 5900 fe80::217:f2ff:fee6:6f5a%eth0:5900 - - The -r option reverses the direction of translation (e.g. for ipv4 - clients that need to connect to ipv6 servers.) Reversing is the default - if this script is named 'inet4to6' (e.g. by a symlink.) - - Use Ctrl-C to stop this program. - - You can also set env. vars INET6TO4_LOOP=1 or INET6TO4_LOOP=BG - to have an outer loop restarting this program (BG means do that - in the background), and INET6TO4_LOGFILE for a log file. - Also set INET6TO4_VERBOSE to verbosity level and INET6TO4_WAITTIME - and INET6TO4_PIDFILE (see below.) - - The "INET6TO4_LOOP=BG" and "INET6TO4_LOGFILE=..." env. variables make - the tool run reliably as a daemon for very long periods. Read the top - part of the script for more information. - _________________________________________________________________ - - Encrypted Tunnels with IPv6 Support: - For SSH tunnelled encrypted VNC connections, one can of course use the - IPv6 support in ssh(1). - - For SSL encrypted VNC connections, one possibility is to use the IPv6 - support in stunnel(1). This includes the built-in support via the - -stunnel option. For example: - x11vnc -stunnel SAVE -env STUNNEL_LISTEN=:: -env STUNNEL_DEBUG=1 ... - _________________________________________________________________ - - SSH IPv6 Tricks: - It is interesting to note that ssh(1) can do basically the same thing - as inet6to4 above by: - ssh -g -L 5900:localhost:5901 localhost "printf 'Press Enter to Exit: '; read - x" - - (where we have x11vnc running via "-rfbport 5901" in this case.) - - Note that one can also make a home-brew SOCKS5 ipv4-to-ipv6 gateway - proxy using ssh like this: - ssh -D '*:1080' localhost "printf 'Press Enter to Exit: '; read x" - - then specify a proxy like socks://hostname:1080 where hostname is the - machine running the above ssh command (add -v to ssh for connection - logging info.) - _________________________________________________________________ - - IPv6 SSVNC Viewer: - Our SSVNC VNC Viewer is basically a wrapper for ssh(1) and stunnel(1), - and so it already has good IPv6 support because these two commands do. - On Unix, MacOSX, and Windows nearly all of the the remaining parts of - SSVNC (e.g. the built-in proxying and un-encrypted connections) have - been modified to support IPv6 in SSVNC 1.0.26. - - - - - - - Contributions: - - Q-132: Thanks for your program or for your help! Can I make a - donation? - - Please do (any amount is appreciated; very few have donated) and thank - you for your support! Click on the PayPal button below for more info. - - [x-click-but04.gif]-Submit - - - Q-133: I am experiencing extreme framebuffer update lags and am - using an Intel graphics card. What to do? - - Depending on your graphics card model and x.org driver used, several - approaches might work out for you: - - Some users [have reported](https://github.com/LibVNC/x11vnc/issues/58) - that when using the 'intel' x.org driver, switching the driver's - option named "AccelMethod" to "UXA" helped. - - Others [reported](https://github.com/LibVNC/x11vnc/issues/100) that - using the 'modesetting' x.org driver caused the lags and switching to - the 'intel' x.org driver helped. - - Some [reported](https://github.com/LibVNC/x11vnc/issues/102) that - lags only occured with xfwm as window manager and with x11vnc started - with monitors off, no matter what the x.org driver. In their case, one - of disabling vsync, using 'modesetting' with "AccelMethod" "none" or - disabling compositing all helped. - - -======================================================================= -http://www.karlrunge.com/x11vnc/chainingssh.html: - - - _________________________________________________________________ - - Chaining ssh's: Note that for use of a ssh gateway and -L redirection - to an internal host (e.g. "-L 5900:otherhost:5900") the VNC traffic - inside the firewall is not encrypted and you have to manually log into - otherhost to start x11vnc. Kyle Amon shows a method where you chain - two ssh's together that encrypts all network traffic and also - automatically starts up x11vnc on the internal workstation: -#!/bin/sh -# -gateway="example.com" # or "user@example.com" -host="labyrinth" # or "user@hostname" -user="kyle" - -# Need to sleep long enough for all of the passwords and x11vnc to start up. -# The /dev/null) & - -# Chain the vnc connection thru 2 ssh's, and connect x11vnc to user's display: -# -exec /usr/bin/ssh -t -L 5900:localhost:5900 $gateway \ - /usr/bin/ssh -t -L 5900:localhost:5900 $host \ - sudo /usr/bin/x11vnc -localhost -auth /home/$user/.Xauthority \ - -rfbauth .vnc/passwd -display :0 - - Also note the use of sudo(1) to switch to root so that the different - user's .Xauthority file can be accessed. See the visudo(8) manpage for - details on how to set this up (remove the sudo if you do not want to - do this). One can also chain together ssh's for reverse connections - with vncviewers using the -listen option. For this case -R would - replace the -L (and 5500 the 5900, see the #2 example script above). - If the gateway machine's sshd is configured with GatewayPorts=no (the - default) then the double chaining of "ssh -R ..." will be required for - reverse connections to work. - -======================================================================= -http://www.karlrunge.com/x11vnc/miscbuild.html: - - - _________________________________________________________________ - - Misc. Build problems: We collect here rare build problems some users - have reported and the corresponding workarounds. See also the FAQ's on - building. - _________________________________________________________________ - - ENV parameter: One user had a problem where the build script below was - failing because his work environment had the ENV variable set to a - script that was resetting his PATH so that gcc could no longer be - found. Make sure you do not have any ENV or BASH_ENV in your - environment doing things like that. Typing "unset ENV", etc. before - configuring and building should clear it. - _________________________________________________________________ - - Bash xpg: One user had his bash shell compiled with - --enable-xpg-echo-default that causes some strange behavior with - things like echo "\\1 ..." the configure script executes. In - particular instead of getting "\1" the non-printable character "^A" is - produced, and causes failures at compile time like: - ../rfb/rfbconfig.h:9:22: warning: extra tokens at end of #ifndef directive - - The workaround is to configure like this: - env CONFIG_SHELL=/bin/sh /bin/sh ./configure - - i.e. avoid using the bash with the misbehavior. A bug has been filed - against autoconf to guard against this. - _________________________________________________________________ - - AIX: one user had to add the "X11.adt" package to AIX to get build - header files like XShm.h, etc. - _________________________________________________________________ - - Ubuntu Feisty Fawn 7.04: In May/2007 one user said he needed to add - these packages to compile x11vnc on that Linux distro and version: - apt-get install build-essential make bin86 libjpeg62-dev libssl-dev libxtst-d -ev - - Note that Ubuntu is based on Debian, so perhaps this is the list - needed on Debian (testing?) as well. To build in Avahi (mDNS service - advertising) support it would appear that libavahi-client-dev is - needed as well. - _________________________________________________________________ - - Exceedingly slow compilation: x11vnc has a couple of files which - contain very large "case statements" (over 100 cases) that on some - platforms can take a very long time to compile (in extreme cases over - an hour). However on 32bit Linux with intel/amd processor and gcc - these files usually take less than 10 seconds to compile. For 64bit - systems using gcc the problem appears to be much worse. - - The two files with the large number of cases, remote.c and x11vnc.c, - have no real need to be optimized (the code is used only very - infrequently). So it is fine to supply "-O0" (disables optimization) - to CFLAGS when compiling them. However, it is tricky with - autoconf/automake to do this (especially since both the compiler and - make versions have a big effect). - - So if the compile times are getting too long for you for these two - files you will need to manually change some things. First, run - configure and when it has finished, edit the generated file - x11vnc/Makefile and put these lines at the very top: -x11vnc-x11vnc.o : CFLAGS += -O0 -x11vnc-remote.o : CFLAGS += -O0 - - Those lines assume gnu make (gmake) is being used. If you are using - another make, say Solaris make, insert these instead: -x11vnc-x11vnc.o := CFLAGS += -O0 -x11vnc-remote.o := CFLAGS += -O0 - - You could write a build shell script that modified the Makefile this - way before running make. - - The "-O0" (note it is "capital Oh" followed by "zero") assumes the gcc - compiler. If you are using a different compiler you will need to find - the command line option to disable optimization, or otherwise have the - lines set CFLAGS to the empty string. - _________________________________________________________________ - - Broken Thread Local Storage on SuSE 9.2: Starting with x11vnc 0.9.8 - the bundled libvncserver uses the __thread keyword to make some of the - encodings (i.e. tight) thread safe (multiple VNC clients can be using - tight at the same time in x11vnc -threads mode.) Evidently on the old - SuSE 9.2 system the compiler does not support the thread local storage - properly. Here is an example build failure: -tight.c:1126: error: unrecognizable insn: -(insn:HI 11 10 13 0 (nil) (set (reg/f:SI 59) - (const:SI (plus:SI (symbol_ref:SI ("%lpalette")) - (const_int 2048 [0x800])))) -1 (nil) - (expr_list:REG_EQUAL (const:SI (plus:SI (symbol_ref:SI ("%lpalette")) - (const_int 2048 [0x800]))) - (nil))) -tight.c:1126: internal compiler error: in extract_insn, at recog.c:2175 -Please submit a full bug report, -with preprocessed source if appropriate. -See URL:http://www.suse.de/feedback for instructions. - - The workaround is to disable thread local storage at configure time - like this: -env CPPFLAGS="-DTLS=''" ./configure - - and then build it. - _________________________________________________________________ - -======================================================================= -http://www.karlrunge.com/x11vnc/sunray.html: - - - Sun Ray Notes: - - You can run x11vnc on your (connected or disconnected) SunRay session - (Please remember to use settings like -wait 200, -sb 15, and not - running a screensaver animation (blank instead) to avoid being a - resource hog! x11vnc does induce a lot of memory I/O from polling the - X server. It also helps to have a solid background color, e.g. - -solid). - - News: Sun Ray Remote Control Toolkit: See the nice set of tools in the - Sun Ray Remote Control Toolkit that launch x11vnc automatically for - you for certain usage modes. - - You have to know the name of the machine your SunRay session X server - is running on (so you can ssh into it and start x11vnc). You also need - to know the X11 DISPLAY number for the session: on a SunRay it could - be a large number, e.g. :137, since there are many people with X - sessions (Xsun processes) on the same machine. If you don't know it, - you can get it by running who(1) in a shell on the SunRay server and - looking for the dtlocal entry with your username (and if you don't - even know which server machine has your session, you could login to - all possible ones looking at the who output for your username...). - - I put some code in my ~/.dtprofile script that stores $DISPLAY - (including the hostname) in a ~/.sunray_current file at session - startup (and deletes it when the X session ends) to make it easy to - get at the hostname and X11 display number info for my current X - sessions when I ssh in and am about to start x11vnc. - - SunRay Gotcha #1: Note that even though your SunRay X11 DISPLAY is - something like :137, x11vnc still tries for port 5900 as its listening - port if it can get it, in which case the VNC display (i.e. the - information you supply to the VNC viewer) is something like - sunray-server:0 (note the :0 corresponding to port 5900, it is not - :137). If it cannot get 5900, it tries for 5901, and so on. You can - also try to force the port (and thereby the VNC display) using the - -rfbport NNNN option. - - Especially on a busy Sun Ray server it is often difficult to find free - ports for both VNC and the HTTP Java applet server to listen on. This - script, vnc_findports may be of use for doing this automatically. It - suggests x11vnc command line options based on netstat output that - lists the occupied ports. It is even more difficult to start - vncserver/Xvnc on a busy Sun Ray because then 3 ports (HTTP, VNC, and - X11), all separated by 100 are needed! This script, findvncports may - be helpful as well. Both scripts start at VNC display :10 and work - their way up. - - SunRay Gotcha #2: If you get an error like: - shmget(tile) failed. - shmget: No space left on device - - when starting up x11vnc that most likely means all the shared memory - (shm) slots are filled up on your machine. The Solaris default is only - 100, and that can get filled up in a week or so on a SunRay server - with lots of users. If the shm slot is orphaned (e.g. creator process - dies) the slot is not reclaimed. You can view the shm slots with the - "ipcs -mA" command. If there are about 100 then you've probably hit - this problem. They can be cleaned out (by the owner or by root) using - the ipcrm command. I wrote a script shm_clear that finds the orphans - and lists or removes them. Longer term, have your SunRay sysadmin add - something like this to /etc/system: - set shmsys:shminfo_shmmax = 0x2000000 - set shmsys:shminfo_shmmni = 0x1000 - - SunRay Gotcha #3: Some SunRay installations have implemented - suspending certain applications when a SunRay session is in a - disconnected state (e.g. Java Badge pulled out, utdetach, etc). This - is a good thing because it limits hoggy or runaway apps from wasting - the shared CPU resource. Think how much CPU and memory I/O is wasted - by a bunch of Firefox windows running worthless Flash animations while - your session is disconnected! - - So some sites have implemented scripts to suspend (e.g. kill -STOP) - certain apps when your badge is removed from the SunRay terminal. When - you reattach, it kill -CONT them. This causes problems for viewing the - detached SunRay session via x11vnc: those suspended apps will not - respond (their windows will be blank or otherwise inactive). - - What to do? Well, since you are going to be using the application you - might as well unfreeze it rather than starting up a 2nd instance. Here - is one way to do it using the kill -CONT mechanism: - kill -CONT `ps -ealf | grep ' T ' | grep $LOGNAME | awk '{print $4}'` - - If you want to be a good citizen and re-freeze them before you exit - x11vnc this script could be of use: -#!/bin/sh -# -# kill -STOP/-CONT script for x11vnc (or other) SunRay usage ("freezes" -# certain apps from hogging resources when disconnected). -# -# Put here a pattern that matches the apps that are frozen: -# -appmatch="java_vm|jre|netscape-bin|firefox-bin|realplay|acroread|mozilla-bin" - -if [ "X$1" = "Xfreeze" ]; then - pkill -STOP -U $LOGNAME "$appmatch" -elif [ "X$1" = "Xthaw" ]; then - pkill -CONT -U $LOGNAME "$appmatch" - -elif [ "$RFB_MODE" = "afteraccept" -a "$RFB_STATE" = "NORMAL" ]; then - # a valid x11vnc login. - if [ "$RFB_CLIENT_COUNT" = "1" ]; then - # only one client present. - pkill -CONT -U $LOGNAME "$appmatch" - fi -elif [ "$RFB_MODE" = "gone" -a "$RFB_STATE" = "NORMAL" ]; then - # a valid x11vnc login. - if [ "$RFB_CLIENT_COUNT" = "0" ]; then - # last client present has just left. - pkill -STOP -U $LOGNAME "$appmatch" - fi -fi -exit 0 - - If you called the script "goodcitizen" you could type "goodcitizen - thaw" to unfreeze them, and then "goodcitizen freeze" to refreeze - them. One could also use these x11vnc options "-afteraccept - goodcitizen -gone goodcitizen" to do it automatically. - - SunRay Gotcha #4: Recent versions of the Sun Ray Server Software - SRSS (seems to be version 3.0 or 3.1) have a "misfeature" that when - the session is disconnected (i.e. badge/smartcard out) the screen - locker (xscreensaver) will freeze the X server just when the "Enter - Password" dialog box appears. So you cannot unlock the screen remotely - via x11vnc! - - Update: please see Bob Doolittle's detailed description of the this - issue at the bottom of this section. - - Here "freeze" means "stop other X clients from inserting keyboard and - mouse input and from viewing the current contents of the screen". Or - something like that; the upshot is x11vnc can't do its normal thing. - - There are several workarounds for this. - - 1) The easiest one by far is to put these lines in your - $HOME/.dtprofile file: -SUN_SUNRAY_UTXLOCK_PREF="/usr/openwin/bin/xlock -mode blank" -export SUN_SUNRAY_UTXLOCK_PREF - - One might argue that xlock isn't particularly "pretty". (Just IMHO, - but if something like this not being pretty actually gets in the way - of your work I think some introspection may be in order. :-) - - 2) The problem has been traced to the pam_sunray.so PAM module. - Evidently xscreensaver invokes this pam module and it communicates - with utsessiond who in turn instructs the Xsun server to not process - any synthetic mouse/keyboard input or to update the screen - framebuffer. It is not clear if this is by design (security?) or - something else. - - In any event, the problem can be avoided, somewhat drastically, by - commenting out the corresponding line in /etc/pam.conf: -#xscreensaver auth sufficient /opt/SUNWut/lib/pam_sunray.so syncondisplay - - Leave the other xscreensaver pam authentication lines unchanged. The - dtsession-SunRay line may also need to be commented out to avoid the - problem for CDE sessions. N.B. it is possible the application of a - SSRS patch, etc, may re-enable that /etc/pam.conf line. It may be - difficult to convince a sysadmin to make this change. - - 3) A more forceful way is to kill the xscreensaver process from a - shell prompt whenever you connect via x11vnc and the screen is in a - locked state: -pkill -U $LOGNAME '^xscreensaver$' - - And then after you are in be sure to restart it by typing something - like: -xscreensaver & - - You may want to avoid restarting it until you are about to disconnect - your VNC viewer (since if it locks the screen while you are working - you'll be stuck again). - - 3') The above idea can be done a bit more cleanly by having x11vnc do - it. Suppose we called the following script xss_killer: -#!/bin/sh -# -# xss_killer: kill xscreensaver after a valid x11vnc client logs in. -# Restart xscreensaver and lock it when the last client -# disconnects. - -PATH=/usr/openwin/bin:/usr/bin:$PATH -export PATH - -if [ "$RFB_MODE" = "afteraccept" -a "$RFB_STATE" = "NORMAL" ]; then - # a valid x11vnc login. - if [ "$RFB_CLIENT_COUNT" = "1" ]; then - # only one client present. - pkill -U $LOGNAME '^xscreensaver$' - pkill -KILL -U $LOGNAME -f xscreensaver/hacks - fi -elif [ "$RFB_MODE" = "gone" -a "$RFB_STATE" = "NORMAL" ]; then - # a valid x11vnc login. - if [ "$RFB_CLIENT_COUNT" = "0" ]; then - # last client present has just left. - xscreensaver -nosplash & - sleep 1 - xscreensaver-command -lock & - fi -fi - - Then we would run x11vnc with these options: "-afteraccept xss_killer - -gone xss_killer". The -afteraccept option (introduced in version 0.8) - is used to run a command after a vncviewer has successfully logged in - (note that this is a VNC login, not a Unix login, so you may not want - to do this if you are really paranoid...) - - Note if you use the above script and also plan to Ctrl-C (SIGINT) - x11vnc you have to run the xscreensaver in a new process group to - avoid killing it as well. One way to do this is via this kludge: -perl -e 'setpgrp(0,0); exec "xscreensaver -nosplash &"' - - in the above script. - - 4) There appears to be a bug in pam_sunray.so in that it doesn't seem - to honor the convention that, say, DISPLAY=unix:3 means to use Unix - sockets to connect to display 3 on the local machine (this is a bit - faster than TCP sockets). Rather, it thinks the display is a non-local - one to a machine named "unix" (that usually does not resolve to an IP - address). - - Amusingly, this can be used to bypass the pam_sunray.so blocking of - Xsun that prevents one from unlocking the screen remotely via x11vnc. - One could put something like this in $HOME/.dtprofile to kill any - existing xscreensavers and then start up a fresh xscreensaver using - DISPLAY=unix:N -# stop/kill any running xscreensavers (probably not running yet, but to be sure -) -xscreensaver-command -exit -pkill -U $LOGNAME '^xscreensaver$' -env DISPLAY=`echo $DISPLAY | sed -e 's/^.*:/unix:/'` xscreensaver & - - - Important: Note that all of the above workarounds side-step the - pam_sunray.so PAM module in one way or another. You'll need to see if - that is appropriate for your site's SunRay / smartcard usage. Also, - these hacks may break other things and so you may want to test various - scenarios carefully. E.g. check corner cases like XDMCP/dtremote, - NSCM, etc. - - - Update May 2008: Here is a useful description of this issue from Bob - Doolittle who is a developer for Sun Ray at Sun. I don't have the time - to digest and distill it and then adjust the above methods to provide - a clearer description, so I just include below the description he sent - me with the hope that it will help some users: - - In SRSS 4.0 and earlier, the purpose of pam_sunray.so in the "auth" - PAM stack of screensavers is to enable NSCM (and, although this is - much less commonly used, "SC", which is configured when 3rd-party - software is installed to allow smartcards to be used as part of the - authentication process) to work. It should have no effect with - smartcards. Currently, however, it does block the PAM stack for all - sessions, which causes xscreensaver, when it locks a disconnected - session, to not process any mouse or keyboard events as you - describe (unless xscreensaver does an X server grab, however, other - applications should still be able to draw in the session although - xscreensaver may be playing tricks like putting a black window on - top of everything). In both of the NSCM and SC models, - authentication occurs in a separate session before SRSS will - reconnect to the user session, in which case pam_sunray.so causes - xscreensaver to just unlock the screen without prompting the user - to enter their password again. To do this, pam_sunray.so has to - block until the session becomes reconnected, so it can query SRSS - at that time to determine whether the user has already - authenticated or not. In SRSS 4.0 and earlier releases, - pam_sunray.so could have been optimized to not block smartcard - sessions, although since the session is disconnected this typically - isn't important (except in the x11vnc case, as you've observed). - - In SRSS 4.1, however, for increased security the out-of-session - authentication model has been extended to *all* session types, so - pam_sunray.so will be required in all cases unless users are - willing to authenticate twice upon hotdesking (e.g. when their card - is inserted). In future, we may do away with pam_sunray.so, and in - fact with any traditional screen locker in the user session, since - SRSS itself will be providing better security than a screen locker - running entirely within the user's X session is capable of - providing. - - Your trick of setting DISPLAY to unix:DPY will effectively disable - pam_sunray.so (I'm not sure I'd call that a bug - you're going out - of your way to do something that wouldn't occur in the normal - course of events, and really provides no useful value other than to - tickle this behavior in pam_sunray.so). This will mean that, in - SRSS 4.0 and earlier releases, users will be prompted for their - passwords twice when reconnecting to their sessions for NSCM and SC - session types. In 4.1, disabling pam_sunray.so in this way will - cause this double-authentication to occur for *all* sessions, - including simple smartcard sessions. Users may be willing to pay - that price in order to be able to use x11vnc in disconnected - sessions. I like this hack, personally. It's a little less - convenient than some of the other approaches you describe, but it's - lighter-weight and more secure than most of the other approaches, - and provides the value of being able to use x11vnc in locked - sessions. - - Here are some other minor notes: - I wouldn't recommend storing - your display in your .dtprofile, unless you're willing to live with - a single session at a time. Personally, I often find myself using - several sessions, in several FoGs, for short periods of time so - this would certainly break. IMO it's pretty easy to use $DISPLAY to - do what you want on the fly, as needed, so I don't think the price - of breaking multiple-session functionality would be worth the - convenience, to me at least. Here's some ksh/bash syntax to extract - the hostname and display number on the fly which you may find - useful: -HOSTNAME=${DISPLAY%:*} -FULLDPY=${DISPLAY#*:} -DPYNUM=${FULLDPY%.*} - - A final note may give you some insight into other clever hacks in - this area: - Check out utaction. It's a very handy little utility - that can be run as a daemon in the user session which will invoke a - specified command upon session connects and/or disconnects. - Personally, I start one up in my .dtprofile as follows: -utaction -c $HOME/.srconnectrc -d $HOME/.srdisconnectrc & - - This then allows me to construct a .srconnectrc script containing - useful commands I'd like to have run every time I insert my - smartcard, and a .srdisconnectrc script of commands to be run every - time I remove my smartcard (or, connect/disconnect to my session - via NSCM or SC). This can be used for things like notifying a chat - client of away status, as well as some of the hacks you've - described on your page such as freeze/unfreeze, or perhaps to - terminate an xscreensaver and start up a new one with the unix:DPY - $DISPLAY specification as you describe (although it probably makes - most sense to do this at login time, as opposed to every connect or - disconnect event). - -======================================================================= -http://www.karlrunge.com/x11vnc/ssl.html: - - - _________________________________________________________________ - - Notes on x11vnc SSL Certificates and Key Management: - - The simplest scheme ("x11vnc -ssl TMP") is where x11vnc generates a - temporary, self-signed certificate each time (automatically using - openssl(1)) and the VNC viewer client accepts the certificate without - question (e.g. user clicks "Yes" in a dialog box. Perhaps the dialog - allows them to view the certificate too). Also note stunnel's default - is to quietly accept all certificates. - - The encryption this provides protects against all passive sniffing of - the VNC traffic and passwords on the network and so it is quite good, - but it does not prevent a Man-In-The-Middle active attack: e.g. an - attacker intercepts the VNC client stream and sends it his own Public - key for SSL negotiation (pretending to be the server). Then it makes a - connection to SSL x11vnc itself and forwards the data back and forth. - He can see all the traffic and modify it as well. - - Most people don't seem to worry about Man-In-The-Middle attacks these - days; they are more concerned about passive sniffing of passwords, - etc. Perhaps someday that will change if attack tools are used more - widely to perform the attack. NOTE: There are hacker tools like - dsniff/webmitm and cain that implement SSL Man-In-The-Middle attacks. - They all rely on the client not bothering to check that the cert is - valid. - - If you are not worried about Man-In-The-Middle attacks you do not have - to read the techniques described in the rest of this document. - - To prevent Man-In-The-Middle attacks, certificates must somehow be - verified. This requires the VNC client side have some piece of - information that can be used to verify the SSL x11vnc server. - Alternatively, although rarely done, x11vnc can verify VNC Clients' - certificates, see the -sslverify option that is discussed below. - - There are a number of ways to have the client authenticate the SSL - x11vnc server. The quickest way perhaps would be to copy (safely) the - certificate x11vnc prints out: -26/03/2006 21:12:00 Creating a temporary, self-signed PEM certificate... -... ------BEGIN CERTIFICATE----- -MIIC4TCCAkqgAwIBAgIJAMnwCaOjvEKaMA0GCSqGSIb3DQEBBAUAMIGmMQswCQYD -VQQGEwJBVTEOMAwGA1UEBxMFTGludXgxITAfBgNVBAsTGGFuZ2VsYS0xMTQzNDI1 -NTIwLjQxMTE2OTEPMA0GA1UEChMGeDExdm5jMS4wLAYDVQQDEyV4MTF2bmMtU0VM -(more lines) ... ------END CERTIFICATE----- - - to the client machine(s) and have the client's SSL machinery (e.g. - stunnel, Web Browser, or Java plugin) import the certificate. That way - when the connection to x11vnc is made the client can verify that is it - the desired server on the other side of the SSL connection. - - So, for example suppose the user is using the SSL enabled Java VNC - Viewer and has incorporated the x11vnc certificate into his Web - browser on the viewing side. If he gets a dialog that the certificate - is not verified he knows something is wrong. It may be a - Man-In-The-Middle attack, but more likely x11vnc certificate has - changed or expired or his browser was reinstalled and/or lost the - certificate, etc, etc. - - As another example, if the user was using stunnel with his VNC viewer - (this is mentioned in this FAQ), e.g. STUNNEL.EXE on Windows, then he - would have to set the "CAfile = path-to-the-cert" and "verify = 2" - options in the stunnel.conf file before starting up the tunnel. If a - x11vnc certificate cannot be verified, stunnel will drop the - connection (and print a failure message in its log file). - - A third example, using the VNC viewer on Unix with stunnel the wrapper - script can be used this way: "ss_vncviewer -verify ./x11vnc.crt - far-away.east:0" where ./x11vnc.crt is the copied certificate x11vnc - printed out. - - As fourth example, our SSVNC enhanced tightvnc viewer can also use - these certificate files for server authentication. You can load them - via the SSVNC 'Certs...' dialog and set 'ServerCert' to the - certificate file you safely copied there. - - Note that in principle the copying of the certificate to the client - machine(s) itself could be altered by a Man-In-The-Middle attack! You - can't win; it is very difficult to be completely secure. It is - unlikely the attacker could predict how you were going to send it - unless you had, say, done it many times before the same way. SSH is a - very good way to send it (but of course it too depends on public keys - being sent unaltered between the two machines!). - - If you are really paranoid, I'm sure you'll figure out a really good - way to transport the certificates. See the Certificate Authority - scheme below for a way to make this easier (you just have to do it - once). - - _________________________________________________________________ - - Saving SSL certificates and keys: - - Now, it would be very inconvenient to copy the new temporary - certificate every time x11vnc is run in SSL mode. So for convenience - there is the "SAVE" keyword to instruct x11vnc to save the certificate - it creates: - x11vnc -ssl SAVE -display :0 ... - - This behavior is now the default, you must use "TMP" for a temporary - one. It will save the certificate and private key in these files: - ~/.vnc/certs/server.crt - ~/.vnc/certs/server.pem - - The ".crt" file contains only the certificate and should be safely - copied to the VNC Viewer machine(s) that will be authenticating the - x11vnc server. The ".pem" file contains both the certificate and the - private key and should be kept secret. (If you don't like the default - location ~/.vnc/certs, e.g. it is on an NFS share and you are worried - about local network sniffing, use the -ssldir dir option to point to a - different directory.) - - So the next time you run "x11vnc -ssl SAVE ..." it will read the - server.pem file directly instead of creating a new one. - - You can manage multiple SSL x11vnc server keys in this simple way by - using: - x11vnc -ssl SAVE-key2 -display :0 ... - - etc, where you put whatever name you choose for the key after "SAVE-". - E.g. "-ssl SAVE-fred". - - Also, if you want to be prompted to possibly change the made up names, - etc. that x11vnc creates (e.g. "x11vnc-SELF-SIGNED-CERT-7762" for the - CommonName) for the certificates distinguished name (DN), then use - "x11vnc -ssl SAVE_PROMPT ...", "x11vnc -ssl SAVE_PROMPT-fred ..." etc. - when you create the key the first time. - - Tip: when prompting, if you choose the CommonName entry to be the full - internet hostname of the machine the clients will be connecting to - then that will avoid an annoying dialog box in their Web browsers that - warn that the CommonName doesn't match the hostname. - - _________________________________________________________________ - - Passphrases for server keys: - - Well, since now with the "SAVE" keyword the certificate and key will - be longer lived, one can next worry about somebody stealing the - private key and pretending to be the x11vnc server! How to guard - against this? - - The first is that the file is created with perms 600 (i.e. -rw-------) - to make it harder for an untrusted user to copy the file. A better way - is to also encrypt the private key with a passphrase. You are prompted - whether you want to do this or not when the key is first created under - "-ssl SAVE" mode ("Protect key with a passphrase? y/n"). It is - suggested that you use a passphrase. The inconvenience is every time - you run "x11vnc -ssl SAVE ..." you will need to supply the passphrase - to access the private key: - 06/04/2006 11:39:11 using PEM /home/runge/.vnc/certs/server.pem 0.000s - - A passphrase is needed to unlock an OpenSSL private key (PEM file). - Enter passphrase> - - before x11vnc can continue. - - _________________________________________________________________ - - Being your own Certificate Authority: - - A very sophisticated way that scales well if the number of users is - large is to use a Certificate Authority (CA) whose public certificate - is available to all of the VNC clients and whose private key has been - used to digitally sign the x11vnc server certificate(s). - - The idea is as follows: - * A special CA cert and key is generated. - * Its private key is always protected by a good passphrase since it - is only used for signing. - * The CA cert is (safely) distributed to all machines where VNC - clients will run. - * One or more x11vnc server certs and keys are generated. - * The x11vnc server cert is signed with the CA private key. - * x11vnc is run using the server key. (e.g. "-ssl SAVE") - * VNC clients (viewers) can now authenticate the x11vnc server - because they have the CA certificate. - - The advantage is the CA cert only needs to be distributed once to the - various machines, that can be done even before x11vnc server certs are - generated. - - As above, it is important the CA private key and the x11vnc server key - are kept secret, otherwise someone could steal them and pretend to be - the CA or the x11vnc server if they copied the key. It is recommended - that the x11vnc server keys are also protected via a passphrase (see - the previous section). - - Optionally, VNC viewer certs and keys could also be generated to - enable the x11vnc server to authenticate each client. This is not - normally done (usually a simple viewer password scheme is used), but - this can be useful in some situations. These optional steps go like - this: - * One or more VNC client certs and keys are generated. - * These VNC client certs are signed with the CA private key. - * The VNC client certs+keys are safely distributed to the - corresponding client machines. - * x11vnc is told to verify clients by using the CA cert. (e.g. - "-sslverify CA") - * When VNC clients (viewers) connect, they must authenticate - themselves to x11vnc by using their client key. - - Again, it is a good idea if the client private keys are protected with - a passphrase, otherwise if stolen they could be used to gain access to - the x11vnc server. Once distributed to the client machines, there is - no need to keep the client key on the CA machine that generated and - signed it. You can keep the client certs if you like because they are - public. - - _________________________________________________________________ - - How to do the above CA steps with x11vnc: - - Some utility commands are provided to ease the cert+key creation, - signing, and management: -sslGenCA, -sslGenCert, -sslDelCert, - -sslEncKey, -sslCertInfo. They basically run the openssl(1) command - for you to manage the certs/keys. It is required that openssl(1) is - installed on the machine and available in PATH. All commands can be - pointed to an alternate toplevel certificate directory via the -ssldir - option if you don't want to use the default ~/.vnc/certs. - - 1) To generate your Certificate Authority (CA) cert and key run this: - x11vnc -sslGenCA - - Follow the prompts, you can modify any informational strings you care - to. You will also be required to encrypt the CA private key with a - passphrase. This generates these files: - ~/.vnc/certs/CA/cacert.pem (the CA public certificate) - ~/.vnc/certs/CA/private/cakey.pem (the encrypted CA private key) - - If you want to use a different directory use -ssldir It must supplied - with all subsequent SSL utility options to point them to the correct - directory. - - 2) To generate a signed x11vnc server cert and key run this: - x11vnc -sslGenCert server - - As with the CA generation, follow the prompts and you can modify any - informational strings that you care to. This will create the files: - ~/.vnc/certs/server.crt (the server public certificate) - ~/.vnc/certs/server.pem (the server private key + public cert) - - It is recommended to protect the server private key with a passphrase - (you will be prompted whether you want to). You will need to provide - it whenever you start x11vnc using this key. - - 3) Start up x11vnc using this server key: - x11vnc -ssl SAVE -display :0 ... - - (SAVE corresponds to server.pem, see -sslGenCert server somename info - on creating additional server keys, server-somename.crt ...) - - 4) Next, safely copy the CA certificate to the VNC viewer (client) - machine(s). Perhaps: - scp ~/.vnc/CA/cacert.pem clientmachine:. - - 5) Then the tricky part, make it so the SSL VNC Viewer uses this - certificate! There are a number of ways this might be done, it depends - on what your client and/or SSL tunnel is. Some examples: - - For the SSL Java VNC viewer supplied with x11vnc in - classes/ssl/VncViewer.jar or classes/ssl/SignedVncViewer.jar: - * Import the cacert.pem cert into your Web Browser (e.g. Edit -> - Preferences -> Privacy & Security -> Manage Certificates -> - WebSites -> Import) - * Or Import the cacert.pem cert into your Java Plugin (e.g. run - ControlPanel, then Security -> Certificates -> Secure Site -> - Import) - - When importing, one would give the browser/java-plugin the path to the - copied cacert.pem file in some dialog. Note that the Web browser or - Java plugin is used for the server authentication. If the user gets a - "Site not verified" message while connecting he should investigate - further. - - For the use of stunnel (e.g. on Windows) one would add this to the - stunnel.conf: - # stunnel.conf: - client = yes - options = ALL - CAfile = /path/to/cacert.pem # or maybe C:\path\to\cacert.pem - [myvncssl] - accept = 5901 - connect = far-away.east:5900 - - (then point the VNC viewer to localhost:1). - - Here is an example for the Unix stunnel wrapper script ss_vncviewer in - our SSVNC package: - ss_vncviewer -verify ./cacert.pem far-away.east:0 - - Our SSVNC enhanced tightvnc viewer GUI can also use the certificate - file for server authentication. You can load it via the SSVNC - 'Certs...' dialog and set 'ServerCert' to the cacert.pem file you - safely copied there. - - _________________________________________________________________ - - Tricks for server keys: - - To create additional x11vnc server keys do something like this: - x11vnc -sslGenCert server myotherkey - - and use it this way: - x11vnc -ssl SAVE-myotherkey ... - - The files will be ~/.vnc/certs/server-myotherkey.{crt,pem} - - You can also create a self-signed server key: - x11vnc -sslGenCert server self:third_key - - and use it this way: - x11vnc -ssl SAVE-self:third_key ... - - This key is not signed by your CA. This can be handy to have a key set - separate from your CA when you do not want to create a 2nd CA - cert+key. - - _________________________________________________________________ - - Using external CA's: - - You don't have to use your own CA cert+key, you can use a third - party's instead. Perhaps you have a company-wide CA or you can even - have your x11vnc certificate signed by a professional CA (e.g. - www.thawte.com or www.verisign.com or perhaps the free certificate - service www.startcom.org or www.cacert.org). - - The advantage to doing this is that the VNC client machines will - already have the CA certificates installed and you don't have to - install it on each machine. - - To generate an x11vnc server cert+key this way you should generate a - "request" for a certicate signing something like this (we use the name - "external" in this example, it could be anything you want): - x11vnc -sslGenCert server req:external - - This will create the request file: - ~/.vnc/certs/server-req:external.req - - Which you should send to the external CA. When you get the signed - certificate back from them, save it in the file: - ~/.vnc/certs/server-req:external.crt - - and create the .pem this way: - mv ~/.vnc/certs/server-req:external.key ~/.vnc/certs/server-req:external. -pem - chmod 600 ~/.vnc/certs/server-req:external.pem - cat ~/.vnc/certs/server-req:external.crt >> ~/.vnc/certs/server-req:external. -pem - - You also rename the two files (.crt and .pem) to have a shorter - basename if you like. E.g.: - mv ~/.vnc/certs/server-req:external.pem ~/.vnc/certs/server-ext.pem - mv ~/.vnc/certs/server-req:external.crt ~/.vnc/certs/server-ext.crt - - and the use via "x11vnc -ssl SAVE-ext ...", etc. - - On the viewer side make sure the external CA's certificate is - installed an available for the VNC viewer software you plan to use. - - _________________________________________________________________ - - Using Client Keys for Authentication: - - You can optionally create certs+keys for your VNC client machines as - well. After distributing them to the client machines you can have - x11vnc verify the clients using SSL. Here is how to do this: - - x11vnc -sslGenCert client dilbert - x11vnc -sslGenCert client wally - x11vnc -sslGenCert client alice - ... - - As usual, follow the prompts if you want to change any of the info - field values. As always, it is a good idea (although inconvenient) to - protect the private keys with a passphrase. These files are created: - ~/.vnc/certs/clients/dilbert.crt - ~/.vnc/certs/clients/dilbert.pem - ... - - Note that these are kept in a clients subdirectory. - - Next, safely copy the .pem files to each corresponding client machine - and incorporate them into the VNC viewer / SSL software (see the ideas - mentioned above for the CA and server keys). The only difference is - these certificates might be referred to as "My Certificates" or - "Client Certificates". They are used for client authentication (which - is relatively rare for SSL). - - After copying them you can delete the clients/*.pem files for extra - safety because the private keys are not needed by the x11vnc server. - You don't really need the clients/*.crt files either (because they - have been signed by the CA). But they could come in handy for tracking - or troubleshooting, etc. - - Now start up x11vnc and instruct it to verify connecting clients via - SSL and the CA cert: - x11vnc -ssl SAVE -sslverify CA - - The "CA" special token instructs x11vnc to use its CA signed certs for - verification. - - For arbitrary self-signed client certificates (no CA) it might be - something like this: - x11vnc -ssl SAVE -sslverify path/to/client.crt - x11vnc -ssl SAVE -sslverify path/to/client-hash-dir - x11vnc -ssl SAVE -sslverify path/to/certs.txt - - Where client.crt would be an individual client certificate; - client-hash-dir a directory of file names based on md5 hashes of the - certs (see -sslverify); and certs.txt signifies a single file full of - client certificates. - - Finally, connect with your VNC viewer using the key. Here is an - example for the Unix stunnel wrapper script ss_vncviewer: using client - authentication (and the standard server authentication with the CA - cert): - ss_vncviewer -mycert ./dilbert.pem -verify ./cacert.pem far-away.east:0 - - Our SSVNC enhanced tightvnc viewer can also use these openssl .pem - files (you can load them via Certs... -> MyCert dialog). - - It is also possible to use -sslverify on a per-client key basis, and - also using self-signed client keys (x11vnc -sslGenCert client - self:dilbert) - - Now a tricky part is to get Web browsers or Java Runtime to import and - use the openssl .pem cert+key files. See the next paragraph on how to - convert them to pkcs12 format. If you find a robust way to import them - and and get them to use the cert please let us know! - - Here is how to convert our openssl crt/pem files to pkcs12 format - (contains both the client certificate and key) that can be read by Web - browsers and Java for use in client authentication: - openssl pkcs12 -export -in mycert.crt -inkey mycert.pem -out mycert.p12 - - it will ask for a passphrase to protect mycert.p12. Some software - (e.g. Java ControlPanel) may require a non-empty passphrase. Actually, - since our .pem contains both the certificate and private key, you - could just supply it for the -in and remove the -inkey option. It - appears that for certificates only importing, our .crt file is - sufficient and can be read by Mozilla/Firefox and Java... - - If you have trouble getting your Java Runtime to import and use the - cert+key, there is a workaround for the SSL-enabled Java applet. On - the Web browser URL that retrieves the VNC applet, simply add a - "/?oneTimeKey=..." applet parameter (see ssl-portal for more details - on applet parameters; you don't need to do the full portal setup - though). The value of the oneTimeKey will be the very long string that - is output of the onetimekey program found in the classes/ssl x11vnc - directory. Or you can set oneTimeKey=PROMPT in which case the applet - will ask you to paste in the long string. These scheme is pretty ugly, - but it works. A nice application of it is to make one time keys for - users that have already logged into a secure HTTPS site via password. - A cgi program then makes a one time key for the logged in user to use: - it is passed back over HTTPS as the applet parameter in the URL and so - cannot be sniffed. x11vnc is run to use that key via -sslverify. - - Update: as of Apr 2007 in the 0.9.1 x11vnc tarball there is a new - option setting "-users sslpeer=" that will do a switch user much like - -unixpw does, but this time using the emailAddress field of the - Certificate subject of the verified Client. This mode requires - -sslverify turned on to verify the clients via SSL. This mode can be - useful in situations using -create or -svc where a new X server needs - to be started up as the authenticated user (but unlike in -unixpw - mode, the unix username is not obviously known). - - _________________________________________________________________ - - Revoking Certificates: - - A large, scaled-up installation may benefit from being able to revoke - certificates (e.g. suppose a user's laptop with a vnc client or server - key is compromised.) You can use this option with x11vnc: -sslCRL. See - the info at that link for a guide on what openssl(1) commands you will - need to run to revoke a certificate. - - _________________________________________________________________ - - Additional utlities: - - You can get information about your keys via -sslCertInfo. These lists - all your keys: - x11vnc -sslCertInfo list - x11vnc -sslCertInfo ll - - (the latter is long format). - - These print long output, including the public certificate, for - individual keys: - x11vnc -sslCertInfo server - x11vnc -sslCertInfo dilbert - x11vnc -sslCertInfo all (every key, very long) - - If you want to add a protecting passphrase to a key originally created - without one: - x11vnc -sslEncKey SAVE - x11vnc -sslEncKey SAVE-fred - - To delete a cert+key: - x11vnc -sslDelCert SAVE - x11vnc -sslDelCert SAVE-fred - x11vnc -sslDelCert wally - - (but rm(1) will be just as effective). - - _________________________________________________________________ - - Chained Certificates: - - There is increasing interest in using chained CA's instead of a single - CA. The merits of using chained CA's are not described here besides to - say its use may make some things easier when a certificate needs to be - revoked. - - x11vnc supports chained CA certificates. We describe a basic use case - here. - - Background: Of course the most straight forward way to use SSL with - x11vnc is to use no CA at all (see above): a self-signed certificate - and key is used and its certificate needs to be safely copied to the - client side. This is basically the same as the SSH style of managing - keys. Next level up, one can use a single CA to sign server keys: then - only the CA's certificate needs to be safely copied to the client - side, this can happen even before any server certs are created (again, - see all of the discussion above.) - - With a certificate chain there are two or more CA's involved. Perhaps - it looks like this: - root_CA ---> intermediate_CA ---> server_cert - - Where the arrow basically means "signs". - - In this usage mode the client (viewer-side) will have root_CA's - certificate available for verifying (and nothing else.) If the viewer - only received server_cert's certificate, it would not have enough info - to verify the server. The client needs to have intermediate_CA's cert - as well. The way to do this with x11vnc (i.e. an OpenSSL using app) is - to concatenate the server_cert's pem and the intermediate_CA's - certificate together. - - For example, suppose the file intermediate_CA.crt had - intermediate_CA's certificate. And suppose the file server_cert.pem - had the server's certificate and private key pair as described above - on this page. We need to do this: - cat intermediate_CA.crt >> server_cert.pem - - (Note: the order of the items inside the file matters; intermediate_CA - must be after the server key and cert) and then we run x11vnc like - this: - x11vnc -ssl ./server_cert.pem ... - - Then, on the VNC viewer client side, the viewer authenticates the - x11vnc server by using root_CA's certificate. Suppose that is in a - file named root_CA.crt, then using the SSVNC wrapper script - ss_vncviewer (which is also included in the SSVNC package) as our - example, we have: - ss_vncviewer -verify ./root_CA.crt hostname:0 - - (where "hostname" is the machine where x11vnc is running.) One could - also use the SSVNC GUI setting Certs -> ServerCert to the root_CA.crt - file. Any other SSL enabled VNC viewer would use root_CA.crt in a - similar way. - _________________________________________________________________ - - Creating Chained Certificates: - - Here is a fun example using VeriSign's "Trial Certificate" program. - Note that VeriSign has a Root CA and also an Intermediate CA and uses - the latter to sign customers certificates. So this provides an easy - way to test out the chained certificates mechanism with x11vnc. - - First we created a test x11vnc server key: - openssl genrsa -out V1.key 1024 - - then we created a certificate signing request (CSR) for it: - openssl req -new -key V1.key -out V1.csr - - (we followed the prompts and supplied information for the various - fields.) - - Then we went to VeriSign's page http://www.verisign.com/ssl/index.html - and clicked on "FREE TRIAL" (the certificate is good for 14 days.) We - filled in the forms and got to the point where it asked for the CSR - and so we pasted in the contents of the above V1.csr file. Then, after - a few more steps, VeriSign signed and emailed us our certificate. - - The VeriSign Trial certificates were found here: - http://www.verisign.com/support/verisign-intermediate-ca/Trial_Secure_Server_ -Root/index.html - http://www.verisign.com/support/verisign-intermediate-ca/trial-secure-server- -intermediate/index.html - - The former was pasted into a file V-Root.crt and the latter was pasted - into V-Intermediate.crt - - We pasted our Trial certificate that VeriSign signed and emailed to us - into a file named V1.crt and then we typed: - cat V1.key V1.crt > V1.pem - cat V1.pem V-Intermediate.crt > V1-combined.pem - chmod 600 V1.pem V1-combined.pem - - So now the file V1-combined.pem has our private key and (VeriSign - signed) certificate and VeriSign's Trial Intermediate certificate. - - Next, we start x11vnc: - x11vnc -ssl ./V1-combined.pem ... - - and finally, on the viewer side (SSVNC wrapper script example): - ss_vncviewer -verify ./V-Root.crt hostname:0 - - One will find that only that combination of certs and keys will work, - i.e. allow the SSL connection to be established. Every other - combination we tried failed (note that ss_vncviewer uses the external - stunnel command to handle the SSL so we are really testing stunnel's - SSL implementation on the viewer side); and so the system works as - expected. - _________________________________________________________________ - - VNC Client Authentication using Certificate Chains: - - Now, going the other way around with the client authenticating himself - via this chain of SSL certificates, x11vnc is run this way: - x11vnc -ssl SAVE -sslverify ./V-Root.crt ... - - (note since the server must always supply a cert, we use its normal - self-signed, etc., one via "-ssl SAVE" and use the VeriSign root cert - for client authentication via -sslverify. The viewer must now supply - the combined certificates, e.g.: - ss_vncviewer -mycert ./V1-combined.pem hostname:0 - _________________________________________________________________ - - Using OpenSSL and x11vnc to create Certificate Chains: - - Although the x11vnc CA mechanism (-sslGenCA and -sslGenCert; see - above) was designed to only handle a single root CA (to sign server - and/or client certs) it can be coerced into creating a certificate - chain by way of an extra openssl(1) command. - - We will first create two CA's via -sslGenCA; then use one of these CA - to sign the other; create a new (non-CA) server cert; and append the - intermediate CA's cert to the server cert to have everything needed in - the one file. - - Here are the commands we ran to do what the previous paragraph - outlines. - - First we create the two CA's, called CA_root and CA_Intermediate here, - in separate directories via x11vnc: - x11vnc -ssldir ~/CA_Root -sslGenCA - (follow the prompts, we included "CA_Root", e.g. Common Name, to aid ident -ifying it) - - x11vnc -ssldir ~/CA_Intermediate -sslGenCA - (follow the prompts, we included "CA_Intermediate", e.g. Common Name, to a -id identifying it) - - Next backup CA_Intermediate's cert and then sign it with CA_Root: - mv ~/CA_Intermediate/CA/cacert.pem ~/CA_Intermediate/CA/cacert.pem.ORIG - cd ~/CA_Root - openssl ca -config ./CA/ssl.cnf -policy policy_anything -extensions v3_ca -no -text -ss_cert ~/CA_Intermediate/CA/cacert.pem.ORIG -out ~/CA_Intermediate/CA/ca -cert.pem - - Note that it is required to cd to the ~/CA_Root directory and run the - openssl command from there. - - You can print out info about the cert you just modified by: - openssl x509 -noout -text -in ~/CA_Intermediate/CA/cacert.pem - - Now we create an x11vnc server cert named "test_chain" that is signed - by CA_Intermediate: - x11vnc -ssldir ~/CA_Intermediate -sslGenCert server test_chain - (follow the prompts) - - You can print out information about this server cert just created via - this command: - x11vnc -ssldir ~/CA_Intermediate -sslCertInfo SAVE-test_chain - - This will tell you the full path to the server certificate, which is - needed because we need to manually append the CA_Intermediate cert for - the chain to work: - cat ~/CA_Intermediate/CA/cacert.pem >> ~/CA_Intermediate/server-test_chain.pe -m - - Now we are finally ready to use it. We can run x11vnc using this - server cert+key by either this command: - x11vnc -ssldir ~/CA_Intermediate -ssl SAVE-test_chain ... - - or this command: - x11vnc -ssl ~/CA_Intermediate/server-test_chain.pem ... - - since they are equivalent (both load the same pem file.) - - Finally we connect via VNC viewer that uses CA_Root to verify the - server. As before we use ss_vncviewer: - ss_vncviewer -verify ~/CA_Root/CA/cacert.pem hostname:0 - - Client Certificates (see above) work in a similar manner. - - So although it is a little awkward with the extra steps (e.g. - appending the CA_Intermediate cert) it is possible. If you want to do - this entirely with openssl(1) you will have to learn the openssl - commands corresponding to -genCA and -genCert. You may be able to find - guides on the Internet to do this. Starting with x11vnc 0.9.10, you - can have it print out the wrapper scripts it uses via: -sslScripts - (you will still need to fill in a few pieces of information; ask if it - is not clear from the source code.) - - _________________________________________________________________ - - More info: - - See also this article for some some general info and examples using - stunnel and openssl on Windows with VNC. Also - http://www.stunnel.org/faq/certs.html is a very good source of - information on SSL certificate creation and management. - -======================================================================= -http://www.karlrunge.com/x11vnc/ssl-portal.html: - - - _________________________________________________________________ - - Using Apache as an SSL Gateway to multiple x11vnc servers inside a - firewall: - - Background: - - The typical way to allow access to x11vnc (or any other VNC server) - running on multiple workstations inside a firewall is via SSH. The - user somewhere out on the Internet logs in to the SSH gateway machine - and uses port forwarding (e.g. ssh -t -L 5900:myworkstation:5900 - user@gateway) to set up the encrypted channel that VNC is then - tunneled through. Next he starts up the VNC viewer on the machine - where he is sitting directed to the local tunnel port (e.g. - localhost:0). - - The SSH scheme is nice because it is a widely used and well tested - login technique for users connecting to machines inside their company - or home firewall. For VNC access it is a bit awkward, however, because - SSH needs to be installed on the Viewer machine and the user usually - has to rig up his own port redirection plumbing (however, see our - other tool). - - Also, some users have restrictive work environments where SSH and - similar applications are prohibited (i.e. only outgoing connections to - standard WWW ports from a browser are allowed, perhaps mediated by a - proxy server). These users have successfully used the method described - here for remote access. - - With the SSL support in x11vnc and the SSL enabled Java VNC viewer - applet, a convenient and secure alternative exists that uses the - Apache webserver as a gateway. The idea is that the company or home - internet connection is already running apache as a web server (either - SSL or non-SSL) and we add to it the ability to act as a gateway for - SSL VNC connections. The only thing needed on the Viewer side is a - Java enabled Web Browser: the user simply enters a URL that starts the - entire VNC connection process. No VNC or SSH specific software needs - to be installed on the viewer side machine. - - The stunnel VNC viewer stunnel wrapper script provided (ss_vncviewer) - can also take advantage of the method described here with its -proxy - option. - - _________________________________________________________________ - - Simpler Solutions: This apache SSL VNC portal solution may be too much - for you. It is mainly intended for automatically redirecting to - MULTIPLE workstations inside the firewall. If you only have one or two - inside machines that you want to access, the method described here is - overly complicated! See below for some simpler (and still non-SSH) - encrypted setups. - - Also see the recent (Mar/2010) desktop.cgi x11vnc desktop web login - CGI script that achieves much of what the method describes here - (especially if its 'port redirection' feature is enabled.) - _________________________________________________________________ - - - - There are numerous ways to achieve this with Apache. We present one of - the simplest ones here. - - Important: these sorts of schemes allow incoming connections from - anywhere on the Internet to fixed ports on machines inside the - firewall. Care must be taken to implement and test thoroughly. If one - is paranoid one can (and should) add extra layers of protection. (e.g. - extra passwords, packet filtering, SSL certificate verification, etc). - - Also, it is easy to miss the point that unless precautions are taken - to verify SSL Certificates, then the VNC Viewer is vulnerable to - man-in-the-middle attacks (but not to the more common passive sniffing - attacks). Note that there are hacker tools like dsniff/webmitm and - cain that implement SSL Man-In-The-Middle attacks. They rely on the - client not bothering to check the cert. - _________________________________________________________________ - - The Holy Grail: a single https port (443) - - Before we discuss the self-contained apache examples here, we want to - mention that many x11vnc users who read this page and implement the - apache SSL VNC portal ask for something that (so far) seems difficult - or impossible to do entirely inside apache: - * A single port, 443 (the default https:// port), is open to the - Internet - * It is HTTPS/SSL encrypted - * It handles both VNC traffic and Java VNC Applet downloads. - * And the server can also serve normal HTTPS webpages, CGI, etc. - - It is the last item that makes it tricky (otherwise the method - described on this page will work). If you are interested in such a - solution and are willing to run a separate helper program - (connect_switch) look here. Also, see this apache patch. - _________________________________________________________________ - - Example: - - The scheme described here sets up apache on the firewall/gateway as a - regular Web proxy into the intranet and allows connections to a single - fixed port on a limited set of machines. - - The configuration described in this section does not use the mod_ssl - apache module (the optional configuration described in the section - "Downloading the Java applet to the browser via HTTPS" does take - advantage of mod_ssl) - - In this example suppose the gateway machine running apache is named - "www.gateway.east" (e.g. it may also provide normal web service). We - also choose the Internet-facing port for this VNC service to be port - 563. One could choose any port, including the default HTTP port 80. - - Detail: We choose 563 because it is the rarely used SNEWS port that is - often allowed by Web proxies for the CONNECT method. The idea is the - user may be coming out of another firewall using a proxy (not the one - we describe here, that is, the case when two proxies are involved, - e.g. one at work and another Apache (described here) at home - redirecting into our firewall; the "double proxy" or "double firewall" - problem). Using port 563 simplifies things because CONNECT's to it are - usually allowed by default. - - We also assume all of the x11vnc servers on the internal machines are - all listening on port 5915 ("-rfbport 5915") instead of the default - 5900. This is to limit any unintended proxy redirections to a lesser - used port, and also to stay out of the way of normal VNC servers on - the same machines. One could obviously implement a scheme that handles - different ports, but we just discuss this simple setup here. - - So we basically assume x11vnc has been started this way on all of the - workstations to be granted VNC access: - x11vnc -ssl SAVE -http -display :0 -forever -rfbauth ~/.vnc/passwd -rfbport 5 -915 - - i.e. we force SSL VNC connections, port 5915, serve the Java VNC - viewer applet, and require a VNC password (another option would be - -unixpw). The above command could also be run out of inetd(8). It can - also be used to autodetect the user's display and Xauthority data. - - - These sections are added to the httpd.conf apache configuration file - on www.gateway.east: - -# In the global section you need to enable these modules. -# Note that the ORDER MATTERS! mod_rewrite must be before mod_proxy -# (so that we can check the allowed host list via rewrite) -# -LoadModule rewrite_module modules/mod_rewrite.so -LoadModule proxy_module modules/mod_proxy.so -LoadModule proxy_connect_module modules/mod_proxy_connect.so -LoadModule proxy_ftp_module modules/mod_proxy_ftp.so -LoadModule proxy_http_module modules/mod_proxy_http.so - -LoadModule ssl_module modules/mod_ssl.so - - - -# Near the bottom of httpd.conf you put the port 563 virtual host: - -Listen 563 - - - - # Allow proxy CONNECT requests *only* to port 5915. - # If the machines use different ports, e.g. 5916 list them here as well: - # - ProxyRequests On - AllowCONNECT 5915 - - RewriteEngine On - - # Convenience rules to expand applet parameters. These do not have a traili -ng "/" - # - # /vnc for http jar file downloading: - # - RewriteRule /vnc/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PO -RT=563&urlPrefix=_2F_vnc_2F_$1 [R,NE,L] - RewriteRule /vnc/trust/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PO -RT=563&urlPrefix=_2F_vnc_2F_$1&trustAllVncCerts=yes [R,NE,L] - RewriteRule /vnc/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PO -RT=563&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes [R,NE,L] - RewriteRule /vnc/trust/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PO -RT=563&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes&trustAllVncCerts=yes [R,NE,L] - - # Read in the allowed host to vnc display mapping file. It looks like: - # - # host1 15 - # host2 15 - # ... - # - # the display "15" means 5815 for http applet download, 5915 for SSL vnc. - # - RewriteMap vnchosts txt:/dist/apache/conf/vnc.hosts - - # Proxy: check for the CONNECT hostname and port being in the vnc.hosts list -. - # - RewriteCond %{THE_REQUEST} ^CONNECT [NC] - RewriteCond %{REQUEST_URI} ^(.*):(.*)$ - RewriteCond ${vnchosts:%1|NOTFOUND} NOTFOUND - RewriteRule ^.*$ /VNCFAIL [F,L] - - RewriteCond %{THE_REQUEST} ^CONNECT [NC] - RewriteCond %{REQUEST_URI} ^(.*):(.*)$ - RewriteCond 59${vnchosts:%1}=%2 !^(.*)=(\1)$ - RewriteRule ^.*$ /VNCFAIL [F,L] - - - # Remap /vnc to the proxy http download (e.g. http://host:5815) - # - # First, fail if it starts with the string /vnc0: - # - RewriteRule ^/vnc0.* /VNCFAIL [F,L] - # - # Next, map the prefix to /vnc0/host:protocol:port - # - RewriteRule ^/vnc/([^/]+)/(.*) /vnc0/$1:http:58${vnchosts:$1|NOTFOUND}/$2 -[NE] - # - # Drop any not found: - # - RewriteRule ^/vnc0.*NOTFOUND.* /VNCFAIL [F,L] - - # Construct the proxy URL and retrieve it: - # - RewriteRule ^/vnc0/([^/]+):([^/]+):([^/]+)/(.*) $2://$1:$3/$4 [P,NE,L] - - - - Then restart apache (perhaps: "apachectl stop; apachectl start"). - - Note that the listing of allowed internal workstations is done in an - external file (/dist/apache/conf/vnc.hosts in the example above), the - format is like this: -# allowed vnc hosts file: -hostname1 15 -hostname2 15 -... - - You list the hostname and the VNC display (always 15 in our example). - Only to these hosts will the external VNC viewers be able to connect - to (via the HTTP CONNECT method). - - The above setup requires mod_rewrite and mod_proxy be enabled in the - apache web server. In this example they are loaded as modules (and - note that mod_rewrite must be listed before mod_proxy); - - The user at the Java enabled Web browser would simply enter this URL - into the browser: - http://www.gateway.east:563/vnc/host2 - - to connect to internal workstation host2, etc. - - Important: do not put a trailing "/" on the URL, since that will - defeat the RewriteRules that look for the hostname at the very end. - - There will be a number of SSL certificate, etc, dialogs he will have - to respond to in addition to any passwords he is required to provide - (this depends on how you set up user authentication for x11vnc). - - If a second Web proxy is involved (i.e. the user's browser is inside - another firewall and policy requires using a Web proxy server) then - use this URL: - http://www.gateway.east:563/vnc/proxy/host2 - - This will involve downloading a signed java viewer applet jar file - that is able to interact with the internal proxy for the VNC - connection. See this FAQ for more info on how this works. Note: - sometimes with the Proxy case if you see 'Bad Gateway' error you will - have to wait 10 or so seconds and then hit reload. This seems to be - due to having to wait for a Connection Keepalive to terminate... - - For completeness, the "trust" cases that skip a VNC certificate dialog - (discussed below) would be entered as: - http://www.gateway.east:563/vnc/trust/host2 - http://www.gateway.east:563/vnc/trust/proxy/host2 - - You can of course choose shorter or more easy to remember URL formats. - Just change the Convenience RewriteRules in httpd.conf. - - _________________________________________________________________ - - Port Variations: - - Note that you can run this on the default HTTP port 80 instead of port - 563. If you do not expect to have a browser connecting from inside a - proxying firewall (where sometimes only connections to ports 443 and - 563 are allowed) this should be fine. Use "80" instead of "563" in the - httpd.conf config file (you may need to merge it with other default - port 80 things you have there). - - Then the URL's will be a bit simpler: - http://www.gateway.east/vnc/host2 - http://www.gateway.east/vnc/trust/host2 - - etc. - - Besides 80 one could use any other random port number (since there are - so many port scans on 80, a little obscurity might be useful). - - One option is to use port "443" (the default https:// port) instead of - "563". In this case Apache is not configured for mod_ssl; we just - happen to use port "443" in the way any random port would be used. - This could be handy if the Viewer side environment is restrictive in - that it only allows outgoing connections to ports 80 and 443 (and, - say, you didn't want to use port 80, or you wanted to use 80 for - something else). Another reason for using 443 would be some web proxy - environments only allow the CONNECT method to go to port 443 (and not - even the case 563 we use above). - - _________________________________________________________________ - - Details: - - Let's go through the httpd.conf additions in detail from the top. - - The LoadModules directives load the necessary apache modules. Note - that mod_rewrite must be listed first. If you are compiling from - scratch something like this worked for us: - ./configure --enable-proxy=shared --enable-proxy-connect=shared --enable-ssl= -shared --enable-rewrite=shared --prefix=/dist/apache - - Then the VirtualHost *:563 virtual host section starts. - - The "ProxyRequests On" and "AllowCONNECT 5915" enable the web server - to forward proxy requests to port 5915 (and only this port) INSIDE the - firewall. Think about the implications of this thoroughly and test it - carefully. - - The RewriteRule's are for convenience only so that the URL entered - into the Web browser does not need the various extra parameters, e.g.: - http://www.gateway.east:563/vnc/host2/index.vnc?CONNECT=host2+5915&PORT=563, -blah,blah... - - (or otherwise make direct edits to index.vnc to set these parameters). - The forceProxy=yes parameter is passed to the applet to force the use - of a outgoing proxy socket connection. Use it only if the Web browser - is inside a separate Web proxying environment (i.e. large corporation) - - The rewrites with parameter urlPrefix are described under Tricks for - Better Response. The "trust" ones (also described under Tricks) with - trustAllVncCerts tell the Java VNC applet to skip a dialog asking - about the VNC Certificate. They are a bit faster and more reliable - than the original method. In the best situation they lead to being - logged in 20 seconds or less (without them the time to login can be - much longer since a number of connections must timeout). - - All of the x11vnc Java Viewer applet parameters are described in the - file classes/ssl/README - - The external file /dist/apache/conf/vnc.hosts containing the allowed - VNC server hostnames is read in. Its 2nd column contains the VNC - display of the host (always 15 in our example; if you make it vary you - will need to adjust some lines in the httpd.conf accordingly, e.g. - AllowCONNECT). This list is used to constrain both the Jar file - download URL and the proxy CONNECT the VNC viewer makes to only the - intended VNC servers. - - Limiting the proxy CONNECT is done with the two sets of RewriteCond - conditions. - - Limiting the Jar file download URL is done in the remaining 4 - RewriteRule's. - - Note that these index.vnc and VncViewer.jar downloads to the browser - are not encrypted via SSL, and so in principle could be tampered with - by a really bad guy. The subsequent VNC connection, however, is - encrypted through a single SSL connection (it makes a CONNECT straight - to x11vnc). See below for how to have these initial downloads - encrypted as well (if the apache web server has SSL/mod_ssl, i.e. - https, enabled and configured). - - Unfortunately the Java VNC viewer applet currently is not able to save - its own list of Certificates (e.g. the user says trust this VNC - certificate 'always'). This is because an applet it cannot open local - files, etc. Sadly, the applet cannot even remember certificates in the - same browser session because it is completely reinitialized for each - connection (see below). - - _________________________________________________________________ - - Too Much? - - If these apache rules are a little too much for you, there is a little - bit simpler scheme where you have to list each of the individual - machines in the httpd.conf and ssl.conf files. It may be a little more - typing to maintain, but perhaps being more straight forward (less - RewriteRule's) is desirable. - - _________________________________________________________________ - - Problems? - - To see example x11vnc output for a successful https://host:5900/ - connection with the Java Applet see This Page. - - _________________________________________________________________ - - Some Ideas for adding extra authentication, etc. for the paranoid: - * VNC passwords: -rfbauth, -passwdfile, or -usepw. Even adding a - simple company-wide VNC password helps block unwanted access. - * Unix passwords: -unixpw - * SSL Client certificates: -sslverify - * Apache AuthUserFile directive: .htaccess, etc. - * Filter connections based on IP address or hostname. - * Use Port-knocking on your firewall as described in: Enhanced - TightVNC Viewer (ssvnc). - * Add proxy password authentication (requires Viewer changes?) - * Run a separate instance of Apache that provides this VNC service - so it can be brought up and down independently of the normal web - server. - * How secure is the Client side? Public machines in internet cafes, - etc, are often hacked, with backdoors and VNC servers of their - own. Prefer using your own firewalled laptop to a public machine. - - - _________________________________________________________________ - - Using non-Java viewers with this scheme: - - The ss_vncviewer stunnel wrapper script for VNC viewers has the -proxy - option that can take advantage of this method. - ss_vncviewer -proxy www.gateway.east:563 host1:15 - - For the case of the "double proxy" situation (see below) supply both - separated by a comma. - ss_vncviewer -proxy proxy1.foobar.com:8080,www.gateway.east:563 host1:15 - - For the Enhanced TightVNC Viewer (ssvnc) GUI (it uses ss_vncviewer on - Unix) put 'host1:15' into the 'VNC Server' entry box, and here are - possible Proxy/Gateway entries - Proxy/Gateway: www.gateway.east:563 - Proxy/Gateway: proxy1.foobar.com:8080,www.gateway.east:563 - - then click on the 'Connect' button. - - _________________________________________________________________ - - Downloading the Java applet to the browser via HTTPS: - - To have the Java applet downloaded to the user's Web Browser via an - encrypted (and evidently safer) SSL connection the Apache webserver - should be configured for SSL via mod_ssl. - - It is actually possible to use the x11vnc Key Management utility - "-sslGenCert" to generate your Apache/SSL .crt and .key files. (In - brief, run something like "x11vnc -sslGenCert server self:apache" then - copy the resulting self:apache.crt file to conf/ssl.crt/server.crt and - extract the private key part from self:apache.pem and paste it into - conf/ssl.key/server.key). Setting the env var REQ_ARGS='-days 1095' - before running x11vnc will bump up the expiration date (3 years in - this case). - - Or you can use the standard methods described in the Apache mod_ssl - documentation to create your keys. Then restart Apache, usually - something like "apachectl stop" followed by "apachectl startssl" - - In addition to the above sections in httpd.conf one should add the - following to ssl.conf: - SSLProxyEngine On - - RewriteEngine On - - # Convenience rules to expand applet parameters. These do not have a traili -ng "/" - # - # /vnc http jar file downloading: - # - RewriteRule /vnc/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$ -1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vnc_2F_$1 [R,NE,L] - RewriteRule /vnc/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$ -1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes [R,N -E,L] - # - # (we skipped the "trust" ones above, put them in if you like) - # - # /vncs https jar file downloading: - # - RewriteRule /vncs/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$ -1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1 [R,NE,L] - RewriteRule /vncs/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$ -1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes [R, -NE,l] - RewriteRule /vncs/trust/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$ -1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&trustAllVncCerts=y -es [R,NE,L] - RewriteRule /vncs/trust/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$ -1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes&tru -stAllVncCerts=yes [R,NE,L] - - # Convenience rules used for the connect_switch helper (requires Listen 127. -0.0.1:443 above): - # - RewriteRule /vnc443/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$ -1+5915&PORT=443&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1 [R,NE,L] - RewriteRule /vnc443/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$ -1+5915&PORT=443&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes [R, -NE,L] - RewriteRule /vnc443/trust/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$ -1+5915&PORT=443&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&trustAllVncCerts=y -es [R,NE,L] - RewriteRule /vnc443/trust/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$ -1+5915&PORT=443&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes&tru -stAllVncCerts=yes [R,NE,L] - - # Read in the allowed host to vnc display mapping file. It looks like: - # - # host1 15 - # host2 15 - # ... - # - # the display "15" means 5915 for SSL VNC and 5815 for http applet download. - # - RewriteMap vnchosts txt:/dist/apache/conf/vnc.hosts - - - # Remap /vnc and /vncs to the proxy http download (e.g. https://host:5915) - # - # First, fail if it starts with the string /vnc0: - # - RewriteRule ^/vnc0.* /VNCFAIL [F,L] - # - # Next, map the prefix to /vnc0:host:protocol:port - # - RewriteRule ^/vnc/([^/]+)/(.*) /vnc0/$1:http:58${vnchosts:$1|NOTFOUND}/$2 -[NE] - RewriteRule ^/vncs/([^/]+)/(.*) /vnc0/$1:https:59${vnchosts:$1|NOTFOUND}/$2 -[NE] - # - # Drop any not found: - # - RewriteRule ^/vnc0.*NOTFOUND.* /VNCFAIL [F,L] - - # Construct the proxy URL and retrieve it: - # - RewriteRule ^/vnc0/([^/]+):([^/]+):([^/]+)/(.*) $2://$1:$3/$4 [P,NE,L] - - This is all in the "" section of ssl.conf. - - The user could then point the Web Browser to: - https://www.gateway.east/vnc/host2 - - or - https://www.gateway.east/vnc/proxy/host2 - - for the "double proxy" case. (Important: do not put a trailing "/" on - the URL, since that will defeat the RewriteRules.) - - As with the httpd.conf case, the external file - (/dist/apache/conf/vnc.hosts in the above example) contains the - hostnames of the allowed VNC servers. - - Note that inside the firewall the Java applet download traffic is not - encrypted (only over the Internet is SSL used) for these cases: - https://www.gateway.east/vnc/host2 - https://www.gateway.east/vnc/proxy/host2 - - However for the special "vncs" rules above: - https://www.gateway.east/vncs/host2 - - the Java applet download is encrypted via SSL for both legs. Note that - the two legs are two separate SSL sessions. So the data is decrypted - inside an apache process and reencrypted by the apache process for the - 2nd SSL session inside the same apache process (a very small gap one - might overlook). - - The "vncs/trust" ones are like the "trust" ones described earlier - https://www.gateway.east/vncs/trust/mach2 - - and similarly for the httpsPort ones. See Tricks for Better Response. - - In all of the above cases the VNC traffic from Viewer to x11vnc is - encrypted end-to-end in a single SSL session, even for the "double - proxy" case because the CONNECT method is used (there are actually two - CONNECT's for the "double proxy" case). This part (the VNC traffic) is - the most important part to have encrypted. - - Note that the Certificate dialogs the user has in his web browser will - be for the Apache Certificate, while for the Java applet it will be - the x11vnc certificate. - - Note also that you can have Apache serve up the Jar file VncViewer.jar - and/or index.vnc/proxy.vnc instead of each x11vnc if you want to. - - The rules in ssl.conf are similar to the ones in httpd.conf and so are - not discussed in detail. The only really new thing is the /vncs - handling to download the applet jar via HTTPS on port 5915. - - The special entries "/vnc443" are only used for the special helper - program (connect_switch) for the https port 443 only mode discussed - here. - - _________________________________________________________________ - - INETD automation: - - The "single-port" (i.e. 5915) HTTPS applet download and VNC connection - aspect shown here is convenient and also enables having x11vnc run out - of inetd. That way x11vnc is run on demand instead of being run all - the time (the user does not have to remember to start it). The first - connections to inetd download index.vnc and the Jar file (via https) - and the the last connection to inetd establishes the SSL VNC - connection. Since x11vnc is restarted for each connection, this will - be a bit slower than the normal process. - - For example, the /etc/inetd.conf line could be: - 5915 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc_ssl.sh - - where the script x11vnc_ssl.sh looks something like this: -#!/bin/sh - -/usr/local/bin/x11vnc -inetd -oa /var/log/x11vnc-15.log \ - -ssl SAVE -http -unixpw -localhost \ - -display :0 -auth /home/THE_USER/.Xauthority - - where, as usual, the inetd launching needs to know which user is - typically using the display on that machine. One could imagine giving - different users different ports, 5915, 5916, etc. to distinguish (then - the script would need to be passed the username). mod_rewrite could be - used to automatically map username in the URL to his port number. - - A better way is to use the "-display WAIT:cmd=FINDDISPLAY" feature to - autodetect the user and Xauthority data: -#!/bin/sh - -/usr/local/bin/x11vnc -inetd -oa /var/log/x11vnc-15.log \ - -ssl SAVE -http -unixpw -localhost -users unixpw= \ - -find - - (we have used the alias -find for "-display WAIT:cmd=FINDDISPLAY".) - This way the user must supply his Unix username and password and then - his display and Xauthority data on that machine will be located and - returned to x11vnc to allow it to attach. If he doesn't have a display - running on that machine or he fails to log in correctly, the - connection will be dropped. - - The variant "-display WAIT:cmd=FINDCREATEDISPLAY" (aliased by - "-create") will actually create a (virtual or real) X server session - for the user if one doesn't already exist. See here for details. - - To enable inetd operation for the non-HTTPS Java viewer download (port - 5815 in the above httpd.conf example) you will need to run x11vnc in - HTTPONCE mode on port 5815: For example, the /etc/inetd.conf line - could be: - 5815 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc \ - -inetd -prog /usr/local/bin/x11vnc -oa /var/log/x11vnc-15.log \ - -http_ssl -display WAIT:cmd=HTTPONCE - - where the long inetd.conf line has been split. Note how the -http_ssl - tries to automatically find the .../classes/ssl subdirectory. This - requires the -prog option available in x11vnc 0.8.4 (a shell script - wrapper, e.g. /usr/local/bin/x11vnc_http.sh can be used to work around - this). - - Also note the use of "-ssl SAVE" above. This way a saved server.pem is - used for each inetd invocation (rather generating a new one each time - as happens for "-ssl TMP"). Note that it cannot have a protecting - passphrase because inetd will not be able to supply it. - - Another option is: - 5815 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc \ - -inetd -httpdir /usr/local/share/x11vnc/classes/ssl \ - -oa /var/log/x11vnc-15.log -display WAIT:cmd=HTTPONCE - - (this also requires a feature found in x11vnc 0.8.4). - _________________________________________________________________ - - Other Ideas: - - - The above schemes work, but they are a bit complicated with all of - the rigging. There should be more elegant ways to configure Apache to - do these, but we have not found them (please let us know if you - discover something nice). However, once this scheme has been set up - and is working it is easy to maintain and add/delete workstations, - etc. - - - In general Apache is not required, but it makes things convenient. - The firewall itself could do the port redirection via its firewall - rules. Evidently different Internet-facing ports would be required for - each workstation. This could be set up using iptables rules for - example. If there were just one or two machines this would be the - easiest method. For example: - iptables -t nat -A PREROUTING -p tcp -d 24.35.46.57 --dport 5901 -j DNAT --to --destination 192.168.1.2:5915 - iptables -t nat -A PREROUTING -p tcp -d 24.35.46.57 --dport 5902 -j DNAT --to --destination 192.168.1.3:5915 - - Where 24.35.46.57 is the internet IP address of the gateway. In this - example 24.35.46.57:5901 is redirected to the internal machine - 192.168.1.2:5915 and 24.35.46.57:5902 is redirected to another - internal machine 192.168.1.3:5915, both running x11vnc -ssl ... in SSL - mode. For this example, the user would point the web browser to, e.g.: - https://24.35.46.57:5901/?PORT=5901 - - or using the stunnel wrapper script: - ss_vncviewer 24.35.46.57:1 - - One can achieve similar things with dedicated firewall/routers (e.g. - Linksys) using the device's web or other interface to configure the - firewall. - - If the user may be coming out of a firewall using a proxy it may be - better to redirect ports 443 and 563 (instead of 5901 and 5902) to the - internal machines so that the user's proxy will allow CONNECTing to - them. - - - The redirection could also be done at the application level using a - TCP redirect program (e.g. ip_relay or fancier ones). Evidently more - careful internal hostname checking, etc., could be performed by the - special purpose application to add security. See connect_switch which - is somewhat related. - - - One might imagine the ProxyPass could be done for the VNC traffic as - well (for the ssl.conf case) to avoid the CONNECT proxying completely - (which would be nice to avoid). Unfortunately we were not able to get - this to work. Since HTTP is a request-response protocol (as opposed to - a full bidirectional link required by VNC that CONNECT provides) this - makes it difficult to do. It may be possible, but we haven't found out - how yet. - - All of the x11vnc Java Viewer applet parameters are described in the - file classes/ssl/README - - _________________________________________________________________ - - Tricks for Better Response and reliability: - - The "original scheme" using httpd.conf and ssl.conf rewrites without - urlPrefix and trustAllVncCerts above should work OK, but may lead to - slow and/or unreliable loading of the applet and final connection to - x11vnc. The following are what I do now to get better response and - reliability. YMMV. - - The problem with the "original scheme" is that there is a point where - the VNC Viewer applet can try up to 3 times to retrieve the x11vnc - certificate, since it needs to get it to show it to you and ask you if - you accept it. This can add about 45 seconds to the whole process - (which takes 1 to 1.5 minutes with all the dialogs) since a couple of - those connections must time out. The "trust" items in the config add a - parameter trustAllVncCerts=yes similar to the forceProxy=yes - parameter. This can cut the total time to the VNC password prompt down - to 15 seconds which is pretty good. (Note by ignoring the certificate - this does not protect against man-in-the-middle attacks which are - rare, but maybe the won't be so rare in the future... see - dsniff/webmitm and cain) - - First make sure the x11vnc SSL certificate+key is the same as - Apache's. (otherwise you may get one extra dialog and/or one extra - connection that has to time out). - - The following RewriteRule's are the same now advocated in the - instructions above. - - The httpsPort and urlPrefix= parameters give hints to the applet to - improve connecting: This is what goes in httpd.conf: - RewriteEngine On - RewriteRule /vnc/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PO -RT=563&urlPrefix=_2F_vnc_2F_$1 [R,NE] - RewriteRule /vnc/trust/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PO -RT=563&urlPrefix=_2F_vnc_2F_$1&trustAllVncCerts=yes [R,NE] - RewriteRule /vnc/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PO -RT=563&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes [R,NE] - RewriteRule /vnc/trust/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PO -RT=563&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes&trustAllVncCerts=yes [R,NE] - - The httpsPort and urlPrefix provide useful hints to the VNC Viewer - applet when it connects to x11vnc to glean information about Proxies, - certificates, etc. - - This is what goes into ssl.conf: - RewriteEngine On - RewriteRule /vnc/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&P -ORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vnc_2F_$1 [R,NE] - RewriteRule /vnc/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&P -ORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes [R,NE] - RewriteRule /vncs/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$1+5915&P -ORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1 [R,NE] - RewriteRule /vncs/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$1+5915&P -ORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes [R,NE] - RewriteRule /vncs/trust/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$1+5915&P -ORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&trustAllVncCerts=yes [R,NE -] - RewriteRule /vncs/trust/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$1+5915&P -ORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes&trustAllVnc -Certs=yes [R,NE] - - The rest is the same. - - The httpsPort and urlPrefix and GET provide useful hints to the VNC - Viewer applet when it connects to x11vnc to glean information about - Proxies, certificates, etc, and also for the ultimate VNC connection - (GET speeds this up by sending a special HTTP GET to cause x11vnc to - immediately switch to the VNC protocol). - - To turn these into URLs, as was done above, take the string in the - RewriteRule, e.g. /vncs and turn it into - https://gateway/vncs/machinename Similarly for non-https: - http://gateway:563/vnc/machinename - - If you use the 'trust' ones, you are performing NO checks, visual or - otherwise, on the VNC SSL certificate. It is trusted without question. - This speeds things up because it avoids a dialog about certificates, - but of course has some risk WRT Man in the Middle attacks. I don't - recommend them. It is better to use /vnc or /vncs and the first time - you connect carefully check the Certificate and then tell your Browser - and Java Virtual Machine to trust the certificate 'Always'. Then if - you later get an unexpected dialog, you know something is wrong. - Nearly always it is just a changed or expired certificate, but better - safe than sorry... - -======================================================================= -http://www.karlrunge.com/x11vnc/enhanced_tightvnc_viewer.html: - - - _________________________________________________________________ - -Enhanced TightVNC Viewer (SSVNC: SSL/SSH VNC viewer) - - (To Downloads) (To Quick Start) - - [ssvnc.gif] [ssvnc_windows.gif] [ssvnc_macosx.gif] . . - - - The Enhanced TightVNC Viewer, SSVNC, adds encryption security to VNC - connections. - - The package provides a GUI for Windows, Mac OS X, and Unix that - automatically starts up an STUNNEL SSL tunnel for SSL or ssh/plink for - SSH connections to any VNC server, such as x11vnc, and then launches - the VNC Viewer to use the encrypted tunnel. - - The x11vnc server has built-in SSL support, however SSVNC can make SSL - encrypted VNC connections to any VNC Server if they are running an SSL - tunnel, such as STUNNEL or socat, at their end. SSVNC's SSH tunnel - will work to any VNC Server host running sshd that you can log into. - - The Enhanced TightVNC Viewer package started as a project to add some - patches to the long neglected Unix TightVNC Viewer. However, now the - front-end GUI, encryption, and wrapper scripts features possibly - outweigh the Unix TightVNC Viewer improvements (see the lists below to - compare). - - The SSVNC Unix vncviewer can also be run without the SSVNC encryption - GUI as an enhanced replacement for the xvncviewer, xtightvncviewer, - etc., viewers. - - In addition to normal SSL, SSVNC also supports the VeNCrypt SSL/TLS - and Vino/ANONTLS encryption extensions to VNC on Unix, Mac OS X, and - Windows. Via the provided SSVNC VeNCrypt bridge, VeNCrypt and ANONTLS - encryption also works with any third party VNC Viewer (e.g. RealVNC, - TightVNC, UltraVNC, etc...) you select via 'Change VNC Viewer'. - - The short name for this project is "ssvnc" for SSL/SSH VNC Viewer. - This is the name of the command to start it. - - There is a simplified SSH-Only mode (sshvnc). And an even more - simplified Terminal-Services mode (tsvnc) for use with x11vnc on the - remote side. - - The tool has many additional features; see the descriptions below. - - It is a self-contained bundle, you could carry it around on, say, a - USB memory stick / flash drive for secure VNC viewing from almost any - machine, Unix, Mac OS X, and Windows (and if you create a directory - named "Home" in the toplevel ssvnc directory on the drive your VNC - profiles and certs will be kept there as well). For Unix, there is - also a conventional source tarball to build and install in the normal - way and not use a pre-built bundle. - - _________________________________________________________________ - - Announcements: - - Important: If you created any SSL certificates with SSVNC (or anything - else) on a Debian or Ubuntu system from Sept. 2006 through May 2008, - then those keys are likely extremely weak and can be easily cracked. - The certificate files should be deleted and recreated on a non-Debian - system or an updated one. See - http://www.debian.org/security/2008/dsa-1571 for details. The same - applies to SSH keys. - - Please read this information on using SSVNC on workstations with - Untrusted Local Users. - - _________________________________________________________________ - - Feature List: - - Wrapper scripts and a tcl/tk GUI were written to create these features - for Unix, Mac OS X, and Windows: - * SSL support for connections using the bundled stunnel program. - * Automatic SSH connections from the GUI (system ssh is used on Unix - and MacOS X; bundled plink is used on Windows) - * Ability to Save and Load VNC profiles for different hosts. - * You can also use your own VNC Viewer, e.g. UltraVNC or RealVNC, - with the SSVNC encryption GUI front-end if you prefer. - * Create or Import SSL Certificates and Private Keys. - * Reverse (viewer listening) VNC connections via SSL and SSH. - * VeNCrypt SSL/TLS VNC encryption support (used by VeNCrypt, QEMU, - ggi, libvirt/virt-manager/xen, vinagre/gvncviewer/gtk-vnc) - * ANONTLS SSL/TLS VNC encryption support (used by Vino) - * VeNCrypt and ANONTLS are also enabled for any 3rd party VNC Viewer - (e.g. RealVNC, TightVNC, UltraVNC ...) on Unix, MacOSX, and - Windows via the provided SSVNC VeNCrypt Viewer Bridge tool (use - 'Change VNC Viewer' to select the one you want.) - * Support for Web Proxies, SOCKS Proxies, and the UltraVNC repeater - proxy (e.g. repeater://host:port+ID:1234). Multiple proxies may be - chained together (3 max). - * Support for SSH Gateway connections and non-standard SSH ports. - * Automatic Service tunnelling via SSH for CUPS and SMB Printing, - ESD/ARTSD Audio, and SMB (Windows/Samba) filesystem mounting. - * Sets up any additional SSH port redirections that you want. - * Zeroconf (aka Bonjour) is used on Unix and Mac OS X to find VNC - servers on your local network if the avahi-browse or dns-sd - program is available and in your PATH. - * Port Knocking for "closed port" SSH/SSL connections. In addition - to a simple fixed port sequence and one-time-pad implementation, a - hook is also provided to run any port knocking client before - connecting. - * Support for native MacOS X usage with bundled Chicken of the VNC - viewer (the Unix X11 viewer is also provided for MacOS X, and is - better IMHO. It is now the default on MacOS X.) - * Dynamic VNC Server Port determination and redirection (using ssh's - builtin SOCKS proxy, ssh -D) for servers like x11vnc that print - out PORT= at startup. - * Unix Username and Password entry for use with "x11vnc -unixpw" - type login dialogs. - * Simplified mode launched by command "sshvnc" that is SSH Only. - * Simplified mode launched by command "tsvnc" that provides a VNC - "Terminal Services" mode (uses x11vnc on the remote side). - * IPv6 support for all connection modes on Unix, MacOSX, and - Windows. - - Patches to TightVNC 1.3.9 vnc_unixsrc tree were created for Unix - TightVNC Viewer improvements (these only apply to the Unix VNC viewer, - including MacOSX XQuartz): - * rfbNewFBSize VNC support (dynamic screen resizing) - * Client-side Scaling of the Desktop in the viewer. - * ZRLE VNC encoding support (RealVNC's encoding) - * Support for the ZYWRLE encoding, a wavelet based extension to ZRLE - to improve compression of motion video and photo regions. - * TurboVNC support (VirtualGL's modified TightVNC encoding; requires - TurboJPEG library) - * Pipelined Updates of the framebuffer as in TurboVNC (asks for the - next update before the current one has finished downloading; this - gives some speedup on high latency connections.) - * Cursor alphablending with x11vnc at 32bpp (-alpha option) - * Option "-unixpw ..." for use with "x11vnc -unixpw" type login - dialogs. - * Support for UltraVNC extensions: 1/n Server side scaling, Text - Chat, Single Window, Disable Server-side Input. Both UltraVNC and - x11vnc servers support these extensions. - * UltraVNC File Transfer via an auxiliary Java helper program (java - must be in $PATH). Note that the x11vnc server also supports - UltraVNC file transfer. - * Connection support for the UltraVNC repeater proxy (-repeater - option). - * Support for UltraVNC Single Click operation. (both unencrypted: SC - I, and SSL encrypted: SC III) - * Support for UltraVNC DSM Encryption Plugin symmetric encryption - mode. (ARC4, AESV2, MSRC4, and SecureVNC) - * Support for UltraVNC MS-Logon authentication (NOTE: the UltraVNC - MS-Logon key exchange implementation is very weak; an eavesdropper - on the network can recover your Windows password easily in a few - seconds; you need to use an additional encrypted tunnel with - MS-Logon.) - * Support for symmetric encryption (including blowfish and 3des - ciphers) to Non-UltraVNC Servers. Any server using the same - encryption method will work, e.g.: x11vnc -enc blowfish:./my.key - * Instead of hostname:display one can also supply "exec=command - args..." to connect the viewer to the stdio of an external command - (e.g. stunnel or socat) rather than using a TCP/IP socket. Unix - domain sockets, e.g. /path/to/unix/socket, and a previously opened - file descriptor fd=0, work too. - * Local Port Protections for STUNNEL and SSH: avoid having for long - periods of time a listening port on the the local (VNC viewer) - side that redirects to the remote side. - * Reverse (viewer listening) VNC connections can show a Popup dialog - asking whether to accept the connection or not (-acceptpopup.) The - extra info provided by UltraVNC Single Click reverse connections - is also supported (-acceptpopupsc) - * Extremely low color modes: 64 and 8 colors in 8bpp - (-use64/-bgr222, -use8/-bgr111) - * Medium color mode: 16bpp mode on a 32bpp Viewer display - (-16bpp/-bgr565) - * For use with x11vnc's client-side caching -ncache method use the - cropping option -ycrop n. This will "hide" the large pixel buffer - cache below the actual display. Set to the actual height or use -1 - for autodetection (also, tall screens, H > 2*W, are autodetected - by default). - * Escape Keys: specify a set of modifier keys so that when they are - all pressed down you can invoke Popup menu actions via keystrokes. - I.e., a set of 'Hot Keys'. One can also pan (move) the desktop - inside the viewport via Arrow keys or a mouse drag. - * Scrollbar width setting: -sbwidth n, the default is very thin, 2 - pixels, for less distracting -ycrop usage. - * Selection text sending and receiving can be fine-tuned with the - -sendclipboard, -sendalways, and -recvtext options. - * TightVNC compression and quality levels are automatically set - based on observed network latency (n.b. not bandwidth.) - * Improvements to the Popup menu, all of these can now be changed - dynamically via the menu: ViewOnly, Toggle Bell, CursorShape - updates, X11 Cursor, Cursor Alphablending, Toggle Tight/ZRLE, - Toggle JPEG, FullColor/16bpp/8bpp (256/64/8 colors), Greyscale for - low color modes, Scaling the Viewer resolution, Escape Keys, - Pipeline Updates, and others, including UltraVNC extensions. - * Maintains its own BackingStore if the X server does not. - * The default for localhost:0 connections is not raw encoding since - same-machine connections are pretty rare. Default assumes you are - using a SSL or SSH tunnel. Use -rawlocal to revert. - * XGrabServer support for fullscreen mode, for old window managers - (-grab/-graball option). - * Fix for Popup menu positioning for old window managers (-popupfix - option). - * The VNC Viewer ssvncviewer supports IPv6 natively (no helpers - needed.) - - The list of 3rd party software bundled in the archive files: - * TightVNC Viewer (windows, unix, macosx) - * Chicken of the VNC Viewer (macosx) - * Stunnel (windows, unix, macosx) - * Putty/Plink/Pageant (windows) - * OpenSSL (windows) - * esound (windows) - - These are all self-contained in the bundle directory: they will not be - installed on your system. Just un-zip or un-tar the file you - downloaded and run the frontend ssvnc straight from its directory. - Alternatively, on Unix you can use the conventional source tarball. - - _________________________________________________________________ - - Here is the Quick Start info from the README for how to setup and use - SSVNC: -Quick Start: ------------ - -Unix and Mac OS X: - - Inside a Terminal do something like the following. - - Unpack the archive: - - % gzip -dc ssvnc-1.0.29.tar.gz | tar xvf - - - Run the GUI: - - % ./ssvnc/Unix/ssvnc (for Unix) - - % ./ssvnc/MacOSX/ssvnc (for Mac OS X) - - The smaller file "ssvnc_no_windows-1.0.29.tar.gz" - could have been used as well. - - On MacOSX you could also click on the SSVNC app icon in the Finder. - - On MacOSX if you don't like the Chicken of the VNC (e.g. no local - cursors, no screen size rescaling, and no password prompting), and you - have the XDarwin X server installed, you can set DISPLAY before starting - ssvnc (or type DISPLAY=... in Host:Disp and hit Return). Then our - enhanced TightVNC viewer will be used instead of COTVNC. - Update: there is now a 'Use X11 vncviewer on MacOSX' under Options ... - - - If you want a SSH-only tool (without the distractions of SSL) run - the command: - - sshvnc - - instead of "ssvnc". Or click "SSH-Only Mode" under Options. - Control-h will toggle between the two modes. - - - If you want a simple VNC Terminal Services only mode (requires x11vnc - on the remote server) run the command: - - tsvnc - - instead of "ssvnc". Or click "Terminal Services" under Options. - Control-t will toggle between the two modes. - - "tsvnc profile-name" and "tsvnc user@hostname" work too. - - -Unix/MacOSX Install: - - There is no standard install for the bundles, but you can make - symlinks like so: - - cd /a/directory/in/PATH - ln -s /path/to/ssvnc/bin/{s,t}* . - - Or put /path/to/ssvnc/bin, /path/to/ssvnc/Unix, or /path/to/ssvnc/MacOSX - in your PATH. - - For the conventional source tarball it will compile and install, e.g.: - - gzip -dc ssvnc-1.0.29.src.tar.gz | tar xvf - - cd ssvnc-1.0.29 - make config - make all - make PREFIX=/my/install/dir install - - then have /my/install/dir/bin in your PATH. - - - -Windows: - - Unzip, using WinZip or a similar utility, the zip file: - - ssvnc-1.0.29.zip - - Run the GUI, e.g.: - - Start -> Run -> Browse - - and then navigate to - - .../ssvnc/Windows/ssvnc.exe - - select Open, and then OK to launch it. - - The smaller file "ssvnc_windows_only-1.0.29.zip" - could have been used as well. - - You can make a Windows shortcut to this program if you want to. - - See the Windows/README.txt for more info. - - - If you want a SSH-only tool (without the distractions of SSL) run - the command: - - sshvnc.bat - - Or click "SSH-Only Mode" under Options. - - - If you want a simple VNC Terminal Services only mode (requires x11vnc - on the remote server) run the command: - - tsvnc.bat - - Or click "Terminal Services" under Options. Control-t will toggle - between the two modes. "tsvnc profile-name" and "tsvnc user@hostname" - work too. - - _________________________________________________________________ - - You can read all of the SSVNC GUI's Online Help Text here. - _________________________________________________________________ - - The bundle unpacks a directory/folder named: ssvnc. It contains these - programs to launch the GUI: - Windows/ssvnc.exe for Windows - MacOSX/ssvnc for Mac OS X - Unix/ssvnc for Unix - - (the Mac OS X and Unix launchers are simply links to the bin - directory). See the README for more information. - - The SSH-Only mode launcher program has name sshvnc. The Terminal - Services mode launcher program (assumes x11vnc 0.8.4 or later and Xvfb - installed on the server machine) has name tsvnc. - - The Viewer SSL support is done via a wrapper script (bin/ssvnc_cmd - that calls bin/util/ss_vncviewer) that starts up the STUNNEL tunnel - first and then starts the TightVNC viewer pointed at that tunnel. The - bin/ssvnc program is a GUI front-end to that script. See this FAQ for - more details on SSL tunnelling. In SSH connection mode, the wrappers - start up SSH appropriately. - - - Memory Stick Usage: If you create a directory named "Home" in that - toplevel ssvnc directory then that will be used as the base for - storing VNC profiles and certificates. Also, for convenience, if you - first run the command with "." as an argument (e.g. "ssvnc .") it will - automatically create the "Home" directory for you. This is handy if - you want to place SSVNC on a USB flash drive that you carry around for - mobile use and you want the profiles you create to stay with the drive - (otherwise you'd have to browse to the drive directory each time you - load or save). - - One user on Windows created a BAT file to launch SSVNC and needed to - do this to get the Home directory correct: -cd \ssvnc\Windows -start \ssvnc\Windows\ssvnc.exe - - (an optional profile name can be supplied to the ssvnc.exe line) - - WARNING: if you use ssvnc from an "Internet Cafe", i.e. some untrusted - computer, please be aware that someone may have set up that machine to - be capturing your keystrokes, etc. - - - SSH-Only version: The command "sshvnc" can be run instead of "ssvnc" - to get an SSH-only version of the tool: - - [sshvnc.gif] - - These also work: "sshvnc myprofile" and "sshvnc user@hostname". To - switch from the regular SSVNC mode, click "SSH-Only Mode" under - Options. This mode is less distracting if you never plan to use SSL, - manage certificates, etc. - - - Terminal Services Only: The command "tsvnc" can be run instead of - "ssvnc" to get a "Terminal Services" only version of the tool: - - [tsvnc.gif] - - These also work: "tsvnc myprofile" and "tsvnc user@hostname". To - switch from the regular SSVNC mode, click "Terminal Services" under - Options. - - This mode requires x11vnc (0.9.3 or later) installed on the remote - machine to find, create, and manage the user sessions. SSH is used to - create the encrypted and authenticated tunnel. The Xvfb (virtual - framebuffer X server) program must also be installed on the remote - system. However tsvnc will also connect to a real X session (i.e. on - the physical hardware) if you are already logged into the X session; - this is a useful access mode and does not require Xvfb on the remote - system. - - This mode should be very easy for beginner users to understand and - use. On the remote end you only need to have x11vnc and Xvfb available - in $PATH, and on the local end you just run something like: - tsvnc myname@myhost.com - - (or start up the tsvnc GUI first and then enter myname@myhost.com and - press "Connect"). - - Normally the Terminal Services sessions created are virtual (RAM-only) - ones (e.g. Xvfb, Xdummy, or Xvnc), however a nice feature is if you - have a regular X session (i.e displaying on the physical hardware) on - the remote machine that you are ALREADY logged into, then the x11vnc - run from tsvnc will find it for you as well. - - Also, there is setting "X Login" under Advanced Options that allows - you to attach to a real X server with no one logged in yet (i.e. - XDM/GDM/KDM Login Greeter screen) as long as you have sudo(1) - permission on the remote machine. - - Nice features to soon to be added to the tsvnc mode are easy CUPS - printing (working fairly well) and Sound redirection (needs much work) - of the Terminal Services Desktop session. It is easier in tsvnc mode - because the entire desktop session can be started with the correct - environment. ssvnc tries to handle the general case of an already - started desktop and that is more difficult. - - - Proxies: Web proxies, SOCKS proxies, and the UltraVNC repeater proxy - are supported to allow the SSVNC connection to go through the proxy to - the otherwise unreachable VNC Server. SSH gateway machines can be used - in the same way. Read more about SSVNC proxy support here. - - - Dynamic VNC Server Port determination: If you are running SSVNC on - Unix and are using SSH to start the remote VNC server and the VNC - server prints out the line "PORT=NNNN" to indicate which dynamic port - it is using (x11vnc does this), then if you prefix the SSH command - with "PORT=" SSVNC will watch for the PORT=NNNN line and uses ssh's - built in SOCKS proxy (ssh -D ...) to connect to the dynamic VNC server - port through the SSH tunnel. For example: - VNC Host:Display user@somehost.com - Remote SSH Command: PORT= x11vnc -find - - or "PORT= x11vnc -display :0 -localhost", etc. Or use "P= x11vnc ..." - - There is also code to detect the display of the regular Unix - vncserver(1). It extracts the display (and hence port) from the lines - "New 'X' desktop is hostname:4" and also "VNC server is already - running as :4". So you can use something like: - PORT= vncserver; sleep 15 -or: PORT= vncserver :4; sleep 15 - - the latter is preferred because when you reconnect with it will find - the already running one. The former one will keep creating new X - sessions if called repeatedly. - - If you use PORT= on Windows, a large random port is selected instead - and the -rfbport option is passed to x11vnc (it does not work with - vncserver). - - - - Patches for Unix Tightvnc viewer: - - The rfbNewFBSize support allows the enhanced TightVNC Unix viewer to - resize when the server does (e.g. "x11vnc -R scale=3/4" remote control - command). - - The cursor alphablending is described here. - - The RealVNC ZRLE encoding is supported, in addition to some low colors - modes (16bpp and 8bpp at 256, 64, and even 8 colors, for use on very - slow connections). Greyscales are also enabled for the low color - modes. - - The Popup menu (F8) is enhanced with the ability to change many things - on the fly. F9 is added as a shortcut to toggle FullScreen mode. - - Client Side Caching: The x11vnc client-side caching is handled nicely - by this viewer. The very large pixel cache below the actual display in - this caching method is distracting. Our Unix VNC viewer will - automatically try to autodetect the actual display height if the - framebuffer is very tall (more than twice as high as it is wide). One - can also set the height to the known value via -ycrop n, or use -ycrop - -1 to force autodection. In fullscreen mode one is not possible to - scroll down to the pixel cache region. In non-fullscreen mode the - window manager frame is "shrink-wrapped" around the actual screen - display. You can still scroll down to the pixel cache region. The - scrollbars are set to be very thin (2 pixels) to be less distracting. - Use the -sbwidth n to make them wider. - - Probably nobody is interested in the grabserver patch for old window - managers when the viewer is in fullscreen mode... This and some other - unfixed bugs have been fixed in our patches (fullscreen toggle works - with KDE, -x11cursor has been fixed, and the dot cursor has been made - smaller). - - From the -help output: -SSVNC Viewer (based on TightVNC viewer version 1.3.9) - -Usage: vncviewer [] [][:] - vncviewer [] [][::] - vncviewer [] exec=[CMD ARGS...] - vncviewer [] fd=n - vncviewer [] /path/to/unix/socket - vncviewer [] -listen [] - vncviewer -help - - are standard Xt options, or: - -via - -shared (set by default) - -noshared - -viewonly - -fullscreen - -noraiseonbeep - -passwd (standard VNC authentication) - -user (Unix login authentication) - -encodings (e.g. "tight,copyrect") - -bgr233 - -owncmap - -truecolour - -depth - -compresslevel (0..9: 0-fast, 9-best) - -quality (0..9: 0-low, 9-high) - -nojpeg - -nocursorshape - -x11cursor - -autopass - -Option names may be abbreviated, e.g. -bgr instead of -bgr233. -See the manual page for more information. - - -Enhanced TightVNC viewer (SSVNC) options: - - URL http://www.karlrunge.com/x11vnc/ssvnc.html - - Note: ZRLE and ZYWRLE encodings are now supported. - - Note: F9 is shortcut to Toggle FullScreen mode. - - Note: In -listen mode set the env var. SSVNC_MULTIPLE_LISTEN=1 - to allow more than one incoming VNC server at a time. - This is the same as -multilisten described below. Set - SSVNC_MULTIPLE_LISTEN=MAX:n to allow no more than "n" - simultaneous reverse connections. - - Note: If the host:port is specified as "exec=command args..." - then instead of making a TCP/IP socket connection to the - remote VNC server, "command args..." is executed and the - viewer is attached to its stdio. This enables tunnelling - established via an external command, e.g. an stunnel(8) - that does not involve a listening socket. This mode does - not work for -listen reverse connections. - - If the host:port is specified as "fd=n" then it is assumed - n is an already opened file descriptor to the socket. (i.e - the parent did fork+exec) - - If the host:port contains a '/' it is interpreted as a - unix-domain socket (AF_LOCAL insead of AF_INET) - - -multilisten As in -listen (reverse connection listening) except - allow more than one incoming VNC server to be connected - at a time. The default for -listen of only one at a - time tries to play it safe by not allowing anyone on - the network to put (many) desktops on your screen over - a long window of time. Use -multilisten for no limit. - - -acceptpopup In -listen (reverse connection listening) mode when - a reverse VNC connection comes in show a popup asking - whether to Accept or Reject the connection. The IP - address of the connecting host is shown. Same as - setting the env. var. SSVNC_ACCEPT_POPUP=1. - - -acceptpopupsc As in -acceptpopup except assume UltraVNC Single - Click (SC) server. Retrieve User and ComputerName - info from UltraVNC Server and display in the Popup. - - -use64 In -bgr233 mode, use 64 colors instead of 256. - -bgr222 Same as -use64. - - -use8 In -bgr233 mode, use 8 colors instead of 256. - -bgr111 Same as -use8. - - -16bpp If the vnc viewer X display is depth 24 at 32bpp - request a 16bpp format from the VNC server to cut - network traffic by up to 2X, then tranlate the - pixels to 32bpp locally. - -bgr565 Same as -16bpp. - - -grey Use a grey scale for the 16- and 8-bpp modes. - - -alpha Use alphablending transparency for local cursors - requires: x11vnc server, both client and server - must be 32bpp and same endianness. - - -scale str Scale the desktop locally. The string "str" can - a floating point ratio, e.g. "0.9", or a fraction, - e.g. "3/4", or WxH, e.g. 1280x1024. Use "fit" - to fit in the current screen size. Use "auto" to - fit in the window size. "str" can also be set by - the env. var. SSVNC_SCALE. - - If you observe mouse trail painting errors, enable - X11 Cursor mode (either via Popup or -x11cursor.) - - Note that scaling is done in software and so can be - slow and requires more memory. Some speedup Tips: - - ZRLE is faster than Tight in this mode. When - scaling is first detected, the encoding will - be automatically switched to ZRLE. Use the - Popup menu if you want to go back to Tight. - Set SSVNC_PRESERVE_ENCODING=1 to disable this. - - Use a solid background on the remote side. - (e.g. manually or via x11vnc -solid ...) - - If the remote server is x11vnc, try client - side caching: x11vnc -ncache 10 ... - - -ycrop n Only show the top n rows of the framebuffer. For - use with x11vnc -ncache client caching option - to help "hide" the pixel cache region. - Use a negative value (e.g. -1) for autodetection. - Autodetection will always take place if the remote - fb height is more than 2 times the width. - - -sbwidth n Scrollbar width for x11vnc -ncache mode (-ycrop), - default is very narrow: 2 pixels, it is narrow to - avoid distraction in -ycrop mode. - - -nobell Disable bell. - - -rawlocal Prefer raw encoding for localhost, default is - no, i.e. assumes you have a SSH tunnel instead. - - -notty Try to avoid using the terminal for interactive - responses: use windows for messages and prompting - instead. Messages will also be printed to terminal. - - -sendclipboard Send the X CLIPBOARD selection (i.e. Ctrl+C, - Ctrl+V) instead of the X PRIMARY selection (mouse - select and middle button paste.) - - -sendalways Whenever the mouse enters the VNC viewer main - window, send the selection to the VNC server even if - it has not changed. This is like the Xt resource - translation SelectionToVNC(always) - - -recvtext str When cut text is received from the VNC server, - ssvncviewer will set both the X PRIMARY and the - X CLIPBOARD local selections. To control which - is set, specify 'str' as 'primary', 'clipboard', - or 'both' (the default.) - - -graball Grab the entire X server when in fullscreen mode, - needed by some old window managers like fvwm2. - - -popupfix Warp the popup back to the pointer position, - needed by some old window managers like fvwm2. - -sendclipboard Send the X CLIPBOARD selection (i.e. Ctrl+C, - Ctrl+V) instead of the X PRIMARY selection (mouse - select and middle button paste.) - - -sendalways Whenever the mouse enters the VNC viewer main - window, send the selection to the VNC server even if - it has not changed. This is like the Xt resource - translation SelectionToVNC(always) - - -recvtext str When cut text is received from the VNC server, - ssvncviewer will set both the X PRIMARY and the - X CLIPBOARD local selections. To control which - is set, specify 'str' as 'primary', 'clipboard', - or 'both' (the default.) - - -graball Grab the entire X server when in fullscreen mode, - needed by some old window managers like fvwm2. - - -popupfix Warp the popup back to the pointer position, - needed by some old window managers like fvwm2. - - -grabkbd Grab the X keyboard when in fullscreen mode, - needed by some window managers. Same as -grabkeyboard. - -grabkbd is the default, use -nograbkbd to disable. - - -bs, -nobs Whether or not to use X server Backingstore for the - main viewer window. The default is to not, mainly - because most Linux, etc, systems X servers disable - *all* Backingstore by default. To re-enable it put - - Option "Backingstore" - - in the Device section of /etc/X11/xorg.conf. - In -bs mode with no X server backingstore, whenever an - area of the screen is re-exposed it must go out to the - VNC server to retrieve the pixels. This is too slow. - - In -nobs mode, memory is allocated by the viewer to - provide its own backing of the main viewer window. This - actually makes some activities faster (changes in large - regions) but can appear to "flash" too much. - - -noshm Disable use of MIT shared memory extension (not recommended -) - - -termchat Do the UltraVNC chat in the terminal vncviewer is in - instead of in an independent window. - - -unixpw str Useful for logging into x11vnc in -unixpw mode. "str" is a - string that allows many ways to enter the Unix Username - and Unix Password. These characters: username, newline, - password, newline are sent to the VNC server after any VNC - authentication has taken place. Under x11vnc they are - used for the -unixpw login. Other VNC servers could do - something similar. - - You can also indicate "str" via the environment - variable SSVNC_UNIXPW. - - Note that the Escape key is actually sent first to tell - x11vnc to not echo the Unix Username back to the VNC - viewer. Set SSVNC_UNIXPW_NOESC=1 to override this. - - If str is ".", then you are prompted at the command line - for the username and password in the normal way. If str is - "-" the stdin is read via getpass(3) for username@password. - Otherwise if str is a file, it is opened and the first line - read is taken as the Unix username and the 2nd as the - password. If str prefixed by "rm:" the file is removed - after reading. Otherwise, if str has a "@" character, - it is taken as username@password. Otherwise, the program - exits with an error. Got all that? - - -repeater str This is for use with UltraVNC repeater proxy described - here: http://www.uvnc.com/addons/repeater.html. The "str" - is the ID string to be sent to the repeater. E.g. ID:1234 - It can also be the hostname and port or display of the VNC - server, e.g. 12.34.56.78:0 or snoopy.com:1. Note that when - using -repeater, the host:dpy on the cmdline is the repeate -r - server, NOT the VNC server. The repeater will connect you. - - Example: vncviewer ... -repeater ID:3333 repeat.host:5900 - Example: vncviewer ... -repeater vhost:0 repeat.host:5900 - - Use, e.g., '-repeater SCIII=ID:3210' if the repeater is a - Single Click III (SSL) repeater (repeater_SSL.exe) and you - are passing the SSL part of the connection through stunnel, - socat, etc. This way the magic UltraVNC string 'testB' - needed to work with the repeater is sent to it. - - -rfbversion str Set the advertised RFB version. E.g.: -rfbversion 3.6 - For some servers, e.g. UltraVNC this needs to be done. - - -ultradsm UltraVNC has symmetric private key encryption DSM plugins: - http://www.uvnc.com/features/encryption.html. It is assumed - you are using a unix program (e.g. our ultravnc_dsm_helper) - to encrypt and decrypt the UltraVNC DSM stream. IN ADDITION - TO THAT supply -ultradsm to tell THIS viewer to modify the - RFB data sent so as to work with the UltraVNC Server. For - some reason, each RFB msg type must be sent twice under DSM -. - - -mslogon user Use Windows MS Logon to an UltraVNC server. Supply the - username or "1" to be prompted. The default is to - autodetect the UltraVNC MS Logon server and prompt for - the username and password. - - IMPORTANT NOTE: The UltraVNC MS-Logon Diffie-Hellman - exchange is very weak and can be brute forced to recover - your username and password in a few seconds of CPU time. - To be safe, be sure to use an additional encrypted tunnel - (e.g. SSL or SSH) for the entire VNC session. - - -chatonly Try to be a client that only does UltraVNC text chat. This - mode is used by x11vnc to present a chat window on the - physical X11 console (i.e. chat with the person at the - display). - - -env VAR=VALUE To save writing a shell script to set environment variables -, - specify as many as you need on the command line. For - example, -env SSVNC_MULTIPLE_LISTEN=MAX:5 -env EDITOR=vi - - -noipv6 Disable all IPv6 sockets. Same as VNCVIEWER_NO_IPV6=1. - - -noipv4 Disable all IPv4 sockets. Same as VNCVIEWER_NO_IPV4=1. - - -printres Print out the Ssvnc X resources (appdefaults) and then exit - You can save them to a file and customize them (e.g. the - keybindings and Popup menu) Then point to the file via - XENVIRONMENT or XAPPLRESDIR. - - -pipeline Like TurboVNC, request the next framebuffer update as soon - as possible instead of waiting until the end of the current - framebuffer update coming in. Helps 'pipeline' the updates -. - This is currently the default, use -nopipeline to disable. - - -appshare Enable features for use with x11vnc's -appshare mode where - instead of sharing the full desktop only the application's - windows are shared. Viewer multilisten mode is used to - create the multiple windows: -multilisten is implied. - See 'x11vnc -appshare -help' more information on the mode. - - Features enabled in the viewer under -appshare are: - Minimum extra text in the title, auto -ycrop is disabled, - x11vnc -remote_prefix X11VNC_APPSHARE_CMD: message channel, - x11vnc initial window position hints. See also Escape Keys - below for additional key and mouse bindings. - - -escape str This sets the 'Escape Keys' modifier sequence and enables - escape keys mode. When the modifier keys escape sequence - is held down, the next keystroke is interpreted locally - to perform a special action instead of being sent to the - remote VNC server. - - Use '-escape default' for the default modifier sequence. - (Unix: Alt_L,Super_L and MacOSX: Control_L,Meta_L) - - Here are the 'Escape Keys: Help+Set' instructions from the Popup Menu: - - Escape Keys: Enter a comma separated list of modifier keys to be the - 'escape sequence'. When these keys are held down, the next keystroke is - interpreted locally to invoke a special action instead of being sent to - the remote VNC server. In other words, a set of 'Hot Keys'. - - To enable or disable this, click on 'Escape Keys: Toggle' in the Popup. - - Here is the list of hot-key mappings to special actions: - - r: refresh desktop b: toggle bell c: toggle full-color - f: file transfer x: x11cursor z: toggle Tight/ZRLE - l: full screen g: graball e: escape keys dialog - s: scale dialog +: scale up (=) -: scale down (_) - t: text chat a: alphablend cursor - V: toggle viewonly Q: quit viewer 1 2 3 4 5 6: UltraVNC scale 1/n - - Arrow keys: pan the viewport about 10% for each keypress. - PageUp / PageDown: pan the viewport by a screenful vertically. - Home / End: pan the viewport by a screenful horizontally. - KeyPad Arrow keys: pan the viewport by 1 pixel for each keypress. - Dragging the Mouse with Button1 pressed also pans the viewport. - Clicking Mouse Button3 brings up the Popup Menu. - - The above mappings are *always* active in ViewOnly mode, unless you set the - Escape Keys value to 'never'. - - If the Escape Keys value below is set to 'default' then a default list of - of modifier keys is used. For Unix it is: Alt_L,Super_L and for MacOSX it - is Control_L,Meta_L. Note: the Super_L key usually has a Windows(TM) Flag - on it. Also note the _L and _R mean the key is on the LEFT or RIGHT side - of the keyboard. - - On Unix the default is Alt and Windows keys on Left side of keyboard. - On MacOSX the default is Control and Command keys on Left side of keyboard. - - Example: Press and hold the Alt and Windows keys on the LEFT side of the - keyboard and then press 'c' to toggle the full-color state. Or press 't' - to toggle the ultravnc Text Chat window, etc. - - To use something besides the default, supply a comma separated list (or a - single one) from: Shift_L Shift_R Control_L Control_R Alt_L Alt_R Meta_L - Meta_R Super_L Super_R Hyper_L Hyper_R or Mode_switch. - - - New Popup actions: - - ViewOnly: ~ -viewonly - Disable Bell: ~ -nobell - Cursor Shape: ~ -nocursorshape - X11 Cursor: ~ -x11cursor - Cursor Alphablend: ~ -alpha - Toggle Tight/Hextile: ~ -encodings hextile... - Toggle Tight/ZRLE: ~ -encodings zrle... - Toggle ZRLE/ZYWRLE: ~ -encodings zywrle... - Quality Level ~ -quality (both Tight and ZYWRLE) - Compress Level ~ -compresslevel - Disable JPEG: ~ -nojpeg (Tight) - Pipeline Updates ~ -pipeline - - Full Color as many colors as local screen allows. - Grey scale (16 & 8-bpp) ~ -grey, for low colors 16/8bpp modes only. - 16 bit color (BGR565) ~ -16bpp / -bgr565 - 8 bit color (BGR233) ~ -bgr233 - 256 colors ~ -bgr233 default # of colors. - 64 colors ~ -bgr222 / -use64 - 8 colors ~ -bgr111 / -use8 - Scale Viewer ~ -scale - Escape Keys: Toggle ~ -escape - Escape Keys: Help+Set ~ -escape - Set Y Crop (y-max) ~ -ycrop - Set Scrollbar Width ~ -sbwidth - XGrabServer ~ -graball - - UltraVNC Extensions: - - Set 1/n Server Scale Ultravnc ext. Scale desktop by 1/n. - Text Chat Ultravnc ext. Do Text Chat. - File Transfer Ultravnc ext. File xfer via Java helper. - Single Window Ultravnc ext. Grab and view a single window. - (select then click on the window you want). - Disable Remote Input Ultravnc ext. Try to prevent input and - viewing of monitor at physical display. - - Note: the Ultravnc extensions only apply to servers that support - them. x11vnc/libvncserver supports some of them. - - Send Clipboard not Primary ~ -sendclipboard - Send Selection Every time ~ -sendalways - - Nearly all of these can be changed dynamically in the Popup menu - (press F8 for it): - - [viewer_menu.gif] [unixviewer.jpg] - - _________________________________________________________________ - - Windows: - - For Windows, SSL Viewer support is provided by a GUI Windows/ssvnc.exe - that prompts for the VNC display and then starts up STUNNEL followed - by the Stock TightVNC Windows Viewer. Both are bundled in the package - for your convenience. The GUI has other useful features. When the - connection is finished, you will be asked if you want to terminate the - STUNNEL program. For SSH connections from Windows the GUI will use - PLINK instead of STUNNEL. - - Unix and Mac OS X: - - Run the GUI (ssvnc, see above) and let me know how it goes. - _________________________________________________________________ - - Hopefully this tool will make it convenient for people to help test - and use the built-in SSL support in x11vnc. Extra testing of this - feature is much appreciated!! Thanks. - - Please Help Test the newly added features: - * Automatic Service tunnelling via SSH for CUPS and SMB Printing - * ESD/ARTSD Audio - * SMB (Windows/Samba) filesystem mounting - - These allow you to print from the remote (VNC Server) machine to local - printers, listen to sounds (with some limitations) from the remote VNC - Server machine, and to mount your local Windows or Samba shares on the - remote VNC Server machine. Basically these new features try to - automate the tricks described here: - http://www.karlrunge.com/x11vnc/faq.html#faq-smb-shares - http://www.karlrunge.com/x11vnc/faq.html#faq-cups - http://www.karlrunge.com/x11vnc/faq.html#faq-sound - _________________________________________________________________ - - Downloading: Downloads for this project are hosted at Sourceforge.net. - - Choose the archive file bundle that best suits you (e.g. no source - code, windows only, unix only, zip, tar etc). - - A quick guide: - - On some flavor of Unix, e.g. Linux or Solaris? Use - "ssvnc_unix_only" (or "ssvnc_no_windows" to recompile). - On Mac OS X? Use "ssvnc_no_windows". - On Windows? Use "ssvnc_windows_only". - ssvnc_windows_only-1.0.28.zip Windows Binaries Only. No source included - (6.2MB) - ssvnc_no_windows-1.0.28.tar.gz Unix and Mac OS X Only. No Windows binarie -s. Source included. (10.1MB) - ssvnc_unix_only-1.0.28.tar.gz Unix Binaries Only. No source included -. (7.2MB) - ssvnc_unix_minimal-1.0.28.tar.gz Unix Minimal. You must supply your own vn -cviewer and stunnel. (0.2MB) - - ssvnc-1.0.28.tar.gz All Unix, Mac OS X, and Windows binaries a -nd source TGZ. (16.1MB) - ssvnc-1.0.28.zip All Unix, Mac OS X, and Windows binaries a -nd source ZIP. (16.4MB) - ssvnc_all-1.0.28.zip All Unix, Mac OS X, and Windows binaries a -nd source AND full archives in the zip dir. (19.2MB) - - - Here is a conventional source tarball: - ssvnc-1.0.28.src.tar.gz Conventional Source for SSVNC GUI and Unix - VNCviewer (0.5MB) - - it will be of use to those who do not want the SSVNC - "one-size-fits-all" bundles. For example, package/distro maintainers - will find this more familiar and useful to them (i.e. they run: "make - config; make all; make install"). Note that it does not include the - stunnel source, and so has a dependency that the system stunnel is - installed. - - Read the README.src file for more information on using the - conventional source tarball. - - - Note: even with the Unix bundles, e.g. "ssvnc_no_windows" or - "ssvnc_all", you may need to run the "./build.unix" script in the top - directory to recompile for your operating system. - - Here are the corresponding 1.0.29 development bundles (Please help - test them): - - ssvnc_windows_only-1.0.29.zip - ssvnc_no_windows-1.0.29.tar.gz - ssvnc_unix_only-1.0.29.tar.gz - ssvnc_unix_minimal-1.0.29.tar.gz - - ssvnc-1.0.29.tar.gz - ssvnc-1.0.29.zip - ssvnc_all-1.0.29.zip - - ssvnc-1.0.29.src.tar.gz Conventional Source for SSVNC GUI and Unix - VNCviewer (0.5MB) - - - For any Unix system, a self-extracting and running file for the - "ssvnc_unix_minimal" package is here: ssvnc. Save it as filename - "ssvnc", type "chmod 755 ./ssvnc", and then launch the GUI via typing - "./ssvnc". Note that this "ssvnc_unix_minimal" mode requires you - install the "stunnel" and "vncviewer" programs externally (for - example, install your distros' versions, e.g. on debian: "apt-get - install stunnel4 xtightvncviewer".) It will work, but many of the - SSVNC features will be missing. - - Previous releases: - Release 1.0.18 at Sourceforge.net - Release 1.0.19 at Sourceforge.net - Release 1.0.20 at Sourceforge.net - Release 1.0.21 at Sourceforge.net - Release 1.0.22 at Sourceforge.net - Release 1.0.23 at Sourceforge.net - Release 1.0.24 at Sourceforge.net - Release 1.0.25 at Sourceforge.net - Release 1.0.26 at Sourceforge.net - Release 1.0.27 at Sourceforge.net - Release 1.0.28 at Sourceforge.net - - - Please help test the UltraVNC File Transfer support in the native Unix - VNC viewer! Let us know how it went. - - Current Unix binaries in the archives: - Linux.i686 - Linux.x86_64 - Linux.ppc64 X (removed) - Linux.alpha X (removed) - SunOS.sun4u - SunOS.sun4m - SunOS.i86pc - Darwin.Power.Macintosh - Darwin.i386 - HP-UX.9000 X (removed) - FreeBSD.i386 X (removed) - NetBSD.i386 X (removed) - OpenBSD.i386 X (removed) - - (some of these are out of date, marked with 'X' above, because I no - longer have access to machines running those OS's. Use the - "build.unix" script to recompile on your system). - - Note: some of the above binaries depend on libssl.so.0.9.7, whereas - some recent distros only provide libssl.so.0.9.8 by default (for - compatibility reasons they should install both by default but not all - do). So you may need to instruct your distro to install the 0.9.7 - library (it is fine to have both runtimes installed simultaneously - since the libraries have different names). Update: I now try to - statically link libssl.a for all of the binaries in the archive. - - You can also run the included build.unix script to try to - automatically build the binaries if your OS is not in the above list - or the included binary does not run properly on your system. Let me - know how that goes. - _________________________________________________________________ - - IMPORTANT: there may be restrictions for you to download, use, or - redistribute the above because of cryptographic software they contain - or for other reasons. Please check out your situation and information - at the following and related sites: - http://stunnel.mirt.net - http://www.stunnel.org - http://www.openssl.org - http://www.chiark.greenend.org.uk/~sgtatham/putty/ - http://www.tightvnc.com - http://www.realvnc.com - http://sourceforge.net/projects/cotvnc/ - _________________________________________________________________ - - README: Here is the toplevel README from the bundle. - -======================================================================= -http://www.karlrunge.com/x11vnc/x11vnc_opts.html: - - - _________________________________________________________________ - -x11vnc: a VNC server for real X displays - - Here are all of x11vnc command line options: -% x11vnc -opts (see below for -help long descriptions) - -x11vnc: allow VNC connections to real X11 displays. 0.9.13 lastmod: 2010-12-27 - -x11vnc options: - -display disp -auth file -N - -autoport n -rfbport str -6 - -no6 -noipv6 -noipv4 - -reopen -reflect host:N -id windowid - -sid windowid -appshare -clip WxH+X+Y - -flashcmap -shiftcmap n -notruecolor - -advertise_truecolor -visual n -overlay - -overlay_nocursor -8to24 [opts] -24to32 - -scale fraction -geometry WxH -scale_cursor frac - -viewonly -shared -once - -forever -loop -timeout n - -sleepin n -inetd -tightfilexfer - -ultrafilexfer -http -http_ssl - -avahi -mdns -zeroconf - -connect string -connect_or_exit str -proxy string - -vncconnect -novncconnect -allow host1[,host2..] - -localhost -unixsock str -listen6 str - -nolookup -input string -grabkbd - -grabptr -ungrabboth -grabalways - -viewpasswd string -passwdfile filename -showrfbauth filename - -unixpw [list] -unixpw_nis [list] -unixpw_cmd cmd - -find -finddpy -listdpy - -findauth [disp] -create -xdummy - -xvnc -xvnc_redirect -xdummy_xvfb - -create_xsrv str -svc -svc_xdummy - -svc_xvnc -svc_xdummy_xvfb -xdmsvc - -sshxdmsvc -unixpw_system_greeter -redirect port - -display WAIT:... -vencrypt mode -anontls mode - -sslonly -dhparams file -nossl - -ssl [pem] -ssltimeout n -sslnofail - -ssldir dir -sslverify path -sslCRL path - -sslGenCA [dir] -sslGenCert type name -sslEncKey pem - -sslCertInfo pem -sslDelCert pem -sslScripts - -stunnel [pem] -stunnel3 [pem] -enc cipher:keyfile - -https [port] -httpsredir [port] -http_oneport - -ssh user@host:disp -usepw -storepasswd pass file - -nopw -accept string -afteraccept string - -gone string -users list -noshm - -flipbyteorder -onetile -solid [color] - -blackout string -xinerama -noxinerama - -xtrap -xrandr [mode] -rotate string - -padgeom WxH -o logfile -flag file - -rmflag file -rc filename -norc - -env VAR=VALUE -prog /path/to/x11vnc -h, -help - -?, -opts -V, -version -license - -dbg -q, -quiet -v, -verbose - -bg -modtweak -nomodtweak - -xkb -noxkb -capslock - -skip_lockkeys -noskip_lockkeys -skip_keycodes string - -sloppy_keys -skip_dups -noskip_dups - -add_keysyms -noadd_keysyms -clear_mods - -clear_keys -clear_all -remap string - -norepeat -repeat -nofb - -nobell -nosel -noprimary - -nosetprimary -noclipboard -nosetclipboard - -seldir string -cursor [mode] -nocursor - -cursor_drag -arrow n -noxfixes - -alphacut n -alphafrac fraction -alpharemove - -noalphablend -nocursorshape -cursorpos - -nocursorpos -xwarppointer -noxwarppointer - -always_inject -buttonmap string -nodragging - -ncache n -ncache_cr -ncache_no_moveraise - -ncache_no_dtchange -ncache_no_rootpixmap -ncache_keep_anims - -ncache_old_wm -ncache_pad n -debug_ncache - -wireframe [str] -nowireframe -nowireframelocal - -wirecopyrect mode -nowirecopyrect -debug_wireframe - -scrollcopyrect mode -noscrollcopyrect -scr_area n - -scr_skip list -scr_inc list -scr_keys list - -scr_term list -scr_keyrepeat lo-hi -scr_parms string - -fixscreen string -debug_scroll -noxrecord - -grab_buster -nograb_buster -debug_grabs - -debug_sel -pointer_mode n -input_skip n - -allinput -input_eagerly -speeds rd,bw,lat - -wmdt string -debug_pointer -debug_keyboard - -defer time -wait time -extra_fbur n - -wait_ui factor -setdefer n -nowait_bog - -slow_fb time -xrefresh time -nap - -nonap -sb time -readtimeout n - -ping n -nofbpm -fbpm - -nodpms -dpms -forcedpms - -clientdpms -noserverdpms -noultraext - -chatwindow -noxdamage -xd_area A - -xd_mem f -sigpipe string -threads - -nothreads -fs f -gaps n - -grow n -fuzz n -debug_tiles - -snapfb -rawfb string -freqtab file - -pipeinput cmd -macnodim -macnosleep - -macnosaver -macnowait -macwheel n - -macnoswap -macnoresize -maciconanim n - -macmenu -macuskbd -macnoopengl - -macnorawfb -gui [gui-opts] -remote command - -query variable -QD variable -sync - -query_retries str -remote_prefix str -noremote - -yesremote -unsafe -safer - -privremote -nocmds -allowedcmds list - -deny_all - -LibVNCServer options: --rfbport port TCP port for RFB protocol --rfbwait time max time in ms to wait for RFB client --rfbauth passwd-file use authentication on RFB protocol - (use 'storepasswd' to create a password file) --rfbversion 3.x Set the version of the RFB we choose to advertise --permitfiletransfer permit file transfer support --passwd plain-password use authentication - (use plain-password as password, USE AT YOUR RISK) --deferupdate time time in ms to defer updates (default 40) --deferptrupdate time time in ms to defer pointer updates (default none) --desktop name VNC desktop name (default "LibVNCServer") --alwaysshared always treat new clients as shared --nevershared never treat new clients as shared --dontdisconnect don't disconnect existing clients when a new non-shared - connection comes in (refuse new connection instead) --httpdir dir-path enable http server using dir-path home --httpport portnum use portnum for http connection --enablehttpproxy enable http proxy support --progressive height enable progressive updating for slow links --listen ipaddr listen for connections only on network interface with - addr ipaddr. '-listen localhost' and hostname work too. - -libvncserver-tight-extension options: --disablefiletransfer disable file transfer --ftproot string set ftp root - - - - -% x11vnc -help - -x11vnc: allow VNC connections to real X11 displays. 0.9.13 lastmod: 2010-12-27 - -(type "x11vnc -opts" to just list the options.) - -Typical usage is: - - Run this command in a shell on the remote machine "far-host" - with X session you wish to view: - - x11vnc -display :0 - - Then run this in another window on the machine you are sitting at: - - vncviewer far-host:0 - -Once x11vnc establishes connections with the X11 server and starts listening -as a VNC server it will print out a string: PORT=XXXX where XXXX is typically -5900 (the default VNC server port). One would next run something like -this on the local machine: "vncviewer hostname:N" where "hostname" is -the name of the machine running x11vnc and N is XXXX - 5900, i.e. usually -"vncviewer hostname:0". - -By default x11vnc will not allow the screen to be shared and it will exit -as soon as the client disconnects. See -shared and -forever below to override -these protections. See the FAQ for details how to tunnel the VNC connection -through an encrypted channel such as ssh(1). In brief: - - ssh -t -L 5900:localhost:5900 far-host 'x11vnc -localhost -display :0' - - vncviewer -encodings 'copyrect tight zrle hextile' localhost:0 - -Also, use of a VNC password (-rfbauth or -passwdfile) is strongly recommended. - -For additional info see: http://www.karlrunge.com/x11vnc/ - and http://www.karlrunge.com/x11vnc/faq.html - - -Config file support: if the file $HOME/.x11vncrc exists then each line in -it is treated as a single command line option. Disable with -norc. For -each option name, the leading character "-" is not required. E.g. a line -that is either "forever" or "-forever" may be used and are equivalent. -Likewise "wait 100" or "-wait 100" are acceptable and equivalent lines. -The "#" character comments out to the end of the line in the usual way -(backslash it for a literal). Leading and trailing whitespace is trimmed off. -Lines may be continued with a "\" as the last character of a line (it -becomes a space character). - -Options: - --display disp X11 server display to connect to, usually :0. The X - server process must be running on same machine and - support MIT-SHM. Equivalent to setting the DISPLAY - environment variable to "disp". - - See the description below of the "-display WAIT:..." - extensions, where alias "-find" will find the user's - display automatically, and "-create" will create a - Xvfb session if no session is found. - --auth file Set the X authority file to be "file", equivalent to - setting the XAUTHORITY environment variable to "file" - before startup. Same as -xauth file. See Xsecurity(7), - xauth(1) man pages for more info. - - Use '-auth guess' to have x11vnc use its -findauth - mechanism (described below) to try to guess the - XAUTHORITY filename and use it. - - XDM/GDM/KDM: if you are running x11vnc as root and want - to find the XAUTHORITY before anyone has logged into an - X session yet, use: x11vnc -env FD_XDM=1 -auth guess ... - (This will also find the XAUTHORITY if a user is already - logged into the X session.) When running as root, - FD_XDM=1 will be tried if the initial -auth guess fails. - --N If the X display is :N, try to set the VNC display to - also be :N This just sets the -rfbport option to 5900+N - The program will exit immediately if that port is not - available. The -N option only works with normal -display - usage, e.g. :0 or :8, -N is ignored in the -display - WAIT:..., -create, -find, -svc, -redirect, etc modes. - --autoport n Automatically probe for a free VNC port starting at n. - The default is to start probing at 5900. Use this to - stay away from other VNC servers near 5900. - --rfbport str The VNC port to listen on (a LibVNCServer option), e.g. - 5900, 5901, etc. If specified as "-rfbport PROMPT" - then the x11vnc -gui is used to prompt the user to - enter the port number. - --6 IPv6 listening support. In addition to IPv4, the - IPv6 address is listened on for incoming connections. - The same port number as IPv4 is used. - - NOTE: This x11vnc binary was compiled to have the - "-6" IPv6 listening mode ENABLED by default (CPPFLAGS - -DX11VNC_LISTEN6=1). So to disable IPv6 listening mode - you MUST supply the "-no6" option (see below.) - - The "-6" mode works for both normal connections and - -ssl encrypted ones. Nearly everything is supported - for the IPv6 case, but there are a few exceptions. - See -stunnel for its IPv6 support. - - Currently, for absolutely everything to work correctly - the machine may need to have some IPv4 support, at the - least for the loopback interface. However, for nearly - all usage modes no IPv4 support is required. See -noipv4 -. - - If you have trouble compiling or running in IPv6 mode, - set -DX11VNC_IPV6=0 in CPPFLAGS when configuring to - disable IPv6 support. - --no6 Disable IPv6 listening support (only useful if the - "-6" mode is compiled in to be the default; see the - X11VNC_LISTEN6 description above under "-6".) - --noipv6 Do not try to use IPv6 for any listening or connecting - sockets. This includes both the listening service - port(s) and outgoing connections from -connect, - -connect_or_exit, or -proxy. Use this if you are having - problems due to IPv6. - --noipv4 Do not try to use IPv4 for any listening or connecting - sockets. This is mainly for exploring the behavior of - x11vnc on an IPv6-only system, but may have other uses. - --reopen If the X server connection is disconnected, try to - reopen the X display (up to one time.) This is of use - for display managers like GDM (KillInitClients option) - that kill x11vnc just after the user logs into the - X session. Note: the reopened state may be unstable. - Set X11VNC_REOPEN_DISPLAY=n to reopen n times and - set X11VNC_REOPEN_SLEEP_MAX to the number of seconds, - default 10, to keep trying to reopen the display (once - per second.) - - Update: as of 0.9.9, x11vnc tries to automatically avoid - being killed by the display manager by delaying creating - windows or using XFIXES. So you shouldn't need to use - KillInitClients=false as long as you log in quickly - enough (within 45 seconds of connecting.) You can - disable this by setting X11VNC_AVOID_WINDOWS=never. - You can also set it to the number of seconds to delay. - --reflect host:N Instead of connecting to and polling an X display, - connect to the remote VNC server host:N and be a - reflector/repeater for it. This is useful for trying - to manage the case of many simultaneous VNC viewers - (e.g. classroom broadcasting) where, e.g. you put - a repeater on each network switch, etc, to improve - performance by distributing the load and network - traffic. Implies -shared (use -noshared as a later - option to disable). See the discussion below under - -rawfb vnc:host:N for more details. - --id windowid Show the X window corresponding to "windowid" not - the entire display. New windows like popup menus, - transient toplevels, etc, may not be seen or may be - clipped. Disabling SaveUnders or BackingStore in the - X server may help show them. x11vnc may crash if the - window is initially partially obscured, changes size, - is iconified, etc. Some steps are taken to avoid this - and the -xrandr mechanism is used to track resizes. Use - xwininfo(1) to get the window id, or use "-id pick" - to have x11vnc run xwininfo(1) for you and extract - the id. The -id option is useful for exporting very - simple applications (e.g. the current view on a webcam). --sid windowid As -id, but instead of using the window directly it - shifts a root view to it: this shows SaveUnders menus, - etc, although they will be clipped if they extend beyond - the window. - --appshare Simple application sharing based on the -id/-sid - mechanism. Every new toplevel window that the - application creates induces a new viewer window via - a reverse connection. The -id/-sid and -connect - options are required. Run 'x11vnc -appshare -help' - for more info. - --clip WxH+X+Y Only show the sub-region of the full display that - corresponds to the rectangle geometry with size WxH and - offset +X+Y. The VNC display has size WxH (i.e. smaller - than the full display). This also works for -id/-sid - mode where the offset is relative to the upper left - corner of the selected window. An example use of this - option would be to split a large (e.g. Xinerama) display - into two parts to be accessed via separate viewers by - running a separate x11vnc on each part. - - Use '-clip xinerama0' to clip to the first xinerama - sub-screen (if xinerama is active). xinerama1 for the - 2nd sub-screen, etc. This way you don't need to figure - out the WxH+X+Y of the desired xinerama sub-screen. - screens are sorted in increasing distance from the - (0,0) origin (I.e. not the Xserver's order). - --flashcmap In 8bpp indexed color, let the installed colormap flash - as the pointer moves from window to window (slow). - Also try the -8to24 option to avoid flash altogether. --shiftcmap n Rare problem, but some 8bpp displays use less than 256 - colorcells (e.g. 16-color grayscale, perhaps the other - bits are used for double buffering) *and* also need to - shift the pixels values away from 0, .., ncells. "n" - indicates the shift to be applied to the pixel values. - To see the pixel values set DEBUG_CMAP=1 to print out - a colormap histogram. Example: -shiftcmap 240 --notruecolor For 8bpp displays, force indexed color (i.e. a colormap) - even if it looks like 8bpp TrueColor (rare problem). --advertise_truecolor If the X11 display is indexed color, lie to clients - when they first connect by telling them it is truecolor. - To workaround RealVNC: inPF has colourMap but not 8bpp - Use '-advertise_truecolor reset' to reset client fb too. - --visual n This option probably does not do what you think. - It simply *forces* the visual used for the framebuffer; - this may be a bad thing... (e.g. messes up colors or - cause a crash). It is useful for testing and for some - workarounds. n may be a decimal number, or 0x hex. - Run xdpyinfo(1) for the values. One may also use - "TrueColor", etc. see for a list. If the - string ends in ":m" then for better or for worse - the visual depth is forced to be m. You may want to - use -noshm when using this option (so XGetImage may - automatically translate the pixel data). - --overlay Handle multiple depth visuals on one screen, e.g. 8+24 - and 24+8 overlay visuals (the 32 bits per pixel are - packed with 8 for PseudoColor and 24 for TrueColor). - - Currently -overlay only works on Solaris via - XReadScreen(3X11) and IRIX using XReadDisplay(3). - On Solaris there is a problem with image "bleeding" - around transient popup menus (but not for the menu - itself): a workaround is to disable SaveUnders - by passing the "-su" argument to Xsun (in - /etc/dt/config/Xservers). - - Use -overlay as a workaround for situations like these: - Some legacy applications require the default visual to - be 8bpp (8+24), or they will use 8bpp PseudoColor even - when the default visual is depth 24 TrueColor (24+8). - In these cases colors in some windows will be incorrect - in x11vnc unless -overlay is used. Another use of - -overlay is to enable showing the exact mouse cursor - shape (details below). - - Under -overlay, performance will be somewhat slower - due to the extra image transformations required. - For optimal performance do not use -overlay, but rather - configure the X server so that the default visual is - depth 24 TrueColor and try to have all apps use that - visual (e.g. some apps have -use24 or -visual options). --overlay_nocursor Sets -overlay, but does not try to draw the exact mouse - cursor shape using the overlay mechanism. - --8to24 [opts] Try this option if -overlay is not supported on your - OS, and you have a legacy 8bpp app that you want to - view on a multi-depth display with default depth 24 - (and is 32 bpp) OR have a default depth 8 display with - depth 24 overlay windows for some apps. This option - may not work on all X servers and hardware (tested - on XFree86/Xorg mga driver and Xsun). The "opts" - string is not required and is described below. - - This mode enables a hack where x11vnc monitors windows - within 3 levels from the root window. If it finds - any that are 8bpp it extracts the indexed color - pixel values using XGetImage() and then applies a - transformation using the colormap(s) to create TrueColor - RGB values that it in turn inserts into bits 1-24 of - the framebuffer. This creates a depth 24 "view" - of the display that is then exported via VNC. - - Conversely, for default depth 8 displays, the depth - 24 regions are read by XGetImage() and everything is - transformed and inserted into a depth 24 TrueColor - framebuffer. - - Note that even if there are *no* depth 24 visuals or - windows (i.e. pure 8bpp), this mode is potentially - an improvement over -flashcmap because it avoids the - flashing and shows each window in the correct color. - - This method works OK, but may still have bugs and it - does hog resources. If there are multiple 8bpp windows - using different colormaps, one may have to iconify all - but one for the colors to be correct. - - There may be painting errors for clipping and switching - between windows of depths 8 and 24. Heuristics are - applied to try to minimize the painting errors. One can - also press 3 Alt_L's in a row to refresh the screen - if the error does not repair itself. Also the option - -fixscreen 8=3.0 or -fixscreen V=3.0 may be used to - periodically refresh the screen at the cost of bandwidth - (every 3 sec for this example). - - The [opts] string can contain the following settings. - Multiple settings are separated by commas. - - For for some X servers with default depth 24 a - speedup may be achieved via the option "nogetimage". - This enables a scheme were XGetImage() is not used - to retrieve the 8bpp data. Instead, it assumes that - the 8bpp data is in bits 25-32 of the 32bit X pixels. - There is no requirement that the X server should put - the data there for our poll requests, but some do and - so the extra steps to retrieve it can be skipped. - Tested with mga driver with XFree86/Xorg. For the - default depth 8 case this option is ignored. - - To adjust how often XGetImage() is used to poll the - non-default visual regions for changes, use the option - "poll=t" where "t" is a floating point time. - (default: 0.05) - - Setting the option "level2" will limit the search - for non-default visual windows to two levels from the - root window. Do this on slow machines where you know - the window manager only imposes one extra window between - the app window and the root window. - - Also for very slow machines use "cachewin=t" - where t is a floating point amount of time to cache - XGetWindowAttributes results. E.g. cachewin=5.0. - This may lead to the windows being unnoticed for this - amount of time when deiconifying, painting errors, etc. - - While testing on a very old SS20 these options gave - tolerable response: -8to24 poll=0.2,cachewin=5.0. For - this machine -overlay is supported and gives better - response. - - Debugging for this mode can be enabled by setting - "dbg=1", "dbg=2", or "dbg=3". - --24to32 Very rare problem: if the framebuffer (X display - or -rawfb) is 24bpp instead of the usual 32bpp, then - dynamically transform the pixels to 32bpp. This will be - slower, but can be used to work around problems where - VNC viewers cannot handle 24bpp (e.g. "main: setPF: - not 8, 16 or 32 bpp?"). See the FAQ for more info. - - In the case of -rawfb mode, the pixels are directly - modified by inserting a 0 byte to pad them out to 32bpp. - For X displays, a kludge is done that is equivalent to - "-noshm -visual TrueColor:32". (If better performance - is needed for the latter, feel free to ask). - --scale fraction Scale the framebuffer by factor "fraction". Values - less than 1 shrink the fb, larger ones expand it. Note: - the image may not be sharp and response may be slower. - If "fraction" contains a decimal point "." it - is taken as a floating point number, alternatively - the notation "m/n" may be used to denote fractions - exactly, e.g. -scale 2/3 - - To scale asymmetrically in the horizontal and vertical - directions, specify a WxH geometry to stretch to: - e.g. '-scale 1024x768', or also '-scale 0.9x0.75' - - Scaling Options: can be added after "fraction" via - ":", to supply multiple ":" options use commas. - If you just want a quick, rough scaling without - blending, append ":nb" to "fraction" (e.g. -scale - 1/3:nb). No blending is the default for 8bpp indexed - color, to force blending for this case use ":fb". - - To disable -scrollcopyrect and -wirecopyrect under - -scale use ":nocr". If you need to to enable them use - ":cr" or specify them explicitly on the command line. - If a slow link is detected, ":nocr" may be applied - automatically. Default: :cr - - More esoteric options: for compatibility with vncviewers - the scaled width is adjusted to be a multiple of 4: - to disable this use ":n4". ":in" use interpolation - scheme even when shrinking, ":pad" pad scaled width - and height to be multiples of scaling denominator - (e.g. 3 for 2/3). - --geometry WxH Same as -scale WxH - --scale_cursor frac By default if -scale is supplied the cursor shape is - scaled by the same factor. Depending on your usage, - you may want to scale the cursor independently of the - screen or not at all. If you specify -scale_cursor - the cursor will be scaled by that factor. When using - -scale mode to keep the cursor at its "natural" size - use "-scale_cursor 1". Most of the ":" scaling - options apply here as well. - --viewonly All VNC clients can only watch (default off). --shared VNC display is shared, i.e. more than one viewer can - connect at the same time (default off). --once Exit after the first successfully connected viewer - disconnects, opposite of -forever. This is the Default. --forever Keep listening for more connections rather than exiting - as soon as the first client(s) disconnect. Same as -many - - To get the standard non-shared VNC behavior where when - a new VNC client connects the existing VNC client is - dropped use: -nevershared -forever This method can - also be used to guard against hung TCP connections that - do not go away. - --loop Create an outer loop restarting the x11vnc process - whenever it terminates. -bg and -inetd are ignored - in this mode (however see -loopbg below). - - Useful for continuing even if the X server terminates - and restarts (at that moment the process will need - permission to reconnect to the new X server of course). - - Use, e.g., -loop100 to sleep 100 millisecs between - restarts, etc. Default is 2000ms (i.e. 2 secs) Use, - e.g. -loop300,5 to sleep 300 ms and only loop 5 times. - - If -loopbg (plus any numbers) is specified instead, - the "-bg" option is implied and the mode approximates - inetd(8) usage to some degree. In this case when - it goes into the background any listening sockets - (i.e. ports 5900, 5800) are closed, so the next one - in the loop can use them. This mode will only be of - use if a VNC client (the only client for that process) - is already connected before the process goes into the - background, for example, usage of -display WAIT:.., - -svc, and -connect can make use of this "poor man's" - inetd mode. The default wait time is 500ms in this - mode. This usage could use useful: -svc -bg -loopbg - --timeout n Exit unless a client connects within the first n seconds - after startup. - - If there have been no connection attempts after n - seconds x11vnc exits immediately. If a client is - trying to connect but has not progressed to the normal - operating state, x11vnc gives it a few more seconds - to finish and exits if it does not make it to the - normal state. - - For reverse connections via -connect or -connect_or_exit - a timeout of n seconds will be set for all reverse - connects. If the connect timeout alarm goes off, - x11vnc will exit immediately. - --sleepin n At startup sleep n seconds before proceeding (e.g. to - allow redirs and listening clients to start up) - - If a range is given: '-sleepin min-max', a random value - between min and max is slept. E.g. '-sleepin 0-20' and - '-sleepin 10-30'. Floats are allowed too. - --inetd Launched by inetd(8): stdio instead of listening socket. - Note: if you are not redirecting stderr to a log file - (via shell 2> or -o option) you MUST also specify the -q - option, otherwise the stderr goes to the viewer which - will cause it to abort. Specifying both -inetd and -q - and no -o will automatically close the stderr. - --tightfilexfer Enable the TightVNC file transfer extension. Note that - that when the -viewonly option is supplied all file - transfers are disabled. Also clients that log in - viewonly cannot transfer files. However, if the remote - control mechanism is used to change the global or - per-client viewonly state the filetransfer permissions - will NOT change. - - IMPORTANT: please understand if -tightfilexfer is - specified and you run x11vnc as root for, say, inetd - or display manager (gdm, kdm, ...) access and you do - not have it switch users via the -users option, then - VNC Viewers that connect are able to do filetransfer - reads and writes as *root*. - - Also, tightfilexfer is disabled in -unixpw mode. - --ultrafilexfer Note: to enable UltraVNC filetransfer and to get it to - work you probably need to supply these LibVNCServer - options: "-rfbversion 3.6 -permitfiletransfer" - "-ultrafilexfer" is an alias for this combination. - - IMPORTANT: please understand if -ultrafilexfer is - specified and you run x11vnc as root for, say, inetd - or display manager (gdm, kdm, ...) access and you do - not have it switch users via the -users option, then - VNC Viewers that connect are able to do filetransfer - reads and writes as *root*. - - Note that sadly you cannot do both -tightfilexfer and - -ultrafilexfer at the same time because the latter - requires setting the version to 3.6 and tightvnc will - not do filetransfer when it sees that version number. - --http Instead of using -httpdir (see below) to specify - where the Java vncviewer applet is, have x11vnc try - to *guess* where the directory is by looking relative - to the program location and in standard locations - (/usr/local/share/x11vnc/classes, etc). Under -ssl or - -stunnel the ssl classes subdirectory is sought. --http_ssl As -http, but force lookup for ssl classes subdir. - - Note that for HTTPS, single-port Java applet delivery - you can set X11VNC_HTTPS_DOWNLOAD_WAIT_TIME to the - max number of seconds to wait for the applet download - to finish. The default is 15. - --avahi Use the Avahi/mDNS ZeroConf protocol to advertise - this VNC server to the local network. (Related terms: - Rendezvous, Bonjour). Depending on your setup, you - may need to start avahi-daemon and open udp port 5353 - in your firewall. - - You can set X11VNC_AVAHI_NAME, X11VNC_AVAHI_HOST, - and/or X11VNC_AVAHI_PORT environment variables - to override the default values. For example: - -env X11VNC_AVAHI_NAME=wally - - If the avahi API cannot be found at build time, a helper - program like avahi-publish(1) or dns-sd(1) will be tried - --mdns Same as -avahi. --zeroconf Same as -avahi. - --connect string For use with "vncviewer -listen" reverse connections. - If "string" has the form "host" or "host:port" - the connection is made once at startup. - - Use commas for a list of host's and host:port's. - E.g. -connect host1,host2 or host1:0,host2:5678. - Note that to reverse connect to multiple hosts at the - same time you will likely need to also supply: -shared - - Note that unlike most vnc servers, x11vnc will require a - password for reverse as well as for forward connections. - (provided password auth has been enabled, -rfbauth, etc) - If you do not want to require a password for reverse - connections set X11VNC_REVERSE_CONNECTION_NO_AUTH=1 in - your environment before starting x11vnc. - - If "string" contains "/" it is instead interpreted - as a file to periodically check for new hosts. - The first line is read and then the file is truncated. - Be careful about the location of this file if x11vnc - is running as root (e.g. via gdm(1), etc). - - - Repeater mode: Some services provide an intermediate - "vnc repeater": http://www.uvnc.com/addons/repeater.html - (and also http://koti.mbnet.fi/jtko/ for linux port) - that acts as a proxy/gateway. Modes like these require - an initial string to be sent for the reverse connection - before the VNC protocol is started. Here are the ways - to do this: - - -connect pre=some_string+host:port - -connect pre128=some_string+host:port - -connect repeater=ID:1234+host:port - -connect repeater=23.45.67.89::5501+host:port - - SSVNC notation is also supported: - - -connect repeater://host:port+ID:1234 - - As with normal -connect usage, if the repeater port is - not supplied 5500 is assumed. - - The basic idea is between the special tag, e.g. "pre=" - and "+" is the pre-string to be sent. Note that in - this case host:port is the repeater server, NOT the - vnc viewer. Somehow the pre-string tells the repeater - server how to find the vnc viewer and connect you to it. - - In the case pre=some_string+host:port, "some_string" - is simply sent. In the case preNNN=some_string+host:port - "some_string" is sent in a null padded buffer of - length NNN. repeater= is the same as pre250=, this is - the ultravnc repeater buffer size. - - Strings like "\n" and "\r", etc. are expanded to - newline and carriage return. "\c" is expanded to - "," since the connect string is comma separated. - - See also the -proxy option below for additional ways - to plumb reverse connections. - - Reverse SSL: using -connect in -ssl mode makes x11vnc - act as an SSL client (initiates SSL connection) rather - than an SSL server. The idea is x11vnc might be - connecting to stunnel on the viewer side with the - viewer in listening mode. If you do not want this - behavior, use -env X11VNC_DISABLE_SSL_CLIENT_MODE=1. - With this the viewer side can act as the SSL client - as it normally does for forward connections. - - Reverse SSL Repeater mode: This will work, but note - that if the VNC Client does any sort of a 'Fetch Cert' - action before connecting, then the Repeater will - likely drop the connection and both sides will need - to restart. Consider the use of -connect_or_exit - and -loop300,2 to have x11vnc reconnect once to the - repeater after the fetch. You will probably also want - to supply -sslonly to avoid x11vnc thinking the delay - in response means the connection is VeNCrypt. The env - var X11VNC_DISABLE_SSL_CLIENT_MODE=1 discussed above - may also be useful (i.e. the viewer can do a forward - connection as it normally does.) - - IPv6: as of x11vnc 0.9.10 the -connect option should - connect to IPv6 hosts properly. If there are problems - you can disable IPv6 by setting -DX11VNC_IPV6=0 - in CPPFLAGS when configuring. If there problems - connecting to IPv6 hosts consider a relay like the - included inet6to4 script or the -proxy option. - --connect_or_exit str As with -connect, except if none of the reverse - connections succeed, then x11vnc shuts down immediately - - An easier to type alias for this option is '-coe' - - By the way, if you do not want x11vnc to listen on - ANY interface use -rfbport 0 which is handy for the - -connect_or_exit mode. - --proxy string Use proxy in string (e.g. host:port) as a proxy for - making reverse connections (-connect or -connect_or_exit - options). - - Web proxies are supported, but note by default most of - them only support destination connections to ports 443 - or 563, so this might not be very useful (the viewer - would need to listen on that port or the router would - have to do a port redirection). - - A web proxy may be specified by either "host:port" - or "http://host:port" (the port is required even if - it is the common choices 80 or 8080) - - SOCKS4, SOCKS4a, and SOCKS5 are also supported. - SOCKS proxies normally do not have restrictions on the - destination port number. - - Use a format like this: socks://host:port or - socks5://host:port. Note that ssh -D does not support - SOCKS4a, so use socks5://. For socks:// SOCKS4 is used - on a numerical IP and "localhost", otherwise SOCKS4a - is used (and so the proxy tries to do the DNS lookup). - - An experimental mode is "-proxy http://host:port/..." - Note the "/" after the port that distinguishes it from - a normal web proxy. The port must be supplied even if - it is the default 80. For this mode a GET is done to - the supplied URL with the string host=H&port=P appended. - H and P will be the -connect reverse connect host - and port. Use the string "__END__" to disable the - appending. The basic idea here is that maybe some cgi - script provides the actual viewer hookup and tunnelling. - How to actually achieve this within cgi, php, etc. is - not clear... A custom web server or apache module - would be straight-forward. - - Another experimental mode is "-proxy ssh://user@host" - in which case a SSH tunnel is used for the proxying. - "user@" is not needed unless your unix username is - different on "host". For a non-standard SSH port - use ssh://user@host:port. If proxies are chained (see - next paragraph) then the ssh one must be the first one. - If ssh-agent is not active, then the ssh password needs - to be entered in the terminal where x11vnc is running. - Examples: - - -connect localhost:0 -proxy ssh://me@friends-pc:2222 - - -connect snoopy:0 -proxy ssh://ssh.company.com - - Multiple proxies may be chained together in case one - needs to ricochet off of a number of hosts to finally - reach the VNC viewer. Up to 3 may be chained, separate - them by commas in the order they are to be connected to. - E.g.: http://host1:port1,socks5://host2:port2 or three - like: first,second,third - - IPv6: as of x11vnc 0.9.10 the -proxy option should - connect to IPv6 hosts properly. If there are problems - you can disable IPv6 by setting -DX11VNC_IPV6=0 - in CPPFLAGS when configuring. If there problems - connecting to IPv6 hosts consider a relay like the - included inet6to4 script. - --vncconnect Monitor the VNC_CONNECT X property set by the standard --novncconnect VNC program vncconnect(1). When the property is - set to "host" or "host:port" establish a reverse - connection. Using xprop(1) instead of vncconnect may - work (see the FAQ). The -remote control mechanism uses - X11VNC_REMOTE channel, and this option disables/enables - it as well. Default: -vncconnect - - To use different names for these X11 properties (e.g. to - have separate communication channels for multiple - x11vnc's on the same display) set the VNC_CONNECT or - X11VNC_REMOTE env. vars. to the string you want, for - example: -env X11VNC_REMOTE=X11VNC_REMOTE_12345 - Both sides of the channel must use the same unique name. - The same can be done for the internal X11VNC_TICKER - property (heartbeat and timestamp) if desired. - --allow host1[,host2..] Only allow client connections from hosts matching - the comma separated list of hostnames or IP addresses. - Can also be a numerical IP prefix, e.g. "192.168.100." - to match a simple subnet, for more control build - LibVNCServer with libwrap support (See the FAQ). If the - list contains a "/" it instead is a interpreted - as a file containing addresses or prefixes that is - re-read each time a new client connects. Lines can be - commented out with the "#" character in the usual way. - - -allow applies in -ssl mode, but not in -stunnel mode. - - IPv6: as of x11vnc 0.9.10 a host can be specified - in IPv6 numerical format, e.g. 2001:4860:b009::93. - --localhost Basically the same as "-allow 127.0.0.1". - - Note: if you want to restrict which network interface - x11vnc listens on, see the -listen option below. - E.g. "-listen localhost" or "-listen 192.168.3.21". - As a special case, the option "-localhost" implies - "-listen localhost". - - A rare case, but for non-localhost -listen usage, if - you use the remote control mechanism (-R) to change - the -listen interface you may need to manually adjust - the -allow list (and vice versa) to avoid situations - where no connections (or too many) are allowed. - - If you do not want x11vnc to listen on ANY interface - (evidently you are using -connect or -connect_or_exit, - or plan to use remote control: -R connect:host), use - -rfbport 0 - - IPv6: if IPv6 is supported, this option automatically - implies the IPv6 loopback address '::1' as well. - --unixsock str Listen on the unix socket (AF_UNIX) 'str' - for connections. This mode is for either local - connections or a tunnel endpoint where one wants the - file permission of the unix socket file to determine - what can connect to it. (This currently requires an - edit to libvnserver/rfbserver.c: comment out lines 310 - and 311, 'close(sock)' and 'return NULL' in rfbserver.c - after the setsockopt() call.) Note that to disable all - tcp listening ports specify '-rfbport 0' and should be - useful with this mode. Example: - mkdir ~/s; chmod 700 ~/s; - x11vnc -unixsock ~/s/mysock -rfbport 0 ... - The SSVNC unix vncviewer can connect to unix sockets. - --listen6 str When in IPv6 listen mode "-6", listen only on the - network interface with address "str". It also works - for link scope addresses (fe80::219:dbff:fee5:3f92%eth0) - and IPv6 hostname strings (e.g. ipv6.google.com.) - Use LibVNCServer -listen option for the IPv4 interface. - --nolookup Do not use gethostbyname() or gethostbyaddr() to look up - host names or IP numbers. Use this if name resolution - is incorrectly set up and leads to long pauses as name - lookups time out, etc. - --input string Fine tuning of allowed user input. If "string" does - not contain a comma "," the tuning applies only to - normal clients. Otherwise the part before "," is - for normal clients and the part after for view-only - clients. "K" is for Keystroke input, "M" for - Mouse-motion input, "B" for Button-click input, "C" - is for Clipboard input, and "F" is for File transfer - (ultravnc only). Their presence in the string enables - that type of input. E.g. "-input M" means normal - users can only move the mouse and "-input KMBCF,M" - lets normal users do anything and enables view-only - users to move the mouse. This option is ignored when - a global -viewonly is in effect (all input is discarded - in that case). - --grabkbd When VNC viewers are connected, attempt to the grab - the keyboard so a (non-malicious) user sitting at the - physical display is not able to enter keystrokes. - This method uses XGrabKeyboard(3X11) and so it is - not secure and does not rule out the person at the - physical display injecting keystrokes by flooding the - server with them, grabbing the keyboard himself, etc. - Some degree of cooperation from the person at the - display is assumed. This is intended for remote - help-desk or educational usage modes. - - Note: on some recent (12/2010) X servers and/or - desktops, -grabkbd no longer works: it prevents the - window manager from resizing windows and similar things. - Try -ungrabboth below (might not work.) - --grabptr As -grabkbd, but for the mouse pointer using - XGrabPointer(3X11). Unfortunately due to the way the X - server works, the mouse can still be moved around by the - user at the physical display, but he will not be able to - change window focus with it. Also some window managers - that call XGrabServer(3X11) for resizes, etc, will - act on the local user's input. Again, some degree of - cooperation from the person at the display is assumed. - --ungrabboth Whenever there is any input (either keyboard or - pointer), ungrab *both* the keyboard and the pointer - while injecting the synthetic input. This is to allow - window managers, etc. a chance to grab. - --grabalways Apply both -grabkbd and -grabptr even when no VNC - viewers are connected. If you only want one of them, - use the -R remote control to turn the other back on, - e.g. -R nograbptr. - --viewpasswd string Supply a 2nd password for view-only logins. The -passwd - (full-access) password must also be supplied. - --passwdfile filename Specify the LibVNCServer password via the first line - of the file "filename" (instead of via -passwd on - the command line where others might see it via ps(1)). - - See the descriptions below for how to supply multiple - passwords, view-only passwords, to specify external - programs for the authentication, and other features. - - If the filename is prefixed with "rm:" it will be - removed after being read. Perhaps this is useful in - limiting the readability of the file. In general, the - password file should not be readable by untrusted users - (BTW: neither should the VNC -rfbauth file: it is NOT - encrypted, only obscured with a fixed key). - - If the filename is prefixed with "read:" it will - periodically be checked for changes and reread. It is - guaranteed to be reread just when a new client connects - so that the latest passwords will be used. - - If "filename" is prefixed with "cmd:" then the - string after the ":" is run as an external command: - the output of the command will be interpreted as if it - were read from a password file (see below). If the - command does not exit with 0, then x11vnc terminates - immediately. To specify more than 1000 passwords this - way set X11VNC_MAX_PASSWDS before starting x11vnc. - The environment variables are set as in -accept. - - Note that due to the VNC protocol only the first 8 - characters of a password are used (DES key). - - If "filename" is prefixed with "custom:" then a - custom password checker is supplied as an external - command following the ":". The command will be run - when a client authenticates. If the command exits with - 0 the client is accepted, otherwise it is rejected. - The environment variables are set as in -accept. - - The standard input to the custom command will be a - decimal digit "len" followed by a newline. "len" - specifies the challenge size and is usually 16 (the - VNC spec). Then follows len bytes which is the random - challenge string that was sent to the client. This is - then followed by len more bytes holding the client's - response (i.e. the challenge string encrypted via DES - with the user password in the standard situation). - - The "custom:" scheme can be useful to implement - dynamic passwords or to implement methods where longer - passwords and/or different encryption algorithms - are used. The latter will require customizing the VNC - client as well. One could create an MD5SUM based scheme - for example. - - File format for -passwdfile: - - If multiple non-blank lines exist in the file they are - all taken as valid passwords. Blank lines are ignored. - Password lines may be "commented out" (ignored) if - they begin with the character "#" or the line contains - the string "__SKIP__". Lines may be annotated by use - of the "__COMM__" string: from it to the end of the - line is ignored. An empty password may be specified - via the "__EMPTY__" string on a line by itself (note - your viewer might not accept empty passwords). - - If the string "__BEGIN_VIEWONLY__" appears on a - line by itself, the remaining passwords are used for - viewonly access. For compatibility, as a special case - if the file contains only two password lines the 2nd - one is automatically taken as the viewonly password. - Otherwise the "__BEGIN_VIEWONLY__" token must be - used to have viewonly passwords. (tip: make the 3rd - and last line be "__BEGIN_VIEWONLY__" to have 2 - full-access passwords) - --showrfbauth filename Print to the screen the obscured VNC password kept in - the rfbauth file "filename" and then exit. - --unixpw [list] Use Unix username and password authentication. x11vnc - will use the su(1) program to verify the user's - password. [list] is an optional comma separated list - of allowed Unix usernames. If the [list] string begins - with the character "!" then the entire list is taken - as an exclude list. See below for per-user options - that can be applied. - - A familiar "login:" and "Password:" dialog is - presented to the user on a black screen inside the - vncviewer. The connection is dropped if the user fails - to supply the correct password in 3 tries or does not - send one before a 45 second timeout. Existing clients - are view-only during this period. - - If the first character received is "Escape" then the - unix username will not be displayed after "login:" - as it is typed. This could be of use for VNC viewers - that automatically type the username and password. - - Since the detailed behavior of su(1) can vary from - OS to OS and for local configurations, test the mode - before deployment to make sure it is working properly. - x11vnc will attempt to be conservative and reject a - login if anything abnormal occurs. - - One case to note: FreeBSD and the other BSD's by - default it is impossible for the user running x11vnc to - validate his *own* password via su(1) (commenting out - the pam_self.so entry in /etc/pam.d/su eliminates this - behavior). So the x11vnc login will always *FAIL* for - this case (even when the correct password is supplied). - - A possible workaround for this on *BSD would be to - start x11vnc as root with the "-users +nobody" option - to immediately switch to user nobody where the su'ing - will proceed normally. - - Another source of potential problems are PAM modules - that prompt for extra info, e.g. password aging modules. - These logins will fail as well even when the correct - password is supplied. - - **IMPORTANT**: to prevent the Unix password being sent - in *clear text* over the network, one of two schemes - will be enforced: 1) the -ssl builtin SSL mode, or 2) - require both -localhost and -stunnel be enabled. - - Method 1) ensures the traffic is encrypted between - viewer and server. A PEM file will be required, see the - discussion under -ssl below (under some circumstances - a temporary one can be automatically generated). - - Method 2) requires the viewer connection to appear - to come from the same machine x11vnc is running on - (e.g. from a ssh -L port redirection). And that the - -stunnel SSL mode be used for encryption over the - network. (see the description of -stunnel below). - - Note: as a convenience, if you ssh(1) in and start - x11vnc it will check if the environment variable - SSH_CONNECTION is set and appears reasonable. If it - does, then the -ssl or -stunnel requirement will be - dropped since it is assumed you are using ssh for the - encrypted tunnelling. -localhost is still enforced. - Use -ssl or -stunnel to force SSL usage even if - SSH_CONNECTION is set. - - To override the above restrictions you can set - environment variables before starting x11vnc: - - Set UNIXPW_DISABLE_SSL=1 to disable requiring either - -ssl or -stunnel (as under SSH_CONNECTION.) Evidently - you will be using a different method to encrypt the - data between the vncviewer and x11vnc: perhaps ssh(1) - or an IPSEC VPN. -localhost is still enforced (however, - see the next paragraph.) - - Set UNIXPW_DISABLE_LOCALHOST=1 to disable the -localhost - requirement in -unixpw modes. One should never do this - (i.e. allow the Unix passwords to be sniffed on the - network.) This also disables the localhost requirement - for reverse connections (see below.) - - Note that use of -localhost with ssh(1) (and no -unixpw) - is roughly the same as requiring a Unix user login - (since a Unix password or the user's public key - authentication is used by sshd on the machine where - x11vnc runs and only local connections from that machine - are accepted). - - Regarding reverse connections (e.g. -R connect:host - and -connect host), when the -localhost constraint is - in effect then reverse connections can only be used - to connect to the same machine x11vnc is running on - (default port 5500). Please use a ssh or stunnel port - redirection to the viewer machine to tunnel the reverse - connection over an encrypted channel. - - In -inetd mode the Method 1) will be enforced (not - Method 2). With -ssl in effect reverse connections - are disabled. If you override this via env. var, be - sure to also use encryption from the viewer to inetd. - Tip: you can also have your own stunnel spawn x11vnc - in -inetd mode (thereby bypassing inetd). See the FAQ - for details. - - The user names in the comma separated [list] may have - per-user options after a ":", e.g. "fred:opts" - where "opts" is a "+" separated list of - "viewonly", "fullaccess", "input=XXXX", or - "deny", e.g. "karl,wally:viewonly,boss:input=M". - For "input=" it is the K,M,B,C described under -input. - - If an item in the list is "*" that means those - options apply to all users. It ALSO implies all users - are allowed to log in after supplying a valid password. - Use "deny" to explicitly deny some users if you use - "*" to set a global option. If [list] begins with the - "!" character then "*" is ignored for checking if - the user is allowed, but the option values associated - with it do apply as normal. - - There are also some utilities for checking passwords - if [list] starts with the "%" character. See the - quick_pw() function for more details. Description: - "%-" or "%stdin" means read one line from stdin. - "%env" means it is in $UNIXPW env var. A leading - "%/" or "%." means read the first line from the - filename that follows after the % character. % by - itself means prompt for the username and password. - Otherwise: %user:pass E.g. -unixpw %fred:swordfish - For the other cases user:pass is read from the indicated - source. If the password is correct 'Y user' is printed - and the program exit code is 0. If the password is - incorrect it prints 'N user' and the exit code is 1. - If there is some other error the exit code is 2. - This feature enables x11vnc to be a general unix user - password checking tool; it could be used from scripts - or other programs. These % password checks also apply - to the -unixpw_nis and -unixpw_cmd options. - - For the % password check, if the env. var. UNIXPW_CMD - is set to a command then it is run as the user (assuming - the password is correct.) The output of the command is - not printed, the program or script must manage that by - some other means. The exit code of x11vnc will depend - on the exit code of the command that is run. - - Use -nounixpw to disable unixpw mode if it was enabled - earlier in the cmd line (e.g. -svc mode) - --unixpw_nis [list] As -unixpw above, however do not use su(1) but rather - use the traditional getpwnam(3) + crypt(3) method to - verify passwords. All of the above -unixpw options and - constraints apply. - - This mode requires that the encrypted passwords be - readable. Encrypted passwords stored in /etc/shadow - will be inaccessible unless x11vnc is run as root. - - This is called "NIS" mode simply because in most - NIS setups user encrypted passwords are accessible - (e.g. "ypcat passwd") by an ordinary user and so that - user can authenticate ANY user. - - NIS is not required for this mode to work (only that - getpwnam(3) return the encrypted password is required), - but it is unlikely it will work (as an ordinary user) - for most modern environments unless NIS is available. - On the other hand, when x11vnc is run as root it will - be able to to access /etc/shadow even if NIS is not - available (note running as root is often done when - running x11vnc from inetd and xdm/gdm/kdm). - - Looked at another way, if you do not want to use the - su(1) method provided by -unixpw (i.e. su_verify()), you - can run x11vnc as root and use -unixpw_nis. Any users - with passwords in /etc/shadow can then be authenticated. - - In -unixpw_nis mode, under no circumstances is x11vnc's - user password verifying function based on su called - (i.e. the function su_verify() that runs /bin/su - in a pseudoterminal to verify passwords.) However, - if -unixpw_nis is used in conjunction with the -find - and -create -display WAIT:... modes then, if x11vnc is - running as root, /bin/su may be called externally to - run the find or create commands. - --unixpw_cmd cmd As -unixpw above, however do not use su(1) but rather - run the externally supplied command "cmd". The first - line of its stdin will be the username and the second - line the received password. If the command exits - with status 0 (success) the VNC user will be accepted. - It will be rejected for any other return status. - - Dynamic passwords and non-unix passwords, e.g. LDAP, - can be implemented this way by providing your own custom - helper program. Note that the remote viewer is given 3 - tries to enter the correct password, and so the program - may be called in a row that many (or more) times. - - If a list of allowed users is needed to limit who can - log in, use -unixpw [list] in addition to this option. - - In FINDDISPLAY and FINDCREATEDISPLAY modes the "cmd" - will also be run with the RFB_UNIXPW_CMD_RUN env. var. - non-empty and set to the corresponding display - find/create command. The first two lines of input are - the username and passwd as in the normal case described - above. To support FINDDISPLAY and FINDCREATEDISPLAY, - "cmd" should run the requested command as the user - (and most likely refusing to run it if the password is - not correct.) Here is an example script (note it has - a hardwired bogus password "abc"!) - - #!/bin/sh - # Example x11vnc -unixpw_cmd script. - # Read the first two lines of stdin (user and passwd) - read user - read pass - - debug=0 - if [ $debug = 1 ]; then - echo "user: $user" 1>&2 - echo "pass: $pass" 1>&2 - env | egrep -i 'rfb|vnc' 1>&2 - fi - - # Check if the password is valid. - # (A real example would use ldap lookup, etc!) - if [ "X$pass" != "Xabc" ]; then - exit 1 # incorrect password - fi - - if [ "X$RFB_UNIXPW_CMD_RUN" = "X" ]; then - exit 0 # correct password - else - # Run the requested command (finddisplay) - if [ $debug = 1 ]; then - echo "run: $RFB_UNIXPW_CMD_RUN" 1>&2 - fi - exec /bin/su - "$user" -c "$RFB_UNIXPW_CMD_RUN" - fi - - In -unixpw_cmd mode, under no circumstances is x11vnc's - user password verifying function based on su called - (i.e. the function su_verify() that runs /bin/su in a - pseudoterminal to verify passwords.) It is up to the - supplied unixpw_cmd to do user switching if desired - and if it has the permissions to do so. - --find Find the user's display using FINDDISPLAY. This - is an alias for "-display WAIT:cmd=FINDDISPLAY". - - Note: if a -display occurs later on the command line - it will override the -find setting. - - For this and the next few options see -display WAIT:... - below for all of the details. - --finddpy Run the FINDDISPLAY program, print out the found - display (if any) and exit. Output is like: DISPLAY=:0.0 - DISPLAY=:0.0,XPID=12345 or DISPLAY=:0.0,VT=7. XPID is - the process ID of the found X server. VT is the Linux - virtual terminal of the X server. --listdpy Have the FINDDISPLAY program list all of your displays - (i.e. all the X displays on the local machine that you - have access rights to). x11vnc then exits. - --findauth [disp] Apply the -find/-finddpy heuristics to try to guess - the XAUTHORITY file for DISPLAY 'disp'. If 'disp' - is not supplied, then the value in the -display on - the cmdline is used; failing that $DISPLAY is used; - and failing that ":0" is used. x11vnc then exits. - - If nothing is printed out, that means no XAUTHORITY was - found for 'disp'; i.e. failure. If "XAUTHORITY=" - is printed out, that means use the default (i.e. do - not set XAUTHORITY). If "XAUTHORITY=/path/to/file" - is printed out, then use that file. - - XDM/GDM/KDM: if you are running x11vnc as root and want - to find the XAUTHORITY before anyone has logged into an - X session yet, use: x11vnc -env FD_XDM=1 -findauth ... - (This will also find the XAUTHORITY if a user is already - logged into the X session.) When running as root, - FD_XDM=1 will be tried if the initial -findauth fails. - --create First try to find the user's display using FINDDISPLAY, - if that doesn't succeed create an X session via the - FINDCREATEDISPLAY method. This is an alias for - "-display WAIT:cmd=FINDCREATEDISPLAY-Xvfb". - - Note: if a -display occurs later on the command line - it will override the -create setting. - - SSH NOTE: for both -find and -create you can (should!) - add the "-localhost" option to force SSH tunnel access. - --xdummy As in -create, except Xdummy instead of Xvfb. --xvnc As in -create, except Xvnc instead of Xvfb. --xvnc_redirect As in -create, except Xvnc.redirect instead of Xvfb. --xdummy_xvfb Sets WAIT:cmd=FINDCREATEDISPLAY-Xdummy,Xvfb - --create_xsrv str Sets WAIT:cmd=FINDCREATEDISPLAY- Can be on cmdline - after anything that sets WAIT:.. and other things - (e.g. -svc, -xdmsvc) to adjust the X server list. - Example: -svc ... -create_xsrv Xdummy,X - --svc Terminal services mode based on SSL access. Alias for - -display WAIT:cmd=FINDCREATEDISPLAY-Xvfb -unixpw -users - unixpw= -ssl SAVE Also "-service". - - Note: if a -display, -unixpw, -users, or -ssl occurs - later on the command line it will override the -svc - setting. - --svc_xdummy As -svc except Xdummy instead of Xvfb. --svc_xvnc As -svc except Xvnc instead of Xvfb. --svc_xdummy_xvfb As -svc with Xdummy,Xvfb. - --xdmsvc Display manager Terminal services mode based on SSL. - Alias for -display WAIT:cmd=FINDCREATEDISPLAY-Xvfb.xdmcp - -unixpw -users unixpw= -ssl SAVE Also "-xdm_service". - - Note: if a -display, -unixpw, -users, or -ssl occurs - later on the command line it will override the -xdmsvc - setting. - - To create a session a user will have to first log in - to the -unixpw dialog and then log in again to the - XDM/GDM/KDM prompt. Subsequent re-connections will - only require the -unixpw password. See the discussion - under -display WAIT:... for more details about XDM, - etc configuration. - - Remember to enable XDMCP in the xdm-config, gdm.conf, - or kdmrc configuration file. See -display WAIT: for - more info. - --sshxdmsvc Display manager Terminal services mode based on SSH. - Alias for -display WAIT:cmd=FINDCREATEDISPLAY-Xvfb.xdmcp - -localhost. - - The -localhost option constrains connections to come - in via a SSH tunnel (which will require a login). - To create a session a user will also have to log into - the XDM GDM KDM prompt. Subsequent re-connections will - only only require the SSH login. See the discussion - under -display WAIT:... for more details about XDM, - etc configuration. - - Remember to enable XDMCP in the xdm-config, gdm.conf, - or kdmrc configuration file. See -display WAIT: for - more info. - --unixpw_system_greeter Present a "Press 'Escape' for System Greeter" option - to the connecting VNC client in combined -unixpw - and xdmcp FINDCREATEDISPLAY modes (e.g. -xdmsvc). - - Normally in a -unixpw mode the VNC client must - supply a valid username and password to gain access. - However, if -unixpw_system_greeter is supplied AND - the FINDCREATEDISPLAY command matches 'xdmcp', then - the user has the option to press Escape and then get a - XDM/GDM/KDM login/greeter panel instead. They will then - supply a username and password directly to the greeter. - - Otherwise, in xdmcp FINDCREATEDISPLAY mode the user - must supply his username and password TWICE. First to - the initial unixpw login dialog, and second to the - subsequent XDM/GDM/KDM greeter. Note that if the user - re-connects and supplies his username and password in - the unixpw dialog the xdmcp greeter is skipped and - he is connected directly to his existing X session. - So the -unixpw_system_greeter option avoids the extra - password at X session creation time. - - Example: x11vnc -xdmsvc -unixpw_system_greeter - See -unixpw and -display WAIT:... for more info. - - The special options after a colon at the end of the - username (e.g. user:solid) described under -display - WAIT: are also applied in this mode if they are typed - in before the user hits Escape. The username is ignored - but the colon options are not. - - The default message is 2 lines in a small font, set - the env. var. X11VNC_SYSTEM_GREETER1=true for a 1 line - message in a larger font. - - If the user pressed Escape the FINDCREATEDISPLAY command - will be run with the env. var. X11VNC_XDM_ONLY=1. - - Remember to enable XDMCP in the xdm-config, gdm.conf, - or kdmrc configuration file. See -display WAIT: for - more info. - --redirect port As in FINDCREATEDISPLAY-Xvnc.redirect mode except - redirect immediately (i.e. without X session finding - or creation) to a VNC server listening on port. You - can also supply host:port to redirect to a different - machine. - - If 0 <= port < 200 it is taken as a VNC display (5900 is - added to get the actual port), if port < 0 then -port - is used. - - Probably the only reason to use the -redirect option - is in conjunction with SSL support, e.g. -ssl SAVE. - This provides an easy way to add SSL encryption to a VNC - server that does not support SSL (e.g. Xvnc or vnc.so) - In fact, the protocol does not even need to be VNC, - and so "-rfbport port1 -ssl SAVE -redirect host:port2" - can act as a replacement for stunnel(1). - - This mode only allows one redirected connection. - The -forever option does not apply. Use -inetd or - -loop for persistent service. - --display_WAIT :... A special usage mode for the normal -display option. - Useful with -unixpw, but can be used independently - of it. If the display string begins with WAIT: then - x11vnc waits until a VNC client connects before opening - the X display (or -rawfb device). - - This could be useful for delaying opening the display - for certain usage modes (say if x11vnc is started at - boot time and no X server is running or users logged - in yet). - - If the string is, e.g. WAIT:0.0 or WAIT:1, i.e. "WAIT" - in front of a normal X display, then that indicated - display is used. - - One can also insert a geometry between colons, e.g. - WAIT:1280x1024:... to set the size of the display the - VNC client first attaches to since some VNC viewers - will not automatically adjust to a new framebuffer size. - - A more interesting case is like this: - - WAIT:cmd=/usr/local/bin/find_display - - in which case the command after "cmd=" is run to - dynamically work out the DISPLAY and optionally the - XAUTHORITY data. The first line of the command output - must be of the form DISPLAY=. On Linux - if the virtual terminal is known append ",VT=n" to - this string and the chvt(1) program will also be run. - Any remaining output is taken as XAUTHORITY data. - It can be either of the form XAUTHORITY= or raw - xauthority data for the display. For example; - - xauth extract - $DISPLAY" - - NOTE: As specified in the previous paragraph, you can - supply your own WAIT:cmd=... program or script, BUT - there are two very useful *BUILT-IN* ones: FINDDISPLAY - (alias -find above) and FINDCREATEDISPLAY (alias -create - above.) Most people use these instead of creating - their own script. Read the following (especially the - BUILT-IN modes sections) to see how to configure these - two useful builtin -display WAIT: modes. - - In the case of -unixpw (and -unixpw_nis only if x11vnc - is running as root), then the cmd= command is run - as the user who just authenticated via the login and - password prompt. - - In the case of -unixpw_cmd, the commands will also be - run as the logged-in user, as long as the user-supplied - helper program supports RFB_UNIXPW_CMD_RUN (see the - -unixpw_cmd option.) - - Also in the case of -unixpw, the user logging in can - place a colon at the end of her username and supply - a few options: scale=, scale_cursor= (or sc=), solid - (or so), id=, clear_mods (or cm), clear_keys (or - ck), clear_all (or ca), repeat, speeds= (or sp=), - readtimeout= (or rd=), viewonly (or vo), nodisplay= - (or nd=), rotate= (or ro=), or noncache (or nc), - all separated by commas if there is more than one. - After the user logs in successfully, these options will - be applied to the VNC screen. For example, - - login: fred:scale=3/4,sc=1,repeat - Password: ... - - login: runge:sp=modem,rd=120,solid - - for convenience m/n implies scale= e.g. fred:3/4 If you - type and enter your password incorrectly, to retrieve - your long "login:" line press the Up arrow once - (before typing anything else). - - Most of these colon options only apply to the builtin - FINDDISPLAY and FINDCREATEDISPLAY modes, but note - that they are passed to the extrenal command in the - environment as well and so could be used. - - In the login panel, press F1 to get a list of the - available options that you can add after the username. - - Another option is "geom=WxH" or "geom=WxHxD" (or - ge=). This only has an effect in FINDCREATEDISPLAY - mode when a virtual X server such as Xvfb is going - to be created. It sets the width and height of - the new display, and optionally the color depth as - well. - - You can also supply "gnome", "kde", "twm", - "fvwm", "mwm", "dtwm", "wmaker", "xfce", - "lxde", "enlightenment", "Xsession", or - "failsafe" (same as "xterm") to have the created - display use that mode for the user session. - - Specify "tag=..." to set the unique FD_TAG desktop - session tag described below. Note: this option will - be ignored if the FD_TAG env. var. is already set or - if the viewer-side supplied value is not completely - composed of alphanumeric or '_' or '-' characters. - - User preferences file: Instead of having the user type - in geom=WxH,... etc. every time he logs in to find - or create his X session, if you set FD_USERPREFS to - a string that does not contain the "/" character, - then the user's home directory is prepended to that - string and if the file exists its first line is read - and appended to any options he supplied at the login: - prompt. For example -env FD_USERPREFS=.x11vnc_create - and the user put "geom=1600x1200" in his - ~/.x11vnc_create file. - - To disable the option setting set the environment - variable X11VNC_NO_UNIXPW_OPTS=1 before starting x11vnc. - To set any other options, the user can use the gui - (x11vnc -gui connect) or the remote control method - (x11vnc -R opt:val) during his VNC session. - - So we see the combination of -display WAIT:cmd=... and - -unixpw allows automatic pairing of an unix - authenticated VNC user with his desktop. This could - be very useful on SunRays and also any system where - multiple users share a given machine. The user does - not need to remember special ports or passwords set up - for his desktop and VNC. - - A nice way to use WAIT:cmd=... is out of inetd(8) - (it automatically forks a new x11vnc for each user). - You can have the x11vnc inetd spawned process run as, - say, root or nobody. When run as root (for either inetd - or display manager), you can also supply the option - "-users unixpw=" to have the x11vnc process switch to - the user as well. Note: there will be a 2nd SSL helper - process that will not switch, but it is only encoding - and decoding the encrypted stream at that point. - - BUILT-IN modes: - - -- Automatic Finding of User X Sessions -- - - As a special case, WAIT:cmd=FINDDISPLAY will run a - script that works on most Unixes to determine a user's - DISPLAY variable and xauthority data (see who(1)). - - NOTE: The option "-find" is an alias for this mode. - - To have this default script printed to stdout (e.g. for - customization) run with WAIT:cmd=FINDDISPLAY-print To - have the script run to print what display it would find - use "-finddpy" or WAIT:cmd=FINDDISPLAY-run - - The standard script runs xdpyinfo(1) run on potential - displays. If your X server(s) have a login greeter - that exclusively grabs the Xserver, then xdpyinfo - blocks forever and this mode will not work. See - www.karlrunge.com/x11vnc/faq.html#faq-display-manager - for how to disable this for dtgreet on Solaris and - possibly for other greeters. - - In -find/cmd=FINDDISPLAY mode, if you set FD_XDM=1, - e.g. 'x11vnc -env FD_XDM=1 -find ...' and x11vnc is - running as root (e.g. inetd) then it will try to find - the XAUTHORITY file of a running XDM/GDM/KDM login - greeter (i.e. no user has logged into an X session yet.) - - As another special case, WAIT:cmd=HTTPONCE will allow - x11vnc to service one http request and then exit. - This is usually done in -inetd mode to run on, say, - port 5800 and allow the Java vncviewer to be downloaded - by client web browsers. For example: - - 5815 stream tcp nowait root /usr/sbin/tcpd /.../x11vnc -\ - -inetd -q -http_ssl -prog /.../x11vnc \ - -display WAIT:cmd=HTTPONCE - - Where /.../x11vnc is the full path to x11vnc. - It is used in the Apache SSL-portal example (see FAQ). - - In this mode you can set X11VNC_SKIP_DISPLAY to a - comma separated list of displays (e.g. ":0,:1") to - ignore in the finding process. The ":" is optional. - Ranges n-m e.g. 0-20 can also be supplied. This string - can also be set by the connecting user via "nd=" - using "+" instead of "," If "nd=all" or you set - X11VNC_SKIP_DISPLAY=all then all display finding fails - as if you set X11VNC_FINDDISPLAY_ALWAYS_FAILS=1 (below.) - - On some systems lsof(1) can be very slow. Set the - env. var. FIND_DISPLAY_NO_LSOF=1 to skip using lsof to - try to find the Linux VT the X server is running on. - set FIND_DISPLAY_NO_VT_FIND=1 to avoid looking at all. - - -- Automatic Creation of User X Sessions -- - - An interesting option is WAIT:cmd=FINDCREATEDISPLAY - that is like FINDDISPLAY in that is uses the same method - to find an existing display. However, if it does not - find one it will try to *start* up an X server session - for the user. This is the only time x11vnc tries to - actually start up an X server. - - NOTE: The option "-create" is an alias for this mode. - - It will start looking for an open display number at :20 - Override via X11VNC_CREATE_STARTING_DISPLAY_NUMBER=n - By default 80 X displays are allowed (i.e. going to :99) - Override via X11VNC_CREATE_MAX_DISPLAYS=n - - For its heuristics, the create display script sets - LC_ALL=C so that command output is uniform. By default - it will try to restore LC_ALL right before starting the - user session. However, if you don't mind it keeping - LC_ALL=C set the env. var.: X11VNC_CREATE_LC_ALL_C_OK=1 - - By default FINDCREATEDISPLAY will try Xvfb and then - Xdummy: - - The Xdummy wrapper is part of the x11vnc source code - (x11vnc/misc/Xdummy) It should be available in PATH - and have run "Xdummy -install" once to create the - shared library. Xdummy only works on Linux. As of - 12/2009 it no longer needs to be run as root, and the - default is to not run as root. In some circumstances - permissions may require running it as root, in these - cases specify FD_XDUMMY_RUN_AS_ROOT=1, this is the same - as supplying -root to the Xdummy cmdline. - - Xvfb is available on most platforms and does not - require root. - - An advantage of Xdummy over Xvfb is that Xdummy supports - RANDR dynamic screen resizing. - - When x11vnc exits (i.e. user disconnects) the X - server session stays running in the background. - The FINDDISPLAY will find it directly next time. - The user must exit the X session in the usual way for - it to terminate (or kill the X server process if all - else fails). - - To troubleshoot the FINDCREATEDISPLAY mechanism, - set the following env. var. to an output log file, - e.g -env CREATE_DISPLAY_OUTPUT=/tmp/mydebug.txt - - So this is a somewhat odd mode for x11vnc in that it - will start up and poll virtual X servers! This can - be used from, say, inetd(8) to provide a means of - definitely getting a desktop (either real or virtual) - on the machine. E.g. a desktop service: - - 5900 stream tcp nowait root /usr/sbin/tcpd /.../x11vnc - -inetd -q -http -ssl SAVE -unixpw -users unixpw=\ - -passwd secret -prog /.../x11vnc \ - -display WAIT:cmd=FINDCREATEDISPLAY - - Where /.../x11vnc is the full path to x11vnc. - - See the -svc/-service option alias above. - - If for some reason you do not want x11vnc to ever - try to find an existing display set the env. var - X11VNC_FINDDISPLAY_ALWAYS_FAILS=1 (also -env ...) - This is the same as setting X11VNC_SKIP_DISPLAY=all or - supplying "nd=all" after "username:" - - Use WAIT:cmd=FINDCREATEDISPLAY-print to print out the - script that is used for this. - - You can specify the preferred X server order via e.g., - WAIT:cmd=FINDCREATEDISPLAY-Xdummy,Xvfb,X and/or leave - out ones you do not want. The the case "X" means try - to start up a real, hardware X server using xinit(1) - or startx(1). If there is already an X server running - the X case may only work on Linux (see startx(1)). - - "Xvnc" will start up a VNC X server (real- - or tight-vnc, e.g. use if Xvfb is not available). - "Xsrv" will start up the server program in the - variable "FD_XSRV" if it is non-empty. You can make - this be a wrapper script if you like (it must handle :N, - -geometry, and -depth and other X server options). - - You can set the environment variable FD_GEOM (or - X11VNC_CREATE_GEOM) to WxH or WxHxD to set the width - and height and optionally the color depth of the - created display. You can also set FD_SESS to be the - session (short name of the windowmanager: kde, gnome, - twm, failsafe, etc.). FD_OPTS contains extra options - to pass to the X server. You can also set FD_PROG to - be the full path to the session/windowmanager program. - - More FD tricks: FD_CUPS=port or FD_CUPS=host:port - will set the cups printing environment. Similarly for - FD_ESD=port or FD_ESD=host:port for esddsp sound - redirection. Set FD_EXTRA to a command to be run a - few seconds after the X server starts up. Set FD_TAG - to be a unique name for the session, it is set as an - X property, that makes FINDDISPLAY only find sessions - with that tag value. - - Set FD_XDMCP_IF to the network interface that the - display manager is running on; default is 'localhost' - but you may need to set it to '::1' on some IPv6 only - systems or misconfigured display managers. - - If you want the FINDCREATEDISPLAY session to contact an - XDMCP login manager (xdm/gdm/kdm) on the same machine, - then use "Xvfb.xdmcp" instead of "Xvfb", etc. - The user will have to supply his username and password - one more time (but he gets to select his desktop type - so that can be useful). For this to work, you will - need to enable localhost XDMCP (udp port 177) for the - display manager. This seems to be: - - for gdm in gdm.conf: Enable=true in section [xdmcp] - for kdm in kdmrc: Enable=true in section [Xdmcp] - for xdm in xdm-config: DisplayManager.requestPort: 177 - - See the shorthand options above "-svc", "-xdmsvc" - and "-sshxdmsvc" that specify the above options for - some useful cases. - - If you set the env. var WAITBG=1 x11vnc will go into - the background once listening in wait mode. - - Another special mode is FINDCREATEDISPLAY-Xvnc.redirect, - (or FINDDISPLAY-Xvnc.redirect). In this case it will - start up Xvnc as above if needed, but instead of - polling it in its normal way, it simply does a socket - redirection of the connected VNC viewer to the Xvnc. - - So in Xvnc.redirect x11vnc does no VNC but merely - transfers the data back and forth. This should be - faster then x11vnc's polling method, but not as fast - as connecting directly to the Xvnc with the VNC Viewer. - The idea here is to take advantage of x11vnc's display - finding/creating scheme, SSL, and perhaps a few others. - Most of x11vnc's options do not apply in this mode. - - Xvnc.redirect should also work for the vnc.so X server - module for the h/w display however it will work only - for finding the display and the user must already be - logged into the X console. - --vencrypt mode The VeNCrypt extension to the VNC protocol allows - encrypted SSL/TLS connections. If the -ssl mode is - enabled, then VeNCrypt is enabled as well BY DEFAULT - (they both use a SSL/TLS tunnel, only the protocol - handshake is a little different.) - - To control when and how VeNCrypt is used, specify the - mode string. If mode is "never", then VeNCrypt is - not used. If mode is "support" (the default) then - VeNCrypt is supported. If mode is "only", then the - similar and older ANONTLS protocol is not simultaneously - supported. x11vnc's normal SSL mode (vncs://) will be - supported under -ssl unless you set mode to "force". - - If mode is prefixed with "nodh:", then Diffie Hellman - anonymous key exchange is disabled. If mode is prefixed - with "nox509:", then X509 key exchange is disabled. - - To disable all Anonymous Diffie-Hellman access - (susceptible to Man-In-The-Middle attack) you will need - to supply "-vencrypt nodh:support -anontls never" - or "-vencrypt nodh:only" - - If mode is prefixed with "newdh:", then new Diffie - Hellman parameters are generated for each connection - (this can be time consuming: 1-60 secs; see -dhparams - below for a faster way) rather than using the - fixed values in the program. Using fixed, publicly - known values is not known to be a security problem. - This setting applies to ANONTLS as well. - - Long example: -vencrypt newdh:nox509:support - - Also, if mode is prefixed with "plain:", then - if -unixpw mode is active the VeNCrypt "*Plain" - username+passwd method is enabled for Unix logins. - Otherwise in -unixpw mode the normal login panel is - provided. - - You *MUST* supply the -ssl option for VeNCrypt to - be active. The -vencrypt option only fine-tunes its - operation. - --anontls mode The ANONTLS extension to the VNC protocol allows - encrypted SSL/TLS connections. If the -ssl mode is - enabled, then ANONTLS is enabled as well BY DEFAULT - (they both use a SSL/TLS tunnel, only the protocol - handshake is a little different.) - - ANONTLS is an older SSL/TLS mode introduced by vino. - - It is referred to as 'TLS' for its registered VNC - security-type name, but we use the more descriptive - 'ANONTLS' here because it provides only Anonymous - Diffie-Hellman encrypted connections, and hence no - possibility for certificate authentication. - - To control when and how ANONTLS is used, specify the - mode string. If mode is "never", then ANONTLS is not - used. If mode is "support" (the default) then ANONTLS - is supported. If mode is "only", then the similar - VeNCrypt protocol is not simultaneously supported. - x11vnc's normal SSL mode (vncs://) will be supported - under -ssl unless you set mode to "force". - - If mode is prefixed with "newdh:", then new Diffie - Hellman parameters are generated for each connection - (this can be time consuming: 1-60 secs; see -dhparams - below for a faster way) rather than using the - fixed values in the program. Using fixed, publicly - known values is not known to be a security problem. - This setting applies to VeNCrypt as well. See the - description of "plain:" under -vencrypt. - - Long example: -anontls newdh:plain:support - - You *MUST* supply the -ssl option for ANONTLS to - be active. The -anontls option only fine-tunes its - operation. - --sslonly Same as: "-vencrypt never -anontls never" i.e. it - disables the VeNCrypt and ANONTLS encryption methods - and only allows standard SSL tunneling. You must also - supply the -ssl ... option (see below.) - - --dhparams file For some operations a set of Diffie Hellman parameters - (prime and generator) is needed. If so, use the - parameters in "file". In particular, the VeNCrypt and - ANONTLS anonymous DH mode need them. By default a - fixed set is used. If you do not want to do that you - can specify "newdh:" to the -vencrypt and -anontls - options to generate a new set each session. If that - is too slow for you, use -dhparams file to a set you - created manually via "openssl dhparam -out file 1024" - --nossl Disable the -ssl option (see below). Since -ssl is off - by default -nossl would only be used on the commandline - to unset any *earlier* -ssl option (or -svc...) - --ssl [pem] Use the openssl library (www.openssl.org) to provide a - built-in encrypted SSL/TLS tunnel between VNC viewers - and x11vnc. This requires libssl support to be - compiled into x11vnc at build time. If x11vnc is not - built with libssl support it will exit immediately when - -ssl is prescribed. See the -stunnel option below for - an alternative. - - The VNC Viewer-side needs to support SSL/TLS as well. - See this URL and also the discussion below for - ideas on how to enable SSL support for the viewer: - http://www.karlrunge.com/x11vnc/faq.html#faq-ssl-tun - nel-viewers . x11vnc provides an SSL enabled Java - viewer applet in the classes/ssl directory (-http or - -httpdir options.) The SSVNC viewer package supports - SSL tunnels too. - - If the VNC Viewer supports VeNCrypt or ANONTLS (vino's - encryption mode) they are also supported by the -ssl - mode (see the -vencrypt and -anontls options for more - info; use -sslonly to disable both of them.) - - Use "-ssl /path/to/mycert.pem" to specify an SSL - certificate file in PEM format to use to identify and - provide a key for this server. See openssl(1) for more - info about PEMs and the -sslGenCert and "-ssl SAVE" - options below for how to create them. - - The connecting VNC viewer SSL tunnel can (at its option) - authenticate this server if it has the public key part - of the certificate (or a common certificate authority, - CA, is a more sophisticated way to verify this server's - cert, see -sslGenCA below). This authentication is - done to prevent Man-In-The-Middle attacks. Otherwise, - if the VNC viewer simply accepts this server's key - WITHOUT verification, the traffic is protected from - passive sniffing on the network, but *NOT* from - Man-In-The-Middle attacks. There are hacker tools - like dsniff/webmitm and cain that implement SSL - Man-In-The-Middle attacks. - - If [pem] is empty or the string "SAVE" then the - openssl(1) command must be available to generate the - certificate the first time. A self-signed certificate - is generated (see -sslGenCA and -sslGenCert for use - of a Certificate Authority.) It will be saved to the - file ~/.vnc/certs/server.pem. On subsequent calls if - that file already exists it will be used directly. - - Use "SAVE_NOPROMPT" to avoid being prompted to - protect the generated key with a passphrase. However in - -inetd and -bg modes there will be no prompting for a - passphrase in either case. - - If [pem] is "SAVE_PROMPT" the server.pem certificate - will be created based on your answers to its prompts for - all info such as OrganizationalName, CommonName, etc. - - Use "SAVE-" and "SAVE_PROMPT-" - to refer to the file ~/.vnc/certs/server-.pem - instead (it will be generated if it does not already - exist). E.g. "SAVE-charlie" will store to the file - ~/.vnc/certs/server-charlie.pem - - Examples: x11vnc -ssl SAVE -display :0 ... - x11vnc -ssl SAVE-someother -display :0 ... - - If [pem] is "TMP" and the openssl(1) utility - command exists in PATH, then a temporary, self-signed - certificate will be generated for this session. If - openssl(1) cannot be used to generate a temporary - certificate x11vnc exits immediately. The temporary - cert will be discarded when x11vnc exits. - - If successful in using openssl(1) to generate a - temporary certificate in "SAVE" or "TMP" creation - modes, the public part of it will be displayed to stderr - (e.g. one could copy it to the client-side to provide - authentication of the server to VNC viewers.) - - NOTE: In "TMP" mode, unless you safely copy the - public part of the temporary Cert to the viewer for - authenticate *every time* (unlikely...), then only - passive sniffing attacks are prevented and you are - still open to Man-In-The-Middle attacks. This is - why the default "SAVE" mode is preferred (and more - sophisticated CA mode too). Only with saved keys AND - the VNC viewer authenticating them (via the public - certificate), are Man-In-The-Middle attacks prevented. - - If [pem] is "ANON" then the Diffie-Hellman anonymous - key exchange method is used. In this mode there - are *no* SSL certificates and so it is not possible - to authenticate either the VNC server or VNC client. - Thus only passive network sniffing attacks are avoided: - the "ANON" method is susceptible to Man-In-The-Middle - attacks. "ANON" is not recommended; instead use - a SSL PEM you created or the default "SAVE" method. - - See -ssldir below to use a directory besides the - default ~/.vnc/certs - - If your x11vnc binary was not compiled with OpenSSL - library support, use of the -ssl option will induce an - immediate failure and exit. For such binaries, consider - using the -stunnel option for SSL encrypted connections. - - Misc Info: In temporary cert creation mode "TMP", set - the env. var. X11VNC_SHOW_TMP_PEM=1 to have x11vnc print - out the entire certificate, including the PRIVATE KEY - part, to stderr. There are better ways to get/save this - info. See "SAVE" above and "-sslGenCert" below. - --ssltimeout n Set SSL read timeout to n seconds. In some situations - (i.e. an iconified viewer in Windows) the viewer stops - talking and the connection is dropped after the default - timeout (25s for about the first minute, 43200s later). - Set to zero to poll forever. Set to a negative value - to use the builtin setting. - - Note that this value does NOT apply to the *initial* ssl - init connection. The default timeout for that is 20sec. - Use -env SSL_INIT_TIMEOUT=n to modify it. - --sslnofail Exit at the first SSL connection failure. Useful when - scripting SSL connections (e.g. x11vnc is started via - ssh) and you do not want x11vnc waiting around for more - connections, tying up ports, etc. - --ssldir dir Use "dir" as an alternate ssl certificate and key - management toplevel directory. The default is - ~/.vnc/certs - - This directory is used to store server and other - certificates and keys and also other materials. E.g. in - the simplest case, "-ssl SAVE" will store the x11vnc - server cert in dir/server.pem - - Use of alternate directories via -ssldir allows you to - manage multiple VNC Certificate Authority (CA) keys. - Another use is if ~/.vnc/cert is on an NFS share you - might want your certificates and keys to be on a local - filesystem to prevent network snooping (for example - -ssldir /var/lib/x11vnc-certs). - - -ssldir affects nearly all of the other -ssl* options, - e.g. -ssl SAVE, -sslGenCert, etc.. - --sslverify path For either of the -ssl or -stunnel modes, use "path" - to provide certificates to authenticate incoming VNC - *Client* connections (normally only the server is - authenticated in SSL.) This can be used as a method - to replace standard password authentication of clients. - - If "path" is a directory it contains the client (or CA) - certificates in separate files. If path is a file, - it contains one or more certificates. See special tokens - below. These correspond to the "CApath = dir" and - "CAfile = file" stunnel options. See the stunnel(8) - manpage for details. - - Examples: - x11vnc -ssl -sslverify ~/my.crt - x11vnc -ssl -sslverify ~/my_pem_dir/ - - Note that if path is a directory, it must contain - the certs in separate files named like .0, where - the value of is found by running the command - "openssl x509 -hash -noout -in file.crt". Evidently - one uses .1 if there is a collision... - - The the key-management utility "-sslCertInfo HASHON" - and "-sslCertInfo HASHOFF" will create/delete these - hashes for you automatically (via symlink) in the HASH - subdirs it manages. Then you can point -sslverify to - the HASH subdir. - - Special tokens: in -ssl mode, if "path" is not a file or - a directory, it is taken as a comma separated list of - tokens that are interpreted as follows: - - If a token is "CA" that means load the CA/cacert.pem - file from the ssl directory. If a token is "clients" - then all the files clients/*.crt in the ssl directory - are loaded. Otherwise the file clients/token.crt - is attempted to be loaded. As a kludge, use a token - like ../server-foo to load a server cert if you find - that necessary. - - Use -ssldir to use a directory different from the - ~/.vnc/certs default. - - Note that if the "CA" cert is loaded you do not need - to load any of the certs that have been signed by it. - You will need to load any additional self-signed certs - however. - - Examples: - x11vnc -ssl -sslverify CA - x11vnc -ssl -sslverify self:fred,self:jim - x11vnc -ssl -sslverify CA,clients - - Usually "-sslverify CA" is the most effective. - See the -sslGenCA and -sslGenCert options below for - how to set up and manage the CA framework. - - - - NOTE: the following utilities, -sslGenCA, -sslGenCert, - -sslEncKey, -sslCertInfo, and -sslCRL are provided for - completeness, but for casual usage they are overkill. - - They provide VNC Certificate Authority (CA) key creation - and server / client key generation and signing. So they - provide a basic Public Key management framework for - VNC-ing with x11vnc. (note that they require openssl(1) - be installed on the system) - - However, the simplest usage mode, "-ssl TMP" (where - x11vnc automatically generates its own, self-signed, - temporary key and the VNC viewers always accept it, - e.g. accepting via a dialog box) is probably safe enough - for most scenarios. CA management is not needed. - - To protect against Man-In-The-Middle attacks the "TMP" - mode can be improved by using "-ssl SAVE" (same as - "-ssl", i.e. the default) to have x11vnc create a - longer term self-signed certificate, and then (safely) - copy the corresponding public key cert to the desired - client machines (care must be taken the private key part - is not stolen; you will be prompted for a passphrase). - - So keep in mind no CA key creation or management - (-sslGenCA and -sslGenCert) is needed for either of - the above two common usage modes. - - One might want to use -sslGenCA and -sslGenCert - if you had a large number of VNC client and server - workstations. That way the administrator could generate - a single CA key with -sslGenCA and distribute its - certificate part to all of the workstations. - - Next, he could create signed VNC server keys - (-sslGenCert server ...) for each workstation or user - that then x11vnc would use to authenticate itself to - any VNC client that has the CA cert. - - Optionally, the admin could also make it so the - VNC clients themselves are authenticated to x11vnc - (-sslGenCert client ...) For this -sslverify would be - pointed to the CA cert (and/or self-signed certs). - - x11vnc will be able to use all of these cert and - key files. On the VNC client side, they will need to - be "imported" somehow. Web browsers have "Manage - Certificates" actions as does the Java applet plugin - Control Panel. stunnel can also use these files (see - the ss_vncviewer example script in the FAQ and SSVNC.) - --sslCRL path Set the Certificate Revocation Lists (CRL) to "path". - This setting applies for both -ssl and -stunnel modes. - - If path is a file, the file contains one or more CRLs - in PEM format. If path is a directory, it contains - hash named files of CRLs in the usual OpenSSL manner. - See the OpenSSL and stunnel(8) documentation for - more info. - - This option only applies if -sslverify has been - supplied: it checks for revocation along the - certificate chain used to verify the VNC client. - The -sslCRL setting will be ignored when -sslverify is - not specified. - - Note that if a CRL's expiration date has passed, all - SSL connections will fail regardless of if they are - related to the subject of the CRL or not. - - Only rarely will one's x11vnc -ssl infrastructure be so - large that this option would be useful (since normally - maintaining the contents of the -sslverify file or - directory should be enough.) However, when using - x11vnc with a Certificate Authority (see -sslGenCA) - to authenticate Clients via SSL/TLS, the -sslCRL option - can be useful to revoke users' certs whose private SSL - keys were lost or stolen (e.g. laptop.) This way a new - CA cert+key does not need to be created and new signed - client keys generated and distributed to all users. - - To create a CRL file with revoked certificates the - commands 'openssl ca -revoke ...' and 'openssl ca - -gencrl ...' are useful. (Run them in ~/.vnc/certs) - --sslGenCA [dir] Generate your own Certificate Authority private key, - certificate, and other files in directory [dir]. - x11vnc then exits. - - If [dir] is not supplied, a -ssldir setting is used, - or otherwise ~/.vnc/certs is used. - - This command also creates directories where server and - client certs and keys will be stored. The openssl(1) - program must be installed on the system and available - in PATH. - - After the CA files and directories are created the - x11vnc command exits; the VNC server is not run. - - You will be prompted for information to put into the CA - certificate. The info does not have to be accurate just - as long as clients accept the cert for VNC connections. - You will also need to supply a passphrase of at least - 4 characters for the CA private key. - - Once you have generated the CA you can distribute - its certificate part, [dir]/CA/cacert.pem, to other - workstations where VNC viewers will be run. One will - need to "import" this certificate in the applications, - e.g. Web browser, Java applet plugin, stunnel, etc. - Next, you can create and sign keys using the CA with - the -sslGenCert option below. - - Examples: - x11vnc -sslGenCA - x11vnc -sslGenCA ~/myCAdir - x11vnc -ssldir ~/myCAdir -sslGenCA - - (the last two lines are equivalent) - --sslGenCert type name Generate a VNC server or client certificate and private - key pair signed by the CA created previously with - -sslGenCA. The openssl(1) program must be installed - on the system and available in PATH. - - After the Certificate is generated x11vnc exits; the - VNC server is not run. - - The type of key to be generated is the string "type". - It is either "server" (i.e. for use by x11vnc) or - "client" (for a VNC viewer). Note that typically - only "server" is used: the VNC clients authenticate - themselves by a non-public-key method (e.g. VNC or - unix password). "type" is required. - - An arbitrary default name you want to associate with - the key is supplied by the "name" string. You can - change it at the various prompts when creating the key. - "name" is optional. - - If name is left blank for clients keys then "nobody" - is used. If left blank for server keys, then the - primary server key: "server.pem" is created (this - is the saved one referenced by "-ssl SAVE" when the - server is started) - - If "name" begins with the string "self:" then - a self-signed certificate is created instead of one - signed by your CA key. - - If "name" begins with the string "req:" then only a - key (.key) and a certificate signing *request* (.req) - are generated. You can then send the .req file to - an external CA (even a professional one, e.g. Thawte) - and then combine the .key and the received cert into - the .pem file with the same basename. - - The distinction between "server" and "client" is - simply the choice of output filenames and sub-directory. - This makes it so the -ssl SAVE-name option can easily - pick up the x11vnc PEM file this option generates. - And similarly makes it easy for the -sslverify option - to pick up your client certs. - - There is nothing special about the filename or directory - location of either the "server" and "client" certs. - You can rename the files or move them to wherever - you like. - - Precede this option with -ssldir [dir] to use a - directory other than the default ~/.vnc/certs You will - need to run -sslGenCA on that directory first before - doing any -sslGenCert key creation. - - Note you cannot recreate a cert with exactly the same - distiguished name (DN) as an existing one. To do so, - you will need to edit the [dir]/CA/index.txt file to - delete the line. - - Similar to -sslGenCA, you will be prompted to fill - in some information that will be recorded in the - certificate when it is created. - - Tip: if you know the fully-qualified hostname other - people will be connecting to, you can use that as the - CommonName "CN" to avoid some applications (e.g. web - browsers and java plugin) complaining that it does not - match the hostname. - - You will also need to supply the CA private key - passphrase to unlock the private key created from - -sslGenCA. This private key is used to sign the server - or client certificate. - - The "server" certs can be used by x11vnc directly by - pointing to them via the -ssl [pem] option. The default - file will be ~/.vnc/certs/server.pem. This one would - be used by simply typing -ssl SAVE. The pem file - contains both the certificate and the private key. - server.crt file contains the cert only. - - The "client" cert + private key file will need - to be copied and imported into the VNC viewer - side applications (Web browser, Java plugin, - stunnel, etc.) Once that is done you can delete the - "client" private key file on this machine since - it is only needed on the VNC viewer side. The, - e.g. ~/.vnc/certs/clients/.pem contains both - the cert and private key. The .crt contains the - certificate only. - - NOTE: It is very important to know one should - generate new keys with a passphrase. Otherwise if an - untrusted user steals the key file he could use it to - masquerade as the x11vnc server (or VNC viewer client). - You will be prompted whether to encrypt the key with - a passphrase or not. It is recommended that you do. - One inconvenience to a passphrase is that it must - be typed in EVERY time x11vnc or the client app is - started up. - - Examples: - - x11vnc -sslGenCert server - x11vnc -ssl SAVE -display :0 ... - - and then on viewer using ss_vncviewer stunnel wrapper - (see the FAQ): - ss_vncviewer -verify ./cacert.crt hostname:0 - - (this assumes the cacert.crt cert from -sslGenCA - was safely copied to the VNC viewer machine where - ss_vncviewer is run) - - Example using a name: - - x11vnc -sslGenCert server charlie - x11vnc -ssl SAVE-charlie -display :0 ... - - Example for a client certificate (rarely used): - - x11vnc -sslGenCert client roger - scp ~/.vnc/certs/clients/roger.pem somehost:. - rm ~/.vnc/certs/clients/roger.pem - - x11vnc is then started with the option -sslverify - ~/.vnc/certs/clients/roger.crt (or simply -sslverify - roger), and on the viewer user on somehost could do - for example: - - ss_vncviewer -mycert ./roger.pem hostname:0 - - If you set the env. var REQ_ARGS='...' it will be - passed to openssl req(1). A common use would be - REQ_ARGS='-days 1095' to bump up the expiration date - (3 years in this case). - --sslEncKey pem Utility to encrypt an existing PEM file with a - passphrase you supply when prompted. For that key to be - used (e.g. by x11vnc) the passphrase must be supplied - each time. - - The "SAVE" notation described under -ssl applies as - well. (precede this option with -ssldir [dir] to refer - a directory besides the default ~/.vnc/certs) - - The openssl(1) program must be installed on the system - and available in PATH. After the Key file is encrypted - the x11vnc command exits; the VNC server is not run. - - Examples: - x11vnc -sslEncKey /path/to/foo.pem - x11vnc -sslEncKey SAVE - x11vnc -sslEncKey SAVE-charlie - --sslCertInfo pem Prints out information about an existing PEM file. - In addition the public certificate is also printed. - The openssl(1) program must be in PATH. Basically the - command "openssl x509 -text" is run on the pem. - - After the info is printed the x11vnc command exits; - the VNC server is not run. - - The "SAVE" notation described under -ssl applies - as well. - - Using "LIST" will give a list of all certs being - managed (in the ~/.vnc/certs dir, use -ssldir to refer - to another dir). "ALL" will print out the info for - every managed key (this can be very long). Giving a - client or server cert shortname will also try a lookup - (e.g. -sslCertInfo charlie). Use "LISTL" or "LL" - for a long (ls -l style) listing. - - Using "HASHON" will create subdirs [dir]/HASH and - [dir]/HASH with OpenSSL hash filenames (e.g. 0d5fbbf1.0) - symlinks pointing up to the corresponding *.crt file. - ([dir] is ~/.vnc/certs or one given by -ssldir.) - This is a useful way for other OpenSSL applications - (e.g. stunnel) to access all of the certs without - having to concatenate them. x11vnc will not use them - unless you specifically reference them. "HASHOFF" - removes these HASH subdirs. - - The LIST, LISTL, LL, ALL, HASHON, HASHOFF words can - also be lowercase, e.g. "list". - --sslDelCert pem Prompts you to delete all .crt .pem .key .req files - associated with [pem]. x11vnc then exits. "SAVE" - and lookups as in -sslCertInfo apply as well. - --sslScripts Prints out both the 'genCA' and 'genCert' x11vnc - openssl wrapper scripts for you to examine, modify, etc. - The scripts are printed to stdout and then the x11vnc - program exits. - - --stunnel [pem] Use the stunnel(8) (stunnel.mirt.net) to provide an - encrypted SSL tunnel between viewers and x11vnc. - - This external tunnel method was implemented prior to the - integrated -ssl encryption described above. It still - works well and avoids the requirement of linking with - the OpenSSL libraries. This mode requires stunnel - to be installed on the system and available via PATH - (n.b. stunnel is often installed in sbin directories). - Version 4.x of stunnel is assumed (but see -stunnel3 - below.) - - [pem] is optional, use "-stunnel /path/to/stunnel.pem" - to specify a PEM certificate file to pass to stunnel. - See the -ssl option for more info on certificate files. - - Whether or not your stunnel has its own certificate - depends on your stunnel configuration; stunnel often - generates one at install time. See your stunnel - documentation for details. In any event, if you want to - use this certificate you must supply the full path to it - as [pem]. Note: the file may only be readable by root. - - [pem] may also be the special strings "TMP", "SAVE", - and "SAVE..." as described in the -ssl option. - If [pem] is not supplied, "SAVE" is assumed. - - Note that the VeNCrypt, ANONTLS, and "ANON" modes - are not supported in -stunnel mode. - - stunnel is started up as a child process of x11vnc and - any SSL connections stunnel receives are decrypted and - sent to x11vnc over a local socket. The strings - "The SSL VNC desktop is ..." and "SSLPORT=..." - are printed out at startup to indicate this. - - The -localhost option is enforced by default to avoid - people routing around the SSL channel. Use -env - STUNNEL_DISABLE_LOCALHOST=1 to disable this security - requirement. - - Set -env STUNNEL_DEBUG=1 for more debugging printout. - - Set -env STUNNEL_PROG=xxx to the full path of stunnel - program you want to be used (e.g. /usr/bin/stunnel4). - - Set -env STUNNEL_LISTEN=xxx to the address of the - network interface to listen on (the default is to listen - on all interfaces), e.g. STUNNEL_LISTEN=192.168.1.100. - - A simple way to add IPv6 support is STUNNEL_LISTEN=:: - - Your VNC viewer will also need to be able to connect - via SSL. Unfortunately not too many do this. See the - information about SSL viewers under the -ssl option. - The x11vnc project's SSVNC is an option. - - Also, in the x11vnc distribution, patched TightVNC - and UltraVNC Java applet jar files are provided in - the classes/ssl directory that do SSL connections. - Enable serving them with the -http, -http_ssl, or - -httpdir (see the option descriptions for more info.) - - Note that for the Java viewer applet usage the - "?PORT=xxxx" in the various URLs printed at startup - will need to be supplied to the web browser to connect - properly. - - Currently the automatic "single port" HTTPS mode of - -ssl is not fully supported in -stunnel mode. However, - it can be emulated via: - - % x11vnc -stunnel -http_ssl -http_oneport ... - - In general, it is also not too difficult to set up - an stunnel or other SSL tunnel on the viewer side. - A simple example on Unix using stunnel 3.x is: - - % stunnel -c -d localhost:5901 -r remotehost:5900 - % vncviewer localhost:1 - - For Windows, stunnel has been ported to it and there - are probably other such tools available. See the FAQ - and SSVNC for more examples. - --stunnel3 [pem] Use version 3.x stunnel command line syntax instead of - version 4.x. The -http/-httpdir Java applet serving - is currently not available in this mode. - --enc cipher:keyfile Use symmetric encryption with cipher "cipher" - and secret key data in "keyfile". If keyfile is - pw= then "string" is used as the key data. - - NOTE: It is recommended that you use SSL via the -ssl - option instead of this option because SSL is well - understood and takes great care to establish unique - session keys and is more compatible with other software. - Use this option if you do not want to deal with SSL - certificates for authentication and do not want to - use SSH but want some encryption for your VNC session. - Or if you must interface with a symmetric key tunnel - that you do not have control over. - - Note that this mode will NOT work with the UltraVNC DSM - plugins because they alter the RFB protocol in addition - to tunnelling with the symmetric cipher (an unfortunate - choice of implementation...) - - cipher can be one of: arc4, aesv2, aes-cfb, blowfish, - aes256, or 3des. See the OpenSSL documentation for - more info. The keysize is 128 bits (except for aes256). - Here is one way to make a keyfile with that many bits: - - dd if=/dev/random of=./my.key bs=16 count=1 - - you will need to securely share this key with the other - side of the VNC connection (See SSVNC for examples). - - Example: -enc blowfish:./my.key - Example: -enc blowfish:pw=swordfish - - By default 16 bytes of random salt followed by 16 bytes - of random initialization vector are sent at the very - beginning of the stream. The other side must read these - and initialize their cipher with them. These values - make the session key unique (without them the security - is minimal). Similarly, the other side must send us - its random salt and IV with those same lengths. - - The salt and key data are combined to create a session - key using an md5 hash as described in EVP_BytesToKey(3). - - The exact call is: EVP_BytesToKey(Cipher, EVP_md5(), - salt, keydata, len, 1, keystr, NULL); where salt is - the random data as described above, and keydata is the - shared secret key data. keystr is the resulting session - key. The cipher is then seeded with keystr and uses - the random initialization vector as its first block. - - To modify the amount of random salt and initialization - vector use cipher@n,m where n is the salt length and - m the initialization vector length. E.g. - - -enc aes-cfb@8,16:./my.key - - It is not a good idea to set either one to zero, - although you may be forced to if the other side of the - tunnel is not under your control. - - To skip the salt and EVP_BytesToKey MD5 entirely (no - hashing is done: the keydata is directly inserted into - the cipher) specify "-1" for the salt, e.g. - - -enc blowfish@-1,16:./my.key - - The message digest can also be changed to something - besides the default MD5. Use cipher@md+n,m where "md" - can be one of sha, sha1, md5, or ripe. For example: - - -enc arc4@sha+8,16:./my.key - - The SSVNC vnc viewer project supplies a symmetric - encryption tool named "ultravnc_dsm_helper" that can - be used on the viewer side. For example: - - ssvncviewer exec='ultravnc_dsm_helper arc4 my.key 0 h:p' - - where h:p is the hostname and port of the x11vnc server. - ultravnc_dsm_helper may also be used standalone to - provide a symmetric encryption tunnel for any viewer - or server (VNC or otherwise.) The cipher (1st arg) - is basically the same syntax as we use above. - - Also see the 'Non-Ultra DSM' SSVNC option for the - 'UltraVNC DSM Encryption Plugin' advanced option. - - For both ways of using the viewer, you can specify the - salt,ivec sizes (in GUI or, e.g. arc4@8,16). - --https [port] Use a special, separate HTTPS port (-ssl and - -stunnel modes only) for HTTPS Java viewer applet - downloading. I.e. not 5900 and not 5800 (the defaults.) - - BACKGROUND: In -ssl mode, it turns out you can use the - single VNC port (e.g. 5900) for both VNC and HTTPS - connections. (HTTPS is used to retrieve a SSL-aware - VncViewer.jar applet that is provided with x11vnc). - Since both use SSL the implementation was extended to - detect if HTTP traffic (i.e. GET) is taking place and - handle it accordingly. The URL would be, e.g.: - - https://mymachine.org:5900/ - - This is convenient for firewalls, etc, because only one - port needs to be allowed in. However, this heuristic - adds a few seconds delay to each connection and can be - unreliable (especially if the user takes much time to - ponder the Certificate dialogs in his browser, Java VM, - or VNC Viewer applet. That's right 3 separate "Are - you sure you want to connect?" dialogs!) - - END OF BACKGROUND. - - USAGE: So use the -https option to provide a separate, - more reliable HTTPS port that x11vnc will listen on. If - [port] is not provided (or is 0), one is autoselected. - The URL to use is printed out at startup. - - The SSL Java applet directory is specified via the - -httpdir option. If not supplied, -https will try - to guess the directory as though the -http option - was supplied. - --httpsredir [port] In -ssl mode with the Java applet retrieved via HTTPS, - when the HTML file containing applet parameters - ('index.vnc' or 'proxy.vnc') is sent do NOT set the - applet PORT parameter to the actual VNC port but set it - to "port" instead. If "port" is not supplied, then - the port number is guessed from the Host: HTTP header. - - This is useful when an incoming TCP connection - redirection is performed by a router/gateway/firewall - from one port to an internal machine where x11vnc is - listening on a different port. The Java applet needs to - connect to the firewall/router port, not the VNC port - on the internal workstation. For example, one could - redir from mygateway.com:443 to workstation:5900. - - This spares the user from having to type in - https://mygateway.com/?PORT=443 into their web - browser. Note that port 443 is the default https port; - other ports must be explicitly indicated, for example: - https://mygateway.com:8000/?PORT=8000. To avoid having - to include the PORT= in the browser URL, simply supply - "-httpsredir" to x11vnc. - - This option does not work in -stunnel mode. - - More tricks: set the env var X11VNC_EXTRA_HTTPS_PARAMS - to be extra URL parameters to use. This way you do - not need to specify extra PARAMS in the index.vnc file. - E.g. x11vnc -env X11VNC_EXTRA_HTTPS_PARAMS='?GET=1' ... - - If you do not want to expose the non-SSL HTTP port to - the network (i.e. you just want the single VNC/HTTPS - port, e.g. 5900, open for connections) then specify the - option -env X11VNC_HTTP_LISTEN_LOCALHOST=1 This way - the connection to the LibVNCServer httpd server will - only be available on localhost (note that in -ssl mode, - HTTPS requests are redirected from SSL to the non-SSL - LibVNCServer HTTP server.) - --http_oneport For UN-encrypted connections mode (i.e. no -ssl, - -stunnel, or -enc options), allow the Java VNC Viewer - applet to be downloaded thru the VNC port via HTTP. - - That is to say, you can use a single port for Java - applet viewer connections by using a URL in your web - browser like this, for example: - - http://hostname:5900 - - The regular, two-port mode, URL http://hostname:5800 - will continue to work as well. - - As mentioned above, this mode will NOT work with - the -ssl, -stunnel, or -enc encryption options. - Note that is it equivalent to '-enc none' (i.e. it - uses the same detection mechanism as for HTTPS, but - with no encryption.) - - HTTPS single-port is on by default in -ssl encrypted - mode (and -enc too), so you only need -http_oneport - when doing non-SSL encrypted connections. - - This mode could also be useful for SSH tunnels since - it means only one port needs to be redirected. - - The -httpsredir option may also be useful for this - mode when using an SSH tunnel as well as for router - port redirections. - - Note that the -env X11VNC_HTTP_LISTEN_LOCALHOST=1 - option described above under -httpsredir applies for - the LibVNCServer httpd server in all cases (ssl or not.) - --ssh user@host:disp Create a remote listening port on machine "host" - via a SSH tunnel using the -R rport:localhost:lport - method. lport will be the local x11vnc listening port, - so a connection to rport (5900+disp) on "host" - will reach x11vnc. E.g. fred@snoopy.com:0 - - This could be useful if a firewall/router prevents - incoming connections to the x11vnc machine, but - the ssh machine "host" can be reached by the VNC - viewer. "user@" is not needed unless the remote unix - username differs from the current one. - - By default the remote sshd is usually configured to - listen only on localhost for rport, so the viewer may - need to ssh -L redir to "host" as well (See SSVNC to - automate this). The sshd setting GatewayPorts enables - listening on all interfaces for rport; viewers can - reach it more easily. - - "disp" is the VNC display for the remote SSH side, - e.g. 0 corresponds to port 5900, etc. If disp is - greater than 200 the value is used as the port. Use a - negative value to force a low port, e.g. host:-80 will - use port 80. - - If ssh-agent is not active, then the ssh password needs - to be entered in the terminal where x11vnc is running. - - By default the remote ssh will issue a 'sleep 300' to - wait for the incoming connection for 5 mins. To modify - this use user@host:disp+secs. - - If the remote SSH server is on a non-standard port - (i.e. not 22) use user@host:port:disp+secs. - - Note that the ssh process MAY NOT be killed when - x11vnc exits. It tries by looking at ps(1) output. - --usepw If no other password method was supplied on the command - line, first look for ~/.vnc/passwd and if found use it - with -rfbauth; next, look for ~/.vnc/passwdfile and - use it with -passwdfile; otherwise, prompt the user - for a password to create ~/.vnc/passwd and use it with - the -rfbauth option. If none of these succeed x11vnc - exits immediately. - --storepasswd pass file Store password "pass" as the VNC password in the - file "file". Once the password is stored the - program exits. Use the password via "-rfbauth file" - - If called with no arguments, "x11vnc -storepasswd", - the user is prompted for a password and it is stored - in the file ~/.vnc/passwd. Called with one argument, - that will be the file to store the prompted password in. - --nopw Disable the big warning message when you use x11vnc - without some sort of password. - --accept string Run a command (possibly to prompt the user at the - X11 display) to decide whether an incoming client - should be allowed to connect or not. "string" is - an external command run via system(3) or some special - cases described below. Be sure to quote "string" - if it contains spaces, shell characters, etc. If the - external command returns 0 the client is accepted, - otherwise the client is rejected. See below for an - extension to accept a client view-only. - - If x11vnc is running as root (say from inetd(8) or from - display managers xdm(1), gdm(1), etc), think about the - security implications carefully before supplying this - option (likewise for the -gone option). - - Environment: The RFB_CLIENT_IP environment variable will - be set to the incoming client IP number and the port - in RFB_CLIENT_PORT (or -1 if unavailable). Similarly, - RFB_SERVER_IP and RFB_SERVER_PORT (the x11vnc side - of the connection), are set to allow identification - of the tcp virtual circuit. The x11vnc process - id will be in RFB_X11VNC_PID, a client id number in - RFB_CLIENT_ID, and the number of other connected clients - in RFB_CLIENT_COUNT. RFB_MODE will be "accept". - RFB_STATE will be PROTOCOL_VERSION, SECURITY_TYPE, - AUTHENTICATION, INITIALISATION, NORMAL, or UNKNOWN - indicating up to which state the client has achieved. - RFB_LOGIN_VIEWONLY will be 0, 1, or -1 (unknown). - RFB_USERNAME, RFB_LOGIN_TIME, and RFB_CURRENT_TIME may - also be set. - - If "string" is "popup" then a builtin popup window - is used. The popup will time out after 120 seconds, - use "popup:N" to modify the timeout to N seconds - (use 0 for no timeout). - - In the case of "popup" and when the -unixpw option - is specified, then a *second* window will be popped - up after the user successfully logs in via his UNIX - password. This time the user will be identified as - UNIX:username@hostname, the "UNIX:" prefix indicates - which user the viewer logged as via -unixpw. The first - popup is only for whether to allow him to even *try* - to login via unix password. - - If "string" is "xmessage" then an xmessage(1) - invocation is used for the command. xmessage must be - installed on the machine for this to work. - - Both "popup" and "xmessage" will present an option - for accepting the client "View-Only" (the client - can only watch). This option will not be presented if - -viewonly has been specified, in which case the entire - display is view only. - - If the user supplied command is prefixed with something - like "yes:0,no:*,view:3 mycommand ..." then this - associates the numerical command return code with - the actions: accept, reject, and accept-view-only, - respectively. Use "*" instead of a number to indicate - the default action (in case the command returns an - unexpected value). E.g. "no:*" is a good choice. - - Note that x11vnc blocks while the external command - or popup is running (other clients may see no updates - during this period). So a person sitting a the physical - display is needed to respond to an popup prompt. (use - a 2nd x11vnc if you lock yourself out). - - More -accept tricks: use "popupmouse" to only allow - mouse clicks in the builtin popup to be recognized. - Similarly use "popupkey" to only recognize - keystroke responses. These are to help avoid the - user accidentally accepting a client by typing or - clicking. All 3 of the popup keywords can be followed - by +N+M to supply a position for the popup window. - The default is to center the popup window. --afteraccept string As -accept, except to run a user supplied command after - a client has been accepted and authenticated. RFB_MODE - will be set to "afteraccept" and the other RFB_* - variables are as in -accept. Unlike -accept, the - command return code is not interpreted by x11vnc. - Example: -afteraccept 'killall xlock &' --gone string As -accept, except to run a user supplied command when - a client goes away (disconnects). RFB_MODE will be - set to "gone" and the other RFB_* variables are as - in -accept. The "popup" actions apply as well. - Unlike -accept, the command return code is not - interpreted by x11vnc. Example: -gone 'xlock &' - --users list If x11vnc is started as root (say from inetd(8) or from - display managers xdm(1), gdm(1), etc), then as soon - as possible after connections to the X display are - established try to switch to one of the users in the - comma separated "list". If x11vnc is not running as - root this option is ignored. - - Why use this option? In general it is not needed since - x11vnc is already connected to the X display and can - perform its primary functions. The option was added - to make some of the *external* utility commands x11vnc - occasionally runs work properly. In particular under - GNOME and KDE to implement the "-solid color" feature - external commands (gconftool-2 and dcop) unfortunately - must be run as the user owning the desktop session. - Since this option switches userid it also affects the - userid used to run the processes for the -accept and - -gone options. It also affects the ability to read - files for options such as -connect, -allow, and -remap - and also the ultra and tight filetransfer feature if - enabled. Note that the -connect file is also sometimes - written to. - - So be careful with this option since in some situations - its use can decrease security. - - In general the switch to a user will only take place - if the display can still be successfully opened as that - user (this is primarily to try to guess the actual owner - of the session). Example: "-users fred,wilma,betty". - Note that a malicious local user "barney" by - quickly using "xhost +" when logging in may possibly - get the x11vnc process to switch to user "fred". - What happens next? - - Under display managers it may be a long time before - the switch succeeds (i.e. a user logs in). To instead - make it switch immediately regardless if the display - can be reopened prefix the username with the "+" - character. E.g. "-users +bob" or "-users +nobody". - - The latter (i.e. switching immediately to user - "nobody") is the only obvious use of the -users option - that increases security. - - Use the following notation to associate a group with - a user: user1.group1,user2.group2,... Note that - initgroups(2) will still be called first to try to - switch to ALL of a user's groups (primary and additional - groups). Only if that fails or it is not available - then the single group specified as above (or the user's - primary group if not specified) is switched to with - setgid(2). Use -env X11VNC_SINGLE_GROUP=1 to prevent - trying initgroups(2) and only switch to the single - group. This sort of setting is only really needed to - make the ultra or tight filetransfer permissions work - properly. This format applies to any comma separated lis -t - of users, even the special "=" modes described below. - - In -unixpw mode, if "-users unixpw=" is supplied - then after a user authenticates himself via the - -unixpw mechanism, x11vnc will try to switch to that - user as though "-users +username" had been supplied. - If you want to limit which users this will be done for, - provide them as a comma separated list after "unixpw=" - Groups can also be specified as described above. - - Similarly, in -ssl mode, if "-users sslpeer=" is - supplied then after an SSL client authenticates with his - cert (the -sslverify option is required for this) x11vnc - will extract a UNIX username from the "emailAddress" - field (username@hostname.com) of the "Subject" of the - x509 SSL cert and then try to switch to that user as - though "-users +username" had been supplied. If you - want to limit which users this will be done for, provide - them as a comma separated list after "sslpeer=". - Set the env. var X11VNC_SSLPEER_CN to use the Common - Name (normally a hostname) instead of the Email field. - - NOTE: for sslpeer= mode the x11vnc administrator must - take care that any client certs he adds to -sslverify - have the intended UNIX username in the "emailAddress" - field of the cert. Otherwise a user may be able to - log in as another. This command can be of use in - checking: "openssl x509 -text -in file.crt", see the - "Subject:" line. Also, along with the normal RFB_* - env. vars. (see -accept) passed to external cmd= - commands, RFB_SSL_CLIENT_CERT will be set to the - client's x509 certificate string. - - The sslpeer= mode can aid finding X sessions via the - FINDDISPLAY and FINDCREATEDISPLAY mechanisms. - - To immediately switch to a user *before* connections - to the X display are made or any files opened use the - "=" character: "-users =bob". That user needs to - be able to open the X display and any files of course. - - The special user "guess=" means to examine the utmpx - database (see who(1)) looking for a user attached to - the display number (from DISPLAY or -display option) - and try him/her. To limit the list of guesses, use: - "-users guess=bob,betty". - - Even more sinister is the special user "lurk=" - that means to try to guess the DISPLAY from the utmpx - login database as well. So it "lurks" waiting for - anyone to log into an X session and then connects to it. - Specify a list of users after the = to limit which users - will be tried. To enable a different searching mode, if - the first user in the list is something like ":0" or - ":0-2" that indicates a range of DISPLAY numbers that - will be tried (regardless of whether they are in the - utmpx database) for all users that are logged in. Also - see the "-display WAIT:..." functionality. Examples: - "-users lurk=" and also "-users lurk=:0-1,bob,mary" - - Be especially careful using the "guess=" and "lurk=" - modes. They are not recommended for use on machines - with untrustworthy local users. - --noshm Do not use the MIT-SHM extension for the polling. - Remote displays can be polled this way: be careful this - can use large amounts of network bandwidth. This is - also of use if the local machine has a limited number - of shm segments and -onetile is not sufficient. --flipbyteorder Sometimes needed if remotely polled host has different - endianness. Ignored unless -noshm is set. --onetile Do not use the new copy_tiles() framebuffer mechanism, - just use 1 shm tile for polling. Limits shm segments - used to 3. - - To disable any automatic shm reduction set the - env. var. X11VNC_NO_LIMIT_SHM. - --solid [color] To improve performance, when VNC clients are connected - try to change the desktop background to a solid color. - The [color] is optional: the default color is "cyan4". - For a different one specify the X color (rgb.txt name, - e.g. "darkblue" or numerical "#RRGGBB"). - - Currently this option only works on GNOME, KDE, CDE, - XFCE, and classic X (i.e. with the background image - on the root window). The "gconftool-2", "dcop" - and "xfconf-query" external commands are run for - GNOME, KDE, and XFCE respectively. This also works - on native MacOSX. (There is no color selection for - MacOSX or XFCE.) Other desktops won't work, (send - us the corresponding commands if you find them). - If x11vnc is running as root (inetd(8) or gdm(1)), - the -users option may be needed for GNOME, KDE, XFCE. - If x11vnc guesses your desktop incorrectly, you can - force it by prefixing color with "gnome:", "kde:", - "cde:", "xfce:", or "root:". - - Update: -solid no longer works on KDE4. - - This mode works in a limited way on the Mac OS X Console - with one color ('kelp') using the screensaver writing - to the background. Look in "~/Library/Screen Savers" - for VncSolidColor.png to change the color. - --blackout string Black out rectangles on the screen. "string" is a - comma separated list of WxH+X+Y type geometries for - each rectangle. If one of the items on the list is the - string "noptr" the mouse pointer will not be allowed - to go into a blacked out region. --xinerama If your screen is composed of multiple monitors --noxinerama glued together via XINERAMA, and that screen is - not a rectangle this option will try to guess the - areas to black out (if your system has libXinerama). - default: -xinerama - - In general, we have noticed on XINERAMA displays you may - need to use the "-xwarppointer" option if the mouse - pointer misbehaves and it is enabled by default. Use - "-noxwarppointer" if you do not want this. - --xtrap Use the DEC-XTRAP extension for keystroke and mouse - input insertion. For use on legacy systems, e.g. X11R5, - running an incomplete or missing XTEST extension. - By default DEC-XTRAP will be used if XTEST server grab - control is missing, use -xtrap to do the keystroke and - mouse insertion via DEC-XTRAP as well. - --xrandr [mode] If the display supports the XRANDR (X Resize, Rotate - and Reflection) extension, and you expect XRANDR events - to occur to the display while x11vnc is running, this - options indicates x11vnc should try to respond to - them (as opposed to simply crashing by assuming the - old screen size). See the xrandr(1) manpage and run - 'xrandr -q' for more info. [mode] is optional and - described below. - - Since watching for XRANDR events and trapping errors - increases polling overhead, only use this option if - XRANDR changes are expected. For example on a rotatable - screen PDA or laptop, or using a XRANDR-aware Desktop - where you resize often. It is best to be viewing with a - vncviewer that supports the NewFBSize encoding, since it - knows how to react to screen size changes. Otherwise, - LibVNCServer tries to do so something reasonable for - viewers that cannot do this (portions of the screen - may be clipped, unused, etc). - - Note: the default now is to check for XRANDR events, but - do not trap every X call that may fail due to resize. - If a resize event is received, the full -xrandr mode - is enabled. To disable even checking for events supply: - -noxrandr. - - "mode" defaults to "resize", which means create a - new, resized, framebuffer and hope all viewers can cope - with the change. "newfbsize" means first disconnect - all viewers that do not support the NewFBSize VNC - encoding, and then resize the framebuffer. "exit" - means disconnect all viewer clients, and then terminate - x11vnc. - --rotate string Rotate and/or flip the framebuffer view exported by VNC. - This transformation is independent of XRANDR and is - done in software in main memory and so may be slower. - This mode could be useful on a handheld with portrait or - landscape modes that do not correspond to the scanline - order of the actual framebuffer. "string" can be: - - x flip along x-axis - y flip along y-axis - xy flip along x- and y-axes - +90 rotate 90 degrees clockwise - -90 rotate 90 degrees counter-clockwise - +90x rotate 90 degrees CW, then flip along x - +90y rotate 90 degrees CW, then flip along y - - these give all possible rotations and reflections. - - Aliases: same as xy: yx, +180, -180, 180 - same as -90: +270, 270 - same as +90: 90, (ditto for 90x, 90y) - - Like -scale, this transformation is applied at the very - end of any chain of framebuffer transformations and so - any options with geometries, e.g. -blackout, -clip, etc. - are relative to the original X (or -rawfb) framebuffer, - not the final one sent to VNC viewers. - - If you do not want the cursor shape to be rotated - prefix "string" with "nc:", e.g. "nc:+90", - "nc:xy", etc. - --padgeom WxH Whenever a new vncviewer connects, the framebuffer is - replaced with a fake, solid black one of geometry WxH. - Shortly afterwards the framebuffer is replaced with the - real one. This is intended for use with vncviewers - that do not support NewFBSize and one wants to make - sure the initial viewer geometry will be big enough - to handle all subsequent resizes (e.g. under -xrandr, - -remote id:windowid, rescaling, etc.) - - In -unixpw mode this sets the size of the login screen. - Use "once:WxH" it ignore padgeom after the login - screen is set up. - --o logfile Write stderr messages to file "logfile" instead of to - the terminal. Same as "-logfile file". To append - to the file use "-oa file" or "-logappend file". - If "logfile" contains the string "%VNCDISPLAY" - it is expanded to the vnc display (the name may need - to be guessed at.) "%HOME" works too. - --flag file Write the "PORT=NNNN" (e.g. PORT=5900) string to - "file" in addition to stdout. This option could be - useful by wrapper script to detect when x11vnc is ready. - --rmflag file Remove "file" at exit to signal when x11vnc is done. - The file is created at startup if it does not already - exist or if "file" is prefixed with "create:". - If the file is created, the x11vnc PID is placed in - the file. Otherwise the files contents is not changed. - Use prefix "nocreate:" to prevent creation. - --rc filename Use "filename" instead of $HOME/.x11vncrc for rc file. --norc Do not process any .x11vncrc file for options. - --env VAR=VALUE Set the environment variable 'VAR' to value 'VALUE' - at x11vnc startup. This is a convenience utility to - avoid shell script wrappers, etc. to set the env. var. - You may specify as many of these as needed on the - command line. --prog /path/to/x11vnc Set the full path to the x11vnc program for cases when - it cannot be determined from argv[0] (e.g. tcpd/inetd) - --h, -help Print this help text. --?, -opts Only list the x11vnc options. --V, -version Print program version and last modification date. --license Print out license information. Same as -copying and - -warranty. - --dbg Instead of exiting after cleaning up, run a simple - "debug crash shell" when fatal errors are trapped. - --q, -quiet Be quiet by printing less informational output to - stderr. (use -noquiet to undo an earlier -quiet.) - - The -quiet option does not eliminate all informational - output, it only reduces it. It is ignored in most - auxiliary usage modes, e.g. -storepasswd. To eliminate - all output use: 2>/dev/null 1>&2, etc. - --v, -verbose Print out more information to stderr. - --bg Go into the background after screen setup. Messages to - stderr are lost unless -o logfile is used. Something - like this could be useful in a script: - port=`ssh -t $host "x11vnc -display :0 -bg" | grep PORT -` - port=`echo "$port" | sed -e 's/PORT=//'` - port=`expr $port - 5900` - vncviewer $host:$port - --modtweak Option -modtweak automatically tries to adjust the AltGr --nomodtweak and Shift modifiers for differing language keyboards - between client and host. Otherwise, only a single key - press/release of a Keycode is simulated (i.e. ignoring - the state of the modifiers: this usually works for - identical keyboards). Also useful in resolving cases - where a Keysym is bound to multiple keys (e.g. "<" + ">" - and "," + "<" keys). Default: -modtweak - - If you are having trouble with with keys and -xkb or - -noxkb, and similar things don't help, try -nomodtweak. - - On some HP-UX systems it is been noted that they have - an odd keymapping where a single keycode will have a - keysym, e.g. "#", up to three times. You can check - via "xmodmap -pk" or the -dk option. The failure - is when you try to type "#" it yields "3". If you - see this problem try setting the environment variable - MODTWEAK_LOWEST=1 to see if it helps. - --xkb When in modtweak mode, use the XKEYBOARD extension (if --noxkb the X display supports it) to do the modifier tweaking. - This is powerful and should be tried if there are still - keymapping problems when using -modtweak by itself. - The default is to check whether some common keysyms, - e.g. !, @, [, are only accessible via -xkb mode and if - so then automatically enable the mode. To disable this - automatic detection use -noxkb. - - When -xkb mode is active you can set these env. vars. - They apply only when there is ambiguity as to which - key to choose (i.e the mapping is not one-to-one). - NOKEYHINTS=1: for up ascii keystrokes do not use score - hints saved when the key was pressed down. NOANYDOWN=1: - for up keystrokes do not resort to searching through - keys that are currently pressed down. KEYSDOWN=N: - remember the last N keys press down for tie-breaking - when an up keystroke comes in. - --capslock When in -modtweak (the default) or -xkb mode, - if a keysym in the range A-Z comes in check the X - server to see if the Caps_Lock is set. If it is do - not artificially press Shift to generate the keysym. - This will enable the CapsLock key to behave correctly - in some circumstances: namely *both* the VNC viewer - machine and the x11vnc X server are in the CapsLock - on state. If one side has CapsLock on and the other - off and the keyboard is not behaving as you think it - should you should correct the CapsLock states (hint: - pressing CapsLock inside and outside of the viewer can - help toggle them both to the correct state). However, - for best results do not use this option, but rather - *only* enable CapsLock on the VNC viewer side (i.e. by - pressing CapsLock outside of the viewer window, also - -skip_lockkeys below). Also try -nomodtweak for a - possible workaround. - --skip_lockkeys Have x11vnc ignore all Caps_Lock, Shift_Lock, Num_Lock, --noskip_lockkeys Scroll_Lock keysyms received from viewers. The idea is - you press Caps_Lock on the VNC Viewer side but that does - not change the lock state in the x11vnc-side X server. - Nevertheless your capitalized letters come in over - the wire and are applied correctly to the x11vnc-side - X server. Note this mode probably won't do what you - want in -nomodtweak mode. Also, a kludge for KP_n - digits is always done in this mode: they are mapped to - regular digit keysyms. See also -capslock above. - The default is -noskip_lockkeys. - --skip_keycodes string Ignore the comma separated list of decimal keycodes. - Perhaps these are keycodes not on your keyboard but - your X server thinks exist. Currently only applies - to -xkb mode. Use this option to help x11vnc in the - reverse problem it tries to solve: Keysym -> Keycode(s) - when ambiguities exist (more than one Keycode per - Keysym). Run 'xmodmap -pk' to see your keymapping. - Example: "-skip_keycodes 94,114" --sloppy_keys Experimental option that tries to correct some - "sloppy" key behavior. E.g. if at the viewer you - press Shift+Key but then release the Shift before - Key that could give rise to extra unwanted characters - (usually only between keyboards of different languages). - Only use this option if you observe problems with - some keystrokes. --skip_dups Some VNC viewers send impossible repeated key events, --noskip_dups e.g. key-down, key-down, key-up, key-up all for the same - key, or 20 downs in a row for the same modifier key! - Setting -skip_dups means to skip these duplicates and - just process the first event. Note: some VNC viewers - assume they can send down's without the corresponding - up's and so you should not set this option for - these viewers (symptom: some keys do not autorepeat) - Default: -noskip_dups --add_keysyms If a Keysym is received from a VNC viewer and that --noadd_keysyms Keysym does not exist in the X server, then add the - Keysym to the X server's keyboard mapping on an unused - key. Added Keysyms will be removed periodically and - also when x11vnc exits. Default: -add_keysyms --clear_mods At startup and exit clear the modifier keys by sending - KeyRelease for each one. The Lock modifiers are skipped. - Used to clear the state if the display was accidentally - left with any pressed down. --clear_keys As -clear_mods, except try to release ANY pressed key. - Note that this option and -clear_mods can interfere - with a person typing at the physical keyboard. --clear_all As -clear_keys, except try to release any CapsLock, - NumLock, etc. locks as well. - --remap string Read Keysym remappings from file named "string". - Format is one pair of Keysyms per line (can be name - or hex value) separated by a space. If no file named - "string" exists, it is instead interpreted as this - form: key1-key2,key3-key4,... See - header file for a list of Keysym names, or use xev(1). - - To map a key to a button click, use the fake Keysyms - "Button1", ..., etc. E.g: "-remap Super_R-Button2" - (useful for pasting on a laptop) - - I use these if the machine I am viewing from does not - have a scrollwheel or I don't like using the one it has: - - -remap Super_R-Button4,Menu-Button5 - -remap KP_Add-Button4,KP_Enter-Button5 - - the former would be used on a PC, the latter on a - MacBook. This way those little used keys can be used - to generate bigger hops than the Up and Down arrows - provide. One can scroll through text or web pages more - quickly this way (especially if x11vnc scroll detection - is active.) - - Use Button44, Button12, etc. for multiple clicks. - - To disable a keysym (i.e. make it so it will not be - injected), remap it to "NoSymbol" or "None". - - Dead keys: "dead" (or silent, mute) keys are keys that - do not produce a character but must be followed by a 2nd - keystroke. This is often used for accenting characters, - e.g. to put "`" on top of "a" by pressing the dead - key and then "a". Note that this interpretation - is not part of core X11, it is up to the toolkit or - application to decide how to react to the sequence. - The X11 names for these keysyms are "dead_grave", - "dead_acute", etc. However some VNC viewers send the - keysyms "grave", "acute" instead thereby disabling - the accenting. To work around this -remap can be used. - For example "-remap grave-dead_grave,acute-dead_acute" - As a convenience, "-remap DEAD" applies these remaps: - - g grave-dead_grave - a acute-dead_acute - c asciicircum-dead_circumflex - t asciitilde-dead_tilde - m macron-dead_macron - b breve-dead_breve - D abovedot-dead_abovedot - d diaeresis-dead_diaeresis - o degree-dead_abovering - A doubleacute-dead_doubleacute - r caron-dead_caron - e cedilla-dead_cedilla - - If you just want a subset use the first letter - label, e.g. "-remap DEAD=ga" to get the first two. - Additional remaps may also be supplied via commas, - e.g. "-remap DEAD=ga,Super_R-Button2". Finally, - "DEAD=missing" means to apply all of the above as - long as the left hand member is not already in the - X11 keymap. - --norepeat Option -norepeat disables X server key auto repeat when --repeat VNC clients are connected and VNC keyboard input is - not idle for more than 5 minutes. This works around a - repeating keystrokes bug (triggered by long processing - delays between key down and key up client events: - either from large screen changes or high latency). - Default: -norepeat - - You can set the env. var. X11VNC_IDLE_TIMEOUT to the - number of idle seconds you want (5min = 300secs). - - Note: your VNC viewer side will likely do autorepeating, - so this is no loss unless someone is simultaneously at - the real X display. - - Use "-norepeat N" to set how many times norepeat will - be reset if something else (e.g. X session manager) - undoes it. The default is 2. Use a negative value - for unlimited resets. - --nofb Ignore video framebuffer: only process keyboard and - pointer. Intended for use with Win2VNC and x2vnc - dual-monitor setups. --nobell Do not watch for XBell events. (no beeps will be heard) - Note: XBell monitoring requires the XKEYBOARD extension. --nosel Do not manage exchange of X selection/cutbuffer between - VNC viewers and the X server at all. --noprimary Do not poll the PRIMARY selection for changes to send - back to clients. (PRIMARY is still set on received - changes, however). --nosetprimary Do not set the PRIMARY selection for changes received - from VNC clients. --noclipboard Do not poll the CLIPBOARD selection for changes to send - back to clients. (CLIPBOARD is still set on received - changes, however). --nosetclipboard Do not set the CLIPBOARD selection for changes - received from VNC clients. --seldir string If direction string is "send", only send the selection - to viewers, and if it is "recv" only receive it from - viewers. To work around apps setting the selection - too frequently and messing up the other end. You can - actually supply a comma separated list of directions, - including "debug" to turn on debugging output. - --cursor [mode] Sets how the pointer cursor shape (little icon at the --nocursor mouse pointer) should be handled. The "mode" string - is optional and is described below. The default - is to show some sort of cursor shape(s). How this - is done depends on the VNC viewer and the X server. - Use -nocursor to disable cursor shapes completely. - - Some VNC viewers support the TightVNC CursorPosUpdates - and CursorShapeUpdates extensions (cuts down on - network traffic by not having to send the cursor image - every time the pointer is moved), in which case these - extensions are used (see -nocursorshape and -nocursorpos - below to disable). For other viewers the cursor shape - is written directly to the framebuffer every time the - pointer is moved or changed and gets sent along with - the other framebuffer updates. In this case, there - will be some lag between the vnc viewer pointer and - the remote cursor position. - - If the X display supports retrieving the cursor shape - information from the X server, then the default is - to use that mode. On Solaris this can be done with - the SUN_OVL extension using -overlay (see also the - -overlay_nocursor option). A similar overlay scheme - is used on IRIX. Xorg (e.g. Linux) and recent Solaris - Xsun servers support the XFIXES extension to retrieve - the exact cursor shape from the X server. If XFIXES - is present it is preferred over Overlay and is used by - default (see -noxfixes below). This can be disabled - with -nocursor, and also some values of the "mode" - option below. - - Note that under XFIXES cursors with transparency (alpha - channel) will usually not be exactly represented and one - may find Overlay preferable. See also the -alphacut - and -alphafrac options below as fudge factors to try - to improve the situation for cursors with transparency - for a given theme. - - The "mode" string can be used to fine-tune the - displaying of cursor shapes. It can be used the - following ways: - - "-cursor arrow" - just show the standard arrow - nothing more or nothing less. - - "-cursor none" - same as "-nocursor" - - "-cursor X" - when the cursor appears to be on the - root window, draw the familiar X shape. Some desktops - such as GNOME cover up the root window completely, - and so this will not work, try "X1", etc, to try to - shift the tree depth. On high latency links or slow - machines there will be a time lag between expected and - the actual cursor shape. - - "-cursor some" - like "X" but use additional - heuristics to try to guess if the window should have - a windowmanager-like resizer cursor or a text input - I-beam cursor. This is a complete hack, but may be - useful in some situations because it provides a little - more feedback about the cursor shape. - - "-cursor most" - try to show as many cursors as - possible. Often this will only be the same as "some" - unless the display has overlay visuals or XFIXES - extensions available. On Solaris and IRIX if XFIXES - is not available, -overlay mode will be attempted. - --cursor_drag Show cursor shape changes even when the mouse is being - dragged with a mouse button down. This is useful if you - want to be able to see Drag-and-Drop cursor icons, etc. - --arrow n Choose an alternate "arrow" cursor from a set of - some common ones. n can be 1 to 6. Default is: 1 - Ignored when in XFIXES cursor-grabbing mode. - --noxfixes Do not use the XFIXES extension to draw the exact cursor - shape even if it is available. - - Note: To work around a crash in Xorg 1.5 and later - some people needed to use -noxfixes. The Xorg crash - occurred right after a Display Manager (e.g. GDM) login. - Starting with x11vnc 0.9.9 it tries to automatically - avoid using XFIXES until it is sure a window manager - is running. See the -reopen option for more info and - how to use X11VNC_AVOID_WINDOWS=never to disable it. - --alphacut n When using the XFIXES extension for the cursor shape, - cursors with transparency will not usually be displayed - exactly (but opaque ones will). This option sets n as - a cutoff for cursors that have transparency ("alpha - channel" with values ranging from 0 to 255) Any cursor - pixel with alpha value less than n becomes completely - transparent. Otherwise the pixel is completely opaque. - Default 240 - --alphafrac fraction With the threshold in -alphacut some cursors will become - almost completely transparent because their alpha values - are not high enough. For those cursors adjust the - alpha threshold until fraction of the non-zero alpha - channel pixels become opaque. Default 0.33 --alpharemove By default, XFIXES cursors pixels with transparency have - the alpha factor multiplied into the RGB color values - (i.e. that corresponding to blending the cursor with a - black background). Specify this option to remove the - alpha factor. (useful for light colored semi-transparent - cursors). --noalphablend In XFIXES mode do not send cursor alpha channel data - to LibVNCServer. The default is to send it. The - alphablend effect will only be visible in -nocursorshape - mode or for clients with cursorshapeupdates turned - off. (However there is a hack for 32bpp with depth 24, - it uses the extra 8 bits to store cursor transparency - for use with a hacked vncviewer that applies the - transparency locally. See the FAQ for more info). - --nocursorshape Do not use the TightVNC CursorShapeUpdates extension - even if clients support it. See -cursor above. --cursorpos Option -cursorpos enables sending the X cursor position --nocursorpos back to all vnc clients that support the TightVNC - CursorPosUpdates extension. Other clients will be able - to see the pointer motions. Default: -cursorpos --xwarppointer Move the pointer with XWarpPointer(3X) instead of --noxwarppointer the XTEST extension. Use this as a workaround - if the pointer motion behaves incorrectly, e.g. - on touchscreens or other non-standard setups. - - It is also sometimes needed on XINERAMA displays and is - enabled by default if XINERAMA is found to be active. - To prevent this, use -noxwarppointer. - --always_inject Even if there is no displacement (dx = dy = 0) for a - VNC mouse event force the pointer to the indicated x,y - position anyway. Recent (2009) gui toolkits (gnome) - have problems with x11vnc's original mouse input - injection method. So x11vnc's mouse input injection - method has been modified. To regain the OLD behavior - use this option: -always_inject. Then x11vnc will - always force positioning the mouse to the x,y position - even if that position has not changed since the previous - VNC input event. - - The first place this problem was noticed was in gnome - terminal: if you pressed and released mouse button 3, a - menu was posted and then its first element 'New Terminal - Window' was activated. This was because x11vnc injected - the mouse position twice: once on ButtonPress and again - on ButtonRelease. The toolkit interpreted the 2nd one - as mouse motion even though the mouse hadn't moved. - So now by default x11vnc tries to avoid injecting the - 2nd one. - - Note that with the new default x11vnc will be oblivious - to applications moving the pointer (warping) or the - user at the physical display moving it. So it might, - e.g., inject ButtonRelease at the wrong position. - If this (or similar scenarios) causes problems in your - environment, specify -always_inject for the old method. - --buttonmap string String to remap mouse buttons. Format: IJK-LMN, this - maps buttons I -> L, etc., e.g. -buttonmap 13-31 - - Button presses can also be mapped to keystrokes: replace - a button digit on the right of the dash with :: - or :+: etc. for multiple keys. For example, - if the viewing machine has a mouse-wheel (buttons 4 5) - but the x11vnc side does not, these will do scrolls: - -buttonmap 12345-123:Prior::Next: - -buttonmap 12345-123:Up+Up+Up::Down+Down+Down: - - See header file for a list of Keysyms, - or use the xev(1) program. Note: mapping of button - clicks to Keysyms may not work if -modtweak or -xkb is - needed for the Keysym. - - If you include a modifier like "Shift_L" the - modifier's up/down state is toggled, e.g. to send - "The" use :Shift_L+t+Shift_L+h+e: (the 1st one is - shift down and the 2nd one is shift up). (note: the - initial state of the modifier is ignored and not reset) - To include button events use "Button1", ... etc. - - -buttonmap currently does not work on MacOSX console - or in -rawfb mode. - - Workaround: use -buttonmap IJ...-LM...=n to limit the - number of mouse buttons to n, e.g. 123-123=3. This will - prevent x11vnc from crashing if the X server reports - there are 5 buttons (4/5 scroll wheel), but there are - only really 3. - --nodragging Do not update the display during mouse dragging events - (mouse button held down). Greatly improves response on - slow setups, but you lose all visual feedback for drags, - text selection, and some menu traversals. It overrides - any -pointer_mode setting. - --ncache n Client-side caching scheme. Framebuffer memory "n" - (an integer) times that of the full display is allocated - below the actual framebuffer to cache screen contents - for rapid retrieval. So a W x H frambuffer is expanded - to a W x (n+1)*H one. Use 0 to disable. - - The "n" is actually optional, the default is 10. - - For this and the other -ncache* options below you can - abbreviate "-ncache" with "-nc". Also, "-nonc" - is the same as "-ncache 0" - - This is an experimental option, currently implemented in - an awkward way in that in the VNC Viewer you can see the - pixel cache contents if you scroll down, etc. So you - will have to set things up so you can't see that region. - If this method is successful, the changes required for - clients to do this less awkwardly will be investigated. - - The SSVNC viewer does a good job at automatically hiding - the pixel cache region. Or use SSVNC's -ycrop option - to explicitly hide the region. - - Note that this mode consumes a huge amount of memory, - both on the x11vnc server side and on the VNC Viewer - side. If n=2 then the amount of RAM used is roughly - tripled for both x11vnc and the VNC Viewer. As a rule - of thumb, note that 1280x1024 at depth 24 is about 5MB - of pixel data. - - For reasonable response when cycling through 4 to 6 - large (e.g. web browser) windows a value n of 6 to 12 - is recommended. (that's right: ~10X more memory...) - - Because of the way window backingstore and saveunders - are implemented, n must be even. It will be incremented - by 1 if it is not. - - This mode also works for native MacOS X, but may not - be as effective as the X version. This is due to a - number of things, one is the drop-shadow compositing - that leaves extra areas that need to be repaired (see - -ncache_pad). Another is the window iconification - animations need to be avoided (see -macicontime). - It appears the that the 'Scale' animation mode gives - better results than the 'Genie' one. Also, window event - detection not as accurate as the X version. - --ncache_cr In -ncache mode, try to do copyrect opaque window - moves/drags instead of wireframes (this can induce - painting errors). The wireframe will still be used when - moving a window whose save-unders has not yet been set - or has been invalidated. - - Some VNC Viewers provide better response than others - with this option. On Unix, realvnc viewer gives - smoother drags than tightvnc viewer. Response may also - be choppy if the server side machine is too slow. - - Sometimes on very slow modem connections, this actually - gives an improvement because no pixel data at all - (not even the box animation) is sent during the drag. - --ncache_no_moveraise In -ncache mode, do not assume that moving a window - will cause the window manager to raise it to the top - of the stack. The default is to assume it does, and - so at the beginning of any wireframe, etc, window moves - the window will be pushed to top in the VNC viewer. - --ncache_no_dtchange In -ncache mode, do not try to guess when the desktop - (viewport) changes to another one (i.e. another - workarea). The default is to try to guess and when - detected try to make the transistion more smoothly. - --ncache_no_rootpixmap In -ncache mode, do not try to snapshot the desktop - background to use in guessing or reconstructing window - save-unders. - --ncache_keep_anims In -ncache mode, do not try to disable window - manager animations and other effects (that usually - degrade ncache performance or cause painting errors). - The default is to try to disable them on KDE (but not - GNOME) when VNC clients are connected. - - For other window managers or desktops that provide - animations, effects, compositing, translucency, - etc. that interfere with the -ncache method you will - have to disable them manually. - --ncache_old_wm In -ncache mode, enable some heuristics for old style - window managers such as fvwm and twm. - --ncache_pad n In -ncache mode, pad each window with n pixels for the - caching rectangles. This can be used to try to improve - the situation with dropshadows or other compositing - (e.g. MacOS X window manager), although it could make - things worse. The default is 0 on Unix and 24 on - MacOS X. --debug_ncache Turn on debugging and profiling output under -ncache. - --wireframe [str] Try to detect window moves or resizes when a mouse --nowireframe button is held down and show a wireframe instead of - the full opaque window. This is based completely on - heuristics and may not always work: it depends on your - window manager and even how you move things around. - See -pointer_mode below for discussion of the "bogging - down" problem this tries to avoid. - Default: -wireframe - - Shorter aliases: -wf [str] and -nowf - - The value "str" is optional and, of course, is - packed with many tunable parameters for this scheme: - - Format: shade,linewidth,percent,T+B+L+R,mod,t1+t2+t3+t4 - Default: 0xff,2,0,32+8+8+8,all,0.15+0.30+5.0+0.125 - - If you leave nothing between commas: ",," the default - value is used. If you don't specify enough commas, - the trailing parameters are set to their defaults. - - "shade" indicate the "color" for the wireframe, - usually a greyscale: 0-255, however for 16 and 32bpp you - can specify an rgb.txt X color (e.g. "dodgerblue") or - a value > 255 is treated as RGB (e.g. red is 0xff0000). - "linewidth" sets the width of the wireframe in pixels. - "percent" indicates to not apply the wireframe scheme - to windows with area less than this percent of the - full screen. - - "T+B+L+R" indicates four integers for how close in - pixels the pointer has to be from the Top, Bottom, Left, - or Right edges of the window to consider wireframing. - This is a speedup to quickly exclude a window from being - wireframed: set them all to zero to not try the speedup - (scrolling and selecting text will likely be slower). - - "mod" specifies if a button down event in the - interior of the window with a modifier key (Alt, Shift, - etc.) down should indicate a wireframe opportunity. - It can be "0" or "none" to skip it, "1" or "all" - to apply it to any modifier, or "Shift", "Alt", - "Control", "Meta", "Super", or "Hyper" to only - apply for that type of modifier key. - - "t1+t2+t3+t4" specify four floating point times in - seconds: t1 is how long to wait for the pointer to move, - t2 is how long to wait for the window to start moving - or being resized (for some window managers this can be - rather long), t3 is how long to keep a wireframe moving - before repainting the window. t4 is the minimum time - between sending wireframe "animations". If a slow - link is detected, these values may be automatically - changed to something better for a slow link. - --nowireframelocal By default, mouse motion and button presses of a - user sitting at the LOCAL display are monitored for - wireframing opportunities (so that the changes will be - sent efficiently to the VNC clients). Use this option - to disable this behavior. - --wirecopyrect mode Since the -wireframe mechanism evidently tracks moving --nowirecopyrect windows accurately, a speedup can be obtained by - telling the VNC viewers to locally copy the translated - window region. This is the VNC CopyRect encoding: - the framebuffer update doesn't need to send the actual - new image data. - - Shorter aliases: -wcr [mode] and -nowcr - - "mode" can be "never" (same as -nowirecopyrect) - to never try the copyrect, "top" means only do it if - the window was not covered by any other windows, and - "always" means to translate the orginally unobscured - region (this may look odd as the remaining pieces come - in, but helps on a slow link). Default: "always" - - Note: there can be painting errors or slow response - when using -scale so you may want to disable CopyRect - in this case "-wirecopyrect never" on the command - line or by remote-control. Or you can also use the - "-scale xxx:nocr" scale option. - --debug_wireframe Turn on debugging info printout for the wireframe - heuristics. "-dwf" is an alias. Specify multiple - times for more output. - --scrollcopyrect mode Like -wirecopyrect, but use heuristics to try to guess --noscrollcopyrect if a window has scrolled its contents (either vertically - or horizontally). This requires the RECORD X extension - to "snoop" on X applications (currently for certain - XCopyArea and XConfigureWindow X protocol requests). - Examples: Hitting in a terminal window when the - cursor was at the bottom, the text scrolls up one line. - Hitting arrow in a web browser window, the web - page scrolls up a small amount. Or scrolling with a - scrollbar or mouse wheel. - - Shorter aliases: -scr [mode] and -noscr - - This scheme will not always detect scrolls, but when - it does there is a nice speedup from using the VNC - CopyRect encoding (see -wirecopyrect). The speedup - is both in reduced network traffic and reduced X - framebuffer polling/copying. On the other hand, it may - induce undesired transients (e.g. a terminal cursor - being scrolled up when it should not be) or other - painting errors (window tearing, bunching-up, etc). - These are automatically repaired in a short period - of time. If this is unacceptable disable the feature - with -noscrollcopyrect. - - Screen clearing kludges: for testing at least, there - are some "magic key sequences" (must be done in less - than 1 second) to aid repairing painting errors that - may be seen when using this mode: - - 3 Alt_L's in a row: resend whole screen, - 4 Alt_L's in a row: reread and resend whole screen, - 3 Super_L's in a row: mark whole screen for polling, - 4 Super_L's in a row: reset RECORD context, - 5 Super_L's in a row: try to push a black screen - - note: Alt_L is the Left "Alt" key (a single key) - Super_L is the Left "Super" key (Windows flag). - Both of these are modifier keys, and so should not - generate characters when pressed by themselves. Also, - your VNC viewer may have its own refresh hot-key - or button. - - "mode" can be "never" (same as -noscrollcopyrect) - to never try the copyrect, "keys" means to try it - in response to keystrokes only, "mouse" means to - try it in response to mouse events only, "always" - means to do both. Default: "always" - - Note: there can be painting errors or slow response - when using -scale so you may want to disable CopyRect - in this case "-scrollcopyrect never" on the command - line or by remote-control. Or you can also use the - "-scale xxx:nocr" scale option. - --scr_area n Set the minimum area in pixels for a rectangle - to be considered for the -scrollcopyrect detection - scheme. This is to avoid wasting the effort on small - rectangles that would be quickly updated the normal way. - E.g. suppose an app updated the position of its skinny - scrollbar first and then shifted the large panel - it controlled. We want to be sure to skip the small - scrollbar and get the large panel. Default: 60000 - --scr_skip list Skip scroll detection for applications matching - the comma separated list of strings in "list". - Some applications implement their scrolling in - strange ways where the XCopyArea, etc, also applies - to invisible portions of the window: if we CopyRect - those areas it looks awful during the scroll and - there may be painting errors left after the scroll. - Soffice.bin is the worst known offender. - - Use "##" to denote the start of the application class - (e.g. "##XTerm") and "++" to denote the start - of the application instance name (e.g. "++xterm"). - The string your list is matched against is of the form - "^^WM_NAME##Class++Instance" - The "xlsclients -la" command will provide this info. - - If a pattern is prefixed with "KEY:" it only applies - to Keystroke generated scrolls (e.g. Up arrow). If it - is prefixed with "MOUSE:" it only applies to Mouse - induced scrolls (e.g. dragging on a scrollbar). - Default: ##Soffice.bin,##StarOffice,##OpenOffice - --scr_inc list Opposite of -scr_skip: this list is consulted first - and if there is a match the window will be monitored - via RECORD for scrolls irrespective of -scr_skip. - Use -scr_skip '*' to skip anything that does not match - your -scr_inc. Use -scr_inc '*' to include everything. - --scr_keys list For keystroke scroll detection, only apply the RECORD - heuristics to the comma separated list of keysyms in - "list". You may find the RECORD overhead for every - one of your keystrokes disrupts typing too much, but you - don't want to turn it off completely with "-scr mouse" - and -scr_parms does not work or is too confusing. - - The listed keysyms can be numeric or the keysym - names in the header file or from the - xev(1) program. Example: "-scr_keys Up,Down,Return". - One probably wants to have application specific lists - (e.g. for terminals, etc) but that is too icky to think - about for now... - - If "list" begins with the "-" character the list - is taken as an exclude list: all keysyms except those - list will be considered. The special string "builtin" - expands to an internal list of keysyms that are likely - to cause scrolls. BTW, by default modifier keys, - Shift_L, Control_R, etc, are skipped since they almost - never induce scrolling by themselves. - --scr_term list Yet another cosmetic kludge. Apply shell/terminal - heuristics to applications matching comma separated - list (same as for -scr_skip/-scr_inc). For example an - annoying transient under scroll detection is if you - hit Enter in a terminal shell with full text window, - the solid text cursor block will be scrolled up. - So for a short time there are two (or more) block - cursors on the screen. There are similar scenarios, - (e.g. an output line is duplicated). - - These transients are induced by the approximation of - scroll detection (e.g. it detects the scroll, but not - the fact that the block cursor was cleared just before - the scroll). In nearly all cases these transient errors - are repaired when the true X framebuffer is consulted - by the normal polling. But they are distracting, so - what this option provides is extra "padding" near the - bottom of the terminal window: a few extra lines near - the bottom will not be scrolled, but rather updated - from the actual X framebuffer. This usually reduces - the annoying artifacts. Use "none" to disable. - Default: "term" - --scr_keyrepeat lo-hi If a key is held down (or otherwise repeats rapidly) and - this induces a rapid sequence of scrolls (e.g. holding - down an Arrow key) the "scrollcopyrect" detection - and overhead may not be able to keep up. A time per - single scroll estimate is performed and if that estimate - predicts a sustainable scrollrate of keys per second - between "lo" and "hi" then repeated keys will be - DISCARDED to maintain the scrollrate. For example your - key autorepeat may be 25 keys/sec, but for a large - window or slow link only 8 scrolls per second can be - sustained, then roughly 2 out of every 3 repeated keys - will be discarded during this period. Default: "4-20" - --scr_parms string Set various parameters for the scrollcopyrect mode. - The format is similar to that for -wireframe and packed - with lots of parameters: - - Format: T+B+L+R,t1+t2+t3,s1+s2+s3+s4+s5 - Default: 0+64+32+32,0.02+0.10+0.9,0.03+0.06+0.5+0.1+5.0 - - If you leave nothing between commas: ",," the default - value is used. If you don't specify enough commas, - the trailing parameters are set to their defaults. - - "T+B+L+R" indicates four integers for how close in - pixels the pointer has to be from the Top, Bottom, Left, - or Right edges of the window to consider scrollcopyrect. - If -wireframe overlaps it takes precedence. This is a - speedup to quickly exclude a window from being watched - for scrollcopyrect: set them all to zero to not try - the speedup (things like selecting text will likely - be slower). - - "t1+t2+t3" specify three floating point times in - seconds that apply to scrollcopyrect detection with - *Keystroke* input: t1 is how long to wait after a key - is pressed for the first scroll, t2 is how long to keep - looking after a Keystroke scroll for more scrolls. - t3 is how frequently to try to update surrounding - scrollbars outside of the scrolling area (0.0 to - disable) - - "s1+s2+s3+s4+s5" specify five floating point times - in seconds that apply to scrollcopyrect detection with - *Mouse* input: s1 is how long to wait after a mouse - button is pressed for the first scroll, s2 is how long - to keep waiting for additional scrolls after the first - Mouse scroll was detected. s3 is how frequently to - try to update surrounding scrollbars outside of the - scrolling area (0.0 to disable). s4 is how long to - buffer pointer motion (to try to get fewer, bigger - mouse scrolls). s5 is the maximum time to spend just - updating the scroll window without updating the rest - of the screen. - --fixscreen string Periodically "repair" the screen based on settings - in "string". Hopefully you won't need this option, - it is intended for cases when the -scrollcopyrect or - -wirecopyrect features leave too many painting errors, - but it can be used for any scenario. This option - periodically performs costly operations and so - interactive response may be reduced when it is on. - You can use 3 Alt_L's (the Left "Alt" key) taps in - a row (as described under -scrollcopyrect) instead to - manually request a screen repaint when it is needed. - - "string" is a comma separated list of one or more of - the following: "V=t", "C=t", "X=t", and "8=t". - In these "t" stands for a time in seconds (it is - a floating point even though one should usually use - values > 2 to avoid wasting resources). V sets how - frequently the entire screen should be sent to viewers - (it is like the 3 Alt_L's). C sets how long to wait - after a CopyRect to repaint the full screen. X sets - how frequently to reread the full X11 framebuffer from - the X server and push it out to connected viewers. - Use of X should be rare, please report a bug if you - find you need it. 8= applies only for -8to24 mode: it - sets how often the non-default visual regions of the - screen (e.g. 8bpp windows) are refreshed. Examples: - -fixscreen V=10 -fixscreen C=10 - --debug_scroll Turn on debugging info printout for the scroll - heuristics. "-ds" is an alias. Specify it multiple - times for more output. - --noxrecord Disable any use of the RECORD extension. This is - currently used by the -scrollcopyrect scheme and to - monitor X server grabs. - --grab_buster Some of the use of the RECORD extension can leave a --nograb_buster tiny window for XGrabServer deadlock. This is only if - the whole-server grabbing application expects mouse or - keyboard input before releasing the grab. It is usually - a window manager that does this. x11vnc takes care to - avoid the problem, but if caught x11vnc will freeze. - Without -grab_buster, the only solution is to go the - physical display and give it some input to satisfy the - grabbing app. Or manually kill and restart the window - manager if that is feasible. With -grab_buster, x11vnc - will fork a helper thread and if x11vnc appears to be - stuck in a grab after a period of time (20-30 sec) then - it will inject some user input: button clicks, Escape, - mouse motion, etc to try to break the grab. If you - experience a lot of grab deadlock, please report a bug. - --debug_grabs Turn on debugging info printout with respect to - XGrabServer() deadlock for -scrollcopyrect mode. - --debug_sel Turn on debugging info printout with respect to - PRIMARY, CLIPBOARD, and CUTBUFFER0 selections. - --pointer_mode n Various pointer motion update schemes. "-pm" is - an alias. The problem is pointer motion can cause - rapid changes on the screen: consider the rapid - changes when you drag a large window around opaquely. - Neither x11vnc's screen polling and vnc compression - routines nor the bandwidth to the vncviewers can keep - up these rapid screen changes: everything will bog down - when dragging or scrolling. So a scheme has to be used - to "eat" much of that pointer input before re-polling - the screen and sending out framebuffer updates. The - mode number "n" can be 0 to 4 and selects one of - the schemes desribed below. - - Note that the -wireframe and -scrollcopyrect modes - complement -pointer_mode by detecting (and improving) - certain periods of "rapid screen change". - - n=0: does the same as -nodragging. (all screen polling - is suspended if a mouse button is pressed.) - - n=1: was the original scheme used to about Jan 2004: - it basically just skips -input_skip keyboard or pointer - events before repolling the screen. - - n=2 is an improved scheme: by watching the current rate - of input events it tries to detect if it should try to - "eat" additional pointer events before continuing. - - n=3 is basically a dynamic -nodragging mode: it detects - when the mouse motion has paused and then refreshes - the display. - - n=4 attempts to measures network rates and latency, - the video card read rate, and how many tiles have been - changed on the screen. From this, it aggressively tries - to push screen "frames" when it decides it has enough - resources to do so. NOT FINISHED. - - The default n is 2. Note that modes 2, 3, 4 will skip - -input_skip keyboard events (but it will not count - pointer events). Also note that these modes are not - available in -threads mode which has its own pointer - event handling mechanism. - - To try out the different pointer modes to see which - one gives the best response for your usage, it is - convenient to use the remote control function, for - example "x11vnc -R pm:4" or the tcl/tk gui (Tuning -> - pointer_mode -> n). - --input_skip n For the pointer handling when non-threaded: try to - read n user input events before scanning display. n < 0 - means to act as though there is always user input. - Default: 10 - --allinput Have x11vnc read and process all available client input - before proceeding. - --input_eagerly Similar to -allinput but use the handleEventsEagerly - mechanism built into LibVNCServer. - --speeds rd,bw,lat x11vnc tries to estimate some speed parameters that - are used to optimize scheduling (e.g. -pointer_mode - 4, -wireframe, -scrollcopyrect) and other things. - Use the -speeds option to set these manually. - The triple "rd,bw,lat" corresponds to video h/w - read rate in MB/sec, network bandwidth to clients in - KB/sec, and network latency to clients in milliseconds, - respectively. If a value is left blank, e.g. "-speeds - ,100,15", then the internal scheme is used to estimate - the empty value(s). - - Typical PC video cards have read rates of 5-10 MB/sec. - If the framebuffer is in main memory instead of video - h/w (e.g. SunRay, shadowfb, dummy driver, Xvfb), the - read rate may be much faster. "x11perf -getimage500" - can be used to get a lower bound (remember to factor - in the bytes per pixel). It is up to you to estimate - the network bandwith and latency to clients. For the - latency the ping(1) command can be used. - - For convenience there are some aliases provided, - e.g. "-speeds modem". The aliases are: "modem" for - 6,4,200; "dsl" for 6,100,50; and "lan" for 6,5000,1 - --wmdt string For some features, e.g. -wireframe and -scrollcopyrect, - x11vnc has to work around issues for certain window - managers or desktops (currently kde and xfce). - By default it tries to guess which one, but it can - guess incorrectly. Use this option to indicate which - wm/dt. "string" can be "gnome", "kde", "cde", - "xfce", or "root" (classic X wm). Anything else - is interpreted as "root". - --debug_pointer Print debugging output for every pointer event. --debug_keyboard Print debugging output for every keyboard event. - Same as -dp and -dk, respectively. Use multiple - times for more output. - --defer time Time in ms to delay sending updates to connected clients - (deferUpdateTime) Default: 20 - --wait time Time in ms to pause between screen polls. Used to cut - down on load. Default: 20 - --extra_fbur n Perform extra FrameBufferUpdateRequests checks to - try to be in better sync with the client's requests. - What this does is perform extra polls of the client - socket at critical times (before '-defer' and '-wait' - calls.) The default is n=1. Set to a larger number to - insert more checks or set to n=0 to disable. A downside - of these extra calls is that more mouse input may be - processed than desired. - --wait_ui factor Factor by which to cut the -wait time if there - has been recent user input (pointer or keyboard). - Improves response, but increases the load whenever you - are moving the mouse or typing. Default: 2.00 --setdefer n When the -wait_ui mechanism cuts down the wait time ms, - set the defer time to the same ms value. n=1 to enable, - 0 to disable, and -1 to set defer to 0 (no delay). - Similarly, 2 and -2 indicate 'urgent_update' mode should - be used to push the updates even sooner. Default: 1 --nowait_bog Do not detect if the screen polling is "bogging down" - and sleep more. Some activities with no user input can - slow things down a lot: consider a large terminal window - with a long build running in it continuously streaming - text output. By default x11vnc will try to detect this - (3 screen polls in a row each longer than 0.25 sec with - no user input), and sleep up to 1.5 secs to let things - "catch up". Use this option to disable that detection. --slow_fb time Floating point time in seconds to delay all screen - polling. For special purpose usage where a low frame - rate is acceptable and desirable, but you want the - user input processed at the normal rate so you cannot - use -wait. --xrefresh time Floating point time in seconds to indicate how often to - do the equivalent of xrefresh(1) to force all windows - (in the viewable area if -id, -sid, or -clip is used) - to repaint themselves. Use this only if applications - misbehave by not repainting themselves properly. - See also -noxdamage. --nap Monitor activity and if it is low take longer naps --nonap between screen polls to really cut down load when idle. - Default: take naps --sb time Time in seconds after NO activity (e.g. screen blank) - to really throttle down the screen polls (i.e. sleep - for about 1.5 secs). Use 0 to disable. Default: 60 - Set the env. var. X11VNC_SB_FACTOR to scale it. - --readtimeout n Set LibVNCServer rfbMaxClientWait to n seconds. On - slow links that take a long time to paint the first - screen LibVNCServer may hit the timeout and drop the - connection. Default: 20 seconds. --ping n Send a 1x1 framebuffer update to all clients every n - seconds (e.g. to try to keep a network connection alive) - --nofbpm If the system supports the FBPM (Frame Buffer Power --fbpm Management) extension (i.e. some Sun systems), then - prevent the video h/w from going into a reduced power - state when VNC clients are connected. - - FBPM capable video h/w save energy when the workstation - is idle by going into low power states (similar to DPMS - for monitors). This interferes with x11vnc's polling - of the framebuffer data. - - "-nofbpm" means prevent FBPM low power states whenever - VNC clients are connected, while "-fbpm" means to not - monitor the FBPM state at all. See the xset(1) manpage - for details. -nofbpm is basically the same as running - "xset fbpm force on" periodically. Default: -fbpm - --nodpms If the system supports the DPMS (Display Power Managemen -t --dpms Signaling) extension, then prevent the monitor from - going into a reduced power state when VNC clients - are connected. - - DPMS reduced power monitor states are a good thing - and you normally want the power down to take place - (usually x11vnc has no problem exporting the display in - this state). You probably only want to use "-nodpms" - to work around problems with Screen Savers kicking - on in DPMS low power states. There is known problem - with kdesktop_lock on KDE where the screen saver keeps - kicking in every time user input stops for a second - or two. Specifying "-nodpms" works around it. - - "-nodpms" means prevent DPMS low power states whenever - VNC clients are connected, while "-dpms" means to not - monitor the DPMS state at all. See the xset(1) manpage - for details. -nodpms is basically the same as running - "xset dpms force on" periodically. Default: -dpms - --forcedpms If the system supports the DPMS (Display Power - Management Signaling) extension, then try to keep the - monitor in a powered off state. This is to prevent - nosey people at the physical display from viewing what - is on the screen. Be sure to lock the screen before - disconnecting. - - This method is far from bullet proof, e.g. suppose - someone attaches a non-DPMS monitor, or loads the - machine so that there is a gap of time before x11vnc - restores the powered off state? On many machines if - he floods it with keyboard and mouse input he can see - flashes of what is on the screen before the DPMS off - state is reestablished. For this to work securely - there would need to be support in the X server to do - this exactly rather than approximately with DPMS. - --clientdpms As -forcedpms but only when VNC clients are connected. - --noserverdpms The UltraVNC ServerInput extension is supported. - This allows the VNC viewer to click a button that will - cause the server (x11vnc) to try to disable keyboard - and mouse input at the physical display and put the - monitor in dpms powered off state. Use this option to - skip powering off the monitor. - --noultraext Disable the following UltraVNC extensions: SingleWindow - and ServerInput. The others managed by LibVNCServer - (textchat, 1/n scaling, rfbEncodingUltra) are not. - --chatwindow Place a local UltraVNC chat window on the X11 display - that x11vnc is polling. That way the person on the VNC - viewer-side can chat with the person at the physical - X11 console. (e.g. helpdesk w/o telephone) - - For this to work the SSVNC package (version 1.0.21 or - later) MUST BE installed on the system where x11vnc runs - and the 'ssvnc' command must be available in $PATH. - The ssvncviewer is used as a chat window helper. - See http://www.karlrunge.com/x11vnc/ssvnc.html - - This option implies '-rfbversion 3.6' so as to trick - UltraVNC viewers, otherwise they assume chat is not - available. To specify a different rfbversion, place - it after the -chatwindow option on the cmdline. - - See also the remote control 'chaton' and 'chatoff' - actions. These can also be set from the tkx11vnc GUI. - --noxdamage Do not use the X DAMAGE extension to detect framebuffer - changes even if it is available. Use -xdamage if your - default is to have it off. - - x11vnc's use of the DAMAGE extension: 1) significantly - reduces the load when the screen is not changing much, - and 2) detects changed areas (small ones by default) - more quickly. - - Currently the DAMAGE extension is overly conservative - and often reports large areas (e.g. a whole terminal - or browser window) as damaged even though the actual - changed region is much smaller (sometimes just a few - pixels). So heuristics were introduced to skip large - areas and use the damage rectangles only as "hints" - for the traditional scanline polling. The following - tuning parameters are introduced to adjust this - behavior: - --xd_area A Set the largest DAMAGE rectangle area "A" (in - pixels: width * height) to trust as truly damaged: - the rectangle will be copied from the framebuffer - (slow) no matter what. Set to zero to trust *all* - rectangles. Default: 20000 --xd_mem f Set how long DAMAGE rectangles should be "remembered", - "f" is a floating point number and is in units of the - scanline repeat cycle time (32 iterations). The default - (1.0) should give no painting problems. Increase it if - there are problems or decrease it to live on the edge - (perhaps useful on a slow machine). - --sigpipe string Broken pipe (SIGPIPE) handling. "string" can be - "ignore" or "exit". For "ignore" LibVNCServer - will handle the abrupt loss of a client and continue, - for "exit" x11vnc will cleanup and exit at the 1st - broken connection. - - This option is not really needed since LibVNCServer - is doing the correct thing now for quite some time. - However, for convenience you can use it to ignore other - signals, e.g. "-sigpipe ignore:HUP,INT,TERM" in case - that would be useful for some sort of application. - You can also put "exit:.." in the list to have x11vnc - cleanup on the listed signals. "-sig" is an alias - for this option if you don't like the 'pipe'. Example: - -sig ignore:INT,TERM,exit:USR1 - --threads Whether or not to use the threaded LibVNCServer --nothreads algorithm [rfbRunEventLoop] if libpthread is available. - In this mode new threads (one for input and one - for output) are created to handle each new client. - Default: -nothreads. - - Thread stability is much improved in version 0.9.8. - - Multiple clients in threaded mode should be stable - for the ZRLE encoding on all platforms. The Tight and - Zlib encodings are currently only stable on Linux for - multiple clients. Compile with -DTLS=__thread if your - OS and compiler and linker support it. - - For resizes (randr, etc.) set this env. var. to the numb -er - of milliseconds to sleep: X11VNC_THREADS_NEW_FB_SLEEP - at various places in the do_new_fb() action. This is to - let various activities settle. Default is about 500ms. - - Multiple clients in threaded mode could yield better - performance for 'class-room' broadcasting usage; also in - -appshare broadcast mode. See also the -reflect option. - --fs f If the fraction of changed tiles in a poll is greater - than f, the whole screen is updated. Default: 0.75 --gaps n Heuristic to fill in gaps in rows or cols of n or - less tiles. Used to improve text paging. Default: 4 --grow n Heuristic to grow islands of changed tiles n or wider - by checking the tile near the boundary. Default: 3 --fuzz n Tolerance in pixels to mark a tiles edges as changed. - Default: 2 --debug_tiles Print debugging output for tiles, fb updates, etc. - --snapfb Instead of polling the X display framebuffer (fb) - for changes, periodically copy all of X display fb - into main memory and examine that copy for changes. - (This setting also applies for non-X -rawfb modes). - Under some circumstances this will improve interactive - response, or at least make things look smoother, but in - others (most!) it will make the response worse. If the - video h/w fb is such that reading small tiles is very - slow this mode could help. To keep the "framerate" - up the screen size x bpp cannot be too large. Note that - this mode is very wasteful of memory I/O resources - (it makes full screen copies even if nothing changes). - It may be of use in video capture-like applications, - webcams, or where window tearing is a problem. - --rawfb string Instead of polling X, poll the memory object specified - in "string". - - For file polling, to memory map mmap(2) a file use: - "map:/path/to/a/file@WxHxB", with framebuffer Width, - Height, and Bits per pixel. "mmap:..." is the - same. - - If there is trouble with mmap, use "file:/..." - for slower lseek(2) based reading. - - Use "snap:..." to imply -snapfb mode and the "file:" - access (this is for unseekable devices that only provide - the fb all at once, e.g. a video camera provides the - whole frame). - - For shared memory segments string is of the form: - "shm:N@WxHxB" which specifies a shmid N and with - WxHxB as above. See shmat(1) and ipcs(1) - - If you do not supply a type "map" is assumed if - the file exists (see the next paragraphs for some - exceptions to this.) - - If string is "setup:cmd", then the command "cmd" - is run and the first line from it is read and used - as "string". This allows initializing the device, - determining WxHxB, etc. These are often done as root - so take care. - - If the string begins with "video", see the VIDEO4LINUX - discussion below where the device may be queried for - (and possibly set) the framebuffer parameters. - - If the string begins with "console", "/dev/fb", - "fb", or "vt", see the LINUX CONSOLE discussion - below where the framebuffer device is opened and - keystrokes (and possibly mouse events) are inserted - into the console. - - If the string begins with "vnc", see the VNC HOST - discussion below where the framebuffer is taken as that - of another remote VNC server. - - Optional suffixes are ":R/G/B", "+O", and "#VWxVH" to - specify red, green, and blue masks (in hex), offset into - the memory object, and virtual width and height. - - If the masks are not provided x11vnc guesses them based on - the bpp (if the colors look wrong, you need to provide the - masks.) - - Another optional suffix is the Bytes Per Line which in - some cases is not WxB/8. Specify it as WxHxB-BPL - e.g. 800x600x16-2048. This could be a normal width - 1024 at 16bpp fb, but only width 800 shows up. - - The last optional suffix is virtual dimensions VWxVH. Some - devices will double buffer the display in the framebuffer, - allowing updating contents of display and then "panning" - to the buffer via yoffset. x11vnc will map the virutal - size specified by the options stead of just WxH, and track - yoffset appropriately so remote clients get all updates to - the frame buffer. - - So the full format is: mode:file@WxHxB:R/G/B+O-BPL#VWxVH - - Examples: - -rawfb shm:210337933@800x600x32:ff/ff00/ff0000 - -rawfb map:/dev/fb0@1024x768x32 - -rawfb map:/dev/fb0@800x480x16#800x960 - -rawfb map:/tmp/Xvfb_screen0@640x480x8+3232 - -rawfb file:/tmp/my.pnm@250x200x24+37 - -rawfb file:/dev/urandom@128x128x8 - -rawfb snap:/dev/video0@320x240x24 -24to32 - -rawfb video0 - -rawfb video -pipeinput VID - -rawfb console - -rawfb vt2 - -rawfb vnc:somehost:0 - - (see ipcs(1) and fbset(1) for the first two examples) - - In general all user input is discarded by default (see - the -pipeinput option for how to use a helper program - to insert). Most of the X11 (screen, keyboard, mouse) - options do not make sense and many will cause this - mode to crash, so please think twice before setting or - changing them in a running x11vnc. - - If you DO NOT want x11vnc to close the X DISPLAY in - rawfb mode, prepend a "+" e.g. +file:/dev/fb0... - Keeping the display open enables the default - remote-control channel, which could be useful. - Alternatively, if you specify -noviewonly, then the - mouse and keyboard input are STILL sent to the X - display, this usage should be very rare, i.e. doing - something strange with /dev/fb0. - - If the device is not "seekable" (e.g. webcam) try - reading it all at once in full snaps via the "snap:" - mode (note: this is a resource hog). If you are using - file: or map: AND the device needs to be reopened for - *every* snapfb snapshot, set the environment variable: - SNAPFB_RAWFB_RESET=1 as well. - - If you want x11vnc to dynamically transform a 24bpp - rawfb to 32bpp (note that this will be slower) also - supply the -24to32 option. This would be useful for, - say, a video camera that delivers the pixel data as - 24bpp packed RGB. This is the default under "video" - mode if the bpp is 24. - - Normally the bits per pixel, B, is 8, 16, or 32 (or - rarely 24), however there is also some support for - B < 8 (e.g. old graphics displays 4 bpp or 1 bpp). - In this case you certainly must supply the masks as - well: WxHxB:R/G/B. The pixels will be padded out to - 8 bpp using depth 8 truecolor. The scheme currently - does not work with snap fb (ask if interested.) B=1 - monochrome example: file:/dev/urandom@128x128x1:1/1/1 - Some other like this are 128x128x2:3/3/3 128x128x4:7/7/7 - - For B < 8 framebuffers you can also set the env. var - RAWFB_CGA=1 to try a CGA mapping for B=4 (e.g. linux - vga16fb driver.) Note with low bpp and/or resolution - VGA and VGA16 modes on the Linux console one's attempt - to export them via x11vnc can often be thwarted due to - special color palettes, pixel packings, and even video - painting buffering. OTOH, often experimenting with the - RGB masks can yield something recognizable. - - VIDEO4LINUX: on Linux some attempt is made to handle - video devices (webcams or TV tuners) automatically. - The idea is the WxHxB will be extracted from the - device itself. So if you do not supply "@WxHxB... - parameters x11vnc will try to determine them. It first - tries the v4l API if that support has been compiled in. - Otherwise it will run the v4l-info(1) external program - if it is available. - - The simplest examples are "-rawfb video" and "-rawfb - video1" which imply the device file /dev/video and - /dev/video1, respectively. You can also supply the - /dev if you like, e.g. "-rawfb /dev/video0" - - Since the video capture device framebuffer usually - changes continuously (e.g. brightness fluctuations), - you may want to use the -wait, -slow_fb, or -defer - options to lower the "framerate" to cut down on - network VNC traffic. - - A more sophisticated video device scheme allows - initializing the device's settings using: - - -rawfb video: - - The prefix could also be, as above, e.g. "video1:" to - specify the device file. The v4l API must be available - for this to work. Otherwise, you will need to try - to initialize the device with an external program, - e.g. xawtv, spcaview, and hope they persist when x11vnc - re-opens the device. - - is a comma separated list of key=value pairs. - The device's brightness, color, contrast, and hue can - be set to percentages, e.g. br=80,co=50,cn=44,hu=60. - - The device filename can be set too if needed (if it - does not start with "video"), e.g. fn=/dev/qcam. - - The width, height and bpp of the framebuffer can be - set via, e.g., w=160,h=120,bpp=16. - - Related to the bpp above, the pixel format can be set - via the fmt=XXX, where XXX can be one of: GREY, HI240, - RGB555, RGB565, RGB24, and RGB32 (with bpp 8, 8, 16, 16, - 24, and 32 respectively). See http://www.linuxtv.org - for more info (V4L api). - - For TV/rf tuner cards one can set the tuning mode - via tun=XXX where XXX can be one of PAL, NTSC, SECAM, - or AUTO. - - One can switch the input channel by the inp=XXX setting, - where XXX is the name of the input channel (Television, - Composite1, S-Video, etc). Use the name that is in the - information about the device that is printed at startup. - - For input channels with tuners (e.g. Television) one - can change which station is selected by the sta=XXX - setting. XXX is the station number. Currently only - the ntsc-cable-us (US cable) channels are built into - x11vnc. See the -freqtab option below to supply one - from xawtv. If XXX is greater than 500, then it is - interpreted as a raw frequency in KHz. - - Example: - - -rawfb video:br=80,w=320,h=240,fmt=RGB32,tun=NTSC,sta=47 - - one might need to add inp=Television too for the input - channel to be TV if the card doesn't come up by default - in that one. - - Note that not all video capture devices will support - all of the above settings. - - See the -pipeinput VID option below for a way to control - the settings through the VNC Viewer via keystrokes. - As a shortcut, if the string begins "Video.." instead - of "video.." then -pipeinput VID is implied. - - As above, if you specify a "@WxHxB..." after the - string they are used verbatim: the device - is not queried for the current values. Otherwise the - device will be queried. - - LINUX CONSOLE: The following describes some ways to - view and possibly interact with the Linux text/graphics - console (i.e. not X11 XFree86/Xorg) - - Note: If the LibVNCServer LinuxVNC program is on your - system you may want to use that instead of the following - method because it will be faster and more accurate - for the Linux text console and includes mouse support. - There is, however, the basic LinuxVNC functionality in - x11vnc if you replace "console" with "vt" in the - examples below. - - If the rawfb string begins with "console" the - framebuffer device /dev/fb0 is opened and /dev/tty0 is - opened too. The latter is used to inject keystrokes - (not all are supported, but the basic ones are). - You will need to be root to inject keystrokes, but - not necessarily to open /dev/fb0. /dev/tty0 refers to - the active VT, to indicate one explicitly, use, e.g., - "console2" for /dev/tty2, etc. by indicating the - specific VT number. - - For the Linux framebuffer device, /dev/fb0, (fb1, - etc) to be enabled the appropriate kernel drivers must - be loaded. E.g. vesafb or vga16fb and also by setting - the boot parameter vga=0x301 (or 0x314, 0x317, etc.) - (The vga=... method is the preferred way; set your - machines up that way.) Otherwise there will be a - 'No such device' error. You can also load a Linux - framebuffer driver specific to your make of video card - for more functionality. Once the machine is booted one - can often 'modprobe' the fb driver as root to obtain - a framebuffer device. - - If you cannot get /dev/fb0 working on Linux, try - using the LinuxVNC emulation mode by "-rawfb vtN" - where N = 1, ... 6 is the Linux Virtual Terminal (aka - virtual console) you wish to view, e.g. "-rawfb vt2". - Unlike /dev/fb mode, it need not be the active Virtual - Terminal. Note that this mode can only show text and - not graphics. x11vnc polls the text in /dev/vcsaN - - Set the env. var. RAWFB_VCSA_BW=1 to disable colors in - the "vtN" mode (i.e. black and white only.) If you - do not prefer the default 16bpp set RAWFB_VCSA_BPP to - 8 or 32. If you need to tweak the rawfb parameters by - using the 'console_guess' string printed at startup, - be sure to indicate the snap: method. - - uinput: If the Linux version appears to be 2.6 - or later and the "uinput" module appears to be - present (modprobe uinput), then the uinput method - will be used instead of /dev/ttyN. uinput allows - insertion of BOTH keystrokes and mouse input and so it - preferred when accessing graphical (e.g. QT-embedded) - linux console apps. It also provides more accurate - keystroke insertion. See -pipeinput UINPUT below for - more information on this mode; you will have to use - -pipeinput if you want to tweak any UINPUT parameters. - You may also want to also use the -nodragging and - -cursor none options. Use "console0", etc or - -pipeinput CONSOLE to force the /dev/ttyN method. - - Note you can change the Linux VT remotely using the - chvt(1) command to make the one you want be the active - one (e.g. 'chvt 3'). Sometimes switching out and back - corrects the framebuffer's graphics state. For the - "-rawfb vtN" mode there is no need to switch the VT's. - - To skip input injecting entirely use "consolex" - or "vtx". - - The string "/dev/fb0" (1, etc.) can be used instead - of "console". This can be used to specify a different - framebuffer device, e.g. /dev/fb1. As a shortcut the - "/dev/" can be dropped. If the name is something - nonstandard, use "console:/dev/foofb" - - If you do not want x11vnc to guess the framebuffer's - WxHxB and masks automatically (sometimes the kernel - gives incorrect information), specify them with a @WxHxB - (and optional :R/G/B masks) at the end of the string. - - Examples: - -rawfb console - -rawfb /dev/fb0 (same) - -rawfb console3 (force /dev/tty3) - -rawfb consolex (no keystrokes or mouse) - -rawfb console:/dev/nonstd - -rawfb console -pipeinput UINPUT:accel=4.0 - -rawfb vt3 (/dev/tty3 w/o /dev/fb0) - - VNC HOST: if the -rawfb string is of the form - "vnc:host:N" then the VNC display "N" on the remote - VNC server "host" is connected to (i.e. x11vnc acts as - a VNC client itself) and that framebuffer is exported. - - This mode is really only of use if you are trying - to improve performance in the case of many (e.g. > - 10) simultaneous VNC viewers, and you try a divide - and conquer scheme to reduce bandwidth and improve - responsiveness. (However, another user found this mode - useful to export a demo display through a slow link: - then multiple demo viewers connected to the reflecting - x11vnc on the fast side of the link, and so avoided - all of the demo viewers going through the slow link.) - - For example, if there will be 64 simultaneous VNC - viewers this can lead to a lot of redundant VNC traffic - to and from the server host:N, extra CPU usage, - and all viewers response can be reduced by having - to wait for writes to the slowest client to finish. - However, if you set up 8 reflectors/repeaters started - with option -rawfb vnc:host:N, then there are only - 8 connections to host:N. Each repeater then handles - 8 vnc viewer connections thereby spreading the load - around. In classroom broadcast usage, try to put the - repeaters on different switches. This mode is the same - as -reflect host:N. Replace "host:N" by "listen" - or "listen:port" for a reverse connection. - - Overall performance will not be as good as a single - direct connection because, among other things, - there is an additional level of framebuffer polling - and pointer motion can still induce many changes per - second that must be propagated. Tip: if the remote VNC - is x11vnc doing wireframing, or an X display that does - wireframing that gives much better response than opaque - window dragging. Consider the -nodragging option if - the problem is severe. - - The env. var. X11VNC_REFLECT_PASSWORD can be set to - the password needed to log into the vnc host server, or - to "file:path_to_file" to indicate a file containing - the password as its first line. - - To set the pixel format that x11vnc requests as a VNC - CLIENT set the env. vars: X11VNC_REFLECT_bitsPerSample - X11VNC_REFLECT_samplesPerPixel, and - X11VNC_REFLECT_bytesPerPixel; the defaults are 8, 3, 4. - 2, 3, 1 would give a low color mode. See the function - rfbGetClient() in libvncclient for more info. - - The VNC HOST mode implies -shared. Use -noshared as - a subsequent cmdline option to disable sharing. - --freqtab file For use with "-rawfb video" for TV tuner devices to - specify station frequencies. Instead of using the built - in ntsc-cable-us mapping of station number to frequency, - use the data in file. For stations that are not - numeric, e.g. SE20, they are placed above the highest - numbered station in the order they are found. Example: - "-freqtab /usr/X11R6/share/xawtv/europe-west.list" - You can make your own freqtab by copying the xawtv - format. - --pipeinput cmd This option lets you supply an external command in - "cmd" that x11vnc will pipe all of the user input - events to in a simple format. In -pipeinput mode by - default x11vnc will not process any of the user input - events. If you prefix "cmd" with "tee:" it will - both send them to the pipe command and process them. - For a description of the format run "-pipeinput - tee:/bin/cat". Another prefix is "reopen" which - means to reopen pipe if it exits. Separate multiple - prefixes with commas. - - In combination with -rawfb one might be able to - do amusing things (e.g. control non-X devices). - To facilitate this, if -rawfb is in effect then the - value is stored in X11VNC_RAWFB_STR for the pipe command - to use if it wants. Do 'env | grep X11VNC' for more. - - Built-in pipeinput modes (no external program required): - - If cmd is "VID" and you are using the -rawfb for a - video capture device, then an internal list of keyboard - mappings is used to set parameters of the video. - The mappings are: - - "B" and "b" adjust the brightness up and down. - "H" and "h" adjust the hue. - "C" and "c" adjust the colour. - "N" and "n" adjust the contrast. - "S" and "s" adjust the size of the capture screen. - "I" and "i" cycle through input channels. - Up and Down arrows adjust the station (if a tuner) - F1, F2, ..., F6 will switch the video capture pixel - format to HI240, RGB565, RGB24, RGB32, RGB555, and - GREY respectively. See -rawfb video for details. - - If cmd is "CONSOLE" or "CONSOLEn" where n - is a Linux console number, then the linux console - keystroke insertion to /dev/ttyN (see -rawfb console) - is performed. - - If cmd begins with "UINPUT" then the Linux uinput - module is used to insert both keystroke and mouse events - to the Linux console (see -rawfb above). This usually - is the /dev/input/uinput device file (you may need to - create it with "mknod /dev/input/uinput c 10 223" - and insert the module with "modprobe uinput". - - The UINPUT mode currently only does US keyboards (a - scan code option may be added), and not all keysyms - are supported. But it is probably more accurate than - the "CONSOLE" method. - - You may want to use the options -cursor none and - -nodragging in this mode. - - Additional tuning options may be supplied via: - UINPUT:opt1,opt2,... (a comma separated list). If an - option begins with "/" it is taken as the uinput - device file. - - Which uinput is injected can be controlled by an option - string made of the characters "K", "M", and "B" - (see the -input option), e.g. "KM" allows keystroke - and motion but not button clicks. - - A UINPUT option of the form: accel=f, or accel=fx+fy - sets the mouse motion "acceleration". This is used - to correct raw mouse relative motion into how much the - application cursor moves (x11vnc has no control over, - or knowledge of how the windowing application interprets - the raw mouse motions). Typically the acceleration - for an X display is 2 (see xset "m" option). "f" - is a floating point number, e.g. 3.0. Use "fx+fy" - if you need to supply different corrections for x and y. - - Note: the default acceleration is 2.0 since it seems - both X and qt-embedded often (but not always) use - this value. - - Even with a correct accel setting the mouse position - will get out of sync (probably due to a mouse - "threshold" setting where the acceleration doe not - apply, set xset(1)). The option reset=N sets the - number of ms (default 150) after which the cursor is - attempted to be reset (by forcing the mouse to (0, - 0) via small increments and then back out to (x, y) - in 1 jump), This correction seems to be needed but can - cause jerkiness or unexpected behavior with menus, etc. - Use reset=0 to disable. - - If you set the env. var X11VNC_UINPUT_THRESHOLDS then - the thresh=n mode will be enabled. It is currently - not working well. If |dx| <= thresh and |dy| < thresh - no acceleration is applied. Use "thresh=+n" |dx| + - |dy| < thresh to be used instead (X11?) - - Example: - -pipeinput UINPUT:accel=4.0 -cursor none - - If the uinput device has an absolute pointer (as opposed - to a normal mouse that is a relative pointer) you can - specify the option "abs". Note that a touchpad - on a laptop is an absolute device to some degree. - This (usually) avoids all the problems with mouse - acceleration. If x11vnc has trouble deducing the - size of the device, use "abs=WxH". Furthermore, - if the device is a touchscreen (assumed to have an - absolute pointer) use "touch" or "touch=WxH". - For touchscreens, when a mouse button is pressed, - a pressure increase is injected, and when the button - is released a pressure of zero is injected. - - If touch has been set, use "touch_always=1" to - indicate whenever the mouse moves with no button - pressed, a touch event of zero pressure should be - sent anyway. Also use "btn_touch=1" to indicate a - BTN_TOUCH keystroke press or release should be sent - instead of a pressure change. Set "dragskip=n" to - skip n dragged mouse touches (with pressure applied) - before injecting one. To indicate the pressure that - should be sent when there is a button click for a - touchscreen device, specify pressure=n, e.g. n=5. The - default is n=1. - - If a touch screen is being used ("touch" above) - and it is having its input processed by tslib, you can - specify the tslib calibration file via tslib_cal=. - For example, tslib_cal=/etc/pointercal. To get accurate - or even usable positioning this is required when tslib - is in use. - - The Linux uinput mechanism can be bypassed and one can - write input events DIRECTLY to the devices instead. - To do this, specify one or more of the following - for the input classes: direct_rel= - direct_abs= direct_btn= or - direct_key=. The file is usually - something like /dev/input/event1 but you can specify - any device file or pipe. You must specify each one - of the above classes even if they correspond to the - same device file (rel/abs and btn are often the same.) - Look at the file /proc/bus/input/devices to get an idea - what is available and the device filenames. Note: - The /dev/input/mouse* devices do not seem to work, - use the corresponding /dev/input/event* file instead. - Any input class not directly specified as above will be - handled via the uinput mechanism. To disable creating a - uinput device (and thereby discarding unhandled input), - specify "nouinput". - - Examples: - - -pipeinput UINPUT:direct_abs=/dev/input/event1 - - this was used on a qtmoko Neo freerunner (armel): - - -pipeinput UINPUT:touch,tslib_cal=/etc/pointercal, - direct_abs=/dev/input/event1,nouinput,dragskip=4 - - (where the long line has been split into two.) - - You can set the env. var X11VNC_UINPUT_DEBUG=1 or higher - to get debugging output for UINPUT mode. - --macnodim For the native MacOSX server, disable dimming. --macnosleep For the native MacOSX server, disable display sleep. --macnosaver For the native MacOSX server, disable screensaver. --macnowait For the native MacOSX server, do not wait for the - user to switch back to his display. --macwheel n For the native MacOSX server, set the mouse wheel - speed to n (default 5). --macnoswap For the native MacOSX server, do not swap mouse - buttons 2 and 3. --macnoresize For the native MacOSX server, do not resize or reset - the framebuffer even if it is detected that the screen - resolution or depth has changed. --maciconanim n For the native MacOSX server, set n to the number - of milliseconds that the window iconify/deiconify - animation takes. In -ncache mode this value will be - used to skip the animation if possible. (default 400) --macmenu For the native MacOSX server, in -ncache client-side - caching mode, try to cache pull down menus (not perfect - because they have animated fades, etc.) --macuskbd For the native MacOSX server, use the original - keystroke insertion code based on a US keyboard. --macnoopengl For the native MacOSX server, do not use OpenGL for - screen capture, but rather use the original, deprecated - raw memory access method: addr = CGDisplayBaseAddress(). --macnorawfb For the native MacOSX server, disable the raw memory - address screen capture method. - - MACOSX NOTE: There are some deprecated MacOSX interfaces - to inject keyboard and mouse events and the raw memory - access method is deprecated as well (however, OpenGL - will be preferred if available because it is faster.) - One can force not using any deprecated interfaces at - compile time by setting -DX11VNC_MACOSX_NO_DEPRECATED=1 - in CPPFLAGS. Or to turn them off one by one: - -DX11VNC_MACOSX_NO_DEPRECATED_LOCALEVENTS=1, - -DX11VNC_MACOSX_NO_DEPRECATED_POSTEVENTS=1 or - -DX11VNC_MACOSX_NO_DEPRECATED_FRAMEBUFFER=1 - At run time, for testing and workarounds, one can - disable them by using: - -env X11VNC_MACOSX_NO_DEPRECATED=1 - -env X11VNC_MACOSX_NO_DEPRECATED_LOCALEVENTS=1 - -env X11VNC_MACOSX_NO_DEPRECATED_POSTEVENTS=1 or - -env X11VNC_MACOSX_NO_DEPRECATED_FRAMEBUFFER=1 - Note: When doing either of these for the mouse input - not everything works currently, e.g. double clicks and - wireframing. Also, screen resolution and pixel depth - changes will not be automatically detected unless the - deprecated framebuffer interfaces are allowed. - - Conversely, if you are compiling on an - older machine that does not have some of - the newer interfaces, you may need to specify - -DX11VNC_MACOSX_NO_CGEVENTCREATESCROLLWHEELEVENT - -DX11VNC_MACOSX_NO_CGEVENTCREATEMOUSEEVENT or - -DX11VNC_MACOSX_NO_CGEVENTCREATEKEYBOARDEVENT. Use - -DX11VNC_MACOSX_USE_GETMAINDEVICE to regain the very - old QuickDraw GetMainDevice() interface (rare...) - --gui [gui-opts] Start up a simple tcl/tk gui based on the remote - control options -remote/-query described below. - Requires the "wish" program to be installed on the - machine. "gui-opts" is not required: the default - is to start up both the full gui and x11vnc with the - gui showing up on the X display in the environment - variable DISPLAY. - - "gui-opts" can be a comma separated list of items. - Currently there are these types of items: 1) a gui - mode, a 2) gui "simplicity", 3) the X display the - gui should display on, 4) a "tray" or "icon" mode, - and 5) a gui geometry. - - 1) The gui mode can be "start", "conn", or "wait" - "start" is the default mode above and is not required. - "conn" means do not automatically start up x11vnc, - but instead just try to connect to an existing x11vnc - process. "wait" means just start the gui and nothing - else (you will later instruct the gui to start x11vnc - or connect to an existing one.) - - 2) The gui simplicity is off by default (a power-user - gui with all options is presented) To start with - something less daunting supply the string "simple" - ("ez" is an alias for this). Once the gui is - started you can toggle between the two with "Misc -> - simple_gui". - - 3) Note the possible confusion regarding the potentially - two different X displays: x11vnc polls one, but you - may want the gui to appear on another. For example, if - you ssh in and x11vnc is not running yet you may want - the gui to come back to you via your ssh redirected X - display (e.g. localhost:10). - - If you do not specify a gui X display in "gui-opts" - then the DISPLAY environment variable and -display - option are tried (in that order). Regarding the x11vnc - X display the gui will try to communication with, it - first tries -display and then DISPLAY. For example, - "x11vnc -display :0 -gui otherhost:0", will remote - control an x11vnc polling :0 and display the gui on - otherhost:0 The "tray/icon" mode below reverses this - preference, preferring to display on the x11vnc display. - - 4) When "tray" or "icon" is specified, the gui - presents itself as a small icon with behavior typical - of a "system tray" or "dock applet". The color - of the icon indicates status (connected clients) and - there is also a balloon status. Clicking on the icon - gives a menu from which properties, etc, can be set and - the full gui is available under "Advanced". To be - fully functional, the gui mode should be "start" - (the default). - - Note that tray or icon mode will imply the -forever - x11vnc option (if the x11vnc server is started along - with the gui) unless -connect or -connect_or_exit has - been specified. So x11vnc (and the tray/icon gui) - will wait for more connections after the first client - disconnects. If you want only one viewer connection - include the -once option. - - For "icon" the gui just a small standalone window. - For "tray" it will attempt to embed itself in the - "system tray" if possible. If "=setpass" is appended the -n - at startup the X11 user will be prompted to set the - VNC session password. If = is appended - that icon will attempt to embed itself in the window - given by hexnumber. Use =noadvanced to disable the - full gui. (To supply more than one, use "+" sign). - E.g. -gui tray=setpass and -gui icon=0x3600028 - - Other modes: "full", the default and need not be - specified. "-gui none", do not show a gui, useful - to override a ~/.x11vncrc setting, etc. - - 5) When "geom=+X+Y" is specified, that geometry - is passed to the gui toplevel. This is the icon in - icon/tray mode, or the full gui otherwise. You can - also specify width and height, i.e. WxH+X+Y, but it - is not recommended. In "tray" mode the geometry is - ignored unless the system tray manager does not seem - to be running. One could imagine using something like - "-gui tray,geom=+4000+4000" with a display manager - to keep the gui invisible until someone logs in... - - More icon tricks, "icon=minimal" gives an icon just - with the VNC display number. You can also set the font - with "iconfont=...". The following could be useful: - "-gui icon=minimal,iconfont=5x8,geom=24x10+0-0" - - General examples of the -gui option: "x11vnc -gui", - "x11vnc -gui ez" "x11vnc -gui localhost:10", - "x11vnc -gui conn,host:0", "x11vnc -gui tray,ez" - "x11vnc -gui tray=setpass" - - If you do not intend to start x11vnc from the gui - (i.e. just remote control an existing one), then the - gui process can run on a different machine from the - x11vnc server as long as X permissions, etc. permit - communication between the two. - - FONTS: On some systems the tk fonts can be too small, - jagged, or otherwise unreadable. There are 4 env vars - you can set to be the tk font you prefer: - - X11VNC_FONT_BOLD main font for menus and buttons. - X11VNC_FONT_FIXED font for fixed width text. - - X11VNC_FONT_BOLD_SMALL tray icon font. - X11VNC_FONT_REG_SMALL tray icon menu font. - - The last two only apply for the tray icon mode. - - Here are some examples: - - -env X11VNC_FONT_BOLD='Helvetica -16 bold' - -env X11VNC_FONT_FIXED='Courier -14' - -env X11VNC_FONT_REG_SMALL='Helvetica -12' - - You can put the lines like the above (without the - quotes) in your ~/.x11vncrc file to avoid having to - specify them on the x11vnc command line. - --remote command Remotely control some aspects of an already running - x11vnc server. "-R" and "-r" are aliases for - "-remote". After the remote control command is - sent to the running server the 'x11vnc -remote ...' - x11vnc command exits. You can often use the -query - command (see below) to see if the x11vnc server - processed your -remote command. - - The default communication channel is that of X - properties (specifically X11VNC_REMOTE), and so this - command must be run with correct settings for DISPLAY - and possibly XAUTHORITY to connect to the X server - and set the property. Alternatively, use the -display - and -auth options to set them to the correct values. - The running server cannot use the -novncconnect option - because that disables the communication channel. - See below for alternate channels. - - For example: 'x11vnc -remote stop' (which is the same as - 'x11vnc -R stop') will close down the x11vnc server. - 'x11vnc -R shared' will enable shared connections, and - 'x11vnc -R scale:3/4' will rescale the desktop. - - To use a different name for the X11 property (e.g. to - have separate communication channels for multiple - x11vnc's on the same display) set the X11VNC_REMOTE - environment variable to the string you want, for - example: -env X11VNC_REMOTE=X11VNC_REMOTE_12345 - Both sides of the channel must use the same unique name. - - To run a bunch of commands in a sequence use something - like: x11vnc -R 'script:firstcmd;secondcmd;...' - - Use x11vnc -R script:file=/path/to/file to read commands - from a file (can be multi-line and use the comment '#' - character in the normal way. The ';' separator must - still be used to separate each command.) - - To not try to contact another x11vnc process and instead - just run the command (or query) directly, prefix the - command with the string "DIRECT:" - - The following -remote/-R commands are supported: - - stop terminate the server, same as "quit" - "exit" or "shutdown". - ping see if the x11vnc server responds. - return is: ans=ping: - ping:mystring as above, but use your own unique string -. - return is: ans=ping:mystring: - blacken try to push a black fb update to all - clients (due to timings a client - could miss it). Same as "zero", also - "zero:x1,y1,x2,y2" for a rectangle. - refresh send the entire fb to all clients. - reset recreate the fb, polling memory, etc. - id:windowid set -id window to "windowid". empty - or "root" to go back to root window - sid:windowid set -sid window to "windowid" - id_cmd:cmd cmds: raise, lower, map, unmap, iconify, - move:dXdY, resize:dWdH, geom:WxH+X+Y. dX - dY, dW, and dH must have a leading "+" - or "-" e.g.: move:-30+10 resize:+20+35 - also: wm_delete, wm_name:string and - icon_name:string. Also id_cmd:win=N:cmd - waitmapped wait until subwin is mapped. - nowaitmapped do not wait until subwin is mapped. - clip:WxH+X+Y set -clip mode to "WxH+X+Y" - flashcmap enable -flashcmap mode. - noflashcmap disable -flashcmap mode. - shiftcmap:n set -shiftcmap to n. - notruecolor enable -notruecolor mode. - truecolor disable -notruecolor mode. - overlay enable -overlay mode (if applicable). - nooverlay disable -overlay mode. - overlay_cursor in -overlay mode, enable cursor drawing. - overlay_nocursor disable cursor drawing. same as - nooverlay_cursor. - 8to24 enable -8to24 mode (if applicable). - no8to24 disable -8to24 mode. - 8to24_opts:str set the -8to24 opts to "str". - 24to32 enable -24to32 mode (if applicable). - no24to32 disable -24to32 mode. - visual:vis set -visual to "vis" - scale:frac set -scale to "frac" - scale_cursor:f set -scale_cursor to "f" - viewonly enable -viewonly mode. - noviewonly disable -viewonly mode. - shared enable -shared mode. - noshared disable -shared mode. - forever enable -forever mode. - noforever disable -forever mode. - timeout:n reset -timeout to n, if there are - currently no clients, exit unless one - connects in the next n secs. - tightfilexfer enable filetransfer for NEW clients. - notightfilexfer disable filetransfer for NEW clients. - ultrafilexfer enable filetransfer for clients. - noultrafilexfer disable filetransfer for clients. - rfbversion:n.m set -rfbversion for new clients. - http enable http client connections. - nohttp disable http client connections. - deny deny any new connections, same as "lock" - nodeny allow new connections, same as "unlock" - avahi enable avahi service advertising. - noavahi disable avahi service advertising. - mdns enable avahi service advertising. - nomdns disable avahi service advertising. - zeroconf enable avahi service advertising. - nozeroconf disable avahi service advertising. - connect:host do reverse connection to host, "host" - may be a comma separated list of hosts - or host:ports. See -connect. Passwords - required as with fwd connections. - See X11VNC_REVERSE_CONNECTION_NO_AUTH=1 - disconnect:host disconnect any clients from "host" - same as "close:host". Use host - "all" to close all current clients. - If you know the client internal hex ID, - e.g. 0x3 (returned by "-query clients" - and RFB_CLIENT_ID) you can use that too. - proxy:host:port set reverse connection proxy (empty to - disable). - allowonce:host For the next connection only, allow - connection from "host". In -ssl mode - two connections are allowed (i.e. Fetch - Cert) unless X11VNC_NO_SSL_ALLOW_TWICE=1 - allow:hostlist set -allow list to (comma separated) - "hostlist". See -allow and -localhost. - Do not use with -allow /path/to/file - Use "+host" to add a single host, and - use "-host" to delete a single host - localhost enable -localhost mode - nolocalhost disable -localhost mode - listen:str set -listen to str, empty to disable. - noipv6 enable -noipv6 mode. - ipv6 disable -noipv6 mode. - noipv4 enable -noipv4 mode. - ipv4 disable -noipv4 mode. - 6 enable -6 IPv6 listening mode. - no6 disable -6 IPv6 listening mode. - lookup disable -nolookup mode. - nolookup enable -nolookup mode. - lookup disable -nolookup mode. - input:str set -input to "str", empty to disable. - grabkbd enable -grabkbd mode. - nograbkbd disable -grabkbd mode. - grabptr enable -grabptr mode. - nograbptr disable -grabptr mode. - grabalways enable -grabalways mode. - nograbalways disable -grabalways mode. - grablocal:n set -grablocal to n. - client_input:str set the K, M, B -input on a per-client - basis. select which client as for - disconnect, e.g. client_input:host:MB - or client_input:0x2:K - accept:cmd set -accept "cmd" (empty to disable). - afteraccept:cmd set -afteraccept (empty to disable). - gone:cmd set -gone "cmd" (empty to disable). - noshm enable -noshm mode. - shm disable -noshm mode (i.e. use shm). - flipbyteorder enable -flipbyteorder mode, you may need - to set noshm for this to do something. - noflipbyteorder disable -flipbyteorder mode. - onetile enable -onetile mode. (you may need to - set shm for this to do something) - noonetile disable -onetile mode. - solid enable -solid mode - nosolid disable -solid mode. - solid_color:color set -solid color (and apply it). - blackout:str set -blackout "str" (empty to disable). - See -blackout for the form of "str" - (basically: WxH+X+Y,...) - Use "+WxH+X+Y" to append a single - rectangle use "-WxH+X+Y" to delete one - xinerama enable -xinerama mode. (if applicable) - noxinerama disable -xinerama mode. - xtrap enable -xtrap input mode(if applicable) - noxtrap disable -xtrap input mode. - xrandr enable -xrandr mode. (if applicable) - noxrandr disable -xrandr mode. - xrandr_mode:mode set the -xrandr mode to "mode". - rotate:mode set the -rotate mode to "mode". - padgeom:WxH set -padgeom to WxH (empty to disable) - If WxH is "force" or "do" the padded - geometry fb is immediately applied. - quiet enable -quiet mode. - noquiet disable -quiet mode. - modtweak enable -modtweak mode. - nomodtweak enable -nomodtweak mode. - xkb enable -xkb modtweak mode. - noxkb disable -xkb modtweak mode. - capslock enable -capslock mode. - nocapslock disable -capslock mode. - skip_lockkeys enable -skip_lockkeys mode. - noskip_lockkeys disable -skip_lockkeys mode. - skip_keycodes:str enable -xkb -skip_keycodes "str". - sloppy_keys enable -sloppy_keys mode. - nosloppy_keys disable -sloppy_keys mode. - skip_dups enable -skip_dups mode. - noskip_dups disable -skip_dups mode. - add_keysyms enable -add_keysyms mode. - noadd_keysyms stop adding keysyms. those added will - still be removed at exit. - clear_mods enable -clear_mods mode and clear them. - noclear_mods disable -clear_mods mode. - clear_keys enable -clear_keys mode and clear them. - noclear_keys disable -clear_keys mode. - clear_locks do the clear_locks action. - clear_all do the clear_all action. - keystate have x11vnc print current keystate. - remap:str set -remap "str" (empty to disable). - See -remap for the form of "str" - (basically: key1-key2,key3-key4,...) - Use "+key1-key2" to append a single - keymapping, use "-key1-key2" to delete. - norepeat enable -norepeat mode. - repeat disable -norepeat mode. - nofb enable -nofb mode. - fb disable -nofb mode. - bell enable bell (if supported). - nobell disable bell. - sendbell ring the bell now. - nosel enable -nosel mode. - sel disable -nosel mode. - noprimary enable -noprimary mode. - primary disable -noprimary mode. - nosetprimary enable -nosetprimary mode. - setprimary disable -nosetprimary mode. - noclipboard enable -noclipboard mode. - clipboard disable -noclipboard mode. - nosetclipboard enable -nosetclipboard mode. - setclipboard disable -nosetclipboard mode. - seldir:str set -seldir to "str" - resend_cutbuffer resend the most recent CUTBUFFER0 copy - resend_clipboard resend the most recent CLIPBOARD copy - resend_primary resend the most recent PRIMARY copy - cursor:mode enable -cursor "mode". - show_cursor enable showing a cursor. - noshow_cursor disable showing a cursor. (same as - "nocursor") - cursor_drag enable cursor changes during drag. - nocursor_drag disable cursor changes during drag. - arrow:n set -arrow to alternate n. - xfixes enable xfixes cursor shape mode. - noxfixes disable xfixes cursor shape mode. - alphacut:n set -alphacut to n. - alphafrac:f set -alphafrac to f. - alpharemove enable -alpharemove mode. - noalpharemove disable -alpharemove mode. - alphablend disable -noalphablend mode. - noalphablend enable -noalphablend mode. - cursorshape disable -nocursorshape mode. - nocursorshape enable -nocursorshape mode. - cursorpos disable -nocursorpos mode. - nocursorpos enable -nocursorpos mode. - xwarp enable -xwarppointer mode. - noxwarp disable -xwarppointer mode. - always_inject enable -always_inject mode. - noalways_inject disable -always_inject mode. - buttonmap:str set -buttonmap "str", empty to disable - dragging disable -nodragging mode. - nodragging enable -nodragging mode. - ncache reenable -ncache mode. - noncache disable -ncache mode. - ncache_size:n set -ncache size to n. - ncache_cr enable -ncache_cr mode. - noncache_cr disable -ncache_cr mode. - ncache_no_moveraise enable no_moveraise mode. - noncache_no_moveraise disable no_moveraise mode. - ncache_no_dtchange enable ncache_no_dtchange mode. - noncache_no_dtchange disable ncache_no_dtchange mode. - ncache_old_wm enable ncache_old_wm mode. - noncache_old_wm disable ncache_old_wm mode. - ncache_no_rootpixmap enable ncache_no_rootpixmap. - noncache_no_rootpixmap disable ncache_no_rootpixmap. - ncache_reset_rootpixmap recheck the root pixmap, ncrp - ncache_keep_anims enable ncache_keep_anims. - noncache_keep_anims disable ncache_keep_anims. - ncache_pad:n set -ncache_pad to n. - wireframe enable -wireframe mode. same as "wf" - nowireframe disable -wireframe mode. same as "nowf" - wireframe:str enable -wireframe mode string. - wireframe_mode:str enable -wireframe mode string. - wireframelocal enable wireframelocal. same as "wfl" - nowireframe disable wireframelocal. same as "nowfl" - wirecopyrect:str set -wirecopyrect string. same as "wcr: -" - scrollcopyrect:str set -scrollcopyrect string. same "scr -" - noscrollcopyrect disable -scrollcopyrect mode. "noscr" - scr_area:n set -scr_area to n - scr_skip:list set -scr_skip to "list" - scr_inc:list set -scr_inc to "list" - scr_keys:list set -scr_keys to "list" - scr_term:list set -scr_term to "list" - scr_keyrepeat:str set -scr_keyrepeat to "str" - scr_parms:str set -scr_parms parameters. - fixscreen:str set -fixscreen to "str". - noxrecord disable all use of RECORD extension. - xrecord enable use of RECORD extension. - reset_record reset RECORD extension (if avail.) - pointer_mode:n set -pointer_mode to n. same as "pm" - input_skip:n set -input_skip to n. - allinput enable use of -allinput mode. - noallinput disable use of -allinput mode. - input_eagerly enable use of -input_eagerly mode. - noinput_eagerly disable use of -input_eagerly mode. - ssltimeout:n set -ssltimeout to n. - speeds:str set -speeds to str. - wmdt:str set -wmdt to str. - debug_pointer enable -debug_pointer, same as "dp" - nodebug_pointer disable -debug_pointer, same as "nodp" - debug_keyboard enable -debug_keyboard, same as "dk" - nodebug_keyboard disable -debug_keyboard, same as "nodk" - keycode:n inject keystroke 'keycode' (xmodmap -pk) - keycode:n,down inject 'keycode' (down=0,1) - keysym:str inject keystroke 'keysym' (number/name) - keysym:str,down inject 'keysym' (down=0,1) - ptr:x,y,mask inject pointer event x, y, button-mask - fakebuttonevent:button,down direct XTestFakeButtonEvent. - sleep:t sleep floating point time t. - get_xprop:p get X property named 'p'. - set_xprop:p:val set X property named 'p' to 'val'. - p -> id=NNN:p for hex/dec window id. - wininfo:id get info about X window id. use 'root' - for root window, use +id for children. - grab_state get state of pointer and keyboard grab. - pointer_pos print XQueryPointer x,y cursor position. - pointer_x print XQueryPointer x cursor position. - pointer_y print XQueryPointer y cursor position. - pointer_same print XQueryPointer ptr on same screen. - pointer_root print XQueryPointer curr ptr rootwin. - pointer_mask print XQueryPointer button and mods mask - mouse_x print x11vnc's idea of cursor position. - mouse_y print x11vnc's idea of cursor position. - noop do nothing. - defer:n set -defer to n ms,same as deferupdate:n - wait:n set -wait to n ms. - extra_fbur:n set -extra_fbur to n. - wait_ui:f set -wait_ui factor to f. - setdefer:n set -setdefer to -2,-1,0,1, or 2. - wait_bog disable -nowait_bog mode. - nowait_bog enable -nowait_bog mode. - slow_fb:f set -slow_fb to f seconds. - xrefresh:f set -xrefresh to f seconds. - readtimeout:n set read timeout to n seconds. - nap enable -nap mode. - nonap disable -nap mode. - sb:n set -sb to n s, same as screen_blank:n - fbpm disable -nofbpm mode. - nofbpm enable -nofbpm mode. - dpms disable -nodpms mode. - nodpms enable -nodpms mode. - forcedpms enable -forcedpms mode. - noforcedpms disable -forcedpms mode. - clientdpms enable -clientdpms mode. - noclientdpms disable -clientdpms mode. - noserverdpms enable -noserverdpms mode. - serverdpms disable -noserverdpms mode. - noultraext enable -noultraext mode. - ultraext disable -noultraext mode. - chatwindow enable local chatwindow mode. - nochatwindow disable local chatwindow mode. - chaton begin chat using local window. - chatoff end chat using local window. - xdamage enable xdamage polling hints. - noxdamage disable xdamage polling hints. - xd_area:A set -xd_area max pixel area to "A" - xd_mem:f set -xd_mem remembrance to "f" - fs:frac set -fs fraction to "frac", e.g. 0.5 - gaps:n set -gaps to n. - grow:n set -grow to n. - fuzz:n set -fuzz to n. - snapfb enable -snapfb mode. - nosnapfb disable -snapfb mode. - rawfb:str set -rawfb mode to "str". - uinput_accel:f set uinput_accel to f. - uinput_thresh:n set uinput_thresh to n. - uinput_reset:n set uinput_reset to n ms. - uinput_always:n set uinput_always to 1/0. - progressive:n set LibVNCServer -progressive slice - height parameter to n. - desktop:str set -desktop name to str for new clients -. - rfbport:n set -rfbport to n. - macnosaver enable -macnosaver mode. - macsaver disable -macnosaver mode. - macnowait enable -macnowait mode. - macwait disable -macnowait mode. - macwheel:n set -macwheel to n. - macnoswap enable -macnoswap mouse button mode. - macswap disable -macnoswap mouse button mode. - macnoresize enable -macnoresize mode. - macresize disable -macnoresize mode. - maciconanim:n set -maciconanim to n. - macmenu enable -macmenu mode. - macnomenu disable -macmenu mode. - macuskbd enable -macuskbd mode. - macnouskbd disable -macuskbd mode. - httpport:n set -httpport to n. - httpdir:dir set -httpdir to dir (and enable http). - enablehttpproxy enable -enablehttpproxy mode. - noenablehttpproxy disable -enablehttpproxy mode. - alwaysshared enable -alwaysshared mode. - noalwaysshared disable -alwaysshared mode. - (may interfere with other options) - nevershared enable -nevershared mode. - nonevershared disable -nevershared mode. - (may interfere with other options) - dontdisconnect enable -dontdisconnect mode. - nodontdisconnect disable -dontdisconnect mode. - (may interfere with other options) - debug_xevents enable debugging X events. - nodebug_xevents disable debugging X events. - debug_xdamage enable debugging X DAMAGE mechanism. - nodebug_xdamage disable debugging X DAMAGE mechanism. - debug_wireframe enable debugging wireframe mechanism. - nodebug_wireframe disable debugging wireframe mechanism. - debug_scroll enable debugging scrollcopy mechanism. - nodebug_scroll disable debugging scrollcopy mechanism. - debug_tiles enable -debug_tiles - nodebug_tiles disable -debug_tiles - debug_grabs enable -debug_grabs - nodebug_grabs disable -debug_grabs - debug_sel enable -debug_sel - nodebug_sel disable -debug_sel - debug_ncache enable -debug_ncache - nodebug_ncache disable -debug_ncache - dbg enable -dbg crash shell - nodbg disable -dbg crash shell - - noremote disable the -remote command processing, - it cannot be turned back on. - - bcx_xattach:str This remote control command is for - use with the BARCO xattach program or the x2x program. - Both of these programs are for 'pointer and keyboard' - sharing between separate X displays. In general the - two displays are usually nearby, e.g. on the same desk, - and this allows the user to share a single pointer and - keyboard between them. The user moves the mouse to - an edge and then the mouse pointer appears to 'jump' - to the other display screen. Thus it emulates what a - single X server would do for two screens (e.g. :0.0 and - :0.1) The illusion of a single Xserver with multiple - screens is achieved by forwarding events to the 2nd - one via the XTEST extension. - - What the x11vnc bcx_xattach command does is to perform - some pointer movements to try to INDUCE xattach/x2x - to 'jump' to the other display. In what follows the - 'master' display refers to the one that when it has - 'focus' it is basically doing nothing besides watching - for the mouse to go over an edge. The 'slave' - display refers to the one to which the mouse and - keyboard is redirected to once an edge in the master - has been crossed. Note that the x11vnc executing the - bcx_xattach command MUST be the one connected to the - *master* display. - - Also note that when input is being redirected (via - XTEST) from the master display to the slave display, - the master display's pointer and keyboard are *grabbed* - by xattach/x2x. x11vnc can use this info to verify that - the master/slave mode change has taken place correctly. - If you specify the "ifneeded" option (see below) - and the initial grab state is that of the desired - final state, then no pointer movements are injected - and "DONE,GRAB_OK" is returned. - - "str" must contain one of "up", "down", "left", - or "right" to indicate the direction of the 'jump'. - "str" must also contain one of "master_to_slave" - or "slave_to_master" to indicate the type of mode - change induced by the jump. Use "M2S" and "S2M" - as shorter aliases. - - "str" may be a "+" separated list of additional - tuning options. The "shift=n" option indicates an - offset shift position away from (0,0) (default 20). - "final=x+y" specifies the final position of the cursor - at the end of the normal move sequence; default 30+30. - "extra_move=x+y" means to do one more pointer move - after "final" to x+y. "dt=n" sets the sleep time - in milliseconds between pointer moves (default: 40ms) - "retry=n" specifies the maximum number of retries if - the grab state change fails. "ifneeded" means to not - apply the pointer movements if the initial grab state is - that of the desired final state. "nograbcheck" means - to not check if the grab state changed as expected and - only apply the pointer movements (default is to check - the grab states.) - - If you do not specify "up", etc., to bcx_xattach - nothing will be attempted and the command returns - the string FAIL,NO_DIRECTION_SPECIFIED. If you do - not specify "master_to_slave" or "M2S", etc., to - bcx_xattach nothing will be attempted and the command - returns the string FAIL,NO_MODE_CHANGE_SPECIFIED. - - Otherwise, the returned string will contain "DONE". - It will be "DONE,GRAB_OK" if the grab state changed - as expected (or if "ifneeded" was supplied and - the initial grab state was already the desired - one.) If the initial grab state was incorrect, - but the final grab state was correct then it is - "DONE,GRAB_FAIL_INIT". If the initial grab state - was correct, but the final grab state was incorrect - then it is "DONE,GRAB_FAIL_FINAL". If both are - incorrect it will be "DONE,GRAB_FAIL". Under grab - failure the string will be followed by ":p1,k1-p2,k2" - where p1,k1 indicates the initial pointer and keyboard - grab states and p2,k2 the final ones. If GRAB_FAIL or - GRAB_FAIL_FINAL occurs, the action will be retried up - to 3 times; trying to reset the state and sleeping a - bit between each try. Set retry=n to adjust the number - of retries, zero to disable retries. - - Examples: - -R bcx_xattach:down+M2S - -R bcx_xattach:up+S2M - -R bcx_xattach:up+S2M+nograbcheck+dt=30 - -R bcx_xattach:down+M2S+extra_move=100+100 - - or use -Q instead of -R to retrieve the result text. - - End of the bcx_xattach:str description. - - The vncconnect(1) command from standard VNC - distributions may also be used if string is prefixed - with "cmd=" E.g. 'vncconnect cmd=stop'. Under some - circumstances xprop(1) can used if it supports -set - (see the FAQ). - - If "-connect /path/to/file" has been supplied to the - running x11vnc server then that file can be used as a - communication channel (this is the only way to remote - control one of many x11vnc's polling the same X display) - Simply run: 'x11vnc -connect /path/to/file -remote ...' - or you can directly write to the file via something - like: "echo cmd=stop > /path/to/file", etc. - --query variable Like -remote, except just query the value of - "variable". "-Q" is an alias for "-query". - Multiple queries can be done by separating variables - by commas, e.g. -query var1,var2. The results come - back in the form ans=var1:value1,ans=var2:value2,... - to the standard output. If a variable is read-only, - it comes back with prefix "aro=" instead of "ans=". - - Some -remote commands are pure actions that do not make - sense as variables, e.g. "stop" or "disconnect", in - these cases the value returned is "N/A". To direct a - query straight to the X11VNC_REMOTE property or connect - file use "qry=..." instead of "cmd=..." - - ans= stop quit exit shutdown ping resend_cutbuffer - resend_clipboard resend_primary blacken zero refresh - reset close disconnect id_cmd id sid waitmapped - nowaitmapped clip flashcmap noflashcmap shiftcmap - truecolor notruecolor overlay nooverlay overlay_cursor - overlay_yescursor nooverlay_nocursor nooverlay_cursor - nooverlay_yescursor overlay_nocursor 8to24 no8to24 - 8to24_opts 24to32 no24to32 visual scale scale_cursor - viewonly noviewonly shared noshared forever noforever - once timeout tightfilexfer notightfilexfer ultrafilexfer - noultrafilexfer rfbversion deny lock nodeny unlock avahi - mdns zeroconf noavahi nomdns nozeroconf connect proxy - allowonce allow noipv6 ipv6 noipv4 ipv4 no6 6 localhost - nolocalhost listen lookup nolookup accept afteraccept - gone shm noshm flipbyteorder noflipbyteorder onetile - noonetile solid_color solid nosolid blackout xinerama - noxinerama xtrap noxtrap xrandr noxrandr xrandr_mode - rotate padgeom quiet q noquiet modtweak nomodtweak xkb - noxkb capslock nocapslock skip_lockkeys noskip_lockkeys - skip_keycodes sloppy_keys nosloppy_keys skip_dups - noskip_dups add_keysyms noadd_keysyms clear_mods - noclear_mods clear_keys noclear_keys clear_all - clear_locks keystate remap repeat norepeat fb nofb bell - nobell sendbell sel nosel primary noprimary setprimary - nosetprimary clipboard noclipboard setclipboard - nosetclipboard seldir cursorshape nocursorshape - cursorpos nocursorpos cursor_drag nocursor_drag cursor - show_cursor noshow_cursor nocursor arrow xfixes noxfixes - xdamage noxdamage xd_area xd_mem alphacut alphafrac - alpharemove noalpharemove alphablend noalphablend - xwarppointer xwarp noxwarppointer noxwarp always_inject - noalways_inject buttonmap dragging nodragging ncache_cr - noncache_cr ncache_no_moveraise noncache_no_moveraise - ncache_no_dtchange noncache_no_dtchange - ncache_no_rootpixmap noncache_no_rootpixmap - ncache_reset_rootpixmap ncrp ncache_keep_anims - noncache_keep_anims ncache_old_wm noncache_old_wm - ncache_pad ncache noncache ncache_size debug_ncache - nodebug_ncache wireframe_mode wireframe wf nowireframe - nowf wireframelocal wfl nowireframelocal nowfl - wirecopyrect wcr nowirecopyrect nowcr scr_area - scr_skip scr_inc scr_keys scr_term scr_keyrepeat - scr_parms scrollcopyrect scr noscrollcopyrect - noscr fixscreen noxrecord xrecord reset_record - pointer_mode pm input_skip allinput noallinput - input_eagerly noinput_eagerly input grabkbd nograbkbd - grabptr nograbptr grabalways nograbalways grablocal - client_input ssltimeout speeds wmdt debug_pointer dp - nodebug_pointer nodp debug_keyboard dk nodebug_keyboard - nodk keycode keysym ptr fakebuttonevent sleep get_xprop - set_xprop wininfo bcx_xattach deferupdate defer - setdefer extra_fbur wait_ui wait_bog nowait_bog - slow_fb xrefresh wait readtimeout nap nonap sb - screen_blank fbpm nofbpm dpms nodpms clientdpms - noclientdpms forcedpms noforcedpms noserverdpms - serverdpms noultraext ultraext chatwindow nochatwindow - chaton chatoff fs gaps grow fuzz snapfb nosnapfb - rawfb uinput_accel uinput_thresh uinput_reset - uinput_always progressive rfbport http nohttp httpport - httpdir enablehttpproxy noenablehttpproxy alwaysshared - noalwaysshared nevershared noalwaysshared dontdisconnect - nodontdisconnect desktop debug_xevents nodebug_xevents - debug_xevents debug_xdamage nodebug_xdamage - debug_xdamage debug_wireframe nodebug_wireframe - debug_wireframe debug_scroll nodebug_scroll debug_scroll - debug_tiles dbt nodebug_tiles nodbt debug_tiles - debug_grabs nodebug_grabs debug_sel nodebug_sel dbg - nodbg macnosaver macsaver nomacnosaver macnowait macwait - nomacnowait macwheel macnoswap macswap nomacnoswap - macnoresize macresize nomacnoresize maciconanim macmenu - macnomenu nomacmenu macuskbd nomacuskbd noremote - - aro= noop display vncdisplay icon_mode autoport - loop loopbg desktopname guess_desktop guess_dbus - http_url auth xauth users rootshift clipshift scale_str - scaled_x scaled_y scale_numer scale_denom scale_fac_x - scale_fac_y scaling_blend scaling_nomult4 scaling_pad - scaling_interpolate inetd privremote unsafe safer nocmds - passwdfile unixpw unixpw_nis unixpw_list ssl ssl_pem - sslverify stunnel stunnel_pem https httpsredir usepw - using_shm logfile o flag rmflag rc norc h help V version - lastmod bg sigpipe threads readrate netrate netlatency - pipeinput clients client_count pid ext_xtest ext_xtrap - ext_xrecord ext_xkb ext_xshm ext_xinerama ext_overlay - ext_xfixes ext_xdamage ext_xrandr rootwin num_buttons - button_mask mouse_x mouse_y grab_state pointer_pos - pointer_x pointer_y pointer_same pointer_root - pointer_mask bpp depth indexed_color dpy_x dpy_y wdpy_x - wdpy_y off_x off_y cdpy_x cdpy_y coff_x coff_y rfbauth - passwd viewpasswd - --QD variable Just like -query variable, but returns the default - value for that parameter (no running x11vnc server - is consulted) - --sync By default -remote commands are run asynchronously, that - is, the request is posted and the program immediately - exits. Use -sync to have the program wait for an - acknowledgement from the x11vnc server that command was - processed (somehow). On the other hand -query requests - are always processed synchronously because they have - to wait for the answer. - - Also note that if both -remote and -query requests are - supplied on the command line, the -remote is processed - first (synchronously: no need for -sync), and then - the -query request is processed in the normal way. - This allows for a reliable way to see if the -remote - command was processed by querying for any new settings. - Note however that there is timeout of a few seconds - (see the next paragraph) so if the x11vnc takes longer - than that to process the requests the requester will - think that a failure has taken place. - - The default is to wait 3.5 seconds. Or if cmd=stop - only 1.0 seconds. If cmd matches 'script:' then it - will wait up to 10.0 seconds. Set X11VNC_SYNC_TIMEOUT - to the number of seconds you want it to wait. - --query_retries str If a query fails to get a response from an x11vnc - server, retry up to n times. "str" is specified as - n[:t][/match] Optionally the delay between tries may - be specified by "t" a floating point time (default - 0.5 seconds.) Note: the response is not checked for - validity or whether it corresponds to the query sent. - The query "ping:mystring" may be used to help uniquely - identify the query. Optionally, a matching string after - a "/" will be used to check the result text. Up to - n retries will take place until the matching string is - found in the output text. If the match string is never - found the program's exit code is 1; if the match is - found it exits with 0. Note that there may be stdout - printed for each retry (i.e. multiple lines printed - out to stdout.) - Example: -query_retries 4:1.5/grab_state - --remote_prefix str Enable a remote-control communication channel for - connected VNC clients. str is a non-empty string. If a - VNC client sends rfbCutText having the prefix "str" - then the part after it is processed as though it were - sent via 'x11vnc -remote ...'. If it begins with - neither 'cmd=' nor 'qry=' then 'qry=' is assumed. - Any corresponding output text for that remote control - command is sent back to all client as rfbCutText. - The returned output is also prefixed with "str". - Example: -remote_prefix DO_THIS: - - Note that enabling -remote_prefix allows the remote - VNC viewers to run x11vnc -remote commands. Do not - use this option if they are not to be trusted. - --noremote Do not process any remote control commands or queries. --yesremote Do process remote control commands or queries. - Default: -yesremote - - A note about security wrt remote control commands. - If someone can connect to the X display and change - the property X11VNC_REMOTE, then they can remotely - control x11vnc. Normally access to the X display is - protected. Note that if they can modify X11VNC_REMOTE - on the X server, they have enough permissions to also - run their own x11vnc and thus have complete control - of the desktop. If the "-connect /path/to/file" - channel is being used, obviously anyone who can write - to /path/to/file can remotely control x11vnc. So be - sure to protect the X display and that file's write - permissions. See -privremote below. - - If you are paranoid and do not think -noremote is - enough, to disable the X11VNC_REMOTE property channel - completely use -novncconnect, or use the -safer option - that shuts many things off. - --unsafe A few remote commands are disabled by default - (currently: id:pick, accept:, gone:, and - rawfb:setup:) because they are associated with - running external programs. If you specify -unsafe, then - these remote-control commands are allowed. Note that - you can still specify these parameters on the command - line, they just cannot be invoked via remote-control. --safer Equivalent to: -novncconnect -noremote and prohibiting - -gui and the -connect file. Shuts off communcation - channels. --privremote Perform some sanity checks and disable remote-control - commands if it appears that the X DISPLAY and/or - connectfile can be accessed by other users. Once - remote-control is disabled it cannot be turned back on. --nocmds No external commands (e.g. system(3), popen(3), exec(3)) - will be run at all. --allowedcmds list "list" contains a comma separated list of the only - external commands that can be run. The full list of - associated options is: - - stunnel, ssl, unixpw, WAIT, zeroconf, id, accept, - afteraccept, gone, pipeinput, v4l-info, rawfb-setup, - dt, gui, ssh, storepasswd, passwdfile, custom_passwd, - findauth, crash. - - See each option's help to learn the associated external - command. Note that the -nocmds option takes precedence - and disables all external commands. - --deny_all For use with -remote nodeny: start out denying all - incoming clients until "-remote nodeny" is used to - let them in. - - - -These options are passed to LibVNCServer: - --rfbport port TCP port for RFB protocol --rfbwait time max time in ms to wait for RFB client --rfbauth passwd-file use authentication on RFB protocol - (use 'storepasswd' to create a password file) --rfbversion 3.x Set the version of the RFB we choose to advertise --permitfiletransfer permit file transfer support --passwd plain-password use authentication - (use plain-password as password, USE AT YOUR RISK) --deferupdate time time in ms to defer updates (default 40) --deferptrupdate time time in ms to defer pointer updates (default none) --desktop name VNC desktop name (default "LibVNCServer") --alwaysshared always treat new clients as shared --nevershared never treat new clients as shared --dontdisconnect don't disconnect existing clients when a new non-shared - connection comes in (refuse new connection instead) --httpdir dir-path enable http server using dir-path home --httpport portnum use portnum for http connection --enablehttpproxy enable http proxy support --progressive height enable progressive updating for slow links --listen ipaddr listen for connections only on network interface with - addr ipaddr. '-listen localhost' and hostname work too. - -libvncserver-tight-extension options: --disablefiletransfer disable file transfer --ftproot string set ftp root - - Pretty wild huh? Contact me if you have any questions or problems. - - Personally, I use: -x11vnc -rfbauth $HOME/.vnc/passwd -solid + We have seen a few cases where the hardware fb read speed is + greater than 65 MB/sec: on high end graphics workstations from SGI + and Sun, and also from a Linux user using nvidia proprietary + drivers for his nvidia video card. Update 2008: thankfully, these + sped up drivers are becoming more common on Linux and *BSD systems + and that makes x11vnc run somewhat more quickly. Sometimes they + have a read rate of over 400 MB/sec. + On XFree86/Xorg it is actually possible to increase the + framebuffer read speed considerably (10-100 times) by using the + Shadow Framebuffer (a copy of the framebuffer is kept in main + memory and this can be read much more quickly.) To do this one + puts the line Option "ShadowFB" "true" in the Device section of + the /etc/X11/XF86Config or /etc/X11/xorg.conf file. Note that this + disables 2D acceleration at the physical display and so that might + be unacceptable if one plays games, etc. on the machine's local + display. Nevertheless this could be handy in some circumstances, + e.g. if the slower speed while sitting at the physical display was + acceptable (this seems to be true for most video cards these + days.) Unfortunately it does not seem shadowfb can be turned on + and off dynamically... + Another amusing thing one can do is use Xvfb as the X server, e.g. + "xinit $HOME/.xinitrc -- /usr/X11R6/bin/Xvfb :1 -screen 0 + 1024x768x16" x11vnc can poll Xvfb efficiently via main memory. + It's not exactly clear why one would want to do this instead of + using vncserver/Xvnc, (perhaps to take advantage of an x11vnc + feature, such as framebuffer scaling or built-in SSL encryption), + but we mention it because it may be of use for special purpose + applications. You may need to use the "-cc 4" option to force Xvfb + to use a TrueColor visual instead of DirectColor. See also the + description of the -create option that does all of this + automatically for you (be sure to install the Xvfb package, e.g. + apt-get install xvfb.) + Also, a faster and more accurate way is to use the "dummy" + Xorg/XFree86 device driver (or our Xdummy wrapper script.) See + this FAQ for details. +* Somewhat surprisingly, the X11 mouse (cursor) shape is write-only + and cannot be queried from the X server. So traditionally in + x11vnc the cursor shape stays fixed at an arrow. (see the "-cursor + X" and "-cursor some" options, however, for a partial hack for the + root window, etc.) However, on Solaris using the SUN_OVL overlay + extension, x11vnc can show the correct mouse cursor when the + -overlay option is also supplied. A similar thing is done on IRIX + as well when -overlay is supplied. + More generally, as of Dec/2004 x11vnc supports the new XFIXES + extension (in Xorg and Solaris 10) to query the X server for the + exact cursor shape, this works pretty well except that cursors + with transparency (alpha channel) need to approximated to solid + RGB values (some cursors look worse than others.) +* Audio from applications is of course not redirected (separate + redirectors do exist, e.g. esd, see the FAQ on this below.) The + XBell() "beeps" will work if the X server supports the XKEYBOARD + extension. (Note that on Solaris XKEYBOARD is disabled by default. + Passing +kb to Xsun enables it.) +* The scroll detection algorithm for the -scrollcopyrect option can + give choppy or bunched up transient output and occasionally + painting errors. +* Using -threads can expose some bugs/crashes in libvncserver. diff --git a/doc/FAQ.md b/doc/FAQ.md new file mode 100755 index 0000000..65500d9 --- /dev/null +++ b/doc/FAQ.md @@ -0,0 +1,7505 @@ +# x11vnc FAQ + +## Building and Starting + +### Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed (null)" or "Xlib: connection to ":0.0" refused by server Xlib: No protocol specified" and then exits. What do I need to do? + +For the former error, you need to specify the X display to connect to +(it also needs to be on the same machine the x11vnc process is to run +on.) Set your DISPLAY environment variable (or use the -display +option) to specify it. Nearly always the correct value will be ":0" +(in fact, x11vnc will now assume :0 if given no other information.) + +For the latter error, you need to set up the X11 permissions +correctly. + +To make sure X11 permissions are the problem do this simple test: +while sitting at the physical X display open a terminal window +(gnome-terminal, xterm, etc.) You should be able to run x11vnc +successfully without any need for special steps or command line +options in that terminal (i.e. just type "x11vnc".) If that works OK +then you know X11 permissions are the only thing preventing it from +working when you try to start x11vnc via, say, a remote shell. + +How to Solve: See the xauth(1), Xsecurity(7), and xhost(1) man pages +or this Howto for much info on X11 permissions. For example, you may +need to set your XAUTHORITY environment variable (or use the -auth +option) to point to the correct MIT-MAGIC-COOKIE file (e.g. +/home/joe/.Xauthority or /var/gdm/:0.Xauth or /var/lib/kdm/A:0-crWk72K +or /tmp/.gdmzndVlR, etc, etc.), or simply be sure you run x11vnc as +the correct user (i.e. the user who is logged into the X session you +wish to view.) + +Note: The MIT cookie file contains the secret key that allows x11vnc +to connect to the desired X display. + +If, say, sshd has set XAUTHORITY to point to a random file it has +created for X forwarding that will cause problems. (Under some +circumstances even su(1) and telnet(1) can set XAUTHORITY. See also +the gdm parameter NeverPlaceCookiesOnNFS that sets XAUTHORITY to a +random filename in /tmp for the whole X session.) + +Running x11vnc as root is often not enough: you need to know where the +MIT-MAGIC-COOKIE file for the desired X display is. + +Example solution: + +``` +x11vnc -display :0 -auth /var/gdm/:0.Xauth +``` + +(this is for the display manager gdm and requires root permission to +read the gdm cookie file, see this faq for other display manager +cookie file names.) + +Note as of Feb/2007 you can also try the -find option instead of +"-display ..." and see if that finds your display and Xauthority. + +Less safe, but to avoid figuring out where the correct XAUTHORITY file +is, if the person sitting at the physical X session types "xhost ++localhost" then one should be able to attach x11vnc to the session +(from the same machine.) The person could then type "xhost -localhost" +after x11vnc has connected to go back to the default permissions. +Also, for some situations the "-users lurk=" option may soon be of use +(please read the documentation on the -users option.) + +To test out your X11 permissions from a remote shell, set DISPLAY and +possibly XAUTHORITY (see your shell's man page, bash(1), tcsh(1), on +how to set environment variables) and type xdpyinfo in the same place +you will be typing (or otherwise running) x11vnc. If information is +printed out about the X display (screen sizes, supported extensions, +color visuals info) that means the X11 permissions are set up +properly: xdpyinfo successfully connected to DISPLAY! You could also +type xclock and make sure no errors are reported (a clock should +appear on the X display, press Ctrl-C to stop it.) If these work, then +typing "x11vnc" in the same environment should also work. + +Important: if you cannot get your X11 permissions so that the xdpyinfo +or xclock tests work, x11vnc also will not work (all of these X +clients must be allowed to connect to the X server to function +properly.) + +Firewalls: Speaking of permissions, it should go without saying that +the host-level firewall will need to be configured to allow +connections in on a port. E.g. 5900 (default VNC port) or 22 (default +SSH port for tunnelling VNC.) Most systems these days have firewalls +turned on by default, so you will actively have to do something to +poke a hole in the firewall at the desired port number. See your +system administration tool for Firewall settings (Yast, Firestarter, +etc.) + +### Q-2: I can't get x11vnc and/or libvncserver to compile. + +Make sure you have gcc (or other C compiler) and all of the required +libraries and the corresponding -dev/-devel packages installed. These +include Xorg/XFree86, libX11, libjpeg, libz, libssl, ... and don't +forget the devs: libjpeg-dev, libssl-dev ... + +The most common build problem that people encounter is that the +necessary X11 libraries are installed on their system however it does +not have the corresponding -dev/-devel packages installed. These dev +packages include C header files and build-time .so symlink. It is a +shame the current trend in distros is to not install the dev package +by default when the the library runtime package is installed... (it +diminishes the power of open source) + +As of Nov/2006 here is a list of libraries that x11vnc usually likes +to use: + +``` +libc.so libX11.so libXtst.so libXext.so +libXfixes.so libXdamage.so libXinerama.so libXrandr.so +libz.so libjpeg.so libpthread.so +libssl.so libcrypto.so libcrypt.so +``` + +although x11vnc will be pretty usable with the subset: libc.so, +libX11.so, libXtst.so, libXext.so, libz.so, and libjpeg.so. + +After running the libvncserver configure, carefully examine the output +and the messages in the config.log file looking for missing +components. For example, if the configure output looks like: + +``` +checking how to run the C preprocessor... gcc -E +checking for X... no +checking for XkbSelectEvents in -lX11... no +checking for XineramaQueryScreens in -lXinerama... no +checking for XTestFakeKeyEvent in -lXtst... no +``` + +or even worse: + +``` +checking for C compiler default output file name... configure: error: +C compiler cannot create executables +See `config.log' for more details. +``` + +there is quite a bit wrong with the build environment. Hopefully +simply adding -dev packages and/or gcc or make will fix it. + +For Debian the list seems to be: + +``` +gcc +make +libc6-dev +libjpeg8-dev (formerly libjpeg62-dev) +libx11-dev +x11proto-core-dev (formerly x-dev) +libxext-dev +libxtst-dev +libxdamage-dev +libxfixes-dev +libxrandr-dev +libxinerama-dev +libxss-dev (formerly xlibs-static-dev) +zlib1g-dev +libssl-dev +libavahi-client-dev +linux-libc-dev (only needed for linux console rawfb support) +``` + +Note that depending on your OS version the above names may have been +changed and/or additional packages may be needed. + +For Redhat the list seems to be: + +``` +gcc +make +glibc-devel +libjpeg-devel +libX11-devel +xorg-x11-proto-devel +libXdamage-devel +libXfixes-devel +libXrandr-devel +zlib-devel +openssl-devel +avahi-devel +kernel-headers (only needed for linux console rawfb support) +``` + +For other distros or OS's the package names may not be the same but +will look similar. Also, distros tend to rename packages as well so +the above list may be out of date. So only use the above lists as +hints for the package names that are needed. + +Have a look at Misc. Build Problems for additional fixes. + +Note: there is growing trend in Linux and other distros to slice up +core X11 software into more and smaller packages. So be prepared for +more headaches compiling software... + +### Q-3: I just built x11vnc successfully, but when I use it my keystrokes and mouse button clicks are ignored (I am able to move the mouse though.) + +This is most likely due to you not having a working build environment +for the XTEST client library libXtst.so. The library is probably +present on your system, but the package installing the build header +file is missing. + +If you were watching carefully while configure was running you would +have seen: +checking for XTestFakeKeyEvent in -lXtst... no + +The solution is to add the necessary build environment package (and +the library package if that is missing too.) On Debian the build +package is libxtst-dev. Other distros/OS's may have it in another +package. + +x11vnc will build without support for this library (e.g. perhaps one +wants a view-only x11vnc on a stripped down or embedded system...) And +at runtime it will also continue to run even if the X server it +connects to does not support XTEST. In both cases it cannot inject +keystrokes or button clicks since XTEST is needed for that (it can +still move the mouse pointer using the X API XWarpPointer().) + +You will see a warning message something like this at run time: + +``` +20/03/2005 22:33:09 WARNING: XTEST extension not available (either missing from +20/03/2005 22:33:09 display or client library libXtst missing at build time.) +20/03/2005 22:33:09 MOST user input (pointer and keyboard) will be DISCARDED. +20/03/2005 22:33:09 If display does have XTEST, be sure to build x11vnc with +20/03/2005 22:33:09 a working libXtst build environment (e.g. libxtst-dev, +20/03/2005 22:33:09 or other packages.) +20/03/2005 22:33:09 No XTEST extension, switching to -xwarppointer mode for +20/03/2005 22:33:09 pointer motion input. +``` + +Also, as of Nov/2006 there will be a configure build time warning as +well: + +``` +... +checking for XFixesGetCursorImage in -lXfixes... yes +checking for XDamageQueryExtension in -lXdamage... yes +configure: WARNING: +========================================================================== +A working build environment for the XTEST extension was not found (libXtst). +An x11vnc built this way will be only barely usable. You will be able to +move the mouse but not click or type. There can also be deadlocks if an +application grabs the X server. + +It is recommended that you install the necessary development packages +for XTEST (perhaps it is named something like libxtst-dev) and run +configure again. +========================================================================== +``` + +### Q-4: Help, I need to run x11vnc on Solaris 2.5.1 (or other old Unix/Linux) and it doesn't compile! + +We apologize that x11vnc does not build cleanly on older versions of +Solaris, Linux, etc.: very few users are on these old releases. + +We have heard that since Dec/2004 a Solaris 2.6 built x11vnc will run +on Solaris Solaris 2.5 and 2.5.1 (since a workaround for XConvertCase +is provided.) + +In any event, here is a workaround for Solaris 2.5.1 (and perhaps +earlier and perhaps non-Solaris): + +First use the environment settings (CPPFLAGS, LDFLAGS, etc.) in the +above Solaris build script to run the configure command. That should +succeed without failure. Then you have to hand edit the autogenerated +rfb/rfbconfig.h file in the source tree, and just before the last +#endif at the bottom of that file insert these workaround lines: + +``` +struct timeval _tmp_usleep_tv; +#define usleep(x) \ + _tmp_usleep_tv.tv_sec = (x) / 1000000; \ + _tmp_usleep_tv.tv_usec = (x) % 1000000; \ + select(0, NULL, NULL, NULL, &_tmp_usleep_tv); +int gethostname(char *name, int namelen); +long random(); +int srandom(unsigned int seed); +#undef LIBVNCSERVER_HAVE_LIBPTHREAD +#define SHUT_RDWR 2 +typedef unsigned int in_addr_t; +#define snprintf(a, n, args...) sprintf((a), ## args) +``` + +Then run make with the Solaris build script environment, everything +should compile without problems, and the resulting x11vnc binary +should work OK. If some non-x11vnc related programs fail (e.g. test +programs) and the x11vnc binary is not created try "make -k" to have +it keep going. Similar sorts of kludges in rfb/rfbconfig.h can be done +on other older OS (Solaris, Linux, ...) releases. + +Here are some notes for similar steps that need to be done to build on +SunOS 4.x + +Please let us know if you had to use the above workaround (and whether +it worked or not.) If there is enough demand we will try to push clean +compilations back to earlier Solaris, Linux, etc, releases. + +### Q-5: Where can I get a precompiled x11vnc binary for my Operating System? + +Hopefully the build steps above and FAQ provide enough info for a +painless compile for most environments. Please report problems with +the x11vnc configure, make, etc. on your system (if your system is +known to compile other GNU packages successfully.) + +There are precompiled x11vnc binaries built by other groups that are +available at the following locations: + +* Slackware: (.tgz) http://www.linuxpackages.net/ +* SuSE: (.rpm) http:/software.opensuse.org/ +* Gentoo: (info) + http://gentoo-wiki.com/ and http://gentoo-portage.com/ +* FreeBSD: (.tbz) + http://www.freebsd.org/ http://www.freshports.org/net/x11vnc +* NetBSD: (src) http://pkgsrc.se/x11/x11vnc +* OpenBSD: (.tgz) http://openports.se/ +* Arch Linux: (.tgz) http://www.archlinux.org/ +* Nokia 770 (.deb) http://mike.saunby.googlepages.com/x11vncfornokia7702 +* Sharp Zaurus: http://www.focv.com/ +* Debian: (.deb) http://packages.debian.org/x11vnc +* Redhat/Fedora: (.rpm) http://packages.sw.be/x11vnc RPMforge + http://dag.wieers.com/rpm/packages/x11vnc/ (N.B.: unmaintained after + 0.9.3) +* Solaris: (pkg) http://www.sunfreeware.com/ + +If the above binaries don't work and building x11vnc on your OS fails +(and all else fails!) you can try one of My Collection of x11vnc +Binaries for various OS's and x11vnc releases. + +As a general note, the x11vnc program is simple enough you don't +really need to install a package: the binary will in most cases work +as is and from any location (as long as your system libraries are not +too old, etc.) So, for Linux distributions that are not one of the +above, the x11vnc binary from the above packages has a good chance of +working. You can "install" it by just copying the x11vnc binary to the +desired directory in your PATH. Tip on extracting files from a Debian +package: extract the archive via a command like: "ar x +x11vnc_0.6-2_i386.deb" and then you can find the binary in the +resulting data.tar.gz tar file. Also, rpm2cpio(1) is useful in +extracting files from rpm packages. + +If you use a standalone binary like this and also want x11vnc to serve +up the Java VNC Viewer jar file (either SSL enabled or regular one), +then you will need to extract the classes subdirectory from the source +tarball and point x11vnc to it via the -httpdir option. E.g.: +x11vnc -httpdir /path/to/x11vnc-0.9.9/classes/ssl ... + +Alternatively, you can also go for a more up-to-date approach and use +the very decent noVNC viewer (https://kanaka.github.io/noVNC/) that is +purely HTML5 and does not need any plugins at all. + + +### Q-6: Where can I get a VNC Viewer binary (or source code) for the Operating System I will be viewing from? + +To obtain VNC viewers for the viewing side (Windows, Mac OS, or Unix) +try here: + +* http://www.tightvnc.com/download.html +* http://www.realvnc.com/download-free.html +* http://sourceforge.net/projects/cotvnc/ +* http://www.ultravnc.com/ +* Our Enhanced TightVNC Viewer (SSVNC)[ssvnc.gif] + +### Q-7: How can I see all of x11vnc's command line options and documentation on how to use them? + +Run: x11vnc -opts to list just the option names or run: x11vnc +-help for long descriptions about each option. The output is listed +here as well. Yes, x11vnc does have a lot of options, doesn't it... + +### Q-8: I don't like typing arcane command line options every time I start x11vnc. What can I do? Is there a config file? Or a GUI? + +You could create a shell script that calls x11vnc with your options: + +``` +#!/bin/sh +# +# filename: X11vnc (i.e. not "x11vnc") +# It resides in a directory in $PATH. "chmod 755 X11vnc" has been run on it. +# +x11vnc -wait 50 -localhost -rfbauth $HOME/.vnc/passwd -display :0 $* +``` + +a similar thing can be done via aliases in your shell (bash, tcsh, +csh, etc..) + +Or as of Jun/2004 you can use the simple $HOME/.x11vncrc config file +support. If that file exists, each line is taken as a command line +option. E.g. the above would be: + +``` +# this is a comment in my ~/.x11vncrc file +wait 50 # this is a comment to the end of the line. +-localhost # note: the leading "-" is optional. +rfbauth /home/fred/.vnc/passwd +display :0 +``` + +As of Dec/2004 there is now a simple Tcl/Tk GUI based on the +remote-control functionality ("-R") that was added. The /usr/bin/wish +program is needed for operation. The gui is not particularly +user-friendly, it just provides a point and click mode to set all the +many x11vnc parameters and obtain help on them. It is also very useful +for testing. See the -gui option for more info. Examples: "x11vnc ... +-gui" and "x11vnc ... -gui other:0" in the latter case the gui is +displayed on other:0, not the X display x11vnc is polling. There is +also a "-gui tray" system tray mode. + +[tkx11vnc.gif] + +NOTE: You may need to install the "wish" or "tk" or "tk8.4" package +for the gui mode to work (the package name depends on your OS/distro.) +The tcl/tk "wish" interpreter is used. In debian (and so ubuntu too) +one would run "apt-get install tk" or perhaps "apt-get install tk8.4" + +### Q-9: How can I get the GUI to run in the System Tray, or at least be a smaller, simpler icon? + +As of Jul/2005 the gui can run in a more friendly small icon mode +"-gui icon" or in the system tray: "-gui tray". It has balloon status, +a simple menu, and a Properities dialog. The full, complicated, gui is +only available under "Advanced". Other improvements were added as +well. Try "Misc -> simple_gui" for a gui with fewer esoteric menu +items. + +If the gui fails to embed itself in the system tray, do a retry via +"Window View -> icon" followed by "Window View -> tray" with the popup +menu. + +For inexperienced users starting up x11vnc and the GUI while sitting +at the physical X display (not remotely), using something like "x11vnc +-display :0 -gui tray=setpass" might be something for them that they +are accustomed to in a Desktop environment (it prompts for an initial +password, etc.) This is a basic "Share My Desktop" usage mode. + +As of Nov/2008 in x11vnc 0.9.6 there is a desktop menu item +(x11vnc.desktop) that runs this command: + +``` +x11vnc -gui tray=setpass -rfbport PROMPT -logfile %HOME/.x11vnc.log.%VNCDISPLAY +``` + +which also prompts for which VNC port to use and a couple other +parameters. + + +### Q-10: How can I get x11vnc to listen on a different port besides the default VNC port (5900)? + +Use something like, e.g., "x11vnc -rfbport 5901" to force it to use +port 5901 (this is VNC display :1.) If something else is using that +port x11vnc will exit immediately. If you do not supply the -rfbport +option, it will autoprobe starting at 5900 and work its way up to 5999 +looking for a free port to listen on. In that case, watch for the +PORT=59xx line to see which port it found, then subtract 5900 from it +for the VNC display number to enter into the VNC Viewer(s). + +The "-N" option will try to match the VNC display number to the X +display (e.g. X11 DISPLAY of :5 (port 6005) will have VNC display :5 +(port 5905).) + +Also see the "-autoport n" option to indicated at which value the auto +probing should start at. + + +### Q-11: My Firewall/Router doesn't allow VNC Viewers to connect to x11vnc. + +See the Firewalls/Routers discussion. + + +### Q-12: Is it possible for a VNC Viewer and a VNC Server to connect to each other even though both are behind Firewalls that block all incoming connections? + +This is very difficult or impossible to do unless a third machine, +reachable by both, is used as a relay. So we assume a third machine is +somehow being used as a relay. + +(Update: It may be possible to do "NAT-2-NAT" without a relay machine +by using a UDP tunnel such as http://samy.pl/pwnat/. All that is +required is that both NAT firewalls allow in UDP packets from an IP +address to which a UDP packet has recently been sent to. If you try it +out let us know how it went.) + +In the following discussion, we will suppose port 5950 is being used +on the relay machine as the VNC port for the rendezvous. + +A way to rendezvous is to have the VNC Server start a reverse +connection to the relay machine: +x11vnc -connect third-machine.net:5950 ... + +and the VNC viewer forward connects as usual: +vncviewer third-machine.net:50 + +Or maybe two ports would be involved, e.g. the viewer goes to display +:51 (5951.) It depends on the relay software being used. + +What software to run on third-machine? A TCP relay of some sort could +be used... Try a google search on "tcp relay" or "ip relay". However, +note that this isn't a simple redirection because it hooks up two +incoming connections. You can look at our UltraVNC repeater +implementation ultravnc_repeater.pl for ideas and possibly to +customize. + +Also, if you are not the admin of third-machine you'd have to convince +the owner to allow you to install this software (and he would likely +need to open his server's firewall to allow the port through.) + +It is recommended that SSL is used for encryption (e.g. "-ssl SAVE") +when going over the internet. + +We have a prototype for performing a rendezvous via a Web Server +acting as the relay machine. Download the vncxfer CGI script and see +the instructions at the top. + +Once that CGI script is set up on the website, both users go to, say, +http://somesite.com/vncxfer (or maybe a "/cgi-bin" directory or ".cgi" +suffix must be used.) Previously, both have agreed on the same session +name (say by phone or email) , e.g. "5cows", and put that into the +entry form on the vncxfer starting page (hopefully separated by a few +seconds, so the relay helper can fully start up at the first request.) + +The page returned tells them the hostname and port number and possible +command to use for forward (VNC Viewer) and reverse (VNC Server, i.e. +x11vnc) connections as described above. + +Also since Oct/2007, x11vnc can connect directly (no web browser), +like this: + +``` +x11vnc ... -connect localhost:0 -proxy 'http://somesite.com/vncxfer?session=5cows&' +``` + +Unfortunately the prototype requires that the Web server's firewall +allow in the port (e.g. 5950) used for the rendezvous. Most web +servers are not configured to do this, so you would need to ask the +admin to do this for you. Nearly all free webspace sites, e.g. +www.zendurl.com, will not allow your CGI script to be an open relay +like this. (If you find one that does allow this, let me know!) + +Maybe someday a clever trick will be thought up to relax the listening +port requirement (e.g. use HTTP/CGI itself for the transfer... it is +difficult to emulate a full-duplex TCP connection with them.) + +See also the Firewalls/Routers discussion and Reverse Connection Proxy +discussion. + +SSH method: If both users (i.e. one on Viewer-side and the other on +x11vnc server side) have SSH access to a common machine on the +internet (or otherwise mutually reachable), then SSH plumbing can be +used to solve this problem. The users create SSH tunnels going through +the SSH login machine. + +Instead of assuming port 5900 is free on the SSH machine, we will +assume both users agreed to use 5933. This will illustrate how to use +a different port for the redir. It could be any port, what matters is +that both parties refer to the same one. + +Set up the Tunnel from the VNC Server side: + +``` +ssh -t -R 5933:localhost:5900 user@third-machine.net +``` + +Set up the Tunnel from the VNC Viewer side: + +``` +ssh -t -L 5900:localhost:5933 user@third-machine.net +``` + + Run Server on the VNC Server side: + +``` +x11vnc -rfbport 5900 -localhost ... +``` + + Run Viewer on the VNC Viewer side: + +``` +vncviewer -encodings "copyrect tight zrle hextile" localhost:0 +``` + +(we assume the old-style -encodings option needs to be used. See here +for details.) + +If the SSH machine has been configured (see sshd_config(5)) with the +option GatewayPorts=yes, then the tunnel set up by the VNC Server will +be reachable directly by the VNC viewer (as long as the SSH machine's +firewall does not block the port, 5933 in this example.) So in that +case the Viewer side does not need to run any ssh command, but rather +only runs: +vncviewer third-machine.net:33 + +In this case we recommend SSL be used for encryption. + +The creation of both tunnels can be automated. As of Oct/2007 the -ssh +x11vnc option is available and so only this command needs to be run on +the VNC Server side: +x11vnc -ssh user@third-machine.net:33 ... + +(the SSH passphrase may need to be supplied.) + +To automate on the VNC Viewer side, the user can use the Enhanced +TightVNC Viewer (SSVNC) by: + +* Clicking on 'Use SSH' +* Entering user@third-machine.net:33 into 'VNC Host:Display' entry + box +* Clicking on 'Connect' + +As above, if the SSH GatewayPorts=yes setting is configured the Viewer +side doesn't need to create a SSH tunnel. In SSVNC the Viewer user +could instead select 'Use SSL' and then, e.g., on the Server side +supply "-ssl SAVE" to x11vnc. Then end-to-end SSL encryption would be +used (in addition to the SSH encryption on the Server-side leg.) + + +### Q-13: Can I make x11vnc more quiet and also go into the background after starting up? + +Use the -q and -bg options, respectively. (also: -quiet is an alias +for -q) + +Note that under -bg the stderr messages will be lost unless you use +the "-o logfile" option. + + +### Q-14: Sometimes when a VNC viewer dies abruptly, x11vnc also dies with the error message like: "Broken pipe". I'm using the -forever mode and I want x11vnc to keep running. + +As of Jan/2004 the SIGPIPE signal is ignored. So if a viewer client +terminates abruptly, libvncserver will notice on the next I/O +operation and will close the connection and continue on. + +Up until of Apr/2004 the above fix only works for BSD signal systems +(Linux, FreeBSD, ...) For SYSV systems there is a workaround in place +since about Jun/2004. + + +### Q-15: The Windows TightVNC 1.3.9 Viewer cannot connect to x11vnc. + +This appears to be fixed in x11vnc version 0.9 and later. If you need +to use an earlier version of x11vnc, try using the "-rfbversion 3.7" +option. In general sometimes one can get a misbehaving viewer to work +by supplying rfb versions 3.7 or 3.3. + + +### Q-16: KDE's krdc VNC viewer cannot connect to x11vnc. + +This has been fixed in x11vnc version 0.8.4. More info here, here, and +here. + + +### Q-17: When I start x11vnc on an Alpha Tru64 workstation the X server crashes! + +This is a bug in the X server obviously; an X client should never be +able to crash it. + +The problem seems to be with the RECORD X extension and so a +workaround is to use the "-noxrecord" x11vnc command line option. + + +### Q-18: When running x11vnc on an IBM AIX workstation after a few minutes the VNC connection freezes. + +One user reports when running x11vnc on AIX 5.3 in his CDE session +after a few minutes or seconds x11vnc will "freeze" (no more updates +being sent, etc.) The freezing appeared to be worse for versions later +than 0.9.2. + +The problem seems to be with the RECORD X extension on AIX and so a +workaround is to use the "-noxrecord" x11vnc command line option. The +user found no freezes occurred when using that option. + + +### Q-19: Are there any build-time customizations possible, e.g. change defaults, create a smaller binary, etc? + +There are some options. They are enabled by adding something like +-Dxxxx=1 to the CPPFLAGS environment variable before running configure +(see the build notes for general background.) + +``` +/* + * Mar/2006 + * Build-time customization via CPPFLAGS. + * + * Summary of options to include in CPPFLAGS for custom builds: + * + * -DVNCSHARED to have the vnc display shared by default. + * -DFOREVER to have -forever on by default. + * -DNOREPEAT=0 to have -repeat on by default. + * -DADDKEYSYMS=0 to have -noadd_keysyms the default. + * + * -DREMOTE_DEFAULT=0 to disable remote-control on by default (-yesremote.) + * -DREMOTE_CONTROL=0 to disable remote-control mechanism completely. + * -DEXTERNAL_COMMANDS=0 to disable the running of all external commands. + * -DFILEXFER=0 disable filexfer. + * + * -DHARDWIRE_PASSWD=... hardwired passwords, quoting necessary. + * -DHARDWIRE_VIEWPASSWD=... + * -DNOPW=1 make -nopw the default (skip warning) + * -DUSEPW=1 make -usepw the default + * -DPASSWD_REQUIRED=1 exit unless a password is supplied. + * -DPASSWD_UNLESS_NOPW=1 exit unless a password is supplied and no -nopw. + * + * -DWIREFRAME=0 to have -nowireframe as the default. + * -DWIREFRAME_COPYRECT=0 to have -nowirecopyrect as the default. + * -DWIREFRAME_PARMS=... set default -wirecopyrect parameters. + * -DSCROLL_COPYRECT=0 to have -noscrollcopyrect as the default. + * -DSCROLL_COPYRECT_PARMS=... set default -scrollcopyrect parameters. + * -DSCALING_COPYRECT=0 + * -DXDAMAGE=0 to have -noxdamage as the default. + * -DSKIPDUPS=0 to have -noskip_dups as the default or vice versa. + * + * -DPOINTER_MODE_DEFAULT={0,1,2,3,4} set default -pointer_mode. + * -DBOLDLY_CLOSE_DISPLAY=0 to not close X DISPLAY under -rawfb. + * -DSMALL_FOOTPRINT=1 for smaller binary size (no help, no gui, etc) + * use 2 or 3 for even smaller footprint. + * -DNOGUI do not include the gui tkx11vnc. + * -DPOLL_8TO24_DELAY=N + * -DDEBUG_XEVENTS=1 enable printout for X events. + * + * Set these in CPPFLAGS before running configure. E.g.: + * + * % env CPPFLAGS="-DFOREVER -DREMOTE_CONTROL=0" ./configure + * % make + */ +``` + +If other things (e.g. "-I ...") are needed in CPPFLAGS add them as +well. + +On some systems is seems you need to set LC_ALL=C for configure to +work properly... + +Be careful the following two variables: HARDWIRE_PASSWD and +HARDWIRE_VIEWPASSWD. If set (remember to include the double quotes +around the string), they will be used as default values for the +-passwd and -viewpasswd options. Of course the strings will exist +unobscured in the x11vnc binary: it better not be readable by +unintendeds. Perhaps this is of use in remote access for an embedded +application, etc... + +Let us know if more build-time customizations would be useful. + + +## Win2VNC Related + +### Q-20: I have two separate machine displays in front of me, one Windows the other X11: can I use x11vnc in combination with Win2VNC in dual-screen mode to pass the keystrokes and mouse motions to the X11 display? + +Yes, for best response start up x11vnc with the "-nofb" option +(disables framebuffer polling, and does other optimizations) on the +secondary display (X11) machine. Then start up Win2VNC on the primary +display (Windows) referring it to the secondary display. + +This will also work X11 to X11 using x2vnc, however you would probably +just want to avoid VNC and use x2x for that. + +For reference, here are some links to Win2VNC-like programs for +multiple monitor setups: + +* Original Win2VNC +* Enhanced Win2VNC (broken?) and sourceforge link +* x2vnc +* x2x +* zvnc (MorphOS) + +All of them will work with x11vnc (except x2x where it is not needed.) + + +### Q-21: I am running Win2VNC on my Windows machine and "x11vnc -nofb" on Unix to pass keyboard and mouse to the Unix monitor. Whenever I start Win2VNC it quickly disconnects and x11vnc says: rfbProcessClientNormalMessage: read: Connection reset by peer + +Is the default visual of the X display you run x11vnc on low color +(e.g. 8 bit per pixel PseudoColor)? (you can run xdpyinfo to check, +look in the "screen" section.) There seems to be a bug in Win2VNC in +that it cannot deal correctly with colormaps (PseudoColor is the most +common example of a visual with a colormap.) + +If so, there are a couple options. 1) Can you set the default visual +on your display to be depth 24 TrueColor? Sun machines often have 8+24 +overlay/multi-depth visuals, and you can make the default visual depth +24 TrueColor (see fbconfig(1) and Xsun(1).) 2) As of Feb/2004 x11vnc +has the -visual option to allow you to force the framebuffer visual to +whatever you want (this usually messes up the colors unless you are +very clever.) In this case, the option provides a convenient +workaround for the Win2VNC bug: + +``` +x11vnc -nofb -visual TrueColor -display :0 ... +``` + +So the visual will be set to 8bpp TrueColor and Win2VNC can handle +this. Since Win2VNC does not use the framebuffer data there should be +no problems in doing this. + +### Q-22: Can I run "x11vnc -nofb" on a Mac OS X machine to redirect mouse and keyboard input to it from Windows and X11 machines via Win2VNC and x2vnc, respectively? + +Yes, as of Nov/2006 you can. There may be a trick or two you'll need +to do to get the Clipboard exchange between the machines to work. + + + +## Color Issues + +### Q-23: The X display I run x11vnc on is only 8 bits per pixel (bpp) PseudoColor (i.e. only 256 distinct colors.) The x11vnc colors may start out OK, but after a while they are incorrect in certain windows. + +Use the -flashcmap option to have x11vnc watch for changes in the +colormap, and propagate those changes back to connected clients. This +can be slow (since the whole screen must be updated over the network +whenever the colormap changes.) This flashing colormap behavior often +happens if an application installs its own private colormap when the +mouse is in its window. "netscape -install" is a well-known historical +example of this. Consider reconfiguring the system to 16 bpp or depth +24 TrueColor if at all possible. + +Also note the option -8to24 (Jan/2006) can often remove the need for +flashing the colormap. Everything is dynamically transformed to depth +24 at 32 bpp using the colormaps. There may be painting errors however +(see the following FAQ for tips on reducing and correcting them.) + +In some rare cases (SCO unixware) the -notruecolor option has +corrected colors on 8bpp displays. The red, green, and blue masks were +non-zero in 8bpp PseudoColor on an obscure setup, and this option +corrected the problems. + + +### Q-24: Color problems: Why are the colors for some windows incorrect in x11vnc? BTW, my X display has nice overlay/multi-depth visuals of different color depths: e.g. there are both depth 8 and 24 visuals available at the same time. + +You may want to review the previous question regarding 8 bpp +PseudoColor. + +On some hardware (Sun/SPARC and SGI), the -overlay option discussed a +couple paragraphs down may solve this for you (you may want to skip to +it directly.) On other hardware the less robust -8to24 option may help +(also discussed below.) + +Run xdpyinfo(1) to see what the default visual is and what the depths +of the other visuals are. Does the default visual have a depth of 8 +but there are other visuals of depth 24? If it does, can you possibly +re-configure your X server to make a depth 24 visual the default? If +you can do it, this will save you a lot of grief WRT colors and x11vnc +(and for general usage too!) Here is how I do this on an old +Sparcstation 20 running Solaris 9 with SX graphics + +``` +xinit -- -dev /dev/fb defclass TrueColor defdepth 24 +``` + +and it works nicely (note: to log into console from the dtlogin +window, select "Options -> Command Line Login", then login and enter +the above command.) See the -dev section of the Xsun(1) manpage for a +description of the above arguments. If you have root permission, a +more permanent and convenient thing to do is to record the arguments +in a line like: + +``` +:0 Local local_uid@console root /usr/openwin/bin/Xsun -dev /dev/fb defclass TrueColor defdepth 24 +``` + +in /etc/dt/config/Xservers (copy /usr/dt/config/Xservers.) Also look +at the fbconfig(1) and related manpages (e.g. ffbconfig, m64config, +pgxconfig, SUNWjfb_config, etc ...) for hardware framebuffer settings +that may achieve the same effect. + +In general for non-Sun machines, look at the "-cc class" and related +options in your X server manpage (perhaps Xserver(1)), it may allow +modifying the default visual (e.g. "-cc 4", see for the +visual class numbers.) On XFree86 some video card drivers (e.g. Matrox +mga) have settings like Option "Overlay" "24,8" to support multi-depth +overlays. For these, use the "-cc 4" X server command line option to +get a depth 24 default visual. + + +The -overlay mode: Another option is if the system with overlay +visuals is a Sun system running Solaris or SGI running IRIX you can +use the -overlay x11vnc option (Aug/2004) to have x11vnc use the +Solaris XReadScreen(3X11) function to poll the "true view" of the +whole screen at depth 24 TrueColor. XReadDisplay(3X11) is used on +IRIX. This is useful for Legacy applications (older versions of +Cadence CAD apps are mentioned by x11vnc users) that require the +default depth be 8bpp, or the app will use a 8bpp visual even if depth +24 visuals are available, and so the default depth workaround +described in the previous paragraph is not sufficient for these apps. + +It seems that Xorg is working toward supporting XReadDisplay(3X11) as +part of the RENDER extension work. When it does support it and +provides a library API x11vnc will be modified to take advantage of +the feature to support -overlay on Linux, *BSD, etc. Until then see +the -8to24 mode below. + +Misc. notes on -overlay mode: An amusing by-product of -overlay mode +is that the mouse cursor shape is correct! (i.e. XFIXES is not +needed.) The -overlay mode may be somewhat slower than normal mode due +to the extra framebuffer manipulations that must be performed. Also, +on Solaris there is a bug in that for some popup menus, the windows +they overlap will have painting errors (flashing colors) while the +popup is up (a workaround is to disable SaveUnders by passing -su to +Xsun, e.g. in your /etc/dt/config/Xservers file.) + + +The -8to24 mode: The -8to24 x11vnc option (Jan/2006) is a kludge to +try to dynamically rewrite the pixel values so that the 8bpp part of +the screen is mapped onto depth 24 TrueColor. This is less robust than +the -overlay mode because it is done by x11vnc outside of the X +server. So only use it on OS's that do not support -overlay. The +-8to24 mode will work if the default visual is depth 24 or depth 8. It +scans for any windows within 3 levels of the root window that are 8bpp +(i.e. legacy application), or in general ones that are not using the +default visual. For the windows it finds it uses XGetSubImage() to +retrieve the pixels values and uses the correct indexed colormap to +create a depth 24 TrueColor view of the whole screen. This depth 24, +32bpp view is exported via VNC. + +Even on pure 8bpp displays it can be used as an alternative to +-flashcmap to avoid color flashing completely. + +This scheme is approximate and can often lead to painting errors. You +can manually correct most painting errors by pressing 3 Alt_L's in a +row, or by using something like: -fixscreen V=3.0 to automatically +refresh the screen every 3 seconds. Also -fixscreen 8=3.0 has been +added to just refresh the non-default visual parts of the screen. + +In general the scheme uses many resources and may give rise to +sluggish behavior. If multiple windows are using different 8bpp +indexed colormaps all but one window may need to be iconified for the +colors to be correct. There are a number of tunable parameters to try +to adjust performance and painting accuracy. The option -8to24 +nogetimage can give a nice speedup if the default depth 24 X server +supports hiding the 8bpp bits in bits 25-32 of the framebuffer data. +On very slow machines -8to24 poll=0.2,cachewin=5.0 gives an useful +speedup. See the -8to24 help description for information on tunable +parameters, etc. + + +Colors still not working correctly? Run xwininfo on the application +with the incorrect colors to verify that the depth of its visual is +different from the default visual depth (gotten from xdpyinfo.) One +possible workaround in this case is to use the -id option to point +x11vnc at the application window itself. If the application is +complicated (lots of toplevel windows and popup menus) this may not be +acceptable, and may even crash x11vnc (but not the application.) See +also -appshare. + +It is theoretically possible to solve this problem in general (see +xwd(1) for example), but it does not seem trivial or sufficiently fast +for x11vnc to be able to do so in real time. The -8to24 method does +this approximately and is somewhat usable. Fortunately the -overlay +option works for Solaris machines with overlay visuals where most of +this problem occurs. + + +### Q-25: I am on a high color system (depth >= 24) but I seem to have colormap problems. They either flash or everything is very dark. + +This can happen if the default Visual (use xdpyinfo to list them) is +DirectColor instead of TrueColor. These are both usually used in high +color modes, but whereas TrueColor uses static ramps for the Red, +Green, and Blue components, DirectColor has arbitrary colormaps for +the Red, Green, and Blue Components. Currently x11vnc cannot decode +these colormaps and treats them just like TrueColor. + +The only workaround so far is to restart the X server with the "-cc 4" +option to force TrueColor as the default visual (DirectColor is "-cc +5"; see /usr/include/X11/X.h.) The only place we have seen this is +with the virtual framebuffer server Xvfb on Xorg 7.2. So in that case +you probably should restart it with something like this: "Xvfb :1 -cc +4 -screen 0 1280x1024x24". It should be possible for x11vnc to handle +DirectColor, but this hasn't been implemented due to its rare usage. + +You may also see this problem on an X display with a TrueColor default +visual where an application chooses a DirectColor visual for its +window(s). It seems the application also needs to install its own +colormap for the visual for the colors to be messed up in x11vnc. One +can make xwud do this for example. + + +### Q-26: How do I figure out the window id to supply to the -id windowid option? + +Run the xwininfo program in a terminal. It will ask you to click on +the desired application window. After clicking, it will print out much +information, including the window id (e.g. 0x6000010.) Also, the +visual and depth of the window printed out is often useful in +debugging x11vnc color problems. + +Also, as of Dec/2004 you can use "-id pick" to have x11vnc run +xwininfo(1) for you and after you click the window it extracts the +windowid. Besides "pick" there is also "id:root" to allow you to go +back to root window when doing remote-control. + + +### Q-27: Why don't menus or other transient windows come up when I am using the -id windowid option to view a single application window? + +This is related to the behavior of the XGetImage(3X11) and +XShmGetImage() interfaces regarding backingstore, saveunders, etc. The +way the image is retrieved depends on some aspects of how the X server +maintains the display image data and whether other windows are +clipping or obscuring it. See the XGetImage(3X11) man page for more +details. If you disable BackingStore and SaveUnders in the X server +you should be able to see these transient windows. + +If things are not working and you still want to do the single window +polling, try the -sid windowid option ("shifted" windowid.) + +Update: as of Nov/2009 in the 0.9.9 x11vnc development tarball, there +is an experimental Application Sharing mode that improves upon the +-id/-sid single window sharing: -appshare (run "x11vnc -appshare +-help" for more info.) It is still very primitive and approximate, but +at least it displays multiple top-level windows. + + +### Q-28: My X display is depth 24 at 24bpp (instead of the normal depth 24 at 32bpp.) I'm having lots of color and visual problems with x11vnc and/or vncviewer. What's up? + +First off, depth 24 at 24bpp (bpp=bits-per-pixel) is fairly uncommon +and can cause problems in general. It also can be slower than depth 24 +at 32bpp. You might want to switch to 32bpp (for XFree86 see the +"-fbbpp 32", DefaultFbBpp, FbBpp and related options.) Perhaps you +have 24bpp because the video memory of the machine is low and the +screen wouldn't fit in video RAM at 32bpp. For this case depth 16 at +16bpp might be an acceptable option. + +In any event x11vnc should handle depth 24 at 24bpp (although +performance may be slower, and you may need to use the ZRLE encoding +instead of Tight.) There are some caveats involving the viewer +however: + +The RealVNC Unix viewer cannot handle 24bpp from the server, it will +say: "main: setPF: not 8, 16 or 32 bpp?" and exit. I have not checked +the RealVNC Windows viewer. + +So you need to use the TightVNC Unix viewer. However there are some +problems with that too. It seems libvncserver does not do 24bpp +correctly with the Tight encoding. The colors and screen ultimately +get messed up. So you have to use a different encoding with the +TightVNC vncviewer, try "zlib", "hextile", or one of the other +encodings (e.g. vncviewer -encodings "zlib hextile" ....) I have not +checked the TightVNC or UltraVNC Windows viewers. + +It appears the older RealVNC Unix viewers (e.g. 3.3.3 and 3.3.7) can +handle 24bpp from the server, so you may want to use those. They +evidently request 32 bpp and libvncserver obliges. + +Update: as of Apr/2006 you can use the -24to32 option to have x11vnc +dynamically transform the 24bpp pixel data to 32bpp. This extra +transformation could slow things down further however. + +Now coming the opposite direction if you are running the vncviewer on +the 24bpp display, TightVNC will fail with "Can't cope with 24 +bits-per-pixel. Sorry." and RealVNC will fail with "main: Error: +couldn't find suitable pixmap format" so evidently you cannot use +24bpp for the vncviewers to work on that X display. + +Note, however, that the Unix viewer in the Enhanced TightVNC Viewer +(SSVNC) project can handle 24bpp X displays. It does this by +requesting a 16bpp pixel format (or 8bpp if the -bgr233 option has +been supplied) from the VNC server, and translates that to 24bpp +locally. + +## Xterminals + +### Q-29: Can I use x11vnc to view and interact with an Xterminal (e.g. NCD) that is not running UNIX and so x11vnc cannot be run on it directly? + +You can, but it will likely be very wasteful of network bandwidth +since you will be polling the X display over the network as opposed to +over the local hardware. To do this, run x11vnc on a UNIX machine as +close as possible network-wise (e.g. same switch) to the Xterminal +machine. Use the -display option to point the display to that of the +Xterminal (you'll of course need basic X11 permission to do that) and +finally supply the -noshm option (this enables the polling over the +network.) + +If the Xterminal's X display is open to the network for connections, +you might use something like "-display xterm123:0". If you are trying +to do this via an SSH tunnel (assuming you can actually ssh into the +Xterminal) it will be a little tricky (either use the ssh "-R" option +or consider ssh-ing in the other direction.) In all cases the X11 +permissions need to allow the connection. + +The response will likely be sluggish (maybe only one "frame" per +second.) This mode is not recommended except for "quick checks" of +hard to get to X servers. Use something like "-wait 150" to cut down +on the polling rate. You may also need -flipbyteorder if the colors +get messed up due to endian byte order differences. + + +### Q-30: How do I get my X permissions (MIT-MAGIC-COOKIE file) correct for a Unix/Linux machine acting as an Xterminal? + +If the X display machine is a traditional Xterminal (where the X +server process runs on the Xterminal box, but all of the X client +applications (firefox, etc) run on a central server (aka "terminal +server")), you will need to log into the Xterminal machine (i.e. get a +shell running there) and then start the x11vnc program. If the +Xterminal Linux/Unix machine is stripped down (e.g. no users besides +root) that may be difficult. + +The next problem is the login Display Manager (e.g. gdm, kdm), and +hence the MIT-MAGIC-COOKIE auth files, are on the central server and +not on the Xterminal box where the X server and x11vnc processes are. + +So unless X permissions are completely turned off (e.g. "xhost +"), to +run the x11vnc process on the Xterminal box the MIT-MAGIC-COOKIE auth +file data (XAUTHORITY or $HOME/.Xauthority) must be accessible by or +copied to the Xterminal. If $HOME/.Xauthority is exported via NFS +(this is insecure of course, but has been going on for decades), then +x11vnc can simply pick it up via NFS (you may need to use the -auth +option to point to the correct file.) Other options include copying +the auth file using scp, or something like: + +``` +central-server> xauth nextract - xterm123:0 | ssh xterm123 xauth nmerge - +``` + +and then, say, ssh from central-server to xterm123 to start x11vnc. +Here "xterm123" refers to the computer acting as the Xterminal and +"central-server" is the terminal server. You can use "xauth -f +/path/to/cookie-file list" to examine the contents of the cookie(s) in +a file "/path/to/cookie-file". See the xauth(1) manpage for more +details. + +If the display name in the cookie file needs to be changed between the +two hosts, see this note on the "xauth add ..." command. + +A less secure option is to run something like "xhost +127.0.0.1" while +sitting at the Xterminal box to allow cookie-free local access for +x11vnc. You can run "xhost -127.0.0.1" after x11vnc connects if you +want to go back to the original permissions. + +If the Xterminal is really stripped down and doesn't have any user +accounts, NFS, etc. you'll need to contact your system administrator +to set something up. It can be done!!! Some Xterminal projects have +actually enabled "run locally" facilities for the running of an +occasional app more efficiently locally on the Xterminal box (e.g. +realplayer.) + +Not recommended, but as a last resort, you could have x11vnc poll the +Xterminal Display over the network. For this you would run a "x11vnc +-noshm ..." process on the central-server (and hope the network admin +doesn't get angry...) + +Note: use of Display Manager (gdm, kdm, ...) auth cookie files (i.e. +from /var/..., /tmp/..., or elsewhere) may require modification via +xauth(1) to correctly include the display x11vnc refers to (e.g. +"xauth -f cookie-file add :0 . 45be51ae2ce9dfbacd882ab3ef8e96b1", +where the "45be51..." cookie value was found from an "xauth -f +/path/to/original/cookie-file list") or other reasons. See xauth(1) +manpage for full details on how to transfer an MIT-MAGIC-COOKIE +between machines and displays. + +VNCviewer performance on Xterminals: This isn't related to x11vnc on +Xterminals, but we mention it here anyway because of the similar +issues. If you are on an Xterminal and want to use vncviewer to +connect to a VNC server somewhere, then performance would be best if +you ran the viewer on the Xterminal box. Otherwise, (i.e. running the +viewer process on the central-server) all of the vncviewer screen +drawing is done more inefficiently over the network. Something to +consider, especially on a busy network. (BTW, this has all of the +above permission, etc, problems: both vncviewer and x11vnc are X +client apps desired to be run on the Xterminal box.) + +## Sun Rays + +### Q-31: I'm having trouble using x11vnc with my Sun Ray session. + +The Sun Ray technology is a bit like "VNC done in hardware" (the Sun +Ray terminal device, DTU, playing the role of the vncviewer.) +Completely independent of that, the SunRay user's session is still an +X server that speaks the X11 protocol and so x11vnc simply talks to +the X server part to export the SunRay desktop to any place in the +world (i.e. not only to a Sun Ray terminal device), creating a sort of +"Soft Ray". Please see this discussion of Sun Ray issues for solutions +to problems. + +Also see the Sun Ray Remote Control Toolkit that uses x11vnc. + + +## Remote Control + +### Q-32: How do I stop x11vnc once it is running in the background? + +As of Dec/2004 there is a remote control feature. It can change a huge +number of parameters on the fly: see the -remote and -query options. +To shut down the running x11vnc server just type "x11vnc -R stop". To +disconnect all clients do "x11vnc -R disconnect:all", etc. + +If the -forever option has not been supplied, x11vnc will +automatically exit after the first client disconnects. In general if +you cannot use the remote control, then you will have to kill the +x11vnc process This can be done via: "kill NNNNN" (where NNNNN is the +x11vnc process id number found from ps(1)), or "pkill x11vnc", or +"killall x11vnc" (Linux only.) + +If you have not put x11vnc in the background via the -bg option or +shell & operator, then simply press Ctrl-C in the shell where x11vnc +is running to stop it. + +Potential Gotcha: If somehow your Keypress of Ctrl-C went through +x11vnc to the Xserver that then delivered it to x11vnc it is possible +one or both of the Ctrl or C keys will be left stuck in the pressed +down state in the Xserver. Tapping the stuck key (either via a new +x11vnc or at the physical console) will release it from the stuck +state. If the keyboard seems to be acting strangely it is often fixed +by tapping Ctrl, Shift, and Alt. Alternatively, the -clear_mods option +and -clear_keys option can be used to release pressed keys at startup +and exit. The option -clear_all will also try to unset Caps_Lock, +Num_Lock, etc. + + +### Q-33: Can I change settings in x11vnc without having to restart it? Can I remote control it? + +Look at the -remote (an alias is -R) and -query (an alias is -Q) +options added in Dec/2004. They allow nearly everything to be changed +dynamically and settings to be queried. Examples: "x11vnc -R shared", +"x11vnc -R forever", "x11vnc -R scale:3/4", "x11vnc -Q modtweak", +"x11vnc -R stop", "x11vnc -R disconnect:all", etc.. + +These commands do not start a x11vnc server, but rather communicate +with one that is already running. The X display (X11VNC_REMOTE +property) is used as the communication channel, so the X permissions +and DISPLAY must be set up correctly for communication to be possible. + +There is also a simple Tcl/Tk gui based on this remote control +mechanism. See the -gui option for more info. You will need to have +Tcl/Tk (i.e. /usr/bin/wish) installed for it to work. It can also run +in the system tray: "-gui tray" or as a standalone small icon window: +"-gui icon". Use "-gui tray=setpass" for a naive user "Share My +Desktop" mode. + + +## Security and Permissions + +### Q-34: How do I create a VNC password for use with x11vnc? + +You may already have one in $HOME/.vnc/passwd if you have used, say, +the vncserver program from the regular RealVNC or TightVNC packages +(i.e. launching the Xvnc server.) Otherwise, you could use the +vncpasswd(1) program from those packages. + +As of Jun/2004 x11vnc supports the -storepasswd "pass" "file" option, +which is the same functionality of storepasswd. Be sure to quote the +"pass" if it contains shell meta characters, spaces, etc. Example: + +``` +x11vnc -storepasswd 'sword*fish' $HOME/myvncpasswd +``` + +You then use the password via the x11vnc option: "-rfbauth +$HOME/myvncpasswd" + +As of Jan/2006 if you do not supply any arguments: + +``` +x11vnc -storepasswd +``` + +you will be prompted for a password to save to ~/.vnc/passwd (your +keystrokes when entering the password will not be echoed to the +screen.) If you supply one argument, e.g. "x11vnc -storepasswd +~/.mypass", the password you are prompted for will be stored in that +file. + +x11vnc also has the -passwdfile and -passwd/-viewpasswd plain text +(i.e. not obscured like the -rfbauth VNC passwords) password options. + +You can use the -usepw option to automatically use any password file +you have in ~/.vnc/passwd or ~/.vnc/passwdfile (the latter is used +with the -passwdfile option.) + +``` +x11vnc -usepw -display :0 ... +``` + +If neither file exists you are prompted to store a password in +~/.vnc/passwd. If a password file cannot be found or created x11vnc +exits immediately. An admin may want to set it up this way for users +who do not know better. + + +### Q-35: Can I make it so -storepasswd doesn't show my password on the screen? + +You can use the vncpasswd program from RealVNC or TightVNC mentioned +above. As of Jan/2006 the -storepasswd option without any arguments +will not echo your password as you type it and save the file to +~/.vnc/passwd: + +``` +# x11vnc -storepasswd +Enter VNC password: +Verify password: +Write password to /home/myname/.vnc/passwd? [y]/n +Password written to: /home/myname/.vnc/passwd +``` + +You can also give it an alternate filename, e.g. "x11vnc -storepasswd +~/.mypass" + + +### Q-36: Can I have two passwords for VNC viewers, one for full access and the other for view-only access to the display? + +Yes, as of May/2004 there is the -viewpasswd option to supply the +view-only password. Note the full-access password option -passwd must +be supplied at the same time. E.g.: -passwd sword -viewpasswd fish. + +To avoid specifying the passwords on the command line (where they +could be observed via the ps(1) command by any user) you can use the +-passwdfile option to specify a file containing plain text passwords. +Presumably this file is readable only by you, and ideally it is +located on the machine x11vnc is run on (to avoid being snooped on +over the network.) The first line of this file is the full-access +password. If there is a second line in the file and it is non-blank, +it is taken as the view-only password. (use "__EMPTY__" to supply an +empty one.) + +View-only passwords currently do not work for the -rfbauth password +option (standard VNC password storing mechanism.) FWIW, note that +although the output (usually placed in $HOME/.vnc/passwd) by the +vncpasswd or storepasswd programs (or from x11vnc -storepasswd) looks +encrypted they are really just obscured to avoid "casual" password +stealing. It takes almost no skill to figure out how to extract the +plain text passwords from $HOME/.vnc/passwd since it is very +straight-forward to work out what to do from the VNC source code. + + +### Q-37: Can I have as many full-access and view-only passwords as I like? + +Yes, as of Jan/2006 in the libvncserver CVS the -passwdfile option has +been extended to handle as many passwords as you like. You put the +view-only passwords after a line __BEGIN_VIEWONLY__. + +You can also easily annotate and comment out passwords in the file. +You can have x11vnc re-read the file dynamically when it is modified. + + +### Q-38: Does x11vnc support Unix usernames and passwords? Can I further limit the set of Unix usernames who can connect to the VNC desktop? + +Update: as of Feb/2006 x11vnc has the -unixpw option that does this +outside of the VNC protocol and libvncserver. The standard su(1) +program is used to validate the user's password. A familiar "login:" +and "Password:" dialog is presented to the user on a black screen +inside the vncviewer. The connection is dropped if the user fails to +supply the correct password in 3 tries or does not send one before a +25 second timeout. Existing clients are view-only during this period. +A list of allowed Unix usernames may also be supplied along with +per-user settings. + +There is also the -unixpw_nis option for non-shadow-password +(typically NIS environments, hence the name) systems where the +traditional getpwnam() and crypt() functions are used instead of +su(1). The encrypted user passwords must be accessible to the user +running x11vnc in -unixpw_nis mode, otherwise the logins will always +fail even when the correct password is supplied. See ypcat(1) and +shadow(5). + +Two settings are enforced in the -unixpw and -unixpw_nis modes to +provide extra security: the 1) -localhost and 2) -stunnel or -ssl +options. Without these one might send the Unix username and password +data in clear text over the network which is a very bad idea. They can +be relaxed if you want to provide encryption other than stunnel or +-ssl (the constraint is automatically relaxed if SSH_CONNECTION is set +and indicates you have ssh-ed in, however the -localhost requirement +is still enforced.) + +The two -unixpw modes have been tested on Linux, Solaris, Mac OS X, +HP-UX, AIX, Tru64, FreeBSD, OpenBSD, and NetBSD. Additional testing is +appreciated. For the last 4 it appears that su(1) will not prompt for +a password if su-ing to oneself. Since x11vnc requires a password +prompt from su, x11vnc forces those logins to fail even when the +correct password is supplied. On *BSD it appears this can be corrected +by removing the pam_self.so entry in /etc/pam.d/su. + + +Previous older discussion (prior to the -unixpw option): + +Until the VNC protocol and libvncserver support this things will be +approximate at best. + +One approximate method involves starting x11vnc with the -localhost +option. This basically requires the viewer user to log into the +workstation where x11vnc is running via their Unix username and +password, and then somehow set up a port redirection of his vncviewer +connection to make it appear to emanate from the local machine. As +discussed above, ssh is useful for this: "ssh -L 5900:localhost:5900 +user@hostname ..." See the ssh wrapper scripts mentioned elsewhere on +this page. stunnel does this as well. + +Of course a malicious user could allow other users to get in through +his channel, but that is a problem with every method. Another thing to +watch out for is a malicious user on the viewer side (where ssh is +running) trying to sneak in through the ssh port redirection there. + +Regarding limiting the set of Unix usernames who can connect, the +traditional way would be to further require a VNC password to supplied +(-rfbauth, -passwd, etc) and only tell the people allowed in what the +VNC password is. A scheme that avoids a second password involves using +the -accept option that runs a program to examine the connection +information to determine which user is connecting from the local +machine. That may be difficult to do, but, for example, the program +could use the ident service on the local machine (normally ident +should not be trusted over the network, but on the local machine it +should be accurate: otherwise root has been compromised and so there +are more serious problems! Unfortunately recent Linux distros seem to +provide a random string (MD5 hash?) instead of the username.) An +example script passed in via -accept scriptname that deduces the Unix +username and limits who can be accepted might look something like +this: + +``` +#!/bin/sh +if [ "$RFB_CLIENT_IP" != "127.0.0.1" -o "$RFB_SERVER_IP" != "127.0.0.1" ]; then + exit 1 # something fishy... reject it. +fi +user=`echo "$RFB_CLIENT_PORT, $RFB_SERVER_PORT" | nc -w 1 $RFB_CLIENT_IP 113 \ + | grep 'USERID.*UNIX' | head -n 1 | sed -e 's/[\r ]//g' | awk -F: '{pri +nt $4}'` + +for okuser in fred barney wilma betty +do + if [ "X$user" = "X$okuser" ]; then + exit 0 # accept it + fi +done +exit 1 # reject it + + For this to work with ssh port redirection, the ssh option + UsePrivilegeSeparation must be enabled otherwise the userid will + always be "root". + + Here is a similar example based on Linux netstat(1) output: +#!/bin/sh +# +# accept_local_netstat: x11vnc -accept command to accept a local +# vncviewer connection from acceptable users. Linux netstat -nte is used. + +PATH=/bin:/usr/bin:$PATH; export PATH; # set to get system utils + +allowed="`id -u fred`"; # add more user numbers if desired. + +# check required settings +ok=1 +if [ "X$allowed" = "X" ]; then + ok=0; # something wrong with allowed list +fi +if [ "X$RFB_CLIENT_IP" != "X127.0.0.1" -o "X$RFB_SERVER_IP" != "X127.0.0.1" ]; +then + ok=0; # connection not over localhost +fi +if [ "$RFB_CLIENT_PORT" -le 0 -o "$RFB_SERVER_PORT" -le 0 ]; then + ok=0; # something wrong with tcp port numbers +fi +if [ "$ok" = 0 ]; then + echo "$0: invalid setting:" 1>&2 + env | grep ^RFB | sort 1>&2 + exit 1 +fi + +# Linux netstat -nte: +# Proto Recv-Q Send-Q Local Address Foreign Address State + User Inode +# 0 0 0 RFB_CLIENT RFB_SERVER ESTABLISHED + nnnn .... +# +user=`netstat -nte | grep ESTABLISHED \ + | grep " $RFB_CLIENT_IP:$RFB_CLIENT_PORT *$RFB_SERVER_IP:$RFB_SERVER_P +ORT "` + +echo "netstat match: $user" 1>&2 +user=`echo "$user" | head -n 1 | sed -e 's/^.*ESTABLISHED/ /' | awk '{print $1} +'` + +ok=0 +for u in $allowed +do + if [ "X$user" = "X$u" ]; then + ok=1 + break + fi +done + +if [ "X$ok" = "X1" ]; then + echo "$0: user accepted: '$user'" 1>&2 + exit 0 +else + echo "$0: user '$user' invalid:" 1>&2 + echo "$0: allowed: $allowed" 1>&2 + env | grep ^RFB | sort 1>&2 + exit 1 +fi +``` + +### Q-39: Can I supply an external program to provide my own custom login method (e.g. Dynamic/One-time passwords or non-Unix (LDAP) usernames and passwords)? + +Yes, there are several possibilities. For background see the FAQ on +the -accept where an external program may be run to decide if a VNC +client should be allowed to try to connect and log in. If the program +(or local user prompted by a popup) answers "yes", then -accept +proceeds to the normal VNC and x11vnc authentication methods, +otherwise the connection is dropped. + +To provide more direct coupling to the VNC client's username and/or +supplied password the following options were added in Sep/2006: + +* -unixpw_cmd command +* -passwdfile cmd:command +* -passwdfile custom:command + +In each case "command" is an external command run by x11vnc. You +supply it. For example, it may couple to your LDAP system or other +servers you set up. + +For -unixpw_cmd the normal -unixpw Login: and Password: prompts are +supplied to the VNC viewer and the strings the client returns are then +piped into "command" as the first two lines of its standard input. If +the command returns success, i.e. exit(0), the VNC client is accepted, +otherwise it is rejected. + +For "-passwdfile cmd:command" the command is run and it returns a +password list (like a password file, see the -passwdfile read:filename +mode.) Perhaps a dynamic, one-time password is retrieved from a server +this way. + +For "-passwdfile custom:command" one gets complete control over the +VNC challenge-response dialog with the VNC client. x11vnc sends out a +string of random bytes (16 by the VNC spec) and the client returns the +same number of bytes in a way the server can verify only the +authorized user could have created. The VNC protocol specifies DES +encryption with a password. If you are willing to modify the VNC +viewers, you can have it be anything you want, perhaps a less +crackable MD5 hash scheme or one-time pad. Your program will read from +its standard input the size of the challenge-response followed by a +newline, then the challenge bytes followed by the response bytes. If +your command then returns success, i.e. exit(0), the VNC client is +accepted, otherwise it is rejected. + +In all cases the "RFB_*" environment variables are set as under +-accept. These variables can provide useful information for the +externally supplied program to use. + + +### Q-40: Why does x11vnc exit as soon as the VNC viewer disconnects? And why doesn't it allow more than one VNC viewer to connect at the same time? + +These defaults are simple safety measures to avoid someone unknowingly +leaving his X11 desktop exposed (to the internet, say) for long +periods of time. Use the -forever option (aka -many) to have x11vnc +wait for more connections after the first client disconnects. Use the +-shared option to have x11vnc allow multiple clients to connect +simultaneously. + +Recommended additional safety measures include using ssh (see above), +stunnel, -ssl, or a VPN to authenticate and encrypt the viewer +connections or to at least use the -rfbauth passwd-file option to use +VNC password protection (or -passwdfile) It is up to YOU to apply +these security measures, they will not be done for you automatically. + + +### Q-41: Can I limit which machines incoming VNC clients can connect from? + +Yes, look at the -allow and -localhost options to limit connections by +hostname or IP address. E.g. + +``` +x11vnc -allow 192.168.0.1,192.168.0.2 +``` + +for those two hosts or + +``` +x11vnc -allow 192.168.0. +``` + +for a subnet. For individual hosts you can use the hostname instead of +the IP number, e.g.: "-allow snoopy", and "-allow darkstar,wombat". +Note that -localhost achieves the same thing as "-allow 127.0.0.1" + +For more control, build libvncserver with libwrap support +(tcp_wrappers) and then use /etc/hosts.allow See hosts_access(5) for +complete details. + + +### Q-42: How do I build x11vnc/libvncserver with libwrap (tcp_wrappers) support? + +Here is one way to pass this information to the configure script: + +``` +env CPPFLAGS=-DUSE_LIBWRAP LDFLAGS=-lwrap ./configure +``` + +then run make as usual. This requires libwrap and its development +package (tcpd.h) to be installed on the build machine. If additional +CPPFLAGS or LDFLAGS options are needed supply them as well using +quotes. + +The resulting x11vnc then uses libwrap/tcp_wrappers for connections. +The service name you will use in /etc/hosts.allow and /etc/hosts.deny +is "vnc", e.g.: + +``` +vnc: 192.168.100.3 .example.com +``` + +Note that if you run x11vnc out of inetd you do not need to build +x11vnc with libwrap support because the /usr/sbin/tcpd reference in +/etc/inetd.conf handles the tcp_wrappers stuff. + + +### Q-43: Can I have x11vnc only listen on one network interface (e.g. internal LAN) rather than having it listen on all network interfaces and relying on -allow to filter unwanted connections out? + +As of Mar/2005 there is the "-listen ipaddr" option that enables this. +For ipaddr either supply the desired network interface's IP address +(or use a hostname that resolves to it) or use the string "localhost". +For additional filtering simultaneously use the "-allow host1,..." +option to allow only specific hosts in. + +This option is useful if you want to insure that no one can even begin +a dialog with x11vnc from untrusted network interfaces (e.g. ppp0.) +The option -localhost now implies "-listen localhost" since that is +what most people expect it to do. + + +### Q-44: Now that -localhost implies listening only on the loopback interface, how I can occasionally allow in a non-localhost via the -R allowonce remote control command? + +To do this specify "-allow localhost". Unlike -localhost this will +leave x11vnc listening on all interfaces (but of course only allowing +in local connections, e.g. ssh redirs.) Then you can later run "x11vnc +-R allowonce:somehost" or use to gui to permit a one-shot connection +from a remote host. + + +### Q-45: Can I fine tune what types of user input are allowed? E.g. have some users just be able to move the mouse, but not click or type anything? + +As of Feb/2005, the -input option allows you to do this. "K", "M", +"B", "C", and "F" stand for Keystroke, Mouse-motion, Button-clicks, +Clipboard, and File-Transfer, respectively. The setting: "-input M" +makes attached viewers only able to move the mouse. "-input KMBC,M" +lets normal clients do everything and enables view-only clients to +move the mouse. + +These settings can also be applied on a per-viewer basis via the +remote control mechanism or the GUI. E.g. x11vnc -R input:hostname:M + + +### Q-46: Can I prompt the user at the local X display whether the incoming VNC client should be accepted or not? Can I decide to make some clients view-only? How about running an arbitrary program to make the decisions? + +Yes, look at the "-accept command" option, it allows you to specify an +external command that is run for each new client. (use quotes around +the command if it contains spaces, etc.) If the external command +returns 0 (success) the client is accepted, otherwise with any other +return code the client is rejected. See below how to also accept +clients view-only. + +The external command will have the RFB_CLIENT_IP environment variable +set to the client's numerical IP address, RFB_CLIENT_PORT its port +number. Similarly for RFB_SERVER_IP and RFB_SERVER_PORT to allow +identification of the tcp virtual circuit. DISPLAY will be set to that +of the X11 display being polled. Also, RFB_X11VNC_PID is set to the +x11vnc process id (e.g. in case you decided to kill it), RFB_CLIENT_ID +will be an id number, and RFB_CLIENT_COUNT the number of other clients +currently connected. RFB_MODE will be "accept". + +Built-in Popup Window: As a special case, "-accept popup" will +instruct x11vnc to create its own simple popup window. To accept the +client press "y" or click mouse on the "Yes" button. To reject the +client press "n" or click mouse on the "No" button. To accept the +client View-only, press "v" or click mouse on the "View" button. If +the -viewonly option has been supplied, the "View" action will not be +present: the whole display is view only in that case. + +The popup window times out after 120 seconds, to change this behavior +use "-accept popup:N" where N is the number of seconds (use 0 for no +timeout.) More tricks: "-accept popupmouse" will only take mouse click +responses, while "-accept popupkey" will only take keystroke responses +(popup takes both.) After any of the 3 popup keywords you can supply a +position of the window: +N+M, (the default is to center the window) +e.g. -accept popupmouse+10+10. + +Also as a special case "-accept xmessage" will run the xmessage(1) +program to prompt the user whether the client should be accepted or +not. This requires that you have xmessage installed and available via +PATH. In case it is not already on your system, the xmessage program +is available at ftp://ftp.x.org/ +(End of Built-in Popup Window:) + +To include view-only decisions for the external commands, prefix the +command something like this: "yes:0,no:*,view:3 mycommand ..." This +associates the three actions: yes(accept), no(reject), and +view(accept-view-only), with the numerical return (i.e. exit()) codes. +Use "*" instead of a number to set the default action (e.g. in case +the external command returns an unexpected return code.) + +Here is an example -accept script called accept_or_lock. It uses +xmessage and xlock (replace with your screen lock command, maybe it is +"xscreensaver-command -lock", or kdesktop_lock, or "dtaction +LockDisplay".) It will prompt the user at the X display whether to +accept, reject, or accept view-only the client, but if the prompt +times out after 60 seconds the screen is locked and the VNC client is +accepted. This allows the remote access when no one is at the display. + +``` +#!/bin/sh +# +# accept_or_lock: prompt user at X display whether to accept an incoming +# VNC connection. If timeout expires, screen is locked +# and the VNC viewer is accepted (allows remote access +# when no one is sitting at the display.) +# +# usage: x11vnc ... -forever -accept 'yes:0,no:*,view:4 accept_or_lock' +# +xmessage -buttons yes:2,no:3,view-only:4 -center \ + -timeout 60 "x11vnc: accept connection from $RFB_CLIENT_IP?" +rc=$? +if [ $rc = 0 ]; then + xlock & # or "xlock -mode blank" for no animations. + sleep 5 + exit 0 +elif [ $rc = 2 ]; then + exit 0 +elif [ $rc = 4 ]; then + exit 4 +fi +exit 1 +``` + +Stefan Radman has written a nice dtksh script dtVncPopup for use in +CDE environments to do the same sort of thing. Information on how to +use it is found at the top of the file. He encourages you to provide +feedback to him to help improve the script. + +Note that in all cases x11vnc will block while the external command or +popup is being run, so attached clients will not receive screen +updates, etc during this period. + +To run a command when a client disconnects, use the "-gone command" +option. This is for the user's convenience only: the return code of +the command is not interpreted by x11vnc. The same environment +variables are set as in "-accept command" (except that RFB_MODE will +be "gone".) + +As of Jan/2006 the "-afteraccept command" option will run the command +only after the VNC client has been accepted and authenticated. Like +-gone the return code is not interpreted. RFB_MODE will be +"afteraccept".) + + +### Q-47: I start x11vnc as root because it is launched via inetd(8) or a display manager like gdm(1). Can I have x11vnc later switch to a different user? + +As of Feb/2005 x11vnc has the -users option that allows things like +this. Please read the documentation on it (also in the x11vnc -help +output) carefully for features and caveats. It's use can often +decrease security unless care is taken. + +BTW, a nice use of it is "-users +nobody" that switches to the Unix +user nobody right after connections to the X display are established. + +In any event, while running x11vnc as root, remember it comes with no +warranty ;-). + + +### Q-48: I use a screen-lock when I leave my workstation (e.g. xscreensaver or xlock.) When I remotely access my workstation desktop via x11vnc I can unlock the desktop fine, but I am worried people will see my activities on the physical monitor. What can I do to prevent this, or at least make it more difficult? + +Probably most work environments would respect your privacy if you +powered off the monitor. Also remember if people have physical access +to your workstation they basically can do anything they want with it +(e.g. install a backdoor for later use, etc.) + +In any event, as of Jun/2004 there is an experimental utility to make +it more difficult for nosey people to see your x11vnc activities. The +source for it is blockdpy.c The idea behind it is simple (but +obviously not bulletproof): when a VNC client attaches to x11vnc put +the display monitor in the DPMS "off" state, if the DPMS state ever +changes immediately start up the screen-lock program. The x11vnc user +will notice something is happening and think about what to do next +(while the screen is in a locked state.) + +This works (or at least has a chance of working) because if the +intruder moves the mouse or presses a key on the keyboard, the monitor +wakes up out of the DPMS off state, and this induces the screen lock +program to activate as soon as possible. Of course there are cracks in +this, the eavesdropper could detach your monitor and insert a non-DPMS +one, and there are race conditions. As mentioned above this is not +bulletproof. A really robust solution would likely require X server +and perhaps even video hardware support. + +The blockdpy utility is launched by the -accept option and told to +exit via the -gone option (the vnc client user should obviously +re-lock the screen before disconnecting!) Instructions can be found in +the source code for the utility at the above link. Roughly it is +something like this: + +``` +x11vnc ... -accept "blockdpy -bg -f $HOME/.bdpy" -gone "touch $HOME/.bdpy" +``` + +but please read the top of the file. + +Update: As of Feb/2007 there is some builtin support for this: +-forcedpms and -clientdpms however, they are probably less robust than +the above blockdpy.c scheme, since if the person floods the physical +machine with mouse or pointer input he can usually see flashes of the +screen before the monitor is powered off again. See also the -grabkbd, +-grabptr, and -grabalways options. + + +### Q-49: Can I have x11vnc automatically lock the screen when I disconnect the VNC viewer? + +Yes, a user mentions he uses the -gone option under CDE to run a +screen lock program: + +``` +x11vnc -display :0 -forever -gone 'dtaction LockDisplay' +``` + +Other possibilities are: + +``` +x11vnc -display :0 -forever -gone 'xscreensaver-command -lock' +x11vnc -display :0 -forever -gone 'kdesktop_lock' +x11vnc -display :0 -forever -gone 'xlock &' +x11vnc -display :0 -forever -gone 'xlock -mode blank &' +``` + +Here is a scheme using the -afteraccept option (in version 0.8) to +unlock the screen after the first valid VNC login and to lock the +screen after the last valid VNC login disconnects: + +``` +x11vnc -display :0 -forever -shared -afteraccept ./myxlocker -gone ./myxlocker +``` + +Where the script ./myxlocker is: + +``` +#!/bin/sh + +#/usr/bin/env | grep RFB_ | sort # for viewing RFB_* settings. + +if [ "X$RFB_MODE" = "Xafteraccept" ]; then + if [ "X$RFB_STATE" = "XNORMAL" ]; then # require valid login + if [ "X$RFB_CLIENT_COUNT" = "X1" ]; then + killall xlock # Linux only. + fi + fi +elif [ "X$RFB_MODE" = "Xgone" ]; then + if [ "X$RFB_STATE" = "XNORMAL" ]; then # require valid login + if [ "X$RFB_CLIENT_COUNT" = "X0" ]; then + xlock -mode blank & + fi + fi +fi +``` + +Note the xlock option "-mode blank" to avoid animations. + +There is a problem if you have x11vnc running this way in -forever +mode and you hit Ctrl-C to stop it. The xlock (or other program) will +get killed too. To work around this make a little script called +setpgrp that looks like: + +``` +#!/usr/bin/perl +setpgrp(0, 0); +exec @ARGV; +``` + +then use -gone "setpgrp xlock &", etc. + + +## Encrypted Connections + +### Q-50: How can I tunnel my connection to x11vnc via an encrypted SSH channel between two Unix machines? + +See the description earlier on this page on how to tunnel VNC via SSH +from Unix to Unix. A number of ways are described along with some +issues you may encounter. + +Other secure encrypted methods exists, e.g. stunnel, IPSEC, various +VPNs, etc. + +See also the Enhanced TightVNC Viewer (SSVNC) page where much of this +is now automated. + + +### Q-51: How can I tunnel my connection to x11vnc via an encrypted SSH channel from Windows using an SSH client like Putty? + +Above we described how to tunnel VNC via SSH from Unix to Unix, you +may want to review it. To do this from Windows using Putty it would go +something like this: + +* In the Putty dialog window under 'Session' enter the hostname or + IP number of the Unix machine with display to be viewed. +* Make sure the SSH protocol is selected and the server port is + correct. +* Under 'Connections/SSH/Tunnels' Add a Local connection with + 'Source port: 5900' and 'Destination: localhost:5900' +* Log into the remote machine by pressing 'Open' and supplying + username, password, etc. +* In that SSH shell, start up x11vnc by typing the command: x11vnc + -display :0 plus any other desired options (e.g. -localhost.) +* Finally, start up your VNC Viewer in Windows and enter + 'localhost:0' as the VNC server. + +You can keep all of the settings in a Putty 'Saved Session'. Also, +once everything is working, you can consider putting x11vnc -display +:0 (plus other cmdline options) in the 'Remote command' Putty setting +under 'Connections/SSH'. + +See also the Enhanced TightVNC Viewer (SSVNC) page where much of this +is now automated via the Putty plink utility. + +For extra protection feel free to run x11vnc with the -localhost and +-rfbauth/-passwdfile options. + +If the machine you SSH into via Putty is not the same machine with the +X display you wish to view (e.g. your company provides incoming SSH +access to a gateway machine), then you need to change the above Putty +dialog setting to: 'Destination: otherhost:5900', Once logged in, +you'll need to do a second login (ssh or rsh) to the workstation +machine 'otherhost' and then start up x11vnc on it. This can also be +automated by Chaining SSH's. + +As discussed above another option is to first start the VNC viewer in +"listen" mode, and then launch x11vnc with the "-connect localhost" +option to establish the reverse connection. In this case a Remote port +redirection (not Local) is needed for port 5500 instead of 5900 (i.e. +'Source port: 5500' and 'Destination: localhost:5500' for a Remote +connection.) + + +### Q-52: How can I tunnel my connection to x11vnc via an encrypted SSL channel using an external tool like stunnel? + +It is possible to use a "lighter weight" encryption setup than SSH or +IPSEC. SSL tunnels such as stunnel (also stunnel.org) provide an +encrypted channel without the need for Unix users, passwords, and key +passphrases required for ssh (and at the other extreme SSL can also +provide a complete signed certificate chain of trust.) On the other +hand, since SSH is usually installed everywhere and firewalls often +let its port through, ssh is frequently the path of least resistance +(it also nicely manages public keys for you.) + +Update: As of Feb/2006 x11vnc has the options -ssl, -stunnel, and +-sslverify to provide integrated SSL schemes. They are discussed in +the Next FAQ (you probably want to skip to it now.) + +We include these non-built-in method descriptions below for historical +reference. They are handy because can be used to create SSL tunnels to +any VNC (or other type of) server. + + +Here are some basic examples using stunnel but the general idea for +any SSL tunnel utility is the same: + +* Start up x11vnc and constrain it to listen on localhost. +* Then start up the SSL tunnel running on the same machine to + forward incoming connections to that x11vnc. +* Set up and run a similar SSL tunnel for the outgoing connection on + the VNC viewer machine pointing it to the SSL/x11vnc server. +* Optionally, set up server (or even client) public/private keys for + use in authenticating one side to the other. +* Finally, start the VNC Viewer and tell it to connect to the local + port (e.g. a vnc display localhost:0) where its outgoing SSL + tunnel is listening. + +We'll first use the stunnel version 3 syntax since it is the most +concise and Unixy. + +Start up x11vnc listening on port 5900: + +``` +x11vnc -display :0 -rfbport 5900 -localhost -bg -passwdfile ~/mypass +``` + +Then start stunnel (version 3, not 4) with this command: + +``` +stunnel -d 5901 -r 5900 -p /path/to/stunnel.pem +``` + +The above two commands are run on host "far-away.east". The +stunnel.pem is the self-signed PEM file certificate created when +stunnel is built. One can also create certificates signed by +Certificate Authorities or self-signed if desired using the x11vnc +utilities described there. + +SSL Viewers: Next, on the VNC viewer side we need an SSL tunnel to +encrypt the outgoing connection. The nice thing is any SSL tunnel can +be used because the protocol is a standard. For this example we'll +also use stunnel on the viewer side on Unix. First start up the +client-side stunnel (version 3, not 4): + +``` +stunnel -c -d localhost:5902 -r far-away.east:5901 +``` + +Then point the viewer to the local tunnel on port 5902: + +``` +vncviewer -encodings "copyrect tight zrle hextile" localhost:2 +``` + +That's it. Note that the ss_vncviewer script can automate this +easily, and so can the Enhanced TightVNC Viewer (SSVNC) package. + +Be sure to use a VNC password because unlike ssh by default the +encrypted SSL channel provides no authentication (only privacy.) With +some extra configuration one could also set up certificates to provide +authentication of either or both sides as well (and hence avoid +man-in-the-middle attacks.) See the stunnel and openssl documentation +and also the key management section for details. + +stunnel has also been ported to Windows, and there are likely others +to choose from for that OS. Much info for using it on Windows can be +found at the stunnel site and in this article The article also shows +the detailed steps to set up all the authentication certificates. (for +both server and clients, see also the x11vnc utilities that do this.) +The default Windows client setup (no certs) is simpler and only 4 +files are needed in a folder: stunnel.exe, stunnel.conf, libssl32.dll, +libeay32.dll. We used an stunnel.conf containing: + +``` +# stunnel.conf: +client = yes +options = ALL +[myvncssl] +accept = localhost:5902 +connect = far-away.east:5901 +``` + +then double click on the stunnel.exe icon to launch it (followed by +pointing the VNC viewer to localhost:2). + +stunnel inetd-like mode: + +As an aside, if you don't like the little "gap" of unencrypted TCP +traffic (and a localhost listening socket) on the local machine +between stunnel and x11vnc it can actually be closed by having stunnel +start up x11vnc in -inetd mode: + +``` +stunnel -p /path/to/stunnel.pem -P none -d 5900 -l ./x11vnc_sh +``` + +Where the script x11vnc_sh starts up x11vnc: + +``` +#!/bin/sh +x11vnc -q -inetd -display :0 -passwdfile ~/mypass +``` + +Note that this creates a separate x11vnc process for each incoming +connection (as any inetd x11vnc usage would), but for the case of +normally just one viewer at a time it should not be a big problem. + + +stunnel 4 syntax: + +Somewhat sadly, the stunnel version 4 syntax is not so amenable to the +command line or scripts. You need to create a config file with the +parameters. E.g.: + +``` +stunnel x11vnc.cfg +``` + +Where the file x11vnc.cfg contains: + +``` +foreground = yes +pid = +cert = /path/to/stunnel.pem +[x11vnc_stunnel] +accept = 5901 +connect = 5900 +``` + +One nice thing about version 4 is often the PEM file does not need to +be specified because stunnel finds it in its installed area. One other +gotcha the PEM file is usually only readable by root (it has the +private key afterall), so you'll need to relax the permissions or make +a copy that the user running x11vnc/stunnel can read. + + +SSL VNC Viewers: + +Regarding VNC viewers that "natively" do SSL unfortunately there do +not seem to be many. The SingleClick UltraVNC Java Viewer is SSL and +is compatible with x11vnc's -ssl option and stunnel.) Commercial +versions of VNC seem to have some SSL-like encryption built in, but we +haven't tried those either and they probably wouldn't work since their +(proprietary) SSL-like negotiation is likely embedded in the VNC +protocol unlike our case where it is external. + +Note: as of Mar/2006 libvncserver/x11vnc provides a SSL-enabled Java +applet that can be served up via the -httpdir or -http options when +-ssl is enabled. It will also be served via HTTPS via either the VNC +port (e.g. https://host:5900/) or a 2nd port via the -https option. + +In general current SSL VNC solutions are not particularly "seemless". +But it can be done, and with a wrapper script on the viewer side and +the -stunnel or -ssl option on the server side it works well and is +convenient. Here is a simple script ss_vncviewer that automates +running stunnel on the VNC viewer side on Unix a little more carefully +than the commands printed above. (One could probably do a similar +thing with a .BAT file on Windows in the stunnel folder.) + +Update Jul/2006: we now provide an Enhanced TightVNC Viewer (SSVNC) +package that starts up STUNNEL automatically along with some other +features. All binaries (stunnel, vncviewer, and some utilities) are +provided in the package. It works on Unix, Mac OS X, and Windows. + + +### Q-53: Does x11vnc have built-in SSL tunneling? + +You can read about non-built-in methods in the Previous FAQ for +background. + +SSL tunnels provide an encrypted channel without the need for Unix +users, passwords, and key passphrases required for ssh (and at the +other extreme SSL can also provide a complete signed certificate chain +of trust.) On the other hand, since SSH is usually installed +everywhere and firewalls often let its port through, ssh is frequently +the path of least resistance. + +Built-in SSL x11vnc options: + +As of Feb/2006 the x11vnc -ssl option automates the SSL tunnel +creation on the x11vnc server side. An SSL-enabled Java Viewer applet +is also provided that can be served via HTTP or HTTPS to automate SSL +on the client side. + +The -ssl mode uses the www.openssl.org library if available at build +time. + +The mode requires an SSL certificate and key (i.e. .pem file.) These +are usually created via the openssl(1) program (in fact in for "-ssl" +(same as "-ssl SAVE") it will run openssl for you automatically.) So +the SSL is not completely "built-in" since this external tool needs to +be installed, but at least x11vnc runs it for you automatically. + +An -ssl example: + +``` +x11vnc -display :0 -ssl -passwdfile ~/mypass +``` + +You'll get output like this: + +``` +09/04/2006 19:27:35 Creating a self-signed PEM certificate... +09/04/2006 19:27:35 +... + +The SSL VNC desktop is: far-away.east:0 +PORT=5900 +SSLPORT=5900 +``` + +In this case openssl(1) was used to create a PEM automatically. It +will prompt you if you want to protect it with with a passphrase. Use +"-ssl SAVE_NOPROMPT" to not be prompted. Use "-ssl TMP" to create a +temporary self-signed cert that will be discarded when x11vnc exits. + +Update: As of Nov/2008 x11vnc also supports the VeNCrypt SSL/TLS +tunnel extension to the VNC protocol. The older ANONTLS method (vino) +is also supported. This support is on by default when the -ssl option +is in use and can be fine-tuned using these options: -vencrypt, +-anontls, and -sslonly. + +The normal x11vnc -ssl operation is somewhat like a URL method +vncs://hostname if vnc://hostname indicates a standard unencrypted VNC +connection. Just as https://hostname is an SSL encrypted version of +http://hostname. The entire VNC session goes through the SSL tunnel. +VeNCrypt, on the other hand, switches to SSL/TLS early in the VNC +protocol handshake. x11vnc 0.9.6 supports both simultaneously when +-ssl is active. + +Note: With the advent of OpenSSL 1.1.0, SSLv2 is dropped and SSLv3 +deactivated per default. A couple broken ciphers have also gone, most +importantly though is that clients trying to connect to x11vnc will +now have to support TLS if encryption is to be used. You can of +course always cook up your own build and run time OpenSSL 1.1.x if +SSLv3 is absolutely required, but it isn't wise from a security point +of view. + + +SSL VNC Viewers:. Viewer-side will need to use SSL as well. See the +next FAQ and here for SSL enabled VNC Viewers, including SSVNC, to +connect to the above x11vnc via SSL. + + +As seen above, the PEM (privacy enhanced mail) file does not need to +be supplied if the openssl(1) command is available in PATH, in that +case a self-signed, certificate good the current and subsequent x11vnc +sessions is created (this may take a while on very slow machines.) + +In general, the PEM file contains both the Certificate (i.e. public +key) and the Private Key. Because of the latter, the file should be +protected from being read by untrusted users. The best way to do this +is to encrypt the key with a passphrase (note however this requires +supplying the passphrase each time x11vnc is started up.) + +See the discussion on x11vnc Key Management for some utilities +provided for creating and managing certificates and keys and even for +creating your own Certificate Authority (CA) for signing VNC server +and client certificates. This may be done by importing the certificate +into Web Browser or Java plugin keystores, or pointing stunnel to it. +The wrapper script ss_vncviewer provides an example on unix (see the +-verify option.) + +Here are some notes on the simpler default (non-CA) operation. To have +x11vnc save the generated certificate and key, use the "SAVE" keyword +like this: + +``` +x11vnc -ssl SAVE -display :0 ... +``` + +(this is the same as the default: "-ssl".) This way it will be saved +in the default directory ~/.vnc/certs/ as server.crt (the certificate +only) and server.pem (both certificate and private key.) This opens up +the possibility of copying the server.crt to machines where the VNC +Viewer will be run to enable authenticating the x11vnc SSL VNC server +to the clients. When authentication takes place this way (or via the +more sophisticated CA signing described here), then +Man-In-The-Middle-Attacks are prevented. Otherwise, the SSL encryption +only provides protection against passive network traffic "sniffing" +(i.e. you are not protected against M-I-T-M attacks.) Nowadays, most +people seem mostly concerned mainly about passive sniffing (and the +default x11vnc SSL mode protects against it.) Note that there are +hacker tools like dsniff/webmitm and cain that implement SSL +Man-In-The-Middle attacks. They rely on the client not bothering to +check the cert. + + +One can test to some degree that SSL is working after starting x11vnc +with the -stunnel or -ssl option. From another machine one can use the +openssl command something like this: + +``` +openssl s_client -debug -msg -showcerts -connect far-away.east:5900 +``` + +After all of the debugging output and informational messages you'll +see the string "RFB 003.008" that came from x11vnc. Pointing a web +browser connecting to: https://far-away.east:5900/ and then viewing +the SSL certificate information about the connection in the panels +will also work. + +Note: If you serve up the SSL enabled Java VNC Viewer via something +like: + +``` +x11vnc -ssl -httpdir /usr/local/share/x11vnc/classes/ssl +``` + +(or just the -http option), you can test it out completely using that, +including using https to download it into the browser and connect to +x11vnc. + + +The older -stunnel option: Before the -ssl option there was a +convenience option -stunnel that would start an external SSL tunnel +for you using stunnel. The -ssl method is the preferred way, but for +historical reference we keep the -stunnel info here. + +The -stunnel mode requires the stunnel.mirt.net command stunnel(8) to +be installed on the system. + +Some -stunnel examples: + +``` +x11vnc -display :0 -stunnel /path/to/stunnel.pem -passwdfile ~/mypass + +x11vnc -display :0 -stunnel SAVE ... +``` + +You'll get output like this: + +``` +The VNC desktop is: localhost:50 +The SSL VNC desktop is: far-away.east:0 +PORT=5950 +SSLPORT=5900 +``` + +That indicates stunnel is listening on port 5900 for incoming +SSL-wrapped VNC connections from viewers. x11vnc is listening for +local connections on port 5950 in this case (remote viewers cannot +connect to it directly.) For -stunnel to work the stunnel command must +be installed on the machine and available in PATH (note stunnel is +often installed in sbin directories rather than bin.) Note that the +default "-stunnel" by itself creates a temporary cert (as in "-ssl +TMP".) + + +### Q-54: How do I use VNC Viewers with built-in SSL tunneling? + +Notes on using "native" VNC Viewers with SSL: + +There aren't any native VNC Viewers that do SSL (ask your VNC viewer +developer to add the feature.) So a tunnel must be setup that you +point the VNC Viewer to. This is often STUNNEL. You can do this +manually, or use the ss_vncviewer script on Unix, or our Enhanced +TightVNC Viewer (SSVNC) package on Unix, Windows, or MacOSX. See the +next section for Java Web browser SSL VNC Viewers (you only need a +Java-enabled Web browser for it to work.) + +Notes on the SSL enabled Java VNC Viewer provided in x11vnc +classes/ssl/VncViewer.jar: + +A Java applet VNC Viewer allows you to connect to a VNC Server from a +Java-enabled Web browser. + +The SSL enabled Java VNC Viewer (VncViewer.jar) in the x11vnc package +supports only SSL based connections by default. As mentioned above the +-httpdir can be used to specify the path to .../classes/ssl. A typical +location might be /usr/local/share/x11vnc/classes/ssl. Or -http can be +used to try to have it find the directory automatically. + +Also note that the SingleClick UltraVNC Java Viewer is compatible with +x11vnc's -ssl SSL mode. (We tested it this way: "java -cp +./VncViewer.jar VncViewer HOST far-away.east PORT 5900 USESSL 1 +TRUSTALL 1") + +The Java viewer uses SSL to communicate securely with x11vnc. Note +that the applet can optionally also be downloaded into your web +browser via HTTPS (which is HTTP over SSL.) This way the HTML page and +the Java applet itself are also delivered securely with SSL (as +opposed to only the VNC traffic being encrypted with SSL.) + +For this case the output will be something like this: + +``` +x11vnc -ssl SAVE -http +... +The SSL VNC desktop is: far-away.east:0 +Java SSL viewer URL: https://far-away.east:5900/ +Java SSL viewer URL: http://far-away.east:5800/ +PORT=5900 +SSLPORT=5900 +``` + +Indicating the two URLs (the first one encrypted, the second not) one +could point the web browser at to get the VNC viewer applet. E.g. put +this + +``` +http://far-away.east:5800/ +``` + +or: + +``` +https://far-away.east:5900/ +``` + +into your Java-enabled Web browser. + +Note that KDE's Konqueror web browser seems to have problems with +https Java applets, so you'll have to use the http/5800 with it (if +you get https/5900 working let us know how you did it.) + +If you are using a router/firewall with port-redirection, and you are +redirecting ports other than the default ones (5800, 5900) listed +above see here. + +The https service provided thru the actual VNC port (5900 in the above +example) can occasionally be slow or unreliable (it has to read some +input and try to guess if the connection is VNC or HTTP.) If it is +unreliable for you and you still want to serve the Java applet via +https, use the -https option to get an additional port dedicated to +https (its URL will also be printed in the output.) + +Another possibility is to add the GET applet parameter: + +``` +https://far-away.east:5900/?GET=1 +``` + +This will have the VNC Viewer send a special HTTP GET string "GET +/request.https.vnc.connection HTTP/1.0" that x11vnc will notice more +quickly as a request for a VNC connection. Otherwise it must wait for +a timeout to expire before it assumes a VNC connection. + +You may also use "urlPrefix=somestring" to have /somestring prepended +to /request.https.vnc.connection". Perhaps you are using a web server +proxy scheme to enter a firewall or otherwise have rules applied to +the URL. If you need to have any slashes "/" in "somestring" use +"_2F_" (a deficiency in libvncserver prevents using the more natural +"%2F".) + +You apply multiple applet parameters in the regular URL way, e.g.: + +``` +https://far-away.east:5900/?GET=1&urlPrefix=mysubdir&... +``` + +All of the x11vnc Java Viewer applet parameters are described in the +file classes/ssl/README + + +Tips on Getting the SSL Java Applet Working the First Time: +Unfortunately, it can be a little tricky getting the SSL VNC Java +Viewer working with x11vnc. Here are some tips to getting working the +first time (afterwards you can incrementally customize with more +complex settings.) + +* First try it on the LAN: Do NOT try to have it work the first time + going through firewalls, Web proxies, home router port + redirections, or Apache portal. Just try a direct connection over + your LAN first (if you only have 1 machine and no LAN, just do a + direct connection to the same machine: localhost.) If the LAN + machine you run x11vnc on has its own host-level firewall (most + linux machine come with that on by default), disable it or at + least let tcp ports 5800-6000 through. +* First try HTTP to download the Java Applet: x11vnc can serve both + the Java Applet jar file and VNC out of the same port (both + tunneled through SSL, see below.) But it can lead to timing and + other problems. So first try HTTP instead of HTTPS to download the + Applet jar file (VncViewer.jar.) That is to say try + http://hostname:5800 in your web browser first before trying + https://hostname:5900. x11vnc will print out the ports and URLs it + is using, so use the HTTP one it prints out. +* Always Restart the Browser: If you are having failures and have to + repeatedly retry things ALWAYS restart the browser (i.e. + completely exit it and then start a new browser process) each + time. Otherwise as you are changing things the browser may + "remember" failed applet downloads, etc. and just add to the + confusion and irreproducibility. If you see it trying to download + VncViewer.class (instead of VncViewer.jar) you know it is really + confused and needs to be restarted. +* Step Lively: If you get Browser or Java VM or VNC Viewer applet + dialog boxes saying things like "Do you want to trust this + certificate?" or "The hostname does not match the one on the + certificate", etc. just go through them as quickly as possible. + x11vnc cannot wait forever for each SSL connection, and so if you + dawdle too long inspecting the certs, etc it can lead to problems. + Get it working first before taking your time to read the details + in the dialogs, etc. +* No inetd, Please: Even if you intend to deploy via inetd or xinetd + eventually, get that working later (and remember do not use + something like "-ssl TMP" that creates a new temporary SSL + certificate for every new socket connection.) +* Nothing Fancy: Do not try fancy stuff like -svc, -create, -unixpw, + "-users unixpw=", "-users sslpeer=", -sslverify, etc. Just get the + simplest connection working first and then incrementally add what + you need. + +So the recommended test command lines are: + +``` +x11vnc -ssl SAVE -http +x11vnc -ssl SAVE -httpdir /path/to/x11vnc/classes/ssl +``` + +Use the latter if x11vnc cannot automatically find the classes/ssl +directory (this what the -http option instructs it to do.) Then point +your browser to the HTTP (not HTTPS) URL it prints out. + +Following the above guidelines, did it work? If so, Congratulations!! +you created an SSL encrypted connection between the SSL Java applet +running in your web browser and x11vnc. The fact that you used HTTP +instead of HTTPS to download the applet is not the end of the world +(some users do it this way), the main thing is that the VNC traffic is +encrypted with SSL. If you are having trouble even with the above +baseline test case feel free to contact me (please send the Full +x11vnc output, not just part of it; the complete x11vnc command line; +the URL(s) entered in the browser; the full Java Console output; and +anything else you can think of.) + +Next, you can add the features you want one by one testing it still +works each time. I suggest first turning on the HTTPS applet download +(https://hostname:5900) if that is what you intend to use. That one +gives the most trouble because of the ambiguity of passing two +different protocols (HTTP and VNC) through the same SSL service port. + +Next, turn on inetd if you intend to use that (this can be tricky too, +be sure to use -oa logfile and inspect it carefully if there are +problems.) If you are going to use non-standard ports (e.g. "-rfbport +443" as root), work on that next. Then enable the firewall, router +port redirection channel (you will somehow need to be outside to do +that, maybe test that through another VNC session.) + +Then, if you plan to use them, enable "fancy stuff" like "-svc" or +"-unixpw", etc, etc. Be sure to add a password either "-rfbauth" or +"-unixpw" or both. If you need to have the web browser use a corporate +Web Proxy (i.e. it cannot connect directly) work on that last. Ditto +for the Apache portal. + + +Router/Firewall port redirs: If you are doing port redirection at +your router to an internal machine running x11vnc AND the internet +facing port is different from the internal machine's VNC port, you +will need to apply the PORT applet parameter to indicate to the applet +the Internet facing port number (otherwise by default the internal +machine's port, say 5900, is sent and that of course is rejected at +the firewall/router.) For example: + +``` +https://far-away.east:443/?GET=1&PORT=443 +``` + +So in this example the user configures his router to redirect +connections to port 443 on his Internet side to, say, port 5900 on the +internal machine running x11vnc. See also the -httpsredir option that +will try to automate this for you. + +To configure your router to do port redirection, see its instructions. +Typically, from the inside you point a web browser to a special URL +(e.g. http://192.168.1.1) and you get a web interface to configure it. +Look for something like "Port Redirection" or "Port Forwarding", +probably under "Advanced" or something like that. If you have a Linux +or Unix system acting as your firewall/router, see its firewall +configuration. + +You can also use x11vnc options -rfbport NNNNN and -httpport NNNNN to +match the ports that your firewall will be redirecting to the machine +where x11vnc is run. + +Tedious Dialogs: If you do serve the SSL enabled Java viewer via https +be prepared for quite a number of "are you sure you trust this site?" +dialogs: + +* First from the Web browser that cannot verify the self-signed + certificate when it downloads index.vnc. +* From the Web browser again noting that the common name on the + certificate does not match the hostname of the remote machine. +* Next from the Java VM that cannot verify the self-signed + certificate when it downloads VncViewer.jar. +* And also from the Java VM again noting that the common name on the + certificate does not match the hostname of the remote machine. +* Finally from the Java VncViewer applet itself saying it cannot + verify the certificate! (or a popup asking you if you want to see + the certificate.) + +Note that sometimes if you pause too long at one of the above dialogs +then x11vnc may exceed a timeout and assume the current socket +connection is VNC instead of the HTTPS it actually is (but since you +have paused too long at the dialog the GET request comes too late.) +Often hitting Reload and going through the dialogs more quickly will +let you connect. The Java VM dialogs are the most important ones to +NOT linger at. If you see in the x11vnc output a request for +VncViewer.class instead of VncViewer.jar it is too late... you will +need to completely restart the Web browser to get it to try for the +jar again. You can use the -https option if you want a dedicated port +for HTTPS connections instead of sharing the VNC port. + +To see example x11vnc output for a successful https://host:5900/ +connection with the Java Applet see This Page. And here is a newer +example including the Java Console output. + +All of the x11vnc Java Viewer applet parameters are described in the +file classes/ssl/README + + +Notes on the VNC Viewer ss_vncviewer wrapper script: + +If you want to use a native VNC Viewer with the SSL enabled x11vnc you +will need to run an external SSL tunnel on the Viewer side. There do +not seem to be any native SSL VNC Viewers outside of our x11vnc and +SSVNC packages. The basic ideas of doing this were discussed for +external tunnel utilities here. + +The ss_vncviewer script provided with x11vnc and SSVNC can set up the +stunnel tunnel automatically on unix as long as the stunnel command is +installed on the Viewer machine and available in PATH (and vncviewer +too of course.) Note that on a Debian based system you will need to +install the package stunnel4 not stunnel. You can set the environment +variables STUNNEL and VNCVIEWERCMD to point to the correct programs if +you want to override the defaults. + +Here are some examples: + +``` +1) ss_vncviewer far-away.east:0 + +2) ss_vncviewer far-away.east:0 -encodings "copyrect tight zrle hextile" + +3) ss_vncviewer -verify ./server.crt far-away.east:0 + +4) ss_vncviewer -mycert ./client.pem far-away.east:0 + +5) ss_vncviewer -proxy far-away.east:8080 myworkstation:0 +``` + +The first one is the default mode and accepts the x11vnc certificate +without question. The second one is as the first, but adds the +-encodings options to the vncviewer command line. + +The third one requires that the x11vnc server authenticate itself to +the client against the certificate in the file ./server.crt (e.g. one +created by "x11vnc -ssl SAVE" and safely copied to the VNC viewer +machine.) + +The fourth one is for VNC Viewer authentication, it uses ./client.pem +to authenticate itself to x11vnc. One can supply both -verify and +-mycert simultaneously. + +The fifth one shows that Web proxies can be used if that is the only +way to get out of the firewall. If the "double proxy" situation arises +separate the two by commas. See this page for more information on how +Web proxies come into play. + +If one uses a Certificate Authority (CA) scheme described here, the +wrapper script would use the CA cert instead of the server cert: + +``` +3') ss_vncviewer -verify ./cacert.crt far-away.east:0 +``` + +Update Jul/2006: we now provide an Enhanced TightVNC Viewer (SSVNC) +package that starts up STUNNEL automatically along with some other +features. All binaries (stunnel, vncviewer, and some utilities) are +provided in the package. It works on Unix, Mac OS X, and Windows. + + +### Q-55: How do I use the Java applet VNC Viewer with built-in SSL tunneling when going through a Web Proxy? + +The SSL enabled Java VNC Viewer and firewall Proxies: + +SSL and HTTPS aside, there is a general problem with Firewall Proxies +and Java Applets that open sockets. The applet is downloaded +successfully (through the browser) using HTTP and the proxy, but when +the applet tries to reconnect to the originating host (the only one +allowed by security) it does not use the proxy channel. So it cannot +reconnect to the server the applet came from! + +We have found a convenient workaround: in the directory where +VncViewer.jar resides there is a digitally signed version of the same +applet called SignedVncViewer.jar. Since the applet is digitally +signed, there will be an additional dialog from the Java VM plugin +asking you if you want to trust the applet fully. + +You should say "Yes". If you do, the applet will be run in a mode +where it can try to determine the firewall proxy host name and port +(it will ask you for them if it cannot find them.) This way it can +connect directly to the Proxy and then request the CONNECT method to +be redirected to the originating host (the x11vnc VNC Server.) SSL is +then layered over this socket. + +To do this you should use the proxy.vnc HTML file like via this URL in +your browser: + +``` +https://yourmachine.com:5900/proxy.vnc +``` + +(instead of the unsigned one in https://yourmachine.com:5900/ that +gives the default index.vnc) + +Proxies that limit CONNECT to ports 443 and 563: + +Things become trickier if the Web proxy restricts which CONNECT ports +can be redirected to. For security, some (most?) proxies only allow +port 443 (HTTPS) and 563 (SNEWS) by default. In this case, the only +thing to do is run x11vnc on that low port, e.g. "-rfbport 443", (or +use a port redirection on, say, a firewall or router port 443 to the +internal machine.) + +If you do such a redirection to an internal machine and x11vnc is not +listening on port 443, you will probably need to edit proxy.vnc. +Suppose the SSL x11vnc server was listening on port 5901. You should +change the line in proxy.vnc from: + +``` + +``` +to: + +``` + +``` + +Since otherwise $PORT will be expanded to 5901 by x11vnc and the +viewer applet will fail to connect to that port on the firewall. + +Another way to achieve the same thing is to use the applet PORT +parameter: + +``` +https://yourmachine.com/proxy.vnc?PORT=443 +``` + +this is cleaner because it avoids editing the file, but requires more +parameters in the URL. See also the -httpsredir x11vnc option that +will try to automate this for you. To use the GET trick discussed +above, do: + +``` +https://yourmachine.com/proxy.vnc?GET=1&PORT=443 +``` + +All of the x11vnc Java Viewer applet parameters are described in the +file classes/ssl/README + +Here is an example of Java Console and x11vnc output for the Web proxy +case. + + +Note that both the ss_vncviewer stunnel Unix wrapper script and +Enhanced TightVNC Viewer (SSVNC) can use Web proxies as well even +though they do not involve a Web browser. + + +### Q-56: Can Apache web server act as a gateway for users to connect via SSL from the Internet with a Web browser to x11vnc running on their workstations behind a firewall? + +Yes. You will need to configure apache to forward these connections. +It is discussed here. This SSL VNC portal provides a clean alternative +to the traditional method where the user uses SSH to log in through +the gateway to create the encrypted port redirection to x11vnc running +on her desktop. + +Also see the desktop.cgi CGI script method that achieves much of what +this Apache VNC SSL portal method does (as long as desktop.cgi's 'port +redirection' mode is enabled.) + + +### Q-57: Can I create and use my own SSL Certificate Authority (CA) with x11vnc? + +Yes, see this page for how to do this and the utility commands x11vnc +provides to create and manage many types of certificates and private +keys. + + +## Display Managers and Services + +### Q-58: How can I run x11vnc as a "service" that is always available? + +There are a number of ways to do this. The primary thing you need to +decide is whether you want x11vnc to connect to the X session on the +machine 1) regardless of who (or if anyone) has the X session, or 2) +only if a certain user has the X session. Because X sessions are +protected by X permissions (MIT-MAGIC-COOKIE files XAUTHORITY and +$HOME/.Xauthority) the automatically started x11vnc will of course +need to have sufficient permissions to connect to the X display. + +Here are some ideas: + +* Use the description under "Continuously" in the FAQ on x11vnc and + Display Managers +* Use the description in the FAQ on x11vnc and inetd(8) +* Use the description in the FAQ on Unix user logins and inetd(8) +* Start x11vnc from your $HOME/.xsession (or $HOME/.xinitrc or + autostart script or ...) +* Although less reliable, see the x11vnc_loop rc.local hack below. + +The display manager scheme will not be specific to which user has the +X session unless a test is specifically put into the display startup +script (often named Xsetup.) The inetd(8) scheme may or may not be +specific to which user has the X session (and it may not be able to do +all users via the XAUTHORITY permission issues.) + +The .xsession/.xinitrc scheme is obviously is specific to a particular +user and only when they are logged into X. If you do not know what a +$HOME/.xsession script is or how to use one, perhaps your desktop has +a "session startup commands" configuration option. The command to be +run in the .xsession or .xinitrc file may look like this: + +``` +x11vnc -logfile $HOME/.x11vnc.log -rfbauth $HOME/.vnc/passwd -forever -bg +``` + +plus any other options you desire. + +Depending on your desktop and/or OS/distribution the automatically run +X startup scripts (traditionally .xsession/.xinitrc) may have to be in +a different directory or have a different basename. One user +recommends the description under 'Running Scripts Automatically' at +this link. + +Firewalls: note all methods will require the host-level firewall to be +configured to allow connections in on a port. E.g. 5900 (default VNC +port) or 22 (default SSH port for tunnelling VNC.) Most systems these +days have firewalls turned on by default, so you will actively have to +do something to poke a hole in the firewall at the desired port +number. See your system administration tool for Firewall settings +(Yast, Firestarter, etc.) + + +### Q-59: How can I use x11vnc to connect to an X login screen like xdm, GNOME gdm, KDE kdm, or CDE dtlogin? (i.e. nobody is logged into an X session yet.) + +We describe two scenarios here. The first is called 'One time only' +meaning you just need to do it quickly once and don't want to repeat; +and the second is called 'Continuously' meaning you want the access to +be available after every reboot and after every desktop logout. + --- + +One time only: If the X login screen is running and you just want to +connect to it once (i.e. a one-shot): + +It is usually possible to do this by just adjusting the XAUTHORITY +environment variable to point to the correct MIT-COOKIE auth file +while running x11vnc as root, e.g. for the gnome display manager, GDM: + +``` +x11vnc -auth /var/gdm/:0.Xauth -display :0 +``` + +(the -auth option sets the XAUTHORITY variable for you.) + +There will be a similar thing to do for xdm using however a different +auth directory path (perhaps something like +/var/lib/xdm/authdir/authfiles/A:0-XQvaJk) for the xdm greeter or +/var/lib/kdm/A:0-crWk72 (or /var/run/xauth/A:0-qQPftr, etc. etc) for +the kdm greeter. Of course, the random characters in the file basename +will vary and you will need to use the actual filename on your system. +Read your system docs to find out where the display manager cookie +files are kept. + +Trick: sometimes ps(1) can reveal the X server process -auth argument +(e.g. "ps wwaux | grep auth") and hence the path to the auth file. + +x11vnc must be run as root for this because the /var/gdm/:0.Xauth, +/var/lib/kdm/A:0-crWk72, etc. auth files are only readable by root. If +you do not want to run x11vnc as root, you can copy (as root or sudo) +the auth file to some location and make it readable by your userid. +Then run x11vnc as your userid with -auth pointed to the copied file. + +Update Dec/2009: use "-auth guess" to have x11vnc try to guess the +location of the auth file for you. + +You next connect to x11vnc with a VNC viewer, give your username and +password to the X login prompt to start your session. + +Note: GDM: gdm seems to have an annoying setting that causes x11vnc +(and any other X clients) to be killed after the user logs in. Setting +KillInitClients=false in the [daemon] section of /etc/X11/gdm/gdm.conf +(or /etc/gdm/gdm.conf, etc.) avoids this. Otherwise, just restart +x11vnc and then reconnect your viewer. Other display managers (kdm, +etc) may also have a similar problem. One user reports having to alter +"gdm.conf-custom" as well. + +Note: Solaris: For dtlogin in addition to the above sort of trick +(BTW, the auth file should be in /var/dt), you'll also need to add +something like Dtlogin*grabServer:False to the Xconfig file +(/etc/dt/config/Xconfig or /usr/dt/config/Xconfig on Solaris, see the +example at the end of this FAQ.) Then restart dtlogin, e.g.: +/etc/init.d/dtlogin stop; /etc/init.d/dtlogin start or reboot. + +Update Nov/2008: Regarding GDM KillInitClients: see the -reopen option +for another possible workaround. + +Update Oct/2009: Regarding GDM KillInitClients: starting with x11vnc +0.9.9 it will try to apply heuristics to detect if a window manager is +not running (i.e. whether the Display Manager Greeter Login panel is +still up.) If it thinks the display manager login is still up it will +delay creating windows or using XFIXES. The former is what GDM uses to +kill the initial clients, use of the latter can cause a different +problem: an Xorg server crash. So with 0.9.9 and later it should all +work without needing to set KillInitClients=false (which is a good +because recent GDM, v2.24, has removed this option) or use -noxfixes. +To disable the heuristics and delaying set X11VNC_AVOID_WINDOWS=never; +to set the delay time explicitly use, e.g., X11VNC_AVOID_WINDOWS=120 +(delays for 120 seconds after the VNC connection; you have that long +to log in.) + +Continuously: Have x11vnc reattach each time the X server is +restarted (i.e. after each logout and reboot): + +To make x11vnc always attached to the X server including the login +screen you will need to add a command to a display manager startup +script. + +Please consider the security implications of this! The VNC display for +the X session always accessible (but hopefully password protected.) +Add -localhost if you only plan to access via a SSH tunnel. + +The name of the display manager startup script file depends on desktop +used and seem to be: + +``` +GDM (GNOME) /etc/X11/gdm/Init/Default + /etc/gdm/Init/Default +KDM (KDE) /etc/kde*/kdm/Xsetup +XDM /etc/X11/xdm/Xsetup (or sometimes xdm/Xsetup_0) +CDE /etc/dt/config/Xsetup +``` + +although the exact location can be operating system, distribution, and +time dependent. See the documentation for your display manager: +gdm(1), kdm(1), xdm(1), dtlogin(1) for additional details. There may +also be display number specific scripts: e.g. Xsetup_0 vs. Xsetup, you +need to watch out for. + +Note: You should read and understand all of the Note's and Update's +in the 'One time only' section above. All of the GDM topics apply here +as well: + +Note: GDM: The above (in 'One time only') gdm setting of +KillInitClients=false in /etc/X11/gdm/gdm.conf (or /etc/gdm/gdm.conf, +etc.) for GDM is needed here as well. Other display managers (KDM, +etc) may also have a similar problem. + +Also see the Update Oct/2009 above where x11vnc 0.9.9 and later +automatically avoids being killed. + +Note: DtLogin: The above (in 'One time only') +Dtlogin*grabServer:False step for Solaris will be needed for dtlogin +here as well. + +In any event, the line you will add to the display manager script +(Xsetup, Default, or whatever) will look something like: + +``` +/usr/local/bin/x11vnc -rfbauth /path/to/the/vnc/passwd -o /var/log/x11vnc.log -forever -bg +``` + +where you should customize the exact command to your needs (e.g. +-localhost for SSH tunnel-only access; -ssl SAVE for SSL access; etc.) + +Happy, happy, joy, joy: Note that we do not need to specify -display +or -auth because happily they are already set for us in the DISPLAY +and XAUTHORITY environment variables for the Xsetup script!!! + +You may also want to force the VNC port with something like "-rfbport +5900" (or -N) to avoid autoselecting one if 5900 is already taken. + +Fedora/gdm: Here is an example of what we did on a vanilla install of +Fedora-C3 (seems to use gdm by default.) Add a line like this to +/etc/X11/gdm/Init/:0 + +``` +/usr/local/bin/x11vnc -rfbauth /etc/x11vnc.passwd -forever -bg -o /var/log/x11vnc.log +``` + +And then add this line to /etc/X11/gdm/gdm.conf (or /etc/gdm/gdm.conf, +etc.) in the [daemon] section: + +``` +KillInitClients=false +``` + +Then restart: /usr/sbin/gdm-restart (or reboot.) The +KillInitClients=false setting is important: without it x11vnc will be +killed immediately after the user logs in. Here are full details on +how to configure gdm + --- + +Solaris/dtlogin: Here is an example of what we did on a vanilla +install of Solaris: +Make the directory /etc/dt/config: + +``` +mkdir -p /etc/dt/config +``` + +Copy over the Xconfig file for customization: + +``` +cp /usr/dt/config/Xconfig /etc/dt/config/Xconfig +``` + +Edit /etc/dt/config/Xconfig and uncomment the line: + +``` +Dtlogin*grabServer: False +``` + +Next, copy over Xsetup for customization: + +``` +cp /usr/dt/config/Xsetup /etc/dt/config/Xsetup +``` + +Edit /etc/dt/config/Xsetup and at the bottom put a line like: + +``` +/usr/local/bin/x11vnc -forever -o /var/log/x11vnc.log -bg +``` +(tweaked to your local setup and preferences, a password via -rfbauth, +etc. would be a very good idea.) + +Restart the X server and dtlogin: + +``` +/etc/init.d/dtlogin stop +/etc/init.d/dtlogin start +``` + +(or reboot or maybe just restart the X session.) + + --- + +KDM: One user running the kdm display manager reports putting this +line: + +``` +x11vnc -forever -rfbauth /home/xyz/.vnc/passwd -bg -o /var/log/x11vnc.log +``` + +in /etc/kde/kdm/Xsetup. After rebooting the system it all seemed to +work fine. + + --- + + +If you do not want to deal with any display manager startup scripts, +here is a kludgey script that can be run manually or out of a boot +file like rc.local: x11vnc_loop It will need some local customization +before running. Because the XAUTHORITY auth file must be guessed by +this script, use of the display manager script method described above +is greatly preferred. There is also the -loop option that does +something similar. + +If the machine is a traditional Xterminal you may want to read this +FAQ. + +Firewalls: note all methods will require the host-level firewall to be +configured to allow connections in on a port. E.g. 5900 (default VNC +port) or 22 (default SSH port for tunnelling VNC.) Most systems these +days have firewalls turned on by default, so you will actively have to +do something to poke a hole in the firewall at the desired port +number. See your system administration tool for Firewall settings +(Yast, Firestarter, etc.) + + +### Q-60: Can I run x11vnc out of inetd(8)? How about xinetd(8)? + +Yes, perhaps a line something like this in /etc/inetd.conf will do it +for you: + +``` +5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc_sh +``` + +where the shell script /usr/local/bin/x11vnc_sh uses the -inetd option +and looks something like (you'll need to customize to your settings.) + +``` +#!/bin/sh +/usr/local/bin/x11vnc -inetd -display :0 -auth /home/fred/.Xauthority \ + -rfbauth /home/fred/.vnc/passwd -o /var/log/x11vnc_sh.log +``` + +Important: Note that you must redirect the standard error output to a +log file (e.g. -o logfile) or "2>/dev/null" for proper operation via +inetd (otherwise the standard error also goes to the VNC vncviewer, +and that confuses it greatly, causing it to abort.) If you do not use +a wrapper script as above but rather call x11vnc directly in +/etc/inetd.conf and do not redirect stderr to a file, then you must +specify the -q (aka -quiet) option: "/usr/local/bin/x11vnc -q -inetd +...". When you supply both -q and -inet and no "-o logfile" then +stderr will automatically be closed (to prevent, e.g. library stderr +messages leaking out to the viewer.) The recommended practice is to +use "-o logfile" to collect the output in a file or wrapper script +with "2>logfile" redirection because the errors and warnings printed +out are very useful in troubleshooting problems. + +Note also the need to set XAUTHORITY via -auth to point to the +MIT-COOKIE auth file to get permission to connect to the X display +(setting and exporting the XAUTHORITY variable accomplishes the same +thing.) See the x11vnc_loop file in the previous question for more +ideas on what that auth file may be, etc. The scheme described in the +FAQ on Unix user logins and inetd(8) works around the XAUTHORITY issue +nicely. + +Note: On Solaris you cannot have the bare number 5900 in +/etc/inetd.conf, you'll need to replace it with a word like x11vnc an +then put something like "x11vnc 5900/tcp" in /etc/services. + +Since the process runs as root, it might be a bad idea to have the +logfile in a world-writable area like /tmp if there are untrustworthy +users on the machine. Perhaps /var/log is a better place. + +Be sure to look at your /etc/hosts.allow and /etc/hosts.deny settings +to limit the machines that can connect to this service (your desktop!) +For the above example with /etc/hosts.allow: + +``` +x11vnc_sh : 123.45.67.89 +``` + +A really safe way to do things is to limit the above inetd to +localhost only (via /etc/hosts.allow) and use ssh to tunnel the +incoming connection. Using inetd for this prevents there being a tiny +window of opportunity between x11vnc starting up and your vncviewer +connecting to it. Always use a VNC password to further protect against +unwanted access. + +For xinetd(8), one user reports he created the file +/etc/xinetd.d/x11vncservice containing the following: + +``` +# default: off +# description: +service x11vncservice +{ + flags = REUSE NAMEINARGS + port = 5900 + type = UNLISTED + socket_type = stream + protocol = tcp + wait = no + user = root + server = /usr/sbin/tcpd + server_args = /usr/local/bin/x11vnc_sh + disable = no +} +``` + +With the contents of /usr/local/bin/x11vnc_sh similar to the example +given above. One user reports this works with avoiding the wrapper +script: + +``` +service x11vncservice +{ + port = 5900 + type = UNLISTED + socket_type = stream + protocol = tcp + wait = no + user = root + server = /usr/local/bin/x11vnc + server_args = -inetd -q -display :0 -auth /var/gdm/:0.Xauth + disable = no +} +``` + +(or one can replace the -q with say "-o /var/log/x11vnc.log" to +capture a log) + +The above works nicely for GDM because the -auth file is a fixed name. +For KDM or XDM the filename varies. Here is one idea for a x11vnc_sh +wrapper to try to guess the name: + +``` +#!/bin/sh +COLUMNS=256 +export COLUMNS +authfile=`ps wwaux | grep '/X.*-auth' | grep -v grep | sed -e 's/^.*-auth *//' +-e 's/ .*$//' | head -n 1` + +if [ -r "$authfile" ]; then + exec /usr/local/bin/x11vnc -inetd -o /var/log/x11vnc.log -display :0 -a +uth "$authfile" +fi +exit 1 +``` + +Starting with x11vnc 0.9.3 this can be automated by: + +``` +#!/bin/sh +exec /usr/local/bin/x11vnc -inetd -o /var/log/x11vnc.log -find -env FD_XDM=1 +``` + + +### Q-61: Can I have x11vnc advertise its VNC service and port via mDNS/Zeroconf (e.g. Avahi) so VNC viewers on the local network can detect it automatically? + +Yes, as of Feb/2007 x11vnc supports mDNS / Zeroconf advertising of its +service via the Avahi client library. Use the option -avahi (same as +-mdns or -zeroconf) to enable it. Depending on your setup you may need +to install Avahi (including the development/build packages), enable +the server: avahi-daemon and avahi-dnsconfd, and possibly open up UDP +port 5353 on your firewall. + +If the Avahi client library or build environment is not available at +build-time, then at run-time x11vnc will try to look for external +helper programs, avahi-browse(1) or dns-sd(1), to do the work. + +The service was tested with Chicken of the VNC ("Use Bonjour" +selected) on a Mac on the same network and the service was noted and +listed in the servers list. Clicking on it and then "Connect" +connected automatically w/o having to enter any hostnames or port +numbers. + +It appears SuSE 10.1 comes with avahi (or you can add packages, e.g. +avahi-0.6.5-27) but not the development package (you can use the +OpenSuSE avahi-devel rpm.) Unfortunately, you may need to disable +another Zeroconf daemon "/etc/init.d/mdnsd stop", before doing +"/etc/init.d/avahi-daemon start" and "/etc/init.d/avahi-dnsconfd +start". We also had to comment out the browse-domains line in +/etc/avahi/avahi-daemon.conf. Hopefully there is "LessConf" to do on +other distros/OS's... + + +### Q-62: Can I have x11vnc allow a user to log in with her UNIX username and password and then have it find her X session display on that machine and then attach to it? How about starting an X session if one cannot be found? + +The easiest way to do this is via inetd(8) using the -unixpw and +-display WAIT options. The reason inetd(8) makes this easier is that +it starts a new x11vnc process for each new user connection. Otherwise +a wrapper would have to listen for connections and spawn new x11vnc's +(see this example and also the -loopbg option.) inetd(8) is not +required for this, but it makes some aspects more general. + +Also with inetd(8) users always connect to a fixed VNC display, say +hostname:0, and do not need to memorize a special VNC display number +just for their personal use, etc. + +Update: Use the -find, -create, -svc, and -xdmsvc options that are +shorthand for common FINDCREATEDISPLAY usage modes (e.g. terminal +services) described below. (i.e. simply use "-svc" instead of the +cumbersome "-display WAIT:cmd=FINDCREATEDISPLAY-Xvfb -unixpw -users +unixpw= -ssl SAVE") + +The -display WAIT option makes x11vnc wait until a VNC viewer is +connected before attaching to the X display. + +Additionally it can be used to run an external command that returns +the DISPLAY and XAUTHORITY data. We provide some useful builtin ones +(FINDDISPLAY and FINDCREATEDISPLAY below), but in principle one could +supply his own script: "-display WAIT:cmd=/path/to/find_display" where +the script find_display might look something like this. + +A default script somewhat like the above is used under "-display +WAIT:cmd=FINDDISPLAY" (same as -find) The format for any such command +is that it returns DISPLAY=:disp as the first line and any remaining +lines are either XAUTHORITY=file or raw xauth data (the above example +does the latter.) If applicable (-unixpw mode), the program is run as +the Unix user name who logged in. + +On Linux if the virtual terminal is known the program appends ",VT=n" +to the DISPLAY line; a chvt n will be attempted automatically. Or if +only the X server process ID is known it appends ",XPID=n" (a chvt +will be attempted by x11vnc.) + +Tip: Note that the -find option is an alias for "-display +WAIT:cmd=FINDDISPLAY". Use it! + + The -unixpw option allows UNIX password logins. It conveniently knows + the Unix username whose X display should be found. Here are a couple + /etc/inetd.conf examples of this usage: + +``` +5900 stream tcp nowait nobody /usr/sbin/tcpd /usr/local/bin/x11vnc -inetd -unixpw \ + -find -o /var/log/x11vnc.log -ssl SAVE -ssldir /usr/local/certs +5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc -inetd -unixpw \ + -find -o /var/log/x11vnc.log -ssl SAVE -users unixpw= +``` + +Note we have used the -find alias and the very long lines have been +split. An alternative is to use a wrapper script, e.g. +/usr/local/bin/x11vnc.sh that has all of the options. (see also the +-svc alias.) + +In the first inetd line x11vnc is run as user "nobody" and stays user +nobody during the whole session. The permissions of the log files and +certs directory will need to be set up to allow "nobody" to use them. + +In the second one x11vnc is run as root and switches to the user that +logs in due to the "-users unixpw=" option. + +Note that SSL is required for this mode because otherwise the Unix +password would be passed in clear text over the network. In general +-unixpw is not required for this sort of scheme, but it is convenient +because it determines exactly who the Unix user is whose display +should be sought. Otherwise the find_display script would have to use +some method to work out DISPLAY, XAUTHORITY, etc (perhaps you use +multiple inetd ports and hardwire usernames for different ports.) + +If you really want to disable the SSL or SSH -localhost constraints +(this is not recommended unless you really know what you are doing: +Unix passwords sent in clear text is a very bad idea...) read the +-unixpw documentation. + + A inetd(8) scheme for a fixed user that doesn't use SSL or unix + passwds could be: + +``` +/usr/local/bin/x11vnc -inetd -users =fred -find -rfbauth /home/fred/.vnc/pass +wd -o /var/log/x11vnc.log +``` + +The "-users =fred" option will cause x11vnc to switch to user fred and +then find his X display. The VNC password (-rfbauth) as opposed to +Unix password (-unixpw) is used to authenticate the VNC client. + +Similar looking commands to the above examples can be run directly and +do not use inetd (just remove the -inetd option and run from the +cmdline, etc.) + + +X Session Creation: An added (Nov/2006) extension to FINDDISPLAY is +FINDCREATEDISPLAY where if it does not find an X display via the +FINDDISPLAY method it will create an X server session for the user +(i.e. desktop/terminal server.) This is the only time x11vnc actually +tries to start up an X server (normally it just attaches to an +existing one.) + +For virtual sessions you will need to install the Xvfb program (e.g. +apt-get install xvfb) or our Xdummy program (see below.) + +By default it will only try to start up virtual (non-hardware) X +servers: first Xvfb and if that is not available then Xdummy (included +in the x11vnc source code.) Note that Xdummy only works on Linux +whereas Xvfb works just about everywhere (and in some situations +Xdummy must be run as root.) An advantage of Xdummy over Xvfb is that +Xdummy supports RANDR dynamic screen resizing, which can be handy if +the user accesses the desktop from different sized screens (e.g. +workstation and laptop.) + + So an inetd(8) example might look like: + +``` +5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc -inetd \ + -o /var/log/x11vnc.log -http -prog /usr/local/bin/x11vnc \ + -ssl SAVE -unixpw -users unixpw= -display WAIT:cmd=FINDCREATEDISPLAY +``` + +Where the very long lines have been split. See below where that long +and cumbersome last line is replaced by the -svc alias. + +The above mode will allow direct SSL (e.g. ss_vncviewer or SSVNC) +access and also Java Web browers access via: https://hostname:5900/. + +Tip: Note that the -create option is an alias for "-display +WAIT:cmd=FINDCREATEDISPLAY-Xvfb". + +Tip: Note that -svc is a short hand for the long "-ssl SAVE -unixpw +-users unixpw= -display WAIT:cmd=FINDCREATEDISPLAY" part. Unlike +-create, this alias also sets up SSL encryption and Unix password +login. + +The above inetd example then simplifies to: + +``` +5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc -inetd \ + -o /var/log/x11vnc.log -http -prog /usr/local/bin/x11vnc \ + -svc +``` + +Tip: In addition to the usual unixpw parameters, inside the VNC viewer +the user can specify after his username (following a ":" see -display +WAIT for details) for FINDCREATEDISPLAY they can add "geom=WxH" or +"geom=WxHxD" to specify the width, height, and optionally the color +depth. E.g. "fred:geom=800x600" at the login: prompt. Also if the env. +var X11VNC_CREATE_GEOM is set to the desired WxH or WxHxD that will be +used by x11vnc. + +You can set the env. var X11VNC_SKIP_DISPLAY to a comma separated list +of displays to ignore in the FINDDISPLAY process (to force creation of +new displays in some cases.) The user logging in via the vncviewer can +also set this via username:nodisplay=...) + +If you do not plan on using the Java Web browser applet you can remove +the -http (and -prog) option since this will speed up logging-in by a +few seconds (x11vnc will not have to wait to see if a connection is +HTTPS or VNC.) + +For reference, xinetd format in the file, say, /etc/xinetd.d/x11vnc: + +``` +service x11vnc +{ + type = UNLISTED + port = 5900 + socket_type = stream + protocol = tcp + wait = no + user = root + server = /usr/local/bin/x11vnc + server_args = -inetd -o /var/log/x11vnc.log -http -prog /usr/local/ +bin/x11vnc -svc + disable = no +} +``` + +To print out the script in this case use "-display +WAIT:cmd=FINDCREATEDISPLAY-print". To change the preference of +Xservers and which to try list them, e.g.: "-display +WAIT:cmd=FINDCREATEDISPLAY-X,Xvfb,Xdummy" or use "-create_xsrv +X,Xvfb,Xdummy". The "X" one means to try to start up a real, hardware +X server, e.g. startx(1) (if there is already a real X server running +this may only work on Linux and the chvt program may need to be run to +switch to the correct Linux virtual terminal.) x11vnc will try to run +chvt automatically if it can determine which VT should be switched to. + +XDM/GDM/KDM Login Greeter Panel: If you want to present the user with +a xdm/gdm/kdm display manager "greeter" login you can use Xvfb.xdmcp +instead of Xvfb, etc in the above list. However, you need to configure +xdm/gdm/kdm to accept localhost XDMCP messages, this can be done by +(from -help output): + +``` +If you want the FINDCREATEDISPLAY session to contact an XDMCP login +manager (xdm/gdm/kdm) on the same machine, then use "Xvfb.xdmcp" +instead of "Xvfb", etc. The user will have to supply his username +and password one more time (but he gets to select his desktop +type so that can be useful.) For this to work, you will need to +enable localhost XDMCP (udp port 177) for the display manager. +This seems to be: + + for gdm in gdm.conf: Enable=true in section [xdmcp] + for kdm in kdmrc: Enable=true in section [Xdmcp] + for xdm in xdm-config: DisplayManager.requestPort: 177 +``` + +Unless you are also providing XDMCP service to xterminals or other +machines, make sure that the host access list only allows local +connections (the name of this file is often Xaccess and it is usually +setup by default to do just that.) Nowadays, host level firewalling +will also typically block UDP (port 177 for XDMCP) by default +effectively limiting the UDP connections to localhost. + + Tip: Note that -xdmsvc is a short hand alias for the long "-ssl SAVE + -unixpw -users unixpw= -display + WAIT:cmd=FINDCREATEDISPLAY-Xvfb.xdmcp". So we simply use: + +``` +service x11vnc +{ + type = UNLISTED + port = 5900 + socket_type = stream + protocol = tcp + wait = no + user = root + server = /usr/local/bin/x11vnc + server_args = -inetd -o /var/log/x11vnc.log -xdmsvc + disable = no +} +``` + +(Note: use "-svc" instead of "-xdmsvc" for no XDMCP login greeter.) + + +Local access (VNC Server and VNC Viewer on the same machine): To +access your virtual X display session locally (i.e. while sitting at +the same machine it is running on) one can perhaps have something like +this in their $HOME/.xinitrc + +``` +#!/bin/sh +x11vnc -create -rfbport 5905 -env WAITBG=1 +vncviewer -geometry +0+0 -encodings raw -passwd $HOME/.vnc/passwd localhost:5 +``` + +You may not need the -passwd. Recent RealVNC viewers might be this: + +``` +#!/bin/sh +x11vnc -create -rfbport 5905 -env WAITBG=1 +vncviewer -FullScreen -PreferredEncoding raw -passwd $HOME/.vnc/passwd localhost:5 +``` + +This way a bare X server is run with no window manager or desktop; it +simply runs only the VNC Viewer on the real X server. The Viewer then +draws the virtual X session on to the real one. On your system it +might not be $HOME/.xinitrc, but rather .xsession, .Xclients, or +something else. You will need to figure out what it is for your system +and configuration. + +There may be a problem if the resolution (WxH) of the virtual X +display does not match that of the physical X display. + +If you do not want to or cannot figure out the X startup script name +(.xinitrc, etc) you could save the above commands to a shell script, +say "vnclocal", and the log in via the normal KDM or GDM greeter +program using the "Failsafe" option. Then in the lone xterm that comes +up type "vnclocal" to connect to your virtual X display via x11vnc and +vncviewer. + +--- + +Summary: The "-display WAIT:cmd=FINDCREATEDISPLAY" scheme can be used +to provide a "desktop service" (i.e. terminal service) on the server +machine: you always get some desktop there, either a real hardware X +server or a virtual one (depending on how you set things up.) + +So it provides simple "terminal services" based on Unix username and +password. The created X server sessions (virtual or real hardware) +will remain running after you disconnect the VNC viewer and will be +found again on reconnecting via VNC and logging in. To terminate them +use the normal way to Exit/LogOut from inside your X session. The user +does not have to memorize which VNC display number is his. They all go +the same one (e.g. hostname:0) and it switches based on username. + + +### Q-63: Can I have x11vnc restart itself after it terminates? + +One could do this in a shell script, but now there is an option -loop +that makes it easier. Of course when x11vnc restarts it needs to have +permissions to connect to the (potentially new) X display. This mode +could be useful if the X server restarts often. Use e.g. "-loop5000" +to sleep 5000 ms between restarts. Also "-loop2000,5" to sleep 2000 ms +and only restart 5 times. + +One can also use the -loopbg to emulate inetd(8) to some degree, where +each connected process runs in the background. It could be combined, +say, with the -svc option to provide simple terminal services without +using inetd(8). + + +### Q-64: How do I make x11vnc work with the Java VNC viewer applet in a web browser? + +To have x11vnc serve up a Java VNC viewer applet to any web browsers +that connect to it, run x11vnc with this option: + +``` + -httpdir /path/to/the/java/classes/dir +``` + +(this directory will contain the files index.vnc and, for example, +VncViewer.jar) Note that libvncserver contains the TightVNC Java +classes jar file for your convenience. (it is the file +classes/VncViewer.jar in the source tree.) + +You will see output something like this: + +``` +14/05/2004 11:13:56 Autoprobing selected port 5900 +14/05/2004 11:13:56 Listening for HTTP connections on TCP port 5800 +14/05/2004 11:13:56 URL http://walnut:5800 +14/05/2004 11:13:56 screen setup finished. +14/05/2004 11:13:56 The VNC desktop is walnut:0 +PORT=5900 +``` + +then you can connect to that URL with any Java enabled browser. Feel +free to customize the default index.vnc file in the classes directory. + +As of May/2005 the -http option will try to guess where the Java +classes jar file is by looking in expected locations and ones relative +to the x11vnc binary. + +Also note that if you wanted to, you could also start the Java viewer +entirely from the viewer-side by having the jar file there and using +either the java or appletviewer commands to run the program. + +``` +java -cp ./VncViewer.jar VncViewer HOST far-away.east PORT 5900 +``` + +Proxies: See the discussion here if the web browser must use a web +proxy to connect to the internet. It is tricky to get Java applets to +work in this case: a signed applet must be used so it can connect to +the proxy and ask for the redirection to the VNC server. One way to do +this is to use the signed SSL one referred to in classes/ssl/proxy.vnc +and set disableSSL=yes (note that this has no encryption; please use +SSL or SSH as discuss elsewhere on this page) in the URL or the file. + + +### Q-65: Are reverse connections (i.e. the VNC server connecting to the VNC viewer) using "vncviewer -listen" and vncconnect(1) supported? + +As of Mar/2004 x11vnc supports reverse connections. On Unix one starts +the VNC viewer in listen mode: "vncviewer -listen" (see your +documentation for Windows, etc), and then starts up x11vnc with the +-connect option. To connect immediately at x11vnc startup time use the +"-connect host:port" option (use commas for a list of hosts to connect +to.) The ":port" is optional (default is VNC listening port is 5500.) + +If a file is specified instead: -connect /path/to/some/file then that +file is checked periodically (about once a second) for new hosts to +connect to. + +The -remote control option (aka -R) can also be used to do this during +an active x11vnc session, e.g.: + +``` +x11vnc -display :0 -R connect:hostname.domain +``` + +Use the "-connect_or_exit" option to have x11vnc exit if the reverse +connection fails. Also, note the "-rfbport 0" option disables TCP +listening for connections (potentially useful for reverse connection +mode, assuming you do not want any "forward" connections.) + +Note that as of Mar/2006 x11vnc requires password authentication for +reverse connections as well as for forward ones (assuming password +auth has been enabled, e.g. via -rfbauth, -passwdfile, etc.) Many VNC +servers do not require any password for reverse connections. To regain +the old behavior supply this option "-env +X11VNC_REVERSE_CONNECTION_NO_AUTH=1" to x11vnc. + +Vncconnect command: To use the vncconnect(1) program (from the core +VNC package at www.realvnc.com) specify the -vncconnect option to +x11vnc (Note: as of Dec/2004 -vncconnect is now the default.) +vncconnect(1) must be pointed to the same X11 DISPLAY as x11vnc (since +it uses X properties to communicate with x11vnc.) If you do not have +or do not want to get the vncconnect(1) program, the following script +(named "Vncconnect") may work if your xprop(1) supports the -set +option: + +``` +#!/bin/sh +# usage: Vncconnect +# Vncconnect +# note: not all xprop(1) support -set. +# +xprop -root -f VNC_CONNECT 8s -set VNC_CONNECT "$1" +``` + + +### Q-66: Can reverse connections be made to go through a Web or SOCKS proxy or SSH? + +Yes, as of Oct/2007 x11vnc supports reverse connections through +proxies: use the "-proxy host:port" option. The default is to assume +the proxy is a Web proxy. Note that most Web proxies only allow proxy +destination connections to ports 443 (HTTPS) and 563 (SNEWS) and so +this might not be too useful unless the proxy has been modified +(AllowCONNECT apache setting) or the VNC viewer listens on one of +those ports (or the router does a port redir.) A web proxy may also be +specified via "-proxy http://host:port" + +For SOCKS4 and SOCKS4a proxies use this format "-proxy +socks://host:port". If the reverse connection hostname is a numerical +IP or "localhost" then SOCKS4 (no host lookup) is used, otherwise +SOCKS4a will be used. For SOCKS5 (proxy will do lookup and many other +things) use "-proxy socks5://host:port". Note that the SSH builtin +SOCKS proxy "ssh -D port" only does SOCKS4 or SOCKS5, so use socks5:// +for a ssh -D proxy. + +The proxying works for both SSL encrypted and normal reverse +connections. + +An experimental mode is "-proxy http://host:port/..." where the URL +(e.g. a CGI script) is retrieved via the GET method. See -proxy for +more info. + +Another experimental mode is "-proxy ssh://user@host" in which case a +SSH tunnel is used for the proxying. See -proxy for more info. + +Up to 3 proxies may be chained together by listing them by commas +e.g.: "-proxy http://host1:port1,socks5://host2:port2" in case one +needs to ricochet off of several machines to ultimately reach the +listening viewer. + + +### Q-67: Can x11vnc provide a multi-user desktop web login service as an Apache CGI or PHP script? + +Yes. See the example script desktop.cgi for ideas. It is in the source +tree in the directory x11vnc/misc. It serves x11vnc's SSL enabled Java +Applet to the web browser with the correct connection information for +the user's virtual desktop (an Xvfb session via -create; be sure to +add the Xvfb package.) HTTPS/SSL enabled Apache should be used to +serve the script to avoid unix and vnc passwords from being sent in +cleartext and sniffed. + +By default it uses a separate VNC port for each user desktop (either +by autoprobing in a range of ports or using a port based on the userid +number.) The web server's firewall must allow incoming connections to +these ports. + +It is somewhat difficult to do all of this with x11vnc listening on a +single port, however there is also a 'fixed port' scheme described in +the script based on -loopbg that works fairly well (but more +experience is needed to see what problems contention for the same port +causes; however at worst one user may need to re-login.) + +There is also an optional 'port redirection' mode for desktop.cgi that +allows redirection to other machines inside the firewall already +running SSL enabled VNC servers. This provides much of the +functionality as the SSL Portal and is easier to set up. + + +### Q-68: Can I use x11vnc as a replacement for Xvnc? (i.e. not for a real display, but for a virtual one I keep around.) + +You can, but you would not be doing this for performance reasons (for +virtual X sessions via VNC, Xvnc should give the fastest response.) +You may want to do this because Xvnc is buggy and crashes, does not +support an X server extension you desire, or you want to take +advantage of one of x11vnc's unending number of options and features. + +One way to achieve this is to have a Xvfb(1) virtual framebuffer X +server running in the background and have x11vnc attached to it. +Another method, faster and more accurate, is to use the "dummy" Device +Driver in XFree86/Xorg (see below.) + +For these virtual sessions you will need to install the Xvfb program +(e.g. apt-get install xvfb) or our Xdummy program (see below.) + +In either case, one can view this desktop both remotely and also +locally using vncviewer. Make sure vncviewer's "-encodings raw" is in +effect for local viewing (compression seems to slow things down +locally.) For local viewing you set up a "bare" window manager that +just starts up vncviewer and nothing else (See how below.) + +Here is one way to start up Xvfb: + +``` +xinit -- /usr/bin/Xvfb :1 -cc 4 -screen 0 1024x768x16 +``` + +This starts up a 16bpp virtual display. To export it via VNC use + +``` +x11vnc -display :1 ... +``` + +Then have the remote vncviewer attach to x11vnc's VNC display (e.g. :0 +which is port 5900.) + +The "-cc 4" Xvfb option is to force it to use a TrueColor visual +instead of DirectColor (this works around a recent bug in the Xorg +Xvfb server.) + +One good thing about Xvfb is that the virtual framebuffer exists in +main memory (rather than in the video hardware), and so x11vnc can +"screen scrape" it very efficiently (more than, say, 100X faster than +normal video hardware.) + +Update Nov/2006: See the FINDCREATEDISPLAY discussion of the "-display +WAIT:cmd=FINDDISPLAY" option where virtual (Xvfb or Xdummy, or even +real ones by changing an option) X servers are started automatically +for new users connecting. This provides a "desktop service" for the +machine. You either get your real X session or your virtual +(Xvfb/Xdummy) one whenever you connect to the machine (inetd(8) is a +nice way to provide this service.) The -find, -create, -svc, and +-xdmsvc aliases can also come in handy here. + +There are some annoyances WRT Xvfb however. The default keyboard +mapping seems to be very poor. One should run x11vnc with -add_keysyms +option to have keysyms added automatically. Also, to add the Shift_R +and Control_R modifiers something like this is needed: + +``` +#!/bin/sh +xmodmap -e "keycode any = Shift_R" +xmodmap -e "add Shift = Shift_L Shift_R" +xmodmap -e "keycode any = Control_R" +xmodmap -e "add Control = Control_L Control_R" +xmodmap -e "keycode any = Alt_L" +xmodmap -e "keycode any = Alt_R" +xmodmap -e "keycode any = Meta_L" +xmodmap -e "add Mod1 = Alt_L Alt_R Meta_L" +``` + +(note: these are applied automatically in the FINDCREATEDISPLAY mode +of x11vnc.) Perhaps the Xvfb options -xkbdb or -xkbmap could be used +to get a better default keyboard mapping... + +Dummy Driver: A user points out a faster and more accurate method is +to use the "dummy" Device Driver of XFree86/Xorg instead of Xvfb. He +uses this to create a persistent and resizable desktop accessible from +anywhere. In the Device Section of the config file set Driver "dummy". +You may also need to set VideoRam NNN to be large enough to hold the +framebuffer. The framebuffer is kept in main memory like Xvfb except +that the server code is closely correlated with the real XFree86/Xorg +Xserver unlike Xvfb. + +The main drawback to this method (besides requiring extra +configuration and possibly root permission) is that it also does the +Linux Virtual Console/Terminal (VC/VT) switching even though it does +not need to (since it doesn't use a real framebuffer.) There are some +"dual headed" (actually multi-headed/multi-user) patches to the X +server that turn off the VT usage in the X server. Update: As of +Jul/2005 we have an LD_PRELOAD script Xdummy that allows you to use a +stock (i.e. unpatched) Xorg or XFree86 server with the "dummy" driver +and not have any VT switching problems! An advantage of Xdummy over +Xvfb is that Xdummy supports RANDR dynamic screen resizing. + + The standard way to start the "dummy" driver would be: + +``` +startx -- :1 -config /etc/X11/xorg.conf.dummy +``` + + where the file /etc/X11/xorg.conf.dummy has its Device Section + modified as described above. To use the LD_PRELOAD wrapper script: + +``` +startx -- /path/to/Xdummy :1 +``` + +An xdm(1) example is also provided. + +In general, one can use these sorts of schemes to use x11vnc to export +other virtual X sessions, say Xnest or even Xvnc itself (useful for +testing x11vnc.) + +Local access (VNC Server and VNC Viewer on the same machine): You use +a VNC viewer to access the display remotely; to access your virtual X +display locally (i.e. while sitting at the same machine it is running +on) one can perhaps have something like this in their $HOME/.xinitrc + +``` +#!/bin/sh +x11vnc -display :5 -rfbport 5905 -bg +vncviewer -geometry +0+0 -encodings raw -passwd $HOME/.vnc/passwd localhost:5 +``` + +The display numbers (VNC and X) will likely be different (you could +also try -find), and you may not need the -passwd. Recent RealVNC +viewers might be this: + +``` +#!/bin/sh +x11vnc -display :5 -rfbport 5905 -bg +vncviewer -FullScreen -PreferredEncoding raw -passwd $HOME/.vnc/passwd localhost:5 +``` + +This way a bare X server is run with no window manager or desktop; it +simply runs only the VNC Viewer on the real X server. The Viewer then +draws the virtual X session on to the real one. On your system it +might not be $HOME/.xinitrc, but rather .xsession, .Xclients, or +something else. You will need to figure out what it is for your system +and configuration. + + +XDM/GDM/KDM One-Shot X sessions: For the general replacement of Xvnc +by Xvfb+x11vnc, one user describes a similar setup he created where +the X sessions are one-shot's (destroyed after the vncviewer +disconnects) and it uses the XDM/GDM/KDM login greeter here. + + +### Q-69: How can I use x11vnc on "headless" machines? Why might I want to? + +An interesting application of x11vnc is to let it export displays of +"headless" machines. For example, you may have some lab or server +machines with no keyboard, mouse, or monitor, but each one still has a +video card. One can use x11vnc to provide a simple "desktop service" +from these server machines. + +An X server can be started on the headless machine (sometimes this +requires configuring the X server to not fail if it cannot detect a +keyboard or mouse, see the next paragraph.) Then you can export that X +display via x11vnc (e.g. see this FAQ) and access it from anywhere on +the network via a VNC viewer. + +Some tips on getting X servers to start on machines without keyboard +or mouse: For XFree86/Xorg the Option "AllowMouseOpenFail" "true" +"ServerFlags" config file option is useful. On Solaris Xsun the ++nkeyboard and +nmouse options are useful (put them in the server +command line args in /etc/dt/config/Xservers.) There are patches +available for Xsun at lease back to Solaris 8 that support this. See +Xserver(1) for more info. + +Although this usage may sound strange it can be quite useful for a GUI +(or other) testing or QA setups: the engineers do not need to walk to +lab machines running different hardware, OS's, versions, etc (or have +many different machines in their office.) They just connect to the +various test machines over the network via VNC. The advantage to +testing this way instead of using Xvnc or even Xvfb is that the test +is done using the real X server, fonts, video hardware, etc. that will +be used in the field. + +One can imagine a single server machine crammed with as many video +cards as it can hold to provide multiple simultaneous access or +testing on different kinds of video hardware. + +See also the FINDCREATEDISPLAY discussion of the "-display +WAIT:cmd=FINDDISPLAY" option where virtual Xvfb or Xdummy, or real X +servers are started automatically for new users connecting. The -find, +-create, -svc, and -xdmsvc aliases can also come in handy here. + + +## Resource Usage and Performance + +### Q-70: I have lots of memory, but why does x11vnc fail with shmget: No space left on device or Minor opcode of failed request: 1 (X_ShmAttach)? + +It is not a matter of free memory, but rather free shared memory (shm) +slots, also known as shm segments. This often occurs on a public +Solaris machine using the default of only 100 slots. You (or the owner +or root) can clean them out with ipcrm(1). x11vnc tries hard to +release its slots, but it, and other programs, are not always able to +(e.g. if kill -9'd.) + +Sometimes x11vnc will notice the problem with shm segments and tries +to get by with fewer, only giving a warning like this: + +``` +19/03/2004 10:10:58 shmat(tile_row) failed. +shmat: Too many open files +19/03/2004 10:10:58 error creating tile-row shm for len=4 +19/03/2004 10:10:58 reverting to single_copytile mode +``` + +Here is a shell script shm_clear to list and prompt for removal of +your unattached shm segments (attached ones are skipped.) I use it +while debugging x11vnc (I use "shm_clear -y" to assume "yes" for each +prompt.) If x11vnc is regularly not cleaning up its shm segments, +please contact me so we can work to improve the situation. + +Longer term, on Solaris you can put something like this in +/etc/system: + +``` +set shmsys:shminfo_shmmax = 0x2000000 +set shmsys:shminfo_shmmni = 0x1000 +``` + +to sweep the problem under the rug (4096 slots.) On Linux, examine +/proc/sys/kernel/shmmni; you can modify the value by writing to that +file. + +Things are even more tight on Solaris 8 and earlier, there is a +default maximum number of shm segments per process of 6. The error is +the X server (not x11vnc) being unable to attach to the segments, and +looks something like this: + +``` +30/04/2004 14:04:26 Got connection from client 192.168.1.23 +30/04/2004 14:04:26 other clients: +X Error of failed request: BadAccess (attempt to access private resource denied) + Major opcode of failed request: 131 (MIT-SHM) + Minor opcode of failed request: 1 (X_ShmAttach) + Serial number of failed request: 14 + Current serial number in output stream: 17 +``` + +This tight limit on Solaris 8 can be increased via: + +``` +set shmsys:shminfo_shmseg = 100 +``` + +in /etc/system. See the next paragraph for more workarounds. + +To minimize the number of shm segments used by x11vnc try using the +-onetile option (corresponds to only 3 shm segments used, and adding +-fs 1.0 knocks it down to 2.) If you are having much trouble with shm +segments, consider disabling shm completely via the -noshm option. +Performance will be somewhat degraded but when done over local machine +sockets it should be acceptable (see an earlier question discussing +-noshm.) + + +### Q-71: How can I make x11vnc use less system resources? + +The -nap (now on by default; use -nonap to disable) and "-wait n" +(where n is the sleep between polls in milliseconds, the default is 30 +or so) option are good places to start. In addition, something like +"-sb 15" will cause x11vnc to go into a deep-sleep mode after 15 +seconds of no activity (instead of the default 60.) + +Reducing the X server bits per pixel depth (e.g. to 16bpp or even +8bpp) will further decrease memory I/O and network I/O. The ShadowFB X +server setting will make x11vnc's screen polling less severe. Using +the -onetile option will use less memory and use fewer shared memory +slots (add -fs 1.0 for one less slot.) + + +### Q-72: How can I make x11vnc use MORE system resources? + +You can try -threads (note this mode can be unstable and/or crash; and +as of May/2008 is strongly discouraged, see the option description) or +dial down the wait time (e.g. -wait 1) and possibly dial down -defer +as well. Note that if you try to increase the "frame rate" too much +you can bog down the server end with the extra work it needs to do +compressing the framebuffer data, etc. + +That said, it is possible to "stream" video via x11vnc if the video +window is small enough. E.g. a 256x192 xawtv TV capture window (using +the x11vnc -id option) can be streamed over a LAN or wireless at a +reasonable frame rate. If the graphics card's framebuffer read rate is +faster than normal then the video window size and frame rate can be +much higher. The use of TurboVNC and/or TurboJPEG can make the frame +rate somewhat higher still (but most of this hinges on the graphics +card's read rate.) + + +### Q-73: I use x11vnc over a slow link with high latency (e.g. dialup modem or broadband), is there anything I can do to speed things up? + +Some things you might want to experiment with (many of which will help +performance on faster links as well): + +X server/session parameters: + +* Configure the X server bits per pixel to be 16bpp or even 8bpp. + (reduces amount of data needed to be polled, compressed, and sent) +* Use a smaller desktop size (e.g. 1024x768 instead of 1280x1024) +* Make sure the desktop background is a solid color (the background + is resent every time it is re-exposed.) Consider using the -solid + [color] option to try to do this automatically. +* Configure your window manager or desktop "theme" to not use fancy + images, shading, and gradients for the window decorations, etc. + Disable window animations, etc. Maybe your desktop has a "low + bandwidth" theme you can easily switch into and out of. Also in + Firefox disable eye-candy, e.g.: Edit -> Preferences -> Advanced + -> Use Smooth Scrolling (deselect it.) +* Avoid small scrolls of large windows using the Arrow keys or + scrollbar. Try to use PageUp/PageDown instead. (not so much of a + problem in x11vnc 0.7.2 if -scrollcopyrect is active and detecting + scrolls for the application.) +* If the -wireframe option is not available (earlier than x11vnc + 0.7.2 or you have disabled it via -nowireframe) then Disable + Opaque Moves and Resizes in the window manager/desktop. +* However if -wireframe is active (on by default in x11vnc 0.7.2) + then you should Enable Opaque Moves and Resizes in the window + manager! This seems counter-intuitive, but because x11vnc detects + the move/resize events early there is a huge speedup over a slow + link when Opaque Moves and Resizes are enabled. (e.g. CopyRect + encoding will be used.) +* Turn off Anti-aliased fonts on your system, web browser, terminal + windows, etc. AA fonts do not compress as well as traditional + fonts (sometimes 10X less.) +* On Firefox/Mozilla (and anything else) turn off "Smooth Scroll" + animations. In Firefox put in the URL "about:config" and set + general.smoothScroll to false. +* On Xorg/XFree86 turn on the Shadow Framebuffer to speed up + reading. (Option "ShadowFB" "true" in the Device section of + /etc/X11/XF86Config) This disables 2D acceleration on the physical + display and so may not be worth it (if you play games, etc), but + could be of use in some situations. Note: If the network link is + very slow, this speedup may not be noticed. + +VNC viewer parameters: + +* Use a TightVNC enabled viewer! (Actually, RealVNC 4.x viewer with + ZRLE encoding is not too bad either; some claim it is faster.) +* Make sure the tight (or zrle) encoding is being used (look at + vncviewer and x11vnc outputs) +* Request 8 bits per pixel using -bgr233 (up to 4X speedup over + depth 24 TrueColor (32bpp), but colors will be off) +* RealVNC 4.x viewer has some extremely low color modes (only 64 and + even 8 colors.) SSVNC does too. The colors are poor, but it is + usually noticeably faster than bgr233 (256 colors.) +* Try increasing the TightVNC -compresslevel (compresses more on + server side before sending, but uses more CPU) +* Try reducing the TightVNC -quality (increases JPEG compression, + but is lossy with painting artifacts) +* Try other VNC encodings via -encodings (tight may be the fastest, + but you should compare it to zrle and maybe some of the others) +* On the machine where vncviewer is run, make sure Backing Store is + enabled (Xorg/XFree86 disables it by default causing re-exposures + of vncviewer to be very slow) Option "backingstore" in config + file. + +x11vnc parameters: + +* Make sure the -wireframe option is active (it should be on by + default) and you have Opaque Moves/Resizes Enabled in the window + manager. +* Make sure the -scrollcopyrect option is active (it should be on by + default.) This detects scrolls in many (but not all) applications + an applies the CopyRect encoding for a big speedup. +* Enforce a solid background when VNC viewers are connected via + -solid +* Try x11vnc's client-side caching client-side caching scheme: + -ncache +* Specify -speeds modem to force the wireframe and scrollcopyrect + heuristic parameters (and any future ones) to those of a dialup + modem connection (or supply the rd,bw,lat numerical values that + characterize your link.) +* If wireframe and scrollcopyrect aren't working, try using the more + drastic -nodragging (no screen updates when dragging mouse, but + sometimes you miss visual feedback) +* Set -fs 1.0 (disables fullscreen updates) +* Try increasing -wait or -defer (reduces the maximum "frame rate", + but won't help much for large screen changes) +* Try the -progressive pixelheight mode with the block pixelheight + 100 or so (delays sending vertical blocks since they may change + while viewer is receiving earlier ones) +* If you just want to watch one (simple) window use -id or -appshare + (cuts down extraneous polling and updates, but can be buggy or + insufficient) +* Set -nosel (disables all clipboard selection exchange) +* Use -nocursor and -nocursorpos (repainting the remote cursor + position and shape takes resources and round trips) +* On very slow links (e.g. <= 28.8) you may need to increase the + -readtimeout n setting if it sometimes takes more than 20sec to + paint the full screen, etc. +* Do not use -fixscreen to automatically refresh the whole screen, + tap three Alt_L's then the screen has painting errors (rare + problem.) + + +Example for the KDE desktop: + +Launch the "KDE Control Center" utility. Sometimes this is called +"Personal Settings". + +Select "Desktop". + +Then Select "Window Behavior". In the "Moving" Tab set these: + +* YES - Display content in moving windows +* YES - Display content in resizing windows +* NO - Display window geometry when moving or resizing +* NO - Animate minimize and restore + +In the "Translucency" Tab set: + +* NO - Use translucency/shadows + +Next hit "Back" and then select "Panels". + +In the "Appearance" Tab set: + +* NO - Enable icon mouseover effects +* NO - Enable transparency + +Now go all the way back up to the top and Select "Appearance & +Themes". + +Select "Background" and set: + +* YES - No picture +* Colors: Single Color + +Select "Fonts" and disable anti-aliased fonts if you are bold enough. + +Select "Launch Feedback" and set: + +* Busy Cursor: No Busy Cursor +* NO - Enable taskbar notification + +Select "Screen Saver" and set: + +* Screen Saver: Blank Screen + +Select "Style" and in the "Effects" Tab set: + +* NO - Enable GUI effects + + +Example for the GNOME desktop: + +* TBD. + + +### Q-74: Does x11vnc support the X DAMAGE Xserver extension to find modified regions of the screen quickly and efficiently? + +Yes, as of Mar/2005 x11vnc will use the X DAMAGE extension by default +if it is available on the display. This requires libXdamage to be +available in the build environment as well (recent Linux distros and +Solaris 10 have it.) + +The DAMAGE extension enables the X server to report changed regions of +the screen back to x11vnc. So x11vnc doesn't have to guess where the +changes are (by polling every pixel of the entire screen every 2-4 +seconds.) The use of X DAMAGE dramatically reduces the load when the +screen is not changing very much (i.e. most of the time.) It also +noticeably improves updates, especially for very small changed areas +(e.g. clock ticking, cursor flashing, typing, etc.) + +Note that the DAMAGE extension does not speed up the actual reading of +pixels from the video card framebuffer memory, by, say, mirroring them +in main memory. So reading the fb is still painfully slow (e.g. +5MB/sec), and so even using X DAMAGE when large changes occur on the +screen the bulk of the time is still spent retrieving them. Not ideal, +but use of the ShadowFB XFree86/Xorg option speeds up the reading +considerably (at the cost of h/w acceleration.) + +Unfortunately the current Xorg DAMAGE extension implementation can at +times be overly conservative and report very large rectangles as +"damaged" even though only a small portion of the pixels have actually +been modified. This behavior is often the fault of the window manager +(e.g. it redraws the entire, unseen, frame window underneath the +application window when it gains focus), or the application itself +(e.g. does large, unnecessary repaints.) + +To work around this deficiency, x11vnc currently only trusts small +DAMAGE rectangles to contain real damage. The larger rectangles are +only used as hints to focus the traditional scanline polling (i.e. if +a scanline doesn't intersect a recent DAMAGE rectangle, the scan is +skipped.) You can use the "-xd_area A" option to adjust the size of +the trusted DAMAGE rectangles. The default is 20000 pixels (e.g. a +140x140 square, etc.) Use "-xd_area 0" to disable the cutoff and trust +all DAMAGE rectangles. + +The option "-xd_mem f" may also be of use in tuning the algorithm. To +disable using DAMAGE entirely use "-noxdamage". + + +### Q-75: My OpenGL application shows no screen updates unless I supply the -noxdamage option to x11vnc. + +One user reports in his environment (MythTV using the NVIDIA OpenGL +drivers) he gets no updates after the initial screen is drawn unless +he uses the "-noxdamage" option. + +This seems to be a bug in the X DAMAGE implementation of that driver. +You may have to use -noxdamage as well. A way to autodetect this will +be tried, probably the best it will do is automatically stop using X +DAMAGE. + +A developer for MiniMyth reports that the 'alphapulse' tag of the +theme G.A.N.T. can also cause problems, and should be avoided when +using VNC. + +Update: see this FAQ too. + + +### Q-76: When I drag windows around with the mouse or scroll up and down things really bog down (unless I do the drag in a single, quick motion.) Is there anything to do to improve things? + +This problem is primarily due to slow hardware read rates from video +cards: as you scroll or move a large window around the screen changes +are much too rapid for x11vnc to keep up them (it can usually only +read the video card at about 5-10 MB/sec, so it can take a good +fraction of a second to read the changes induce from moving a large +window, if this to be done a number of times in succession the window +or scroll appears to "lurch" forward.) See the description in the +-pointer_mode option for more info. The next bottleneck is compressing +all of these changes and sending them out to connected viewers, +however the VNC protocol is pretty much self-adapting with respect to +that (updates are only packaged and sent when viewers ask for them.) + +As of Jan/2004 there are some improvements to libvncserver. The +default should now be much better than before and dragging small +windows around should no longer be a huge pain. If for some reason +these changes make matters worse, you can go back to the old way via +the "-pointer_mode 1" option. + +Also added was the -nodragging option that disables all screen updates +while dragging with the mouse (i.e. mouse motion with a button held +down.) This gives the snappiest response, but might be undesired in +some circumstances when you want to see the visual feedback while +dragging (e.g. menu traversal or text selection.) + +As of Dec/2004 the -pointer_mode n option was introduced. n=1 is the +original mode, n=2 an improvement, etc.. See the -pointer_mode n help +for more info. + +Also, in some circumstances the -threads option can improve response +considerably. Be forewarned that if more than one vncviewer is +connected at the same time then libvncserver may not be thread safe +(try to get the viewers to use different VNC encodings, e.g. tight and +ZRLE.) This option can be unstable and so as of Feb/2008 it is +disabled by default. Set env. X11VNC_THREADED=1 to re-enable. + +As of Apr/2005 two new options (see the wireframe FAQ and +scrollcopyrect FAQ below) provide schemes to sweep this problem under +the rug for window moves or resizes and for some (but not all) window +scrolls. These are the preferred way of avoiding the "lurching" +problem, contact me if they are not working. Note on SuSE and some +other distros the RECORD X extension used by scrollcopyrect is not +enabled by default, turn it on in xorg.conf: + +``` +Section "Module" + ... + Load "record" + ... +EndSection +``` + + +### Q-77: Why not do something like wireframe animations to avoid the windows "lurching" when being moved or resized? + +Nice idea for a hack! As of Apr/2005 x11vnc by default will apply +heuristics to try to guess if a window is being (opaquely) moved or +resized. If such a change is detected framebuffer polling and updates +will be suspended and only an animated "wireframe" (a rectangle +outline drawn where the moved/resized window would be) is shown. When +the window move/resize stops, it returns to normal processing: you +should only see the window appear in the new position. This spares you +from interacting with a "lurching" window between all of the +intermediate steps. BTW the lurching is due to slow video card read +rates (see here too.) A displacement, even a small one, of a large +window requires a non-negligible amount of time, a good fraction of a +second, to read in from the hardware framebuffer. + +Note that Opaque Moves/Resizes must be Enabled by your window manager +for -wireframe to do any good. + +The mode is currently on by default because most people are afflicted +with the problem. It can be disabled with the -nowireframe option (aka +-nowf.) Why might one want to turn off the wireframing? Since x11vnc +is merely guessing when windows are being moved/resized, it may guess +poorly for your window-manager or desktop, or even for the way you +move the pointer. If your window-manager or desktop already does its +own wireframing then this mode is a waste of time and could do the +wrong thing occasionally. There may be other reasons the new mode +feels unnatural. If you have very expensive video hardware (SGI, well +now even proprietary Xorg drivers are fast at reading) or are using an +in-RAM video framebuffer (SunRay, ShadowFB, Xvfb), the read rate from +that framebuffer may be very fast (100's of MB/sec) and so you don't +really see much lurching (at least over a fast LAN): opaque moves look +smooth in x11vnc. Note: ShadowFB is often turned on when you are using +the vesafb or fbdev XFree86 video driver instead of a native one so +you might be using it already and not know. + +The heuristics used to guess window motion or resizing are simple, but +are not fool proof: x11vnc is sometimes tricked and so you'll +occasionally see the lurching opaque move and rarely something even +worse. + +First it assumes that the move/resize will occur with a mouse button +pressed, held down and dragged (of course this is only mostly true.) +Next it will only consider a window for wireframing if the mouse +pointer is initially "close enough" to the edges of the window frame, +e.g. you have grabbed the title bar or a resizer edge (this +requirement can be disabled and it also not applied if a modifier key, +e.g. Alt, is pressed.) If these are true, it will wait an amount of +time to see if the window starts moving or resizing. If it does, it +starts drawing the wireframe "outline" of where the window would be. +When the mouse button is released, or a timeout occurs, it goes back +to the standard mode to allow the actual framebuffer changes to +propagate to the viewers. + +These parameters can be tweaked: + +* Color/Shade of the wireframe. +* Linewidth of the outline frame. +* Cutoff size of windows to not apply wireframing to. +* Cutoffs for closeness to Top, Bottom, Left, and Right edges of + window. +* Modifier keys to enable interior window grabbing. +* Maximum time to wait for dragging pointer events. +* Maximum time to wait for the window to start moving/resizing. +* Maximum time to show a wireframe animation. +* Minimum time between sending wireframe outlines. + +See the "-wireframe tweaks" option for more details. On a slow link, +e.g. dialup modem, the parameters may be automatically adjusted for +better response. + + +CopyRect encoding: In addition to the above there is the +"-wirecopyrect mode" option. It is also on by default. This instructs +x11vnc to not only show the wireframe animation, but to also instruct +all connected VNC viewers to locally translate the window image data +from the original position to the new position on the screen when the +animation is done. This speedup is the VNC CopyRect encoding: the +framebuffer update doesn't need to send the actual new image data. +This is nice in general, and very convenient over a slow link, but +since it is based on heuristics you may need to disable it with the +-nowirecopyrect option (aka -nowcr) if it works incorrectly or +unnaturally for you. + +The -wirecopyrect modes are: "never" (same as -nowirecopyrect); "top", +only apply the CopyRect if the window is appears to be on the top of +the window stack and is not obstructed by other windows; and "always" +to always try to apply the CopyRect (obstructed regions are usually +clipped off and not translated.) + +Note that some desktops (KDE and xfce) appear to mess with the window +stacking in ways that are not yet clear. In these cases x11vnc works +around the problem by applying the CopyRect even if obscuring windows' +data is translated! Use -nowirecopyrect if this yields undesirable +effects for your desktop. + +Also, the CopyRect encoding may give incorrect results under -scale +(depending on the scale factor the CopyRect operation is often only +approximate: the correctly scaled framebuffer will be slightly +different from the translated one.) x11vnc will try to push a +"cleanup" update after the CopyRect if -scale is in effect. Use +-nowirecopyrect if this or other painting errors are unacceptable. + + +### Q-78: Can x11vnc try to apply heuristics to detect when a window is scrolling its contents and use the CopyRect encoding for a speedup? + +Another nice idea for a hack! As of May/2005 x11vnc will by default +apply heuristics to try to detect if the window that has the input +focus is scrolling its contents (but only when x11vnc is feeding user +input, keystroke or pointer, to the X server.) So, when detected, +scrolls induced by dragging on a scrollbar or by typing (e.g. Up or +Down arrows, hitting Return in a terminal window, etc), will show up +much more quickly than via the standard x11vnc screen polling update +mechanism. + +There will be a speedup for both slow and fast links to viewers. For +slow links the speedup is mostly due to the CopyRect encoding not +requiring the image data to be transmitted over the network. For fast +links the speedup is primarily due to x11vnc not having to read the +scrolled framebuffer data from the X server (recall that reading from +the hardware framebuffer is slow.) + +To do this x11vnc uses the RECORD X extension to snoop the X11 +protocol between the X client with the focus window and the X server. +This extension is usually present on most X servers (but SuSE disables +it for some reason.) On XFree86/Xorg it can be enabled via Load +"record" in the Module section of the config file if it isn't already: + +``` +Section "Module" + ... + Load "record" + ... +EndSection +``` + +Currently the RECORD extension is used as little as possible so as to +not slow down regular use. Only simple heuristics are applied to +detect XCopyArea and XConfigureWindow calls from the application. +These catch a lot of scrolls, e.g. in mozilla/firefox and in terminal +windows like gnome-terminal and xterm. Unfortunately the toolkits KDE +applications use make scroll detection less effective (only rarely are +they detected: i.e. Konqueror and Konsole don't work.) An interesting +project, that may be the direction x11vnc takes, is to record all of +the X11 protocol from all clients and try to "tee" the stream into a +modified Xvfb watching for CopyRect and other VNC speedups. A +potential issue is the RECORD stream is delayed from actual view on +the X server display: if one falls too far behind it could become a +mess... + +The initial implementation of -scrollcopyrect option is useful in that +it detects many scrolls and thus gives a much nicer working +environment (especially when combined with the -wireframe +-wirecopyrect options, which are also on by default; and if you are +willing to enable the ShadowFB things are very fast.) The fact that +there aren't long delays or lurches during scrolling is the primary +improvement. + +But there are some drawbacks: + +* Not all scrolls are detected. Some apps scroll windows in ways + that cannot currently be detected, and other times x11vnc "misses" + the scroll due to timeouts, etc. Sometimes it is more distracting + that a speedup occasionally doesn't work as opposed to being + consistently slow! +* For rapid scrolling (i.e. sequence of many scrolls over a short + period) there can be painting errors (tearing, bunching up, etc.) + during the scroll. These will repair themselves after the scroll + is over, but when they are severe it can be distracting. Try to + think of the approximate window contents as a quicker and more + useful "animation" compared to the slower polling scheme... +* Scrolling inside shells in terminal windows (gnome-terminal, + xterm), can lead to odd painting errors. This is because x11vnc + did not have time to detect a screen change just before the scroll + (most common is the terminal undraws the block cursor before + scrolling the text up: in the viewer you temporarily see multiple + block cursors.) Another issue is with things like more(1): scroll + detection for 5-6 lines happens nicely, but then it can't keep up + and so there is a long pause for the standard polling method to + deliver the remaining updates. +* More rarely sometimes painting errors are not repaired after the + scroll is over. This may be a bug in x11vnc or libvncserver, or it + may be an inescapable fact of the CopyRect encoding and the delay + between RECORD callbacks and what is actually on the X display. + One can tap the Alt_L key (Left "Alt" key) 3 times in a row to + signal x11vnc to refresh the screen to all viewers. Your + VNC-viewer may have its own screen refresh hot-key or button. See + also: -fixscreen +* Some applications, notably OpenOffice, do XCopyArea scrolls in + weird ways that assume ancestor window clipping is taking place. + See the -scr_skip option for ways to tweak this on a + per-application basis. +* Selecting text while dragging the mouse may be slower, especially + if the Button-down event happens near the window's edge. This is + because the scrollcopyrect scheme is watching for scrolls via + RECORD and has to wait for a timeout to occur before it does the + update. +* For reasons not yet understood the RECORD extension can stop + responding (and hence scrolls are missed.) As a workaround x11vnc + attempts to reset the RECORD connection every 60 seconds or so. + Another workaround is to type 4 Super_L (Left Super/Windows-Flag + key) in a row to reset RECORD. Work is in progress to try to fix + this bug. +* Sometimes you need to "retrain" x11vnc for a certain window + because it fails to detect scrolls in it. Sometimes clicking + inside the application window or selecting some text in it to + force the focus helps. +* When using the -scale option there will be a quick CopyRect + scroll, but it needs to be followed by a slower "cleanup" update. + This is because for a fixed finite screen resolution (e.g. 75 dpi) + scaling and copyrect-ing are not exactly independent. Scaling + involves a blending of nearby pixels and if you translate a pixel + the neighbor pixel weighting may be different. So you have to wait + a bit for the cleanup update to finish. On slow links x11vnc may + automatically decide to not detect scrolls when -scale is in + effect. In general it will also try to defer the cleanup update if + possible. + +If you find the -scrollcopyrect behavior too approximate or +distracting you can go back to the standard polling-only update method +with the -noscrollcopyrect (or -noscr for short.) If you find some +extremely bad and repeatable behavior for -scrollcopyrect please +report a bug. + +Alternatively, as with -wireframe, there are many tuning parameters to +try to improve the situation. You can also access these parameters +inside the gui under "Tuning". These parameters can be tweaked: + +* The minimum pixel area of a rectangle to be watched for scrolls. +* A list if application names to skip scroll detection. +* Which keystrokes should trigger scroll detection. +* Which applications should have a "terminal" tweak applied to them. +* When repeating keys (e.g. Up arrow) should be discarded to + preserve a scroll. +* Cutoffs for closeness to Top, Bottom, Left, and Right edges of + window for mouse induced scrolls. +* Set timeout parameters for keystroke induced scrolls. +* Set timeout parameters for mouse pointer induced scrolls. +* Have the full screen be periodically refreshed to fix painting + errors. + + +### Q-79: Can x11vnc do client-side caching of pixel data? I.e. so when that pixel data is needed again it does not have to be retransmitted over the network. + +As of Dec/2006 in the 0.9 development tarball there is an experimental +client-side caching implementation enabled by the "-ncache n" option. +In fact, during the test period it was on by default with n set to 10. +To disable it use "-noncache". + +It is a simple scheme where a (very large) lower portion of the +framebuffer (i.e. starting just below the user's actual desktop +display) is used for storing pixel data. CopyRect; a fast, essentially +local viewer-side VNC encoding; is used to swap the pixel data in and +out of the actual display area. It gives an excellent speedup for +iconifying/deiconifying and moving windows and re-posting of menus +(often it doesn't feel like VNC at all: there is no delay waiting for +the pixel data to fill in.) + +This scheme is nice because it does all of this within the existing +VNC protocol, and so it works with all VNC viewers. + +A challenge to doing more sophisticated (e.g. compressed and/or +shared) client-side caching is that one needs to extend the VNC +protocol, modify a viewer and then also convince users to adopt your +modified VNC Viewer (or get the new features to be folded into the +main VNC viewers, patches accepted, etc... likely takes many years +before they might be deployed in the field.) So it is convenient that +the "-ncache n" works with any unaltered VNC viewer. + +A drawback of the "-ncache n" method is that in the VNC Viewer you can +scroll down and actually see the cached pixel data. So it looks like +there is a bug: you can scroll down in your viewer and see a strange +"history" of windows on your desktop. This is working as intended. One +will need to try to adjust the size of his VNC Viewer window so the +cache area cannot be seen. SSVNC (see below) can do this +automatically. + +At some point LibVNCServer may implement a "rfbFBCrop" pseudoencoding +that viewers can use to learn which portion of the framebuffer to +actually show to the users (with the hidden part used for caching, or +perhaps something else, maybe double buffering or other offscreen +rendering...) + +The Enhanced TightVNC Viewer (SSVNC) Unix viewer has a nice -ycrop +option to help hide the pixel cache area from view. It will turn on +automatically if the framebuffer appears to be very tall (height more +than twice the width), or you can supply the actual value for the +height. If the screen is resized by scaling, etc, the ycrop value is +scaled as well. In fullscreen mode you cannot scroll past the end of +the actual screen, and in non-fullscreen mode the window manager frame +is adjusted to fit the actual display (so you don't see the pixel +cache region) and the scrollbars are very thin to avoid distraction +and trouble fitting inside your display. Use the "-sbwidth n" viewer +option to make the scrollbars thicker if you like. + +Another drawback of the scheme is that it is VERY memory intensive, +the n in "-ncache n" is the factor of increase over the base +framebuffer size to use for caching. It is an even integer and should +be fairly large, 6-12, to achieve good response. This usually requires +about 50-100MB of additional RAM on both the client and server sides. +For example with n=6 a 1280x1024 display will use a framebuffer that +is 1280x7168: everything below row 1024 is the pixel buffer cache. If +you are running on low memory machines or memory is tight because of +other running applications you should not use -ncache. + +The reason for so much memory is because the pixel data is not +compressed and so the whole window to be saved must be stored +"offscreen". E.g. for a large web browser window this can be nearly 1 +million pixels, and that is only for a single window! One typically +wants to cycle between 5-10 large active windows. Also because both +backing-store (the window's actual contents) and save-unders (the +pixels covered up by the window) are cached offscreen that introduces +an additional factor of 2 in memory use. + +However, even in the smallest usage mode with n equal 2 and +-ncache_no_rootpixmap set (this requires only 2X additional +framebuffer memory) there is still a noticable improvement for many +activities, although it is not as dramatic as with, say n equal 12 and +rootpixmap (desktop background) caching enabled. + +The large memory consumption of the current implementation can be +thought of as a tradeoff to providing caching and being compatible +with all VNC viewers and also ease of implementing. Hopefully it can +be tuned to use less, or the VNC community will extend the protocol to +allow caching and replaying of compressed blobs of data. + +Another option to experiment with is "-ncache_cr". By specifying it, +x11vnc will try to do smooth opaque window moves instead of its +wireframe. This can give a very nice effect (note: on Unix the realvnc +viewer seems to be smoother than the tightvnc viewer), but can lead to +some painting problems, and can be jerky in some circumstances. + +Surprisingly, for very slow connections, e.g. modem, the -ncache_cr +option can actually improve window drags. This is probably because no +pixel data (only CopyRect instructions) are sent when dragging a +window. Normally, the wireframe must be sent and this involves +compressing and sending the lines that give rise to the moving box +effect (note that real framebuffer data is sent to "erase" the white +lines of the box.) + +If you experience painting errors you can can tap the Alt_L key (Left +"Alt" key) 3 times in a row to signal x11vnc to refresh the screen to +all viewers. You may also need to iconify and then deiconify any +damaged windows to correct their cache data as well. Note that if you +change color viewer depth (e.g. 8bpp to full color) dynamically that +will usually lead to the entire extended framebuffer being resent +which can take a long time over very slow links: it may be better to +reconnect and reset the format right after doing so. x11vnc will try +to detect the format change and clear (make completely black) the +cache region. + +Gotcha for older Unix VNC Viewers: The older Unix VNC viewers (e.g. +current TightVNC Unix Viewer) require X server backingstore to keep +off-viewer screen data local. If the viewer-side X server has +backingstore disabled (sadly, currently the default on Linux, etc), +then to get the offscreen pixels the viewer has to ask for a refresh +over the network, thereby defeating the caching. Use something like +this in your viewer-side /etc/X11/xorg.conf file (or otherwise get +your viewer-side system to do it) + +``` +Section "Device" + ... + Option "backingstore" + ... +EndSection +``` + +No problems like this have been observed with Windows VNC Viewers: +they all seem to keep their entire framebuffer in local memory. + +Gotcha for KDE krdc VNC Viewer: One user found that KDE's krdc viewer +has some sort of hardwired limit on the maximum size of the +framebuffer (64MB?). It fails quickly saying "The connection to the +host has been interrupted." The workaround for his 1280x1024 +x11vnc-side display was to run with "-ncache 10", i.e. a smaller value +to be under the krdc threshold. + +Although this scheme is not as quick (nor as compressed) as +nx/nomachine, say, it does provide a good step in the direction of +improving VNC performance by client side caching. + + +### Q-80: Does x11vnc support TurboVNC? + +As of Feb/2009 (development tarball) there is an experimental kludge +to let you build x11vnc using TurboVNC's modified TightVNC encoding. +TurboVNC is part of the VirtualGL project. It does two main things to +speed up the TightVNC encoding: + +* It eliminates bottlenecks, overheads, wait-times in the TightVNC + encoding implementation and instead only worries about sending + very well (and quickly) compressed JPEG data. +* A fast proprietary JPEG implemention is used (Intel IPP on x86) + instead of the usual libjpeg implementation. TurboJPEG is an + interface library, libturbojpeg, provided by the project that + achieves this. + +TurboVNC works very well over LAN and evidently fast Broadband too. +When using it with x11vnc in such a situation you may want to dial +down the delays, e.g. "-wait 5" and "-defer 5" (or even a smaller +setting) to poll and pump things out more quickly. + +See the instructions in "x11vnc/misc/turbovnc/README" for how to build +x11vnc with TurboVNC support. You will also need to download the +TurboJPEG software. + + In brief, the steps look like this: + +``` +cd x11vnc-x.y.z/x11vnc/misc/turbovnc +./apply_turbovnc +cd ../../.. +env LDFLAGS='-L/DIR -Xlinker --rpath=/DIR' ./configure +make AM_LDFLAGS='-lturbojpeg' +``` + +where you replace "/DIR" with the directory containing libturbojpeg.so +you downloaded separately. If it works out well enough TurboVNC +support will be integrated into x11vnc and more of its tuning features +will be implemented. Support for TurboVNC in SSVNC viewer has been +added as an experiment as well. If you try either one, let us know how +it went. + +There also may be some Linux.i686 and Darwin.i386 x11vnc binaries with +TurboVNC support in the misc. bins directory. For other platforms you +will need to compile yourself. + +On relatively cheap and old hardware (Althon64 X2 5000+ / GeForce +6200) x11vnc and SSVNC, both TurboVNC enabled, were able to sustain +13.5 frames/sec (fps) and 15 Megapixels/sec using the VirtualGL +supplied OpenGL benchmark program glxspheres. VirtualGL on higher-end +hardware can sustain 20-30 fps with the glxspheres benchmark. + +Potential Slowdown: As we describe elsewhere, unless you use x11vnc +with an X server using, say, NVidia proprietary drivers (or a virtual +X server like Xvfb or Xdummy, or in ShadowFB mode), then the read rate +from the graphics card can be rather slow (e.g. 10 MB/sec) and becomes +the bottleneck when using x11vnc over fast networks. Note that all of +Xorg's drivers currently (2009) have slow read rates (only proprietary +drivers appear to have optimized reads.) + +So under these (more or less typical) conditions, the speed +improvement provided by TurboVNC may only be marginal. Look for this +output to see your read rate: + +``` +28/02/2009 11:11:07 Autoprobing TCP port +28/02/2009 11:11:07 Autoprobing selected port 5900 +28/02/2009 11:11:08 fb read rate: 10 MB/sec +28/02/2009 11:11:08 screen setup finished. +``` + +A rate of 10 MB/sec means a 1280x1024x24 screen takes 0.5 seconds to +read in. TurboVNC compresses that to JPEG in a much shorter time. On +the other hand, an NVidia driver may have a read rate of 250 MB/sec +and so only takes 0.02 seconds to read the entire screen in. + + +## Mouse Cursor Shapes + +### Q-81: Why isn't the mouse cursor shape (the little icon shape where the mouse pointer is) correct as I move from window to window? + +On X servers supporting XFIXES or Solaris/IRIX Overlay extensions it +is possible for x11vnc to do this correctly. See a few paragraphs down +for the answer. + +Historically, the X11 mouse cursor shape (i.e. little picture: an +arrow, X, I-beam, resizer, etc) is one of the few WRITE-only objects +in X11. That is, an application can tell the X server what the cursor +shape should be when the pointer is in a given window, but a program +(like x11vnc) unfortunately cannot read this information. I believe +this is because the cursor shape is often downloaded to the graphics +hardware (video card), but I could be mistaken. + +A simple kludge is provided by the "-cursor X" option that changes the +cursor when the mouse is on the root background (or any window has the +same cursor as the root background.) Note that desktops like GNOME or +KDE often cover up the root background, so this won't work for those +cases. Also see the "-cursor some" option for additional kludges. + +Note that as of Aug/2004 on Solaris using the SUN_OVL overlay +extension and IRIX, x11vnc can show the correct mouse cursor when the +-overlay option is supplied. See this FAQ for more info. + +Also as of Dec/2004 XFIXES X extension support has been added to allow +exact extraction of the mouse cursor shape. XFIXES fixes the problem +of the cursor-shape being write-only: x11vnc can now query the X +server for the current shape and send it back to the connected +viewers. XFIXES is available on recent Linux Xorg based distros and +Solaris 10. + +The only XFIXES issue is the handling of alpha channel transparency in +cursors. If a cursor has any translucency then in general it must be +approximated to opaque RGB values for use in VNC. There are some +situations where the cursor transparency can also handled exactly: +when the VNC Viewer requires the cursor shape be drawn into the VNC +framebuffer or if you apply a patch to your VNC Viewer to extract +hidden alpha channel data under 32bpp. Details can be found here. + + +### Q-82: When using XFIXES cursorshape mode, some of the cursors look really bad with extra black borders around the cursor and other cruft. How can I improve their appearance? + +This happens for cursors with transparency ("alpha channel"); regular +X cursors (bitmaps) should be correct. Unfortunately x11vnc 0.7 was +released with a very poor algorithm for approximating the +transparency, which led to the ugly black borders. + +The problem is as follows: XFIXES allows x11vnc to retrieve the +current X server cursor shape, including the alpha channel for +transparency. For traditional bitmap cursors the alpha value will be 0 +for completely transparent pixels and 255 for completely opaque +pixels; whereas for modern, eye-candy cursors an alpha value between 0 +and 255 means to blend in the background colors to that degree with +the cursor colors. The pixel color blending formula is something like +this: Red = Red_cursor * a + Red_background * (1 - a), (where here 0 +=< a =< 1), with similar for Green and Blue. The VNC protocol does not +currently support an alpha channel in cursors: it only supports +regular X bitmap cursors and Rich Cursors that have RGB (Red, Green, +Blue) color data, but no "A" = alpha data. So in general x11vnc has to +approximate a cursor with transparency to create a Rich Cursor. This +is easier said than done: some cursor themes have cursors with +complicated drop shadows and other forms of translucency. + +Anyway, for the x11vnc 0.7.1 release the algorithm for approximating +transparency is much improved and hopefully gives decent cursor shapes +for most cursor themes and you don't have to worry about it. + +In case it still looks bad for your cursor theme, there are (of +course!) some tunable parameters. The "-alphacut n" option lets you +set the threshold "n" (between 0 and 255): cursor pixels with alpha +values below n will be considered completely transparent while values +equal to or above n will be completely opaque. The default is 240. The +"-alphafrac f" option tries to correct individual cursors that did not +fare well with the default -alphacut value: if a cursor has less than +fraction f (between 0.0 and 1.0) of its pixels selected by the default +-alphacut, the threshold is lowered until f of its pixels are +selected. The default fraction is 0.33. + +Finally, there is an option -alpharemove that is useful for themes +where many cursors are light colored (e.g. "whiteglass".) XFIXES +returns the cursor data with the RGB values pre-multiplied by the +alpha value. If the white cursors look too grey, specify -alpharemove +to brighten them by having x11vnc divide out the alpha value. + +One user played with these parameters and reported back: + +``` + Of the cursor themes present on my system: + + gentoo and gentoo-blue: alphacut:192 - noalpharemove + + gentoo-silver: alphacut:127 and alpharemove + + whiteglass and redglass (presumably also handhelds, which is based + heavily on redglass) look fine with the apparent default of alphacut:255. +``` + +### Q-83: In XFIXES mode, are there any hacks to handle cursor transparency ("alpha channel") exactly? + +As of Jan/2005 libvncserver has been modified to allow an alpha +channel (i.e. RGBA data) for Rich Cursors. So x11vnc can now send the +alpha channel data to libvncserver. However, this data will only be +used for VNC clients that do not support the CursorShapeUpdates VNC +extension (or have disabled it.) It can be disabled for all clients +with the -nocursorshape x11vnc option. In this case the cursor is +drawn, correctly blended with the background, into the VNC framebuffer +before being sent out to the client. So the alpha blending is done on +the x11vnc side. Use the -noalphablend option to disable this behavior +(always approximate transparent cursors with opaque RGB values.) + +The CursorShapeUpdates VNC extension complicates matters because the +cursor shape is sent to the VNC viewers supporting it, and the viewers +draw the cursor locally. This improves response over slow links. Alpha +channel data for these locally drawn cursors is not supported by the +VNC protocol. + +However, in the libvncserver CVS there is a patch to the TightVNC +viewer to make this work for CursorShapeUpdates under some +circumstances. This hack is outside of the VNC protocol. It requires +the screens on both sides to be depth 24 at 32bpp (it uses the extra 8 +bits to secretly hide the cursor alpha channel data.) Not only does it +require depth 24 at 32bpp, but it also currently requires the client +and server to be of the same endianness (otherwise the hidden alpha +data gets reset to zero by a libvncserver translation function; we can +fix this at some point if there is interest.) The patch is for the +TightVNC 1.3dev5 Unix vncviewer and it enables the TightVNC viewer to +do the cursor alpha blending locally. The patch code should give an +example on how to change the Windows TightVNC viewer to achieve the +same thing (send me the patch if you get that working.) + +This patch is applied to the Enhanced TightVNC Viewer (SSVNC) package +we provide. + + +## Mouse Pointer + +### Q-84: Why does the mouse arrow just stay in one corner in my vncviewer, whereas my cursor (that does move) is just a dot? + +This default takes advantage of a tightvnc extension +(CursorShapeUpdates) that allows specifying a cursor image shape for +the local VNC viewer. You may disable it with the -nocursor option to +x11vnc if your viewer does not have this extension. + +Note: as of Aug/2004 this should be fixed: the default for +non-tightvnc viewers (or ones that do not support CursorShapeUpdates) +will be to draw the moving cursor into the x11vnc framebuffer. This +can also be disabled via -nocursor. + + +### Q-85: Can I take advantage of the TightVNC extension to the VNC protocol where Cursor Positions Updates are sent back to all connected clients (i.e. passive viewers can see the mouse cursor being moved around by another viewer)? + +Use the -cursorpos option when starting x11vnc. A VNC viewer must +support the Cursor Positions Updates for the user to see the mouse +motions (the TightVNC viewers support this.) As of Aug/2004 -cursorpos +is the default. See also -nocursorpos and -nocursorshape. + + +### Q-86: Is it possible to swap the mouse buttons (e.g. left-handed operation), or arbitrarily remap them? How about mapping button clicks to keystrokes, e.g. to partially emulate Mouse wheel scrolling? + +You can remap the mouse buttons via something like: -buttonmap 13-31 +(or perhaps 12-21.) Also, note that xmodmap(1) lets you directly +adjust the X server's button mappings, but in some circumstances it +might be more desirable to have x11vnc do it. + +One user had an X server with only one mouse button(!) and was able to +map all of the VNC client mouse buttons to it via: -buttonmap 123-111. + +Note that the -debug_pointer option prints out much info for every +mouse/pointer event and is handy in solving problems. + +To map mouse button clicks to keystrokes you can use the alternate +format where the keystrokes are enclosed between colons like this +:: in place of the mouse button digit. For a sequence of +keysyms separate them with "+" signs. Look in the include file +, or use xev(1), or -debug_keyboard to find the +keysym names. Button clicks can also be included in the sequence via +the fake keysyms Button1, etc. + +As an example, suppose the VNC viewer machine has a mouse wheel (these +generate button 4 and 5 events), but the machine that x11vnc is run on +only has the 3 regular buttons. In normal operation x11vnc will +discard the button 4 and 5 events. However, either of the following +button maps could possibly be of use emulating the mouse wheel events +in this case: + +``` +-buttonmap 12345-123:Prior::Next: +-buttonmap 12345-123:Up+Up+Up::Down+Down+Down: +``` + +Exactly what keystroke "scrolling" events they should be bound to +depends on one's taste. If this method is too approximate, one could +consider not using -buttonmap but rather configuring the X server to +think it has a mouse with 5 buttons even though the physical mouse +does not. (e.g. 'Option "ZAxisMapping" "4 5"'.) + +Note that when a keysym-mapped mouse button is clicked down this +immediately generates the key-press and key-release events (for each +keysym in turn if the mapping has a sequence of keysyms.) When the +mouse button goes back up nothing is generated. + +If you include modifier keys like Shift_L instead of key-press +immediately followed by key-release the state of the modifier key is +toggled (however the initial state of the modifier key is ignored.) So +to map the right button to type my name 'Karl Runge' I could use this: + +``` +-buttonmap 3-:Shift_L+k+Shift_L+a+r+l+space+Shift_L+r+Shift_L+u+n+g+e: +``` + +(yes, this is getting a little silly.) + +BTW, Coming the other way around, if the machine you are sitting at +does not have a mouse wheel, but the remote machine does (or at least +has 5 buttons configured), this key remapping can be useful: + +``` +-remap Super_R-Button4,Menu-Button5 +``` + +you just tap those two keys to get the mouse wheel scrolls (this is +more useful than the Up and Down arrow keys because a mouse wheel +"click" usually gives a multi-line scroll.) + + +## Keyboard Issues + +### Q-87: How can I get my AltGr and Shift modifiers to work between keyboards for different languages? + +The option -modtweak should help here. It is a mode that monitors the +state of the Shift and AltGr Modifiers and tries to deduce the correct +keycode to send, possibly by sending fake modifier key presses and +releases in addition to the actual keystroke. + +Update: As of Jul/2004 -modtweak is now the default (use -nomodtweak +to get the old behavior.) This was done because it was noticed on +newer XFree86 setups even on bland "us" keyboards like "pc104 us" +XFree86 included a "ghost" key with both "<" and ">" it. This key does +not exist on the keyboard (see this FAQ for more info.) Without +-modtweak there was then an ambiguity in the reverse map keysym => +keycode, making it so the "<" symbol could not be typed. + +Also see the FAQ about the -xkb option for a more powerful method of +modifier tweaking for use on X servers with the XKEYBOARD extension. + +When trying to resolve keyboard mapping problems, note that the +-debug_keyboard option prints out much info for every keystroke and so +can be useful debugging things. + +Note that for some users, the solution is to disable all of the above, +and use -nomodtweak. This is the simplest form of keystroke insertion and +it actually solved the problem. Try it if the other options don't help. + + +### Q-88: When I try to type a "<" (i.e. less than) instead I get ">" (i.e. greater than)! Strangely, typing ">" works OK!! + +Does your keyboard have a single key with both "<" and ">" on it? Even +if it doesn't, your X server may think your keyboard has such a key +(e.g. pc105 in the XF86Config file when it should be something else, +say pc104.) + +Short Cut: Try the -xkb or -sloppy_keys options and see if that helps +the situation. The discussion below is a bit outdated (e.g. -modtweak +is now the default) but it is useful reference for various tricks and +so is kept. + + +The problem here is that on the Xserver where x11vnc is run there are +two keycodes that correspond to the "<" keysym. Run something like +this to see: + +``` +xmodmap -pk | egrep -i 'KeyCode|less|greater' +There are 4 KeySyms per KeyCode; KeyCodes range from 8 to 255. + KeyCode Keysym (Keysym) ... + 59 0x002c (comma) 0x003c (less) + 60 0x002e (period) 0x003e (greater) + 94 0x003c (less) 0x003e (greater) +``` + +That keycode 94 is the special key with both "<" and ">". When x11vnc +receives the "<" keysym over the wire from the remote VNC client, it +unfortunately maps it to keycode 94 instead of 59, and sends 94 to the +X server. Since Shift is down (i.e. you are Shifting the comma key), +the X server interprets this as Shifted-94, which is ">". + +A workaround in the X server configuration is to "deaden" that special +key: + +``` +xmodmap -e "keycode 94 = " +``` + +However, one user said he had to do this: + +``` +xmodmap -e "keycode 94 = 0x002c 0x003c" +``` + +(If the numerical values are different for your setup, substitute the +ones that correspond to your display. The above xmodmap scheme can +often be used to work around other ambiguous keysym to keycode +mappings.) + +Alternatively, here are some x11vnc options to try to work around the +problem: + +``` +-modtweak +``` + +and + +``` +-remap less-comma +``` + +These are convenient in that they do not modify the actual X server +settings. The former (-modtweak) is a mode that monitors the state of +the Shift and AltGr modifiers and tries to deduce the correct keycode +sequence to send. Since Jul/2004 -modtweak is now the default. The +latter (-remap less-comma) is an immediate remapping of the keysym +less to the keysym comma when it comes in from a client (so when Shift +is down the comma press will yield "<".) + +See also the FAQ about the -xkb option as a possible workaround using +the XKEYBOARD extension. + +Note that the -debug_keyboard option prints out much info for every +keystroke to aid debugging keyboard problems. + + +### Q-89: Extra Character Inserted, E.g.: When I try to type a "<" (i.e. less than) instead I get "<," (i.e. an extra comma.) + +This is likely because you press "Shift" then "<" but then released +the Shift key before releasing the "<". Because of a keymapping +ambiguity the last event "< up" is interpreted as "," because that key +unshifted is the comma. + +This extra character insertion will happen for other combinations of +characters: in general it can happen whenever the Shift key is +released early. + +This should not happen in -xkb mode, because it works hard to resolve +the ambiguities. If you do not want to use -xkb, try the option +-sloppy_keys to attempt a similar type of algorithm. + +One user had this problem for Italian and German keyboards with the +key containing ":" and "." When he typed ":" he would get an extra "." +inserted after the ":". The solution was -sloppy_keys. + + +### Q-90: I'm using an "international" keyboard (e.g. German "de", or Danish "dk") and the -modtweak mode works well if the VNC viewer is run on a Unix/Linux machine with a similar keyboard. But if I run the VNC viewer on Unix/Linux with a different keyboard (e.g. "us") or Windows with any keyboard, I can't type some keys like: "@", "$", "<", ">", etc. How can I fix this? + +The problem with Windows is it does not seem to handle AltGr well. It +seems to fake it up by sending Control_L+Alt_R to applications. The +Windows VNC viewer sends those two down keystrokes out on the wire to +the VNC server, but when the user types the next key to get, e.g., "@" +the Windows VNC viewer sends events bringing the up the +Control_L+Alt_R keys, and then sends the "@" keysym by itself. + +The Unix/Linux VNC viewer on a "us" keyboard does a similar thing +since "@" is the Shift of the "2" key. The keysyms Shift and "@" are +sent to the VNC server. + +In both cases no AltGr is sent to the VNC server, but we know AltGr is +needed on the physical international keyboard to type a "@". + +This all worked fine with x11vnc running with the -modtweak option (it +figures out how to adjust the Modifier keys (Shift or AltGr) to get +the "@".) However it fails under recent versions of XFree86 (and the +X.org fork.) These run the XKEYBOARD extension by default and make +heavy use of it to handle international keyboards. + +To make a long story short, on these newer XFree86 setups the +traditional X keymap lookup x11vnc uses is no longer accurate. x11vnc +can't find the keysym "@" anywhere in the keymapping! (even though it +is in the XKEYBOARD extended keymapping.) + +How to Solve: As of Jul/2004 x11vnc has two changes: + +* -modtweak (tweak Modifier keys) is now the default (use + -nomodtweak to go back to the old way) +* there is a new option -xkb to use the XKEYBOARD extension API to + do the Modifier key tweaking. + +The -xkb option seems to fix all of the missing keys: "@", "<", ">", +etc.: it is recommended that you try it if you have this sort of +problem. Let us know if there are any remaining problems (see the next +paragraph for some known problems.) If you specify the -debug_keyboard +(aka -dk) option twice you will get a huge amount of keystroke +debugging output (send it along with any problems you report.) + +Update: as of Jun/2005 x11vnc will try to automatically enable -xkb if +it appears that would be beneficial (e.g. if it sees any of "@", "<", +">", "[" and similar keys are mapped in a way that needs the -xkb to +access them.) To disable this automatic check use -noxkb. + +Known problems: + +* One user had to disable a "ghost" Mode_switch key that was causing + problems under -xkb. His physical AltGr key was bound to + ISO_Level3_Shift (which seems to be the XKEYBOARD way of doing + things), while there was a ghost key Mode_switch (which seems to + be obsolete) in the mapping as well. Both of these keysyms were + bound to Mod5 and x11vnc was unfortunately choosing Mode_switch. + From the x11vnc -xkb -dk -dk output it was noted that Mode_switch + was attached to keycode 93 (no physical key generates this + keycode) while ISO_Level3_Shift was attached to keycode 113. The + keycode skipping option was used to disable the ghost key: + -skip_keycodes 93 +* In implementing -xkb we noticed that some characters were still + not getting through, e.g. "~" and "^". This is not really an + XKEYBOARD problem. What was happening was the VNC viewer was + sending the keysyms asciitilde and asciicircum to x11vnc, but on + the X server with the international keyboard those keysyms were + not mapped to any keys. So x11vnc had to skip them (Note: as of + May/2005 they are added by default see -add_keysyms below.) + The way these characters are typically entered on international + keyboards is by "dead" (aka "mute") keys. E.g. to enter "~" at the + physical display the keysym dead_tilde is pressed and released + (this usually involves holding AltGr down while another key is + pressed) and then space is pressed. (this can also be used get + characters with the "~" symbol on top, e.g. "\E3" by typing "a" + instead of space.) + What to do? In general the VNC protocol has not really solved this + problem: what should be done if the VNC viewer sends a keysym not + recognized by the VNC server side? Workarounds can possibly be + created using the -remap x11vnc option: + + ``` + -remap asciitilde-dead_tilde,asciicircum-dead_circumflex + ``` + + etc. Use -remap filename if the list is long. Please send us your + workarounds for this problem on your keyboard. Perhaps we can have + x11vnc adjust automatically at some point. Also see the + -add_keysyms option in the next paragraph. + Update: for convenience "-remap DEAD" does many of these mappings + at once. +* To complement the above workaround using the -remap, an option + -add_keysyms was added. This option instructs x11vnc to bind any + unknown Keysyms coming in from VNC viewers to unused Keycodes in + the X server. This modifies the global state of the X server. When + x11vnc exits it removes the extra keymappings it created. Note + that the -remap mappings are applied first, right when the Keysym + is received from a VNC viewer, and only after that would + -add_keysyms, or anything else, come into play. + Update: -add_keysyms is now on by default. Use -noadd_keysyms to + disable. + + +### Q-91: When typing I sometimes get double, triple, or more of my keystrokes repeated. I'm sure I only typed them once, what can I do? + +This may be due to an interplay between your X server's key autorepeat +delay and the extra time delays caused by x11vnc processing. + +Short answer: disable key autorepeating by running the command "xset r +off" on the Xserver where x11vnc is run (restore via "xset r on") or +use the new (Jul/2004) -norepeat x11vnc option. You will still have +autorepeating because that is taken care of on your VNC viewer side. + +Update: as of Dec/2004 -norepeat is now the default. Use -repeat to +disable it. + +Details: +suppose you press a key DOWN and it generates changes in large regions +of the screen. The CPU and I/O work x11vnc does for the large screen +change could be longer than your X server's key autorepeat delay. +x11vnc may not get to processing the key UP event until after the +screen work is completed. The X server believes the key has been held +down all this time, and applies its autorepeat rules. + +Even without inducing changes in large regions of the screen, this +problem could arise when accessing x11vnc via a dialup modem or +otherwise high latency link (e.g. > 250 ms latency.) + +Look at the output of "xset q" for the "auto repeat delay" setting. Is +it low (e.g. < 300 ms)? If you turn off autorepeat completely: "xset r +off", does the problem go away? + +The workaround is to manually apply "xset r off" and "xset r on" as +needed, or to use the -norepeat (which has since Dec/2004 been made +the default.) Note that with X server autorepeat turned off the VNC +viewer side of the connection will (nearly always) do its own +autorepeating so there is no big loss here, unless someone is also +working at the physical display and misses his autorepeating. + + +### Q-92: The x11vnc -norepeat mode is in effect, but I still get repeated keystrokes!! + +Are you using x11vnc to log in to an X session via display manager? +(as described in this FAQ) If so, x11vnc is starting before your +session and it disables autorepeat when you connect, but then after +you log in your session startup (GNOME, KDE, ...) could be resetting +the autorepeat to be on. Or it could be something inside your desktop +trying to be helpful that decides to turn it back on. + +x11vnc in -norepeat mode will by default reset autorepeat to off 2 +times (to help get thru the session startup problem), but it will not +continue to battle with things turning autorepeat back on. It will +also turn autorepeat off whenever it goes from a state of zero clients +to one client. You can adjust the number of resets via "-norepeat N", +or use "-norepeat -1" to have it keep resetting it whenever autorepeat +gets turned back on when clients are connected. + +In general you can manually turn autorepeating off by typing "xset r +off", or a using desktop utility/menu, or "x11vnc -R norepeat". If +something in your desktop is automatically turning it back on you +should figure out how to disable that somehow. + + +### Q-93: After using x11vnc for a while, I find that I cannot type some (or any) characters or my mouse clicks and drags no longer have any effect, or they lead to strange effects. What happened? + +Probably a modifier key, e.g. Control or Alt is "stuck" in a pressed +down state. + +This happens for VNC in general by the following mechanism. Suppose on +the Viewer side desktop there is some hot-key to switch +desktops/rooms/spaces, etc. E.g. suppose Alt+LeftArrow moves to the +left desktop/room/space. Or suppose an Alt+hotkey combination +iconifies a window. This can leave the Alt key pressed down on the +remote side. + +Consider the sequence that happens. The Alt_L key and then the +LeftArrow key go down. Since you are inside the viewer the Alt_L key +press is sent to the other side (x11vnc) and so it is pressed down in +the remote desktop as well. (by "Alt_L" we mean the Alt key on the +left-hand side of the keyboard.) Your local desktop (where the VNC +Viewer is running) then warps to the new desktop/room/space: Leaving +the Alt_L key still pressed down in the remote desktop. + +If someone is sitting at the desktop, or when you return in the viewer +it may be very confusing because the Alt_L is still pressed down but +you (or the person sitting at the desktop) do not realize this. +Depending on which remote desktop (x11vnc side) is used, it can act +very strangely. + +A quick workaround when you notice this is to press and release all of +the Alt, Shift, Control, Windows-Flag, modifier keys to free the +pressed one. You need to do this for both the left and right Shift, +Alt, Control, etc. keys to be sure. + +Note that many VNC Viewers try to guard against this when they are +notified by the window system that the viewer app has "lost focus". +When it receives the "lost focus" event, the viewer sends VNC +Key-Release events for all modifier keys that are currently pressed +down. This does not always work, however, since it depends on how the +desktop manages these "warps". If the viewer is not notified it cannot +know it needs to release the modifiers. + +You can also use the -clear_mods option to try to clear all of the +modifier keys at x11vnc startup. You will still have to be careful +that you do not leave the modifier key pressed down during your +session. It is difficult to prevent this problem from occurring (short +of using -remap to prevent sending all of the problem modifier keys, +which would make the destkop pretty unusable.) + +During a session these x11vnc remote control commands can also help: + +``` +x11vnc -R clear_mods +x11vnc -R clear_keys +x11vnc -R clear_locks +x11vnc -R clear_all +``` + +A similar problem can occur if you accidentally press the Caps_Lock or +Num_Lock down. When these are locked on the remote side it can +sometimes lead to strange desktop behavior (e.g. cannot drag or click +on windows.) As above you may not notice this because the lock isn't +down on the local (Viewer) side. See this FAQ on lock keys problem. +These options may help avoid the problem: -skip_lockkeys and +-capslock. See also -clear_all. + + +### Q-94: The machine where I run x11vnc has an AltGr key, but the local machine where I run the VNC viewer does not. Is there a way I can map a local unused key to send an AltGr? How about a Compose key as well? + +Something like "-remap Super_R-Mode_switch" x11vnc option may work. +Note that Super_R is the "Right Windoze(tm) Flaggie" key; you may want +to choose another. The -debug_keyboard option comes in handy in +finding keysym names (so does xev(1).) + +For Compose how about "-remap Menu-Multi_key" (note that Multi_key is +the official name for Compose.) To do both at the same time: "-remap +Super_R-Mode_switch,Menu-Multi_key" or use "-remap filename" to +specify remappings from a file. + + +### Q-95: I have a Sun machine I run x11vnc on. Its Sun keyboard has just one Alt key labelled "Alt" and two Meta keys labelled with little diamonds. The machine where I run the VNC viewer only has Alt keys. How can I send a Meta keypress? (e.g. emacs needs this) + +Here are a couple ideas. The first one is to simply use xmodmap(1) to +adjust the Sun X server. Perhaps xmodmap -e "keysym Alt_L = Meta_L +Alt_L" will do the trick. (there are other ways to do it, one user +used: xmodmap -e "keycode 26 = Meta_L" for his setup.) + +Since xmodmap(1) modifies the X server mappings you may not want to do +this (because it affects local work on that machine.) Something like +the -remap Alt_L-Meta_L to x11vnc may be sufficient for ones needs, +and does not modify the X server environment. Note that you cannot +send Alt_L in this case, maybe -remap Super_L-Meta_L would be a better +choice if the Super_L key is typically unused in Unix. + + +### Q-96: Running x11vnc on HP-UX I cannot type "#" I just get a "3" instead. + +One user reports this problem on HP-UX Rel_B.11.23. The problem was +traced to a strange keyboard mapping for the machine (e.g. xmodmap -pk +output) that looked like: + +``` +... +039 2 at at at +... +047 3 numbersign numbersign numbersign +``` + +and similar triple mappings (with two in the AltGr/Mode_switch group) +of a keysum to a single keycode. + +Use the -nomodtweak option as a workaround. You can also use xmodmap +to correct these mappings in the server, e.g.: + +``` +xmodmap -e "keycode 47 = 3 numbersign" +``` + +Also, as of Feb/2007, set the environment variable MODTWEAK_LOWEST=1 +(either in your shell or via "-env MODTWEAK_LOWEST=1" option) to +handle these mappings better. + + +### Q-97: Can I map a keystroke to a mouse button click on the remote machine? + +This can be done directly in some X servers using AccessX and +Pointer_EnableKeys, but is a bit awkward. It may be more convenient to +have x11vnc do the remapping. This can be done via the -remap option +using the fake "keysyms" Button1, Button2, etc. as the "to" keys (i.e. +the ones after the "-") + +As an example, consider a laptop where the VNC viewer is run that has +a touchpad with only two buttons. It is difficult to do a middle +button "paste" because (using XFree86/Xorg Emulate3Buttons) you have +to click both buttons on the touch pad at the same time. This +remapping: +-remap Super_R-Button2 + +maps the Super_R "flag" key press to the Button2 click, thereby making +X pasting a bit easier. + +Note that once the key goes down, the button down and button up events +are generated immediately on the x11vnc side. When the key is released +(i.e. goes up) no events are generated. + +### Q-98: How can I get Caps_Lock to work between my VNC viewer and x11vnc? + +This is a little tricky because it is possible to get the Caps_Lock +state out of sync between your viewer-side machine and the x11vnc-side +X server. For best results, we recommend not ever letting the +Caps_Lock keypresses be processed by x11vnc. That way when you press +Caps_Lock in the viewer your local machine goes into the Caps_Lock on +state and sends keysym "A" say when you press "a". x11vnc will then +fake things up so that Shift is held down to generate "A". The +-skip_lockkeys option should help to accomplish this. For finer grain +control use something like: "-remap Caps_Lock-None". + +Also try the -nomodtweak and -capslock options. + +Another useful option that turns off any Lock keys on the remote side +at startup and end is the -clear_all option. During a session you can +run these remote control commands to modify the Lock keys: +x11vnc -R clear_locks +x11vnc -R clear_all + +the former will try to unset any Lock keys, the latter will do same +and also try to make it so no key is pressed down (e.g. "stuck" Alt_L, +etc.) + +## Screen Related Issues and Features + +### Q-99: The remote display is larger (in number of pixels) than the local display I am running the vncviewer on. I don't like the vncviewer scrollbars, what I can do? + +vncviewer has a option (usually accessible via F8 key or -fullscreen +option) for vncviewer to run in full screen, where it will +automatically scroll when the mouse is near the edge of the current +view. For quick scrolling, also make sure Backing Store is enabled on +the machine vncviewer is run on. (XFree86/Xorg disables it by default +for some reason, add Option "backingstore" to XF86Config on the +vncviewer side.) + +BTW, contact me if you are having problems with vncviewer in +fullscreen mode with your window manager (i.e. no keyboard response.) +I have a workaround for vncviewer using XGrabServer(). + +There may also be scaling viewers out there (e.g. TightVNC or UltraVNC +on Windows) that automatically shrink or expand the remote framebuffer +to fit the local display. Especially for hand-held devices. See also +the next FAQ on x11vnc scaling. + + +### Q-100: Does x11vnc support server-side framebuffer scaling? (E.g. to make the desktop smaller.) + +As of Jun/2004 x11vnc provides basic server-side scaling. It is a +global scaling of the desktop, not a per-client setting. To enable it +use the "-scale fraction" option. "fraction" can either be a floating +point number (e.g. -scale 0.75) or the alternative m/n fraction +notation (e.g. -scale 3/4.) Note that if fraction is greater than one +the display is magnified. + +Extra resources (CPU, memory I/O, and memory) are required to do the +scaling. If the machine is slow where x11vnc is run with scaling +enabled, the interactive response can be unacceptable. OTOH, if run +with scaling on a fast machine the performance degradation is usually +not a big issue or even noticeable. + +It may help to compile x11vnc with compiler option -O3 or -O4 to speed +up the scaling code. Set the CFLAGS env. var. before running +configure. + +Also, if you just want a quick, rough "thumbnail" of the display you +can append ":nb" to the fraction to turn on "no blending" mode. E.g.: +"-scale 1/3:nb" Fonts will be difficult to read, but the larger +features will be recognizable. BTW, "no blending" mode is forced on +when scaling 8bpp PseudoColor displays (because blending an indexed +colormap is a bad idea and leads to random colors, use :fb to force it +on.) + +One can also use the ":nb" with an integer scale factor (say "-scale +2:nb") to use x11vnc as a screen magnifier for vision impaired +applications. Since with integer scale factors the framebuffers become +huge and scaling operations time consuming, be sure to use ":nb" for +the fastest response. + +In general for a scaled display if you are using a TightVNC viewer you +may want to turn off jpeg encoding (e.g. vncviewer -nojpeg host:0.) +There appears to be a noise enhancement effect, especially for regions +containing font/text: the scaling can introduce some pixel artifacts +that evidently causes the tight encoding algorithm to incorrectly +detect the regions as image data and thereby introduce additional +pixel artifacts due to the lossiness of the jpeg compression +algorithm. Experiment to see if -nojpeg vncviewer option improves the +readability of text when using -scale to shrink the display size. Also +note that scaling may actually slow down the transfer of text regions +because after being scaled they do not compress as well. (this can +often be a significant slowdown, e.g. 10X.) + +Another issue is that it appears VNC viewers require the screen width +to be a multiple of 4. When scaling x11vnc will round the width to the +nearest multiple of 4. To disable this use the ":n4" sub option (like +":nb" in the previous paragraph; to specify both use a comma: +":nb,n4", etc.) + +If one desires per-client scaling for something like 1:1 from a +workstation and 1:2 from a smaller device (e.g. handheld), currently +the only option is to run two (or more) x11vnc processes with +different scalings listening on separate ports (-rfbport option, etc.) + +Update: As of May/2006 x11vnc also supports the UltraVNC server-side +scaling. This is a per-client scaling by factors 1/2, 1/3, ... and so +may be useful for PDA's ("-scale 1/2", etc. will give similar results +except that it applies to all clients.) You may need to supply +"-rfbversion 3.6" for this to be recognized by UltraVNC viewers. + +BTW, whenever you run two or more x11vnc's on the same X display and +use the GUI, then to avoid all of the x11vnc's simultaneously +answering the gui you will need to use something like "-connect file1 +-gui ..." with different connect files for each x11vnc you want to +control via the gui (or remote-control.) The "-connect file1" usage +gives separate communication channels between a x11vnc process and the +gui process. Otherwise they all share the same X property channels: +VNC_CONNECT and X11VNC_REMOTE. + +Update: As of Mar/2005 x11vnc now scales the mouse cursor with the +same scale factor as the screen. If you don't want that, use the +"-scale_cursor frac" option to set the cursor scaling to a different +factor (e.g. use "-scale_cursor 1" to keep the cursor at its natural +unscaled size.) + + +### Q-101: Does x11vnc work with Xinerama? (i.e. multiple monitors joined together to form one big, single screen.) + +Yes, it should generally work because it simply polls the big +effective screen. + +If the viewing-end monitor is not as big as the remote Xinerama +display, then the vncviewer scrollbars, etc, will have to be used to +pan across the large area. However one user started two x11vnc's, one +with "-clip 1280x1024+0+0" and the other with "-clip 1280x1024+1280+0" +to split the big screen into two and used two VNC viewers to access +them. + +As of Jun/2008: Use "-clip xinerama0" to clip to the first xinerama +sub-screen (if xinerama is active.) xinerama1 for the 2nd sub-screen, +etc. This way you don't need to figure out the WxH+X+Y of the desired +xinerama sub-screen. screens are sorted in increasing distance from +the (0,0) origin (I.e. not the Xserver's order.) + +There are a couple potential issues with Xinerama however. If the +screen is not rectangular (e.g. 1280x1024 and 1024x768 monitors joined +together), then there will be "non-existent" areas on the screen. The +X server will return "garbage" image data for these areas and so they +may be distracting to the viewer. The -blackout x11vnc option allows +you to blacken-out rectangles by manually specifying their WxH+X+Y +geometries. If your system has the libXinerama library, the -xinerama +x11vnc option can be used to have it automatically determine the +rectangles to be blackened out. (Note on 8bpp PseudoColor displays the +fill color may not be black.) Update: -xinerama is now on by default. + +Some users have reported that the mouse does not behave properly for +their Xinerama display: i.e. the mouse cannot be moved to all regions +of the large display. If this happens try using the -xwarppointer +option. This instructs x11vnc to fake mouse pointer motions using the +XWarpPointer function instead of the XTestFakeMotionEvent XTEST +function. (This may be due to a bug in the X server for XTEST when +Xinerama is enabled.) Update: As of Dec/2006 -xwarppointer will be +applied automatically if Xinerama is detected. To disable use: +-noxwarppointer + + +### Q-102: Can I use x11vnc on a multi-headed display that is not Xinerama (i.e. separate screens :0.0, :0.1, ... for each monitor)? + +You can, but it is a little bit awkward: you must start separate +x11vnc processes for each screen, and on the viewing end start up +separate VNC viewer processes connecting to them. e.g. on the remote +end: + +``` +x11vnc -display :0.0 -bg -q -rfbport 5900 +x11vnc -display :0.1 -bg -q -rfbport 5901 +``` + +(this could be automated in the display manager Xsetup for example) +and then on the local machine where you are sitting: + +``` +vncviewer somehost:0 & +vncviewer somehost:1 & +``` + +Note: if you are running on Solaris 8 or earlier you can easily hit up +against the maximum of 6 shm segments per process (for Xsun in this +case) from running multiple x11vnc processes. You should modify +/etc/system as mentioned in another FAQ to increase the limit. It is +probably also a good idea to run with the -onetile option in this case +(to limit each x11vnc to 3 shm segments), or even -noshm to use no shm +segments. + + +### Q-103: Can x11vnc show only a portion of the display? (E.g. for a special purpose application or a very large screen.) + +As of Mar/2005 x11vnc has the "-clip WxH+X+Y" option to select a +rectangle of width W, height H and offset (X, Y). Thus the VNC screen +will be the clipped sub-region of the display and be only WxH in size. +One user used -clip to split up a large Xinerama screen into two more +managable smaller screens. + +This also works to view a sub-region of a single application window if +the -id or -sid options are used. The offset is measured from the +upper left corner of the selected window. + + +### Q-104: Does x11vnc support the XRANDR (X Resize, Rotate and Reflection) extension? Whenever I rotate or resize the screen x11vnc just seems to crash. + +As of Dec/2004 x11vnc supports XRANDR. You enable it with the -xrandr +option to make x11vnc monitor XRANDR events and also trap X server +errors if the screen change occurred in the middle of an X call like +XGetImage. Once it traps the screen change it will create a new +framebuffer using the new screen. + +If the connected vnc viewers support the NewFBSize VNC extension +(Windows TightVNC viewer and RealVNC 4.0 windows and Unix viewers do) +then the viewer will automatically resize. Otherwise, the new +framebuffer is fit as best as possible into the original viewer size +(portions of the screen may be clipped, unused, etc.) For these +viewers you can try the -padgeom option to make the region big enough +to hold all resizes and rotations. We have fixed this problem for the +TightVNC Viewer on Unix: SSVNC + +If you specify "-xrandr newfbsize" then vnc viewers that do not +support NewFBSize will be disconnected before the resize. If you +specify "-xrandr exit" then all will be disconnected and x11vnc will +terminate. + + +### Q-105: Independent of any XRANDR, can I have x11vnc rotate and/or reflect the screen that the VNC viewers see? (e.g. for a handheld whose screen is rotated 90 degrees.) + +As of Jul/2006 there is the -rotate option allow this. E.g's: "-rotate ++90", "-rotate -90", "-rotate x", etc. + + +### Q-106: Why is the view in my VNC viewer completely black? Or why is everything flashing around randomly? + +See the next FAQ for a possible explanation. + + +### Q-107: I use Linux Virtual Terminals (VT's) to implement 'Fast User Switching' between users' sessions (e.g. Betty is on Ctrl-Alt-F7, Bobby is on Ctrl-Alt-F8, and Sid is on Ctrl-Alt-F1: they use those keystrokes to switch between their sessions.) How come the view in a VNC viewer connecting to x11vnc is either completely black or otherwise all messed up unless the X session x11vnc is attached to is in the active VT? + +This seems to have to do with how applications (the X server processes +in this case) must "play nicely" if they are not on the active VT +(sometimes called VC for virtual console.) That is, they should not +read from the keyboard or mouse or manage the video display unless +they have the active VT. Given that it appears the XGetImage() call +must ultimately retrieve the framebuffer data from the video hardware +itself, it would make sense x11vnc's polling wouldn't work unless the +X session had active control of the VT. + +There does not seem to be an easy way to work around this. Even xwd(1) +doesn't work in this case (try it.) Something would need to be done at +a lower level, say in the XFree86/Xorg X server. Also, using the +Shadow Framebuffer (a copy of the video framebuffer is kept in main +memory) does not appear to fix the problem. + +If no one is sitting at the workstation and you just want to remotely +switch the VT over to the one associated with your X session (so +x11vnc can poll it correctly), one can use the chvt(1) command, e.g. +"chvt 7" for VT #7. + + +### Q-108: I am using x11vnc where my local machine has "popup/hidden taskbars" and the remote display where x11vnc runs also has "popup/hidden taskbars" and they interfere and fight with each other. What can I do? + +When you move the mouse to the edge of the screen where the popups +happen, the taskbars interfere with each other in strange ways. This +sometimes happens where the local machine is GNOME or Mac OS X and the +remote machine is GNOME. Is there a way to temporarily disable one or +both of these magic desktop taskbars? + +One x11vnc user suggests: it should be straightforward to right mouse +click on the task bar panel, and uncheck "enable auto-hide" from the +panel properties dialog box. This will make the panel always visible. + +### Q-109: Help! x11vnc and my KDE screensaver keep switching each other on and off every few seconds. + +This is a new (Jul/2006) problem seen, say, on the version of KDE that +is shipped with SuSE 10.1. It is not yet clear what is causing this... +If you move the mouse through x11vnc the screensaver shuts off like it +should but then a second or two after you stop moving the mouse the +screensaver snaps back on. + +This may be a bug in kdesktop_lock. For now the only workaround is to +disable the screensaver. You can try using another one such as +straight xscreensaver (see the instructions here for how to disable +kdesktop_lock.) If you have more info on this or see it outside of KDE +please let us know. + +Update: It appears this is due to kdesktop_lock enabling the screen +saver when the Monitor is in DPMS low-power state (e.g. standby, +suspend, or off.) In Nov/2006 the x11vnc -nodpms option was added as a +workaround. Normally it is a good thing that the monitor powers down +(since x11vnc can still poll the framebuffer in this state), but if +you experience the kdesktop_lock problem you can specify the "-nodpms" +option to keep the Monitor out of low power state while VNC clients +are connected. This is basically the same as typing "xset dpms force +on" periodically. (if you don't want to do these things just disable +the screensaver.) Feel free to file a bug against kdesktop_lock with +KDE. + +### Q-110: I am running the compiz 3D window manager (or beryl, MythTv, Google Earth, or some other OpenGL app) and I do not get screen updates in x11vnc. + +This appears to be because the 3D OpenGL/GLX hardware screen updates +do not get reported via the XDAMAGE mechanism. So this is a bug in +compiz/beryl or XDAMAGE/Xorg or the (possibly 3rd party) video card +driver. + +As a workaround apply the -noxdamage option. As of Feb/2007 x11vnc +will try to autodetect the problem and disable XDAMAGE if is appears +to be missing a lot of updates. But if you know you are using compiz +you might as well always supply -noxdamage. Thanks to this user who +reported the problem and discovered the workaround. + +A developer for MiniMyth reports that the 'alphapulse' tag of the +theme G.A.N.T. can also cause problems, and should be avoided when +using VNC. + +Please report a bug or complaint to Beryl/Compiz and/or Xorg about +this: running x11vnc with -noxdamage disables a nice improvement in +responsiveness (especially for typing) and also leads to unnecessary +CPU and memory I/O load due to the extra polling. + +Update: as of May/2010 NVIDIA may have fixed this problem in their +proprietary drivers. See the NVIDIA Release Notes. (look for +'x11vnc'.) + +### Q-111: Can I use x11vnc to view my VMWare session remotely? + +Yes, since VMWare usually runs as an X application you can view it via +x11vnc in the normal way. + +Note that VMWare has several viewing modes: + +* Normal X application window (with window manager frame) +* Quick-Switch mode (with no window manager frame) +* Fullscreen mode + +The way VMWare does Fullscreen mode on Linux is to display the Guest +desktop in a separate Virtual Terminal (e.g. VT 8) (see this FAQ on +VT's for background.) Unfortunately, this Fullscreen VT is not an X +server. So x11vnc cannot access it (however, see this discussion of +-rawfb for a possible workaround.) x11vnc works fine with "Normal X +application window" and "Quick-Switch mode" because these use X. + +Update: It appears the in VMWare 5.x the Fullscreen mode is X, so +x11vnc access does work. + +One user reports he left his machine with VMWare in the Fullscreen +mode, and even though his X session wasn't in the active VT, he could +still connect x11vnc to the X session and pass the keystrokes Ctrl-Alt +(typing "blind") to the VMWare X app. This induced VMWare to switch +out of Fullscreen into Normal X mode and he could continue working in +the Guest desktop remotely. + + +Aside: Sometimes it is convenient (for performance, etc.) to start +VMWare in its own X session using startx(1). This can be used to have +a minimal window manger (e.g. twm or even no window manager), to +improve response. One can also cut the display depth (e.g. to 16bpp) +in this 2nd X session to improve video performance. This 2nd X session +emulates Fullscreen mode to some degree and can be viewed via x11vnc +as long as the VMWare X session is in the active VT. + +Also note that with a little bit of playing with "xwininfo -all +-children" output one can extract the (non-toplevel) window-id of the +of the Guest desktop only when VMWare is running as a normal X +application. Then one can export just the guest desktop (i.e. without +the VMWare menu buttons) by use of the -id windowid option. The +caveats are the X session VMWare is in must be in the active VT and +the window must be fully visible, so this mode is not terribly +convenient, but could be useful in some circumstances (e.g. running +VMWare on a very powerful server machine in a server room that happens +to have a video card, (but need not have a monitor, Keyboard or +mouse).) + + +## Exporting non-X11 devices via VNC + +### Q-112: Can non-X devices (e.g. a raw framebuffer) be viewed (and even controlled) via VNC with x11vnc? + +As of Apr/2005 there is support for this. Two options were added: +"-rawfb string" (to indicate the raw frame buffer device, file, etc. +and its parameters) and "-pipeinput command" (to provide an external +program that will inject or otherwise process mouse and keystroke +input.) Some useful -pipeinput schemes, VID, CONSOLE, and UINPUT, have +since been built into x11vnc for convenience. + +This non-X mode for x11vnc is somewhat experimental because it is so +removed in scope from the intended usage of the tool. Incomplete +attempt is made to make all of the other options consistent with non-X +framebuffer polling. So all of the X-related options (e.g. +-add_keysyms, -xkb) are just ignored or may cause an error if used. Be +careful applying such an option via remote control. + +The format for the -rawfb string is: + +``` +-rawfb :@xx[-][://][+] +``` + +There are also some useful aliases (e.g. "console".) Some examples: + +``` +-rawfb shm:210337933@800x600x32:ff/ff00/ff0000 + +-rawfb map:/dev/fb0@1024x768x16 + +-rawfb map:/tmp/Xvfb_screen0@640x480x8+3232 + +-rawfb file:/tmp/my.pnm@250x200x24+37 + +-rawfb file:/dev/urandom@128x128x8 + +-rawfb snap:/dev/video0@320x240x24 -24to32 + +-rawfb console + +-rawfb vt2 + +-rawfb video + +-rawfb setup:mycmd.sh +``` + +So the type can be "shm" for shared memory objects, and "map" or +"file" for file objects. "map" uses mmap(2) to map the file into +memory and is preferred over "file" (that uses the slower lseek(2) +access method.) Only use file if map isn't working. BTW, "mmap" is an +alias for "map" and if you do not supply a type and the file exists, +map is assumed (see the -help output and below for some exceptions to +this.) The "snap:" setting applies the -snapfb option with "file:" +type reading (this is useful for exporting webcams or TV tuner video; +see the next FAQ for more info.) + +Also, if the string is of the form "setup:cmd" then cmd is run and the +first line of its output retrieved and used as the rawfb string. This +allows initializing the device, determining WxHxB, etc. + +The object will be the numerical shared memory id for the case of shm. +The idea here is some other program has created this shared memory +segment and periodically updates it with new framebuffer data. x11vnc +polls the area for changes. See shmat(2) and ipcs(8) for more info. +The ipcs command will list current shared memory segments on the +system. Sometimes you can snoop on a program's framebuffer it did not +expect you would be polling! + +The object will be the path to the regular or character special file +for the cases of map and file. The idea here is that in the case of a +regular file some other program is writing/updating framebuffer image +data to it. In the case of a character special (e.g. /dev/fb0) it is +the kernel that is "updating" the framebuffer data. + +In most cases x11vnc needs to be told the width, height, and number of +bits per pixel (bpp) of the framebuffer. This is the @WxHxB field. For +the case of the Linux framebuffer device, /dev/fb0, the fbset(8) may +be of use (but may not always be accurate for what is currently +viewable.) In general some guessing may be required, especially for +the bpp. Update: in "-rawfb console" mode x11vnc will use the linuxfb +API to try to guess (it is still not always accurate.) Also try +"-rawfb vtN" (on x11vnc 0.9.7 and later) for the N-th Linux text +console (aka virtual terminal.) If the number of Bytes Per Line is not +WxHxB/8 (i.e. the framebuffer lines are padded) you can specify this +information after WxHxB via "-BPL", e.g. @800x600x16-2048 + +Based on the bpp x11vnc will try to guess the red, green, and blue +masks (these indicate which bits correspond to each color.) It if gets +it wrong you can specify them manually via the optional ":R/G/B" +field. E.g. ":0xff0000/0x00ff00/0x0000ff" (this is the default for +32bpp.) + +Finally, the framebuffer may not begin at the beginning of the memory +object, so use the optional "+offset" parameter to indicate where the +framebuffer information starts. So as an example, the Xvfb virtual +framebuffer has options -shmem and -fbdir for exporting its virtual +screen to either shm or a mapped file. The format of these is XWD and +so the initial header should be skipped. BTW, since XWD is not +strictly RGB the view will only be approximate, but usable. Of course +for the case of Xvfb x11vnc can poll it much better via the X API, but +you get the idea. + +By default in -rawfb mode x11vnc will actually close any X display it +happened to open. This is basically to shake out bugs (e.g it will +crash rather than mysteriously interacting with the X display.) If you +want x11vnc to keep the X display open while polling the raw +framebuffer prefix a "+" sign at the beginning of the string (e.g. ++file:/dev/urandom@64x64x8) This could be convenient for keeping the +remote control channel active (it uses X properties.) The "-connect +/path/to/file" mechanism could also be used for remote control to +avoid the X property channel. Rare usage, but if you also supply +-noviewonly in this "+" mode then the mouse and keyboard input are +still sent to the X display, presumably for doing something amusing +with /dev/fb... + +Interesting Devices:. Here are some aliases for interesting device +files that can be polled via -rawfb: + +``` +-rawfb console /dev/fb0 Linux Console +-rawfb vt2 /dev/vcsa2 Linux Console (e.g. virtual terminal #2) +-rawfb video /dev/video0 Video4Linux Capture device +-rawfb rand /dev/urandom Random Bytes +-rawfb null /dev/zero Zero Bytes (black screen) +``` + +The Linux console, /dev/fb0, etc needs to have its driver enabled in +the kernel. Some of the drivers are video card specific and +accelerated. The console is either the Text consoles (usually +tty1-tty6), or X graphical display (usually starting at tty7.) In +addition to the text console other graphical ones may be viewed and +interacted with as well, e.g. DirectFB or SVGAlib apps, VMWare non-X +fullscreen, or Qt-embedded apps (PDAs/Handhelds.) By default the +pipeinput mechanisms UINPUT and CONSOLE (keystrokes only) are +automatically attempted in this mode under "-rawfb console". + +The Video4Linux Capture device, /dev/video0, etc is either a Webcam or +a TV capture device and needs to have its driver enabled in the +kernel. See this FAQ for details. If specified via "-rawfb Video" then +the pipeinput method "VID" is applied (it lets you change video +parameters dynamically via keystrokes.) + +The last two, /dev/urandom and /dev/zero are just for fun, but are +also useful in testing. + +All of the above -rawfb options are just for viewing the raw +framebuffer (although some of the aliases do imply keystroke and mouse +pipeinput methods.) That may be enough for certain applications of +this feature (e.g. suppose a video camera mapped its framebuffer into +memory and you just wanted to look at it via VNC.) +To handle the pointer and keyboard input from the viewer users the +"-pipeinput cmd" option was added to indicate a helper program to +process the user input. The input is streamed to it and looks +something like this: + +``` +Pointer 1 205 257 0 None +Pointer 1 198 253 0 None +Pointer 1 198 253 1 ButtonPress-1 +Pointer 1 198 253 0 ButtonRelease-1 +Pointer 1 198 252 0 None +Keysym 1 1 119 w KeyPress +Keysym 1 0 119 w KeyRelease +Keysym 1 1 65288 BackSpace KeyPress +Keysym 1 0 65288 BackSpace KeyRelease +Keysym 1 1 112 p KeyPress +Keysym 1 0 112 p KeyRelease +``` + +Run "-pipeinput tee:/bin/cat" to get a description of the format. Note +that the -pipeinput option is independent of -rawfb mode and so may +have some other interesting uses. The "tee:" prefix means x11vnc will +both process the user input and pipe it to the command. The default is +to just pipe it to the -pipeinput command. + +Note the -pipeinput helper program could actually control the raw +framebuffer. In the libvncserver CVS a simple example program +x11vnc/misc/slide.pl is provided that demonstrates a simple jpeg +"slideshow" application. Also the builtin "-pipeinput VID" mode does +this for webcams and TV capture devices (/dev/video0.) + +The -pipeinput program is run with these environment variables set: +X11VNC_PID, X11VNC_PROG, X11VNC_CMDLINE, X11VNC_RAWFB_STR to aid its +knowing what is up. + +Another example provided in libvncserver CVS is a script to inject +keystrokes into the Linux console (e.g. the virtual consoles: +/dev/tty1, /dev/tty2, etc) in x11vnc/misc/vcinject.pl. It is based on +the vncterm/LinuxVNC.c program also in the libvncserver CVS. So to +view and interact with VT #2 (assuming it is the active VT) one can +run something like: + +``` +x11vnc -rawfb map:/dev/fb0@1024x768x16 -pipeinput './vcinject.pl 2' +``` + +This assumes your Linux framebuffer device (/dev/fb0) is properly +configured. See fbset(8) and other documentation. Try +"file:/dev/fb0@WxHxB" as a last resort. Starting with x11vnc 0.8.1, +the above VT injection is built in, as well as WxHxB determination. +Just use something like: + +``` +x11vnc -rawfb console +``` + +this will try to guess the active virtual console (via /dev/tty0) and +also the /dev/fb0 WxHxB and rgb masks automatically. Use, e.g., +"-rawfb console3" to force the VT number. This input method can be +used generally via "-pipeinput CONSOLE". Also starting with x11vnc +0.8.2 the "-pipeinput UINPUT" mode is tried first (it does both +keyboard and mouse input) and then falls back to CONSOLE mode if it is +not available. Here is the -help output for this mode: + +``` +If the rawfb string begins with "console" the framebuffer device +/dev/fb0 is opened (this requires the appropriate kernel modules to +be installed) and so is /dev/tty0. The latter is used to inject +keystrokes (not all are supported, but the basic ones are.) You +will need to be root to inject keystrokes. /dev/tty0 refers to the +active VT, to indicate one explicitly, use "console2", etc. using +the VT number. + +If the Linux version seems to be 2.6 or later and the "uinput" +module appears to be present, then the uinput method will be used +instead of /dev/ttyN. uinput allows insertion of BOTH keystrokes +and mouse input and so it preferred when accessing graphical (e.g. +Qt-embedded) linux console apps. See -pipeinput UINPUT below for +more information on this mode (you may want to also use the +-nodragging and -cursor none options.) Use "console0", etc or +-pipeinput CONSOLE to force the /dev/ttyN method. + +Note you can change VT remotely using the chvt(1) command. +Sometimes switching out and back corrects the framebuffer state. + +To skip input injecting entirely use "consolex". + +The string "/dev/fb0" (1, etc) can be used instead of "console". +This can be used to specify a different framebuffer device, e.g. +/dev/fb1. As a shortcut the "/dev/" can be dropped. If the name is +something nonstandard, use "console:/dev/foofb" + +If you do not want x11vnc to guess the framebuffer's WxHxB and +masks automatically (sometimes the kernel gives inaccurate +information), specify them with a @WxHxB at the end of the string. +``` + +The above is just an example of what can be done. Note that if you +really want to view and interact with the Linux Text console it is +better to use the more accurate and faster LinuxVNC program. The +advantage x11vnc -rawfb might have is that it can allow interaction +with a non-text application, e.g. one based on SVGAlib or Qt-embedded +Also, for example the VMWare Fullscreen mode is actually viewable +under -rawfb and can be interacted with if uinput is enabled. + +If the Linux uinput driver is available then full keystroke and mouse +input into the Linux console can be performed. You may be able to +enable uinput via commands like these: + +``` +modprobe uinput +mknod /dev/input/uinput c 10 223 +``` + +The -rawfb and -pipeinput features are intended to help one creatively +"get out of a jam" (say on a legacy or embedded device) where X is +absent or doesn't work properly. Feedback and bug reports are welcome. +For more control and less overhead use libvncserver in your own C +program that passes the framebuffer to libvncserver. + + +### Q-113: Can I export the Linux Console (Virtual Terminals) via VNC using x11vnc? + +Yes, you may need to be root to access the devices that make up the +linux console. + +To access the active Linux console via the computer's framebuffer try +something like: + +``` +x11vnc -rawfb console +x11vnc -rawfb console2 +``` + +These will try to access the framebuffer through /dev/fb (or /dev/fb0, +etc.) and if it succeeds it will show any text or graphics that is +currently displayed. Keystrokes will be injected via the device +/dev/tty0 (to force an explicit virtual terminal append a number, e.g. +"console2" to select /dev/tty2.) + +If your Linux system does not have a framebuffer device (/dev/fb) you +can get one by adding, e.g., vga=0x31B boot parameter. This enables +the VGA framebuffer device at 1280x1024x24. 0x317 gives 1024x768x16, +etc. You can also enable a Linux framebuffer device by modprobing a +framebuffer driver specific to your video card. + +Note that this "-rawfb console" mode shows the contents of the +hardware framebuffer, and so will show whatever is on the screen. It +has no concept of Virtual Terminals WRT what there is to view, it +always shows the active virtual terminal. + +Another mode is specific to the Linux text Virtual Terminals, it shows +their text and colors (but no graphics) regardless of whether it is +the active VT or not. It is available on x11vnc 0.9.7 and later. +Enable this mode like this: + +``` +x11vnc -rawfb vt +x11vnc -rawfb vt2 +``` + +The former will select the active one, the latter the 2nd VT. x11vnc +implements this mode by opening the current console text file +"/dev/vcsa2" instead of "/dev/fb". In this way it provides the basic +functionality of the LibVNCServer LinuxVNC program. + +The vt mode can be a useful way to try to get a machine's X server +working remotely, e.g. you edit /etc/X11/xorg.conf and then type +startx (or similar, e.g. gdm) in the virtual terminal. A 2nd x11vnc +could be used to see if the X server is now working correctly. + + +### Q-114: Can I export via VNC a Webcam or TV tuner framebuffer using x11vnc? + +Yes, this is possible to some degree with the -rawfb option. There is +no X11 involved: snapshots from the video capture device are used for +the screen image data. See the previous FAQ on -rawfb for background. +For best results, use x11vnc version 0.8.1 or later. + +Roughly, one would do something like this: + +``` +x11vnc -rawfb snap:/dev/video@320x240x32 +``` + +This requires that the system allows simple read(2) access to the +video device. This is true for video4Linux on Linux kernel 2.6 and +later (it won't work for 2.4, you'll need a separate program to +snapshot to a file that you point -rawfb to; ask me if it is not clear +what to do.) + +The "snap:" enforces -snapfb mode which appears to be necessary. The +read pointer for video capture devices cannot be repositioned (which +would be needed for scanline polling), but you can read a full frame +of data from the device. + +On Linux, if the Video4Linux API is present or the v4l-info(1) program +(related to xawtv) exists in in PATH, then x11vnc can be instructed to +try it to determine the -rawfb WxHxB parameters for you automatically. +In this case one would just type: + +``` +x11vnc -rawfb video +``` + +or "-rawfb video1" for the 2nd video device, etc. + +x11vnc has also been extended to use the Video4Linux API over v4l-info +if it is available at build time. This enables setting parameters +(e.g. size and brightness) via x11vnc. See the description below. +Without Video4Linux you will need to initialize the settings of the +video device using something like xawtv or spcaview (and then hope the +settings persist until x11vnc reopens the device.) + +Many video4linux drivers tend to set the framebuffer to be 24bpp (as +opposed to 32bpp.) Since this can cause problems with VNC viewers, +etc, the -24to32 option will be automatically imposed when in 24bpp. + +Note that by its very nature, video capture involves rapid change in +the framebuffer. This is especially true for cameras where slight +wavering in brightness is always happening. This can lead to much +network bandwidth consumption for the VNC traffic and also local CPU +and I/O resource usage. You may want to experiment with "dialing down" +the framerate via the -wait, -slow_fb, or -defer options. Decreasing +the window size and bpp also helps. + + + Setting Camera/Tuner parameters via x11vnc: + + There is also some support for setting parameters of the capture + device. This is done via "-rawfb video:". This could be + useful for unattended startup at boottime, etc. Here is the -help + description: + + +``` +A more sophisticated video device scheme allows initializing the +device's settings using: + + -rawfb video: + +The prefix could also be, as above, e.g. "video1:" to specify the +device file. The v4l API must be available for this to work. +Otherwise, you will need to try to initialize the device with an +external program, e.g. xawtv, spcaview, and hope they persist when +x11vnc re-opens the device. + + is a comma separated list of key=value pairs. The +device's brightness, color, contrast, and hue can be set to +percentages, e.g. br=80,co=50,cn=44,hu=60. + +The device filename can be set too if needed (if it does not start +with "video"), e.g. fn=/dev/qcam. + +The width, height and bpp of the framebuffer can be set via, e.g., +w=160,h=120,bpp=16. + +Related to the bpp above, the pixel format can be set via the +fmt=XXX, where XXX can be one of: GREY, HI240, RGB555, RGB565, +RGB24, and RGB32 (with bpp 8, 8, 16, 16, 24, and 32 respectively.) +See http://www.linuxtv.org for more info (V4L api.) + +For TV/rf tuner cards one can set the tuning mode via tun=XXX where +XXX can be one of PAL, NTSC, SECAM, or AUTO. + +One can switch the input channel by the inp=XXX setting, where XXX +is the name of the input channel (Television, Composite1, S-Video, +etc.) Use the name that is in the information about the device that +is printed at startup. + +For input channels with tuners (e.g. Television) one can change +which station is selected by the sta=XXX setting. XXX is the +station number. Currently only the ntsc-cable-us (US cable) +channels are built into x11vnc. See the -freqtab option below to +supply one from xawtv. If XXX is greater than 500, then it is +interpreted as a raw frequency in KHz. + +Example: + +-rawfb video:br=80,w=320,h=240,fmt=RGB32,tun=NTSC,sta=47 + +one might need to add inp=Television too for the input channel to +be TV if the card doesn't come up by default in that one. + +Note that not all video capture devices will support all of the +above settings. + +See the -pipeinput VID option below for a way to control the +settings through the VNC Viewer via keystrokes. + +As above, if you specify a "@WxHxB..." after the string +they are used verbatim: the device is not queried for the current +values. Otherwise the device will be queried. +``` + +Also, if you supply the "-pipeinput VID" (or use "-rawfb Video") +option you can control the settings to some degree via keystroke +mappings, e.g. B to increase the brightness or Up arrow to change the +TV station: + +``` +For "-pipeinput VID" and you are using the -rawfb for a video +capture device, then an internal list of keyboard mappings is used +to set parameters of the video. The mappings are: + + "B" and "b" adjust the brightness up and down. + "H" and "h" adjust the hue. + "C" and "c" adjust the colour. + "N" and "n" adjust the contrast. + "S" and "s" adjust the size of the capture screen. + "I" and "i" cycle through input channels. + Up and Down arrows adjust the station (if a tuner) + F1, F2, ..., F6 will switch the video capture pixel + format to HI240, RGB565, RGB24, RGB32, RGB555, and + GREY respectively. See -rawfb video for details. +``` + +See also the -freqtab option to supply your own xawtv channel to +frequency mappings for your country (only ntsc-cable-us is built into +x11vnc.) + + +### Q-115: Can I connect via VNC to a Qt-embedded/Qt-enhanced/Qtopia application running on my handheld, cell phone, or PC using the Linux console framebuffer (i.e. not X11)? + +Yes, the basic method for this is the -rawfb scheme where the Linux +console framebuffer (usually /dev/fb0) is polled and the uinput driver +is used to inject keystrokes and mouse input. Often you will just have +to type: + +``` +x11vnc -rawfb console +``` + +(you may need to enable the uinput driver on the system via "modprobe +uinput; mknod /dev/input/uinput c 10 223") If this does not find the +correct frame buffer properties figure them out or guess them and use +something like: + +``` +x11vnc -rawfb /dev/fb0@640x480x16 +``` + +Also, to force usage of the uinput injection method use "-pipeinput +UINPUT". See the -pipeinput description for tunable parameters, etc. + +One problem with the x11vnc uinput scheme is that it cannot guess the +mouse motion "acceleration" used by the windowing application (e.g. +QWS or X11.) For X11 and Qt-embedded the acceleration is usually 2 +(i.e. a dx of 1 from the mouse yields a 2 pixel displacement of the +mouse cursor.) The default x11vnc uses is 2, since that is often used. +However for one Qt-embedded system we needed to do: + +``` +x11vnc -rawfb console -pipeinput UINPUT:accel=4.0 +``` + +to get reasonable positioning of the mouse. + +Even with the correct acceleration setting there is still some drift +(probably because of the mouse threshold where the acceleration kicks +in) and so x11vnc needs to reposition the cursor from 0,0 about 5 +times a second. See the -pipeinput UINPUT option for tuning parameters +that can be set (there are some experimental thresh=N tuning +parameters as well) + +Currently, one can expect mouse input to be a little flakey. All in +all, the Linux framebuffer input mechanism for Qt-embedded framebuffer +apps is not perfect, but it is usable. + +If you need to create a smaller x11vnc binary for a handheld +environment be sure to run strip(1) on it and also consider +configuring with, e.g. "env CPPFLAGS='-DSMALL_FOOTPRINT=1' ./configure +..." to remove rarely used features and large texts (use 2 or 3 +instead of 1 to remove more.) Currently (Jul/2006) this can lower the +size of the x11vnc from 1.1MB to 0.6-0.7MB. + +The x11vnc uinput method applies to nearly anything on the Linux +framebuffer console, not just Qt-embedded/Qtopia. DirectFB, SDL using +fbcon driver, SVGAlib applications can also be viewed and interacted +with. Even a Linux X session can be viewed and interacted with without +using X11 (and x11vnc does not have to terminate when the X server +restarts!) The Linux Text consoles (F1-F6) also work. + +Note that Qt-embedded supplies its own VNC graphics driver, but it +cannot do both the Linux console framebuffer and VNC at the same time, +which is often what is desired from VNC. + +Update: We are finding some setups like Qtopia on the IPAQ do not +allow mouse input via uinput. Please help us debug this problem by +trying x11vnc on your device and letting us know what does and does +not work. See the next FAQ for a possible workaround for touchscreens. + + +### Q-116: How do I inject touch screen input into an Qt-embedded/Qt-enhanced/Qtopia cell phone such as openmoko/qtmoko Neo Freerunner? + +The qtmoko project does not use X11 for the graphical display. +Unfortunately the Linux uinput method described in the previous FAQ +does not work because Qt is using TSLIB (touch screen library) to +process the input and it only reads from one device (often +/dev/input/event1) and not from the new UINPUT device that x11vnc +creates (under -pipeinput UINPUT) + +So something else needs to be done. It was discovered that by simply +writing the touchscreen events directly to /dev/input/event1 then +input can be injected into the system. There is no x11vnc builtin mode +for this yet (until we understand it better), but there is a working +script provided in x11vnc/misc/qt_tslib_inject.pl. So one could use it +this way for example: + +``` +x11vnc ... -rawfb console -pipeinput path/to/qt_tslib_inject.pl -env INJECT_OPTIONS=clickonly,cal=/etc/pointercal +``` + +Read the script for how to enable other options and what the above +options mean (e.g. /etc/pointercal contains TSLIB's calibration +parameters and are necessary to achieve accurate pointing.) + +The x11vnc/misc/qt_tslib_inject.pl script can potentially be modified +to handle other devices where the uinput method fails. It could also +be modified to create 'hot keys', etc. + +Please let us know how things go if you try this out; there is much to +learn about synthetic input injection in handhelds and cell phones. As +we learn more we can develop a builtin x11vnc mode for this sort of +injection. + +Update Dec/2010: There is experimental built-in UINPUT support in the +x11vnc development tarball for qtmoko with touchpad managed by tslib. +See -pipeinput UINPUT for more info. Here is an example: + +``` +x11vnc -rawfb console -pipeinput UINPUT:touch,tslib_cal=/etc/pointercal,direct_abs=/dev/input/event1,nouinput,dragskip=3 +``` + + +### Q-117: Now that non-X11 devices can be exported via VNC using x11vnc, can I build it with no dependencies on X11 header files and libraries? + +Yes, as of Jul/2006 x11vnc enables building for -rawfb only support. +Just do something like when building: + +``` +./configure --without-x (plus any other flags) +make +``` + +You can then test via "ldd x11vnc" that the binary does not depend on +libX11.so, etc. See the previous FAQ's for non-X11 framebuffer usage. +If you use this for an interesting non-X11 application please let us +know what you did. + + +### Q-118: How do I cross compile x11vnc for a different architecture than my Linux i386 or amd64 PC? + +You will need a cross-compiling toolchain. Perhaps your distro +provides these or you can find a HOWTO for your distro. We found a +nice one at qtmoko.org for building armel binaries on Debian Linux +i386 machines. It includes most of the libraries that x11vnc needs. We +use that example here. + +We ran this script to set PATH, configure, and build: + +``` +#!/bin/sh + +# toolchain from: qtmoko-debian-toolchain-armv4t-eabi.tar.gz + +export PATH=/opt/toolchains/arm920t-eabi/bin:$PATH + +env CC=arm-linux-gcc ./configure --host=arm-linux --without-avahi + +make + +arm-linux-strip ./x11vnc/x11vnc +ls -l ./x11vnc/x11vnc +``` + +Note we had to include --without-avahi due to lack of +libavahi-client.so.3 supplied by the toolchain we used. One would need +to add it if it was desired on the target machine. We also stripped +the binary to make it smaller. + +For an embedded system one may also want to add --without-x if the +embedded system does not use X11 and the -rawfb mechanism must be +used. + + +### Q-119: Does x11vnc support Mac OS X Aqua/Quartz displays natively (i.e. no X11 involved)? + +Yes, since Nov/2006 in the development tree (x11vnc-0.8.4 tarball) +there is support for native Mac OS X Aqua/Quartz displays using the +-rawfb mechanism described above. The mouse and keyboard input is +achieved via Mac OS X API's. + +So you can use x11vnc as an alternative to OSXvnc (aka Vine Server), +or Apple Remote Desktop (ARD). Perhaps there is some x11vnc feature +you'd like to use on Mac OS X, etc. For a number of activities (e.g. +window drags) it seems to be faster than OSXvnc. + +Notes: + +X11: x11vnc will also work (as it has for years) with a X11 server +(XDarwin) running on Mac OS X (people often install this software to +display remote X11 apps on their Mac OS X system, or use some old +favorites locally such as xterm.) However in this case x11vnc will +only work reasonably in single window -id windowid mode (and the +window may need to have mouse focus.) + +If you do not have the DISPLAY env. variable set, x11vnc will assume +native Aqua/Quartz on Mac OS X, however if DISPLAY is set it will +assume an X11 connection. Use "-rawfb console" to force the native +display (or unset DISPLAY.) + +Update: Leopard sets DISPLAY by default in all sessions. Since it +starts with the string "/tmp/" x11vnc will use that to know if it +should ignore it. Use "-display :0.0" to force it. + +Building: If you don't have the X11 build and runtime packages +installed you will need to build it like this: +(cd to the e.g. x11vnc-0.9, source directory) + +``` +./configure --without-x +make +``` + +Win2VNC/x2vnc: One handy use is to use the -nofb mode to redirect +mouse and keyboard input to a nearby Mac (i.e. one to the side of your +desk) via x2vnc or Win2VNC. See this FAQ for more info. + +Options: Here are the Mac OS X specific x11vnc options: + +``` +-macnodim For the native Mac OS X server, disable dimming. +-macnosleep For the native Mac OS X server, disable display sleep. +-macnosaver For the native Mac OS X server, disable screensaver. +-macnowait For the native Mac OS X server, do not wait for the + user to switch back to his display. +-macwheel n For the native Mac OS X server, set the mouse wheel + speed to n (default 5.) +-macnoswap For the native Mac OS X server, do not swap mouse + buttons 2 and 3. +-macnoresize For the native Mac OS X server, do not resize or reset + the framebuffer even if it is detected that the screen + resolution or depth has changed. +-maciconanim n For the native Mac OS X server, set n to the number + of milliseconds that the window iconify/deiconify + animation takes. In -ncache mode this value will be + used to skip the animation if possible. (default 400) +-macmenu For the native Mac OS X server, in -ncache client-side + caching mode, try to cache pull down menus (not perfect + because they have animated fades, etc.) +``` + +PasteBoard/Clipboard: There is a bug that the Clipboard (called +PasteBoard on Mac it appears) exchange will not take place unless +x11vnc was started from inside the Aqua display (e.g. started inside a +Terminal app window.) Otherwise it cannot connect to the PasteBoard +server. So Clipboard exchange won't work for our standard "ssh in" +startup scheme. + +Hopefully this deficiency can be removed, but until then for Clipboard +exchange to work you will need to start x11vnc inside the desktop +session (i.e. either start it running before you leave, or start up a +2nd x11vnc inside from a 1st one started outside, or use the apple +script below) + +Here also is a osascript trick that seems to work (it opens the +Terminal app and instructs it to start x11vnc): + +``` +#!/bin/sh +# +# start_x11vnc: start x11vnc in a Terminal window +# (this will allow Clipboard/Pasteboard exchange to work) + +tmp=/tmp/start_x11vnc.$$ + +cat > $tmp < vncviewer -listen +client2> vncviewer -listen +client3> vncviewer -listen +... +client64> vncviewer -listen +``` + +(e.g. client1> is the cmdline prompt on machine client1 ... etc) and +all the repeaters R are started like this: + +``` +repeater1> x11vnc -reflect listen -connect client1,client2,...client8 +repeater2> x11vnc -reflect listen -connect client9,client10,...client16 +... +repeater8> x11vnc -reflect listen -connect client57,client58,...client64 +``` + +and finally the main server is started to kick the whole thing into +motion: + +``` +vncserver> x11vnc -display :0 -connect repeater1,repeater2,...repeater8 +``` + +(or instruct a non-x11vnc VNC server to reverse connect to the +repeaters.) For a classroom broadcasting setup one might have the +first two sets of commands start automatically at bootup or when +someone logs in, and then start everything up with the S server. One +may even be able to script the forward connection bootstrap case, let +us know what you did. A really nice thing would be some sort of +auto-discovery of your repeater, etc... + +### Q-121: Can x11vnc be used during a Linux, Solaris, etc. system installation so the installation can be done remotely? + +This can be done, but it doesn't always work because it depends on how +the OS does its install. We have to "sneak in" somehow. Note that some +OS's have a remote install (ssh etc.) built in and so you might want +to use that instead. + +Usually the OS install will have to be a network-install in order to +have networking up during the install. Otherwise, you may have a +(slim) chance to configure the networking manually (ifconfig(8) and +route(8).) + +To avoid library dependencies problems in the typical minimal (e.g. +busybox) installation OS it is a good idea to build a statically +linked x11vnc binary. A way that often works is to do a normal build +and then paste the final x11vnc link line into a shell script. Then +change the "gcc" to "gcc -static" and run the shell script. You may +need to disable features (e.g. "--without-xfixes") if there is not a +static library for the feature available. You may also need to add +extra link options (e.g. "-lXrender") to complete library dependencies +manually. + +Let's call the binary x11vnc.static. Place it on a webserver +somewhere. It may be possible to retrieve it via scp(1) too. + +During the install you need to get a shell to retreive x11vnc.static +and run it. + +If the Solaris install is an older X-based one, there will be a menu +for you to get a terminal window. From that window you might be able +to retrieve x11vnc.static via wget, scp, or ftp. Remember to do "chmod +755 ./x11vnc.static" and then find the -auth file as in this FAQ. + +If it is a Linux install that uses an X server (e.g. SuSE and probably +Fedora), then you can often get a shell by pressing Ctrl-Alt-F2 or +similar. Then get the x11vnc binary via something like this: + +``` +cd /tmp +wget http://192.168.0.22/x11vnc.static +chmod 755 ./x11vnc.static +``` + +Find the name of the auth file as in this FAQ. (maybe run "ps wwaux | +grep auth".) Then run it like this: +./x11vnc.static -forever -nopw -display :0 -auth /tmp/wherever/the/authfile + +then press Alt-F7 to go back to the X install. You should now be able +to connect via a vnc viewer and continue the install. Watch out for +the display being :1, etc. + +If there is a firewall blocking incoming connections during the +install, use the "-connect hostname" option option for a reverse +connection to the hostname running the VNC viewer in listen mode. + +Debian based installs are either console-text or console-framebuffer +based. These are install (or expert) and installgui (or expertgui) +boot lines, respectively. For the console-text based installs you +probably need to add a boot cmd line option like vga=0x314 (which is +800x600x16) to get the console-text to use the linux framebuffer +device properly. + +For a Debian console-text based install after the network is +configured press Ctrl-Alt-F2 to get a shell. Retrieve the binary via +wget as above and chmod 755 it. Then run it something like this: +sleep 10; ./x11vnc.static -forever -nopw -rawfb console + +then before the sleep is over press Alt-F1 to get back to the install +virtual console. You should be able to connect via a VNC viewer and +continue with the install. + +For a recent (2009) Debian install we booted with "expert vga=0x301" +and "expert vga=0x311" to get console text based installs at 640x480x8 +and 640x480x16, respectively (replace "expert" with "install" if you +like.) Otherwise it was giving a 16 color 640x480x4 (4 bit per pixel) +display which x11vnc could not handle. + +For Debian console-framebuffer GUI based installs (installgui or +expertgui) we have not be able to enter keystrokes or mouse motions. +This may be resolved if the install had the Linux kernel module +uinput, but it doesn't; one can wget uinput.ko and then run insmod on +it, but the module must match the installation kernel. So, failing +that, you can only do the GUI view-only, which can be handy to watch a +long network install from your desk instead of in front of the machine +being installed. For these, after the network is configured press +Ctrl-Alt-F2 to get a shell. Retrieve the binary via wget as above and +chmod 755 it. Then run it something like this: +sleep 10; ./x11vnc.static -forever -nopw -rawfb console + +then before the sleep is over press Alt-F5 to get back to the GUI +install console. You should be able to connect via a VNC viewer and +watch the install. +[Misc: Clipboard, File Transfer/Sharing, Printing, Sound, Beeps, +Thanks, etc.] + +### Q-122: Does the Clipboard/Selection get transferred between the vncviewer and the X display? + +As of Jan/2004 x11vnc supports the "CutText" part of the RFB (aka VNC) +protocol. When text is selected/copied in the X session that x11vnc is +polling it will be sent to connected VNC viewers. And when CutText is +received from a VNC viewer then x11vnc will set the X11 selections +PRIMARY, CLIPBOARD, and CUTBUFFER0 to it. x11vnc is able to hold the +PRIMARY and CLIPBOARD selections (Xvnc does not seem to do this.) + +The X11 selections can be confusing, especially to those coming from +Windows or MacOSX where there is just a single 'Clipboard'. The X11 +CLIPBOARD selection is a lot like that of Windows and MacOSX, e.g. +highlighted text is sent to the clipboard when the user activates +"Edit -> Copy" or presses "Control+C" (and pasting it via "Edit -> +Paste" or "Control+V".) The X11 PRIMARY selection has been described +as 'for power users' or 'an Easter Egg'. As soon as text is +highlighted it is set to the PRIMARY selection and so it is +immediately ready for pasting, usually via the Middle Mouse Button or +"Shift+Insert". See this jwz link for more information. + +x11vnc's default behavior is to watch both CLIPBOARD and PRIMARY and +whenever one of them changes, it sends the new text to connected +viewers. Note that since the RFB protocol only has a single "CutText" +then both selections are "merged" to some degree (and this can lead to +confusing results.) One user was confused why x11vnc was "forgetting" +his CLIPBOARD selection and the reason was he also changed PRIMARY +some time after he copied text to the clipboard. Usually an app will +set PRIMARY as soon as any text is highlighted so it easy to see how +CLIPBOARD was forgotten. Use the -noprimary described below as a +workaround. Similarly, by default when x11vnc receives CutText it sets +both CLIPBOARD and PRIMARY to it (this is probably less confusing, but +could possibly lead to some failure modes as well.) + +You may not like these defaults. Here are ways to change the behavior: + +* If you don't want the Clipboard/Selection exchanged at all use the + -nosel option. +* If you want changes in PRIMARY to be ignored use the -noprimary + option. +* If you want changes in CLIPBOARD to be ignored use the + -noclipboard option. +* If you don't want x11vnc to set PRIMARY to the "CutText" received + from viewers use the -nosetprimary option. +* If you don't want x11vnc to set CLIPBOARD to the "CutText" + received from viewers use the -nosetclipboard option. + +You can also fine-tune it a bit with the -seldir dir option and also +-input. + +You may need to watch out for desktop utilities such as KDE's +"Klipper" that do odd things with the selection, clipboard, and +cutbuffers. + + +### Q-123: Can I use x11vnc to record a Shock Wave Flash (or other format) video of my desktop, e.g. to record a tutorial or demo? + +Yes, it is possible with a number of tools that record VNC and +transform it to swf format or others. One such popular tool is +pyvnc2swf. There are a number of tutorials (broken link?) on how to do +this. Another option is to use the vnc2mpg that comes in the +LibVNCServer package. +An important thing to remember when doing this is that tuning +parameters should be applied to x11vnc to speed up its polling for +this sort of application, e.g. "-wait 10 -defer 10". + +### Q-124: Can I transfer files back and forth with x11vnc? + +As of Oct/2005 and May/2006 x11vnc enables, respectively, the TightVNC +and UltraVNC file transfer implementations that were added to +libvncserver. This currently works with TightVNC and UltraVNC viewers +(and Windows viewers only support filetransfer it appears... but they +do work to some degree under Wine on Linux.) + +The SSVNC Unix VNC viewer supports UltraVNC file transfer by use of a +Java helper program. + +TightVNC file transfer is off by default, if you want to enable it use +the -tightfilexfer option. + +UltraVNC file transfer is off by default, to enable it use something +like "-rfbversion 3.6 -permitfiletransfer" +options (UltraVNC incorrectly uses the RFB protocol version to +determine if its features are available, so x11vnc has to pretend to +be version 3.6.) As of Sep/2006 "-ultrafilexfer" is an alias for these +two options. Note that running as RFB version 3.6 may confuse other +VNC Viewers. + +Sadly you cannot do both -tightfilexfer and -ultrafilexfer at the same +time because the latter requires setting the version to 3.6 and +tightvnc will not do filetransfer when it sees that version number. + +Also, because of the way the LibVNCServer TightVNC file transfer is +implemented, you cannot do Tightvnc file transfer in -unixpw mode. +However, UltraVNC file transfer does work in -unixpw (but if a client +tries it do a filetransfer during the login process it will be +disconnected.) + +IMPORTANT: please understand if -ultrafilexfer or -tightfilexfer is +specified and you run x11vnc as root for, say, inetd or display +manager (gdm, kdm, ...) access and you do not have it switch users via +the -users option, then VNC Viewers that connect are able to do +filetransfer reads and writes as *root*. + +The UltraVNC and TightVNC settings can be toggled on and off inside +the gui or by -R remote control. However for TightVNC the changed +setting only applies for NEW clients, current clients retain their +TightVNC file transfer ability. For UltraVNC it works better, however +if an UltraVNC client has initiated a file transfer dialog it will +remain in effect until the dialog is closed. If you want to switch +between UltraVNC and TightVNC file transfer in the gui or by remote +control you will probably be foiled by the "-rfbversion 3.6" issue. + + +### Q-125: Which UltraVNC extensions are supported? + +Some of them are supported. To get UltraVNC Viewers to attempt to use +these extensions you will need to supply this option to x11vnc: +-rfbversion 3.6 + +Or use -ultrafilexfer which is an alias for the above option and +"-permitfiletransfer". UltraVNC evidently treats any other RFB version +number as non-UltraVNC. + +Here are a list of the UltraVNC extensions supported by x11vnc: + * ServerInput: "Toggle Remote Input and Remote Blank Monitor" + * FileTransfer: "Open File Transfer..." + * SingleWindow: "Select Single Window..." + * TextChat: "Open Chat..." + * 1/n Server Scaling + +The SSVNC Unix VNC viewer supports these UltraVNC extensions. + +To disable SingleWindow and ServerInput use -noultraext (the others +are managed by LibVNCServer.) See this option too: -noserverdpms. + +Also, the UltraVNC repeater proxy is supported for use with reverse +connections: "-connect repeater://host:port+ID:NNNN". Use it for both +plaintext and SSL connections. This mode can send any string before +switching to the VNC protocol, and so could be used with other +proxy/gateway tools. Also, a perl repeater implemention is here: +ultravnc_repeater.pl + + +### Q-126: Can x11vnc emulate UltraVNC's Single Click helpdesk mode for Unix? I.e. something very simple for a naive user to initiate a reverse vnc connection from their Unix desktop to a helpdesk operator's VNC Viewer. + +Yes, UltraVNC's Single Click (SC) mode can be emulated fairly well on +Unix. + +We use the term "helpdesk" below, but it could be any sort of remote +assistance you want to set up, e.g. something for Unix-using friends +or family to use. This includes Mac OS X. + +Assume you create a helpdesk directory "hd" on your website: +http://www.mysite.com/hd (any website that you can upload files to +should work, although remember the user will be running the programs +you place there.) + +In that "hd" subdirectory copy an x11vnc binary to be run on the Unix +user's machine (e.g. Linux, etc) and also create a file named "vnc" +containing the following: + +``` +#!/bin/sh + +webhost="http://www.mysite.com/hd" # Your helpdesk dir URL. + +vnchost="ip.someplace.net" # Your host running 'vncviewer -listen' + # It could also be your IP number. If it is + # a router/firewall, you will need to + # configure it to redirect port 5500 to your + # workstation running 'vncviewer -listen' + +dir=/tmp/vnc_helpdesk.$$ # Make a temporary working dir. +mkdir $dir || exit 1 +cd $dir || exit 1 + +trap "cd /tmp; rm -rf $dir" 0 2 15 # Cleans up on exit. + +wget $webhost/x11vnc # Fetch x11vnc binary. If multi- +chmod 755 ./x11vnc # platform, use $webhost/`uname`/x11vnc + # or similar. + +./x11vnc -connect_or_exit $vnchost -rfbport 0 -nopw +``` + +with the hostnames / IP addresses customized to your case. + +On the helpdesk VNC viewer machine (ip.someplace.net in this example) +you have the helpdesk operator running VNC viewer in listen mode: +vncviewer -listen + +or if on Windows, etc. somehow have the VNC viewer be in "listen" +mode. + +Then, when the naive user needs assistance you instruct him to open up +a terminal window on his Unix desktop and paste the following into the +shell: + +``` +wget -qO - http://www.mysite.com/hd/vnc | sh - +``` + +and then press Enter. You could have this instruction on a web page or +in an email you send him, etc. This requires that the wget is +installed on the user's Unix machine (he might only have curl or lynx, +see below for more info.) + + +So I guess this is about 3-4 clicks (start a terminal and paste) and +pressing "Enter" instead of "single click"... + +See this page for some variations on this method, e.g. how to add a +password, SSL Certificates, etc. + + +If you don't have a website (there are many free ones) or don't want +to use one you will have to email him all of the ingredients (x11vnc +binary and a launcher script) and tell him how to run it. This could +be easy or challenging depending on the skill of the naive unix +user... + +A bit of obscurity security could be put in with a -passwd, -rfbauth +options, etc. (note that x11vnc will require a password even for +reverse connections.) More info here. + + +Firewalls: If the helpdesk (you) with the vncviewer is behind a +NAT/Firewall/Router the router will have to be configured to redirect +a port (i.e. 5500 or maybe different one if you like) to the vncviewer +machine. If the vncviewer machine also has its own host-level +firewall, you will have to open up the port there as well. + +NAT-2-NAT: There is currently no way to go "NAT-2-NAT", i.e. both User +and Helpdesk workstations behind NAT'ing Firewall/Routers without +configuring a router to do a port redirection (i.e. on your side, the +HelpDesk.) To avoid modifying either firewall/router, one would need +some public (IP address reachable on the internet) redirection/proxy +service. Perhaps such a thing exists. http://sc.uvnc.com provides this +service for their UltraVNC Single Click users. + +Update: It may be possible to do "NAT-2-NAT" with a UDP tunnel such as +http://samy.pl/pwnat/. All that is required is that both NAT firewalls +allow in UDP packets from an IP address to which a UDP packet has +recently been sent to. If you try it out let us know how it went. + + +Very Naive Users: + +If it is beyond the user how to open a terminal window and paste in a +command (you have my condolences...) you would have to somehow setup +his Web browser to download the "vnc" file (or a script containing the +above wget line) and prompt the user if he wants to run it. This may +be tricky to set up (which is probably a good thing to not have the +web browser readily run arbitrary programs downloaded from the +internet...) + +One command-line free way, tested with KDE, is to name the file vnc.sh +and then instruct the user to right-click on the link and do "Save +Link As" to his Desktop. It will appear as an icon, probably one that +looks like a terminal or a command line prompt. He next should +right-click on the icon and select "Properties" and go to the +"Permissions" tab. Then in that dialog select the checkbox "Is +executable". He should then be able to click on the icon to launch it. +Another option is to right-click on the icon and select "Open With -> +Other ..." and for the name of the application type in "/bin/sh". +Unfortunately in both cases the command output is lost and so errors +cannot be debugged as easily. A similar thing appears to work in GNOME +if under "Properties -> Permissions" they click on "Execute" checkbox +for "Owner". Then when they click on the icon, they will get a dialog +where they can select "Run in Terminal". In general for such cases, if +it is feasible, it might be easier to ssh to his machine and set +things up yourself... + + +SSL Encrypted Helpdesk Connections: + +As of Apr/2007 x11vnc supports reverse connections in SSL and so we +can do this. On the Helpdesk side (Viewer) you will need STUNNEL or +better use the Enhanced TightVNC Viewer (SSVNC) package we provide +that automates all of the SSL for you. + +To do this create a file named "vncs" in the website "hd" directory +containing the following: + +``` +#!/bin/sh + +webhost="http://www.mysite.com/hd" # Your helpdesk dir URL. + +vnchost="ip.someplace.net" # Your host running 'vncviewer -listen' + # It could also be your IP number. If it is + # a router/firewall, you will need to + # configure it to redirect port 5500 to your + # workstation running 'vncviewer -listen' + +dir=/tmp/vnc_helpdesk.$$ # Make a temporary working dir. +mkdir $dir || exit 1 +cd $dir || exit 1 + +trap "cd /tmp; rm -rf $dir" 0 2 15 # Cleans up on exit. + +wget $webhost/x11vnc # Fetch x11vnc binary. If multi- +chmod 755 ./x11vnc # platform, use $webhost/`uname`/x11vnc + # or similar. + +./x11vnc -connect_or_exit $vnchost -rfbport 0 -nopw -ssl # Note -ssl option. +``` + +with the hostnames or IP addresses customized to your case. + +The only change from the "vnc" above is the addition of the -ssl +option to x11vnc. This will create a temporary SSL cert: openssl(1) +will need to be installed on the user's end. A fixed SSL cert file +could be used to avoid this (and provide some authentication; more +info here.) + +The naive user will be doing this: + +``` +wget -qO - http://www.mysite.com/hd/vncs | sh - +``` + +(or perhaps even use https:// if available.) + +But before that, the helpdesk operator needs to have "vncviewer +-listen" running as before, however he needs an SSL tunnel at his end. +The easiest way to do this is use Enhanced TightVNC Viewer (SSVNC). +Start it, and select Options -> 'Reverse VNC Connection (-listen)'. +Then UN-select 'Verify All Certs' (this can be enabled later if you +want; you'll need the x11vnc SSL certificate), and click 'Listen'. + +If you don't want to use SSVNC for the viewer, but rather set up +STUNNEL manually instead, make a file "stunnel.cfg" containing: + +``` +foreground = yes +pid = + +[vnc] +accept = 5500 +connect = localhost:5501 +``` + +and run: + +``` +stunnel ./stunnel.cfg +``` + +and then start the "vncviewer -listen 1" (i.e. 1 to correspond to the +5501 port.) Note that this assumes the stunnel install created a +Server SSL cert+key, usually /etc/stunnel/stunnel.pem (not all distros +will do this.) Also, that file is by default only readable by root, so +stunnel needs to be run as root. If your system does not have a key +installed or you do not want to run stunnel as root (or change the +permissions on the file), you can use x11vnc to create one for you for +example: + +``` +x11vnc -sslGenCert server self:mystunnel +``` + +answer the prompts with whatever you want; you can take the default +for all of them if you like. The openssl(1) package must be installed. +See this link and this one too for more info on SSL certs. This +creates $HOME/.vnc/certs/server-self:mystunnel.pem, then you would +change the "stunnel.cfg" to look something like: + +``` +foreground = yes +pid = +cert = /home/myusername/.vnc/certs/server-self:mystunnel.pem + +[vnc] +accept = 5500 +connect = localhost:5501 +``` + +In any event, with stunnel having been setup, the naive user is +instructed to paste in and run: +wget -qO - http://www.mysite.com/hd/vncs | sh - + +to pick up the vncs script this time. + +Of course if a man-in-the-middle can alter what the user downloads +then all bets are off!. + +More SSL variations and info about certificates can be found here. + + +OpenSSL libssl.so.0.9.7 problems: + +If you build your own stunnel or x11vnc for deployment, you may want +to statically link libssl.a and libcrypto.a into it because Linux +distros are currently a bit of a mess regarding which version of +libssl is installed. + +You will find the details here. + + +### Q-127: Can I (temporarily) mount my local (viewer-side) Windows/Samba File share on the machine where x11vnc is running? + +You will have to use an external network redirection for this. +Filesystem mounting is not part of the VNC protocol. + +We show a simple Samba example here. + +First you will need a tunnel to redirect the SMB requests from the +remote machine to the one you sitting at. We use an ssh tunnel: +sitting-here> ssh -C -R 1139:localhost:139 far-away.east + +Or one could combine this with the VNC tunnel at the same time, e.g.: + +``` +sitting-here> ssh -C -R 1139:localhost:139 -t -L 5900:localhost:5900 far-away.east 'x11vnc -localhost -display :0' +``` + +Port 139 is the Windows Service port. For Windows systems instead of +Samba, you may need to use the actual IP address of the Window machine +instead of "localhost" in the -R option (since the Windows service +does not listen on localhost by default.) + +Note that we use 1139 instead of 139 on the remote side because 139 +would require root permission to listen on (and you may have a samba +server running on it already.) + +The ssh -C is to enable compression, which might speed up the data +transfers. + +Depending on the remote system side configuration, it may or may not +be possible to mount the SMB share as a non-root user. Try it first as +a non-root user and if that fails you will have to become root. + +We will assume the user name is "fred" and we will try to mount the +viewer-side Windows SMB share "//haystack/pub" in +/home/fred/smb-haystack-pub. + +``` +far-away> mkdir -p /home/fred/smb-haystack-pub +far-away> smbmount //haystack/pub /home/fred/smb-haystack-pub -o username=fred,ip=127.0.0.1,port=1139 +``` + +(The 2nd command may need to be run as root.) Then run "df" or "ls -l +/home/fred/smb-haystack-pub" to see if it is mounted properly. Consult +the smbmount(8) and related documentation (it may require some +fiddling to get write permissions correct, etc.) To unmount: + +``` +far-away> smbumount /home/fred/smb-haystack-pub +``` + +At some point we hope to fold some automation for SMB ssh redir setup +into the Enhanced TightVNC Viewer (SSVNC) package we provide (as of +Sep 2006 it is there for testing.) + + +### Q-128: Can I redirect CUPS print jobs from the remote desktop where x11vnc is running to a printer on my local (viewer-side) machine? + +You will have to use an external network redirection for this. +Printing is not part of the VNC protocol. + +We show a simple Unix to Unix CUPS example here. Non-CUPS port +redirections (e.g. LPD) should also be possible, but may be a bit more +tricky. If you are viewing on Windows SMB and don't have a local cups +server it may be trickier still (see below.) + +First you will need a tunnel to redirect the print requests from the +remote machine to the one you sitting at. We use an ssh tunnel: +sitting-here> ssh -C -R 6631:localhost:631 far-away.east + +Or one could combine this with the VNC tunnel at the same time, e.g.: + +``` +sitting-here> ssh -C -R 6631:localhost:631 -t -L 5900:localhost:5900 far-away.east 'x11vnc -localhost -display :0' +``` + +Port 631 is the default CUPS port. The above assumes you have a Cups +server running on your viewer machine (localhost:631), if not, use +something like my-cups-srv:631 (the viewer-side Cups server) in the -R +instead. + +Note that we use 6631 instead of 631 on the remote side because 631 +would require root permission to listen on (and you likely have a cups +server running on it already.) + +Now the tricky part: to get applications to notice your cups +server/printer on localhost:6631. + +If you have administrative privilege (i.e. root password) on the +x11vnc side where the desktop is running, it should be easy to add the +printer through some configuration utility (e.g. in KDE: Utilities -> +Printing -> Printing Manager, and then supply admin password, and then +Add Printer/Class, and then fill in the inquisitive wizard. Most +important is the "Remote IPP server" panel where you put in localhost +for Host and 6631 for Port.) The main setting you want to convey is +the host is localhost and the port is non-standard (e.g. 6631.) Some +configuration utilities will take an Internet Printing Protocol (IPP) +URI, e.g. http://localhost:6631/printers/, +ipp://localhost:6631/printers/printer-name, +ipp://localhost:6631/ipp/printer-name, etc. Check your CUPS +documentation and admin interfaces to find what the syntax is and what +the "printer name" is. + +If you do not have root or print admin privileges, but are running a +recent (version 1.2 or greater) of the Cups client software, then an +easy way to temporarily switch Cups servers is to create the directory +and file: $HOME/.cups/client.conf on the remote side with a line like: + +``` +ServerName localhost:6631 +``` + +When not using x11vnc for remote access you can comment the above line +out with a '#' (or rename the client.conf file), to have normal cups +operation. + +Unfortunately, running applications may need to be restarted to notice +the new printers (libcups does not track changes in client.conf.) +Depending on circumstances, a running application may actually notice +the new printers without restarting (e.g. no print dialog has taken +place yet, or there are no CUPS printers configured on the remote +side.) + +Cups client software that is older (1.1) does not support appending +the port number, and for newer ones there is a bug preventing it from +always working (fixed in 1.2.3.) Kludges like these at the command +line will work: + +``` +far-away> env CUPS_SERVER=localhost IPP_PORT=6631 lpstat -p -d +far-away> env CUPS_SERVER=localhost IPP_PORT=6631 lpr -P myprinter file.ps +far-away> env CUPS_SERVER=localhost IPP_PORT=6631 firefox +``` + +but are somewhat awkward since you have to retroactively set the env. +var IPP_PORT. Its value cannot be broadcast to already running apps +(like the $HOME/.cups/client.conf trick sometimes does.) A common +workaround for an already running app is to somehow get it to "Print +To File", e.g. file.ps and then use something like the lpr example +above. Also, the option "-h host:port" works with CUPS lp(1) and +lpr(1). + +You can also print to Windows shares printers in principle. You may do +this with the smbspool(8) command, or configure the remote CUPS via +lpadmin(8), etc, to use a printer URI something like +smb://machine:port/printer (this may have some name resolution +problems WRT localhost.) Also, as with SMB mounting, the port redir +(-R) to the Windows machine must use the actual IP address instead of +"localhost". + +At some point we hope to fold some automation for CUPS ssh redir setup +into the Enhanced TightVNC Viewer (SSVNC) package we provide (as of +Sep 2006 it is there for testing.) + + +### Q-129: How can I hear the sound (audio) from the remote applications on the desktop I am viewing via x11vnc? + +You will have to use an external network audio mechanism for this. +Audio is not part of the VNC protocol. + +We show a simple Unix to Unix esd example here (artsd should be +possible too, we have also verified the esd Windows port works for the +method described below.) + +First you will need a tunnel to redirect the audio from the remote +machine to the one you sitting at. We use an ssh tunnel: +sitting-here> ssh -C -R 16001:localhost:16001 far-away.east + +Or one could combine this with the VNC tunnel at the same time, e.g.: + +``` +sitting-here> ssh -C -R 16001:localhost:16001 -t -L 5900:localhost:5900 far-away.east 'x11vnc -localhost -display :0' +``` + +Port 16001 is the default ESD uses. So when an application on the +remote desktop makes a sound it will connect to this tunnel and be +redirected to port 16001 on the local machine (sitting-here in this +example.) The -C option is an attempt to compress the audio a little +bit. + +So we next need a local (sitting-here) esd daemon running that will +receive those requests and play them on the local sound device: + +``` +sitting-here> esd -promiscuous -port 16001 -tcp -bind 127.0.0.1 +``` + +See the esd(1) man page for the meaning of the options (the above are +not very secure.) (This method also works with the EsounD windows port +esd.exe) + +To test this sound tunnel, we use the esdplay program to play a simple +.wav file: + +``` +far-away> esdplay -s localhost:16001 im_so_happy.wav +``` + +If you hear the sound (Captain Kirk in this example), that means you +are in great shape. + +To run individual audio applications you can use the esddsp(1) +command: + +``` +far-away> esddsp -s localhost:16001 xmms +``` + +Then you could try playing some sounds inside xmms. You could also set +the environment variable ESPEAKER=localhost:16001 to not need to +supply the -s option all the time. (for reasons not clear, sometimes +esddsp can figure it out on its own.) All the script esddsp does is to +set ESPEAKER and LD_PRELOAD for you so that when the application opens +the sound device (usually /dev/dsp) its interactions with the device +will be intercepted and sent to the esd daemon running on sitting-here +(that in turn writes them to the real, local /dev/dsp.) + +Redirecting All sound: + +It does not seem to be possible to switch all of the sound of the +remote machine from its sound device to the above esd+ssh tunnel +without some preparation. But it can be done reasonably well if you +prepare (i.e. restart) the desktop with this in mind. + +Here is one way to redirect all sound. The idea is we run the entire +desktop with sound directed to localhost:16001. When we are sitting at +far-away.east we run "esd -promiscuous -port 16001 -tcp -bind +127.0.0.1" on far-away.east (to be able to hear the sound.) However, +when we are sitting at sitting-here.west we kill that esd process and +run that same esd command on sitting-here.west and start up the above +ssh tunnel. This is a little awkward, but with some scripts one would +probably kill and restart the esd processes automatically when x11vnc +is used. + +So next we have to run the whole desktop pointing toward our esd. Here +is a simple way to test. Log in to the machine via the "FailSafe" +desktop. Then in the lone terminal type something like: + +``` +esddsp -s localhost:16001 gnome-session +``` + +or: + +``` +esddsp -s localhost:16001 startkde +``` + +where the last part is whatever command starts your desktop (even +fvwm2.) This causes the environment variables ESPEAKER and LD_PRELOAD +to be set appropriately and every application (processes with the +desktop as an ancestor) will use them. If this scheme works well you +can make it less klunky by adding the command to your ~/.xsession, +etc. file that starts your default desktop. Or you may be able to +configure your desktop to use localhost:16001, or whatever is needed, +via a gui configuration panel. Some Notes: + +* Not all audio applications are compatible with the esd and artsd + mechanisms, but many are. +* The audio is not compressed so you probably need a broadband or + faster connection. Listening to music may not be very pleasant... + (Although we found streaming music from across the US over cable + modem worked OK, but took 200 KB/sec, to use less bandwidth + consider something like "ssh far-away.east 'cat favorite.mp3' | + mpg123 -b 4000 -") +* Linux does not seem to have the concept of LD_PRELOAD_64 so if you + run on a mixed 64- and 32-bit ABI system (e.g. AMD x86_64) some of + the applications will fail to run because LD_PRELOAD will point to + libraries of the wrong wordsize. +* At some point we hope to fold some automation for esd or artsd ssh + redir setup into the Enhanced TightVNC Viewer (SSVNC) package we + provide (as of Sep/2006 it is there for testing.) + + +### Q-130: Why don't I hear the "Beeps" in my X session (e.g. when typing tput bel in an xterm)? + +As of Dec/2003 "Beep" XBell events are tracked by default. The X +server must support the XKEYBOARD extension (this is not on by default +in Solaris, see Xserver(1) for how to turn it on via +kb), and so you +won't hear them if the extension is not present. + +If you don't want to hear the beeps use the -nobell option. If you +want to hear the audio from the remote applications, consider trying a +redirector such as esd. + + +### Q-131: Does x11vnc work with IPv6? + +Update: as of Apr/2010 in the 0.9.10 x11vnc development tarball, there +is now built-in support for IPv6 (128 bit internet addresses.) See the +-6 and -connect options for details. + +The remainder of this FAQ entry shows how to do with this with pre +0.9.10 x11vnc using IPv6 helper tools. + +--- + +Using an external IPv6 helper: +A way to do this is via a separate helper program such as inetd (or +for encrypted connections: ssh or stunnel.) For example, you configure +x11vnc to be run from inetd or xinetd and instruct it to listen on an +IPv6 address. For xinetd the setting "flags = IPv6" will be needed. +For inetd.conf, an example is: + +``` +5900 stream tcp6 nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc_wrapper.sh +``` + +We also provide a transitional tool in "x11vnc/misc/inet6to4" that +acts as a relay for any IPv4 application to allow connections over +IPv6. For example: + +``` +inet6to4 5900 localhost:5900 +``` + +where x11vnc is listening on IPv4 port 5900. + +Also note that not all VNC Viewers are IPv6 enabled, so a redirector +may also be needed for them. The tool "inet6to4 -r ..." can do this as +well. SSVNC (see below) supports IPv6 without need for the helper. + +``` +# ./inet6to4 -help + +inet6to4: Act as an ipv6-to-ipv4 relay for tcp applications that + do not support ipv6. + +Usage: inet6to4 + inet6to4 -r + +Examples: inet6to4 5900 localhost:5900 + inet6to4 8080 web1:80 + inet6to4 -r 5900 fe80::217:f2ff:fee6:6f5a%eth0:5900 + +The -r option reverses the direction of translation (e.g. for ipv4 +clients that need to connect to ipv6 servers.) Reversing is the default +if this script is named 'inet4to6' (e.g. by a symlink.) + +Use Ctrl-C to stop this program. + +You can also set env. vars INET6TO4_LOOP=1 or INET6TO4_LOOP=BG +to have an outer loop restarting this program (BG means do that +in the background), and INET6TO4_LOGFILE for a log file. +Also set INET6TO4_VERBOSE to verbosity level and INET6TO4_WAITTIME +and INET6TO4_PIDFILE (see below.) +``` + +The "INET6TO4_LOOP=BG" and "INET6TO4_LOGFILE=..." env. variables make +the tool run reliably as a daemon for very long periods. Read the top +part of the script for more information. + +--- + +Encrypted Tunnels with IPv6 Support: +For SSH tunnelled encrypted VNC connections, one can of course use the +IPv6 support in ssh(1). + +For SSL encrypted VNC connections, one possibility is to use the IPv6 +support in stunnel(1). This includes the built-in support via the +-stunnel option. For example: + +``` +x11vnc -stunnel SAVE -env STUNNEL_LISTEN=:: -env STUNNEL_DEBUG=1 ... +``` + +--- + +SSH IPv6 Tricks: +It is interesting to note that ssh(1) can do basically the same thing +as inet6to4 above by: + +``` +ssh -g -L 5900:localhost:5901 localhost "printf 'Press Enter to Exit: '; read x" +``` + +(where we have x11vnc running via "-rfbport 5901" in this case.) + +Note that one can also make a home-brew SOCKS5 ipv4-to-ipv6 gateway +proxy using ssh like this: + +``` +ssh -D '*:1080' localhost "printf 'Press Enter to Exit: '; read x" +``` + +then specify a proxy like socks://hostname:1080 where hostname is the +machine running the above ssh command (add -v to ssh for connection +logging info.) + +--- + +IPv6 SSVNC Viewer: +Our SSVNC VNC Viewer is basically a wrapper for ssh(1) and stunnel(1), +and so it already has good IPv6 support because these two commands do. +On Unix, MacOSX, and Windows nearly all of the the remaining parts of +SSVNC (e.g. the built-in proxying and un-encrypted connections) have +been modified to support IPv6 in SSVNC 1.0.26. + +Contributions: + +### Q-132: Thanks for your program or for your help! Can I make a donation? + +Please do (any amount is appreciated; very few have donated) and thank +you for your support! Click on the PayPal button below for more info. + +[x-click-but04.gif]-Submit + +### Q-133: I am experiencing extreme framebuffer update lags and am using an Intel graphics card. What to do? + +Depending on your graphics card model and x.org driver used, several +approaches might work out for you: + +Some users [have reported](https://github.com/LibVNC/x11vnc/issues/58) +that when using the 'intel' x.org driver, switching the driver's +option named "AccelMethod" to "UXA" helped. + +Others [reported](https://github.com/LibVNC/x11vnc/issues/100) that +using the 'modesetting' x.org driver caused the lags and switching to +the 'intel' x.org driver helped. + +Some [reported](https://github.com/LibVNC/x11vnc/issues/102) that +lags only occured with xfwm as window manager and with x11vnc started +with monitors off, no matter what the x.org driver. In their case, one +of disabling vsync, using 'modesetting' with "AccelMethod" "none" or +disabling compositing all helped. diff --git a/doc/OPTIONS.md b/doc/OPTIONS.md new file mode 100755 index 0000000..29aea5b --- /dev/null +++ b/doc/OPTIONS.md @@ -0,0 +1,5901 @@ +Here are all of x11vnc command line options: + +``` +% x11vnc -opts (see below for -help long descriptions) + +x11vnc: allow VNC connections to real X11 displays. 0.9.13 lastmod: 2010-12-27 + +x11vnc options: + -display disp -auth file -N + -autoport n -rfbport str -6 + -no6 -noipv6 -noipv4 + -reopen -reflect host:N -id windowid + -sid windowid -appshare -clip WxH+X+Y + -flashcmap -shiftcmap n -notruecolor + -advertise_truecolor -visual n -overlay + -overlay_nocursor -8to24 [opts] -24to32 + -scale fraction -geometry WxH -scale_cursor frac + -viewonly -shared -once + -forever -loop -timeout n + -sleepin n -inetd -tightfilexfer + -ultrafilexfer -http -http_ssl + -avahi -mdns -zeroconf + -connect string -connect_or_exit str -proxy string + -vncconnect -novncconnect -allow host1[,host2..] + -localhost -unixsock str -listen6 str + -nolookup -input string -grabkbd + -grabptr -ungrabboth -grabalways + -viewpasswd string -passwdfile filename -showrfbauth filename + -unixpw [list] -unixpw_nis [list] -unixpw_cmd cmd + -find -finddpy -listdpy + -findauth [disp] -create -xdummy + -xvnc -xvnc_redirect -xdummy_xvfb + -create_xsrv str -svc -svc_xdummy + -svc_xvnc -svc_xdummy_xvfb -xdmsvc + -sshxdmsvc -unixpw_system_greeter -redirect port + -display WAIT:... -vencrypt mode -anontls mode + -sslonly -dhparams file -nossl + -ssl [pem] -ssltimeout n -sslnofail + -ssldir dir -sslverify path -sslCRL path + -sslGenCA [dir] -sslGenCert type name -sslEncKey pem + -sslCertInfo pem -sslDelCert pem -sslScripts + -stunnel [pem] -stunnel3 [pem] -enc cipher:keyfile + -https [port] -httpsredir [port] -http_oneport + -ssh user@host:disp -usepw -storepasswd pass file + -nopw -accept string -afteraccept string + -gone string -users list -noshm + -flipbyteorder -onetile -solid [color] + -blackout string -xinerama -noxinerama + -xtrap -xrandr [mode] -rotate string + -padgeom WxH -o logfile -flag file + -rmflag file -rc filename -norc + -env VAR=VALUE -prog /path/to/x11vnc -h, -help + -?, -opts -V, -version -license + -dbg -q, -quiet -v, -verbose + -bg -modtweak -nomodtweak + -xkb -noxkb -capslock + -skip_lockkeys -noskip_lockkeys -skip_keycodes string + -sloppy_keys -skip_dups -noskip_dups + -add_keysyms -noadd_keysyms -clear_mods + -clear_keys -clear_all -remap string + -norepeat -repeat -nofb + -nobell -nosel -noprimary + -nosetprimary -noclipboard -nosetclipboard + -seldir string -cursor [mode] -nocursor + -cursor_drag -arrow n -noxfixes + -alphacut n -alphafrac fraction -alpharemove + -noalphablend -nocursorshape -cursorpos + -nocursorpos -xwarppointer -noxwarppointer + -always_inject -buttonmap string -nodragging + -ncache n -ncache_cr -ncache_no_moveraise + -ncache_no_dtchange -ncache_no_rootpixmap -ncache_keep_anims + -ncache_old_wm -ncache_pad n -debug_ncache + -wireframe [str] -nowireframe -nowireframelocal + -wirecopyrect mode -nowirecopyrect -debug_wireframe + -scrollcopyrect mode -noscrollcopyrect -scr_area n + -scr_skip list -scr_inc list -scr_keys list + -scr_term list -scr_keyrepeat lo-hi -scr_parms string + -fixscreen string -debug_scroll -noxrecord + -grab_buster -nograb_buster -debug_grabs + -debug_sel -pointer_mode n -input_skip n + -allinput -input_eagerly -speeds rd,bw,lat + -wmdt string -debug_pointer -debug_keyboard + -defer time -wait time -extra_fbur n + -wait_ui factor -setdefer n -nowait_bog + -slow_fb time -xrefresh time -nap + -nonap -sb time -readtimeout n + -ping n -nofbpm -fbpm + -nodpms -dpms -forcedpms + -clientdpms -noserverdpms -noultraext + -chatwindow -noxdamage -xd_area A + -xd_mem f -sigpipe string -threads + -nothreads -fs f -gaps n + -grow n -fuzz n -debug_tiles + -snapfb -rawfb string -freqtab file + -pipeinput cmd -macnodim -macnosleep + -macnosaver -macnowait -macwheel n + -macnoswap -macnoresize -maciconanim n + -macmenu -macuskbd -macnoopengl + -macnorawfb -gui [gui-opts] -remote command + -query variable -QD variable -sync + -query_retries str -remote_prefix str -noremote + -yesremote -unsafe -safer + -privremote -nocmds -allowedcmds list + -deny_all +``` + +LibVNCServer options: + +``` +-rfbport port TCP port for RFB protocol +-rfbwait time max time in ms to wait for RFB client +-rfbauth passwd-file use authentication on RFB protocol + (use 'storepasswd' to create a password file) +-rfbversion 3.x Set the version of the RFB we choose to advertise +-permitfiletransfer permit file transfer support +-passwd plain-password use authentication + (use plain-password as password, USE AT YOUR RISK) +-deferupdate time time in ms to defer updates (default 40) +-deferptrupdate time time in ms to defer pointer updates (default none) +-desktop name VNC desktop name (default "LibVNCServer") +-alwaysshared always treat new clients as shared +-nevershared never treat new clients as shared +-dontdisconnect don't disconnect existing clients when a new non-shared + connection comes in (refuse new connection instead) +-httpdir dir-path enable http server using dir-path home +-httpport portnum use portnum for http connection +-enablehttpproxy enable http proxy support +-progressive height enable progressive updating for slow links +-listen ipaddr listen for connections only on network interface with + addr ipaddr. '-listen localhost' and hostname work too. + +libvncserver-tight-extension options: +-disablefiletransfer disable file transfer +-ftproot string set ftp root +``` + +Full x11vnc options: + +``` +% x11vnc -help + +x11vnc: allow VNC connections to real X11 displays. 0.9.13 lastmod: 2010-12-27 + +(type "x11vnc -opts" to just list the options.) + +Typical usage is: + + Run this command in a shell on the remote machine "far-host" + with X session you wish to view: + + x11vnc -display :0 + + Then run this in another window on the machine you are sitting at: + + vncviewer far-host:0 + +Once x11vnc establishes connections with the X11 server and starts listening +as a VNC server it will print out a string: PORT=XXXX where XXXX is typically +5900 (the default VNC server port). One would next run something like +this on the local machine: "vncviewer hostname:N" where "hostname" is +the name of the machine running x11vnc and N is XXXX - 5900, i.e. usually +"vncviewer hostname:0". + +By default x11vnc will not allow the screen to be shared and it will exit +as soon as the client disconnects. See -shared and -forever below to override +these protections. See the FAQ for details how to tunnel the VNC connection +through an encrypted channel such as ssh(1). In brief: + + ssh -t -L 5900:localhost:5900 far-host 'x11vnc -localhost -display :0' + + vncviewer -encodings 'copyrect tight zrle hextile' localhost:0 + +Also, use of a VNC password (-rfbauth or -passwdfile) is strongly recommended. + +For additional info see: http://www.karlrunge.com/x11vnc/ + and http://www.karlrunge.com/x11vnc/faq.html + + +Config file support: if the file $HOME/.x11vncrc exists then each line in +it is treated as a single command line option. Disable with -norc. For +each option name, the leading character "-" is not required. E.g. a line +that is either "forever" or "-forever" may be used and are equivalent. +Likewise "wait 100" or "-wait 100" are acceptable and equivalent lines. +The "#" character comments out to the end of the line in the usual way +(backslash it for a literal). Leading and trailing whitespace is trimmed off. +Lines may be continued with a "\" as the last character of a line (it +becomes a space character). + +Options: + +-display disp X11 server display to connect to, usually :0. The X + server process must be running on same machine and + support MIT-SHM. Equivalent to setting the DISPLAY + environment variable to "disp". + + See the description below of the "-display WAIT:..." + extensions, where alias "-find" will find the user's + display automatically, and "-create" will create a + Xvfb session if no session is found. + +-auth file Set the X authority file to be "file", equivalent to + setting the XAUTHORITY environment variable to "file" + before startup. Same as -xauth file. See Xsecurity(7), + xauth(1) man pages for more info. + + Use '-auth guess' to have x11vnc use its -findauth + mechanism (described below) to try to guess the + XAUTHORITY filename and use it. + + XDM/GDM/KDM: if you are running x11vnc as root and want + to find the XAUTHORITY before anyone has logged into an + X session yet, use: x11vnc -env FD_XDM=1 -auth guess ... + (This will also find the XAUTHORITY if a user is already + logged into the X session.) When running as root, + FD_XDM=1 will be tried if the initial -auth guess fails. + +-N If the X display is :N, try to set the VNC display to + also be :N This just sets the -rfbport option to 5900+N + The program will exit immediately if that port is not + available. The -N option only works with normal -display + usage, e.g. :0 or :8, -N is ignored in the -display + WAIT:..., -create, -find, -svc, -redirect, etc modes. + +-autoport n Automatically probe for a free VNC port starting at n. + The default is to start probing at 5900. Use this to + stay away from other VNC servers near 5900. + +-rfbport str The VNC port to listen on (a LibVNCServer option), e.g. + 5900, 5901, etc. If specified as "-rfbport PROMPT" + then the x11vnc -gui is used to prompt the user to + enter the port number. + +-6 IPv6 listening support. In addition to IPv4, the + IPv6 address is listened on for incoming connections. + The same port number as IPv4 is used. + + NOTE: This x11vnc binary was compiled to have the + "-6" IPv6 listening mode ENABLED by default (CPPFLAGS + -DX11VNC_LISTEN6=1). So to disable IPv6 listening mode + you MUST supply the "-no6" option (see below.) + + The "-6" mode works for both normal connections and + -ssl encrypted ones. Nearly everything is supported + for the IPv6 case, but there are a few exceptions. + See -stunnel for its IPv6 support. + + Currently, for absolutely everything to work correctly + the machine may need to have some IPv4 support, at the + least for the loopback interface. However, for nearly + all usage modes no IPv4 support is required. See -noipv4 +. + + If you have trouble compiling or running in IPv6 mode, + set -DX11VNC_IPV6=0 in CPPFLAGS when configuring to + disable IPv6 support. + +-no6 Disable IPv6 listening support (only useful if the + "-6" mode is compiled in to be the default; see the + X11VNC_LISTEN6 description above under "-6".) + +-noipv6 Do not try to use IPv6 for any listening or connecting + sockets. This includes both the listening service + port(s) and outgoing connections from -connect, + -connect_or_exit, or -proxy. Use this if you are having + problems due to IPv6. + +-noipv4 Do not try to use IPv4 for any listening or connecting + sockets. This is mainly for exploring the behavior of + x11vnc on an IPv6-only system, but may have other uses. + +-reopen If the X server connection is disconnected, try to + reopen the X display (up to one time.) This is of use + for display managers like GDM (KillInitClients option) + that kill x11vnc just after the user logs into the + X session. Note: the reopened state may be unstable. + Set X11VNC_REOPEN_DISPLAY=n to reopen n times and + set X11VNC_REOPEN_SLEEP_MAX to the number of seconds, + default 10, to keep trying to reopen the display (once + per second.) + + Update: as of 0.9.9, x11vnc tries to automatically avoid + being killed by the display manager by delaying creating + windows or using XFIXES. So you shouldn't need to use + KillInitClients=false as long as you log in quickly + enough (within 45 seconds of connecting.) You can + disable this by setting X11VNC_AVOID_WINDOWS=never. + You can also set it to the number of seconds to delay. + +-reflect host:N Instead of connecting to and polling an X display, + connect to the remote VNC server host:N and be a + reflector/repeater for it. This is useful for trying + to manage the case of many simultaneous VNC viewers + (e.g. classroom broadcasting) where, e.g. you put + a repeater on each network switch, etc, to improve + performance by distributing the load and network + traffic. Implies -shared (use -noshared as a later + option to disable). See the discussion below under + -rawfb vnc:host:N for more details. + +-id windowid Show the X window corresponding to "windowid" not + the entire display. New windows like popup menus, + transient toplevels, etc, may not be seen or may be + clipped. Disabling SaveUnders or BackingStore in the + X server may help show them. x11vnc may crash if the + window is initially partially obscured, changes size, + is iconified, etc. Some steps are taken to avoid this + and the -xrandr mechanism is used to track resizes. Use + xwininfo(1) to get the window id, or use "-id pick" + to have x11vnc run xwininfo(1) for you and extract + the id. The -id option is useful for exporting very + simple applications (e.g. the current view on a webcam). +-sid windowid As -id, but instead of using the window directly it + shifts a root view to it: this shows SaveUnders menus, + etc, although they will be clipped if they extend beyond + the window. + +-appshare Simple application sharing based on the -id/-sid + mechanism. Every new toplevel window that the + application creates induces a new viewer window via + a reverse connection. The -id/-sid and -connect + options are required. Run 'x11vnc -appshare -help' + for more info. + +-clip WxH+X+Y Only show the sub-region of the full display that + corresponds to the rectangle geometry with size WxH and + offset +X+Y. The VNC display has size WxH (i.e. smaller + than the full display). This also works for -id/-sid + mode where the offset is relative to the upper left + corner of the selected window. An example use of this + option would be to split a large (e.g. Xinerama) display + into two parts to be accessed via separate viewers by + running a separate x11vnc on each part. + + Use '-clip xinerama0' to clip to the first xinerama + sub-screen (if xinerama is active). xinerama1 for the + 2nd sub-screen, etc. This way you don't need to figure + out the WxH+X+Y of the desired xinerama sub-screen. + screens are sorted in increasing distance from the + (0,0) origin (I.e. not the Xserver's order). + +-flashcmap In 8bpp indexed color, let the installed colormap flash + as the pointer moves from window to window (slow). + Also try the -8to24 option to avoid flash altogether. +-shiftcmap n Rare problem, but some 8bpp displays use less than 256 + colorcells (e.g. 16-color grayscale, perhaps the other + bits are used for double buffering) *and* also need to + shift the pixels values away from 0, .., ncells. "n" + indicates the shift to be applied to the pixel values. + To see the pixel values set DEBUG_CMAP=1 to print out + a colormap histogram. Example: -shiftcmap 240 +-notruecolor For 8bpp displays, force indexed color (i.e. a colormap) + even if it looks like 8bpp TrueColor (rare problem). +-advertise_truecolor If the X11 display is indexed color, lie to clients + when they first connect by telling them it is truecolor. + To workaround RealVNC: inPF has colourMap but not 8bpp + Use '-advertise_truecolor reset' to reset client fb too. + +-visual n This option probably does not do what you think. + It simply *forces* the visual used for the framebuffer; + this may be a bad thing... (e.g. messes up colors or + cause a crash). It is useful for testing and for some + workarounds. n may be a decimal number, or 0x hex. + Run xdpyinfo(1) for the values. One may also use + "TrueColor", etc. see for a list. If the + string ends in ":m" then for better or for worse + the visual depth is forced to be m. You may want to + use -noshm when using this option (so XGetImage may + automatically translate the pixel data). + +-overlay Handle multiple depth visuals on one screen, e.g. 8+24 + and 24+8 overlay visuals (the 32 bits per pixel are + packed with 8 for PseudoColor and 24 for TrueColor). + + Currently -overlay only works on Solaris via + XReadScreen(3X11) and IRIX using XReadDisplay(3). + On Solaris there is a problem with image "bleeding" + around transient popup menus (but not for the menu + itself): a workaround is to disable SaveUnders + by passing the "-su" argument to Xsun (in + /etc/dt/config/Xservers). + + Use -overlay as a workaround for situations like these: + Some legacy applications require the default visual to + be 8bpp (8+24), or they will use 8bpp PseudoColor even + when the default visual is depth 24 TrueColor (24+8). + In these cases colors in some windows will be incorrect + in x11vnc unless -overlay is used. Another use of + -overlay is to enable showing the exact mouse cursor + shape (details below). + + Under -overlay, performance will be somewhat slower + due to the extra image transformations required. + For optimal performance do not use -overlay, but rather + configure the X server so that the default visual is + depth 24 TrueColor and try to have all apps use that + visual (e.g. some apps have -use24 or -visual options). +-overlay_nocursor Sets -overlay, but does not try to draw the exact mouse + cursor shape using the overlay mechanism. + +-8to24 [opts] Try this option if -overlay is not supported on your + OS, and you have a legacy 8bpp app that you want to + view on a multi-depth display with default depth 24 + (and is 32 bpp) OR have a default depth 8 display with + depth 24 overlay windows for some apps. This option + may not work on all X servers and hardware (tested + on XFree86/Xorg mga driver and Xsun). The "opts" + string is not required and is described below. + + This mode enables a hack where x11vnc monitors windows + within 3 levels from the root window. If it finds + any that are 8bpp it extracts the indexed color + pixel values using XGetImage() and then applies a + transformation using the colormap(s) to create TrueColor + RGB values that it in turn inserts into bits 1-24 of + the framebuffer. This creates a depth 24 "view" + of the display that is then exported via VNC. + + Conversely, for default depth 8 displays, the depth + 24 regions are read by XGetImage() and everything is + transformed and inserted into a depth 24 TrueColor + framebuffer. + + Note that even if there are *no* depth 24 visuals or + windows (i.e. pure 8bpp), this mode is potentially + an improvement over -flashcmap because it avoids the + flashing and shows each window in the correct color. + + This method works OK, but may still have bugs and it + does hog resources. If there are multiple 8bpp windows + using different colormaps, one may have to iconify all + but one for the colors to be correct. + + There may be painting errors for clipping and switching + between windows of depths 8 and 24. Heuristics are + applied to try to minimize the painting errors. One can + also press 3 Alt_L's in a row to refresh the screen + if the error does not repair itself. Also the option + -fixscreen 8=3.0 or -fixscreen V=3.0 may be used to + periodically refresh the screen at the cost of bandwidth + (every 3 sec for this example). + + The [opts] string can contain the following settings. + Multiple settings are separated by commas. + + For for some X servers with default depth 24 a + speedup may be achieved via the option "nogetimage". + This enables a scheme were XGetImage() is not used + to retrieve the 8bpp data. Instead, it assumes that + the 8bpp data is in bits 25-32 of the 32bit X pixels. + There is no requirement that the X server should put + the data there for our poll requests, but some do and + so the extra steps to retrieve it can be skipped. + Tested with mga driver with XFree86/Xorg. For the + default depth 8 case this option is ignored. + + To adjust how often XGetImage() is used to poll the + non-default visual regions for changes, use the option + "poll=t" where "t" is a floating point time. + (default: 0.05) + + Setting the option "level2" will limit the search + for non-default visual windows to two levels from the + root window. Do this on slow machines where you know + the window manager only imposes one extra window between + the app window and the root window. + + Also for very slow machines use "cachewin=t" + where t is a floating point amount of time to cache + XGetWindowAttributes results. E.g. cachewin=5.0. + This may lead to the windows being unnoticed for this + amount of time when deiconifying, painting errors, etc. + + While testing on a very old SS20 these options gave + tolerable response: -8to24 poll=0.2,cachewin=5.0. For + this machine -overlay is supported and gives better + response. + + Debugging for this mode can be enabled by setting + "dbg=1", "dbg=2", or "dbg=3". + +-24to32 Very rare problem: if the framebuffer (X display + or -rawfb) is 24bpp instead of the usual 32bpp, then + dynamically transform the pixels to 32bpp. This will be + slower, but can be used to work around problems where + VNC viewers cannot handle 24bpp (e.g. "main: setPF: + not 8, 16 or 32 bpp?"). See the FAQ for more info. + + In the case of -rawfb mode, the pixels are directly + modified by inserting a 0 byte to pad them out to 32bpp. + For X displays, a kludge is done that is equivalent to + "-noshm -visual TrueColor:32". (If better performance + is needed for the latter, feel free to ask). + +-scale fraction Scale the framebuffer by factor "fraction". Values + less than 1 shrink the fb, larger ones expand it. Note: + the image may not be sharp and response may be slower. + If "fraction" contains a decimal point "." it + is taken as a floating point number, alternatively + the notation "m/n" may be used to denote fractions + exactly, e.g. -scale 2/3 + + To scale asymmetrically in the horizontal and vertical + directions, specify a WxH geometry to stretch to: + e.g. '-scale 1024x768', or also '-scale 0.9x0.75' + + Scaling Options: can be added after "fraction" via + ":", to supply multiple ":" options use commas. + If you just want a quick, rough scaling without + blending, append ":nb" to "fraction" (e.g. -scale + 1/3:nb). No blending is the default for 8bpp indexed + color, to force blending for this case use ":fb". + + To disable -scrollcopyrect and -wirecopyrect under + -scale use ":nocr". If you need to to enable them use + ":cr" or specify them explicitly on the command line. + If a slow link is detected, ":nocr" may be applied + automatically. Default: :cr + + More esoteric options: for compatibility with vncviewers + the scaled width is adjusted to be a multiple of 4: + to disable this use ":n4". ":in" use interpolation + scheme even when shrinking, ":pad" pad scaled width + and height to be multiples of scaling denominator + (e.g. 3 for 2/3). + +-geometry WxH Same as -scale WxH + +-scale_cursor frac By default if -scale is supplied the cursor shape is + scaled by the same factor. Depending on your usage, + you may want to scale the cursor independently of the + screen or not at all. If you specify -scale_cursor + the cursor will be scaled by that factor. When using + -scale mode to keep the cursor at its "natural" size + use "-scale_cursor 1". Most of the ":" scaling + options apply here as well. + +-viewonly All VNC clients can only watch (default off). +-shared VNC display is shared, i.e. more than one viewer can + connect at the same time (default off). +-once Exit after the first successfully connected viewer + disconnects, opposite of -forever. This is the Default. +-forever Keep listening for more connections rather than exiting + as soon as the first client(s) disconnect. Same as -many + + To get the standard non-shared VNC behavior where when + a new VNC client connects the existing VNC client is + dropped use: -nevershared -forever This method can + also be used to guard against hung TCP connections that + do not go away. + +-loop Create an outer loop restarting the x11vnc process + whenever it terminates. -bg and -inetd are ignored + in this mode (however see -loopbg below). + + Useful for continuing even if the X server terminates + and restarts (at that moment the process will need + permission to reconnect to the new X server of course). + + Use, e.g., -loop100 to sleep 100 millisecs between + restarts, etc. Default is 2000ms (i.e. 2 secs) Use, + e.g. -loop300,5 to sleep 300 ms and only loop 5 times. + + If -loopbg (plus any numbers) is specified instead, + the "-bg" option is implied and the mode approximates + inetd(8) usage to some degree. In this case when + it goes into the background any listening sockets + (i.e. ports 5900, 5800) are closed, so the next one + in the loop can use them. This mode will only be of + use if a VNC client (the only client for that process) + is already connected before the process goes into the + background, for example, usage of -display WAIT:.., + -svc, and -connect can make use of this "poor man's" + inetd mode. The default wait time is 500ms in this + mode. This usage could use useful: -svc -bg -loopbg + +-timeout n Exit unless a client connects within the first n seconds + after startup. + + If there have been no connection attempts after n + seconds x11vnc exits immediately. If a client is + trying to connect but has not progressed to the normal + operating state, x11vnc gives it a few more seconds + to finish and exits if it does not make it to the + normal state. + + For reverse connections via -connect or -connect_or_exit + a timeout of n seconds will be set for all reverse + connects. If the connect timeout alarm goes off, + x11vnc will exit immediately. + +-sleepin n At startup sleep n seconds before proceeding (e.g. to + allow redirs and listening clients to start up) + + If a range is given: '-sleepin min-max', a random value + between min and max is slept. E.g. '-sleepin 0-20' and + '-sleepin 10-30'. Floats are allowed too. + +-inetd Launched by inetd(8): stdio instead of listening socket. + Note: if you are not redirecting stderr to a log file + (via shell 2> or -o option) you MUST also specify the -q + option, otherwise the stderr goes to the viewer which + will cause it to abort. Specifying both -inetd and -q + and no -o will automatically close the stderr. + +-tightfilexfer Enable the TightVNC file transfer extension. Note that + that when the -viewonly option is supplied all file + transfers are disabled. Also clients that log in + viewonly cannot transfer files. However, if the remote + control mechanism is used to change the global or + per-client viewonly state the filetransfer permissions + will NOT change. + + IMPORTANT: please understand if -tightfilexfer is + specified and you run x11vnc as root for, say, inetd + or display manager (gdm, kdm, ...) access and you do + not have it switch users via the -users option, then + VNC Viewers that connect are able to do filetransfer + reads and writes as *root*. + + Also, tightfilexfer is disabled in -unixpw mode. + +-ultrafilexfer Note: to enable UltraVNC filetransfer and to get it to + work you probably need to supply these LibVNCServer + options: "-rfbversion 3.6 -permitfiletransfer" + "-ultrafilexfer" is an alias for this combination. + + IMPORTANT: please understand if -ultrafilexfer is + specified and you run x11vnc as root for, say, inetd + or display manager (gdm, kdm, ...) access and you do + not have it switch users via the -users option, then + VNC Viewers that connect are able to do filetransfer + reads and writes as *root*. + + Note that sadly you cannot do both -tightfilexfer and + -ultrafilexfer at the same time because the latter + requires setting the version to 3.6 and tightvnc will + not do filetransfer when it sees that version number. + +-http Instead of using -httpdir (see below) to specify + where the Java vncviewer applet is, have x11vnc try + to *guess* where the directory is by looking relative + to the program location and in standard locations + (/usr/local/share/x11vnc/classes, etc). Under -ssl or + -stunnel the ssl classes subdirectory is sought. +-http_ssl As -http, but force lookup for ssl classes subdir. + + Note that for HTTPS, single-port Java applet delivery + you can set X11VNC_HTTPS_DOWNLOAD_WAIT_TIME to the + max number of seconds to wait for the applet download + to finish. The default is 15. + +-avahi Use the Avahi/mDNS ZeroConf protocol to advertise + this VNC server to the local network. (Related terms: + Rendezvous, Bonjour). Depending on your setup, you + may need to start avahi-daemon and open udp port 5353 + in your firewall. + + You can set X11VNC_AVAHI_NAME, X11VNC_AVAHI_HOST, + and/or X11VNC_AVAHI_PORT environment variables + to override the default values. For example: + -env X11VNC_AVAHI_NAME=wally + + If the avahi API cannot be found at build time, a helper + program like avahi-publish(1) or dns-sd(1) will be tried + +-mdns Same as -avahi. +-zeroconf Same as -avahi. + +-connect string For use with "vncviewer -listen" reverse connections. + If "string" has the form "host" or "host:port" + the connection is made once at startup. + + Use commas for a list of host's and host:port's. + E.g. -connect host1,host2 or host1:0,host2:5678. + Note that to reverse connect to multiple hosts at the + same time you will likely need to also supply: -shared + + Note that unlike most vnc servers, x11vnc will require a + password for reverse as well as for forward connections. + (provided password auth has been enabled, -rfbauth, etc) + If you do not want to require a password for reverse + connections set X11VNC_REVERSE_CONNECTION_NO_AUTH=1 in + your environment before starting x11vnc. + + If "string" contains "/" it is instead interpreted + as a file to periodically check for new hosts. + The first line is read and then the file is truncated. + Be careful about the location of this file if x11vnc + is running as root (e.g. via gdm(1), etc). + + + Repeater mode: Some services provide an intermediate + "vnc repeater": http://www.uvnc.com/addons/repeater.html + (and also http://koti.mbnet.fi/jtko/ for linux port) + that acts as a proxy/gateway. Modes like these require + an initial string to be sent for the reverse connection + before the VNC protocol is started. Here are the ways + to do this: + + -connect pre=some_string+host:port + -connect pre128=some_string+host:port + -connect repeater=ID:1234+host:port + -connect repeater=23.45.67.89::5501+host:port + + SSVNC notation is also supported: + + -connect repeater://host:port+ID:1234 + + As with normal -connect usage, if the repeater port is + not supplied 5500 is assumed. + + The basic idea is between the special tag, e.g. "pre=" + and "+" is the pre-string to be sent. Note that in + this case host:port is the repeater server, NOT the + vnc viewer. Somehow the pre-string tells the repeater + server how to find the vnc viewer and connect you to it. + + In the case pre=some_string+host:port, "some_string" + is simply sent. In the case preNNN=some_string+host:port + "some_string" is sent in a null padded buffer of + length NNN. repeater= is the same as pre250=, this is + the ultravnc repeater buffer size. + + Strings like "\n" and "\r", etc. are expanded to + newline and carriage return. "\c" is expanded to + "," since the connect string is comma separated. + + See also the -proxy option below for additional ways + to plumb reverse connections. + + Reverse SSL: using -connect in -ssl mode makes x11vnc + act as an SSL client (initiates SSL connection) rather + than an SSL server. The idea is x11vnc might be + connecting to stunnel on the viewer side with the + viewer in listening mode. If you do not want this + behavior, use -env X11VNC_DISABLE_SSL_CLIENT_MODE=1. + With this the viewer side can act as the SSL client + as it normally does for forward connections. + + Reverse SSL Repeater mode: This will work, but note + that if the VNC Client does any sort of a 'Fetch Cert' + action before connecting, then the Repeater will + likely drop the connection and both sides will need + to restart. Consider the use of -connect_or_exit + and -loop300,2 to have x11vnc reconnect once to the + repeater after the fetch. You will probably also want + to supply -sslonly to avoid x11vnc thinking the delay + in response means the connection is VeNCrypt. The env + var X11VNC_DISABLE_SSL_CLIENT_MODE=1 discussed above + may also be useful (i.e. the viewer can do a forward + connection as it normally does.) + + IPv6: as of x11vnc 0.9.10 the -connect option should + connect to IPv6 hosts properly. If there are problems + you can disable IPv6 by setting -DX11VNC_IPV6=0 + in CPPFLAGS when configuring. If there problems + connecting to IPv6 hosts consider a relay like the + included inet6to4 script or the -proxy option. + +-connect_or_exit str As with -connect, except if none of the reverse + connections succeed, then x11vnc shuts down immediately + + An easier to type alias for this option is '-coe' + + By the way, if you do not want x11vnc to listen on + ANY interface use -rfbport 0 which is handy for the + -connect_or_exit mode. + +-proxy string Use proxy in string (e.g. host:port) as a proxy for + making reverse connections (-connect or -connect_or_exit + options). + + Web proxies are supported, but note by default most of + them only support destination connections to ports 443 + or 563, so this might not be very useful (the viewer + would need to listen on that port or the router would + have to do a port redirection). + + A web proxy may be specified by either "host:port" + or "http://host:port" (the port is required even if + it is the common choices 80 or 8080) + + SOCKS4, SOCKS4a, and SOCKS5 are also supported. + SOCKS proxies normally do not have restrictions on the + destination port number. + + Use a format like this: socks://host:port or + socks5://host:port. Note that ssh -D does not support + SOCKS4a, so use socks5://. For socks:// SOCKS4 is used + on a numerical IP and "localhost", otherwise SOCKS4a + is used (and so the proxy tries to do the DNS lookup). + + An experimental mode is "-proxy http://host:port/..." + Note the "/" after the port that distinguishes it from + a normal web proxy. The port must be supplied even if + it is the default 80. For this mode a GET is done to + the supplied URL with the string host=H&port=P appended. + H and P will be the -connect reverse connect host + and port. Use the string "__END__" to disable the + appending. The basic idea here is that maybe some cgi + script provides the actual viewer hookup and tunnelling. + How to actually achieve this within cgi, php, etc. is + not clear... A custom web server or apache module + would be straight-forward. + + Another experimental mode is "-proxy ssh://user@host" + in which case a SSH tunnel is used for the proxying. + "user@" is not needed unless your unix username is + different on "host". For a non-standard SSH port + use ssh://user@host:port. If proxies are chained (see + next paragraph) then the ssh one must be the first one. + If ssh-agent is not active, then the ssh password needs + to be entered in the terminal where x11vnc is running. + Examples: + + -connect localhost:0 -proxy ssh://me@friends-pc:2222 + + -connect snoopy:0 -proxy ssh://ssh.company.com + + Multiple proxies may be chained together in case one + needs to ricochet off of a number of hosts to finally + reach the VNC viewer. Up to 3 may be chained, separate + them by commas in the order they are to be connected to. + E.g.: http://host1:port1,socks5://host2:port2 or three + like: first,second,third + + IPv6: as of x11vnc 0.9.10 the -proxy option should + connect to IPv6 hosts properly. If there are problems + you can disable IPv6 by setting -DX11VNC_IPV6=0 + in CPPFLAGS when configuring. If there problems + connecting to IPv6 hosts consider a relay like the + included inet6to4 script. + +-vncconnect Monitor the VNC_CONNECT X property set by the standard +-novncconnect VNC program vncconnect(1). When the property is + set to "host" or "host:port" establish a reverse + connection. Using xprop(1) instead of vncconnect may + work (see the FAQ). The -remote control mechanism uses + X11VNC_REMOTE channel, and this option disables/enables + it as well. Default: -vncconnect + + To use different names for these X11 properties (e.g. to + have separate communication channels for multiple + x11vnc's on the same display) set the VNC_CONNECT or + X11VNC_REMOTE env. vars. to the string you want, for + example: -env X11VNC_REMOTE=X11VNC_REMOTE_12345 + Both sides of the channel must use the same unique name. + The same can be done for the internal X11VNC_TICKER + property (heartbeat and timestamp) if desired. + +-allow host1[,host2..] Only allow client connections from hosts matching + the comma separated list of hostnames or IP addresses. + Can also be a numerical IP prefix, e.g. "192.168.100." + to match a simple subnet, for more control build + LibVNCServer with libwrap support (See the FAQ). If the + list contains a "/" it instead is a interpreted + as a file containing addresses or prefixes that is + re-read each time a new client connects. Lines can be + commented out with the "#" character in the usual way. + + -allow applies in -ssl mode, but not in -stunnel mode. + + IPv6: as of x11vnc 0.9.10 a host can be specified + in IPv6 numerical format, e.g. 2001:4860:b009::93. + +-localhost Basically the same as "-allow 127.0.0.1". + + Note: if you want to restrict which network interface + x11vnc listens on, see the -listen option below. + E.g. "-listen localhost" or "-listen 192.168.3.21". + As a special case, the option "-localhost" implies + "-listen localhost". + + A rare case, but for non-localhost -listen usage, if + you use the remote control mechanism (-R) to change + the -listen interface you may need to manually adjust + the -allow list (and vice versa) to avoid situations + where no connections (or too many) are allowed. + + If you do not want x11vnc to listen on ANY interface + (evidently you are using -connect or -connect_or_exit, + or plan to use remote control: -R connect:host), use + -rfbport 0 + + IPv6: if IPv6 is supported, this option automatically + implies the IPv6 loopback address '::1' as well. + +-unixsock str Listen on the unix socket (AF_UNIX) 'str' + for connections. This mode is for either local + connections or a tunnel endpoint where one wants the + file permission of the unix socket file to determine + what can connect to it. (This currently requires an + edit to libvnserver/rfbserver.c: comment out lines 310 + and 311, 'close(sock)' and 'return NULL' in rfbserver.c + after the setsockopt() call.) Note that to disable all + tcp listening ports specify '-rfbport 0' and should be + useful with this mode. Example: + mkdir ~/s; chmod 700 ~/s; + x11vnc -unixsock ~/s/mysock -rfbport 0 ... + The SSVNC unix vncviewer can connect to unix sockets. + +-listen6 str When in IPv6 listen mode "-6", listen only on the + network interface with address "str". It also works + for link scope addresses (fe80::219:dbff:fee5:3f92%eth0) + and IPv6 hostname strings (e.g. ipv6.google.com.) + Use LibVNCServer -listen option for the IPv4 interface. + +-nolookup Do not use gethostbyname() or gethostbyaddr() to look up + host names or IP numbers. Use this if name resolution + is incorrectly set up and leads to long pauses as name + lookups time out, etc. + +-input string Fine tuning of allowed user input. If "string" does + not contain a comma "," the tuning applies only to + normal clients. Otherwise the part before "," is + for normal clients and the part after for view-only + clients. "K" is for Keystroke input, "M" for + Mouse-motion input, "B" for Button-click input, "C" + is for Clipboard input, and "F" is for File transfer + (ultravnc only). Their presence in the string enables + that type of input. E.g. "-input M" means normal + users can only move the mouse and "-input KMBCF,M" + lets normal users do anything and enables view-only + users to move the mouse. This option is ignored when + a global -viewonly is in effect (all input is discarded + in that case). + +-grabkbd When VNC viewers are connected, attempt to the grab + the keyboard so a (non-malicious) user sitting at the + physical display is not able to enter keystrokes. + This method uses XGrabKeyboard(3X11) and so it is + not secure and does not rule out the person at the + physical display injecting keystrokes by flooding the + server with them, grabbing the keyboard himself, etc. + Some degree of cooperation from the person at the + display is assumed. This is intended for remote + help-desk or educational usage modes. + + Note: on some recent (12/2010) X servers and/or + desktops, -grabkbd no longer works: it prevents the + window manager from resizing windows and similar things. + Try -ungrabboth below (might not work.) + +-grabptr As -grabkbd, but for the mouse pointer using + XGrabPointer(3X11). Unfortunately due to the way the X + server works, the mouse can still be moved around by the + user at the physical display, but he will not be able to + change window focus with it. Also some window managers + that call XGrabServer(3X11) for resizes, etc, will + act on the local user's input. Again, some degree of + cooperation from the person at the display is assumed. + +-ungrabboth Whenever there is any input (either keyboard or + pointer), ungrab *both* the keyboard and the pointer + while injecting the synthetic input. This is to allow + window managers, etc. a chance to grab. + +-grabalways Apply both -grabkbd and -grabptr even when no VNC + viewers are connected. If you only want one of them, + use the -R remote control to turn the other back on, + e.g. -R nograbptr. + +-viewpasswd string Supply a 2nd password for view-only logins. The -passwd + (full-access) password must also be supplied. + +-passwdfile filename Specify the LibVNCServer password via the first line + of the file "filename" (instead of via -passwd on + the command line where others might see it via ps(1)). + + See the descriptions below for how to supply multiple + passwords, view-only passwords, to specify external + programs for the authentication, and other features. + + If the filename is prefixed with "rm:" it will be + removed after being read. Perhaps this is useful in + limiting the readability of the file. In general, the + password file should not be readable by untrusted users + (BTW: neither should the VNC -rfbauth file: it is NOT + encrypted, only obscured with a fixed key). + + If the filename is prefixed with "read:" it will + periodically be checked for changes and reread. It is + guaranteed to be reread just when a new client connects + so that the latest passwords will be used. + + If "filename" is prefixed with "cmd:" then the + string after the ":" is run as an external command: + the output of the command will be interpreted as if it + were read from a password file (see below). If the + command does not exit with 0, then x11vnc terminates + immediately. To specify more than 1000 passwords this + way set X11VNC_MAX_PASSWDS before starting x11vnc. + The environment variables are set as in -accept. + + Note that due to the VNC protocol only the first 8 + characters of a password are used (DES key). + + If "filename" is prefixed with "custom:" then a + custom password checker is supplied as an external + command following the ":". The command will be run + when a client authenticates. If the command exits with + 0 the client is accepted, otherwise it is rejected. + The environment variables are set as in -accept. + + The standard input to the custom command will be a + decimal digit "len" followed by a newline. "len" + specifies the challenge size and is usually 16 (the + VNC spec). Then follows len bytes which is the random + challenge string that was sent to the client. This is + then followed by len more bytes holding the client's + response (i.e. the challenge string encrypted via DES + with the user password in the standard situation). + + The "custom:" scheme can be useful to implement + dynamic passwords or to implement methods where longer + passwords and/or different encryption algorithms + are used. The latter will require customizing the VNC + client as well. One could create an MD5SUM based scheme + for example. + + File format for -passwdfile: + + If multiple non-blank lines exist in the file they are + all taken as valid passwords. Blank lines are ignored. + Password lines may be "commented out" (ignored) if + they begin with the character "#" or the line contains + the string "__SKIP__". Lines may be annotated by use + of the "__COMM__" string: from it to the end of the + line is ignored. An empty password may be specified + via the "__EMPTY__" string on a line by itself (note + your viewer might not accept empty passwords). + + If the string "__BEGIN_VIEWONLY__" appears on a + line by itself, the remaining passwords are used for + viewonly access. For compatibility, as a special case + if the file contains only two password lines the 2nd + one is automatically taken as the viewonly password. + Otherwise the "__BEGIN_VIEWONLY__" token must be + used to have viewonly passwords. (tip: make the 3rd + and last line be "__BEGIN_VIEWONLY__" to have 2 + full-access passwords) + +-showrfbauth filename Print to the screen the obscured VNC password kept in + the rfbauth file "filename" and then exit. + +-unixpw [list] Use Unix username and password authentication. x11vnc + will use the su(1) program to verify the user's + password. [list] is an optional comma separated list + of allowed Unix usernames. If the [list] string begins + with the character "!" then the entire list is taken + as an exclude list. See below for per-user options + that can be applied. + + A familiar "login:" and "Password:" dialog is + presented to the user on a black screen inside the + vncviewer. The connection is dropped if the user fails + to supply the correct password in 3 tries or does not + send one before a 45 second timeout. Existing clients + are view-only during this period. + + If the first character received is "Escape" then the + unix username will not be displayed after "login:" + as it is typed. This could be of use for VNC viewers + that automatically type the username and password. + + Since the detailed behavior of su(1) can vary from + OS to OS and for local configurations, test the mode + before deployment to make sure it is working properly. + x11vnc will attempt to be conservative and reject a + login if anything abnormal occurs. + + One case to note: FreeBSD and the other BSD's by + default it is impossible for the user running x11vnc to + validate his *own* password via su(1) (commenting out + the pam_self.so entry in /etc/pam.d/su eliminates this + behavior). So the x11vnc login will always *FAIL* for + this case (even when the correct password is supplied). + + A possible workaround for this on *BSD would be to + start x11vnc as root with the "-users +nobody" option + to immediately switch to user nobody where the su'ing + will proceed normally. + + Another source of potential problems are PAM modules + that prompt for extra info, e.g. password aging modules. + These logins will fail as well even when the correct + password is supplied. + + **IMPORTANT**: to prevent the Unix password being sent + in *clear text* over the network, one of two schemes + will be enforced: 1) the -ssl builtin SSL mode, or 2) + require both -localhost and -stunnel be enabled. + + Method 1) ensures the traffic is encrypted between + viewer and server. A PEM file will be required, see the + discussion under -ssl below (under some circumstances + a temporary one can be automatically generated). + + Method 2) requires the viewer connection to appear + to come from the same machine x11vnc is running on + (e.g. from a ssh -L port redirection). And that the + -stunnel SSL mode be used for encryption over the + network. (see the description of -stunnel below). + + Note: as a convenience, if you ssh(1) in and start + x11vnc it will check if the environment variable + SSH_CONNECTION is set and appears reasonable. If it + does, then the -ssl or -stunnel requirement will be + dropped since it is assumed you are using ssh for the + encrypted tunnelling. -localhost is still enforced. + Use -ssl or -stunnel to force SSL usage even if + SSH_CONNECTION is set. + + To override the above restrictions you can set + environment variables before starting x11vnc: + + Set UNIXPW_DISABLE_SSL=1 to disable requiring either + -ssl or -stunnel (as under SSH_CONNECTION.) Evidently + you will be using a different method to encrypt the + data between the vncviewer and x11vnc: perhaps ssh(1) + or an IPSEC VPN. -localhost is still enforced (however, + see the next paragraph.) + + Set UNIXPW_DISABLE_LOCALHOST=1 to disable the -localhost + requirement in -unixpw modes. One should never do this + (i.e. allow the Unix passwords to be sniffed on the + network.) This also disables the localhost requirement + for reverse connections (see below.) + + Note that use of -localhost with ssh(1) (and no -unixpw) + is roughly the same as requiring a Unix user login + (since a Unix password or the user's public key + authentication is used by sshd on the machine where + x11vnc runs and only local connections from that machine + are accepted). + + Regarding reverse connections (e.g. -R connect:host + and -connect host), when the -localhost constraint is + in effect then reverse connections can only be used + to connect to the same machine x11vnc is running on + (default port 5500). Please use a ssh or stunnel port + redirection to the viewer machine to tunnel the reverse + connection over an encrypted channel. + + In -inetd mode the Method 1) will be enforced (not + Method 2). With -ssl in effect reverse connections + are disabled. If you override this via env. var, be + sure to also use encryption from the viewer to inetd. + Tip: you can also have your own stunnel spawn x11vnc + in -inetd mode (thereby bypassing inetd). See the FAQ + for details. + + The user names in the comma separated [list] may have + per-user options after a ":", e.g. "fred:opts" + where "opts" is a "+" separated list of + "viewonly", "fullaccess", "input=XXXX", or + "deny", e.g. "karl,wally:viewonly,boss:input=M". + For "input=" it is the K,M,B,C described under -input. + + If an item in the list is "*" that means those + options apply to all users. It ALSO implies all users + are allowed to log in after supplying a valid password. + Use "deny" to explicitly deny some users if you use + "*" to set a global option. If [list] begins with the + "!" character then "*" is ignored for checking if + the user is allowed, but the option values associated + with it do apply as normal. + + There are also some utilities for checking passwords + if [list] starts with the "%" character. See the + quick_pw() function for more details. Description: + "%-" or "%stdin" means read one line from stdin. + "%env" means it is in $UNIXPW env var. A leading + "%/" or "%." means read the first line from the + filename that follows after the % character. % by + itself means prompt for the username and password. + Otherwise: %user:pass E.g. -unixpw %fred:swordfish + For the other cases user:pass is read from the indicated + source. If the password is correct 'Y user' is printed + and the program exit code is 0. If the password is + incorrect it prints 'N user' and the exit code is 1. + If there is some other error the exit code is 2. + This feature enables x11vnc to be a general unix user + password checking tool; it could be used from scripts + or other programs. These % password checks also apply + to the -unixpw_nis and -unixpw_cmd options. + + For the % password check, if the env. var. UNIXPW_CMD + is set to a command then it is run as the user (assuming + the password is correct.) The output of the command is + not printed, the program or script must manage that by + some other means. The exit code of x11vnc will depend + on the exit code of the command that is run. + + Use -nounixpw to disable unixpw mode if it was enabled + earlier in the cmd line (e.g. -svc mode) + +-unixpw_nis [list] As -unixpw above, however do not use su(1) but rather + use the traditional getpwnam(3) + crypt(3) method to + verify passwords. All of the above -unixpw options and + constraints apply. + + This mode requires that the encrypted passwords be + readable. Encrypted passwords stored in /etc/shadow + will be inaccessible unless x11vnc is run as root. + + This is called "NIS" mode simply because in most + NIS setups user encrypted passwords are accessible + (e.g. "ypcat passwd") by an ordinary user and so that + user can authenticate ANY user. + + NIS is not required for this mode to work (only that + getpwnam(3) return the encrypted password is required), + but it is unlikely it will work (as an ordinary user) + for most modern environments unless NIS is available. + On the other hand, when x11vnc is run as root it will + be able to to access /etc/shadow even if NIS is not + available (note running as root is often done when + running x11vnc from inetd and xdm/gdm/kdm). + + Looked at another way, if you do not want to use the + su(1) method provided by -unixpw (i.e. su_verify()), you + can run x11vnc as root and use -unixpw_nis. Any users + with passwords in /etc/shadow can then be authenticated. + + In -unixpw_nis mode, under no circumstances is x11vnc's + user password verifying function based on su called + (i.e. the function su_verify() that runs /bin/su + in a pseudoterminal to verify passwords.) However, + if -unixpw_nis is used in conjunction with the -find + and -create -display WAIT:... modes then, if x11vnc is + running as root, /bin/su may be called externally to + run the find or create commands. + +-unixpw_cmd cmd As -unixpw above, however do not use su(1) but rather + run the externally supplied command "cmd". The first + line of its stdin will be the username and the second + line the received password. If the command exits + with status 0 (success) the VNC user will be accepted. + It will be rejected for any other return status. + + Dynamic passwords and non-unix passwords, e.g. LDAP, + can be implemented this way by providing your own custom + helper program. Note that the remote viewer is given 3 + tries to enter the correct password, and so the program + may be called in a row that many (or more) times. + + If a list of allowed users is needed to limit who can + log in, use -unixpw [list] in addition to this option. + + In FINDDISPLAY and FINDCREATEDISPLAY modes the "cmd" + will also be run with the RFB_UNIXPW_CMD_RUN env. var. + non-empty and set to the corresponding display + find/create command. The first two lines of input are + the username and passwd as in the normal case described + above. To support FINDDISPLAY and FINDCREATEDISPLAY, + "cmd" should run the requested command as the user + (and most likely refusing to run it if the password is + not correct.) Here is an example script (note it has + a hardwired bogus password "abc"!) + + #!/bin/sh + # Example x11vnc -unixpw_cmd script. + # Read the first two lines of stdin (user and passwd) + read user + read pass + + debug=0 + if [ $debug = 1 ]; then + echo "user: $user" 1>&2 + echo "pass: $pass" 1>&2 + env | egrep -i 'rfb|vnc' 1>&2 + fi + + # Check if the password is valid. + # (A real example would use ldap lookup, etc!) + if [ "X$pass" != "Xabc" ]; then + exit 1 # incorrect password + fi + + if [ "X$RFB_UNIXPW_CMD_RUN" = "X" ]; then + exit 0 # correct password + else + # Run the requested command (finddisplay) + if [ $debug = 1 ]; then + echo "run: $RFB_UNIXPW_CMD_RUN" 1>&2 + fi + exec /bin/su - "$user" -c "$RFB_UNIXPW_CMD_RUN" + fi + + In -unixpw_cmd mode, under no circumstances is x11vnc's + user password verifying function based on su called + (i.e. the function su_verify() that runs /bin/su in a + pseudoterminal to verify passwords.) It is up to the + supplied unixpw_cmd to do user switching if desired + and if it has the permissions to do so. + +-find Find the user's display using FINDDISPLAY. This + is an alias for "-display WAIT:cmd=FINDDISPLAY". + + Note: if a -display occurs later on the command line + it will override the -find setting. + + For this and the next few options see -display WAIT:... + below for all of the details. + +-finddpy Run the FINDDISPLAY program, print out the found + display (if any) and exit. Output is like: DISPLAY=:0.0 + DISPLAY=:0.0,XPID=12345 or DISPLAY=:0.0,VT=7. XPID is + the process ID of the found X server. VT is the Linux + virtual terminal of the X server. +-listdpy Have the FINDDISPLAY program list all of your displays + (i.e. all the X displays on the local machine that you + have access rights to). x11vnc then exits. + +-findauth [disp] Apply the -find/-finddpy heuristics to try to guess + the XAUTHORITY file for DISPLAY 'disp'. If 'disp' + is not supplied, then the value in the -display on + the cmdline is used; failing that $DISPLAY is used; + and failing that ":0" is used. x11vnc then exits. + + If nothing is printed out, that means no XAUTHORITY was + found for 'disp'; i.e. failure. If "XAUTHORITY=" + is printed out, that means use the default (i.e. do + not set XAUTHORITY). If "XAUTHORITY=/path/to/file" + is printed out, then use that file. + + XDM/GDM/KDM: if you are running x11vnc as root and want + to find the XAUTHORITY before anyone has logged into an + X session yet, use: x11vnc -env FD_XDM=1 -findauth ... + (This will also find the XAUTHORITY if a user is already + logged into the X session.) When running as root, + FD_XDM=1 will be tried if the initial -findauth fails. + +-create First try to find the user's display using FINDDISPLAY, + if that doesn't succeed create an X session via the + FINDCREATEDISPLAY method. This is an alias for + "-display WAIT:cmd=FINDCREATEDISPLAY-Xvfb". + + Note: if a -display occurs later on the command line + it will override the -create setting. + + SSH NOTE: for both -find and -create you can (should!) + add the "-localhost" option to force SSH tunnel access. + +-xdummy As in -create, except Xdummy instead of Xvfb. +-xvnc As in -create, except Xvnc instead of Xvfb. +-xvnc_redirect As in -create, except Xvnc.redirect instead of Xvfb. +-xdummy_xvfb Sets WAIT:cmd=FINDCREATEDISPLAY-Xdummy,Xvfb + +-create_xsrv str Sets WAIT:cmd=FINDCREATEDISPLAY- Can be on cmdline + after anything that sets WAIT:.. and other things + (e.g. -svc, -xdmsvc) to adjust the X server list. + Example: -svc ... -create_xsrv Xdummy,X + +-svc Terminal services mode based on SSL access. Alias for + -display WAIT:cmd=FINDCREATEDISPLAY-Xvfb -unixpw -users + unixpw= -ssl SAVE Also "-service". + + Note: if a -display, -unixpw, -users, or -ssl occurs + later on the command line it will override the -svc + setting. + +-svc_xdummy As -svc except Xdummy instead of Xvfb. +-svc_xvnc As -svc except Xvnc instead of Xvfb. +-svc_xdummy_xvfb As -svc with Xdummy,Xvfb. + +-xdmsvc Display manager Terminal services mode based on SSL. + Alias for -display WAIT:cmd=FINDCREATEDISPLAY-Xvfb.xdmcp + -unixpw -users unixpw= -ssl SAVE Also "-xdm_service". + + Note: if a -display, -unixpw, -users, or -ssl occurs + later on the command line it will override the -xdmsvc + setting. + + To create a session a user will have to first log in + to the -unixpw dialog and then log in again to the + XDM/GDM/KDM prompt. Subsequent re-connections will + only require the -unixpw password. See the discussion + under -display WAIT:... for more details about XDM, + etc configuration. + + Remember to enable XDMCP in the xdm-config, gdm.conf, + or kdmrc configuration file. See -display WAIT: for + more info. + +-sshxdmsvc Display manager Terminal services mode based on SSH. + Alias for -display WAIT:cmd=FINDCREATEDISPLAY-Xvfb.xdmcp + -localhost. + + The -localhost option constrains connections to come + in via a SSH tunnel (which will require a login). + To create a session a user will also have to log into + the XDM GDM KDM prompt. Subsequent re-connections will + only only require the SSH login. See the discussion + under -display WAIT:... for more details about XDM, + etc configuration. + + Remember to enable XDMCP in the xdm-config, gdm.conf, + or kdmrc configuration file. See -display WAIT: for + more info. + +-unixpw_system_greeter Present a "Press 'Escape' for System Greeter" option + to the connecting VNC client in combined -unixpw + and xdmcp FINDCREATEDISPLAY modes (e.g. -xdmsvc). + + Normally in a -unixpw mode the VNC client must + supply a valid username and password to gain access. + However, if -unixpw_system_greeter is supplied AND + the FINDCREATEDISPLAY command matches 'xdmcp', then + the user has the option to press Escape and then get a + XDM/GDM/KDM login/greeter panel instead. They will then + supply a username and password directly to the greeter. + + Otherwise, in xdmcp FINDCREATEDISPLAY mode the user + must supply his username and password TWICE. First to + the initial unixpw login dialog, and second to the + subsequent XDM/GDM/KDM greeter. Note that if the user + re-connects and supplies his username and password in + the unixpw dialog the xdmcp greeter is skipped and + he is connected directly to his existing X session. + So the -unixpw_system_greeter option avoids the extra + password at X session creation time. + + Example: x11vnc -xdmsvc -unixpw_system_greeter + See -unixpw and -display WAIT:... for more info. + + The special options after a colon at the end of the + username (e.g. user:solid) described under -display + WAIT: are also applied in this mode if they are typed + in before the user hits Escape. The username is ignored + but the colon options are not. + + The default message is 2 lines in a small font, set + the env. var. X11VNC_SYSTEM_GREETER1=true for a 1 line + message in a larger font. + + If the user pressed Escape the FINDCREATEDISPLAY command + will be run with the env. var. X11VNC_XDM_ONLY=1. + + Remember to enable XDMCP in the xdm-config, gdm.conf, + or kdmrc configuration file. See -display WAIT: for + more info. + +-redirect port As in FINDCREATEDISPLAY-Xvnc.redirect mode except + redirect immediately (i.e. without X session finding + or creation) to a VNC server listening on port. You + can also supply host:port to redirect to a different + machine. + + If 0 <= port < 200 it is taken as a VNC display (5900 is + added to get the actual port), if port < 0 then -port + is used. + + Probably the only reason to use the -redirect option + is in conjunction with SSL support, e.g. -ssl SAVE. + This provides an easy way to add SSL encryption to a VNC + server that does not support SSL (e.g. Xvnc or vnc.so) + In fact, the protocol does not even need to be VNC, + and so "-rfbport port1 -ssl SAVE -redirect host:port2" + can act as a replacement for stunnel(1). + + This mode only allows one redirected connection. + The -forever option does not apply. Use -inetd or + -loop for persistent service. + +-display_WAIT :... A special usage mode for the normal -display option. + Useful with -unixpw, but can be used independently + of it. If the display string begins with WAIT: then + x11vnc waits until a VNC client connects before opening + the X display (or -rawfb device). + + This could be useful for delaying opening the display + for certain usage modes (say if x11vnc is started at + boot time and no X server is running or users logged + in yet). + + If the string is, e.g. WAIT:0.0 or WAIT:1, i.e. "WAIT" + in front of a normal X display, then that indicated + display is used. + + One can also insert a geometry between colons, e.g. + WAIT:1280x1024:... to set the size of the display the + VNC client first attaches to since some VNC viewers + will not automatically adjust to a new framebuffer size. + + A more interesting case is like this: + + WAIT:cmd=/usr/local/bin/find_display + + in which case the command after "cmd=" is run to + dynamically work out the DISPLAY and optionally the + XAUTHORITY data. The first line of the command output + must be of the form DISPLAY=. On Linux + if the virtual terminal is known append ",VT=n" to + this string and the chvt(1) program will also be run. + Any remaining output is taken as XAUTHORITY data. + It can be either of the form XAUTHORITY= or raw + xauthority data for the display. For example; + + xauth extract - $DISPLAY" + + NOTE: As specified in the previous paragraph, you can + supply your own WAIT:cmd=... program or script, BUT + there are two very useful *BUILT-IN* ones: FINDDISPLAY + (alias -find above) and FINDCREATEDISPLAY (alias -create + above.) Most people use these instead of creating + their own script. Read the following (especially the + BUILT-IN modes sections) to see how to configure these + two useful builtin -display WAIT: modes. + + In the case of -unixpw (and -unixpw_nis only if x11vnc + is running as root), then the cmd= command is run + as the user who just authenticated via the login and + password prompt. + + In the case of -unixpw_cmd, the commands will also be + run as the logged-in user, as long as the user-supplied + helper program supports RFB_UNIXPW_CMD_RUN (see the + -unixpw_cmd option.) + + Also in the case of -unixpw, the user logging in can + place a colon at the end of her username and supply + a few options: scale=, scale_cursor= (or sc=), solid + (or so), id=, clear_mods (or cm), clear_keys (or + ck), clear_all (or ca), repeat, speeds= (or sp=), + readtimeout= (or rd=), viewonly (or vo), nodisplay= + (or nd=), rotate= (or ro=), or noncache (or nc), + all separated by commas if there is more than one. + After the user logs in successfully, these options will + be applied to the VNC screen. For example, + + login: fred:scale=3/4,sc=1,repeat + Password: ... + + login: runge:sp=modem,rd=120,solid + + for convenience m/n implies scale= e.g. fred:3/4 If you + type and enter your password incorrectly, to retrieve + your long "login:" line press the Up arrow once + (before typing anything else). + + Most of these colon options only apply to the builtin + FINDDISPLAY and FINDCREATEDISPLAY modes, but note + that they are passed to the extrenal command in the + environment as well and so could be used. + + In the login panel, press F1 to get a list of the + available options that you can add after the username. + + Another option is "geom=WxH" or "geom=WxHxD" (or + ge=). This only has an effect in FINDCREATEDISPLAY + mode when a virtual X server such as Xvfb is going + to be created. It sets the width and height of + the new display, and optionally the color depth as + well. + + You can also supply "gnome", "kde", "twm", + "fvwm", "mwm", "dtwm", "wmaker", "xfce", + "lxde", "enlightenment", "Xsession", or + "failsafe" (same as "xterm") to have the created + display use that mode for the user session. + + Specify "tag=..." to set the unique FD_TAG desktop + session tag described below. Note: this option will + be ignored if the FD_TAG env. var. is already set or + if the viewer-side supplied value is not completely + composed of alphanumeric or '_' or '-' characters. + + User preferences file: Instead of having the user type + in geom=WxH,... etc. every time he logs in to find + or create his X session, if you set FD_USERPREFS to + a string that does not contain the "/" character, + then the user's home directory is prepended to that + string and if the file exists its first line is read + and appended to any options he supplied at the login: + prompt. For example -env FD_USERPREFS=.x11vnc_create + and the user put "geom=1600x1200" in his + ~/.x11vnc_create file. + + To disable the option setting set the environment + variable X11VNC_NO_UNIXPW_OPTS=1 before starting x11vnc. + To set any other options, the user can use the gui + (x11vnc -gui connect) or the remote control method + (x11vnc -R opt:val) during his VNC session. + + So we see the combination of -display WAIT:cmd=... and + -unixpw allows automatic pairing of an unix + authenticated VNC user with his desktop. This could + be very useful on SunRays and also any system where + multiple users share a given machine. The user does + not need to remember special ports or passwords set up + for his desktop and VNC. + + A nice way to use WAIT:cmd=... is out of inetd(8) + (it automatically forks a new x11vnc for each user). + You can have the x11vnc inetd spawned process run as, + say, root or nobody. When run as root (for either inetd + or display manager), you can also supply the option + "-users unixpw=" to have the x11vnc process switch to + the user as well. Note: there will be a 2nd SSL helper + process that will not switch, but it is only encoding + and decoding the encrypted stream at that point. + + BUILT-IN modes: + + -- Automatic Finding of User X Sessions -- + + As a special case, WAIT:cmd=FINDDISPLAY will run a + script that works on most Unixes to determine a user's + DISPLAY variable and xauthority data (see who(1)). + + NOTE: The option "-find" is an alias for this mode. + + To have this default script printed to stdout (e.g. for + customization) run with WAIT:cmd=FINDDISPLAY-print To + have the script run to print what display it would find + use "-finddpy" or WAIT:cmd=FINDDISPLAY-run + + The standard script runs xdpyinfo(1) run on potential + displays. If your X server(s) have a login greeter + that exclusively grabs the Xserver, then xdpyinfo + blocks forever and this mode will not work. See + www.karlrunge.com/x11vnc/faq.html#faq-display-manager + for how to disable this for dtgreet on Solaris and + possibly for other greeters. + + In -find/cmd=FINDDISPLAY mode, if you set FD_XDM=1, + e.g. 'x11vnc -env FD_XDM=1 -find ...' and x11vnc is + running as root (e.g. inetd) then it will try to find + the XAUTHORITY file of a running XDM/GDM/KDM login + greeter (i.e. no user has logged into an X session yet.) + + As another special case, WAIT:cmd=HTTPONCE will allow + x11vnc to service one http request and then exit. + This is usually done in -inetd mode to run on, say, + port 5800 and allow the Java vncviewer to be downloaded + by client web browsers. For example: + + 5815 stream tcp nowait root /usr/sbin/tcpd /.../x11vnc +\ + -inetd -q -http_ssl -prog /.../x11vnc \ + -display WAIT:cmd=HTTPONCE + + Where /.../x11vnc is the full path to x11vnc. + It is used in the Apache SSL-portal example (see FAQ). + + In this mode you can set X11VNC_SKIP_DISPLAY to a + comma separated list of displays (e.g. ":0,:1") to + ignore in the finding process. The ":" is optional. + Ranges n-m e.g. 0-20 can also be supplied. This string + can also be set by the connecting user via "nd=" + using "+" instead of "," If "nd=all" or you set + X11VNC_SKIP_DISPLAY=all then all display finding fails + as if you set X11VNC_FINDDISPLAY_ALWAYS_FAILS=1 (below.) + + On some systems lsof(1) can be very slow. Set the + env. var. FIND_DISPLAY_NO_LSOF=1 to skip using lsof to + try to find the Linux VT the X server is running on. + set FIND_DISPLAY_NO_VT_FIND=1 to avoid looking at all. + + -- Automatic Creation of User X Sessions -- + + An interesting option is WAIT:cmd=FINDCREATEDISPLAY + that is like FINDDISPLAY in that is uses the same method + to find an existing display. However, if it does not + find one it will try to *start* up an X server session + for the user. This is the only time x11vnc tries to + actually start up an X server. + + NOTE: The option "-create" is an alias for this mode. + + It will start looking for an open display number at :20 + Override via X11VNC_CREATE_STARTING_DISPLAY_NUMBER=n + By default 80 X displays are allowed (i.e. going to :99) + Override via X11VNC_CREATE_MAX_DISPLAYS=n + + For its heuristics, the create display script sets + LC_ALL=C so that command output is uniform. By default + it will try to restore LC_ALL right before starting the + user session. However, if you don't mind it keeping + LC_ALL=C set the env. var.: X11VNC_CREATE_LC_ALL_C_OK=1 + + By default FINDCREATEDISPLAY will try Xvfb and then + Xdummy: + + The Xdummy wrapper is part of the x11vnc source code + (x11vnc/misc/Xdummy) It should be available in PATH + and have run "Xdummy -install" once to create the + shared library. Xdummy only works on Linux. As of + 12/2009 it no longer needs to be run as root, and the + default is to not run as root. In some circumstances + permissions may require running it as root, in these + cases specify FD_XDUMMY_RUN_AS_ROOT=1, this is the same + as supplying -root to the Xdummy cmdline. + + Xvfb is available on most platforms and does not + require root. + + An advantage of Xdummy over Xvfb is that Xdummy supports + RANDR dynamic screen resizing. + + When x11vnc exits (i.e. user disconnects) the X + server session stays running in the background. + The FINDDISPLAY will find it directly next time. + The user must exit the X session in the usual way for + it to terminate (or kill the X server process if all + else fails). + + To troubleshoot the FINDCREATEDISPLAY mechanism, + set the following env. var. to an output log file, + e.g -env CREATE_DISPLAY_OUTPUT=/tmp/mydebug.txt + + So this is a somewhat odd mode for x11vnc in that it + will start up and poll virtual X servers! This can + be used from, say, inetd(8) to provide a means of + definitely getting a desktop (either real or virtual) + on the machine. E.g. a desktop service: + + 5900 stream tcp nowait root /usr/sbin/tcpd /.../x11vnc + -inetd -q -http -ssl SAVE -unixpw -users unixpw=\ + -passwd secret -prog /.../x11vnc \ + -display WAIT:cmd=FINDCREATEDISPLAY + + Where /.../x11vnc is the full path to x11vnc. + + See the -svc/-service option alias above. + + If for some reason you do not want x11vnc to ever + try to find an existing display set the env. var + X11VNC_FINDDISPLAY_ALWAYS_FAILS=1 (also -env ...) + This is the same as setting X11VNC_SKIP_DISPLAY=all or + supplying "nd=all" after "username:" + + Use WAIT:cmd=FINDCREATEDISPLAY-print to print out the + script that is used for this. + + You can specify the preferred X server order via e.g., + WAIT:cmd=FINDCREATEDISPLAY-Xdummy,Xvfb,X and/or leave + out ones you do not want. The the case "X" means try + to start up a real, hardware X server using xinit(1) + or startx(1). If there is already an X server running + the X case may only work on Linux (see startx(1)). + + "Xvnc" will start up a VNC X server (real- + or tight-vnc, e.g. use if Xvfb is not available). + "Xsrv" will start up the server program in the + variable "FD_XSRV" if it is non-empty. You can make + this be a wrapper script if you like (it must handle :N, + -geometry, and -depth and other X server options). + + You can set the environment variable FD_GEOM (or + X11VNC_CREATE_GEOM) to WxH or WxHxD to set the width + and height and optionally the color depth of the + created display. You can also set FD_SESS to be the + session (short name of the windowmanager: kde, gnome, + twm, failsafe, etc.). FD_OPTS contains extra options + to pass to the X server. You can also set FD_PROG to + be the full path to the session/windowmanager program. + + More FD tricks: FD_CUPS=port or FD_CUPS=host:port + will set the cups printing environment. Similarly for + FD_ESD=port or FD_ESD=host:port for esddsp sound + redirection. Set FD_EXTRA to a command to be run a + few seconds after the X server starts up. Set FD_TAG + to be a unique name for the session, it is set as an + X property, that makes FINDDISPLAY only find sessions + with that tag value. + + Set FD_XDMCP_IF to the network interface that the + display manager is running on; default is 'localhost' + but you may need to set it to '::1' on some IPv6 only + systems or misconfigured display managers. + + If you want the FINDCREATEDISPLAY session to contact an + XDMCP login manager (xdm/gdm/kdm) on the same machine, + then use "Xvfb.xdmcp" instead of "Xvfb", etc. + The user will have to supply his username and password + one more time (but he gets to select his desktop type + so that can be useful). For this to work, you will + need to enable localhost XDMCP (udp port 177) for the + display manager. This seems to be: + + for gdm in gdm.conf: Enable=true in section [xdmcp] + for kdm in kdmrc: Enable=true in section [Xdmcp] + for xdm in xdm-config: DisplayManager.requestPort: 177 + + See the shorthand options above "-svc", "-xdmsvc" + and "-sshxdmsvc" that specify the above options for + some useful cases. + + If you set the env. var WAITBG=1 x11vnc will go into + the background once listening in wait mode. + + Another special mode is FINDCREATEDISPLAY-Xvnc.redirect, + (or FINDDISPLAY-Xvnc.redirect). In this case it will + start up Xvnc as above if needed, but instead of + polling it in its normal way, it simply does a socket + redirection of the connected VNC viewer to the Xvnc. + + So in Xvnc.redirect x11vnc does no VNC but merely + transfers the data back and forth. This should be + faster then x11vnc's polling method, but not as fast + as connecting directly to the Xvnc with the VNC Viewer. + The idea here is to take advantage of x11vnc's display + finding/creating scheme, SSL, and perhaps a few others. + Most of x11vnc's options do not apply in this mode. + + Xvnc.redirect should also work for the vnc.so X server + module for the h/w display however it will work only + for finding the display and the user must already be + logged into the X console. + +-vencrypt mode The VeNCrypt extension to the VNC protocol allows + encrypted SSL/TLS connections. If the -ssl mode is + enabled, then VeNCrypt is enabled as well BY DEFAULT + (they both use a SSL/TLS tunnel, only the protocol + handshake is a little different.) + + To control when and how VeNCrypt is used, specify the + mode string. If mode is "never", then VeNCrypt is + not used. If mode is "support" (the default) then + VeNCrypt is supported. If mode is "only", then the + similar and older ANONTLS protocol is not simultaneously + supported. x11vnc's normal SSL mode (vncs://) will be + supported under -ssl unless you set mode to "force". + + If mode is prefixed with "nodh:", then Diffie Hellman + anonymous key exchange is disabled. If mode is prefixed + with "nox509:", then X509 key exchange is disabled. + + To disable all Anonymous Diffie-Hellman access + (susceptible to Man-In-The-Middle attack) you will need + to supply "-vencrypt nodh:support -anontls never" + or "-vencrypt nodh:only" + + If mode is prefixed with "newdh:", then new Diffie + Hellman parameters are generated for each connection + (this can be time consuming: 1-60 secs; see -dhparams + below for a faster way) rather than using the + fixed values in the program. Using fixed, publicly + known values is not known to be a security problem. + This setting applies to ANONTLS as well. + + Long example: -vencrypt newdh:nox509:support + + Also, if mode is prefixed with "plain:", then + if -unixpw mode is active the VeNCrypt "*Plain" + username+passwd method is enabled for Unix logins. + Otherwise in -unixpw mode the normal login panel is + provided. + + You *MUST* supply the -ssl option for VeNCrypt to + be active. The -vencrypt option only fine-tunes its + operation. + +-anontls mode The ANONTLS extension to the VNC protocol allows + encrypted SSL/TLS connections. If the -ssl mode is + enabled, then ANONTLS is enabled as well BY DEFAULT + (they both use a SSL/TLS tunnel, only the protocol + handshake is a little different.) + + ANONTLS is an older SSL/TLS mode introduced by vino. + + It is referred to as 'TLS' for its registered VNC + security-type name, but we use the more descriptive + 'ANONTLS' here because it provides only Anonymous + Diffie-Hellman encrypted connections, and hence no + possibility for certificate authentication. + + To control when and how ANONTLS is used, specify the + mode string. If mode is "never", then ANONTLS is not + used. If mode is "support" (the default) then ANONTLS + is supported. If mode is "only", then the similar + VeNCrypt protocol is not simultaneously supported. + x11vnc's normal SSL mode (vncs://) will be supported + under -ssl unless you set mode to "force". + + If mode is prefixed with "newdh:", then new Diffie + Hellman parameters are generated for each connection + (this can be time consuming: 1-60 secs; see -dhparams + below for a faster way) rather than using the + fixed values in the program. Using fixed, publicly + known values is not known to be a security problem. + This setting applies to VeNCrypt as well. See the + description of "plain:" under -vencrypt. + + Long example: -anontls newdh:plain:support + + You *MUST* supply the -ssl option for ANONTLS to + be active. The -anontls option only fine-tunes its + operation. + +-sslonly Same as: "-vencrypt never -anontls never" i.e. it + disables the VeNCrypt and ANONTLS encryption methods + and only allows standard SSL tunneling. You must also + supply the -ssl ... option (see below.) + + +-dhparams file For some operations a set of Diffie Hellman parameters + (prime and generator) is needed. If so, use the + parameters in "file". In particular, the VeNCrypt and + ANONTLS anonymous DH mode need them. By default a + fixed set is used. If you do not want to do that you + can specify "newdh:" to the -vencrypt and -anontls + options to generate a new set each session. If that + is too slow for you, use -dhparams file to a set you + created manually via "openssl dhparam -out file 1024" + +-nossl Disable the -ssl option (see below). Since -ssl is off + by default -nossl would only be used on the commandline + to unset any *earlier* -ssl option (or -svc...) + +-ssl [pem] Use the openssl library (www.openssl.org) to provide a + built-in encrypted SSL/TLS tunnel between VNC viewers + and x11vnc. This requires libssl support to be + compiled into x11vnc at build time. If x11vnc is not + built with libssl support it will exit immediately when + -ssl is prescribed. See the -stunnel option below for + an alternative. + + The VNC Viewer-side needs to support SSL/TLS as well. + See this URL and also the discussion below for + ideas on how to enable SSL support for the viewer: + http://www.karlrunge.com/x11vnc/faq.html#faq-ssl-tun + nel-viewers . x11vnc provides an SSL enabled Java + viewer applet in the classes/ssl directory (-http or + -httpdir options.) The SSVNC viewer package supports + SSL tunnels too. + + If the VNC Viewer supports VeNCrypt or ANONTLS (vino's + encryption mode) they are also supported by the -ssl + mode (see the -vencrypt and -anontls options for more + info; use -sslonly to disable both of them.) + + Use "-ssl /path/to/mycert.pem" to specify an SSL + certificate file in PEM format to use to identify and + provide a key for this server. See openssl(1) for more + info about PEMs and the -sslGenCert and "-ssl SAVE" + options below for how to create them. + + The connecting VNC viewer SSL tunnel can (at its option) + authenticate this server if it has the public key part + of the certificate (or a common certificate authority, + CA, is a more sophisticated way to verify this server's + cert, see -sslGenCA below). This authentication is + done to prevent Man-In-The-Middle attacks. Otherwise, + if the VNC viewer simply accepts this server's key + WITHOUT verification, the traffic is protected from + passive sniffing on the network, but *NOT* from + Man-In-The-Middle attacks. There are hacker tools + like dsniff/webmitm and cain that implement SSL + Man-In-The-Middle attacks. + + If [pem] is empty or the string "SAVE" then the + openssl(1) command must be available to generate the + certificate the first time. A self-signed certificate + is generated (see -sslGenCA and -sslGenCert for use + of a Certificate Authority.) It will be saved to the + file ~/.vnc/certs/server.pem. On subsequent calls if + that file already exists it will be used directly. + + Use "SAVE_NOPROMPT" to avoid being prompted to + protect the generated key with a passphrase. However in + -inetd and -bg modes there will be no prompting for a + passphrase in either case. + + If [pem] is "SAVE_PROMPT" the server.pem certificate + will be created based on your answers to its prompts for + all info such as OrganizationalName, CommonName, etc. + + Use "SAVE-" and "SAVE_PROMPT-" + to refer to the file ~/.vnc/certs/server-.pem + instead (it will be generated if it does not already + exist). E.g. "SAVE-charlie" will store to the file + ~/.vnc/certs/server-charlie.pem + + Examples: x11vnc -ssl SAVE -display :0 ... + x11vnc -ssl SAVE-someother -display :0 ... + + If [pem] is "TMP" and the openssl(1) utility + command exists in PATH, then a temporary, self-signed + certificate will be generated for this session. If + openssl(1) cannot be used to generate a temporary + certificate x11vnc exits immediately. The temporary + cert will be discarded when x11vnc exits. + + If successful in using openssl(1) to generate a + temporary certificate in "SAVE" or "TMP" creation + modes, the public part of it will be displayed to stderr + (e.g. one could copy it to the client-side to provide + authentication of the server to VNC viewers.) + + NOTE: In "TMP" mode, unless you safely copy the + public part of the temporary Cert to the viewer for + authenticate *every time* (unlikely...), then only + passive sniffing attacks are prevented and you are + still open to Man-In-The-Middle attacks. This is + why the default "SAVE" mode is preferred (and more + sophisticated CA mode too). Only with saved keys AND + the VNC viewer authenticating them (via the public + certificate), are Man-In-The-Middle attacks prevented. + + If [pem] is "ANON" then the Diffie-Hellman anonymous + key exchange method is used. In this mode there + are *no* SSL certificates and so it is not possible + to authenticate either the VNC server or VNC client. + Thus only passive network sniffing attacks are avoided: + the "ANON" method is susceptible to Man-In-The-Middle + attacks. "ANON" is not recommended; instead use + a SSL PEM you created or the default "SAVE" method. + + See -ssldir below to use a directory besides the + default ~/.vnc/certs + + If your x11vnc binary was not compiled with OpenSSL + library support, use of the -ssl option will induce an + immediate failure and exit. For such binaries, consider + using the -stunnel option for SSL encrypted connections. + + Misc Info: In temporary cert creation mode "TMP", set + the env. var. X11VNC_SHOW_TMP_PEM=1 to have x11vnc print + out the entire certificate, including the PRIVATE KEY + part, to stderr. There are better ways to get/save this + info. See "SAVE" above and "-sslGenCert" below. + +-ssltimeout n Set SSL read timeout to n seconds. In some situations + (i.e. an iconified viewer in Windows) the viewer stops + talking and the connection is dropped after the default + timeout (25s for about the first minute, 43200s later). + Set to zero to poll forever. Set to a negative value + to use the builtin setting. + + Note that this value does NOT apply to the *initial* ssl + init connection. The default timeout for that is 20sec. + Use -env SSL_INIT_TIMEOUT=n to modify it. + +-sslnofail Exit at the first SSL connection failure. Useful when + scripting SSL connections (e.g. x11vnc is started via + ssh) and you do not want x11vnc waiting around for more + connections, tying up ports, etc. + +-ssldir dir Use "dir" as an alternate ssl certificate and key + management toplevel directory. The default is + ~/.vnc/certs + + This directory is used to store server and other + certificates and keys and also other materials. E.g. in + the simplest case, "-ssl SAVE" will store the x11vnc + server cert in dir/server.pem + + Use of alternate directories via -ssldir allows you to + manage multiple VNC Certificate Authority (CA) keys. + Another use is if ~/.vnc/cert is on an NFS share you + might want your certificates and keys to be on a local + filesystem to prevent network snooping (for example + -ssldir /var/lib/x11vnc-certs). + + -ssldir affects nearly all of the other -ssl* options, + e.g. -ssl SAVE, -sslGenCert, etc.. + +-sslverify path For either of the -ssl or -stunnel modes, use "path" + to provide certificates to authenticate incoming VNC + *Client* connections (normally only the server is + authenticated in SSL.) This can be used as a method + to replace standard password authentication of clients. + + If "path" is a directory it contains the client (or CA) + certificates in separate files. If path is a file, + it contains one or more certificates. See special tokens + below. These correspond to the "CApath = dir" and + "CAfile = file" stunnel options. See the stunnel(8) + manpage for details. + + Examples: + x11vnc -ssl -sslverify ~/my.crt + x11vnc -ssl -sslverify ~/my_pem_dir/ + + Note that if path is a directory, it must contain + the certs in separate files named like .0, where + the value of is found by running the command + "openssl x509 -hash -noout -in file.crt". Evidently + one uses .1 if there is a collision... + + The the key-management utility "-sslCertInfo HASHON" + and "-sslCertInfo HASHOFF" will create/delete these + hashes for you automatically (via symlink) in the HASH + subdirs it manages. Then you can point -sslverify to + the HASH subdir. + + Special tokens: in -ssl mode, if "path" is not a file or + a directory, it is taken as a comma separated list of + tokens that are interpreted as follows: + + If a token is "CA" that means load the CA/cacert.pem + file from the ssl directory. If a token is "clients" + then all the files clients/*.crt in the ssl directory + are loaded. Otherwise the file clients/token.crt + is attempted to be loaded. As a kludge, use a token + like ../server-foo to load a server cert if you find + that necessary. + + Use -ssldir to use a directory different from the + ~/.vnc/certs default. + + Note that if the "CA" cert is loaded you do not need + to load any of the certs that have been signed by it. + You will need to load any additional self-signed certs + however. + + Examples: + x11vnc -ssl -sslverify CA + x11vnc -ssl -sslverify self:fred,self:jim + x11vnc -ssl -sslverify CA,clients + + Usually "-sslverify CA" is the most effective. + See the -sslGenCA and -sslGenCert options below for + how to set up and manage the CA framework. + + + + NOTE: the following utilities, -sslGenCA, -sslGenCert, + -sslEncKey, -sslCertInfo, and -sslCRL are provided for + completeness, but for casual usage they are overkill. + + They provide VNC Certificate Authority (CA) key creation + and server / client key generation and signing. So they + provide a basic Public Key management framework for + VNC-ing with x11vnc. (note that they require openssl(1) + be installed on the system) + + However, the simplest usage mode, "-ssl TMP" (where + x11vnc automatically generates its own, self-signed, + temporary key and the VNC viewers always accept it, + e.g. accepting via a dialog box) is probably safe enough + for most scenarios. CA management is not needed. + + To protect against Man-In-The-Middle attacks the "TMP" + mode can be improved by using "-ssl SAVE" (same as + "-ssl", i.e. the default) to have x11vnc create a + longer term self-signed certificate, and then (safely) + copy the corresponding public key cert to the desired + client machines (care must be taken the private key part + is not stolen; you will be prompted for a passphrase). + + So keep in mind no CA key creation or management + (-sslGenCA and -sslGenCert) is needed for either of + the above two common usage modes. + + One might want to use -sslGenCA and -sslGenCert + if you had a large number of VNC client and server + workstations. That way the administrator could generate + a single CA key with -sslGenCA and distribute its + certificate part to all of the workstations. + + Next, he could create signed VNC server keys + (-sslGenCert server ...) for each workstation or user + that then x11vnc would use to authenticate itself to + any VNC client that has the CA cert. + + Optionally, the admin could also make it so the + VNC clients themselves are authenticated to x11vnc + (-sslGenCert client ...) For this -sslverify would be + pointed to the CA cert (and/or self-signed certs). + + x11vnc will be able to use all of these cert and + key files. On the VNC client side, they will need to + be "imported" somehow. Web browsers have "Manage + Certificates" actions as does the Java applet plugin + Control Panel. stunnel can also use these files (see + the ss_vncviewer example script in the FAQ and SSVNC.) + +-sslCRL path Set the Certificate Revocation Lists (CRL) to "path". + This setting applies for both -ssl and -stunnel modes. + + If path is a file, the file contains one or more CRLs + in PEM format. If path is a directory, it contains + hash named files of CRLs in the usual OpenSSL manner. + See the OpenSSL and stunnel(8) documentation for + more info. + + This option only applies if -sslverify has been + supplied: it checks for revocation along the + certificate chain used to verify the VNC client. + The -sslCRL setting will be ignored when -sslverify is + not specified. + + Note that if a CRL's expiration date has passed, all + SSL connections will fail regardless of if they are + related to the subject of the CRL or not. + + Only rarely will one's x11vnc -ssl infrastructure be so + large that this option would be useful (since normally + maintaining the contents of the -sslverify file or + directory should be enough.) However, when using + x11vnc with a Certificate Authority (see -sslGenCA) + to authenticate Clients via SSL/TLS, the -sslCRL option + can be useful to revoke users' certs whose private SSL + keys were lost or stolen (e.g. laptop.) This way a new + CA cert+key does not need to be created and new signed + client keys generated and distributed to all users. + + To create a CRL file with revoked certificates the + commands 'openssl ca -revoke ...' and 'openssl ca + -gencrl ...' are useful. (Run them in ~/.vnc/certs) + +-sslGenCA [dir] Generate your own Certificate Authority private key, + certificate, and other files in directory [dir]. + x11vnc then exits. + + If [dir] is not supplied, a -ssldir setting is used, + or otherwise ~/.vnc/certs is used. + + This command also creates directories where server and + client certs and keys will be stored. The openssl(1) + program must be installed on the system and available + in PATH. + + After the CA files and directories are created the + x11vnc command exits; the VNC server is not run. + + You will be prompted for information to put into the CA + certificate. The info does not have to be accurate just + as long as clients accept the cert for VNC connections. + You will also need to supply a passphrase of at least + 4 characters for the CA private key. + + Once you have generated the CA you can distribute + its certificate part, [dir]/CA/cacert.pem, to other + workstations where VNC viewers will be run. One will + need to "import" this certificate in the applications, + e.g. Web browser, Java applet plugin, stunnel, etc. + Next, you can create and sign keys using the CA with + the -sslGenCert option below. + + Examples: + x11vnc -sslGenCA + x11vnc -sslGenCA ~/myCAdir + x11vnc -ssldir ~/myCAdir -sslGenCA + + (the last two lines are equivalent) + +-sslGenCert type name Generate a VNC server or client certificate and private + key pair signed by the CA created previously with + -sslGenCA. The openssl(1) program must be installed + on the system and available in PATH. + + After the Certificate is generated x11vnc exits; the + VNC server is not run. + + The type of key to be generated is the string "type". + It is either "server" (i.e. for use by x11vnc) or + "client" (for a VNC viewer). Note that typically + only "server" is used: the VNC clients authenticate + themselves by a non-public-key method (e.g. VNC or + unix password). "type" is required. + + An arbitrary default name you want to associate with + the key is supplied by the "name" string. You can + change it at the various prompts when creating the key. + "name" is optional. + + If name is left blank for clients keys then "nobody" + is used. If left blank for server keys, then the + primary server key: "server.pem" is created (this + is the saved one referenced by "-ssl SAVE" when the + server is started) + + If "name" begins with the string "self:" then + a self-signed certificate is created instead of one + signed by your CA key. + + If "name" begins with the string "req:" then only a + key (.key) and a certificate signing *request* (.req) + are generated. You can then send the .req file to + an external CA (even a professional one, e.g. Thawte) + and then combine the .key and the received cert into + the .pem file with the same basename. + + The distinction between "server" and "client" is + simply the choice of output filenames and sub-directory. + This makes it so the -ssl SAVE-name option can easily + pick up the x11vnc PEM file this option generates. + And similarly makes it easy for the -sslverify option + to pick up your client certs. + + There is nothing special about the filename or directory + location of either the "server" and "client" certs. + You can rename the files or move them to wherever + you like. + + Precede this option with -ssldir [dir] to use a + directory other than the default ~/.vnc/certs You will + need to run -sslGenCA on that directory first before + doing any -sslGenCert key creation. + + Note you cannot recreate a cert with exactly the same + distiguished name (DN) as an existing one. To do so, + you will need to edit the [dir]/CA/index.txt file to + delete the line. + + Similar to -sslGenCA, you will be prompted to fill + in some information that will be recorded in the + certificate when it is created. + + Tip: if you know the fully-qualified hostname other + people will be connecting to, you can use that as the + CommonName "CN" to avoid some applications (e.g. web + browsers and java plugin) complaining that it does not + match the hostname. + + You will also need to supply the CA private key + passphrase to unlock the private key created from + -sslGenCA. This private key is used to sign the server + or client certificate. + + The "server" certs can be used by x11vnc directly by + pointing to them via the -ssl [pem] option. The default + file will be ~/.vnc/certs/server.pem. This one would + be used by simply typing -ssl SAVE. The pem file + contains both the certificate and the private key. + server.crt file contains the cert only. + + The "client" cert + private key file will need + to be copied and imported into the VNC viewer + side applications (Web browser, Java plugin, + stunnel, etc.) Once that is done you can delete the + "client" private key file on this machine since + it is only needed on the VNC viewer side. The, + e.g. ~/.vnc/certs/clients/.pem contains both + the cert and private key. The .crt contains the + certificate only. + + NOTE: It is very important to know one should + generate new keys with a passphrase. Otherwise if an + untrusted user steals the key file he could use it to + masquerade as the x11vnc server (or VNC viewer client). + You will be prompted whether to encrypt the key with + a passphrase or not. It is recommended that you do. + One inconvenience to a passphrase is that it must + be typed in EVERY time x11vnc or the client app is + started up. + + Examples: + + x11vnc -sslGenCert server + x11vnc -ssl SAVE -display :0 ... + + and then on viewer using ss_vncviewer stunnel wrapper + (see the FAQ): + ss_vncviewer -verify ./cacert.crt hostname:0 + + (this assumes the cacert.crt cert from -sslGenCA + was safely copied to the VNC viewer machine where + ss_vncviewer is run) + + Example using a name: + + x11vnc -sslGenCert server charlie + x11vnc -ssl SAVE-charlie -display :0 ... + + Example for a client certificate (rarely used): + + x11vnc -sslGenCert client roger + scp ~/.vnc/certs/clients/roger.pem somehost:. + rm ~/.vnc/certs/clients/roger.pem + + x11vnc is then started with the option -sslverify + ~/.vnc/certs/clients/roger.crt (or simply -sslverify + roger), and on the viewer user on somehost could do + for example: + + ss_vncviewer -mycert ./roger.pem hostname:0 + + If you set the env. var REQ_ARGS='...' it will be + passed to openssl req(1). A common use would be + REQ_ARGS='-days 1095' to bump up the expiration date + (3 years in this case). + +-sslEncKey pem Utility to encrypt an existing PEM file with a + passphrase you supply when prompted. For that key to be + used (e.g. by x11vnc) the passphrase must be supplied + each time. + + The "SAVE" notation described under -ssl applies as + well. (precede this option with -ssldir [dir] to refer + a directory besides the default ~/.vnc/certs) + + The openssl(1) program must be installed on the system + and available in PATH. After the Key file is encrypted + the x11vnc command exits; the VNC server is not run. + + Examples: + x11vnc -sslEncKey /path/to/foo.pem + x11vnc -sslEncKey SAVE + x11vnc -sslEncKey SAVE-charlie + +-sslCertInfo pem Prints out information about an existing PEM file. + In addition the public certificate is also printed. + The openssl(1) program must be in PATH. Basically the + command "openssl x509 -text" is run on the pem. + + After the info is printed the x11vnc command exits; + the VNC server is not run. + + The "SAVE" notation described under -ssl applies + as well. + + Using "LIST" will give a list of all certs being + managed (in the ~/.vnc/certs dir, use -ssldir to refer + to another dir). "ALL" will print out the info for + every managed key (this can be very long). Giving a + client or server cert shortname will also try a lookup + (e.g. -sslCertInfo charlie). Use "LISTL" or "LL" + for a long (ls -l style) listing. + + Using "HASHON" will create subdirs [dir]/HASH and + [dir]/HASH with OpenSSL hash filenames (e.g. 0d5fbbf1.0) + symlinks pointing up to the corresponding *.crt file. + ([dir] is ~/.vnc/certs or one given by -ssldir.) + This is a useful way for other OpenSSL applications + (e.g. stunnel) to access all of the certs without + having to concatenate them. x11vnc will not use them + unless you specifically reference them. "HASHOFF" + removes these HASH subdirs. + + The LIST, LISTL, LL, ALL, HASHON, HASHOFF words can + also be lowercase, e.g. "list". + +-sslDelCert pem Prompts you to delete all .crt .pem .key .req files + associated with [pem]. x11vnc then exits. "SAVE" + and lookups as in -sslCertInfo apply as well. + +-sslScripts Prints out both the 'genCA' and 'genCert' x11vnc + openssl wrapper scripts for you to examine, modify, etc. + The scripts are printed to stdout and then the x11vnc + program exits. + + +-stunnel [pem] Use the stunnel(8) (stunnel.mirt.net) to provide an + encrypted SSL tunnel between viewers and x11vnc. + + This external tunnel method was implemented prior to the + integrated -ssl encryption described above. It still + works well and avoids the requirement of linking with + the OpenSSL libraries. This mode requires stunnel + to be installed on the system and available via PATH + (n.b. stunnel is often installed in sbin directories). + Version 4.x of stunnel is assumed (but see -stunnel3 + below.) + + [pem] is optional, use "-stunnel /path/to/stunnel.pem" + to specify a PEM certificate file to pass to stunnel. + See the -ssl option for more info on certificate files. + + Whether or not your stunnel has its own certificate + depends on your stunnel configuration; stunnel often + generates one at install time. See your stunnel + documentation for details. In any event, if you want to + use this certificate you must supply the full path to it + as [pem]. Note: the file may only be readable by root. + + [pem] may also be the special strings "TMP", "SAVE", + and "SAVE..." as described in the -ssl option. + If [pem] is not supplied, "SAVE" is assumed. + + Note that the VeNCrypt, ANONTLS, and "ANON" modes + are not supported in -stunnel mode. + + stunnel is started up as a child process of x11vnc and + any SSL connections stunnel receives are decrypted and + sent to x11vnc over a local socket. The strings + "The SSL VNC desktop is ..." and "SSLPORT=..." + are printed out at startup to indicate this. + + The -localhost option is enforced by default to avoid + people routing around the SSL channel. Use -env + STUNNEL_DISABLE_LOCALHOST=1 to disable this security + requirement. + + Set -env STUNNEL_DEBUG=1 for more debugging printout. + + Set -env STUNNEL_PROG=xxx to the full path of stunnel + program you want to be used (e.g. /usr/bin/stunnel4). + + Set -env STUNNEL_LISTEN=xxx to the address of the + network interface to listen on (the default is to listen + on all interfaces), e.g. STUNNEL_LISTEN=192.168.1.100. + + A simple way to add IPv6 support is STUNNEL_LISTEN=:: + + Your VNC viewer will also need to be able to connect + via SSL. Unfortunately not too many do this. See the + information about SSL viewers under the -ssl option. + The x11vnc project's SSVNC is an option. + + Also, in the x11vnc distribution, patched TightVNC + and UltraVNC Java applet jar files are provided in + the classes/ssl directory that do SSL connections. + Enable serving them with the -http, -http_ssl, or + -httpdir (see the option descriptions for more info.) + + Note that for the Java viewer applet usage the + "?PORT=xxxx" in the various URLs printed at startup + will need to be supplied to the web browser to connect + properly. + + Currently the automatic "single port" HTTPS mode of + -ssl is not fully supported in -stunnel mode. However, + it can be emulated via: + + % x11vnc -stunnel -http_ssl -http_oneport ... + + In general, it is also not too difficult to set up + an stunnel or other SSL tunnel on the viewer side. + A simple example on Unix using stunnel 3.x is: + + % stunnel -c -d localhost:5901 -r remotehost:5900 + % vncviewer localhost:1 + + For Windows, stunnel has been ported to it and there + are probably other such tools available. See the FAQ + and SSVNC for more examples. + +-stunnel3 [pem] Use version 3.x stunnel command line syntax instead of + version 4.x. The -http/-httpdir Java applet serving + is currently not available in this mode. + +-enc cipher:keyfile Use symmetric encryption with cipher "cipher" + and secret key data in "keyfile". If keyfile is + pw= then "string" is used as the key data. + + NOTE: It is recommended that you use SSL via the -ssl + option instead of this option because SSL is well + understood and takes great care to establish unique + session keys and is more compatible with other software. + Use this option if you do not want to deal with SSL + certificates for authentication and do not want to + use SSH but want some encryption for your VNC session. + Or if you must interface with a symmetric key tunnel + that you do not have control over. + + Note that this mode will NOT work with the UltraVNC DSM + plugins because they alter the RFB protocol in addition + to tunnelling with the symmetric cipher (an unfortunate + choice of implementation...) + + cipher can be one of: arc4, aesv2, aes-cfb, blowfish, + aes256, or 3des. See the OpenSSL documentation for + more info. The keysize is 128 bits (except for aes256). + Here is one way to make a keyfile with that many bits: + + dd if=/dev/random of=./my.key bs=16 count=1 + + you will need to securely share this key with the other + side of the VNC connection (See SSVNC for examples). + + Example: -enc blowfish:./my.key + Example: -enc blowfish:pw=swordfish + + By default 16 bytes of random salt followed by 16 bytes + of random initialization vector are sent at the very + beginning of the stream. The other side must read these + and initialize their cipher with them. These values + make the session key unique (without them the security + is minimal). Similarly, the other side must send us + its random salt and IV with those same lengths. + + The salt and key data are combined to create a session + key using an md5 hash as described in EVP_BytesToKey(3). + + The exact call is: EVP_BytesToKey(Cipher, EVP_md5(), + salt, keydata, len, 1, keystr, NULL); where salt is + the random data as described above, and keydata is the + shared secret key data. keystr is the resulting session + key. The cipher is then seeded with keystr and uses + the random initialization vector as its first block. + + To modify the amount of random salt and initialization + vector use cipher@n,m where n is the salt length and + m the initialization vector length. E.g. + + -enc aes-cfb@8,16:./my.key + + It is not a good idea to set either one to zero, + although you may be forced to if the other side of the + tunnel is not under your control. + + To skip the salt and EVP_BytesToKey MD5 entirely (no + hashing is done: the keydata is directly inserted into + the cipher) specify "-1" for the salt, e.g. + + -enc blowfish@-1,16:./my.key + + The message digest can also be changed to something + besides the default MD5. Use cipher@md+n,m where "md" + can be one of sha, sha1, md5, or ripe. For example: + + -enc arc4@sha+8,16:./my.key + + The SSVNC vnc viewer project supplies a symmetric + encryption tool named "ultravnc_dsm_helper" that can + be used on the viewer side. For example: + + ssvncviewer exec='ultravnc_dsm_helper arc4 my.key 0 h:p' + + where h:p is the hostname and port of the x11vnc server. + ultravnc_dsm_helper may also be used standalone to + provide a symmetric encryption tunnel for any viewer + or server (VNC or otherwise.) The cipher (1st arg) + is basically the same syntax as we use above. + + Also see the 'Non-Ultra DSM' SSVNC option for the + 'UltraVNC DSM Encryption Plugin' advanced option. + + For both ways of using the viewer, you can specify the + salt,ivec sizes (in GUI or, e.g. arc4@8,16). + +-https [port] Use a special, separate HTTPS port (-ssl and + -stunnel modes only) for HTTPS Java viewer applet + downloading. I.e. not 5900 and not 5800 (the defaults.) + + BACKGROUND: In -ssl mode, it turns out you can use the + single VNC port (e.g. 5900) for both VNC and HTTPS + connections. (HTTPS is used to retrieve a SSL-aware + VncViewer.jar applet that is provided with x11vnc). + Since both use SSL the implementation was extended to + detect if HTTP traffic (i.e. GET) is taking place and + handle it accordingly. The URL would be, e.g.: + + https://mymachine.org:5900/ + + This is convenient for firewalls, etc, because only one + port needs to be allowed in. However, this heuristic + adds a few seconds delay to each connection and can be + unreliable (especially if the user takes much time to + ponder the Certificate dialogs in his browser, Java VM, + or VNC Viewer applet. That's right 3 separate "Are + you sure you want to connect?" dialogs!) + + END OF BACKGROUND. + + USAGE: So use the -https option to provide a separate, + more reliable HTTPS port that x11vnc will listen on. If + [port] is not provided (or is 0), one is autoselected. + The URL to use is printed out at startup. + + The SSL Java applet directory is specified via the + -httpdir option. If not supplied, -https will try + to guess the directory as though the -http option + was supplied. + +-httpsredir [port] In -ssl mode with the Java applet retrieved via HTTPS, + when the HTML file containing applet parameters + ('index.vnc' or 'proxy.vnc') is sent do NOT set the + applet PORT parameter to the actual VNC port but set it + to "port" instead. If "port" is not supplied, then + the port number is guessed from the Host: HTTP header. + + This is useful when an incoming TCP connection + redirection is performed by a router/gateway/firewall + from one port to an internal machine where x11vnc is + listening on a different port. The Java applet needs to + connect to the firewall/router port, not the VNC port + on the internal workstation. For example, one could + redir from mygateway.com:443 to workstation:5900. + + This spares the user from having to type in + https://mygateway.com/?PORT=443 into their web + browser. Note that port 443 is the default https port; + other ports must be explicitly indicated, for example: + https://mygateway.com:8000/?PORT=8000. To avoid having + to include the PORT= in the browser URL, simply supply + "-httpsredir" to x11vnc. + + This option does not work in -stunnel mode. + + More tricks: set the env var X11VNC_EXTRA_HTTPS_PARAMS + to be extra URL parameters to use. This way you do + not need to specify extra PARAMS in the index.vnc file. + E.g. x11vnc -env X11VNC_EXTRA_HTTPS_PARAMS='?GET=1' ... + + If you do not want to expose the non-SSL HTTP port to + the network (i.e. you just want the single VNC/HTTPS + port, e.g. 5900, open for connections) then specify the + option -env X11VNC_HTTP_LISTEN_LOCALHOST=1 This way + the connection to the LibVNCServer httpd server will + only be available on localhost (note that in -ssl mode, + HTTPS requests are redirected from SSL to the non-SSL + LibVNCServer HTTP server.) + +-http_oneport For UN-encrypted connections mode (i.e. no -ssl, + -stunnel, or -enc options), allow the Java VNC Viewer + applet to be downloaded thru the VNC port via HTTP. + + That is to say, you can use a single port for Java + applet viewer connections by using a URL in your web + browser like this, for example: + + http://hostname:5900 + + The regular, two-port mode, URL http://hostname:5800 + will continue to work as well. + + As mentioned above, this mode will NOT work with + the -ssl, -stunnel, or -enc encryption options. + Note that is it equivalent to '-enc none' (i.e. it + uses the same detection mechanism as for HTTPS, but + with no encryption.) + + HTTPS single-port is on by default in -ssl encrypted + mode (and -enc too), so you only need -http_oneport + when doing non-SSL encrypted connections. + + This mode could also be useful for SSH tunnels since + it means only one port needs to be redirected. + + The -httpsredir option may also be useful for this + mode when using an SSH tunnel as well as for router + port redirections. + + Note that the -env X11VNC_HTTP_LISTEN_LOCALHOST=1 + option described above under -httpsredir applies for + the LibVNCServer httpd server in all cases (ssl or not.) + +-ssh user@host:disp Create a remote listening port on machine "host" + via a SSH tunnel using the -R rport:localhost:lport + method. lport will be the local x11vnc listening port, + so a connection to rport (5900+disp) on "host" + will reach x11vnc. E.g. fred@snoopy.com:0 + + This could be useful if a firewall/router prevents + incoming connections to the x11vnc machine, but + the ssh machine "host" can be reached by the VNC + viewer. "user@" is not needed unless the remote unix + username differs from the current one. + + By default the remote sshd is usually configured to + listen only on localhost for rport, so the viewer may + need to ssh -L redir to "host" as well (See SSVNC to + automate this). The sshd setting GatewayPorts enables + listening on all interfaces for rport; viewers can + reach it more easily. + + "disp" is the VNC display for the remote SSH side, + e.g. 0 corresponds to port 5900, etc. If disp is + greater than 200 the value is used as the port. Use a + negative value to force a low port, e.g. host:-80 will + use port 80. + + If ssh-agent is not active, then the ssh password needs + to be entered in the terminal where x11vnc is running. + + By default the remote ssh will issue a 'sleep 300' to + wait for the incoming connection for 5 mins. To modify + this use user@host:disp+secs. + + If the remote SSH server is on a non-standard port + (i.e. not 22) use user@host:port:disp+secs. + + Note that the ssh process MAY NOT be killed when + x11vnc exits. It tries by looking at ps(1) output. + +-usepw If no other password method was supplied on the command + line, first look for ~/.vnc/passwd and if found use it + with -rfbauth; next, look for ~/.vnc/passwdfile and + use it with -passwdfile; otherwise, prompt the user + for a password to create ~/.vnc/passwd and use it with + the -rfbauth option. If none of these succeed x11vnc + exits immediately. + +-storepasswd pass file Store password "pass" as the VNC password in the + file "file". Once the password is stored the + program exits. Use the password via "-rfbauth file" + + If called with no arguments, "x11vnc -storepasswd", + the user is prompted for a password and it is stored + in the file ~/.vnc/passwd. Called with one argument, + that will be the file to store the prompted password in. + +-nopw Disable the big warning message when you use x11vnc + without some sort of password. + +-accept string Run a command (possibly to prompt the user at the + X11 display) to decide whether an incoming client + should be allowed to connect or not. "string" is + an external command run via system(3) or some special + cases described below. Be sure to quote "string" + if it contains spaces, shell characters, etc. If the + external command returns 0 the client is accepted, + otherwise the client is rejected. See below for an + extension to accept a client view-only. + + If x11vnc is running as root (say from inetd(8) or from + display managers xdm(1), gdm(1), etc), think about the + security implications carefully before supplying this + option (likewise for the -gone option). + + Environment: The RFB_CLIENT_IP environment variable will + be set to the incoming client IP number and the port + in RFB_CLIENT_PORT (or -1 if unavailable). Similarly, + RFB_SERVER_IP and RFB_SERVER_PORT (the x11vnc side + of the connection), are set to allow identification + of the tcp virtual circuit. The x11vnc process + id will be in RFB_X11VNC_PID, a client id number in + RFB_CLIENT_ID, and the number of other connected clients + in RFB_CLIENT_COUNT. RFB_MODE will be "accept". + RFB_STATE will be PROTOCOL_VERSION, SECURITY_TYPE, + AUTHENTICATION, INITIALISATION, NORMAL, or UNKNOWN + indicating up to which state the client has achieved. + RFB_LOGIN_VIEWONLY will be 0, 1, or -1 (unknown). + RFB_USERNAME, RFB_LOGIN_TIME, and RFB_CURRENT_TIME may + also be set. + + If "string" is "popup" then a builtin popup window + is used. The popup will time out after 120 seconds, + use "popup:N" to modify the timeout to N seconds + (use 0 for no timeout). + + In the case of "popup" and when the -unixpw option + is specified, then a *second* window will be popped + up after the user successfully logs in via his UNIX + password. This time the user will be identified as + UNIX:username@hostname, the "UNIX:" prefix indicates + which user the viewer logged as via -unixpw. The first + popup is only for whether to allow him to even *try* + to login via unix password. + + If "string" is "xmessage" then an xmessage(1) + invocation is used for the command. xmessage must be + installed on the machine for this to work. + + Both "popup" and "xmessage" will present an option + for accepting the client "View-Only" (the client + can only watch). This option will not be presented if + -viewonly has been specified, in which case the entire + display is view only. + + If the user supplied command is prefixed with something + like "yes:0,no:*,view:3 mycommand ..." then this + associates the numerical command return code with + the actions: accept, reject, and accept-view-only, + respectively. Use "*" instead of a number to indicate + the default action (in case the command returns an + unexpected value). E.g. "no:*" is a good choice. + + Note that x11vnc blocks while the external command + or popup is running (other clients may see no updates + during this period). So a person sitting a the physical + display is needed to respond to an popup prompt. (use + a 2nd x11vnc if you lock yourself out). + + More -accept tricks: use "popupmouse" to only allow + mouse clicks in the builtin popup to be recognized. + Similarly use "popupkey" to only recognize + keystroke responses. These are to help avoid the + user accidentally accepting a client by typing or + clicking. All 3 of the popup keywords can be followed + by +N+M to supply a position for the popup window. + The default is to center the popup window. +-afteraccept string As -accept, except to run a user supplied command after + a client has been accepted and authenticated. RFB_MODE + will be set to "afteraccept" and the other RFB_* + variables are as in -accept. Unlike -accept, the + command return code is not interpreted by x11vnc. + Example: -afteraccept 'killall xlock &' +-gone string As -accept, except to run a user supplied command when + a client goes away (disconnects). RFB_MODE will be + set to "gone" and the other RFB_* variables are as + in -accept. The "popup" actions apply as well. + Unlike -accept, the command return code is not + interpreted by x11vnc. Example: -gone 'xlock &' + +-users list If x11vnc is started as root (say from inetd(8) or from + display managers xdm(1), gdm(1), etc), then as soon + as possible after connections to the X display are + established try to switch to one of the users in the + comma separated "list". If x11vnc is not running as + root this option is ignored. + + Why use this option? In general it is not needed since + x11vnc is already connected to the X display and can + perform its primary functions. The option was added + to make some of the *external* utility commands x11vnc + occasionally runs work properly. In particular under + GNOME and KDE to implement the "-solid color" feature + external commands (gconftool-2 and dcop) unfortunately + must be run as the user owning the desktop session. + Since this option switches userid it also affects the + userid used to run the processes for the -accept and + -gone options. It also affects the ability to read + files for options such as -connect, -allow, and -remap + and also the ultra and tight filetransfer feature if + enabled. Note that the -connect file is also sometimes + written to. + + So be careful with this option since in some situations + its use can decrease security. + + In general the switch to a user will only take place + if the display can still be successfully opened as that + user (this is primarily to try to guess the actual owner + of the session). Example: "-users fred,wilma,betty". + Note that a malicious local user "barney" by + quickly using "xhost +" when logging in may possibly + get the x11vnc process to switch to user "fred". + What happens next? + + Under display managers it may be a long time before + the switch succeeds (i.e. a user logs in). To instead + make it switch immediately regardless if the display + can be reopened prefix the username with the "+" + character. E.g. "-users +bob" or "-users +nobody". + + The latter (i.e. switching immediately to user + "nobody") is the only obvious use of the -users option + that increases security. + + Use the following notation to associate a group with + a user: user1.group1,user2.group2,... Note that + initgroups(2) will still be called first to try to + switch to ALL of a user's groups (primary and additional + groups). Only if that fails or it is not available + then the single group specified as above (or the user's + primary group if not specified) is switched to with + setgid(2). Use -env X11VNC_SINGLE_GROUP=1 to prevent + trying initgroups(2) and only switch to the single + group. This sort of setting is only really needed to + make the ultra or tight filetransfer permissions work + properly. This format applies to any comma separated list + of users, even the special "=" modes described below. + + In -unixpw mode, if "-users unixpw=" is supplied + then after a user authenticates himself via the + -unixpw mechanism, x11vnc will try to switch to that + user as though "-users +username" had been supplied. + If you want to limit which users this will be done for, + provide them as a comma separated list after "unixpw=" + Groups can also be specified as described above. + + Similarly, in -ssl mode, if "-users sslpeer=" is + supplied then after an SSL client authenticates with his + cert (the -sslverify option is required for this) x11vnc + will extract a UNIX username from the "emailAddress" + field (username@hostname.com) of the "Subject" of the + x509 SSL cert and then try to switch to that user as + though "-users +username" had been supplied. If you + want to limit which users this will be done for, provide + them as a comma separated list after "sslpeer=". + Set the env. var X11VNC_SSLPEER_CN to use the Common + Name (normally a hostname) instead of the Email field. + + NOTE: for sslpeer= mode the x11vnc administrator must + take care that any client certs he adds to -sslverify + have the intended UNIX username in the "emailAddress" + field of the cert. Otherwise a user may be able to + log in as another. This command can be of use in + checking: "openssl x509 -text -in file.crt", see the + "Subject:" line. Also, along with the normal RFB_* + env. vars. (see -accept) passed to external cmd= + commands, RFB_SSL_CLIENT_CERT will be set to the + client's x509 certificate string. + + The sslpeer= mode can aid finding X sessions via the + FINDDISPLAY and FINDCREATEDISPLAY mechanisms. + + To immediately switch to a user *before* connections + to the X display are made or any files opened use the + "=" character: "-users =bob". That user needs to + be able to open the X display and any files of course. + + The special user "guess=" means to examine the utmpx + database (see who(1)) looking for a user attached to + the display number (from DISPLAY or -display option) + and try him/her. To limit the list of guesses, use: + "-users guess=bob,betty". + + Even more sinister is the special user "lurk=" + that means to try to guess the DISPLAY from the utmpx + login database as well. So it "lurks" waiting for + anyone to log into an X session and then connects to it. + Specify a list of users after the = to limit which users + will be tried. To enable a different searching mode, if + the first user in the list is something like ":0" or + ":0-2" that indicates a range of DISPLAY numbers that + will be tried (regardless of whether they are in the + utmpx database) for all users that are logged in. Also + see the "-display WAIT:..." functionality. Examples: + "-users lurk=" and also "-users lurk=:0-1,bob,mary" + + Be especially careful using the "guess=" and "lurk=" + modes. They are not recommended for use on machines + with untrustworthy local users. + +-noshm Do not use the MIT-SHM extension for the polling. + Remote displays can be polled this way: be careful this + can use large amounts of network bandwidth. This is + also of use if the local machine has a limited number + of shm segments and -onetile is not sufficient. +-flipbyteorder Sometimes needed if remotely polled host has different + endianness. Ignored unless -noshm is set. +-onetile Do not use the new copy_tiles() framebuffer mechanism, + just use 1 shm tile for polling. Limits shm segments + used to 3. + + To disable any automatic shm reduction set the + env. var. X11VNC_NO_LIMIT_SHM. + +-solid [color] To improve performance, when VNC clients are connected + try to change the desktop background to a solid color. + The [color] is optional: the default color is "cyan4". + For a different one specify the X color (rgb.txt name, + e.g. "darkblue" or numerical "#RRGGBB"). + + Currently this option only works on GNOME, KDE, CDE, + XFCE, and classic X (i.e. with the background image + on the root window). The "gconftool-2", "dcop" + and "xfconf-query" external commands are run for + GNOME, KDE, and XFCE respectively. This also works + on native MacOSX. (There is no color selection for + MacOSX or XFCE.) Other desktops won't work, (send + us the corresponding commands if you find them). + If x11vnc is running as root (inetd(8) or gdm(1)), + the -users option may be needed for GNOME, KDE, XFCE. + If x11vnc guesses your desktop incorrectly, you can + force it by prefixing color with "gnome:", "kde:", + "cde:", "xfce:", or "root:". + + Update: -solid no longer works on KDE4. + + This mode works in a limited way on the Mac OS X Console + with one color ('kelp') using the screensaver writing + to the background. Look in "~/Library/Screen Savers" + for VncSolidColor.png to change the color. + +-blackout string Black out rectangles on the screen. "string" is a + comma separated list of WxH+X+Y type geometries for + each rectangle. If one of the items on the list is the + string "noptr" the mouse pointer will not be allowed + to go into a blacked out region. +-xinerama If your screen is composed of multiple monitors +-noxinerama glued together via XINERAMA, and that screen is + not a rectangle this option will try to guess the + areas to black out (if your system has libXinerama). + default: -xinerama + + In general, we have noticed on XINERAMA displays you may + need to use the "-xwarppointer" option if the mouse + pointer misbehaves and it is enabled by default. Use + "-noxwarppointer" if you do not want this. + +-xtrap Use the DEC-XTRAP extension for keystroke and mouse + input insertion. For use on legacy systems, e.g. X11R5, + running an incomplete or missing XTEST extension. + By default DEC-XTRAP will be used if XTEST server grab + control is missing, use -xtrap to do the keystroke and + mouse insertion via DEC-XTRAP as well. + +-xrandr [mode] If the display supports the XRANDR (X Resize, Rotate + and Reflection) extension, and you expect XRANDR events + to occur to the display while x11vnc is running, this + options indicates x11vnc should try to respond to + them (as opposed to simply crashing by assuming the + old screen size). See the xrandr(1) manpage and run + 'xrandr -q' for more info. [mode] is optional and + described below. + + Since watching for XRANDR events and trapping errors + increases polling overhead, only use this option if + XRANDR changes are expected. For example on a rotatable + screen PDA or laptop, or using a XRANDR-aware Desktop + where you resize often. It is best to be viewing with a + vncviewer that supports the NewFBSize encoding, since it + knows how to react to screen size changes. Otherwise, + LibVNCServer tries to do so something reasonable for + viewers that cannot do this (portions of the screen + may be clipped, unused, etc). + + Note: the default now is to check for XRANDR events, but + do not trap every X call that may fail due to resize. + If a resize event is received, the full -xrandr mode + is enabled. To disable even checking for events supply: + -noxrandr. + + "mode" defaults to "resize", which means create a + new, resized, framebuffer and hope all viewers can cope + with the change. "newfbsize" means first disconnect + all viewers that do not support the NewFBSize VNC + encoding, and then resize the framebuffer. "exit" + means disconnect all viewer clients, and then terminate + x11vnc. + +-rotate string Rotate and/or flip the framebuffer view exported by VNC. + This transformation is independent of XRANDR and is + done in software in main memory and so may be slower. + This mode could be useful on a handheld with portrait or + landscape modes that do not correspond to the scanline + order of the actual framebuffer. "string" can be: + + x flip along x-axis + y flip along y-axis + xy flip along x- and y-axes + +90 rotate 90 degrees clockwise + -90 rotate 90 degrees counter-clockwise + +90x rotate 90 degrees CW, then flip along x + +90y rotate 90 degrees CW, then flip along y + + these give all possible rotations and reflections. + + Aliases: same as xy: yx, +180, -180, 180 + same as -90: +270, 270 + same as +90: 90, (ditto for 90x, 90y) + + Like -scale, this transformation is applied at the very + end of any chain of framebuffer transformations and so + any options with geometries, e.g. -blackout, -clip, etc. + are relative to the original X (or -rawfb) framebuffer, + not the final one sent to VNC viewers. + + If you do not want the cursor shape to be rotated + prefix "string" with "nc:", e.g. "nc:+90", + "nc:xy", etc. + +-padgeom WxH Whenever a new vncviewer connects, the framebuffer is + replaced with a fake, solid black one of geometry WxH. + Shortly afterwards the framebuffer is replaced with the + real one. This is intended for use with vncviewers + that do not support NewFBSize and one wants to make + sure the initial viewer geometry will be big enough + to handle all subsequent resizes (e.g. under -xrandr, + -remote id:windowid, rescaling, etc.) + + In -unixpw mode this sets the size of the login screen. + Use "once:WxH" it ignore padgeom after the login + screen is set up. + +-o logfile Write stderr messages to file "logfile" instead of to + the terminal. Same as "-logfile file". To append + to the file use "-oa file" or "-logappend file". + If "logfile" contains the string "%VNCDISPLAY" + it is expanded to the vnc display (the name may need + to be guessed at.) "%HOME" works too. + +-flag file Write the "PORT=NNNN" (e.g. PORT=5900) string to + "file" in addition to stdout. This option could be + useful by wrapper script to detect when x11vnc is ready. + +-rmflag file Remove "file" at exit to signal when x11vnc is done. + The file is created at startup if it does not already + exist or if "file" is prefixed with "create:". + If the file is created, the x11vnc PID is placed in + the file. Otherwise the files contents is not changed. + Use prefix "nocreate:" to prevent creation. + +-rc filename Use "filename" instead of $HOME/.x11vncrc for rc file. +-norc Do not process any .x11vncrc file for options. + +-env VAR=VALUE Set the environment variable 'VAR' to value 'VALUE' + at x11vnc startup. This is a convenience utility to + avoid shell script wrappers, etc. to set the env. var. + You may specify as many of these as needed on the + command line. +-prog /path/to/x11vnc Set the full path to the x11vnc program for cases when + it cannot be determined from argv[0] (e.g. tcpd/inetd) + +-h, -help Print this help text. +-?, -opts Only list the x11vnc options. +-V, -version Print program version and last modification date. +-license Print out license information. Same as -copying and + -warranty. + +-dbg Instead of exiting after cleaning up, run a simple + "debug crash shell" when fatal errors are trapped. + +-q, -quiet Be quiet by printing less informational output to + stderr. (use -noquiet to undo an earlier -quiet.) + + The -quiet option does not eliminate all informational + output, it only reduces it. It is ignored in most + auxiliary usage modes, e.g. -storepasswd. To eliminate + all output use: 2>/dev/null 1>&2, etc. + +-v, -verbose Print out more information to stderr. + +-bg Go into the background after screen setup. Messages to + stderr are lost unless -o logfile is used. Something + like this could be useful in a script: + port=`ssh -t $host "x11vnc -display :0 -bg" | grep PORT` + port=`echo "$port" | sed -e 's/PORT=//'` + port=`expr $port - 5900` + vncviewer $host:$port + +-modtweak Option -modtweak automatically tries to adjust the AltGr +-nomodtweak and Shift modifiers for differing language keyboards + between client and host. Otherwise, only a single key + press/release of a Keycode is simulated (i.e. ignoring + the state of the modifiers: this usually works for + identical keyboards). Also useful in resolving cases + where a Keysym is bound to multiple keys (e.g. "<" + ">" + and "," + "<" keys). Default: -modtweak + + If you are having trouble with with keys and -xkb or + -noxkb, and similar things don't help, try -nomodtweak. + + On some HP-UX systems it is been noted that they have + an odd keymapping where a single keycode will have a + keysym, e.g. "#", up to three times. You can check + via "xmodmap -pk" or the -dk option. The failure + is when you try to type "#" it yields "3". If you + see this problem try setting the environment variable + MODTWEAK_LOWEST=1 to see if it helps. + +-xkb When in modtweak mode, use the XKEYBOARD extension (if +-noxkb the X display supports it) to do the modifier tweaking. + This is powerful and should be tried if there are still + keymapping problems when using -modtweak by itself. + The default is to check whether some common keysyms, + e.g. !, @, [, are only accessible via -xkb mode and if + so then automatically enable the mode. To disable this + automatic detection use -noxkb. + + When -xkb mode is active you can set these env. vars. + They apply only when there is ambiguity as to which + key to choose (i.e the mapping is not one-to-one). + NOKEYHINTS=1: for up ascii keystrokes do not use score + hints saved when the key was pressed down. NOANYDOWN=1: + for up keystrokes do not resort to searching through + keys that are currently pressed down. KEYSDOWN=N: + remember the last N keys press down for tie-breaking + when an up keystroke comes in. + +-capslock When in -modtweak (the default) or -xkb mode, + if a keysym in the range A-Z comes in check the X + server to see if the Caps_Lock is set. If it is do + not artificially press Shift to generate the keysym. + This will enable the CapsLock key to behave correctly + in some circumstances: namely *both* the VNC viewer + machine and the x11vnc X server are in the CapsLock + on state. If one side has CapsLock on and the other + off and the keyboard is not behaving as you think it + should you should correct the CapsLock states (hint: + pressing CapsLock inside and outside of the viewer can + help toggle them both to the correct state). However, + for best results do not use this option, but rather + *only* enable CapsLock on the VNC viewer side (i.e. by + pressing CapsLock outside of the viewer window, also + -skip_lockkeys below). Also try -nomodtweak for a + possible workaround. + +-skip_lockkeys Have x11vnc ignore all Caps_Lock, Shift_Lock, Num_Lock, +-noskip_lockkeys Scroll_Lock keysyms received from viewers. The idea is + you press Caps_Lock on the VNC Viewer side but that does + not change the lock state in the x11vnc-side X server. + Nevertheless your capitalized letters come in over + the wire and are applied correctly to the x11vnc-side + X server. Note this mode probably won't do what you + want in -nomodtweak mode. Also, a kludge for KP_n + digits is always done in this mode: they are mapped to + regular digit keysyms. See also -capslock above. + The default is -noskip_lockkeys. + +-skip_keycodes string Ignore the comma separated list of decimal keycodes. + Perhaps these are keycodes not on your keyboard but + your X server thinks exist. Currently only applies + to -xkb mode. Use this option to help x11vnc in the + reverse problem it tries to solve: Keysym -> Keycode(s) + when ambiguities exist (more than one Keycode per + Keysym). Run 'xmodmap -pk' to see your keymapping. + Example: "-skip_keycodes 94,114" +-sloppy_keys Experimental option that tries to correct some + "sloppy" key behavior. E.g. if at the viewer you + press Shift+Key but then release the Shift before + Key that could give rise to extra unwanted characters + (usually only between keyboards of different languages). + Only use this option if you observe problems with + some keystrokes. +-skip_dups Some VNC viewers send impossible repeated key events, +-noskip_dups e.g. key-down, key-down, key-up, key-up all for the same + key, or 20 downs in a row for the same modifier key! + Setting -skip_dups means to skip these duplicates and + just process the first event. Note: some VNC viewers + assume they can send down's without the corresponding + up's and so you should not set this option for + these viewers (symptom: some keys do not autorepeat) + Default: -noskip_dups +-add_keysyms If a Keysym is received from a VNC viewer and that +-noadd_keysyms Keysym does not exist in the X server, then add the + Keysym to the X server's keyboard mapping on an unused + key. Added Keysyms will be removed periodically and + also when x11vnc exits. Default: -add_keysyms +-clear_mods At startup and exit clear the modifier keys by sending + KeyRelease for each one. The Lock modifiers are skipped. + Used to clear the state if the display was accidentally + left with any pressed down. +-clear_keys As -clear_mods, except try to release ANY pressed key. + Note that this option and -clear_mods can interfere + with a person typing at the physical keyboard. +-clear_all As -clear_keys, except try to release any CapsLock, + NumLock, etc. locks as well. + +-remap string Read Keysym remappings from file named "string". + Format is one pair of Keysyms per line (can be name + or hex value) separated by a space. If no file named + "string" exists, it is instead interpreted as this + form: key1-key2,key3-key4,... See + header file for a list of Keysym names, or use xev(1). + + To map a key to a button click, use the fake Keysyms + "Button1", ..., etc. E.g: "-remap Super_R-Button2" + (useful for pasting on a laptop) + + I use these if the machine I am viewing from does not + have a scrollwheel or I don't like using the one it has: + + -remap Super_R-Button4,Menu-Button5 + -remap KP_Add-Button4,KP_Enter-Button5 + + the former would be used on a PC, the latter on a + MacBook. This way those little used keys can be used + to generate bigger hops than the Up and Down arrows + provide. One can scroll through text or web pages more + quickly this way (especially if x11vnc scroll detection + is active.) + + Use Button44, Button12, etc. for multiple clicks. + + To disable a keysym (i.e. make it so it will not be + injected), remap it to "NoSymbol" or "None". + + Dead keys: "dead" (or silent, mute) keys are keys that + do not produce a character but must be followed by a 2nd + keystroke. This is often used for accenting characters, + e.g. to put "`" on top of "a" by pressing the dead + key and then "a". Note that this interpretation + is not part of core X11, it is up to the toolkit or + application to decide how to react to the sequence. + The X11 names for these keysyms are "dead_grave", + "dead_acute", etc. However some VNC viewers send the + keysyms "grave", "acute" instead thereby disabling + the accenting. To work around this -remap can be used. + For example "-remap grave-dead_grave,acute-dead_acute" + As a convenience, "-remap DEAD" applies these remaps: + + g grave-dead_grave + a acute-dead_acute + c asciicircum-dead_circumflex + t asciitilde-dead_tilde + m macron-dead_macron + b breve-dead_breve + D abovedot-dead_abovedot + d diaeresis-dead_diaeresis + o degree-dead_abovering + A doubleacute-dead_doubleacute + r caron-dead_caron + e cedilla-dead_cedilla + + If you just want a subset use the first letter + label, e.g. "-remap DEAD=ga" to get the first two. + Additional remaps may also be supplied via commas, + e.g. "-remap DEAD=ga,Super_R-Button2". Finally, + "DEAD=missing" means to apply all of the above as + long as the left hand member is not already in the + X11 keymap. + +-norepeat Option -norepeat disables X server key auto repeat when +-repeat VNC clients are connected and VNC keyboard input is + not idle for more than 5 minutes. This works around a + repeating keystrokes bug (triggered by long processing + delays between key down and key up client events: + either from large screen changes or high latency). + Default: -norepeat + + You can set the env. var. X11VNC_IDLE_TIMEOUT to the + number of idle seconds you want (5min = 300secs). + + Note: your VNC viewer side will likely do autorepeating, + so this is no loss unless someone is simultaneously at + the real X display. + + Use "-norepeat N" to set how many times norepeat will + be reset if something else (e.g. X session manager) + undoes it. The default is 2. Use a negative value + for unlimited resets. + +-nofb Ignore video framebuffer: only process keyboard and + pointer. Intended for use with Win2VNC and x2vnc + dual-monitor setups. +-nobell Do not watch for XBell events. (no beeps will be heard) + Note: XBell monitoring requires the XKEYBOARD extension. +-nosel Do not manage exchange of X selection/cutbuffer between + VNC viewers and the X server at all. +-noprimary Do not poll the PRIMARY selection for changes to send + back to clients. (PRIMARY is still set on received + changes, however). +-nosetprimary Do not set the PRIMARY selection for changes received + from VNC clients. +-noclipboard Do not poll the CLIPBOARD selection for changes to send + back to clients. (CLIPBOARD is still set on received + changes, however). +-nosetclipboard Do not set the CLIPBOARD selection for changes + received from VNC clients. +-seldir string If direction string is "send", only send the selection + to viewers, and if it is "recv" only receive it from + viewers. To work around apps setting the selection + too frequently and messing up the other end. You can + actually supply a comma separated list of directions, + including "debug" to turn on debugging output. + +-cursor [mode] Sets how the pointer cursor shape (little icon at the +-nocursor mouse pointer) should be handled. The "mode" string + is optional and is described below. The default + is to show some sort of cursor shape(s). How this + is done depends on the VNC viewer and the X server. + Use -nocursor to disable cursor shapes completely. + + Some VNC viewers support the TightVNC CursorPosUpdates + and CursorShapeUpdates extensions (cuts down on + network traffic by not having to send the cursor image + every time the pointer is moved), in which case these + extensions are used (see -nocursorshape and -nocursorpos + below to disable). For other viewers the cursor shape + is written directly to the framebuffer every time the + pointer is moved or changed and gets sent along with + the other framebuffer updates. In this case, there + will be some lag between the vnc viewer pointer and + the remote cursor position. + + If the X display supports retrieving the cursor shape + information from the X server, then the default is + to use that mode. On Solaris this can be done with + the SUN_OVL extension using -overlay (see also the + -overlay_nocursor option). A similar overlay scheme + is used on IRIX. Xorg (e.g. Linux) and recent Solaris + Xsun servers support the XFIXES extension to retrieve + the exact cursor shape from the X server. If XFIXES + is present it is preferred over Overlay and is used by + default (see -noxfixes below). This can be disabled + with -nocursor, and also some values of the "mode" + option below. + + Note that under XFIXES cursors with transparency (alpha + channel) will usually not be exactly represented and one + may find Overlay preferable. See also the -alphacut + and -alphafrac options below as fudge factors to try + to improve the situation for cursors with transparency + for a given theme. + + The "mode" string can be used to fine-tune the + displaying of cursor shapes. It can be used the + following ways: + + "-cursor arrow" - just show the standard arrow + nothing more or nothing less. + + "-cursor none" - same as "-nocursor" + + "-cursor X" - when the cursor appears to be on the + root window, draw the familiar X shape. Some desktops + such as GNOME cover up the root window completely, + and so this will not work, try "X1", etc, to try to + shift the tree depth. On high latency links or slow + machines there will be a time lag between expected and + the actual cursor shape. + + "-cursor some" - like "X" but use additional + heuristics to try to guess if the window should have + a windowmanager-like resizer cursor or a text input + I-beam cursor. This is a complete hack, but may be + useful in some situations because it provides a little + more feedback about the cursor shape. + + "-cursor most" - try to show as many cursors as + possible. Often this will only be the same as "some" + unless the display has overlay visuals or XFIXES + extensions available. On Solaris and IRIX if XFIXES + is not available, -overlay mode will be attempted. + +-cursor_drag Show cursor shape changes even when the mouse is being + dragged with a mouse button down. This is useful if you + want to be able to see Drag-and-Drop cursor icons, etc. + +-arrow n Choose an alternate "arrow" cursor from a set of + some common ones. n can be 1 to 6. Default is: 1 + Ignored when in XFIXES cursor-grabbing mode. + +-noxfixes Do not use the XFIXES extension to draw the exact cursor + shape even if it is available. + + Note: To work around a crash in Xorg 1.5 and later + some people needed to use -noxfixes. The Xorg crash + occurred right after a Display Manager (e.g. GDM) login. + Starting with x11vnc 0.9.9 it tries to automatically + avoid using XFIXES until it is sure a window manager + is running. See the -reopen option for more info and + how to use X11VNC_AVOID_WINDOWS=never to disable it. + +-alphacut n When using the XFIXES extension for the cursor shape, + cursors with transparency will not usually be displayed + exactly (but opaque ones will). This option sets n as + a cutoff for cursors that have transparency ("alpha + channel" with values ranging from 0 to 255) Any cursor + pixel with alpha value less than n becomes completely + transparent. Otherwise the pixel is completely opaque. + Default 240 + +-alphafrac fraction With the threshold in -alphacut some cursors will become + almost completely transparent because their alpha values + are not high enough. For those cursors adjust the + alpha threshold until fraction of the non-zero alpha + channel pixels become opaque. Default 0.33 +-alpharemove By default, XFIXES cursors pixels with transparency have + the alpha factor multiplied into the RGB color values + (i.e. that corresponding to blending the cursor with a + black background). Specify this option to remove the + alpha factor. (useful for light colored semi-transparent + cursors). +-noalphablend In XFIXES mode do not send cursor alpha channel data + to LibVNCServer. The default is to send it. The + alphablend effect will only be visible in -nocursorshape + mode or for clients with cursorshapeupdates turned + off. (However there is a hack for 32bpp with depth 24, + it uses the extra 8 bits to store cursor transparency + for use with a hacked vncviewer that applies the + transparency locally. See the FAQ for more info). + +-nocursorshape Do not use the TightVNC CursorShapeUpdates extension + even if clients support it. See -cursor above. +-cursorpos Option -cursorpos enables sending the X cursor position +-nocursorpos back to all vnc clients that support the TightVNC + CursorPosUpdates extension. Other clients will be able + to see the pointer motions. Default: -cursorpos +-xwarppointer Move the pointer with XWarpPointer(3X) instead of +-noxwarppointer the XTEST extension. Use this as a workaround + if the pointer motion behaves incorrectly, e.g. + on touchscreens or other non-standard setups. + + It is also sometimes needed on XINERAMA displays and is + enabled by default if XINERAMA is found to be active. + To prevent this, use -noxwarppointer. + +-always_inject Even if there is no displacement (dx = dy = 0) for a + VNC mouse event force the pointer to the indicated x,y + position anyway. Recent (2009) gui toolkits (gnome) + have problems with x11vnc's original mouse input + injection method. So x11vnc's mouse input injection + method has been modified. To regain the OLD behavior + use this option: -always_inject. Then x11vnc will + always force positioning the mouse to the x,y position + even if that position has not changed since the previous + VNC input event. + + The first place this problem was noticed was in gnome + terminal: if you pressed and released mouse button 3, a + menu was posted and then its first element 'New Terminal + Window' was activated. This was because x11vnc injected + the mouse position twice: once on ButtonPress and again + on ButtonRelease. The toolkit interpreted the 2nd one + as mouse motion even though the mouse hadn't moved. + So now by default x11vnc tries to avoid injecting the + 2nd one. + + Note that with the new default x11vnc will be oblivious + to applications moving the pointer (warping) or the + user at the physical display moving it. So it might, + e.g., inject ButtonRelease at the wrong position. + If this (or similar scenarios) causes problems in your + environment, specify -always_inject for the old method. + +-buttonmap string String to remap mouse buttons. Format: IJK-LMN, this + maps buttons I -> L, etc., e.g. -buttonmap 13-31 + + Button presses can also be mapped to keystrokes: replace + a button digit on the right of the dash with :: + or :+: etc. for multiple keys. For example, + if the viewing machine has a mouse-wheel (buttons 4 5) + but the x11vnc side does not, these will do scrolls: + -buttonmap 12345-123:Prior::Next: + -buttonmap 12345-123:Up+Up+Up::Down+Down+Down: + + See header file for a list of Keysyms, + or use the xev(1) program. Note: mapping of button + clicks to Keysyms may not work if -modtweak or -xkb is + needed for the Keysym. + + If you include a modifier like "Shift_L" the + modifier's up/down state is toggled, e.g. to send + "The" use :Shift_L+t+Shift_L+h+e: (the 1st one is + shift down and the 2nd one is shift up). (note: the + initial state of the modifier is ignored and not reset) + To include button events use "Button1", ... etc. + + -buttonmap currently does not work on MacOSX console + or in -rawfb mode. + + Workaround: use -buttonmap IJ...-LM...=n to limit the + number of mouse buttons to n, e.g. 123-123=3. This will + prevent x11vnc from crashing if the X server reports + there are 5 buttons (4/5 scroll wheel), but there are + only really 3. + +-nodragging Do not update the display during mouse dragging events + (mouse button held down). Greatly improves response on + slow setups, but you lose all visual feedback for drags, + text selection, and some menu traversals. It overrides + any -pointer_mode setting. + +-ncache n Client-side caching scheme. Framebuffer memory "n" + (an integer) times that of the full display is allocated + below the actual framebuffer to cache screen contents + for rapid retrieval. So a W x H frambuffer is expanded + to a W x (n+1)*H one. Use 0 to disable. + + The "n" is actually optional, the default is 10. + + For this and the other -ncache* options below you can + abbreviate "-ncache" with "-nc". Also, "-nonc" + is the same as "-ncache 0" + + This is an experimental option, currently implemented in + an awkward way in that in the VNC Viewer you can see the + pixel cache contents if you scroll down, etc. So you + will have to set things up so you can't see that region. + If this method is successful, the changes required for + clients to do this less awkwardly will be investigated. + + The SSVNC viewer does a good job at automatically hiding + the pixel cache region. Or use SSVNC's -ycrop option + to explicitly hide the region. + + Note that this mode consumes a huge amount of memory, + both on the x11vnc server side and on the VNC Viewer + side. If n=2 then the amount of RAM used is roughly + tripled for both x11vnc and the VNC Viewer. As a rule + of thumb, note that 1280x1024 at depth 24 is about 5MB + of pixel data. + + For reasonable response when cycling through 4 to 6 + large (e.g. web browser) windows a value n of 6 to 12 + is recommended. (that's right: ~10X more memory...) + + Because of the way window backingstore and saveunders + are implemented, n must be even. It will be incremented + by 1 if it is not. + + This mode also works for native MacOS X, but may not + be as effective as the X version. This is due to a + number of things, one is the drop-shadow compositing + that leaves extra areas that need to be repaired (see + -ncache_pad). Another is the window iconification + animations need to be avoided (see -macicontime). + It appears the that the 'Scale' animation mode gives + better results than the 'Genie' one. Also, window event + detection not as accurate as the X version. + +-ncache_cr In -ncache mode, try to do copyrect opaque window + moves/drags instead of wireframes (this can induce + painting errors). The wireframe will still be used when + moving a window whose save-unders has not yet been set + or has been invalidated. + + Some VNC Viewers provide better response than others + with this option. On Unix, realvnc viewer gives + smoother drags than tightvnc viewer. Response may also + be choppy if the server side machine is too slow. + + Sometimes on very slow modem connections, this actually + gives an improvement because no pixel data at all + (not even the box animation) is sent during the drag. + +-ncache_no_moveraise In -ncache mode, do not assume that moving a window + will cause the window manager to raise it to the top + of the stack. The default is to assume it does, and + so at the beginning of any wireframe, etc, window moves + the window will be pushed to top in the VNC viewer. + +-ncache_no_dtchange In -ncache mode, do not try to guess when the desktop + (viewport) changes to another one (i.e. another + workarea). The default is to try to guess and when + detected try to make the transistion more smoothly. + +-ncache_no_rootpixmap In -ncache mode, do not try to snapshot the desktop + background to use in guessing or reconstructing window + save-unders. + +-ncache_keep_anims In -ncache mode, do not try to disable window + manager animations and other effects (that usually + degrade ncache performance or cause painting errors). + The default is to try to disable them on KDE (but not + GNOME) when VNC clients are connected. + + For other window managers or desktops that provide + animations, effects, compositing, translucency, + etc. that interfere with the -ncache method you will + have to disable them manually. + +-ncache_old_wm In -ncache mode, enable some heuristics for old style + window managers such as fvwm and twm. + +-ncache_pad n In -ncache mode, pad each window with n pixels for the + caching rectangles. This can be used to try to improve + the situation with dropshadows or other compositing + (e.g. MacOS X window manager), although it could make + things worse. The default is 0 on Unix and 24 on + MacOS X. +-debug_ncache Turn on debugging and profiling output under -ncache. + +-wireframe [str] Try to detect window moves or resizes when a mouse +-nowireframe button is held down and show a wireframe instead of + the full opaque window. This is based completely on + heuristics and may not always work: it depends on your + window manager and even how you move things around. + See -pointer_mode below for discussion of the "bogging + down" problem this tries to avoid. + Default: -wireframe + + Shorter aliases: -wf [str] and -nowf + + The value "str" is optional and, of course, is + packed with many tunable parameters for this scheme: + + Format: shade,linewidth,percent,T+B+L+R,mod,t1+t2+t3+t4 + Default: 0xff,2,0,32+8+8+8,all,0.15+0.30+5.0+0.125 + + If you leave nothing between commas: ",," the default + value is used. If you don't specify enough commas, + the trailing parameters are set to their defaults. + + "shade" indicate the "color" for the wireframe, + usually a greyscale: 0-255, however for 16 and 32bpp you + can specify an rgb.txt X color (e.g. "dodgerblue") or + a value > 255 is treated as RGB (e.g. red is 0xff0000). + "linewidth" sets the width of the wireframe in pixels. + "percent" indicates to not apply the wireframe scheme + to windows with area less than this percent of the + full screen. + + "T+B+L+R" indicates four integers for how close in + pixels the pointer has to be from the Top, Bottom, Left, + or Right edges of the window to consider wireframing. + This is a speedup to quickly exclude a window from being + wireframed: set them all to zero to not try the speedup + (scrolling and selecting text will likely be slower). + + "mod" specifies if a button down event in the + interior of the window with a modifier key (Alt, Shift, + etc.) down should indicate a wireframe opportunity. + It can be "0" or "none" to skip it, "1" or "all" + to apply it to any modifier, or "Shift", "Alt", + "Control", "Meta", "Super", or "Hyper" to only + apply for that type of modifier key. + + "t1+t2+t3+t4" specify four floating point times in + seconds: t1 is how long to wait for the pointer to move, + t2 is how long to wait for the window to start moving + or being resized (for some window managers this can be + rather long), t3 is how long to keep a wireframe moving + before repainting the window. t4 is the minimum time + between sending wireframe "animations". If a slow + link is detected, these values may be automatically + changed to something better for a slow link. + +-nowireframelocal By default, mouse motion and button presses of a + user sitting at the LOCAL display are monitored for + wireframing opportunities (so that the changes will be + sent efficiently to the VNC clients). Use this option + to disable this behavior. + +-wirecopyrect mode Since the -wireframe mechanism evidently tracks moving +-nowirecopyrect windows accurately, a speedup can be obtained by + telling the VNC viewers to locally copy the translated + window region. This is the VNC CopyRect encoding: + the framebuffer update doesn't need to send the actual + new image data. + + Shorter aliases: -wcr [mode] and -nowcr + + "mode" can be "never" (same as -nowirecopyrect) + to never try the copyrect, "top" means only do it if + the window was not covered by any other windows, and + "always" means to translate the orginally unobscured + region (this may look odd as the remaining pieces come + in, but helps on a slow link). Default: "always" + + Note: there can be painting errors or slow response + when using -scale so you may want to disable CopyRect + in this case "-wirecopyrect never" on the command + line or by remote-control. Or you can also use the + "-scale xxx:nocr" scale option. + +-debug_wireframe Turn on debugging info printout for the wireframe + heuristics. "-dwf" is an alias. Specify multiple + times for more output. + +-scrollcopyrect mode Like -wirecopyrect, but use heuristics to try to guess +-noscrollcopyrect if a window has scrolled its contents (either vertically + or horizontally). This requires the RECORD X extension + to "snoop" on X applications (currently for certain + XCopyArea and XConfigureWindow X protocol requests). + Examples: Hitting in a terminal window when the + cursor was at the bottom, the text scrolls up one line. + Hitting arrow in a web browser window, the web + page scrolls up a small amount. Or scrolling with a + scrollbar or mouse wheel. + + Shorter aliases: -scr [mode] and -noscr + + This scheme will not always detect scrolls, but when + it does there is a nice speedup from using the VNC + CopyRect encoding (see -wirecopyrect). The speedup + is both in reduced network traffic and reduced X + framebuffer polling/copying. On the other hand, it may + induce undesired transients (e.g. a terminal cursor + being scrolled up when it should not be) or other + painting errors (window tearing, bunching-up, etc). + These are automatically repaired in a short period + of time. If this is unacceptable disable the feature + with -noscrollcopyrect. + + Screen clearing kludges: for testing at least, there + are some "magic key sequences" (must be done in less + than 1 second) to aid repairing painting errors that + may be seen when using this mode: + + 3 Alt_L's in a row: resend whole screen, + 4 Alt_L's in a row: reread and resend whole screen, + 3 Super_L's in a row: mark whole screen for polling, + 4 Super_L's in a row: reset RECORD context, + 5 Super_L's in a row: try to push a black screen + + note: Alt_L is the Left "Alt" key (a single key) + Super_L is the Left "Super" key (Windows flag). + Both of these are modifier keys, and so should not + generate characters when pressed by themselves. Also, + your VNC viewer may have its own refresh hot-key + or button. + + "mode" can be "never" (same as -noscrollcopyrect) + to never try the copyrect, "keys" means to try it + in response to keystrokes only, "mouse" means to + try it in response to mouse events only, "always" + means to do both. Default: "always" + + Note: there can be painting errors or slow response + when using -scale so you may want to disable CopyRect + in this case "-scrollcopyrect never" on the command + line or by remote-control. Or you can also use the + "-scale xxx:nocr" scale option. + +-scr_area n Set the minimum area in pixels for a rectangle + to be considered for the -scrollcopyrect detection + scheme. This is to avoid wasting the effort on small + rectangles that would be quickly updated the normal way. + E.g. suppose an app updated the position of its skinny + scrollbar first and then shifted the large panel + it controlled. We want to be sure to skip the small + scrollbar and get the large panel. Default: 60000 + +-scr_skip list Skip scroll detection for applications matching + the comma separated list of strings in "list". + Some applications implement their scrolling in + strange ways where the XCopyArea, etc, also applies + to invisible portions of the window: if we CopyRect + those areas it looks awful during the scroll and + there may be painting errors left after the scroll. + Soffice.bin is the worst known offender. + + Use "##" to denote the start of the application class + (e.g. "##XTerm") and "++" to denote the start + of the application instance name (e.g. "++xterm"). + The string your list is matched against is of the form + "^^WM_NAME##Class++Instance" + The "xlsclients -la" command will provide this info. + + If a pattern is prefixed with "KEY:" it only applies + to Keystroke generated scrolls (e.g. Up arrow). If it + is prefixed with "MOUSE:" it only applies to Mouse + induced scrolls (e.g. dragging on a scrollbar). + Default: ##Soffice.bin,##StarOffice,##OpenOffice + +-scr_inc list Opposite of -scr_skip: this list is consulted first + and if there is a match the window will be monitored + via RECORD for scrolls irrespective of -scr_skip. + Use -scr_skip '*' to skip anything that does not match + your -scr_inc. Use -scr_inc '*' to include everything. + +-scr_keys list For keystroke scroll detection, only apply the RECORD + heuristics to the comma separated list of keysyms in + "list". You may find the RECORD overhead for every + one of your keystrokes disrupts typing too much, but you + don't want to turn it off completely with "-scr mouse" + and -scr_parms does not work or is too confusing. + + The listed keysyms can be numeric or the keysym + names in the header file or from the + xev(1) program. Example: "-scr_keys Up,Down,Return". + One probably wants to have application specific lists + (e.g. for terminals, etc) but that is too icky to think + about for now... + + If "list" begins with the "-" character the list + is taken as an exclude list: all keysyms except those + list will be considered. The special string "builtin" + expands to an internal list of keysyms that are likely + to cause scrolls. BTW, by default modifier keys, + Shift_L, Control_R, etc, are skipped since they almost + never induce scrolling by themselves. + +-scr_term list Yet another cosmetic kludge. Apply shell/terminal + heuristics to applications matching comma separated + list (same as for -scr_skip/-scr_inc). For example an + annoying transient under scroll detection is if you + hit Enter in a terminal shell with full text window, + the solid text cursor block will be scrolled up. + So for a short time there are two (or more) block + cursors on the screen. There are similar scenarios, + (e.g. an output line is duplicated). + + These transients are induced by the approximation of + scroll detection (e.g. it detects the scroll, but not + the fact that the block cursor was cleared just before + the scroll). In nearly all cases these transient errors + are repaired when the true X framebuffer is consulted + by the normal polling. But they are distracting, so + what this option provides is extra "padding" near the + bottom of the terminal window: a few extra lines near + the bottom will not be scrolled, but rather updated + from the actual X framebuffer. This usually reduces + the annoying artifacts. Use "none" to disable. + Default: "term" + +-scr_keyrepeat lo-hi If a key is held down (or otherwise repeats rapidly) and + this induces a rapid sequence of scrolls (e.g. holding + down an Arrow key) the "scrollcopyrect" detection + and overhead may not be able to keep up. A time per + single scroll estimate is performed and if that estimate + predicts a sustainable scrollrate of keys per second + between "lo" and "hi" then repeated keys will be + DISCARDED to maintain the scrollrate. For example your + key autorepeat may be 25 keys/sec, but for a large + window or slow link only 8 scrolls per second can be + sustained, then roughly 2 out of every 3 repeated keys + will be discarded during this period. Default: "4-20" + +-scr_parms string Set various parameters for the scrollcopyrect mode. + The format is similar to that for -wireframe and packed + with lots of parameters: + + Format: T+B+L+R,t1+t2+t3,s1+s2+s3+s4+s5 + Default: 0+64+32+32,0.02+0.10+0.9,0.03+0.06+0.5+0.1+5.0 + + If you leave nothing between commas: ",," the default + value is used. If you don't specify enough commas, + the trailing parameters are set to their defaults. + + "T+B+L+R" indicates four integers for how close in + pixels the pointer has to be from the Top, Bottom, Left, + or Right edges of the window to consider scrollcopyrect. + If -wireframe overlaps it takes precedence. This is a + speedup to quickly exclude a window from being watched + for scrollcopyrect: set them all to zero to not try + the speedup (things like selecting text will likely + be slower). + + "t1+t2+t3" specify three floating point times in + seconds that apply to scrollcopyrect detection with + *Keystroke* input: t1 is how long to wait after a key + is pressed for the first scroll, t2 is how long to keep + looking after a Keystroke scroll for more scrolls. + t3 is how frequently to try to update surrounding + scrollbars outside of the scrolling area (0.0 to + disable) + + "s1+s2+s3+s4+s5" specify five floating point times + in seconds that apply to scrollcopyrect detection with + *Mouse* input: s1 is how long to wait after a mouse + button is pressed for the first scroll, s2 is how long + to keep waiting for additional scrolls after the first + Mouse scroll was detected. s3 is how frequently to + try to update surrounding scrollbars outside of the + scrolling area (0.0 to disable). s4 is how long to + buffer pointer motion (to try to get fewer, bigger + mouse scrolls). s5 is the maximum time to spend just + updating the scroll window without updating the rest + of the screen. + +-fixscreen string Periodically "repair" the screen based on settings + in "string". Hopefully you won't need this option, + it is intended for cases when the -scrollcopyrect or + -wirecopyrect features leave too many painting errors, + but it can be used for any scenario. This option + periodically performs costly operations and so + interactive response may be reduced when it is on. + You can use 3 Alt_L's (the Left "Alt" key) taps in + a row (as described under -scrollcopyrect) instead to + manually request a screen repaint when it is needed. + + "string" is a comma separated list of one or more of + the following: "V=t", "C=t", "X=t", and "8=t". + In these "t" stands for a time in seconds (it is + a floating point even though one should usually use + values > 2 to avoid wasting resources). V sets how + frequently the entire screen should be sent to viewers + (it is like the 3 Alt_L's). C sets how long to wait + after a CopyRect to repaint the full screen. X sets + how frequently to reread the full X11 framebuffer from + the X server and push it out to connected viewers. + Use of X should be rare, please report a bug if you + find you need it. 8= applies only for -8to24 mode: it + sets how often the non-default visual regions of the + screen (e.g. 8bpp windows) are refreshed. Examples: + -fixscreen V=10 -fixscreen C=10 + +-debug_scroll Turn on debugging info printout for the scroll + heuristics. "-ds" is an alias. Specify it multiple + times for more output. + +-noxrecord Disable any use of the RECORD extension. This is + currently used by the -scrollcopyrect scheme and to + monitor X server grabs. + +-grab_buster Some of the use of the RECORD extension can leave a +-nograb_buster tiny window for XGrabServer deadlock. This is only if + the whole-server grabbing application expects mouse or + keyboard input before releasing the grab. It is usually + a window manager that does this. x11vnc takes care to + avoid the problem, but if caught x11vnc will freeze. + Without -grab_buster, the only solution is to go the + physical display and give it some input to satisfy the + grabbing app. Or manually kill and restart the window + manager if that is feasible. With -grab_buster, x11vnc + will fork a helper thread and if x11vnc appears to be + stuck in a grab after a period of time (20-30 sec) then + it will inject some user input: button clicks, Escape, + mouse motion, etc to try to break the grab. If you + experience a lot of grab deadlock, please report a bug. + +-debug_grabs Turn on debugging info printout with respect to + XGrabServer() deadlock for -scrollcopyrect mode. + +-debug_sel Turn on debugging info printout with respect to + PRIMARY, CLIPBOARD, and CUTBUFFER0 selections. + +-pointer_mode n Various pointer motion update schemes. "-pm" is + an alias. The problem is pointer motion can cause + rapid changes on the screen: consider the rapid + changes when you drag a large window around opaquely. + Neither x11vnc's screen polling and vnc compression + routines nor the bandwidth to the vncviewers can keep + up these rapid screen changes: everything will bog down + when dragging or scrolling. So a scheme has to be used + to "eat" much of that pointer input before re-polling + the screen and sending out framebuffer updates. The + mode number "n" can be 0 to 4 and selects one of + the schemes desribed below. + + Note that the -wireframe and -scrollcopyrect modes + complement -pointer_mode by detecting (and improving) + certain periods of "rapid screen change". + + n=0: does the same as -nodragging. (all screen polling + is suspended if a mouse button is pressed.) + + n=1: was the original scheme used to about Jan 2004: + it basically just skips -input_skip keyboard or pointer + events before repolling the screen. + + n=2 is an improved scheme: by watching the current rate + of input events it tries to detect if it should try to + "eat" additional pointer events before continuing. + + n=3 is basically a dynamic -nodragging mode: it detects + when the mouse motion has paused and then refreshes + the display. + + n=4 attempts to measures network rates and latency, + the video card read rate, and how many tiles have been + changed on the screen. From this, it aggressively tries + to push screen "frames" when it decides it has enough + resources to do so. NOT FINISHED. + + The default n is 2. Note that modes 2, 3, 4 will skip + -input_skip keyboard events (but it will not count + pointer events). Also note that these modes are not + available in -threads mode which has its own pointer + event handling mechanism. + + To try out the different pointer modes to see which + one gives the best response for your usage, it is + convenient to use the remote control function, for + example "x11vnc -R pm:4" or the tcl/tk gui (Tuning -> + pointer_mode -> n). + +-input_skip n For the pointer handling when non-threaded: try to + read n user input events before scanning display. n < 0 + means to act as though there is always user input. + Default: 10 + +-allinput Have x11vnc read and process all available client input + before proceeding. + +-input_eagerly Similar to -allinput but use the handleEventsEagerly + mechanism built into LibVNCServer. + +-speeds rd,bw,lat x11vnc tries to estimate some speed parameters that + are used to optimize scheduling (e.g. -pointer_mode + 4, -wireframe, -scrollcopyrect) and other things. + Use the -speeds option to set these manually. + The triple "rd,bw,lat" corresponds to video h/w + read rate in MB/sec, network bandwidth to clients in + KB/sec, and network latency to clients in milliseconds, + respectively. If a value is left blank, e.g. "-speeds + ,100,15", then the internal scheme is used to estimate + the empty value(s). + + Typical PC video cards have read rates of 5-10 MB/sec. + If the framebuffer is in main memory instead of video + h/w (e.g. SunRay, shadowfb, dummy driver, Xvfb), the + read rate may be much faster. "x11perf -getimage500" + can be used to get a lower bound (remember to factor + in the bytes per pixel). It is up to you to estimate + the network bandwith and latency to clients. For the + latency the ping(1) command can be used. + + For convenience there are some aliases provided, + e.g. "-speeds modem". The aliases are: "modem" for + 6,4,200; "dsl" for 6,100,50; and "lan" for 6,5000,1 + +-wmdt string For some features, e.g. -wireframe and -scrollcopyrect, + x11vnc has to work around issues for certain window + managers or desktops (currently kde and xfce). + By default it tries to guess which one, but it can + guess incorrectly. Use this option to indicate which + wm/dt. "string" can be "gnome", "kde", "cde", + "xfce", or "root" (classic X wm). Anything else + is interpreted as "root". + +-debug_pointer Print debugging output for every pointer event. +-debug_keyboard Print debugging output for every keyboard event. + Same as -dp and -dk, respectively. Use multiple + times for more output. + +-defer time Time in ms to delay sending updates to connected clients + (deferUpdateTime) Default: 20 + +-wait time Time in ms to pause between screen polls. Used to cut + down on load. Default: 20 + +-extra_fbur n Perform extra FrameBufferUpdateRequests checks to + try to be in better sync with the client's requests. + What this does is perform extra polls of the client + socket at critical times (before '-defer' and '-wait' + calls.) The default is n=1. Set to a larger number to + insert more checks or set to n=0 to disable. A downside + of these extra calls is that more mouse input may be + processed than desired. + +-wait_ui factor Factor by which to cut the -wait time if there + has been recent user input (pointer or keyboard). + Improves response, but increases the load whenever you + are moving the mouse or typing. Default: 2.00 +-setdefer n When the -wait_ui mechanism cuts down the wait time ms, + set the defer time to the same ms value. n=1 to enable, + 0 to disable, and -1 to set defer to 0 (no delay). + Similarly, 2 and -2 indicate 'urgent_update' mode should + be used to push the updates even sooner. Default: 1 +-nowait_bog Do not detect if the screen polling is "bogging down" + and sleep more. Some activities with no user input can + slow things down a lot: consider a large terminal window + with a long build running in it continuously streaming + text output. By default x11vnc will try to detect this + (3 screen polls in a row each longer than 0.25 sec with + no user input), and sleep up to 1.5 secs to let things + "catch up". Use this option to disable that detection. +-slow_fb time Floating point time in seconds to delay all screen + polling. For special purpose usage where a low frame + rate is acceptable and desirable, but you want the + user input processed at the normal rate so you cannot + use -wait. +-xrefresh time Floating point time in seconds to indicate how often to + do the equivalent of xrefresh(1) to force all windows + (in the viewable area if -id, -sid, or -clip is used) + to repaint themselves. Use this only if applications + misbehave by not repainting themselves properly. + See also -noxdamage. +-nap Monitor activity and if it is low take longer naps +-nonap between screen polls to really cut down load when idle. + Default: take naps +-sb time Time in seconds after NO activity (e.g. screen blank) + to really throttle down the screen polls (i.e. sleep + for about 1.5 secs). Use 0 to disable. Default: 60 + Set the env. var. X11VNC_SB_FACTOR to scale it. + +-readtimeout n Set LibVNCServer rfbMaxClientWait to n seconds. On + slow links that take a long time to paint the first + screen LibVNCServer may hit the timeout and drop the + connection. Default: 20 seconds. +-ping n Send a 1x1 framebuffer update to all clients every n + seconds (e.g. to try to keep a network connection alive) + +-nofbpm If the system supports the FBPM (Frame Buffer Power +-fbpm Management) extension (i.e. some Sun systems), then + prevent the video h/w from going into a reduced power + state when VNC clients are connected. + + FBPM capable video h/w save energy when the workstation + is idle by going into low power states (similar to DPMS + for monitors). This interferes with x11vnc's polling + of the framebuffer data. + + "-nofbpm" means prevent FBPM low power states whenever + VNC clients are connected, while "-fbpm" means to not + monitor the FBPM state at all. See the xset(1) manpage + for details. -nofbpm is basically the same as running + "xset fbpm force on" periodically. Default: -fbpm + +-nodpms If the system supports the DPMS (Display Power Management +-dpms Signaling) extension, then prevent the monitor from + going into a reduced power state when VNC clients + are connected. + + DPMS reduced power monitor states are a good thing + and you normally want the power down to take place + (usually x11vnc has no problem exporting the display in + this state). You probably only want to use "-nodpms" + to work around problems with Screen Savers kicking + on in DPMS low power states. There is known problem + with kdesktop_lock on KDE where the screen saver keeps + kicking in every time user input stops for a second + or two. Specifying "-nodpms" works around it. + + "-nodpms" means prevent DPMS low power states whenever + VNC clients are connected, while "-dpms" means to not + monitor the DPMS state at all. See the xset(1) manpage + for details. -nodpms is basically the same as running + "xset dpms force on" periodically. Default: -dpms + +-forcedpms If the system supports the DPMS (Display Power + Management Signaling) extension, then try to keep the + monitor in a powered off state. This is to prevent + nosey people at the physical display from viewing what + is on the screen. Be sure to lock the screen before + disconnecting. + + This method is far from bullet proof, e.g. suppose + someone attaches a non-DPMS monitor, or loads the + machine so that there is a gap of time before x11vnc + restores the powered off state? On many machines if + he floods it with keyboard and mouse input he can see + flashes of what is on the screen before the DPMS off + state is reestablished. For this to work securely + there would need to be support in the X server to do + this exactly rather than approximately with DPMS. + +-clientdpms As -forcedpms but only when VNC clients are connected. + +-noserverdpms The UltraVNC ServerInput extension is supported. + This allows the VNC viewer to click a button that will + cause the server (x11vnc) to try to disable keyboard + and mouse input at the physical display and put the + monitor in dpms powered off state. Use this option to + skip powering off the monitor. + +-noultraext Disable the following UltraVNC extensions: SingleWindow + and ServerInput. The others managed by LibVNCServer + (textchat, 1/n scaling, rfbEncodingUltra) are not. + +-chatwindow Place a local UltraVNC chat window on the X11 display + that x11vnc is polling. That way the person on the VNC + viewer-side can chat with the person at the physical + X11 console. (e.g. helpdesk w/o telephone) + + For this to work the SSVNC package (version 1.0.21 or + later) MUST BE installed on the system where x11vnc runs + and the 'ssvnc' command must be available in $PATH. + The ssvncviewer is used as a chat window helper. + See http://www.karlrunge.com/x11vnc/ssvnc.html + + This option implies '-rfbversion 3.6' so as to trick + UltraVNC viewers, otherwise they assume chat is not + available. To specify a different rfbversion, place + it after the -chatwindow option on the cmdline. + + See also the remote control 'chaton' and 'chatoff' + actions. These can also be set from the tkx11vnc GUI. + +-noxdamage Do not use the X DAMAGE extension to detect framebuffer + changes even if it is available. Use -xdamage if your + default is to have it off. + + x11vnc's use of the DAMAGE extension: 1) significantly + reduces the load when the screen is not changing much, + and 2) detects changed areas (small ones by default) + more quickly. + + Currently the DAMAGE extension is overly conservative + and often reports large areas (e.g. a whole terminal + or browser window) as damaged even though the actual + changed region is much smaller (sometimes just a few + pixels). So heuristics were introduced to skip large + areas and use the damage rectangles only as "hints" + for the traditional scanline polling. The following + tuning parameters are introduced to adjust this + behavior: + +-xd_area A Set the largest DAMAGE rectangle area "A" (in + pixels: width * height) to trust as truly damaged: + the rectangle will be copied from the framebuffer + (slow) no matter what. Set to zero to trust *all* + rectangles. Default: 20000 +-xd_mem f Set how long DAMAGE rectangles should be "remembered", + "f" is a floating point number and is in units of the + scanline repeat cycle time (32 iterations). The default + (1.0) should give no painting problems. Increase it if + there are problems or decrease it to live on the edge + (perhaps useful on a slow machine). + +-sigpipe string Broken pipe (SIGPIPE) handling. "string" can be + "ignore" or "exit". For "ignore" LibVNCServer + will handle the abrupt loss of a client and continue, + for "exit" x11vnc will cleanup and exit at the 1st + broken connection. + + This option is not really needed since LibVNCServer + is doing the correct thing now for quite some time. + However, for convenience you can use it to ignore other + signals, e.g. "-sigpipe ignore:HUP,INT,TERM" in case + that would be useful for some sort of application. + You can also put "exit:.." in the list to have x11vnc + cleanup on the listed signals. "-sig" is an alias + for this option if you don't like the 'pipe'. Example: + -sig ignore:INT,TERM,exit:USR1 + +-threads Whether or not to use the threaded LibVNCServer +-nothreads algorithm [rfbRunEventLoop] if libpthread is available. + In this mode new threads (one for input and one + for output) are created to handle each new client. + Default: -nothreads. + + Thread stability is much improved in version 0.9.8. + + Multiple clients in threaded mode should be stable + for the ZRLE encoding on all platforms. The Tight and + Zlib encodings are currently only stable on Linux for + multiple clients. Compile with -DTLS=__thread if your + OS and compiler and linker support it. + + For resizes (randr, etc.) set this env. var. to the number + of milliseconds to sleep: X11VNC_THREADS_NEW_FB_SLEEP + at various places in the do_new_fb() action. This is to + let various activities settle. Default is about 500ms. + + Multiple clients in threaded mode could yield better + performance for 'class-room' broadcasting usage; also in + -appshare broadcast mode. See also the -reflect option. + +-fs f If the fraction of changed tiles in a poll is greater + than f, the whole screen is updated. Default: 0.75 +-gaps n Heuristic to fill in gaps in rows or cols of n or + less tiles. Used to improve text paging. Default: 4 +-grow n Heuristic to grow islands of changed tiles n or wider + by checking the tile near the boundary. Default: 3 +-fuzz n Tolerance in pixels to mark a tiles edges as changed. + Default: 2 +-debug_tiles Print debugging output for tiles, fb updates, etc. + +-snapfb Instead of polling the X display framebuffer (fb) + for changes, periodically copy all of X display fb + into main memory and examine that copy for changes. + (This setting also applies for non-X -rawfb modes). + Under some circumstances this will improve interactive + response, or at least make things look smoother, but in + others (most!) it will make the response worse. If the + video h/w fb is such that reading small tiles is very + slow this mode could help. To keep the "framerate" + up the screen size x bpp cannot be too large. Note that + this mode is very wasteful of memory I/O resources + (it makes full screen copies even if nothing changes). + It may be of use in video capture-like applications, + webcams, or where window tearing is a problem. + +-rawfb string Instead of polling X, poll the memory object specified + in "string". + + For file polling, to memory map mmap(2) a file use: + "map:/path/to/a/file@WxHxB", with framebuffer Width, + Height, and Bits per pixel. "mmap:..." is the + same. + + If there is trouble with mmap, use "file:/..." + for slower lseek(2) based reading. + + Use "snap:..." to imply -snapfb mode and the "file:" + access (this is for unseekable devices that only provide + the fb all at once, e.g. a video camera provides the + whole frame). + + For shared memory segments string is of the form: + "shm:N@WxHxB" which specifies a shmid N and with + WxHxB as above. See shmat(1) and ipcs(1) + + If you do not supply a type "map" is assumed if + the file exists (see the next paragraphs for some + exceptions to this.) + + If string is "setup:cmd", then the command "cmd" + is run and the first line from it is read and used + as "string". This allows initializing the device, + determining WxHxB, etc. These are often done as root + so take care. + + If the string begins with "video", see the VIDEO4LINUX + discussion below where the device may be queried for + (and possibly set) the framebuffer parameters. + + If the string begins with "console", "/dev/fb", + "fb", or "vt", see the LINUX CONSOLE discussion + below where the framebuffer device is opened and + keystrokes (and possibly mouse events) are inserted + into the console. + + If the string begins with "vnc", see the VNC HOST + discussion below where the framebuffer is taken as that + of another remote VNC server. + + Optional suffixes are ":R/G/B", "+O", and "#VWxVH" to + specify red, green, and blue masks (in hex), offset into + the memory object, and virtual width and height. + + If the masks are not provided x11vnc guesses them based on + the bpp (if the colors look wrong, you need to provide the + masks.) + + Another optional suffix is the Bytes Per Line which in + some cases is not WxB/8. Specify it as WxHxB-BPL + e.g. 800x600x16-2048. This could be a normal width + 1024 at 16bpp fb, but only width 800 shows up. + + The last optional suffix is virtual dimensions VWxVH. Some + devices will double buffer the display in the framebuffer, + allowing updating contents of display and then "panning" + to the buffer via yoffset. x11vnc will map the virutal + size specified by the options stead of just WxH, and track + yoffset appropriately so remote clients get all updates to + the frame buffer. + + So the full format is: mode:file@WxHxB:R/G/B+O-BPL#VWxVH + + Examples: + -rawfb shm:210337933@800x600x32:ff/ff00/ff0000 + -rawfb map:/dev/fb0@1024x768x32 + -rawfb map:/dev/fb0@800x480x16#800x960 + -rawfb map:/tmp/Xvfb_screen0@640x480x8+3232 + -rawfb file:/tmp/my.pnm@250x200x24+37 + -rawfb file:/dev/urandom@128x128x8 + -rawfb snap:/dev/video0@320x240x24 -24to32 + -rawfb video0 + -rawfb video -pipeinput VID + -rawfb console + -rawfb vt2 + -rawfb vnc:somehost:0 + + (see ipcs(1) and fbset(1) for the first two examples) + + In general all user input is discarded by default (see + the -pipeinput option for how to use a helper program + to insert). Most of the X11 (screen, keyboard, mouse) + options do not make sense and many will cause this + mode to crash, so please think twice before setting or + changing them in a running x11vnc. + + If you DO NOT want x11vnc to close the X DISPLAY in + rawfb mode, prepend a "+" e.g. +file:/dev/fb0... + Keeping the display open enables the default + remote-control channel, which could be useful. + Alternatively, if you specify -noviewonly, then the + mouse and keyboard input are STILL sent to the X + display, this usage should be very rare, i.e. doing + something strange with /dev/fb0. + + If the device is not "seekable" (e.g. webcam) try + reading it all at once in full snaps via the "snap:" + mode (note: this is a resource hog). If you are using + file: or map: AND the device needs to be reopened for + *every* snapfb snapshot, set the environment variable: + SNAPFB_RAWFB_RESET=1 as well. + + If you want x11vnc to dynamically transform a 24bpp + rawfb to 32bpp (note that this will be slower) also + supply the -24to32 option. This would be useful for, + say, a video camera that delivers the pixel data as + 24bpp packed RGB. This is the default under "video" + mode if the bpp is 24. + + Normally the bits per pixel, B, is 8, 16, or 32 (or + rarely 24), however there is also some support for + B < 8 (e.g. old graphics displays 4 bpp or 1 bpp). + In this case you certainly must supply the masks as + well: WxHxB:R/G/B. The pixels will be padded out to + 8 bpp using depth 8 truecolor. The scheme currently + does not work with snap fb (ask if interested.) B=1 + monochrome example: file:/dev/urandom@128x128x1:1/1/1 + Some other like this are 128x128x2:3/3/3 128x128x4:7/7/7 + + For B < 8 framebuffers you can also set the env. var + RAWFB_CGA=1 to try a CGA mapping for B=4 (e.g. linux + vga16fb driver.) Note with low bpp and/or resolution + VGA and VGA16 modes on the Linux console one's attempt + to export them via x11vnc can often be thwarted due to + special color palettes, pixel packings, and even video + painting buffering. OTOH, often experimenting with the + RGB masks can yield something recognizable. + + VIDEO4LINUX: on Linux some attempt is made to handle + video devices (webcams or TV tuners) automatically. + The idea is the WxHxB will be extracted from the + device itself. So if you do not supply "@WxHxB... + parameters x11vnc will try to determine them. It first + tries the v4l API if that support has been compiled in. + Otherwise it will run the v4l-info(1) external program + if it is available. + + The simplest examples are "-rawfb video" and "-rawfb + video1" which imply the device file /dev/video and + /dev/video1, respectively. You can also supply the + /dev if you like, e.g. "-rawfb /dev/video0" + + Since the video capture device framebuffer usually + changes continuously (e.g. brightness fluctuations), + you may want to use the -wait, -slow_fb, or -defer + options to lower the "framerate" to cut down on + network VNC traffic. + + A more sophisticated video device scheme allows + initializing the device's settings using: + + -rawfb video: + + The prefix could also be, as above, e.g. "video1:" to + specify the device file. The v4l API must be available + for this to work. Otherwise, you will need to try + to initialize the device with an external program, + e.g. xawtv, spcaview, and hope they persist when x11vnc + re-opens the device. + + is a comma separated list of key=value pairs. + The device's brightness, color, contrast, and hue can + be set to percentages, e.g. br=80,co=50,cn=44,hu=60. + + The device filename can be set too if needed (if it + does not start with "video"), e.g. fn=/dev/qcam. + + The width, height and bpp of the framebuffer can be + set via, e.g., w=160,h=120,bpp=16. + + Related to the bpp above, the pixel format can be set + via the fmt=XXX, where XXX can be one of: GREY, HI240, + RGB555, RGB565, RGB24, and RGB32 (with bpp 8, 8, 16, 16, + 24, and 32 respectively). See http://www.linuxtv.org + for more info (V4L api). + + For TV/rf tuner cards one can set the tuning mode + via tun=XXX where XXX can be one of PAL, NTSC, SECAM, + or AUTO. + + One can switch the input channel by the inp=XXX setting, + where XXX is the name of the input channel (Television, + Composite1, S-Video, etc). Use the name that is in the + information about the device that is printed at startup. + + For input channels with tuners (e.g. Television) one + can change which station is selected by the sta=XXX + setting. XXX is the station number. Currently only + the ntsc-cable-us (US cable) channels are built into + x11vnc. See the -freqtab option below to supply one + from xawtv. If XXX is greater than 500, then it is + interpreted as a raw frequency in KHz. + + Example: + + -rawfb video:br=80,w=320,h=240,fmt=RGB32,tun=NTSC,sta=47 + + one might need to add inp=Television too for the input + channel to be TV if the card doesn't come up by default + in that one. + + Note that not all video capture devices will support + all of the above settings. + + See the -pipeinput VID option below for a way to control + the settings through the VNC Viewer via keystrokes. + As a shortcut, if the string begins "Video.." instead + of "video.." then -pipeinput VID is implied. + + As above, if you specify a "@WxHxB..." after the + string they are used verbatim: the device + is not queried for the current values. Otherwise the + device will be queried. + + LINUX CONSOLE: The following describes some ways to + view and possibly interact with the Linux text/graphics + console (i.e. not X11 XFree86/Xorg) + + Note: If the LibVNCServer LinuxVNC program is on your + system you may want to use that instead of the following + method because it will be faster and more accurate + for the Linux text console and includes mouse support. + There is, however, the basic LinuxVNC functionality in + x11vnc if you replace "console" with "vt" in the + examples below. + + If the rawfb string begins with "console" the + framebuffer device /dev/fb0 is opened and /dev/tty0 is + opened too. The latter is used to inject keystrokes + (not all are supported, but the basic ones are). + You will need to be root to inject keystrokes, but + not necessarily to open /dev/fb0. /dev/tty0 refers to + the active VT, to indicate one explicitly, use, e.g., + "console2" for /dev/tty2, etc. by indicating the + specific VT number. + + For the Linux framebuffer device, /dev/fb0, (fb1, + etc) to be enabled the appropriate kernel drivers must + be loaded. E.g. vesafb or vga16fb and also by setting + the boot parameter vga=0x301 (or 0x314, 0x317, etc.) + (The vga=... method is the preferred way; set your + machines up that way.) Otherwise there will be a + 'No such device' error. You can also load a Linux + framebuffer driver specific to your make of video card + for more functionality. Once the machine is booted one + can often 'modprobe' the fb driver as root to obtain + a framebuffer device. + + If you cannot get /dev/fb0 working on Linux, try + using the LinuxVNC emulation mode by "-rawfb vtN" + where N = 1, ... 6 is the Linux Virtual Terminal (aka + virtual console) you wish to view, e.g. "-rawfb vt2". + Unlike /dev/fb mode, it need not be the active Virtual + Terminal. Note that this mode can only show text and + not graphics. x11vnc polls the text in /dev/vcsaN + + Set the env. var. RAWFB_VCSA_BW=1 to disable colors in + the "vtN" mode (i.e. black and white only.) If you + do not prefer the default 16bpp set RAWFB_VCSA_BPP to + 8 or 32. If you need to tweak the rawfb parameters by + using the 'console_guess' string printed at startup, + be sure to indicate the snap: method. + + uinput: If the Linux version appears to be 2.6 + or later and the "uinput" module appears to be + present (modprobe uinput), then the uinput method + will be used instead of /dev/ttyN. uinput allows + insertion of BOTH keystrokes and mouse input and so it + preferred when accessing graphical (e.g. QT-embedded) + linux console apps. It also provides more accurate + keystroke insertion. See -pipeinput UINPUT below for + more information on this mode; you will have to use + -pipeinput if you want to tweak any UINPUT parameters. + You may also want to also use the -nodragging and + -cursor none options. Use "console0", etc or + -pipeinput CONSOLE to force the /dev/ttyN method. + + Note you can change the Linux VT remotely using the + chvt(1) command to make the one you want be the active + one (e.g. 'chvt 3'). Sometimes switching out and back + corrects the framebuffer's graphics state. For the + "-rawfb vtN" mode there is no need to switch the VT's. + + To skip input injecting entirely use "consolex" + or "vtx". + + The string "/dev/fb0" (1, etc.) can be used instead + of "console". This can be used to specify a different + framebuffer device, e.g. /dev/fb1. As a shortcut the + "/dev/" can be dropped. If the name is something + nonstandard, use "console:/dev/foofb" + + If you do not want x11vnc to guess the framebuffer's + WxHxB and masks automatically (sometimes the kernel + gives incorrect information), specify them with a @WxHxB + (and optional :R/G/B masks) at the end of the string. + + Examples: + -rawfb console + -rawfb /dev/fb0 (same) + -rawfb console3 (force /dev/tty3) + -rawfb consolex (no keystrokes or mouse) + -rawfb console:/dev/nonstd + -rawfb console -pipeinput UINPUT:accel=4.0 + -rawfb vt3 (/dev/tty3 w/o /dev/fb0) + + VNC HOST: if the -rawfb string is of the form + "vnc:host:N" then the VNC display "N" on the remote + VNC server "host" is connected to (i.e. x11vnc acts as + a VNC client itself) and that framebuffer is exported. + + This mode is really only of use if you are trying + to improve performance in the case of many (e.g. > + 10) simultaneous VNC viewers, and you try a divide + and conquer scheme to reduce bandwidth and improve + responsiveness. (However, another user found this mode + useful to export a demo display through a slow link: + then multiple demo viewers connected to the reflecting + x11vnc on the fast side of the link, and so avoided + all of the demo viewers going through the slow link.) + + For example, if there will be 64 simultaneous VNC + viewers this can lead to a lot of redundant VNC traffic + to and from the server host:N, extra CPU usage, + and all viewers response can be reduced by having + to wait for writes to the slowest client to finish. + However, if you set up 8 reflectors/repeaters started + with option -rawfb vnc:host:N, then there are only + 8 connections to host:N. Each repeater then handles + 8 vnc viewer connections thereby spreading the load + around. In classroom broadcast usage, try to put the + repeaters on different switches. This mode is the same + as -reflect host:N. Replace "host:N" by "listen" + or "listen:port" for a reverse connection. + + Overall performance will not be as good as a single + direct connection because, among other things, + there is an additional level of framebuffer polling + and pointer motion can still induce many changes per + second that must be propagated. Tip: if the remote VNC + is x11vnc doing wireframing, or an X display that does + wireframing that gives much better response than opaque + window dragging. Consider the -nodragging option if + the problem is severe. + + The env. var. X11VNC_REFLECT_PASSWORD can be set to + the password needed to log into the vnc host server, or + to "file:path_to_file" to indicate a file containing + the password as its first line. + + To set the pixel format that x11vnc requests as a VNC + CLIENT set the env. vars: X11VNC_REFLECT_bitsPerSample + X11VNC_REFLECT_samplesPerPixel, and + X11VNC_REFLECT_bytesPerPixel; the defaults are 8, 3, 4. + 2, 3, 1 would give a low color mode. See the function + rfbGetClient() in libvncclient for more info. + + The VNC HOST mode implies -shared. Use -noshared as + a subsequent cmdline option to disable sharing. + +-freqtab file For use with "-rawfb video" for TV tuner devices to + specify station frequencies. Instead of using the built + in ntsc-cable-us mapping of station number to frequency, + use the data in file. For stations that are not + numeric, e.g. SE20, they are placed above the highest + numbered station in the order they are found. Example: + "-freqtab /usr/X11R6/share/xawtv/europe-west.list" + You can make your own freqtab by copying the xawtv + format. + +-pipeinput cmd This option lets you supply an external command in + "cmd" that x11vnc will pipe all of the user input + events to in a simple format. In -pipeinput mode by + default x11vnc will not process any of the user input + events. If you prefix "cmd" with "tee:" it will + both send them to the pipe command and process them. + For a description of the format run "-pipeinput + tee:/bin/cat". Another prefix is "reopen" which + means to reopen pipe if it exits. Separate multiple + prefixes with commas. + + In combination with -rawfb one might be able to + do amusing things (e.g. control non-X devices). + To facilitate this, if -rawfb is in effect then the + value is stored in X11VNC_RAWFB_STR for the pipe command + to use if it wants. Do 'env | grep X11VNC' for more. + + Built-in pipeinput modes (no external program required): + + If cmd is "VID" and you are using the -rawfb for a + video capture device, then an internal list of keyboard + mappings is used to set parameters of the video. + The mappings are: + + "B" and "b" adjust the brightness up and down. + "H" and "h" adjust the hue. + "C" and "c" adjust the colour. + "N" and "n" adjust the contrast. + "S" and "s" adjust the size of the capture screen. + "I" and "i" cycle through input channels. + Up and Down arrows adjust the station (if a tuner) + F1, F2, ..., F6 will switch the video capture pixel + format to HI240, RGB565, RGB24, RGB32, RGB555, and + GREY respectively. See -rawfb video for details. + + If cmd is "CONSOLE" or "CONSOLEn" where n + is a Linux console number, then the linux console + keystroke insertion to /dev/ttyN (see -rawfb console) + is performed. + + If cmd begins with "UINPUT" then the Linux uinput + module is used to insert both keystroke and mouse events + to the Linux console (see -rawfb above). This usually + is the /dev/input/uinput device file (you may need to + create it with "mknod /dev/input/uinput c 10 223" + and insert the module with "modprobe uinput". + + The UINPUT mode currently only does US keyboards (a + scan code option may be added), and not all keysyms + are supported. But it is probably more accurate than + the "CONSOLE" method. + + You may want to use the options -cursor none and + -nodragging in this mode. + + Additional tuning options may be supplied via: + UINPUT:opt1,opt2,... (a comma separated list). If an + option begins with "/" it is taken as the uinput + device file. + + Which uinput is injected can be controlled by an option + string made of the characters "K", "M", and "B" + (see the -input option), e.g. "KM" allows keystroke + and motion but not button clicks. + + A UINPUT option of the form: accel=f, or accel=fx+fy + sets the mouse motion "acceleration". This is used + to correct raw mouse relative motion into how much the + application cursor moves (x11vnc has no control over, + or knowledge of how the windowing application interprets + the raw mouse motions). Typically the acceleration + for an X display is 2 (see xset "m" option). "f" + is a floating point number, e.g. 3.0. Use "fx+fy" + if you need to supply different corrections for x and y. + + Note: the default acceleration is 2.0 since it seems + both X and qt-embedded often (but not always) use + this value. + + Even with a correct accel setting the mouse position + will get out of sync (probably due to a mouse + "threshold" setting where the acceleration doe not + apply, set xset(1)). The option reset=N sets the + number of ms (default 150) after which the cursor is + attempted to be reset (by forcing the mouse to (0, + 0) via small increments and then back out to (x, y) + in 1 jump), This correction seems to be needed but can + cause jerkiness or unexpected behavior with menus, etc. + Use reset=0 to disable. + + If you set the env. var X11VNC_UINPUT_THRESHOLDS then + the thresh=n mode will be enabled. It is currently + not working well. If |dx| <= thresh and |dy| < thresh + no acceleration is applied. Use "thresh=+n" |dx| + + |dy| < thresh to be used instead (X11?) + + Example: + -pipeinput UINPUT:accel=4.0 -cursor none + + If the uinput device has an absolute pointer (as opposed + to a normal mouse that is a relative pointer) you can + specify the option "abs". Note that a touchpad + on a laptop is an absolute device to some degree. + This (usually) avoids all the problems with mouse + acceleration. If x11vnc has trouble deducing the + size of the device, use "abs=WxH". Furthermore, + if the device is a touchscreen (assumed to have an + absolute pointer) use "touch" or "touch=WxH". + For touchscreens, when a mouse button is pressed, + a pressure increase is injected, and when the button + is released a pressure of zero is injected. + + If touch has been set, use "touch_always=1" to + indicate whenever the mouse moves with no button + pressed, a touch event of zero pressure should be + sent anyway. Also use "btn_touch=1" to indicate a + BTN_TOUCH keystroke press or release should be sent + instead of a pressure change. Set "dragskip=n" to + skip n dragged mouse touches (with pressure applied) + before injecting one. To indicate the pressure that + should be sent when there is a button click for a + touchscreen device, specify pressure=n, e.g. n=5. The + default is n=1. + + If a touch screen is being used ("touch" above) + and it is having its input processed by tslib, you can + specify the tslib calibration file via tslib_cal=. + For example, tslib_cal=/etc/pointercal. To get accurate + or even usable positioning this is required when tslib + is in use. + + The Linux uinput mechanism can be bypassed and one can + write input events DIRECTLY to the devices instead. + To do this, specify one or more of the following + for the input classes: direct_rel= + direct_abs= direct_btn= or + direct_key=. The file is usually + something like /dev/input/event1 but you can specify + any device file or pipe. You must specify each one + of the above classes even if they correspond to the + same device file (rel/abs and btn are often the same.) + Look at the file /proc/bus/input/devices to get an idea + what is available and the device filenames. Note: + The /dev/input/mouse* devices do not seem to work, + use the corresponding /dev/input/event* file instead. + Any input class not directly specified as above will be + handled via the uinput mechanism. To disable creating a + uinput device (and thereby discarding unhandled input), + specify "nouinput". + + Examples: + + -pipeinput UINPUT:direct_abs=/dev/input/event1 + + this was used on a qtmoko Neo freerunner (armel): + + -pipeinput UINPUT:touch,tslib_cal=/etc/pointercal, + direct_abs=/dev/input/event1,nouinput,dragskip=4 + + (where the long line has been split into two.) + + You can set the env. var X11VNC_UINPUT_DEBUG=1 or higher + to get debugging output for UINPUT mode. + +-macnodim For the native MacOSX server, disable dimming. +-macnosleep For the native MacOSX server, disable display sleep. +-macnosaver For the native MacOSX server, disable screensaver. +-macnowait For the native MacOSX server, do not wait for the + user to switch back to his display. +-macwheel n For the native MacOSX server, set the mouse wheel + speed to n (default 5). +-macnoswap For the native MacOSX server, do not swap mouse + buttons 2 and 3. +-macnoresize For the native MacOSX server, do not resize or reset + the framebuffer even if it is detected that the screen + resolution or depth has changed. +-maciconanim n For the native MacOSX server, set n to the number + of milliseconds that the window iconify/deiconify + animation takes. In -ncache mode this value will be + used to skip the animation if possible. (default 400) +-macmenu For the native MacOSX server, in -ncache client-side + caching mode, try to cache pull down menus (not perfect + because they have animated fades, etc.) +-macuskbd For the native MacOSX server, use the original + keystroke insertion code based on a US keyboard. +-macnoopengl For the native MacOSX server, do not use OpenGL for + screen capture, but rather use the original, deprecated + raw memory access method: addr = CGDisplayBaseAddress(). +-macnorawfb For the native MacOSX server, disable the raw memory + address screen capture method. + + MACOSX NOTE: There are some deprecated MacOSX interfaces + to inject keyboard and mouse events and the raw memory + access method is deprecated as well (however, OpenGL + will be preferred if available because it is faster.) + One can force not using any deprecated interfaces at + compile time by setting -DX11VNC_MACOSX_NO_DEPRECATED=1 + in CPPFLAGS. Or to turn them off one by one: + -DX11VNC_MACOSX_NO_DEPRECATED_LOCALEVENTS=1, + -DX11VNC_MACOSX_NO_DEPRECATED_POSTEVENTS=1 or + -DX11VNC_MACOSX_NO_DEPRECATED_FRAMEBUFFER=1 + At run time, for testing and workarounds, one can + disable them by using: + -env X11VNC_MACOSX_NO_DEPRECATED=1 + -env X11VNC_MACOSX_NO_DEPRECATED_LOCALEVENTS=1 + -env X11VNC_MACOSX_NO_DEPRECATED_POSTEVENTS=1 or + -env X11VNC_MACOSX_NO_DEPRECATED_FRAMEBUFFER=1 + Note: When doing either of these for the mouse input + not everything works currently, e.g. double clicks and + wireframing. Also, screen resolution and pixel depth + changes will not be automatically detected unless the + deprecated framebuffer interfaces are allowed. + + Conversely, if you are compiling on an + older machine that does not have some of + the newer interfaces, you may need to specify + -DX11VNC_MACOSX_NO_CGEVENTCREATESCROLLWHEELEVENT + -DX11VNC_MACOSX_NO_CGEVENTCREATEMOUSEEVENT or + -DX11VNC_MACOSX_NO_CGEVENTCREATEKEYBOARDEVENT. Use + -DX11VNC_MACOSX_USE_GETMAINDEVICE to regain the very + old QuickDraw GetMainDevice() interface (rare...) + +-gui [gui-opts] Start up a simple tcl/tk gui based on the remote + control options -remote/-query described below. + Requires the "wish" program to be installed on the + machine. "gui-opts" is not required: the default + is to start up both the full gui and x11vnc with the + gui showing up on the X display in the environment + variable DISPLAY. + + "gui-opts" can be a comma separated list of items. + Currently there are these types of items: 1) a gui + mode, a 2) gui "simplicity", 3) the X display the + gui should display on, 4) a "tray" or "icon" mode, + and 5) a gui geometry. + + 1) The gui mode can be "start", "conn", or "wait" + "start" is the default mode above and is not required. + "conn" means do not automatically start up x11vnc, + but instead just try to connect to an existing x11vnc + process. "wait" means just start the gui and nothing + else (you will later instruct the gui to start x11vnc + or connect to an existing one.) + + 2) The gui simplicity is off by default (a power-user + gui with all options is presented) To start with + something less daunting supply the string "simple" + ("ez" is an alias for this). Once the gui is + started you can toggle between the two with "Misc -> + simple_gui". + + 3) Note the possible confusion regarding the potentially + two different X displays: x11vnc polls one, but you + may want the gui to appear on another. For example, if + you ssh in and x11vnc is not running yet you may want + the gui to come back to you via your ssh redirected X + display (e.g. localhost:10). + + If you do not specify a gui X display in "gui-opts" + then the DISPLAY environment variable and -display + option are tried (in that order). Regarding the x11vnc + X display the gui will try to communication with, it + first tries -display and then DISPLAY. For example, + "x11vnc -display :0 -gui otherhost:0", will remote + control an x11vnc polling :0 and display the gui on + otherhost:0 The "tray/icon" mode below reverses this + preference, preferring to display on the x11vnc display. + + 4) When "tray" or "icon" is specified, the gui + presents itself as a small icon with behavior typical + of a "system tray" or "dock applet". The color + of the icon indicates status (connected clients) and + there is also a balloon status. Clicking on the icon + gives a menu from which properties, etc, can be set and + the full gui is available under "Advanced". To be + fully functional, the gui mode should be "start" + (the default). + + Note that tray or icon mode will imply the -forever + x11vnc option (if the x11vnc server is started along + with the gui) unless -connect or -connect_or_exit has + been specified. So x11vnc (and the tray/icon gui) + will wait for more connections after the first client + disconnects. If you want only one viewer connection + include the -once option. + + For "icon" the gui just a small standalone window. + For "tray" it will attempt to embed itself in the + "system tray" if possible. If "=setpass" is appended the +n + at startup the X11 user will be prompted to set the + VNC session password. If = is appended + that icon will attempt to embed itself in the window + given by hexnumber. Use =noadvanced to disable the + full gui. (To supply more than one, use "+" sign). + E.g. -gui tray=setpass and -gui icon=0x3600028 + + Other modes: "full", the default and need not be + specified. "-gui none", do not show a gui, useful + to override a ~/.x11vncrc setting, etc. + + 5) When "geom=+X+Y" is specified, that geometry + is passed to the gui toplevel. This is the icon in + icon/tray mode, or the full gui otherwise. You can + also specify width and height, i.e. WxH+X+Y, but it + is not recommended. In "tray" mode the geometry is + ignored unless the system tray manager does not seem + to be running. One could imagine using something like + "-gui tray,geom=+4000+4000" with a display manager + to keep the gui invisible until someone logs in... + + More icon tricks, "icon=minimal" gives an icon just + with the VNC display number. You can also set the font + with "iconfont=...". The following could be useful: + "-gui icon=minimal,iconfont=5x8,geom=24x10+0-0" + + General examples of the -gui option: "x11vnc -gui", + "x11vnc -gui ez" "x11vnc -gui localhost:10", + "x11vnc -gui conn,host:0", "x11vnc -gui tray,ez" + "x11vnc -gui tray=setpass" + + If you do not intend to start x11vnc from the gui + (i.e. just remote control an existing one), then the + gui process can run on a different machine from the + x11vnc server as long as X permissions, etc. permit + communication between the two. + + FONTS: On some systems the tk fonts can be too small, + jagged, or otherwise unreadable. There are 4 env vars + you can set to be the tk font you prefer: + + X11VNC_FONT_BOLD main font for menus and buttons. + X11VNC_FONT_FIXED font for fixed width text. + + X11VNC_FONT_BOLD_SMALL tray icon font. + X11VNC_FONT_REG_SMALL tray icon menu font. + + The last two only apply for the tray icon mode. + + Here are some examples: + + -env X11VNC_FONT_BOLD='Helvetica -16 bold' + -env X11VNC_FONT_FIXED='Courier -14' + -env X11VNC_FONT_REG_SMALL='Helvetica -12' + + You can put the lines like the above (without the + quotes) in your ~/.x11vncrc file to avoid having to + specify them on the x11vnc command line. + +-remote command Remotely control some aspects of an already running + x11vnc server. "-R" and "-r" are aliases for + "-remote". After the remote control command is + sent to the running server the 'x11vnc -remote ...' + x11vnc command exits. You can often use the -query + command (see below) to see if the x11vnc server + processed your -remote command. + + The default communication channel is that of X + properties (specifically X11VNC_REMOTE), and so this + command must be run with correct settings for DISPLAY + and possibly XAUTHORITY to connect to the X server + and set the property. Alternatively, use the -display + and -auth options to set them to the correct values. + The running server cannot use the -novncconnect option + because that disables the communication channel. + See below for alternate channels. + + For example: 'x11vnc -remote stop' (which is the same as + 'x11vnc -R stop') will close down the x11vnc server. + 'x11vnc -R shared' will enable shared connections, and + 'x11vnc -R scale:3/4' will rescale the desktop. + + To use a different name for the X11 property (e.g. to + have separate communication channels for multiple + x11vnc's on the same display) set the X11VNC_REMOTE + environment variable to the string you want, for + example: -env X11VNC_REMOTE=X11VNC_REMOTE_12345 + Both sides of the channel must use the same unique name. + + To run a bunch of commands in a sequence use something + like: x11vnc -R 'script:firstcmd;secondcmd;...' + + Use x11vnc -R script:file=/path/to/file to read commands + from a file (can be multi-line and use the comment '#' + character in the normal way. The ';' separator must + still be used to separate each command.) + + To not try to contact another x11vnc process and instead + just run the command (or query) directly, prefix the + command with the string "DIRECT:" + + The following -remote/-R commands are supported: + + stop terminate the server, same as "quit" + "exit" or "shutdown". + ping see if the x11vnc server responds. + return is: ans=ping: + ping:mystring as above, but use your own unique string. + return is: ans=ping:mystring: + blacken try to push a black fb update to all + clients (due to timings a client + could miss it). Same as "zero", also + "zero:x1,y1,x2,y2" for a rectangle. + refresh send the entire fb to all clients. + reset recreate the fb, polling memory, etc. + id:windowid set -id window to "windowid". empty + or "root" to go back to root window + sid:windowid set -sid window to "windowid" + id_cmd:cmd cmds: raise, lower, map, unmap, iconify, + move:dXdY, resize:dWdH, geom:WxH+X+Y. dX + dY, dW, and dH must have a leading "+" + or "-" e.g.: move:-30+10 resize:+20+35 + also: wm_delete, wm_name:string and + icon_name:string. Also id_cmd:win=N:cmd + waitmapped wait until subwin is mapped. + nowaitmapped do not wait until subwin is mapped. + clip:WxH+X+Y set -clip mode to "WxH+X+Y" + flashcmap enable -flashcmap mode. + noflashcmap disable -flashcmap mode. + shiftcmap:n set -shiftcmap to n. + notruecolor enable -notruecolor mode. + truecolor disable -notruecolor mode. + overlay enable -overlay mode (if applicable). + nooverlay disable -overlay mode. + overlay_cursor in -overlay mode, enable cursor drawing. + overlay_nocursor disable cursor drawing. same as + nooverlay_cursor. + 8to24 enable -8to24 mode (if applicable). + no8to24 disable -8to24 mode. + 8to24_opts:str set the -8to24 opts to "str". + 24to32 enable -24to32 mode (if applicable). + no24to32 disable -24to32 mode. + visual:vis set -visual to "vis" + scale:frac set -scale to "frac" + scale_cursor:f set -scale_cursor to "f" + viewonly enable -viewonly mode. + noviewonly disable -viewonly mode. + shared enable -shared mode. + noshared disable -shared mode. + forever enable -forever mode. + noforever disable -forever mode. + timeout:n reset -timeout to n, if there are + currently no clients, exit unless one + connects in the next n secs. + tightfilexfer enable filetransfer for NEW clients. + notightfilexfer disable filetransfer for NEW clients. + ultrafilexfer enable filetransfer for clients. + noultrafilexfer disable filetransfer for clients. + rfbversion:n.m set -rfbversion for new clients. + http enable http client connections. + nohttp disable http client connections. + deny deny any new connections, same as "lock" + nodeny allow new connections, same as "unlock" + avahi enable avahi service advertising. + noavahi disable avahi service advertising. + mdns enable avahi service advertising. + nomdns disable avahi service advertising. + zeroconf enable avahi service advertising. + nozeroconf disable avahi service advertising. + connect:host do reverse connection to host, "host" + may be a comma separated list of hosts + or host:ports. See -connect. Passwords + required as with fwd connections. + See X11VNC_REVERSE_CONNECTION_NO_AUTH=1 + disconnect:host disconnect any clients from "host" + same as "close:host". Use host + "all" to close all current clients. + If you know the client internal hex ID, + e.g. 0x3 (returned by "-query clients" + and RFB_CLIENT_ID) you can use that too. + proxy:host:port set reverse connection proxy (empty to + disable). + allowonce:host For the next connection only, allow + connection from "host". In -ssl mode + two connections are allowed (i.e. Fetch + Cert) unless X11VNC_NO_SSL_ALLOW_TWICE=1 + allow:hostlist set -allow list to (comma separated) + "hostlist". See -allow and -localhost. + Do not use with -allow /path/to/file + Use "+host" to add a single host, and + use "-host" to delete a single host + localhost enable -localhost mode + nolocalhost disable -localhost mode + listen:str set -listen to str, empty to disable. + noipv6 enable -noipv6 mode. + ipv6 disable -noipv6 mode. + noipv4 enable -noipv4 mode. + ipv4 disable -noipv4 mode. + 6 enable -6 IPv6 listening mode. + no6 disable -6 IPv6 listening mode. + lookup disable -nolookup mode. + nolookup enable -nolookup mode. + lookup disable -nolookup mode. + input:str set -input to "str", empty to disable. + grabkbd enable -grabkbd mode. + nograbkbd disable -grabkbd mode. + grabptr enable -grabptr mode. + nograbptr disable -grabptr mode. + grabalways enable -grabalways mode. + nograbalways disable -grabalways mode. + grablocal:n set -grablocal to n. + client_input:str set the K, M, B -input on a per-client + basis. select which client as for + disconnect, e.g. client_input:host:MB + or client_input:0x2:K + accept:cmd set -accept "cmd" (empty to disable). + afteraccept:cmd set -afteraccept (empty to disable). + gone:cmd set -gone "cmd" (empty to disable). + noshm enable -noshm mode. + shm disable -noshm mode (i.e. use shm). + flipbyteorder enable -flipbyteorder mode, you may need + to set noshm for this to do something. + noflipbyteorder disable -flipbyteorder mode. + onetile enable -onetile mode. (you may need to + set shm for this to do something) + noonetile disable -onetile mode. + solid enable -solid mode + nosolid disable -solid mode. + solid_color:color set -solid color (and apply it). + blackout:str set -blackout "str" (empty to disable). + See -blackout for the form of "str" + (basically: WxH+X+Y,...) + Use "+WxH+X+Y" to append a single + rectangle use "-WxH+X+Y" to delete one + xinerama enable -xinerama mode. (if applicable) + noxinerama disable -xinerama mode. + xtrap enable -xtrap input mode(if applicable) + noxtrap disable -xtrap input mode. + xrandr enable -xrandr mode. (if applicable) + noxrandr disable -xrandr mode. + xrandr_mode:mode set the -xrandr mode to "mode". + rotate:mode set the -rotate mode to "mode". + padgeom:WxH set -padgeom to WxH (empty to disable) + If WxH is "force" or "do" the padded + geometry fb is immediately applied. + quiet enable -quiet mode. + noquiet disable -quiet mode. + modtweak enable -modtweak mode. + nomodtweak enable -nomodtweak mode. + xkb enable -xkb modtweak mode. + noxkb disable -xkb modtweak mode. + capslock enable -capslock mode. + nocapslock disable -capslock mode. + skip_lockkeys enable -skip_lockkeys mode. + noskip_lockkeys disable -skip_lockkeys mode. + skip_keycodes:str enable -xkb -skip_keycodes "str". + sloppy_keys enable -sloppy_keys mode. + nosloppy_keys disable -sloppy_keys mode. + skip_dups enable -skip_dups mode. + noskip_dups disable -skip_dups mode. + add_keysyms enable -add_keysyms mode. + noadd_keysyms stop adding keysyms. those added will + still be removed at exit. + clear_mods enable -clear_mods mode and clear them. + noclear_mods disable -clear_mods mode. + clear_keys enable -clear_keys mode and clear them. + noclear_keys disable -clear_keys mode. + clear_locks do the clear_locks action. + clear_all do the clear_all action. + keystate have x11vnc print current keystate. + remap:str set -remap "str" (empty to disable). + See -remap for the form of "str" + (basically: key1-key2,key3-key4,...) + Use "+key1-key2" to append a single + keymapping, use "-key1-key2" to delete. + norepeat enable -norepeat mode. + repeat disable -norepeat mode. + nofb enable -nofb mode. + fb disable -nofb mode. + bell enable bell (if supported). + nobell disable bell. + sendbell ring the bell now. + nosel enable -nosel mode. + sel disable -nosel mode. + noprimary enable -noprimary mode. + primary disable -noprimary mode. + nosetprimary enable -nosetprimary mode. + setprimary disable -nosetprimary mode. + noclipboard enable -noclipboard mode. + clipboard disable -noclipboard mode. + nosetclipboard enable -nosetclipboard mode. + setclipboard disable -nosetclipboard mode. + seldir:str set -seldir to "str" + resend_cutbuffer resend the most recent CUTBUFFER0 copy + resend_clipboard resend the most recent CLIPBOARD copy + resend_primary resend the most recent PRIMARY copy + cursor:mode enable -cursor "mode". + show_cursor enable showing a cursor. + noshow_cursor disable showing a cursor. (same as + "nocursor") + cursor_drag enable cursor changes during drag. + nocursor_drag disable cursor changes during drag. + arrow:n set -arrow to alternate n. + xfixes enable xfixes cursor shape mode. + noxfixes disable xfixes cursor shape mode. + alphacut:n set -alphacut to n. + alphafrac:f set -alphafrac to f. + alpharemove enable -alpharemove mode. + noalpharemove disable -alpharemove mode. + alphablend disable -noalphablend mode. + noalphablend enable -noalphablend mode. + cursorshape disable -nocursorshape mode. + nocursorshape enable -nocursorshape mode. + cursorpos disable -nocursorpos mode. + nocursorpos enable -nocursorpos mode. + xwarp enable -xwarppointer mode. + noxwarp disable -xwarppointer mode. + always_inject enable -always_inject mode. + noalways_inject disable -always_inject mode. + buttonmap:str set -buttonmap "str", empty to disable + dragging disable -nodragging mode. + nodragging enable -nodragging mode. + ncache reenable -ncache mode. + noncache disable -ncache mode. + ncache_size:n set -ncache size to n. + ncache_cr enable -ncache_cr mode. + noncache_cr disable -ncache_cr mode. + ncache_no_moveraise enable no_moveraise mode. + noncache_no_moveraise disable no_moveraise mode. + ncache_no_dtchange enable ncache_no_dtchange mode. + noncache_no_dtchange disable ncache_no_dtchange mode. + ncache_old_wm enable ncache_old_wm mode. + noncache_old_wm disable ncache_old_wm mode. + ncache_no_rootpixmap enable ncache_no_rootpixmap. + noncache_no_rootpixmap disable ncache_no_rootpixmap. + ncache_reset_rootpixmap recheck the root pixmap, ncrp + ncache_keep_anims enable ncache_keep_anims. + noncache_keep_anims disable ncache_keep_anims. + ncache_pad:n set -ncache_pad to n. + wireframe enable -wireframe mode. same as "wf" + nowireframe disable -wireframe mode. same as "nowf" + wireframe:str enable -wireframe mode string. + wireframe_mode:str enable -wireframe mode string. + wireframelocal enable wireframelocal. same as "wfl" + nowireframe disable wireframelocal. same as "nowfl" + wirecopyrect:str set -wirecopyrect string. same as "wcr:" + scrollcopyrect:str set -scrollcopyrect string. same "scr" + noscrollcopyrect disable -scrollcopyrect mode. "noscr" + scr_area:n set -scr_area to n + scr_skip:list set -scr_skip to "list" + scr_inc:list set -scr_inc to "list" + scr_keys:list set -scr_keys to "list" + scr_term:list set -scr_term to "list" + scr_keyrepeat:str set -scr_keyrepeat to "str" + scr_parms:str set -scr_parms parameters. + fixscreen:str set -fixscreen to "str". + noxrecord disable all use of RECORD extension. + xrecord enable use of RECORD extension. + reset_record reset RECORD extension (if avail.) + pointer_mode:n set -pointer_mode to n. same as "pm" + input_skip:n set -input_skip to n. + allinput enable use of -allinput mode. + noallinput disable use of -allinput mode. + input_eagerly enable use of -input_eagerly mode. + noinput_eagerly disable use of -input_eagerly mode. + ssltimeout:n set -ssltimeout to n. + speeds:str set -speeds to str. + wmdt:str set -wmdt to str. + debug_pointer enable -debug_pointer, same as "dp" + nodebug_pointer disable -debug_pointer, same as "nodp" + debug_keyboard enable -debug_keyboard, same as "dk" + nodebug_keyboard disable -debug_keyboard, same as "nodk" + keycode:n inject keystroke 'keycode' (xmodmap -pk) + keycode:n,down inject 'keycode' (down=0,1) + keysym:str inject keystroke 'keysym' (number/name) + keysym:str,down inject 'keysym' (down=0,1) + ptr:x,y,mask inject pointer event x, y, button-mask + fakebuttonevent:button,down direct XTestFakeButtonEvent. + sleep:t sleep floating point time t. + get_xprop:p get X property named 'p'. + set_xprop:p:val set X property named 'p' to 'val'. + p -> id=NNN:p for hex/dec window id. + wininfo:id get info about X window id. use 'root' + for root window, use +id for children. + grab_state get state of pointer and keyboard grab. + pointer_pos print XQueryPointer x,y cursor position. + pointer_x print XQueryPointer x cursor position. + pointer_y print XQueryPointer y cursor position. + pointer_same print XQueryPointer ptr on same screen. + pointer_root print XQueryPointer curr ptr rootwin. + pointer_mask print XQueryPointer button and mods mask + mouse_x print x11vnc's idea of cursor position. + mouse_y print x11vnc's idea of cursor position. + noop do nothing. + defer:n set -defer to n ms,same as deferupdate:n + wait:n set -wait to n ms. + extra_fbur:n set -extra_fbur to n. + wait_ui:f set -wait_ui factor to f. + setdefer:n set -setdefer to -2,-1,0,1, or 2. + wait_bog disable -nowait_bog mode. + nowait_bog enable -nowait_bog mode. + slow_fb:f set -slow_fb to f seconds. + xrefresh:f set -xrefresh to f seconds. + readtimeout:n set read timeout to n seconds. + nap enable -nap mode. + nonap disable -nap mode. + sb:n set -sb to n s, same as screen_blank:n + fbpm disable -nofbpm mode. + nofbpm enable -nofbpm mode. + dpms disable -nodpms mode. + nodpms enable -nodpms mode. + forcedpms enable -forcedpms mode. + noforcedpms disable -forcedpms mode. + clientdpms enable -clientdpms mode. + noclientdpms disable -clientdpms mode. + noserverdpms enable -noserverdpms mode. + serverdpms disable -noserverdpms mode. + noultraext enable -noultraext mode. + ultraext disable -noultraext mode. + chatwindow enable local chatwindow mode. + nochatwindow disable local chatwindow mode. + chaton begin chat using local window. + chatoff end chat using local window. + xdamage enable xdamage polling hints. + noxdamage disable xdamage polling hints. + xd_area:A set -xd_area max pixel area to "A" + xd_mem:f set -xd_mem remembrance to "f" + fs:frac set -fs fraction to "frac", e.g. 0.5 + gaps:n set -gaps to n. + grow:n set -grow to n. + fuzz:n set -fuzz to n. + snapfb enable -snapfb mode. + nosnapfb disable -snapfb mode. + rawfb:str set -rawfb mode to "str". + uinput_accel:f set uinput_accel to f. + uinput_thresh:n set uinput_thresh to n. + uinput_reset:n set uinput_reset to n ms. + uinput_always:n set uinput_always to 1/0. + progressive:n set LibVNCServer -progressive slice + height parameter to n. + desktop:str set -desktop name to str for new clients. + rfbport:n set -rfbport to n. + macnosaver enable -macnosaver mode. + macsaver disable -macnosaver mode. + macnowait enable -macnowait mode. + macwait disable -macnowait mode. + macwheel:n set -macwheel to n. + macnoswap enable -macnoswap mouse button mode. + macswap disable -macnoswap mouse button mode. + macnoresize enable -macnoresize mode. + macresize disable -macnoresize mode. + maciconanim:n set -maciconanim to n. + macmenu enable -macmenu mode. + macnomenu disable -macmenu mode. + macuskbd enable -macuskbd mode. + macnouskbd disable -macuskbd mode. + httpport:n set -httpport to n. + httpdir:dir set -httpdir to dir (and enable http). + enablehttpproxy enable -enablehttpproxy mode. + noenablehttpproxy disable -enablehttpproxy mode. + alwaysshared enable -alwaysshared mode. + noalwaysshared disable -alwaysshared mode. + (may interfere with other options) + nevershared enable -nevershared mode. + nonevershared disable -nevershared mode. + (may interfere with other options) + dontdisconnect enable -dontdisconnect mode. + nodontdisconnect disable -dontdisconnect mode. + (may interfere with other options) + debug_xevents enable debugging X events. + nodebug_xevents disable debugging X events. + debug_xdamage enable debugging X DAMAGE mechanism. + nodebug_xdamage disable debugging X DAMAGE mechanism. + debug_wireframe enable debugging wireframe mechanism. + nodebug_wireframe disable debugging wireframe mechanism. + debug_scroll enable debugging scrollcopy mechanism. + nodebug_scroll disable debugging scrollcopy mechanism. + debug_tiles enable -debug_tiles + nodebug_tiles disable -debug_tiles + debug_grabs enable -debug_grabs + nodebug_grabs disable -debug_grabs + debug_sel enable -debug_sel + nodebug_sel disable -debug_sel + debug_ncache enable -debug_ncache + nodebug_ncache disable -debug_ncache + dbg enable -dbg crash shell + nodbg disable -dbg crash shell + + noremote disable the -remote command processing, + it cannot be turned back on. + + bcx_xattach:str This remote control command is for + use with the BARCO xattach program or the x2x program. + Both of these programs are for 'pointer and keyboard' + sharing between separate X displays. In general the + two displays are usually nearby, e.g. on the same desk, + and this allows the user to share a single pointer and + keyboard between them. The user moves the mouse to + an edge and then the mouse pointer appears to 'jump' + to the other display screen. Thus it emulates what a + single X server would do for two screens (e.g. :0.0 and + :0.1) The illusion of a single Xserver with multiple + screens is achieved by forwarding events to the 2nd + one via the XTEST extension. + + What the x11vnc bcx_xattach command does is to perform + some pointer movements to try to INDUCE xattach/x2x + to 'jump' to the other display. In what follows the + 'master' display refers to the one that when it has + 'focus' it is basically doing nothing besides watching + for the mouse to go over an edge. The 'slave' + display refers to the one to which the mouse and + keyboard is redirected to once an edge in the master + has been crossed. Note that the x11vnc executing the + bcx_xattach command MUST be the one connected to the + *master* display. + + Also note that when input is being redirected (via + XTEST) from the master display to the slave display, + the master display's pointer and keyboard are *grabbed* + by xattach/x2x. x11vnc can use this info to verify that + the master/slave mode change has taken place correctly. + If you specify the "ifneeded" option (see below) + and the initial grab state is that of the desired + final state, then no pointer movements are injected + and "DONE,GRAB_OK" is returned. + + "str" must contain one of "up", "down", "left", + or "right" to indicate the direction of the 'jump'. + "str" must also contain one of "master_to_slave" + or "slave_to_master" to indicate the type of mode + change induced by the jump. Use "M2S" and "S2M" + as shorter aliases. + + "str" may be a "+" separated list of additional + tuning options. The "shift=n" option indicates an + offset shift position away from (0,0) (default 20). + "final=x+y" specifies the final position of the cursor + at the end of the normal move sequence; default 30+30. + "extra_move=x+y" means to do one more pointer move + after "final" to x+y. "dt=n" sets the sleep time + in milliseconds between pointer moves (default: 40ms) + "retry=n" specifies the maximum number of retries if + the grab state change fails. "ifneeded" means to not + apply the pointer movements if the initial grab state is + that of the desired final state. "nograbcheck" means + to not check if the grab state changed as expected and + only apply the pointer movements (default is to check + the grab states.) + + If you do not specify "up", etc., to bcx_xattach + nothing will be attempted and the command returns + the string FAIL,NO_DIRECTION_SPECIFIED. If you do + not specify "master_to_slave" or "M2S", etc., to + bcx_xattach nothing will be attempted and the command + returns the string FAIL,NO_MODE_CHANGE_SPECIFIED. + + Otherwise, the returned string will contain "DONE". + It will be "DONE,GRAB_OK" if the grab state changed + as expected (or if "ifneeded" was supplied and + the initial grab state was already the desired + one.) If the initial grab state was incorrect, + but the final grab state was correct then it is + "DONE,GRAB_FAIL_INIT". If the initial grab state + was correct, but the final grab state was incorrect + then it is "DONE,GRAB_FAIL_FINAL". If both are + incorrect it will be "DONE,GRAB_FAIL". Under grab + failure the string will be followed by ":p1,k1-p2,k2" + where p1,k1 indicates the initial pointer and keyboard + grab states and p2,k2 the final ones. If GRAB_FAIL or + GRAB_FAIL_FINAL occurs, the action will be retried up + to 3 times; trying to reset the state and sleeping a + bit between each try. Set retry=n to adjust the number + of retries, zero to disable retries. + + Examples: + -R bcx_xattach:down+M2S + -R bcx_xattach:up+S2M + -R bcx_xattach:up+S2M+nograbcheck+dt=30 + -R bcx_xattach:down+M2S+extra_move=100+100 + + or use -Q instead of -R to retrieve the result text. + + End of the bcx_xattach:str description. + + The vncconnect(1) command from standard VNC + distributions may also be used if string is prefixed + with "cmd=" E.g. 'vncconnect cmd=stop'. Under some + circumstances xprop(1) can used if it supports -set + (see the FAQ). + + If "-connect /path/to/file" has been supplied to the + running x11vnc server then that file can be used as a + communication channel (this is the only way to remote + control one of many x11vnc's polling the same X display) + Simply run: 'x11vnc -connect /path/to/file -remote ...' + or you can directly write to the file via something + like: "echo cmd=stop > /path/to/file", etc. + +-query variable Like -remote, except just query the value of + "variable". "-Q" is an alias for "-query". + Multiple queries can be done by separating variables + by commas, e.g. -query var1,var2. The results come + back in the form ans=var1:value1,ans=var2:value2,... + to the standard output. If a variable is read-only, + it comes back with prefix "aro=" instead of "ans=". + + Some -remote commands are pure actions that do not make + sense as variables, e.g. "stop" or "disconnect", in + these cases the value returned is "N/A". To direct a + query straight to the X11VNC_REMOTE property or connect + file use "qry=..." instead of "cmd=..." + + ans= stop quit exit shutdown ping resend_cutbuffer + resend_clipboard resend_primary blacken zero refresh + reset close disconnect id_cmd id sid waitmapped + nowaitmapped clip flashcmap noflashcmap shiftcmap + truecolor notruecolor overlay nooverlay overlay_cursor + overlay_yescursor nooverlay_nocursor nooverlay_cursor + nooverlay_yescursor overlay_nocursor 8to24 no8to24 + 8to24_opts 24to32 no24to32 visual scale scale_cursor + viewonly noviewonly shared noshared forever noforever + once timeout tightfilexfer notightfilexfer ultrafilexfer + noultrafilexfer rfbversion deny lock nodeny unlock avahi + mdns zeroconf noavahi nomdns nozeroconf connect proxy + allowonce allow noipv6 ipv6 noipv4 ipv4 no6 6 localhost + nolocalhost listen lookup nolookup accept afteraccept + gone shm noshm flipbyteorder noflipbyteorder onetile + noonetile solid_color solid nosolid blackout xinerama + noxinerama xtrap noxtrap xrandr noxrandr xrandr_mode + rotate padgeom quiet q noquiet modtweak nomodtweak xkb + noxkb capslock nocapslock skip_lockkeys noskip_lockkeys + skip_keycodes sloppy_keys nosloppy_keys skip_dups + noskip_dups add_keysyms noadd_keysyms clear_mods + noclear_mods clear_keys noclear_keys clear_all + clear_locks keystate remap repeat norepeat fb nofb bell + nobell sendbell sel nosel primary noprimary setprimary + nosetprimary clipboard noclipboard setclipboard + nosetclipboard seldir cursorshape nocursorshape + cursorpos nocursorpos cursor_drag nocursor_drag cursor + show_cursor noshow_cursor nocursor arrow xfixes noxfixes + xdamage noxdamage xd_area xd_mem alphacut alphafrac + alpharemove noalpharemove alphablend noalphablend + xwarppointer xwarp noxwarppointer noxwarp always_inject + noalways_inject buttonmap dragging nodragging ncache_cr + noncache_cr ncache_no_moveraise noncache_no_moveraise + ncache_no_dtchange noncache_no_dtchange + ncache_no_rootpixmap noncache_no_rootpixmap + ncache_reset_rootpixmap ncrp ncache_keep_anims + noncache_keep_anims ncache_old_wm noncache_old_wm + ncache_pad ncache noncache ncache_size debug_ncache + nodebug_ncache wireframe_mode wireframe wf nowireframe + nowf wireframelocal wfl nowireframelocal nowfl + wirecopyrect wcr nowirecopyrect nowcr scr_area + scr_skip scr_inc scr_keys scr_term scr_keyrepeat + scr_parms scrollcopyrect scr noscrollcopyrect + noscr fixscreen noxrecord xrecord reset_record + pointer_mode pm input_skip allinput noallinput + input_eagerly noinput_eagerly input grabkbd nograbkbd + grabptr nograbptr grabalways nograbalways grablocal + client_input ssltimeout speeds wmdt debug_pointer dp + nodebug_pointer nodp debug_keyboard dk nodebug_keyboard + nodk keycode keysym ptr fakebuttonevent sleep get_xprop + set_xprop wininfo bcx_xattach deferupdate defer + setdefer extra_fbur wait_ui wait_bog nowait_bog + slow_fb xrefresh wait readtimeout nap nonap sb + screen_blank fbpm nofbpm dpms nodpms clientdpms + noclientdpms forcedpms noforcedpms noserverdpms + serverdpms noultraext ultraext chatwindow nochatwindow + chaton chatoff fs gaps grow fuzz snapfb nosnapfb + rawfb uinput_accel uinput_thresh uinput_reset + uinput_always progressive rfbport http nohttp httpport + httpdir enablehttpproxy noenablehttpproxy alwaysshared + noalwaysshared nevershared noalwaysshared dontdisconnect + nodontdisconnect desktop debug_xevents nodebug_xevents + debug_xevents debug_xdamage nodebug_xdamage + debug_xdamage debug_wireframe nodebug_wireframe + debug_wireframe debug_scroll nodebug_scroll debug_scroll + debug_tiles dbt nodebug_tiles nodbt debug_tiles + debug_grabs nodebug_grabs debug_sel nodebug_sel dbg + nodbg macnosaver macsaver nomacnosaver macnowait macwait + nomacnowait macwheel macnoswap macswap nomacnoswap + macnoresize macresize nomacnoresize maciconanim macmenu + macnomenu nomacmenu macuskbd nomacuskbd noremote + + aro= noop display vncdisplay icon_mode autoport + loop loopbg desktopname guess_desktop guess_dbus + http_url auth xauth users rootshift clipshift scale_str + scaled_x scaled_y scale_numer scale_denom scale_fac_x + scale_fac_y scaling_blend scaling_nomult4 scaling_pad + scaling_interpolate inetd privremote unsafe safer nocmds + passwdfile unixpw unixpw_nis unixpw_list ssl ssl_pem + sslverify stunnel stunnel_pem https httpsredir usepw + using_shm logfile o flag rmflag rc norc h help V version + lastmod bg sigpipe threads readrate netrate netlatency + pipeinput clients client_count pid ext_xtest ext_xtrap + ext_xrecord ext_xkb ext_xshm ext_xinerama ext_overlay + ext_xfixes ext_xdamage ext_xrandr rootwin num_buttons + button_mask mouse_x mouse_y grab_state pointer_pos + pointer_x pointer_y pointer_same pointer_root + pointer_mask bpp depth indexed_color dpy_x dpy_y wdpy_x + wdpy_y off_x off_y cdpy_x cdpy_y coff_x coff_y rfbauth + passwd viewpasswd + +-QD variable Just like -query variable, but returns the default + value for that parameter (no running x11vnc server + is consulted) + +-sync By default -remote commands are run asynchronously, that + is, the request is posted and the program immediately + exits. Use -sync to have the program wait for an + acknowledgement from the x11vnc server that command was + processed (somehow). On the other hand -query requests + are always processed synchronously because they have + to wait for the answer. + + Also note that if both -remote and -query requests are + supplied on the command line, the -remote is processed + first (synchronously: no need for -sync), and then + the -query request is processed in the normal way. + This allows for a reliable way to see if the -remote + command was processed by querying for any new settings. + Note however that there is timeout of a few seconds + (see the next paragraph) so if the x11vnc takes longer + than that to process the requests the requester will + think that a failure has taken place. + + The default is to wait 3.5 seconds. Or if cmd=stop + only 1.0 seconds. If cmd matches 'script:' then it + will wait up to 10.0 seconds. Set X11VNC_SYNC_TIMEOUT + to the number of seconds you want it to wait. + +-query_retries str If a query fails to get a response from an x11vnc + server, retry up to n times. "str" is specified as + n[:t][/match] Optionally the delay between tries may + be specified by "t" a floating point time (default + 0.5 seconds.) Note: the response is not checked for + validity or whether it corresponds to the query sent. + The query "ping:mystring" may be used to help uniquely + identify the query. Optionally, a matching string after + a "/" will be used to check the result text. Up to + n retries will take place until the matching string is + found in the output text. If the match string is never + found the program's exit code is 1; if the match is + found it exits with 0. Note that there may be stdout + printed for each retry (i.e. multiple lines printed + out to stdout.) + Example: -query_retries 4:1.5/grab_state + +-remote_prefix str Enable a remote-control communication channel for + connected VNC clients. str is a non-empty string. If a + VNC client sends rfbCutText having the prefix "str" + then the part after it is processed as though it were + sent via 'x11vnc -remote ...'. If it begins with + neither 'cmd=' nor 'qry=' then 'qry=' is assumed. + Any corresponding output text for that remote control + command is sent back to all client as rfbCutText. + The returned output is also prefixed with "str". + Example: -remote_prefix DO_THIS: + + Note that enabling -remote_prefix allows the remote + VNC viewers to run x11vnc -remote commands. Do not + use this option if they are not to be trusted. + +-noremote Do not process any remote control commands or queries. +-yesremote Do process remote control commands or queries. + Default: -yesremote + + A note about security wrt remote control commands. + If someone can connect to the X display and change + the property X11VNC_REMOTE, then they can remotely + control x11vnc. Normally access to the X display is + protected. Note that if they can modify X11VNC_REMOTE + on the X server, they have enough permissions to also + run their own x11vnc and thus have complete control + of the desktop. If the "-connect /path/to/file" + channel is being used, obviously anyone who can write + to /path/to/file can remotely control x11vnc. So be + sure to protect the X display and that file's write + permissions. See -privremote below. + + If you are paranoid and do not think -noremote is + enough, to disable the X11VNC_REMOTE property channel + completely use -novncconnect, or use the -safer option + that shuts many things off. + +-unsafe A few remote commands are disabled by default + (currently: id:pick, accept:, gone:, and + rawfb:setup:) because they are associated with + running external programs. If you specify -unsafe, then + these remote-control commands are allowed. Note that + you can still specify these parameters on the command + line, they just cannot be invoked via remote-control. +-safer Equivalent to: -novncconnect -noremote and prohibiting + -gui and the -connect file. Shuts off communcation + channels. +-privremote Perform some sanity checks and disable remote-control + commands if it appears that the X DISPLAY and/or + connectfile can be accessed by other users. Once + remote-control is disabled it cannot be turned back on. +-nocmds No external commands (e.g. system(3), popen(3), exec(3)) + will be run at all. +-allowedcmds list "list" contains a comma separated list of the only + external commands that can be run. The full list of + associated options is: + + stunnel, ssl, unixpw, WAIT, zeroconf, id, accept, + afteraccept, gone, pipeinput, v4l-info, rawfb-setup, + dt, gui, ssh, storepasswd, passwdfile, custom_passwd, + findauth, crash. + + See each option's help to learn the associated external + command. Note that the -nocmds option takes precedence + and disables all external commands. + +-deny_all For use with -remote nodeny: start out denying all + incoming clients until "-remote nodeny" is used to + let them in. +``` + +These options are passed to LibVNCServer: + +``` +-rfbport port TCP port for RFB protocol +-rfbwait time max time in ms to wait for RFB client +-rfbauth passwd-file use authentication on RFB protocol + (use 'storepasswd' to create a password file) +-rfbversion 3.x Set the version of the RFB we choose to advertise +-permitfiletransfer permit file transfer support +-passwd plain-password use authentication + (use plain-password as password, USE AT YOUR RISK) +-deferupdate time time in ms to defer updates (default 40) +-deferptrupdate time time in ms to defer pointer updates (default none) +-desktop name VNC desktop name (default "LibVNCServer") +-alwaysshared always treat new clients as shared +-nevershared never treat new clients as shared +-dontdisconnect don't disconnect existing clients when a new non-shared + connection comes in (refuse new connection instead) +-httpdir dir-path enable http server using dir-path home +-httpport portnum use portnum for http connection +-enablehttpproxy enable http proxy support +-progressive height enable progressive updating for slow links +-listen ipaddr listen for connections only on network interface with + addr ipaddr. '-listen localhost' and hostname work too. + +libvncserver-tight-extension options: +-disablefiletransfer disable file transfer +-ftproot string set ftp root +``` + +Pretty wild huh? Contact me if you have any questions or problems. + +Personally, I use: + +``` +x11vnc -rfbauth $HOME/.vnc/passwd -solid +``` diff --git a/doc/SSL-PORTAL.md b/doc/SSL-PORTAL.md new file mode 100644 index 0000000..6fc24d9 --- /dev/null +++ b/doc/SSL-PORTAL.md @@ -0,0 +1,838 @@ +# Using Apache as an SSL Gateway to multiple x11vnc servers inside a firewall + +Background: + +The typical way to allow access to x11vnc (or any other VNC server) +running on multiple workstations inside a firewall is via SSH. The +user somewhere out on the Internet logs in to the SSH gateway machine +and uses port forwarding (e.g. ssh -t -L 5900:myworkstation:5900 +user@gateway) to set up the encrypted channel that VNC is then +tunneled through. Next he starts up the VNC viewer on the machine +where he is sitting directed to the local tunnel port (e.g. +localhost:0). + +The SSH scheme is nice because it is a widely used and well tested +login technique for users connecting to machines inside their company +or home firewall. For VNC access it is a bit awkward, however, because +SSH needs to be installed on the Viewer machine and the user usually +has to rig up his own port redirection plumbing (however, see our +other tool). + +Also, some users have restrictive work environments where SSH and +similar applications are prohibited (i.e. only outgoing connections to +standard WWW ports from a browser are allowed, perhaps mediated by a +proxy server). These users have successfully used the method described +here for remote access. + +With the SSL support in x11vnc and the SSL enabled Java VNC viewer +applet, a convenient and secure alternative exists that uses the +Apache webserver as a gateway. The idea is that the company or home +internet connection is already running apache as a web server (either +SSL or non-SSL) and we add to it the ability to act as a gateway for +SSL VNC connections. The only thing needed on the Viewer side is a +Java enabled Web Browser: the user simply enters a URL that starts the +entire VNC connection process. No VNC or SSH specific software needs +to be installed on the viewer side machine. + +The stunnel VNC viewer stunnel wrapper script provided (ss_vncviewer) +can also take advantage of the method described here with its -proxy +option. + +--- + +Simpler Solutions: This apache SSL VNC portal solution may be too much +for you. It is mainly intended for automatically redirecting to +MULTIPLE workstations inside the firewall. If you only have one or two +inside machines that you want to access, the method described here is +overly complicated! See below for some simpler (and still non-SSH) +encrypted setups. + +Also see the recent (Mar/2010) desktop.cgi x11vnc desktop web login +CGI script that achieves much of what the method describes here +(especially if its 'port redirection' feature is enabled.) + +--- + +There are numerous ways to achieve this with Apache. We present one of +the simplest ones here. + +Important: these sorts of schemes allow incoming connections from +anywhere on the Internet to fixed ports on machines inside the +firewall. Care must be taken to implement and test thoroughly. If one +is paranoid one can (and should) add extra layers of protection. (e.g. +extra passwords, packet filtering, SSL certificate verification, etc). + +Also, it is easy to miss the point that unless precautions are taken +to verify SSL Certificates, then the VNC Viewer is vulnerable to +man-in-the-middle attacks (but not to the more common passive sniffing +attacks). Note that there are hacker tools like dsniff/webmitm and +cain that implement SSL Man-In-The-Middle attacks. They rely on the +client not bothering to check the cert. + +--- + +The Holy Grail: a single https port (443) + +Before we discuss the self-contained apache examples here, we want to +mention that many x11vnc users who read this page and implement the +apache SSL VNC portal ask for something that (so far) seems difficult +or impossible to do entirely inside apache: + +* A single port, 443 (the default https:// port), is open to the + Internet +* It is HTTPS/SSL encrypted +* It handles both VNC traffic and Java VNC Applet downloads. +* And the server can also serve normal HTTPS webpages, CGI, etc. + +It is the last item that makes it tricky (otherwise the method +described on this page will work). If you are interested in such a +solution and are willing to run a separate helper program +(connect_switch) look here. Also, see this apache patch. + +--- + +Example: + +The scheme described here sets up apache on the firewall/gateway as a +regular Web proxy into the intranet and allows connections to a single +fixed port on a limited set of machines. + +The configuration described in this section does not use the mod_ssl +apache module (the optional configuration described in the section +"Downloading the Java applet to the browser via HTTPS" does take +advantage of mod_ssl) + +In this example suppose the gateway machine running apache is named +"www.gateway.east" (e.g. it may also provide normal web service). We +also choose the Internet-facing port for this VNC service to be port +563. One could choose any port, including the default HTTP port 80. + +Detail: We choose 563 because it is the rarely used SNEWS port that is +often allowed by Web proxies for the CONNECT method. The idea is the +user may be coming out of another firewall using a proxy (not the one +we describe here, that is, the case when two proxies are involved, +e.g. one at work and another Apache (described here) at home +redirecting into our firewall; the "double proxy" or "double firewall" +problem). Using port 563 simplifies things because CONNECT's to it are +usually allowed by default. + +We also assume all of the x11vnc servers on the internal machines are +all listening on port 5915 ("-rfbport 5915") instead of the default +5900. This is to limit any unintended proxy redirections to a lesser +used port, and also to stay out of the way of normal VNC servers on +the same machines. One could obviously implement a scheme that handles +different ports, but we just discuss this simple setup here. + +So we basically assume x11vnc has been started this way on all of the +workstations to be granted VNC access: + +``` +x11vnc -ssl SAVE -http -display :0 -forever -rfbauth ~/.vnc/passwd -rfbport 5915 +``` + +i.e. we force SSL VNC connections, port 5915, serve the Java VNC +viewer applet, and require a VNC password (another option would be +-unixpw). The above command could also be run out of inetd(8). It can +also be used to autodetect the user's display and Xauthority data. + +These sections are added to the httpd.conf apache configuration file +on www.gateway.east: + +``` +# In the global section you need to enable these modules. +# Note that the ORDER MATTERS! mod_rewrite must be before mod_proxy +# (so that we can check the allowed host list via rewrite) +# +LoadModule rewrite_module modules/mod_rewrite.so +LoadModule proxy_module modules/mod_proxy.so +LoadModule proxy_connect_module modules/mod_proxy_connect.so +LoadModule proxy_ftp_module modules/mod_proxy_ftp.so +LoadModule proxy_http_module modules/mod_proxy_http.so + +LoadModule ssl_module modules/mod_ssl.so + + + +# Near the bottom of httpd.conf you put the port 563 virtual host: + +Listen 563 + + + + # Allow proxy CONNECT requests *only* to port 5915. + # If the machines use different ports, e.g. 5916 list them here as well: + # + ProxyRequests On + AllowCONNECT 5915 + + RewriteEngine On + + # Convenience rules to expand applet parameters. These do not have a trailing "/" + # + # /vnc for http jar file downloading: + # + RewriteRule /vnc/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PORT=563&urlPrefix=_2F_vnc_2F_$1 [R,NE,L] + RewriteRule /vnc/trust/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PORT=563&urlPrefix=_2F_vnc_2F_$1&trustAllVncCerts=yes [R,NE,L] + RewriteRule /vnc/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PORT=563&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes [R,NE,L] + RewriteRule /vnc/trust/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PORT=563&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes&trustAllVncCerts=yes [R,NE,L] + + # Read in the allowed host to vnc display mapping file. It looks like: + # + # host1 15 + # host2 15 + # ... + # + # the display "15" means 5815 for http applet download, 5915 for SSL vnc. + # + RewriteMap vnchosts txt:/dist/apache/conf/vnc.hosts + + # Proxy: check for the CONNECT hostname and port being in the vnc.hosts list. + # + RewriteCond %{THE_REQUEST} ^CONNECT [NC] + RewriteCond %{REQUEST_URI} ^(.*):(.*)$ + RewriteCond ${vnchosts:%1|NOTFOUND} NOTFOUND + RewriteRule ^.*$ /VNCFAIL [F,L] + + RewriteCond %{THE_REQUEST} ^CONNECT [NC] + RewriteCond %{REQUEST_URI} ^(.*):(.*)$ + RewriteCond 59${vnchosts:%1}=%2 !^(.*)=(\1)$ + RewriteRule ^.*$ /VNCFAIL [F,L] + + + # Remap /vnc to the proxy http download (e.g. http://host:5815) + # + # First, fail if it starts with the string /vnc0: + # + RewriteRule ^/vnc0.* /VNCFAIL [F,L] + # + # Next, map the prefix to /vnc0/host:protocol:port + # + RewriteRule ^/vnc/([^/]+)/(.*) /vnc0/$1:http:58${vnchosts:$1|NOTFOUND}/$2 [NE] + # + # Drop any not found: + # + RewriteRule ^/vnc0.*NOTFOUND.* /VNCFAIL [F,L] + + # Construct the proxy URL and retrieve it: + # + RewriteRule ^/vnc0/([^/]+):([^/]+):([^/]+)/(.*) $2://$1:$3/$4 [P,NE,L] + + +``` + +Then restart apache (perhaps: "apachectl stop; apachectl start"). + +Note that the listing of allowed internal workstations is done in an +external file (/dist/apache/conf/vnc.hosts in the example above), the +format is like this: + +``` +# allowed vnc hosts file: +hostname1 15 +hostname2 15 +... +``` + +You list the hostname and the VNC display (always 15 in our example). +Only to these hosts will the external VNC viewers be able to connect +to (via the HTTP CONNECT method). + +The above setup requires mod_rewrite and mod_proxy be enabled in the +apache web server. In this example they are loaded as modules (and +note that mod_rewrite must be listed before mod_proxy); + +The user at the Java enabled Web browser would simply enter this URL +into the browser: +http://www.gateway.east:563/vnc/host2 + +to connect to internal workstation host2, etc. + +Important: do not put a trailing "/" on the URL, since that will +defeat the RewriteRules that look for the hostname at the very end. + +There will be a number of SSL certificate, etc, dialogs he will have +to respond to in addition to any passwords he is required to provide +(this depends on how you set up user authentication for x11vnc). + +If a second Web proxy is involved (i.e. the user's browser is inside +another firewall and policy requires using a Web proxy server) then +use this URL: +http://www.gateway.east:563/vnc/proxy/host2 + +This will involve downloading a signed java viewer applet jar file +that is able to interact with the internal proxy for the VNC +connection. See this FAQ for more info on how this works. Note: +sometimes with the Proxy case if you see 'Bad Gateway' error you will +have to wait 10 or so seconds and then hit reload. This seems to be +due to having to wait for a Connection Keepalive to terminate... + +For completeness, the "trust" cases that skip a VNC certificate dialog +(discussed below) would be entered as: + +``` +http://www.gateway.east:563/vnc/trust/host2 +http://www.gateway.east:563/vnc/trust/proxy/host2 +``` + +You can of course choose shorter or more easy to remember URL formats. +Just change the Convenience RewriteRules in httpd.conf. + +--- + +Port Variations: + +Note that you can run this on the default HTTP port 80 instead of port +563. If you do not expect to have a browser connecting from inside a +proxying firewall (where sometimes only connections to ports 443 and +563 are allowed) this should be fine. Use "80" instead of "563" in the +httpd.conf config file (you may need to merge it with other default +port 80 things you have there). + +Then the URL's will be a bit simpler: + +``` +http://www.gateway.east/vnc/host2 +http://www.gateway.east/vnc/trust/host2 +``` + +etc. + +Besides 80 one could use any other random port number (since there are +so many port scans on 80, a little obscurity might be useful). + +One option is to use port "443" (the default https:// port) instead of +"563". In this case Apache is not configured for mod_ssl; we just +happen to use port "443" in the way any random port would be used. +This could be handy if the Viewer side environment is restrictive in +that it only allows outgoing connections to ports 80 and 443 (and, +say, you didn't want to use port 80, or you wanted to use 80 for +something else). Another reason for using 443 would be some web proxy +environments only allow the CONNECT method to go to port 443 (and not +even the case 563 we use above). + +--- + +Details: + +Let's go through the httpd.conf additions in detail from the top. + +The LoadModules directives load the necessary apache modules. Note +that mod_rewrite must be listed first. If you are compiling from +scratch something like this worked for us: + +``` +./configure --enable-proxy=shared --enable-proxy-connect=shared --enable-ssl=shared --enable-rewrite=shared --prefix=/dist/apache +``` + +Then the VirtualHost *:563 virtual host section starts. + +The "ProxyRequests On" and "AllowCONNECT 5915" enable the web server +to forward proxy requests to port 5915 (and only this port) INSIDE the +firewall. Think about the implications of this thoroughly and test it +carefully. + +The RewriteRule's are for convenience only so that the URL entered +into the Web browser does not need the various extra parameters, e.g.: + +``` +http://www.gateway.east:563/vnc/host2/index.vnc?CONNECT=host2+5915&PORT=563,blah,blah... +``` + +(or otherwise make direct edits to index.vnc to set these parameters). +The forceProxy=yes parameter is passed to the applet to force the use +of a outgoing proxy socket connection. Use it only if the Web browser +is inside a separate Web proxying environment (i.e. large corporation) + +The rewrites with parameter urlPrefix are described under Tricks for +Better Response. The "trust" ones (also described under Tricks) with +trustAllVncCerts tell the Java VNC applet to skip a dialog asking +about the VNC Certificate. They are a bit faster and more reliable +than the original method. In the best situation they lead to being +logged in 20 seconds or less (without them the time to login can be +much longer since a number of connections must timeout). + +All of the x11vnc Java Viewer applet parameters are described in the +file classes/ssl/README + +The external file /dist/apache/conf/vnc.hosts containing the allowed +VNC server hostnames is read in. Its 2nd column contains the VNC +display of the host (always 15 in our example; if you make it vary you +will need to adjust some lines in the httpd.conf accordingly, e.g. +AllowCONNECT). This list is used to constrain both the Jar file +download URL and the proxy CONNECT the VNC viewer makes to only the +intended VNC servers. + +Limiting the proxy CONNECT is done with the two sets of RewriteCond +conditions. + +Limiting the Jar file download URL is done in the remaining 4 +RewriteRule's. + +Note that these index.vnc and VncViewer.jar downloads to the browser +are not encrypted via SSL, and so in principle could be tampered with +by a really bad guy. The subsequent VNC connection, however, is +encrypted through a single SSL connection (it makes a CONNECT straight +to x11vnc). See below for how to have these initial downloads +encrypted as well (if the apache web server has SSL/mod_ssl, i.e. +https, enabled and configured). + +Unfortunately the Java VNC viewer applet currently is not able to save +its own list of Certificates (e.g. the user says trust this VNC +certificate 'always'). This is because an applet it cannot open local +files, etc. Sadly, the applet cannot even remember certificates in the +same browser session because it is completely reinitialized for each +connection (see below). + +--- + +Too Much? + +If these apache rules are a little too much for you, there is a little +bit simpler scheme where you have to list each of the individual +machines in the httpd.conf and ssl.conf files. It may be a little more +typing to maintain, but perhaps being more straight forward (less +RewriteRule's) is desirable. + +--- + +Problems? + +To see example x11vnc output for a successful https://host:5900/ +connection with the Java Applet see This Page. + +--- + +Some Ideas for adding extra authentication, etc. for the paranoid: + +* VNC passwords: -rfbauth, -passwdfile, or -usepw. Even adding a + simple company-wide VNC password helps block unwanted access. +* Unix passwords: -unixpw +* SSL Client certificates: -sslverify +* Apache AuthUserFile directive: .htaccess, etc. +* Filter connections based on IP address or hostname. +* Use Port-knocking on your firewall as described in: Enhanced + TightVNC Viewer (ssvnc). +* Add proxy password authentication (requires Viewer changes?) +* Run a separate instance of Apache that provides this VNC service + so it can be brought up and down independently of the normal web + server. +* How secure is the Client side? Public machines in internet cafes, + etc, are often hacked, with backdoors and VNC servers of their + own. Prefer using your own firewalled laptop to a public machine. + +--- + +Using non-Java viewers with this scheme: + +The ss_vncviewer stunnel wrapper script for VNC viewers has the -proxy +option that can take advantage of this method. + +``` +ss_vncviewer -proxy www.gateway.east:563 host1:15 +``` + +For the case of the "double proxy" situation (see below) supply both +separated by a comma. + +``` +ss_vncviewer -proxy proxy1.foobar.com:8080,www.gateway.east:563 host1:15 +``` + +For the Enhanced TightVNC Viewer (ssvnc) GUI (it uses ss_vncviewer on +Unix) put 'host1:15' into the 'VNC Server' entry box, and here are +possible Proxy/Gateway entries + +``` +Proxy/Gateway: www.gateway.east:563 +Proxy/Gateway: proxy1.foobar.com:8080,www.gateway.east:563 +``` + +then click on the 'Connect' button. + +--- + +Downloading the Java applet to the browser via HTTPS: + +To have the Java applet downloaded to the user's Web Browser via an +encrypted (and evidently safer) SSL connection the Apache webserver +should be configured for SSL via mod_ssl. + +It is actually possible to use the x11vnc Key Management utility +"-sslGenCert" to generate your Apache/SSL .crt and .key files. (In +brief, run something like "x11vnc -sslGenCert server self:apache" then +copy the resulting self:apache.crt file to conf/ssl.crt/server.crt and +extract the private key part from self:apache.pem and paste it into +conf/ssl.key/server.key). Setting the env var REQ_ARGS='-days 1095' +before running x11vnc will bump up the expiration date (3 years in +this case). + +Or you can use the standard methods described in the Apache mod_ssl +documentation to create your keys. Then restart Apache, usually +something like "apachectl stop" followed by "apachectl startssl" + +In addition to the above sections in httpd.conf one should add the +following to ssl.conf: + +``` + SSLProxyEngine On + + RewriteEngine On + + # Convenience rules to expand applet parameters. These do not have a traili +ng "/" + # + # /vnc http jar file downloading: + # + RewriteRule /vnc/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vnc_2F_$1 [R,NE,L] + RewriteRule /vnc/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes [R,N +E,L] + # + # (we skipped the "trust" ones above, put them in if you like) + # + # /vncs https jar file downloading: + # + RewriteRule /vncs/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1 [R,NE,L] + RewriteRule /vncs/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes [R,NE,l] + RewriteRule /vncs/trust/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&trustAllVncCerts=yes [R,NE,L] + RewriteRule /vncs/trust/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes&trustAllVncCerts=yes [R,NE,L] + + # Convenience rules used for the connect_switch helper (requires Listen 127.0.0.1:443 above): + # + RewriteRule /vnc443/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$1+5915&PORT=443&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1 [R,NE,L] + RewriteRule /vnc443/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$1+5915&PORT=443&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes [R,NE,L] + RewriteRule /vnc443/trust/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$1+5915&PORT=443&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&trustAllVncCerts=yes [R,NE,L] + RewriteRule /vnc443/trust/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$1+5915&PORT=443&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes&trustAllVncCerts=yes [R,NE,L] + + # Read in the allowed host to vnc display mapping file. It looks like: + # + # host1 15 + # host2 15 + # ... + # + # the display "15" means 5915 for SSL VNC and 5815 for http applet download. + # + RewriteMap vnchosts txt:/dist/apache/conf/vnc.hosts + + + # Remap /vnc and /vncs to the proxy http download (e.g. https://host:5915) + # + # First, fail if it starts with the string /vnc0: + # + RewriteRule ^/vnc0.* /VNCFAIL [F,L] + # + # Next, map the prefix to /vnc0:host:protocol:port + # + RewriteRule ^/vnc/([^/]+)/(.*) /vnc0/$1:http:58${vnchosts:$1|NOTFOUND}/$2 [NE] + RewriteRule ^/vncs/([^/]+)/(.*) /vnc0/$1:https:59${vnchosts:$1|NOTFOUND}/$2 [NE] + # + # Drop any not found: + # + RewriteRule ^/vnc0.*NOTFOUND.* /VNCFAIL [F,L] + + # Construct the proxy URL and retrieve it: + # + RewriteRule ^/vnc0/([^/]+):([^/]+):([^/]+)/(.*) $2://$1:$3/$4 [P,NE,L] +``` + +This is all in the "" section of ssl.conf. + +The user could then point the Web Browser to: + +``` +https://www.gateway.east/vnc/host2 +``` + +or + +``` +https://www.gateway.east/vnc/proxy/host2 +``` + +for the "double proxy" case. (Important: do not put a trailing "/" on +the URL, since that will defeat the RewriteRules.) + +As with the httpd.conf case, the external file +(/dist/apache/conf/vnc.hosts in the above example) contains the +hostnames of the allowed VNC servers. + +Note that inside the firewall the Java applet download traffic is not +encrypted (only over the Internet is SSL used) for these cases: + +``` +https://www.gateway.east/vnc/host2 +https://www.gateway.east/vnc/proxy/host2 +``` + +However for the special "vncs" rules above: + +``` +https://www.gateway.east/vncs/host2 +``` + +the Java applet download is encrypted via SSL for both legs. Note that +the two legs are two separate SSL sessions. So the data is decrypted +inside an apache process and reencrypted by the apache process for the +2nd SSL session inside the same apache process (a very small gap one +might overlook). + +The "vncs/trust" ones are like the "trust" ones described earlier + +``` +https://www.gateway.east/vncs/trust/mach2 +``` + +and similarly for the httpsPort ones. See Tricks for Better Response. + +In all of the above cases the VNC traffic from Viewer to x11vnc is +encrypted end-to-end in a single SSL session, even for the "double +proxy" case because the CONNECT method is used (there are actually two +CONNECT's for the "double proxy" case). This part (the VNC traffic) is +the most important part to have encrypted. + +Note that the Certificate dialogs the user has in his web browser will +be for the Apache Certificate, while for the Java applet it will be +the x11vnc certificate. + +Note also that you can have Apache serve up the Jar file VncViewer.jar +and/or index.vnc/proxy.vnc instead of each x11vnc if you want to. + +The rules in ssl.conf are similar to the ones in httpd.conf and so are +not discussed in detail. The only really new thing is the /vncs +handling to download the applet jar via HTTPS on port 5915. + +The special entries "/vnc443" are only used for the special helper +program (connect_switch) for the https port 443 only mode discussed +here. + +--- + +INETD automation: + +The "single-port" (i.e. 5915) HTTPS applet download and VNC connection +aspect shown here is convenient and also enables having x11vnc run out +of inetd. That way x11vnc is run on demand instead of being run all +the time (the user does not have to remember to start it). The first +connections to inetd download index.vnc and the Jar file (via https) +and the the last connection to inetd establishes the SSL VNC +connection. Since x11vnc is restarted for each connection, this will +be a bit slower than the normal process. + +For example, the /etc/inetd.conf line could be: + +``` +5915 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc_ssl.sh +``` + +where the script x11vnc_ssl.sh looks something like this: + +``` +#!/bin/sh + +/usr/local/bin/x11vnc -inetd -oa /var/log/x11vnc-15.log \ + -ssl SAVE -http -unixpw -localhost \ + -display :0 -auth /home/THE_USER/.Xauthority +``` + +where, as usual, the inetd launching needs to know which user is +typically using the display on that machine. One could imagine giving +different users different ports, 5915, 5916, etc. to distinguish (then +the script would need to be passed the username). mod_rewrite could be +used to automatically map username in the URL to his port number. + +A better way is to use the "-display WAIT:cmd=FINDDISPLAY" feature to +autodetect the user and Xauthority data: + +``` +#!/bin/sh + +/usr/local/bin/x11vnc -inetd -oa /var/log/x11vnc-15.log \ + -ssl SAVE -http -unixpw -localhost -users unixpw= \ + -find +``` + +(we have used the alias -find for "-display WAIT:cmd=FINDDISPLAY".) +This way the user must supply his Unix username and password and then +his display and Xauthority data on that machine will be located and +returned to x11vnc to allow it to attach. If he doesn't have a display +running on that machine or he fails to log in correctly, the +connection will be dropped. + +The variant "-display WAIT:cmd=FINDCREATEDISPLAY" (aliased by +"-create") will actually create a (virtual or real) X server session +for the user if one doesn't already exist. See here for details. + +To enable inetd operation for the non-HTTPS Java viewer download (port +5815 in the above httpd.conf example) you will need to run x11vnc in +HTTPONCE mode on port 5815: For example, the /etc/inetd.conf line +could be: + +``` +5815 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc \ + -inetd -prog /usr/local/bin/x11vnc -oa /var/log/x11vnc-15.log \ + -http_ssl -display WAIT:cmd=HTTPONCE +``` + +where the long inetd.conf line has been split. Note how the -http_ssl +tries to automatically find the .../classes/ssl subdirectory. This +requires the -prog option available in x11vnc 0.8.4 (a shell script +wrapper, e.g. /usr/local/bin/x11vnc_http.sh can be used to work around +this). + +Also note the use of "-ssl SAVE" above. This way a saved server.pem is +used for each inetd invocation (rather generating a new one each time +as happens for "-ssl TMP"). Note that it cannot have a protecting +passphrase because inetd will not be able to supply it. + +Another option is: + +``` +5815 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc \ + -inetd -httpdir /usr/local/share/x11vnc/classes/ssl \ + -oa /var/log/x11vnc-15.log -display WAIT:cmd=HTTPONCE +``` + +(this also requires a feature found in x11vnc 0.8.4). + +--- + +Other Ideas: + +- The above schemes work, but they are a bit complicated with all of + the rigging. There should be more elegant ways to configure Apache to + do these, but we have not found them (please let us know if you + discover something nice). However, once this scheme has been set up + and is working it is easy to maintain and add/delete workstations, + etc. +- In general Apache is not required, but it makes things convenient. + The firewall itself could do the port redirection via its firewall + rules. Evidently different Internet-facing ports would be required for + each workstation. This could be set up using iptables rules for + example. If there were just one or two machines this would be the + easiest method. For example: + + ``` + iptables -t nat -A PREROUTING -p tcp -d 24.35.46.57 --dport 5901 -j DNAT --to-destination 192.168.1.2:5915 + iptables -t nat -A PREROUTING -p tcp -d 24.35.46.57 --dport 5902 -j DNAT --to-destination 192.168.1.3:5915 + ``` + + Where 24.35.46.57 is the internet IP address of the gateway. In this + example 24.35.46.57:5901 is redirected to the internal machine + 192.168.1.2:5915 and 24.35.46.57:5902 is redirected to another + internal machine 192.168.1.3:5915, both running x11vnc -ssl ... in SSL + mode. For this example, the user would point the web browser to, e.g.: + + ``` + https://24.35.46.57:5901/?PORT=5901 + ``` + + or using the stunnel wrapper script: + + ``` + ss_vncviewer 24.35.46.57:1 + ``` + + One can achieve similar things with dedicated firewall/routers (e.g. + Linksys) using the device's web or other interface to configure the + firewall. + + If the user may be coming out of a firewall using a proxy it may be + better to redirect ports 443 and 563 (instead of 5901 and 5902) to the + internal machines so that the user's proxy will allow CONNECTing to + them. + +- The redirection could also be done at the application level using a + TCP redirect program (e.g. ip_relay or fancier ones). Evidently more + careful internal hostname checking, etc., could be performed by the + special purpose application to add security. See connect_switch which + is somewhat related. +- One might imagine the ProxyPass could be done for the VNC traffic as + well (for the ssl.conf case) to avoid the CONNECT proxying completely + (which would be nice to avoid). Unfortunately we were not able to get + this to work. Since HTTP is a request-response protocol (as opposed to + a full bidirectional link required by VNC that CONNECT provides) this + makes it difficult to do. It may be possible, but we haven't found out + how yet. + +All of the x11vnc Java Viewer applet parameters are described in the +file classes/ssl/README + +--- + +Tricks for Better Response and reliability: + +The "original scheme" using httpd.conf and ssl.conf rewrites without +urlPrefix and trustAllVncCerts above should work OK, but may lead to +slow and/or unreliable loading of the applet and final connection to +x11vnc. The following are what I do now to get better response and +reliability. YMMV. + +The problem with the "original scheme" is that there is a point where +the VNC Viewer applet can try up to 3 times to retrieve the x11vnc +certificate, since it needs to get it to show it to you and ask you if +you accept it. This can add about 45 seconds to the whole process +(which takes 1 to 1.5 minutes with all the dialogs) since a couple of +those connections must time out. The "trust" items in the config add a +parameter trustAllVncCerts=yes similar to the forceProxy=yes +parameter. This can cut the total time to the VNC password prompt down +to 15 seconds which is pretty good. (Note by ignoring the certificate +this does not protect against man-in-the-middle attacks which are +rare, but maybe the won't be so rare in the future... see +dsniff/webmitm and cain) + +First make sure the x11vnc SSL certificate+key is the same as +Apache's. (otherwise you may get one extra dialog and/or one extra +connection that has to time out). + +The following RewriteRule's are the same now advocated in the +instructions above. + +The httpsPort and urlPrefix= parameters give hints to the applet to +improve connecting: This is what goes in httpd.conf: + +``` +RewriteEngine On +RewriteRule /vnc/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PORT=563&urlPrefix=_2F_vnc_2F_$1 [R,NE] +RewriteRule /vnc/trust/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PORT=563&urlPrefix=_2F_vnc_2F_$1&trustAllVncCerts=yes [R,NE] +RewriteRule /vnc/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PORT=563&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes [R,NE] +RewriteRule /vnc/trust/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PORT=563&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes&trustAllVncCerts=yes [R,NE] +``` + +The httpsPort and urlPrefix provide useful hints to the VNC Viewer +applet when it connects to x11vnc to glean information about Proxies, +certificates, etc. + +This is what goes into ssl.conf: + +``` +RewriteEngine On +RewriteRule /vnc/([^/]+)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vnc_2F_$1 [R,NE] +RewriteRule /vnc/proxy/([^/]+)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vnc_2F_$1&forceProxy=yes [R,NE] +RewriteRule /vncs/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1 [R,NE] +RewriteRule /vncs/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes [R,NE] +RewriteRule /vncs/trust/([^/]+)$ /vncs/$1/index.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&trustAllVncCerts=yes [R,NE] +RewriteRule /vncs/trust/proxy/([^/]+)$ /vncs/$1/proxy.vnc?CONNECT=$1+5915&PORT=563&httpsPort=443&GET=1&urlPrefix=_2F_vncs_2F_$1&forceProxy=yes&trustAllVncCerts=yes [R,NE] +``` + +The rest is the same. + +The httpsPort and urlPrefix and GET provide useful hints to the VNC +Viewer applet when it connects to x11vnc to glean information about +Proxies, certificates, etc, and also for the ultimate VNC connection +(GET speeds this up by sending a special HTTP GET to cause x11vnc to +immediately switch to the VNC protocol). + +To turn these into URLs, as was done above, take the string in the +RewriteRule, e.g. /vncs and turn it into +https://gateway/vncs/machinename Similarly for non-https: +http://gateway:563/vnc/machinename + +If you use the 'trust' ones, you are performing NO checks, visual or +otherwise, on the VNC SSL certificate. It is trusted without question. +This speeds things up because it avoids a dialog about certificates, +but of course has some risk WRT Man in the Middle attacks. I don't +recommend them. It is better to use /vnc or /vncs and the first time +you connect carefully check the Certificate and then tell your Browser +and Java Virtual Machine to trust the certificate 'Always'. Then if +you later get an unexpected dialog, you know something is wrong. +Nearly always it is just a changed or expired certificate, but better +safe than sorry... diff --git a/doc/SSL.md b/doc/SSL.md new file mode 100644 index 0000000..7ac0cd0 --- /dev/null +++ b/doc/SSL.md @@ -0,0 +1,878 @@ +# Notes on x11vnc SSL Certificates and Key Management + +The simplest scheme ("x11vnc -ssl TMP") is where x11vnc generates a +temporary, self-signed certificate each time (automatically using +openssl(1)) and the VNC viewer client accepts the certificate without +question (e.g. user clicks "Yes" in a dialog box. Perhaps the dialog +allows them to view the certificate too). Also note stunnel's default +is to quietly accept all certificates. + +The encryption this provides protects against all passive sniffing of +the VNC traffic and passwords on the network and so it is quite good, +but it does not prevent a Man-In-The-Middle active attack: e.g. an +attacker intercepts the VNC client stream and sends it his own Public +key for SSL negotiation (pretending to be the server). Then it makes a +connection to SSL x11vnc itself and forwards the data back and forth. +He can see all the traffic and modify it as well. + +Most people don't seem to worry about Man-In-The-Middle attacks these +days; they are more concerned about passive sniffing of passwords, +etc. Perhaps someday that will change if attack tools are used more +widely to perform the attack. NOTE: There are hacker tools like +dsniff/webmitm and cain that implement SSL Man-In-The-Middle attacks. +They all rely on the client not bothering to check that the cert is +valid. + +If you are not worried about Man-In-The-Middle attacks you do not have +to read the techniques described in the rest of this document. + +To prevent Man-In-The-Middle attacks, certificates must somehow be +verified. This requires the VNC client side have some piece of +information that can be used to verify the SSL x11vnc server. +Alternatively, although rarely done, x11vnc can verify VNC Clients' +certificates, see the -sslverify option that is discussed below. + +There are a number of ways to have the client authenticate the SSL +x11vnc server. The quickest way perhaps would be to copy (safely) the +certificate x11vnc prints out: + +``` +26/03/2006 21:12:00 Creating a temporary, self-signed PEM certificate... +... +-----BEGIN CERTIFICATE----- +MIIC4TCCAkqgAwIBAgIJAMnwCaOjvEKaMA0GCSqGSIb3DQEBBAUAMIGmMQswCQYD +VQQGEwJBVTEOMAwGA1UEBxMFTGludXgxITAfBgNVBAsTGGFuZ2VsYS0xMTQzNDI1 +NTIwLjQxMTE2OTEPMA0GA1UEChMGeDExdm5jMS4wLAYDVQQDEyV4MTF2bmMtU0VM +(more lines) ... +-----END CERTIFICATE----- +``` + +to the client machine(s) and have the client's SSL machinery (e.g. +stunnel, Web Browser, or Java plugin) import the certificate. That way +when the connection to x11vnc is made the client can verify that is it +the desired server on the other side of the SSL connection. + +So, for example suppose the user is using the SSL enabled Java VNC +Viewer and has incorporated the x11vnc certificate into his Web +browser on the viewing side. If he gets a dialog that the certificate +is not verified he knows something is wrong. It may be a +Man-In-The-Middle attack, but more likely x11vnc certificate has +changed or expired or his browser was reinstalled and/or lost the +certificate, etc, etc. + +As another example, if the user was using stunnel with his VNC viewer +(this is mentioned in this FAQ), e.g. STUNNEL.EXE on Windows, then he +would have to set the "CAfile = path-to-the-cert" and "verify = 2" +options in the stunnel.conf file before starting up the tunnel. If a +x11vnc certificate cannot be verified, stunnel will drop the +connection (and print a failure message in its log file). + +A third example, using the VNC viewer on Unix with stunnel the wrapper +script can be used this way: "ss_vncviewer -verify ./x11vnc.crt +far-away.east:0" where ./x11vnc.crt is the copied certificate x11vnc +printed out. + +As fourth example, our SSVNC enhanced tightvnc viewer can also use +these certificate files for server authentication. You can load them +via the SSVNC 'Certs...' dialog and set 'ServerCert' to the +certificate file you safely copied there. + +Note that in principle the copying of the certificate to the client +machine(s) itself could be altered by a Man-In-The-Middle attack! You +can't win; it is very difficult to be completely secure. It is +unlikely the attacker could predict how you were going to send it +unless you had, say, done it many times before the same way. SSH is a +very good way to send it (but of course it too depends on public keys +being sent unaltered between the two machines!). + +If you are really paranoid, I'm sure you'll figure out a really good +way to transport the certificates. See the Certificate Authority +scheme below for a way to make this easier (you just have to do it +once). + +--- + +## Saving SSL certificates and keys + +Now, it would be very inconvenient to copy the new temporary +certificate every time x11vnc is run in SSL mode. So for convenience +there is the "SAVE" keyword to instruct x11vnc to save the certificate +it creates: + +``` +x11vnc -ssl SAVE -display :0 ... +``` + +This behavior is now the default, you must use "TMP" for a temporary +one. It will save the certificate and private key in these files: + +``` +~/.vnc/certs/server.crt +~/.vnc/certs/server.pem +``` + +The ".crt" file contains only the certificate and should be safely +copied to the VNC Viewer machine(s) that will be authenticating the +x11vnc server. The ".pem" file contains both the certificate and the +private key and should be kept secret. (If you don't like the default +location ~/.vnc/certs, e.g. it is on an NFS share and you are worried +about local network sniffing, use the -ssldir dir option to point to a +different directory.) + +So the next time you run "x11vnc -ssl SAVE ..." it will read the +server.pem file directly instead of creating a new one. + +You can manage multiple SSL x11vnc server keys in this simple way by +using: + +``` +x11vnc -ssl SAVE-key2 -display :0 ... +``` + +etc, where you put whatever name you choose for the key after "SAVE-". +E.g. "-ssl SAVE-fred". + +Also, if you want to be prompted to possibly change the made up names, +etc. that x11vnc creates (e.g. "x11vnc-SELF-SIGNED-CERT-7762" for the +CommonName) for the certificates distinguished name (DN), then use +"x11vnc -ssl SAVE_PROMPT ...", "x11vnc -ssl SAVE_PROMPT-fred ..." etc. +when you create the key the first time. + +Tip: when prompting, if you choose the CommonName entry to be the full +internet hostname of the machine the clients will be connecting to +then that will avoid an annoying dialog box in their Web browsers that +warn that the CommonName doesn't match the hostname. + +--- + +## Passphrases for server keys + +Well, since now with the "SAVE" keyword the certificate and key will +be longer lived, one can next worry about somebody stealing the +private key and pretending to be the x11vnc server! How to guard +against this? + +The first is that the file is created with perms 600 (i.e. -rw-------) +to make it harder for an untrusted user to copy the file. A better way +is to also encrypt the private key with a passphrase. You are prompted +whether you want to do this or not when the key is first created under +"-ssl SAVE" mode ("Protect key with a passphrase? y/n"). It is +suggested that you use a passphrase. The inconvenience is every time +you run "x11vnc -ssl SAVE ..." you will need to supply the passphrase +to access the private key: + +``` +06/04/2006 11:39:11 using PEM /home/runge/.vnc/certs/server.pem 0.000s +``` + +A passphrase is needed to unlock an OpenSSL private key (PEM file). + +``` +Enter passphrase> +``` + +before x11vnc can continue. + +--- + +## Being your own Certificate Authority + +A very sophisticated way that scales well if the number of users is +large is to use a Certificate Authority (CA) whose public certificate +is available to all of the VNC clients and whose private key has been +used to digitally sign the x11vnc server certificate(s). + +The idea is as follows: + +* A special CA cert and key is generated. +* Its private key is always protected by a good passphrase since it + is only used for signing. +* The CA cert is (safely) distributed to all machines where VNC + clients will run. +* One or more x11vnc server certs and keys are generated. +* The x11vnc server cert is signed with the CA private key. +* x11vnc is run using the server key. (e.g. "-ssl SAVE") +* VNC clients (viewers) can now authenticate the x11vnc server + because they have the CA certificate. + +The advantage is the CA cert only needs to be distributed once to the +various machines, that can be done even before x11vnc server certs are +generated. + +As above, it is important the CA private key and the x11vnc server key +are kept secret, otherwise someone could steal them and pretend to be +the CA or the x11vnc server if they copied the key. It is recommended +that the x11vnc server keys are also protected via a passphrase (see +the previous section). + +Optionally, VNC viewer certs and keys could also be generated to +enable the x11vnc server to authenticate each client. This is not +normally done (usually a simple viewer password scheme is used), but +this can be useful in some situations. These optional steps go like +this: + +* One or more VNC client certs and keys are generated. +* These VNC client certs are signed with the CA private key. +* The VNC client certs+keys are safely distributed to the + corresponding client machines. +* x11vnc is told to verify clients by using the CA cert. (e.g. + "-sslverify CA") +* When VNC clients (viewers) connect, they must authenticate + themselves to x11vnc by using their client key. + +Again, it is a good idea if the client private keys are protected with +a passphrase, otherwise if stolen they could be used to gain access to +the x11vnc server. Once distributed to the client machines, there is +no need to keep the client key on the CA machine that generated and +signed it. You can keep the client certs if you like because they are +public. + +--- + +## How to do the above CA steps with x11vnc + +Some utility commands are provided to ease the cert+key creation, +signing, and management: -sslGenCA, -sslGenCert, -sslDelCert, +-sslEncKey, -sslCertInfo. They basically run the openssl(1) command +for you to manage the certs/keys. It is required that openssl(1) is +installed on the machine and available in PATH. All commands can be +pointed to an alternate toplevel certificate directory via the -ssldir +option if you don't want to use the default ~/.vnc/certs. + +1. To generate your Certificate Authority (CA) cert and key run this: + + ``` + x11vnc -sslGenCA + ``` + + Follow the prompts, you can modify any informational strings you care + to. You will also be required to encrypt the CA private key with a + passphrase. This generates these files: + + ``` + ~/.vnc/certs/CA/cacert.pem (the CA public certificate) + ~/.vnc/certs/CA/private/cakey.pem (the encrypted CA private key) + ``` + + If you want to use a different directory use -ssldir It must supplied + with all subsequent SSL utility options to point them to the correct + directory. + +2. To generate a signed x11vnc server cert and key run this: + + ``` + x11vnc -sslGenCert server + ``` + + As with the CA generation, follow the prompts and you can modify any + informational strings that you care to. This will create the files: + + ``` + ~/.vnc/certs/server.crt (the server public certificate) + ~/.vnc/certs/server.pem (the server private key + public cert) + ``` + + It is recommended to protect the server private key with a passphrase + (you will be prompted whether you want to). You will need to provide + it whenever you start x11vnc using this key. + +3. Start up x11vnc using this server key: + + ``` + x11vnc -ssl SAVE -display :0 ... + ``` + + (SAVE corresponds to server.pem, see -sslGenCert server somename info + on creating additional server keys, server-somename.crt ...) + +4. Next, safely copy the CA certificate to the VNC viewer (client) + machine(s). Perhaps: + + ``` + scp ~/.vnc/CA/cacert.pem clientmachine:. + ``` + +5. Then the tricky part, make it so the SSL VNC Viewer uses this + certificate! There are a number of ways this might be done, it depends + on what your client and/or SSL tunnel is. Some examples: + + For the SSL Java VNC viewer supplied with x11vnc in + classes/ssl/VncViewer.jar or classes/ssl/SignedVncViewer.jar: + + * Import the cacert.pem cert into your Web Browser (e.g. Edit -> + Preferences -> Privacy & Security -> Manage Certificates -> + WebSites -> Import) + * Or Import the cacert.pem cert into your Java Plugin (e.g. run + ControlPanel, then Security -> Certificates -> Secure Site -> + Import) + + When importing, one would give the browser/java-plugin the path to the + copied cacert.pem file in some dialog. Note that the Web browser or + Java plugin is used for the server authentication. If the user gets a + "Site not verified" message while connecting he should investigate + further. + + For the use of stunnel (e.g. on Windows) one would add this to the + stunnel.conf: + + ``` + # stunnel.conf: + client = yes + options = ALL + CAfile = /path/to/cacert.pem # or maybe C:\path\to\cacert.pem + [myvncssl] + accept = 5901 + connect = far-away.east:5900 + ``` + + (then point the VNC viewer to localhost:1). + + Here is an example for the Unix stunnel wrapper script ss_vncviewer in + our SSVNC package: + + ``` + ss_vncviewer -verify ./cacert.pem far-away.east:0 + ``` + + Our SSVNC enhanced tightvnc viewer GUI can also use the certificate + file for server authentication. You can load it via the SSVNC + 'Certs...' dialog and set 'ServerCert' to the cacert.pem file you + safely copied there. + +--- + +## Tricks for server keys + +To create additional x11vnc server keys do something like this: + +``` +x11vnc -sslGenCert server myotherkey +``` + +and use it this way: + +``` +x11vnc -ssl SAVE-myotherkey ... +``` + +The files will be ~/.vnc/certs/server-myotherkey.{crt,pem} + +You can also create a self-signed server key: + +``` +x11vnc -sslGenCert server self:third_key +``` + +and use it this way: + +``` +x11vnc -ssl SAVE-self:third_key ... +``` + +This key is not signed by your CA. This can be handy to have a key set +separate from your CA when you do not want to create a 2nd CA +cert+key. + +--- + +## Using external CA's + +You don't have to use your own CA cert+key, you can use a third +party's instead. Perhaps you have a company-wide CA or you can even +have your x11vnc certificate signed by a professional CA (e.g. +www.thawte.com or www.verisign.com or perhaps the free certificate +service www.startcom.org or www.cacert.org). + +The advantage to doing this is that the VNC client machines will +already have the CA certificates installed and you don't have to +install it on each machine. + +To generate an x11vnc server cert+key this way you should generate a +"request" for a certicate signing something like this (we use the name +"external" in this example, it could be anything you want): + +``` +x11vnc -sslGenCert server req:external +``` + +This will create the request file: + +``` +~/.vnc/certs/server-req:external.req +``` + +Which you should send to the external CA. When you get the signed +certificate back from them, save it in the file: + +``` +~/.vnc/certs/server-req:external.crt +``` + +and create the .pem this way: + +``` +mv ~/.vnc/certs/server-req:external.key ~/.vnc/certs/server-req:external.pem +chmod 600 ~/.vnc/certs/server-req:external.pem +cat ~/.vnc/certs/server-req:external.crt >> ~/.vnc/certs/server-req:external.pem +``` + +You also rename the two files (.crt and .pem) to have a shorter +basename if you like. E.g.: + +``` +mv ~/.vnc/certs/server-req:external.pem ~/.vnc/certs/server-ext.pem +mv ~/.vnc/certs/server-req:external.crt ~/.vnc/certs/server-ext.crt +``` + +and the use via "x11vnc -ssl SAVE-ext ...", etc. + +On the viewer side make sure the external CA's certificate is +installed an available for the VNC viewer software you plan to use. + +--- + +## Using Client Keys for Authentication + +You can optionally create certs+keys for your VNC client machines as +well. After distributing them to the client machines you can have +x11vnc verify the clients using SSL. Here is how to do this: + +``` +x11vnc -sslGenCert client dilbert +x11vnc -sslGenCert client wally +x11vnc -sslGenCert client alice +... +``` + +As usual, follow the prompts if you want to change any of the info +field values. As always, it is a good idea (although inconvenient) to +protect the private keys with a passphrase. These files are created: + +``` +~/.vnc/certs/clients/dilbert.crt +~/.vnc/certs/clients/dilbert.pem +... +``` + +Note that these are kept in a clients subdirectory. + +Next, safely copy the .pem files to each corresponding client machine +and incorporate them into the VNC viewer / SSL software (see the ideas +mentioned above for the CA and server keys). The only difference is +these certificates might be referred to as "My Certificates" or +"Client Certificates". They are used for client authentication (which +is relatively rare for SSL). + +After copying them you can delete the clients/*.pem files for extra +safety because the private keys are not needed by the x11vnc server. +You don't really need the clients/*.crt files either (because they +have been signed by the CA). But they could come in handy for tracking +or troubleshooting, etc. + +Now start up x11vnc and instruct it to verify connecting clients via +SSL and the CA cert: + +``` +x11vnc -ssl SAVE -sslverify CA +``` + +The "CA" special token instructs x11vnc to use its CA signed certs for +verification. + +For arbitrary self-signed client certificates (no CA) it might be +something like this: + +``` +x11vnc -ssl SAVE -sslverify path/to/client.crt +x11vnc -ssl SAVE -sslverify path/to/client-hash-dir +x11vnc -ssl SAVE -sslverify path/to/certs.txt +``` + +Where client.crt would be an individual client certificate; +client-hash-dir a directory of file names based on md5 hashes of the +certs (see -sslverify); and certs.txt signifies a single file full of +client certificates. + +Finally, connect with your VNC viewer using the key. Here is an +example for the Unix stunnel wrapper script ss_vncviewer: using client +authentication (and the standard server authentication with the CA +cert): + +``` +ss_vncviewer -mycert ./dilbert.pem -verify ./cacert.pem far-away.east:0 +``` + +Our SSVNC enhanced tightvnc viewer can also use these openssl .pem +files (you can load them via Certs... -> MyCert dialog). + +It is also possible to use -sslverify on a per-client key basis, and +also using self-signed client keys (x11vnc -sslGenCert client +self:dilbert) + +Now a tricky part is to get Web browsers or Java Runtime to import and +use the openssl .pem cert+key files. See the next paragraph on how to +convert them to pkcs12 format. If you find a robust way to import them +and and get them to use the cert please let us know! + +Here is how to convert our openssl crt/pem files to pkcs12 format +(contains both the client certificate and key) that can be read by Web +browsers and Java for use in client authentication: + +``` +openssl pkcs12 -export -in mycert.crt -inkey mycert.pem -out mycert.p12 +``` + +it will ask for a passphrase to protect mycert.p12. Some software +(e.g. Java ControlPanel) may require a non-empty passphrase. Actually, +since our .pem contains both the certificate and private key, you +could just supply it for the -in and remove the -inkey option. It +appears that for certificates only importing, our .crt file is +sufficient and can be read by Mozilla/Firefox and Java... + +If you have trouble getting your Java Runtime to import and use the +cert+key, there is a workaround for the SSL-enabled Java applet. On +the Web browser URL that retrieves the VNC applet, simply add a +"/?oneTimeKey=..." applet parameter (see ssl-portal for more details +on applet parameters; you don't need to do the full portal setup +though). The value of the oneTimeKey will be the very long string that +is output of the onetimekey program found in the classes/ssl x11vnc +directory. Or you can set oneTimeKey=PROMPT in which case the applet +will ask you to paste in the long string. These scheme is pretty ugly, +but it works. A nice application of it is to make one time keys for +users that have already logged into a secure HTTPS site via password. +A cgi program then makes a one time key for the logged in user to use: +it is passed back over HTTPS as the applet parameter in the URL and so +cannot be sniffed. x11vnc is run to use that key via -sslverify. + +Update: as of Apr 2007 in the 0.9.1 x11vnc tarball there is a new +option setting "-users sslpeer=" that will do a switch user much like +-unixpw does, but this time using the emailAddress field of the +Certificate subject of the verified Client. This mode requires +-sslverify turned on to verify the clients via SSL. This mode can be +useful in situations using -create or -svc where a new X server needs +to be started up as the authenticated user (but unlike in -unixpw +mode, the unix username is not obviously known). + +--- + +## Revoking Certificates + +A large, scaled-up installation may benefit from being able to revoke +certificates (e.g. suppose a user's laptop with a vnc client or server +key is compromised.) You can use this option with x11vnc: -sslCRL. See +the info at that link for a guide on what openssl(1) commands you will +need to run to revoke a certificate. + +--- + +## Additional utlities + +You can get information about your keys via -sslCertInfo. These lists +all your keys: + +``` +x11vnc -sslCertInfo list +x11vnc -sslCertInfo ll +``` + +(the latter is long format). + +These print long output, including the public certificate, for +individual keys: + +``` +x11vnc -sslCertInfo server +x11vnc -sslCertInfo dilbert +x11vnc -sslCertInfo all (every key, very long) +``` + +If you want to add a protecting passphrase to a key originally created +without one: + +``` +x11vnc -sslEncKey SAVE +x11vnc -sslEncKey SAVE-fred +``` + +To delete a cert+key: + +``` +x11vnc -sslDelCert SAVE +x11vnc -sslDelCert SAVE-fred +x11vnc -sslDelCert wally +``` + +(but rm(1) will be just as effective). + +--- + +## Chained Certificates + +There is increasing interest in using chained CA's instead of a single +CA. The merits of using chained CA's are not described here besides to +say its use may make some things easier when a certificate needs to be +revoked. + +x11vnc supports chained CA certificates. We describe a basic use case +here. + +Background: Of course the most straight forward way to use SSL with +x11vnc is to use no CA at all (see above): a self-signed certificate +and key is used and its certificate needs to be safely copied to the +client side. This is basically the same as the SSH style of managing +keys. Next level up, one can use a single CA to sign server keys: then +only the CA's certificate needs to be safely copied to the client +side, this can happen even before any server certs are created (again, +see all of the discussion above.) + +With a certificate chain there are two or more CA's involved. Perhaps +it looks like this: + +``` +root_CA ---> intermediate_CA ---> server_cert +``` + +Where the arrow basically means "signs". + +In this usage mode the client (viewer-side) will have root_CA's +certificate available for verifying (and nothing else.) If the viewer +only received server_cert's certificate, it would not have enough info +to verify the server. The client needs to have intermediate_CA's cert +as well. The way to do this with x11vnc (i.e. an OpenSSL using app) is +to concatenate the server_cert's pem and the intermediate_CA's +certificate together. + +For example, suppose the file intermediate_CA.crt had +intermediate_CA's certificate. And suppose the file server_cert.pem +had the server's certificate and private key pair as described above +on this page. We need to do this: + +``` +cat intermediate_CA.crt >> server_cert.pem +``` + +(Note: the order of the items inside the file matters; intermediate_CA +must be after the server key and cert) and then we run x11vnc like +this: + +``` +x11vnc -ssl ./server_cert.pem ... +``` + +Then, on the VNC viewer client side, the viewer authenticates the +x11vnc server by using root_CA's certificate. Suppose that is in a +file named root_CA.crt, then using the SSVNC wrapper script +ss_vncviewer (which is also included in the SSVNC package) as our +example, we have: + +``` +ss_vncviewer -verify ./root_CA.crt hostname:0 +``` + +(where "hostname" is the machine where x11vnc is running.) One could +also use the SSVNC GUI setting Certs -> ServerCert to the root_CA.crt +file. Any other SSL enabled VNC viewer would use root_CA.crt in a +similar way. + +--- + +### Creating Chained Certificates + +Here is a fun example using VeriSign's "Trial Certificate" program. +Note that VeriSign has a Root CA and also an Intermediate CA and uses +the latter to sign customers certificates. So this provides an easy +way to test out the chained certificates mechanism with x11vnc. + +First we created a test x11vnc server key: + +``` +openssl genrsa -out V1.key 1024 +``` + +then we created a certificate signing request (CSR) for it: + +``` +openssl req -new -key V1.key -out V1.csr +``` + +(we followed the prompts and supplied information for the various +fields.) + +Then we went to VeriSign's page http://www.verisign.com/ssl/index.html +and clicked on "FREE TRIAL" (the certificate is good for 14 days.) We +filled in the forms and got to the point where it asked for the CSR +and so we pasted in the contents of the above V1.csr file. Then, after +a few more steps, VeriSign signed and emailed us our certificate. + +The VeriSign Trial certificates were found here: + +``` +http://www.verisign.com/support/verisign-intermediate-ca/Trial_Secure_Server_Root/index.html +http://www.verisign.com/support/verisign-intermediate-ca/trial-secure-server-intermediate/index.html +``` + +The former was pasted into a file V-Root.crt and the latter was pasted +into V-Intermediate.crt + +We pasted our Trial certificate that VeriSign signed and emailed to us +into a file named V1.crt and then we typed: + +``` +cat V1.key V1.crt > V1.pem +cat V1.pem V-Intermediate.crt > V1-combined.pem +chmod 600 V1.pem V1-combined.pem +``` + +So now the file V1-combined.pem has our private key and (VeriSign +signed) certificate and VeriSign's Trial Intermediate certificate. + +Next, we start x11vnc: + +``` +x11vnc -ssl ./V1-combined.pem ... +``` + +and finally, on the viewer side (SSVNC wrapper script example): + +``` +ss_vncviewer -verify ./V-Root.crt hostname:0 +``` + +One will find that only that combination of certs and keys will work, +i.e. allow the SSL connection to be established. Every other +combination we tried failed (note that ss_vncviewer uses the external +stunnel command to handle the SSL so we are really testing stunnel's +SSL implementation on the viewer side); and so the system works as +expected. + +--- + +### VNC Client Authentication using Certificate Chains + +Now, going the other way around with the client authenticating himself +via this chain of SSL certificates, x11vnc is run this way: + +``` +x11vnc -ssl SAVE -sslverify ./V-Root.crt ... +``` + + (note since the server must always supply a cert, we use its normal + self-signed, etc., one via "-ssl SAVE" and use the VeriSign root cert + for client authentication via -sslverify. The viewer must now supply + the combined certificates, e.g.: + +``` + ss_vncviewer -mycert ./V1-combined.pem hostname:0 +``` + +--- + +### Using OpenSSL and x11vnc to create Certificate Chains + +Although the x11vnc CA mechanism (-sslGenCA and -sslGenCert; see +above) was designed to only handle a single root CA (to sign server +and/or client certs) it can be coerced into creating a certificate +chain by way of an extra openssl(1) command. + +We will first create two CA's via -sslGenCA; then use one of these CA +to sign the other; create a new (non-CA) server cert; and append the +intermediate CA's cert to the server cert to have everything needed in +the one file. + +Here are the commands we ran to do what the previous paragraph +outlines. + +First we create the two CA's, called CA_root and CA_Intermediate here, +in separate directories via x11vnc: + +``` +x11vnc -ssldir ~/CA_Root -sslGenCA +(follow the prompts, we included "CA_Root", e.g. Common Name, to aid identifying it) +``` + +``` +x11vnc -ssldir ~/CA_Intermediate -sslGenCA +(follow the prompts, we included "CA_Intermediate", e.g. Common Name, to aid identifying it) +``` + +Next backup CA_Intermediate's cert and then sign it with CA_Root: + +``` +mv ~/CA_Intermediate/CA/cacert.pem ~/CA_Intermediate/CA/cacert.pem.ORIG +cd ~/CA_Root +openssl ca -config ./CA/ssl.cnf -policy policy_anything -extensions v3_ca -notext -ss_cert ~/CA_Intermediate/CA/cacert.pem.ORIG -out ~/CA_Intermediate/CA/cacert.pem +``` + +Note that it is required to cd to the ~/CA_Root directory and run the +openssl command from there. + +You can print out info about the cert you just modified by: + +``` +openssl x509 -noout -text -in ~/CA_Intermediate/CA/cacert.pem +``` + +Now we create an x11vnc server cert named "test_chain" that is signed +by CA_Intermediate: + +``` +x11vnc -ssldir ~/CA_Intermediate -sslGenCert server test_chain +(follow the prompts) +``` + +You can print out information about this server cert just created via +this command: + +``` +x11vnc -ssldir ~/CA_Intermediate -sslCertInfo SAVE-test_chain +``` + +This will tell you the full path to the server certificate, which is +needed because we need to manually append the CA_Intermediate cert for +the chain to work: + +``` +cat ~/CA_Intermediate/CA/cacert.pem >> ~/CA_Intermediate/server-test_chain.pem +``` + +Now we are finally ready to use it. We can run x11vnc using this +server cert+key by either this command: + +``` +x11vnc -ssldir ~/CA_Intermediate -ssl SAVE-test_chain ... +``` + +or this command: + +``` +x11vnc -ssl ~/CA_Intermediate/server-test_chain.pem ... +``` + +since they are equivalent (both load the same pem file.) + +Finally we connect via VNC viewer that uses CA_Root to verify the +server. As before we use ss_vncviewer: + +``` +ss_vncviewer -verify ~/CA_Root/CA/cacert.pem hostname:0 +``` + +Client Certificates (see above) work in a similar manner. + +So although it is a little awkward with the extra steps (e.g. +appending the CA_Intermediate cert) it is possible. If you want to do +this entirely with openssl(1) you will have to learn the openssl +commands corresponding to -genCA and -genCert. You may be able to find +guides on the Internet to do this. Starting with x11vnc 0.9.10, you +can have it print out the wrapper scripts it uses via: -sslScripts +(you will still need to fill in a few pieces of information; ask if it +is not clear from the source code.) + +--- + +## More info + +See also this article for some some general info and examples using +stunnel and openssl on Windows with VNC. Also +http://www.stunnel.org/faq/certs.html is a very good source of +information on SSL certificate creation and management. diff --git a/doc/SSVNC.md b/doc/SSVNC.md new file mode 100644 index 0000000..25e0b5c --- /dev/null +++ b/doc/SSVNC.md @@ -0,0 +1,1127 @@ +# Enhanced TightVNC Viewer (SSVNC: SSL/SSH VNC viewer) + +The Enhanced TightVNC Viewer, SSVNC, adds encryption security to VNC +connections. + +The package provides a GUI for Windows, Mac OS X, and Unix that +automatically starts up an STUNNEL SSL tunnel for SSL or ssh/plink for +SSH connections to any VNC server, such as x11vnc, and then launches +the VNC Viewer to use the encrypted tunnel. + +The x11vnc server has built-in SSL support, however SSVNC can make SSL +encrypted VNC connections to any VNC Server if they are running an SSL +tunnel, such as STUNNEL or socat, at their end. SSVNC's SSH tunnel +will work to any VNC Server host running sshd that you can log into. + +The Enhanced TightVNC Viewer package started as a project to add some +patches to the long neglected Unix TightVNC Viewer. However, now the +front-end GUI, encryption, and wrapper scripts features possibly +outweigh the Unix TightVNC Viewer improvements (see the lists below to +compare). + +The SSVNC Unix vncviewer can also be run without the SSVNC encryption +GUI as an enhanced replacement for the xvncviewer, xtightvncviewer, +etc., viewers. + +In addition to normal SSL, SSVNC also supports the VeNCrypt SSL/TLS +and Vino/ANONTLS encryption extensions to VNC on Unix, Mac OS X, and +Windows. Via the provided SSVNC VeNCrypt bridge, VeNCrypt and ANONTLS +encryption also works with any third party VNC Viewer (e.g. RealVNC, +TightVNC, UltraVNC, etc...) you select via 'Change VNC Viewer'. + +The short name for this project is "ssvnc" for SSL/SSH VNC Viewer. +This is the name of the command to start it. + +There is a simplified SSH-Only mode (sshvnc). And an even more +simplified Terminal-Services mode (tsvnc) for use with x11vnc on the +remote side. + +The tool has many additional features; see the descriptions below. + +It is a self-contained bundle, you could carry it around on, say, a +USB memory stick / flash drive for secure VNC viewing from almost any +machine, Unix, Mac OS X, and Windows (and if you create a directory +named "Home" in the toplevel ssvnc directory on the drive your VNC +profiles and certs will be kept there as well). For Unix, there is +also a conventional source tarball to build and install in the normal +way and not use a pre-built bundle. + +--- + +## Announcements + +Important: If you created any SSL certificates with SSVNC (or anything +else) on a Debian or Ubuntu system from Sept. 2006 through May 2008, +then those keys are likely extremely weak and can be easily cracked. +The certificate files should be deleted and recreated on a non-Debian +system or an updated one. See +http://www.debian.org/security/2008/dsa-1571 for details. The same +applies to SSH keys. + +Please read this information on using SSVNC on workstations with +Untrusted Local Users. + +--- + +## Feature List + +Wrapper scripts and a tcl/tk GUI were written to create these features +for Unix, Mac OS X, and Windows: + +* SSL support for connections using the bundled stunnel program. +* Automatic SSH connections from the GUI (system ssh is used on Unix + and MacOS X; bundled plink is used on Windows) +* Ability to Save and Load VNC profiles for different hosts. +* You can also use your own VNC Viewer, e.g. UltraVNC or RealVNC, + with the SSVNC encryption GUI front-end if you prefer. +* Create or Import SSL Certificates and Private Keys. +* Reverse (viewer listening) VNC connections via SSL and SSH. +* VeNCrypt SSL/TLS VNC encryption support (used by VeNCrypt, QEMU, + ggi, libvirt/virt-manager/xen, vinagre/gvncviewer/gtk-vnc) +* ANONTLS SSL/TLS VNC encryption support (used by Vino) +* VeNCrypt and ANONTLS are also enabled for any 3rd party VNC Viewer + (e.g. RealVNC, TightVNC, UltraVNC ...) on Unix, MacOSX, and + Windows via the provided SSVNC VeNCrypt Viewer Bridge tool (use + 'Change VNC Viewer' to select the one you want.) +* Support for Web Proxies, SOCKS Proxies, and the UltraVNC repeater + proxy (e.g. repeater://host:port+ID:1234). Multiple proxies may be + chained together (3 max). +* Support for SSH Gateway connections and non-standard SSH ports. +* Automatic Service tunnelling via SSH for CUPS and SMB Printing, + ESD/ARTSD Audio, and SMB (Windows/Samba) filesystem mounting. +* Sets up any additional SSH port redirections that you want. +* Zeroconf (aka Bonjour) is used on Unix and Mac OS X to find VNC + servers on your local network if the avahi-browse or dns-sd + program is available and in your PATH. +* Port Knocking for "closed port" SSH/SSL connections. In addition + to a simple fixed port sequence and one-time-pad implementation, a + hook is also provided to run any port knocking client before + connecting. +* Support for native MacOS X usage with bundled Chicken of the VNC + viewer (the Unix X11 viewer is also provided for MacOS X, and is + better IMHO. It is now the default on MacOS X.) +* Dynamic VNC Server Port determination and redirection (using ssh's + builtin SOCKS proxy, ssh -D) for servers like x11vnc that print + out PORT= at startup. +* Unix Username and Password entry for use with "x11vnc -unixpw" + type login dialogs. +* Simplified mode launched by command "sshvnc" that is SSH Only. +* Simplified mode launched by command "tsvnc" that provides a VNC + "Terminal Services" mode (uses x11vnc on the remote side). +* IPv6 support for all connection modes on Unix, MacOSX, and + Windows. + +Patches to TightVNC 1.3.9 vnc_unixsrc tree were created for Unix +TightVNC Viewer improvements (these only apply to the Unix VNC viewer, +including MacOSX XQuartz): + +* rfbNewFBSize VNC support (dynamic screen resizing) +* Client-side Scaling of the Desktop in the viewer. +* ZRLE VNC encoding support (RealVNC's encoding) +* Support for the ZYWRLE encoding, a wavelet based extension to ZRLE + to improve compression of motion video and photo regions. +* TurboVNC support (VirtualGL's modified TightVNC encoding; requires + TurboJPEG library) +* Pipelined Updates of the framebuffer as in TurboVNC (asks for the + next update before the current one has finished downloading; this + gives some speedup on high latency connections.) +* Cursor alphablending with x11vnc at 32bpp (-alpha option) +* Option "-unixpw ..." for use with "x11vnc -unixpw" type login + dialogs. +* Support for UltraVNC extensions: 1/n Server side scaling, Text + Chat, Single Window, Disable Server-side Input. Both UltraVNC and + x11vnc servers support these extensions. +* UltraVNC File Transfer via an auxiliary Java helper program (java + must be in $PATH). Note that the x11vnc server also supports + UltraVNC file transfer. +* Connection support for the UltraVNC repeater proxy (-repeater + option). +* Support for UltraVNC Single Click operation. (both unencrypted: SC + I, and SSL encrypted: SC III) +* Support for UltraVNC DSM Encryption Plugin symmetric encryption + mode. (ARC4, AESV2, MSRC4, and SecureVNC) +* Support for UltraVNC MS-Logon authentication (NOTE: the UltraVNC + MS-Logon key exchange implementation is very weak; an eavesdropper + on the network can recover your Windows password easily in a few + seconds; you need to use an additional encrypted tunnel with + MS-Logon.) +* Support for symmetric encryption (including blowfish and 3des + ciphers) to Non-UltraVNC Servers. Any server using the same + encryption method will work, e.g.: x11vnc -enc blowfish:./my.key +* Instead of hostname:display one can also supply "exec=command + args..." to connect the viewer to the stdio of an external command + (e.g. stunnel or socat) rather than using a TCP/IP socket. Unix + domain sockets, e.g. /path/to/unix/socket, and a previously opened + file descriptor fd=0, work too. +* Local Port Protections for STUNNEL and SSH: avoid having for long + periods of time a listening port on the the local (VNC viewer) + side that redirects to the remote side. +* Reverse (viewer listening) VNC connections can show a Popup dialog + asking whether to accept the connection or not (-acceptpopup.) The + extra info provided by UltraVNC Single Click reverse connections + is also supported (-acceptpopupsc) +* Extremely low color modes: 64 and 8 colors in 8bpp + (-use64/-bgr222, -use8/-bgr111) +* Medium color mode: 16bpp mode on a 32bpp Viewer display + (-16bpp/-bgr565) +* For use with x11vnc's client-side caching -ncache method use the + cropping option -ycrop n. This will "hide" the large pixel buffer + cache below the actual display. Set to the actual height or use -1 + for autodetection (also, tall screens, H > 2*W, are autodetected + by default). +* Escape Keys: specify a set of modifier keys so that when they are + all pressed down you can invoke Popup menu actions via keystrokes. + I.e., a set of 'Hot Keys'. One can also pan (move) the desktop + inside the viewport via Arrow keys or a mouse drag. +* Scrollbar width setting: -sbwidth n, the default is very thin, 2 + pixels, for less distracting -ycrop usage. +* Selection text sending and receiving can be fine-tuned with the + -sendclipboard, -sendalways, and -recvtext options. +* TightVNC compression and quality levels are automatically set + based on observed network latency (n.b. not bandwidth.) +* Improvements to the Popup menu, all of these can now be changed + dynamically via the menu: ViewOnly, Toggle Bell, CursorShape + updates, X11 Cursor, Cursor Alphablending, Toggle Tight/ZRLE, + Toggle JPEG, FullColor/16bpp/8bpp (256/64/8 colors), Greyscale for + low color modes, Scaling the Viewer resolution, Escape Keys, + Pipeline Updates, and others, including UltraVNC extensions. +* Maintains its own BackingStore if the X server does not. +* The default for localhost:0 connections is not raw encoding since + same-machine connections are pretty rare. Default assumes you are + using a SSL or SSH tunnel. Use -rawlocal to revert. +* XGrabServer support for fullscreen mode, for old window managers + (-grab/-graball option). +* Fix for Popup menu positioning for old window managers (-popupfix + option). +* The VNC Viewer ssvncviewer supports IPv6 natively (no helpers + needed.) + +The list of 3rd party software bundled in the archive files: + +* TightVNC Viewer (windows, unix, macosx) +* Chicken of the VNC Viewer (macosx) +* Stunnel (windows, unix, macosx) +* Putty/Plink/Pageant (windows) +* OpenSSL (windows) +* esound (windows) + +These are all self-contained in the bundle directory: they will not be +installed on your system. Just un-zip or un-tar the file you +downloaded and run the frontend ssvnc straight from its directory. +Alternatively, on Unix you can use the conventional source tarball. + +--- + +## Here is the Quick Start info from the README for how to setup and use SSVNC: + +``` +Quick Start: +----------- + +Unix and Mac OS X: + + Inside a Terminal do something like the following. + + Unpack the archive: + + % gzip -dc ssvnc-1.0.29.tar.gz | tar xvf - + + Run the GUI: + + % ./ssvnc/Unix/ssvnc (for Unix) + + % ./ssvnc/MacOSX/ssvnc (for Mac OS X) + + The smaller file "ssvnc_no_windows-1.0.29.tar.gz" + could have been used as well. + + On MacOSX you could also click on the SSVNC app icon in the Finder. + + On MacOSX if you don't like the Chicken of the VNC (e.g. no local + cursors, no screen size rescaling, and no password prompting), and you + have the XDarwin X server installed, you can set DISPLAY before starting + ssvnc (or type DISPLAY=... in Host:Disp and hit Return). Then our + enhanced TightVNC viewer will be used instead of COTVNC. + Update: there is now a 'Use X11 vncviewer on MacOSX' under Options ... + + + If you want a SSH-only tool (without the distractions of SSL) run + the command: + + sshvnc + + instead of "ssvnc". Or click "SSH-Only Mode" under Options. + Control-h will toggle between the two modes. + + + If you want a simple VNC Terminal Services only mode (requires x11vnc + on the remote server) run the command: + + tsvnc + + instead of "ssvnc". Or click "Terminal Services" under Options. + Control-t will toggle between the two modes. + + "tsvnc profile-name" and "tsvnc user@hostname" work too. + + +Unix/MacOSX Install: + + There is no standard install for the bundles, but you can make + symlinks like so: + + cd /a/directory/in/PATH + ln -s /path/to/ssvnc/bin/{s,t}* . + + Or put /path/to/ssvnc/bin, /path/to/ssvnc/Unix, or /path/to/ssvnc/MacOSX + in your PATH. + + For the conventional source tarball it will compile and install, e.g.: + + gzip -dc ssvnc-1.0.29.src.tar.gz | tar xvf - + cd ssvnc-1.0.29 + make config + make all + make PREFIX=/my/install/dir install + + then have /my/install/dir/bin in your PATH. + + + +Windows: + + Unzip, using WinZip or a similar utility, the zip file: + + ssvnc-1.0.29.zip + + Run the GUI, e.g.: + + Start -> Run -> Browse + + and then navigate to + + .../ssvnc/Windows/ssvnc.exe + + select Open, and then OK to launch it. + + The smaller file "ssvnc_windows_only-1.0.29.zip" + could have been used as well. + + You can make a Windows shortcut to this program if you want to. + + See the Windows/README.txt for more info. + + + If you want a SSH-only tool (without the distractions of SSL) run + the command: + + sshvnc.bat + + Or click "SSH-Only Mode" under Options. + + + If you want a simple VNC Terminal Services only mode (requires x11vnc + on the remote server) run the command: + + tsvnc.bat + + Or click "Terminal Services" under Options. Control-t will toggle + between the two modes. "tsvnc profile-name" and "tsvnc user@hostname" + work too. +``` + +--- + +You can read all of the SSVNC GUI's Online Help Text here. + +--- + +The bundle unpacks a directory/folder named: ssvnc. It contains these +programs to launch the GUI: + +``` +Windows/ssvnc.exe for Windows +MacOSX/ssvnc for Mac OS X +Unix/ssvnc for Unix +``` + +(the Mac OS X and Unix launchers are simply links to the bin +directory). See the README for more information. + +The SSH-Only mode launcher program has name sshvnc. The Terminal +Services mode launcher program (assumes x11vnc 0.8.4 or later and Xvfb +installed on the server machine) has name tsvnc. + +The Viewer SSL support is done via a wrapper script (bin/ssvnc_cmd +that calls bin/util/ss_vncviewer) that starts up the STUNNEL tunnel +first and then starts the TightVNC viewer pointed at that tunnel. The +bin/ssvnc program is a GUI front-end to that script. See this FAQ for +more details on SSL tunnelling. In SSH connection mode, the wrappers +start up SSH appropriately. + +## Memory Stick Usage + +If you create a directory named "Home" in that +toplevel ssvnc directory then that will be used as the base for +storing VNC profiles and certificates. Also, for convenience, if you +first run the command with "." as an argument (e.g. "ssvnc .") it will +automatically create the "Home" directory for you. This is handy if +you want to place SSVNC on a USB flash drive that you carry around for +mobile use and you want the profiles you create to stay with the drive +(otherwise you'd have to browse to the drive directory each time you +load or save). + +One user on Windows created a BAT file to launch SSVNC and needed to +do this to get the Home directory correct: + +``` +cd \ssvnc\Windows +start \ssvnc\Windows\ssvnc.exe +``` + +(an optional profile name can be supplied to the ssvnc.exe line) + +WARNING: if you use ssvnc from an "Internet Cafe", i.e. some untrusted +computer, please be aware that someone may have set up that machine to +be capturing your keystrokes, etc. + + +## SSH-Only version + +The command "sshvnc" can be run instead of "ssvnc" +to get an SSH-only version of the tool: + +[sshvnc.gif] + +These also work: "sshvnc myprofile" and "sshvnc user@hostname". To +switch from the regular SSVNC mode, click "SSH-Only Mode" under +Options. This mode is less distracting if you never plan to use SSL, +manage certificates, etc. + + +Terminal Services Only: The command "tsvnc" can be run instead of +"ssvnc" to get a "Terminal Services" only version of the tool: + +[tsvnc.gif] + +These also work: "tsvnc myprofile" and "tsvnc user@hostname". To +switch from the regular SSVNC mode, click "Terminal Services" under +Options. + +This mode requires x11vnc (0.9.3 or later) installed on the remote +machine to find, create, and manage the user sessions. SSH is used to +create the encrypted and authenticated tunnel. The Xvfb (virtual +framebuffer X server) program must also be installed on the remote +system. However tsvnc will also connect to a real X session (i.e. on +the physical hardware) if you are already logged into the X session; +this is a useful access mode and does not require Xvfb on the remote +system. + +This mode should be very easy for beginner users to understand and +use. On the remote end you only need to have x11vnc and Xvfb available +in $PATH, and on the local end you just run something like: +tsvnc myname@myhost.com + +(or start up the tsvnc GUI first and then enter myname@myhost.com and +press "Connect"). + +Normally the Terminal Services sessions created are virtual (RAM-only) +ones (e.g. Xvfb, Xdummy, or Xvnc), however a nice feature is if you +have a regular X session (i.e displaying on the physical hardware) on +the remote machine that you are ALREADY logged into, then the x11vnc +run from tsvnc will find it for you as well. + +Also, there is setting "X Login" under Advanced Options that allows +you to attach to a real X server with no one logged in yet (i.e. +XDM/GDM/KDM Login Greeter screen) as long as you have sudo(1) +permission on the remote machine. + +Nice features to soon to be added to the tsvnc mode are easy CUPS +printing (working fairly well) and Sound redirection (needs much work) +of the Terminal Services Desktop session. It is easier in tsvnc mode +because the entire desktop session can be started with the correct +environment. ssvnc tries to handle the general case of an already +started desktop and that is more difficult. + + +## Proxies + +Web proxies, SOCKS proxies, and the UltraVNC repeater proxy +are supported to allow the SSVNC connection to go through the proxy to +the otherwise unreachable VNC Server. SSH gateway machines can be used +in the same way. Read more about SSVNC proxy support here. + + +## Dynamic VNC Server Port determination + +If you are running SSVNC on +Unix and are using SSH to start the remote VNC server and the VNC +server prints out the line "PORT=NNNN" to indicate which dynamic port +it is using (x11vnc does this), then if you prefix the SSH command +with "PORT=" SSVNC will watch for the PORT=NNNN line and uses ssh's +built in SOCKS proxy (ssh -D ...) to connect to the dynamic VNC server +port through the SSH tunnel. For example: + +``` +VNC Host:Display user@somehost.com +Remote SSH Command: PORT= x11vnc -find +``` + +or "PORT= x11vnc -display :0 -localhost", etc. Or use "P= x11vnc ..." + +There is also code to detect the display of the regular Unix +vncserver(1). It extracts the display (and hence port) from the lines +"New 'X' desktop is hostname:4" and also "VNC server is already +running as :4". So you can use something like: + +``` + PORT= vncserver; sleep 15 +or: PORT= vncserver :4; sleep 15 +``` + +the latter is preferred because when you reconnect with it will find +the already running one. The former one will keep creating new X +sessions if called repeatedly. + +If you use PORT= on Windows, a large random port is selected instead +and the -rfbport option is passed to x11vnc (it does not work with +vncserver). + + +## Patches for Unix Tightvnc viewer + +The rfbNewFBSize support allows the enhanced TightVNC Unix viewer to +resize when the server does (e.g. "x11vnc -R scale=3/4" remote control +command). + +The cursor alphablending is described here. + +The RealVNC ZRLE encoding is supported, in addition to some low colors +modes (16bpp and 8bpp at 256, 64, and even 8 colors, for use on very +slow connections). Greyscales are also enabled for the low color +modes. + +The Popup menu (F8) is enhanced with the ability to change many things +on the fly. F9 is added as a shortcut to toggle FullScreen mode. + +## Client Side Caching + +The x11vnc client-side caching is handled nicely +by this viewer. The very large pixel cache below the actual display in +this caching method is distracting. Our Unix VNC viewer will +automatically try to autodetect the actual display height if the +framebuffer is very tall (more than twice as high as it is wide). One +can also set the height to the known value via -ycrop n, or use -ycrop +-1 to force autodection. In fullscreen mode one is not possible to +scroll down to the pixel cache region. In non-fullscreen mode the +window manager frame is "shrink-wrapped" around the actual screen +display. You can still scroll down to the pixel cache region. The +scrollbars are set to be very thin (2 pixels) to be less distracting. +Use the -sbwidth n to make them wider. + +Probably nobody is interested in the grabserver patch for old window +managers when the viewer is in fullscreen mode... This and some other +unfixed bugs have been fixed in our patches (fullscreen toggle works +with KDE, -x11cursor has been fixed, and the dot cursor has been made +smaller). + +From the -help output: + +``` +SSVNC Viewer (based on TightVNC viewer version 1.3.9) + +Usage: vncviewer [] [][:] + vncviewer [] [][::] + vncviewer [] exec=[CMD ARGS...] + vncviewer [] fd=n + vncviewer [] /path/to/unix/socket + vncviewer [] -listen [] + vncviewer -help + + are standard Xt options, or: + -via + -shared (set by default) + -noshared + -viewonly + -fullscreen + -noraiseonbeep + -passwd (standard VNC authentication) + -user (Unix login authentication) + -encodings (e.g. "tight,copyrect") + -bgr233 + -owncmap + -truecolour + -depth + -compresslevel (0..9: 0-fast, 9-best) + -quality (0..9: 0-low, 9-high) + -nojpeg + -nocursorshape + -x11cursor + -autopass + +Option names may be abbreviated, e.g. -bgr instead of -bgr233. +See the manual page for more information. + + +Enhanced TightVNC viewer (SSVNC) options: + + URL http://www.karlrunge.com/x11vnc/ssvnc.html + + Note: ZRLE and ZYWRLE encodings are now supported. + + Note: F9 is shortcut to Toggle FullScreen mode. + + Note: In -listen mode set the env var. SSVNC_MULTIPLE_LISTEN=1 + to allow more than one incoming VNC server at a time. + This is the same as -multilisten described below. Set + SSVNC_MULTIPLE_LISTEN=MAX:n to allow no more than "n" + simultaneous reverse connections. + + Note: If the host:port is specified as "exec=command args..." + then instead of making a TCP/IP socket connection to the + remote VNC server, "command args..." is executed and the + viewer is attached to its stdio. This enables tunnelling + established via an external command, e.g. an stunnel(8) + that does not involve a listening socket. This mode does + not work for -listen reverse connections. + + If the host:port is specified as "fd=n" then it is assumed + n is an already opened file descriptor to the socket. (i.e + the parent did fork+exec) + + If the host:port contains a '/' it is interpreted as a + unix-domain socket (AF_LOCAL insead of AF_INET) + + -multilisten As in -listen (reverse connection listening) except + allow more than one incoming VNC server to be connected + at a time. The default for -listen of only one at a + time tries to play it safe by not allowing anyone on + the network to put (many) desktops on your screen over + a long window of time. Use -multilisten for no limit. + + -acceptpopup In -listen (reverse connection listening) mode when + a reverse VNC connection comes in show a popup asking + whether to Accept or Reject the connection. The IP + address of the connecting host is shown. Same as + setting the env. var. SSVNC_ACCEPT_POPUP=1. + + -acceptpopupsc As in -acceptpopup except assume UltraVNC Single + Click (SC) server. Retrieve User and ComputerName + info from UltraVNC Server and display in the Popup. + + -use64 In -bgr233 mode, use 64 colors instead of 256. + -bgr222 Same as -use64. + + -use8 In -bgr233 mode, use 8 colors instead of 256. + -bgr111 Same as -use8. + + -16bpp If the vnc viewer X display is depth 24 at 32bpp + request a 16bpp format from the VNC server to cut + network traffic by up to 2X, then tranlate the + pixels to 32bpp locally. + -bgr565 Same as -16bpp. + + -grey Use a grey scale for the 16- and 8-bpp modes. + + -alpha Use alphablending transparency for local cursors + requires: x11vnc server, both client and server + must be 32bpp and same endianness. + + -scale str Scale the desktop locally. The string "str" can + a floating point ratio, e.g. "0.9", or a fraction, + e.g. "3/4", or WxH, e.g. 1280x1024. Use "fit" + to fit in the current screen size. Use "auto" to + fit in the window size. "str" can also be set by + the env. var. SSVNC_SCALE. + + If you observe mouse trail painting errors, enable + X11 Cursor mode (either via Popup or -x11cursor.) + + Note that scaling is done in software and so can be + slow and requires more memory. Some speedup Tips: + + ZRLE is faster than Tight in this mode. When + scaling is first detected, the encoding will + be automatically switched to ZRLE. Use the + Popup menu if you want to go back to Tight. + Set SSVNC_PRESERVE_ENCODING=1 to disable this. + + Use a solid background on the remote side. + (e.g. manually or via x11vnc -solid ...) + + If the remote server is x11vnc, try client + side caching: x11vnc -ncache 10 ... + + -ycrop n Only show the top n rows of the framebuffer. For + use with x11vnc -ncache client caching option + to help "hide" the pixel cache region. + Use a negative value (e.g. -1) for autodetection. + Autodetection will always take place if the remote + fb height is more than 2 times the width. + + -sbwidth n Scrollbar width for x11vnc -ncache mode (-ycrop), + default is very narrow: 2 pixels, it is narrow to + avoid distraction in -ycrop mode. + + -nobell Disable bell. + + -rawlocal Prefer raw encoding for localhost, default is + no, i.e. assumes you have a SSH tunnel instead. + + -notty Try to avoid using the terminal for interactive + responses: use windows for messages and prompting + instead. Messages will also be printed to terminal. + + -sendclipboard Send the X CLIPBOARD selection (i.e. Ctrl+C, + Ctrl+V) instead of the X PRIMARY selection (mouse + select and middle button paste.) + + -sendalways Whenever the mouse enters the VNC viewer main + window, send the selection to the VNC server even if + it has not changed. This is like the Xt resource + translation SelectionToVNC(always) + + -recvtext str When cut text is received from the VNC server, + ssvncviewer will set both the X PRIMARY and the + X CLIPBOARD local selections. To control which + is set, specify 'str' as 'primary', 'clipboard', + or 'both' (the default.) + + -graball Grab the entire X server when in fullscreen mode, + needed by some old window managers like fvwm2. + + -popupfix Warp the popup back to the pointer position, + needed by some old window managers like fvwm2. + -sendclipboard Send the X CLIPBOARD selection (i.e. Ctrl+C, + Ctrl+V) instead of the X PRIMARY selection (mouse + select and middle button paste.) + + -sendalways Whenever the mouse enters the VNC viewer main + window, send the selection to the VNC server even if + it has not changed. This is like the Xt resource + translation SelectionToVNC(always) + + -recvtext str When cut text is received from the VNC server, + ssvncviewer will set both the X PRIMARY and the + X CLIPBOARD local selections. To control which + is set, specify 'str' as 'primary', 'clipboard', + or 'both' (the default.) + + -graball Grab the entire X server when in fullscreen mode, + needed by some old window managers like fvwm2. + + -popupfix Warp the popup back to the pointer position, + needed by some old window managers like fvwm2. + + -grabkbd Grab the X keyboard when in fullscreen mode, + needed by some window managers. Same as -grabkeyboard. + -grabkbd is the default, use -nograbkbd to disable. + + -bs, -nobs Whether or not to use X server Backingstore for the + main viewer window. The default is to not, mainly + because most Linux, etc, systems X servers disable + *all* Backingstore by default. To re-enable it put + + Option "Backingstore" + + in the Device section of /etc/X11/xorg.conf. + In -bs mode with no X server backingstore, whenever an + area of the screen is re-exposed it must go out to the + VNC server to retrieve the pixels. This is too slow. + + In -nobs mode, memory is allocated by the viewer to + provide its own backing of the main viewer window. This + actually makes some activities faster (changes in large + regions) but can appear to "flash" too much. + + -noshm Disable use of MIT shared memory extension (not recommended) + + -termchat Do the UltraVNC chat in the terminal vncviewer is in + instead of in an independent window. + + -unixpw str Useful for logging into x11vnc in -unixpw mode. "str" is a + string that allows many ways to enter the Unix Username + and Unix Password. These characters: username, newline, + password, newline are sent to the VNC server after any VNC + authentication has taken place. Under x11vnc they are + used for the -unixpw login. Other VNC servers could do + something similar. + + You can also indicate "str" via the environment + variable SSVNC_UNIXPW. + + Note that the Escape key is actually sent first to tell + x11vnc to not echo the Unix Username back to the VNC + viewer. Set SSVNC_UNIXPW_NOESC=1 to override this. + + If str is ".", then you are prompted at the command line + for the username and password in the normal way. If str is + "-" the stdin is read via getpass(3) for username@password. + Otherwise if str is a file, it is opened and the first line + read is taken as the Unix username and the 2nd as the + password. If str prefixed by "rm:" the file is removed + after reading. Otherwise, if str has a "@" character, + it is taken as username@password. Otherwise, the program + exits with an error. Got all that? + + -repeater str This is for use with UltraVNC repeater proxy described + here: http://www.uvnc.com/addons/repeater.html. The "str" + is the ID string to be sent to the repeater. E.g. ID:1234 + It can also be the hostname and port or display of the VNC + server, e.g. 12.34.56.78:0 or snoopy.com:1. Note that when + using -repeater, the host:dpy on the cmdline is the repeater + server, NOT the VNC server. The repeater will connect you. + + Example: vncviewer ... -repeater ID:3333 repeat.host:5900 + Example: vncviewer ... -repeater vhost:0 repeat.host:5900 + + Use, e.g., '-repeater SCIII=ID:3210' if the repeater is a + Single Click III (SSL) repeater (repeater_SSL.exe) and you + are passing the SSL part of the connection through stunnel, + socat, etc. This way the magic UltraVNC string 'testB' + needed to work with the repeater is sent to it. + + -rfbversion str Set the advertised RFB version. E.g.: -rfbversion 3.6 + For some servers, e.g. UltraVNC this needs to be done. + + -ultradsm UltraVNC has symmetric private key encryption DSM plugins: + http://www.uvnc.com/features/encryption.html. It is assumed + you are using a unix program (e.g. our ultravnc_dsm_helper) + to encrypt and decrypt the UltraVNC DSM stream. IN ADDITION + TO THAT supply -ultradsm to tell THIS viewer to modify the + RFB data sent so as to work with the UltraVNC Server. For + some reason, each RFB msg type must be sent twice under DSM. + + -mslogon user Use Windows MS Logon to an UltraVNC server. Supply the + username or "1" to be prompted. The default is to + autodetect the UltraVNC MS Logon server and prompt for + the username and password. + + IMPORTANT NOTE: The UltraVNC MS-Logon Diffie-Hellman + exchange is very weak and can be brute forced to recover + your username and password in a few seconds of CPU time. + To be safe, be sure to use an additional encrypted tunnel + (e.g. SSL or SSH) for the entire VNC session. + + -chatonly Try to be a client that only does UltraVNC text chat. This + mode is used by x11vnc to present a chat window on the + physical X11 console (i.e. chat with the person at the + display). + + -env VAR=VALUE To save writing a shell script to set environment variables, + specify as many as you need on the command line. For + example, -env SSVNC_MULTIPLE_LISTEN=MAX:5 -env EDITOR=vi + + -noipv6 Disable all IPv6 sockets. Same as VNCVIEWER_NO_IPV6=1. + + -noipv4 Disable all IPv4 sockets. Same as VNCVIEWER_NO_IPV4=1. + + -printres Print out the Ssvnc X resources (appdefaults) and then exit + You can save them to a file and customize them (e.g. the + keybindings and Popup menu) Then point to the file via + XENVIRONMENT or XAPPLRESDIR. + + -pipeline Like TurboVNC, request the next framebuffer update as soon + as possible instead of waiting until the end of the current + framebuffer update coming in. Helps 'pipeline' the updates. + This is currently the default, use -nopipeline to disable. + + -appshare Enable features for use with x11vnc's -appshare mode where + instead of sharing the full desktop only the application's + windows are shared. Viewer multilisten mode is used to + create the multiple windows: -multilisten is implied. + See 'x11vnc -appshare -help' more information on the mode. + + Features enabled in the viewer under -appshare are: + Minimum extra text in the title, auto -ycrop is disabled, + x11vnc -remote_prefix X11VNC_APPSHARE_CMD: message channel, + x11vnc initial window position hints. See also Escape Keys + below for additional key and mouse bindings. + + -escape str This sets the 'Escape Keys' modifier sequence and enables + escape keys mode. When the modifier keys escape sequence + is held down, the next keystroke is interpreted locally + to perform a special action instead of being sent to the + remote VNC server. + + Use '-escape default' for the default modifier sequence. + (Unix: Alt_L,Super_L and MacOSX: Control_L,Meta_L) + + Here are the 'Escape Keys: Help+Set' instructions from the Popup Menu: + + Escape Keys: Enter a comma separated list of modifier keys to be the + 'escape sequence'. When these keys are held down, the next keystroke is + interpreted locally to invoke a special action instead of being sent to + the remote VNC server. In other words, a set of 'Hot Keys'. + + To enable or disable this, click on 'Escape Keys: Toggle' in the Popup. + + Here is the list of hot-key mappings to special actions: + + r: refresh desktop b: toggle bell c: toggle full-color + f: file transfer x: x11cursor z: toggle Tight/ZRLE + l: full screen g: graball e: escape keys dialog + s: scale dialog +: scale up (=) -: scale down (_) + t: text chat a: alphablend cursor + V: toggle viewonly Q: quit viewer 1 2 3 4 5 6: UltraVNC scale 1/n + + Arrow keys: pan the viewport about 10% for each keypress. + PageUp / PageDown: pan the viewport by a screenful vertically. + Home / End: pan the viewport by a screenful horizontally. + KeyPad Arrow keys: pan the viewport by 1 pixel for each keypress. + Dragging the Mouse with Button1 pressed also pans the viewport. + Clicking Mouse Button3 brings up the Popup Menu. + + The above mappings are *always* active in ViewOnly mode, unless you set the + Escape Keys value to 'never'. + + If the Escape Keys value below is set to 'default' then a default list of + of modifier keys is used. For Unix it is: Alt_L,Super_L and for MacOSX it + is Control_L,Meta_L. Note: the Super_L key usually has a Windows(TM) Flag + on it. Also note the _L and _R mean the key is on the LEFT or RIGHT side + of the keyboard. + + On Unix the default is Alt and Windows keys on Left side of keyboard. + On MacOSX the default is Control and Command keys on Left side of keyboard. + + Example: Press and hold the Alt and Windows keys on the LEFT side of the + keyboard and then press 'c' to toggle the full-color state. Or press 't' + to toggle the ultravnc Text Chat window, etc. + + To use something besides the default, supply a comma separated list (or a + single one) from: Shift_L Shift_R Control_L Control_R Alt_L Alt_R Meta_L + Meta_R Super_L Super_R Hyper_L Hyper_R or Mode_switch. + + + New Popup actions: + + ViewOnly: ~ -viewonly + Disable Bell: ~ -nobell + Cursor Shape: ~ -nocursorshape + X11 Cursor: ~ -x11cursor + Cursor Alphablend: ~ -alpha + Toggle Tight/Hextile: ~ -encodings hextile... + Toggle Tight/ZRLE: ~ -encodings zrle... + Toggle ZRLE/ZYWRLE: ~ -encodings zywrle... + Quality Level ~ -quality (both Tight and ZYWRLE) + Compress Level ~ -compresslevel + Disable JPEG: ~ -nojpeg (Tight) + Pipeline Updates ~ -pipeline + + Full Color as many colors as local screen allows. + Grey scale (16 & 8-bpp) ~ -grey, for low colors 16/8bpp modes only. + 16 bit color (BGR565) ~ -16bpp / -bgr565 + 8 bit color (BGR233) ~ -bgr233 + 256 colors ~ -bgr233 default # of colors. + 64 colors ~ -bgr222 / -use64 + 8 colors ~ -bgr111 / -use8 + Scale Viewer ~ -scale + Escape Keys: Toggle ~ -escape + Escape Keys: Help+Set ~ -escape + Set Y Crop (y-max) ~ -ycrop + Set Scrollbar Width ~ -sbwidth + XGrabServer ~ -graball + + UltraVNC Extensions: + + Set 1/n Server Scale Ultravnc ext. Scale desktop by 1/n. + Text Chat Ultravnc ext. Do Text Chat. + File Transfer Ultravnc ext. File xfer via Java helper. + Single Window Ultravnc ext. Grab and view a single window. + (select then click on the window you want). + Disable Remote Input Ultravnc ext. Try to prevent input and + viewing of monitor at physical display. + + Note: the Ultravnc extensions only apply to servers that support + them. x11vnc/libvncserver supports some of them. + + Send Clipboard not Primary ~ -sendclipboard + Send Selection Every time ~ -sendalways +``` + +Nearly all of these can be changed dynamically in the Popup menu +(press F8 for it): + +[viewer_menu.gif] [unixviewer.jpg] + +--- + +## Windows + +For Windows, SSL Viewer support is provided by a GUI Windows/ssvnc.exe +that prompts for the VNC display and then starts up STUNNEL followed +by the Stock TightVNC Windows Viewer. Both are bundled in the package +for your convenience. The GUI has other useful features. When the +connection is finished, you will be asked if you want to terminate the +STUNNEL program. For SSH connections from Windows the GUI will use +PLINK instead of STUNNEL. + +## Unix and Mac OS X + +Run the GUI (ssvnc, see above) and let me know how it goes. + +--- + +Hopefully this tool will make it convenient for people to help test +and use the built-in SSL support in x11vnc. Extra testing of this +feature is much appreciated!! Thanks. + +Please Help Test the newly added features: + +* Automatic Service tunnelling via SSH for CUPS and SMB Printing +* ESD/ARTSD Audio +* SMB (Windows/Samba) filesystem mounting + +These allow you to print from the remote (VNC Server) machine to local +printers, listen to sounds (with some limitations) from the remote VNC +Server machine, and to mount your local Windows or Samba shares on the +remote VNC Server machine. Basically these new features try to +automate the tricks described here: + +* http://www.karlrunge.com/x11vnc/faq.html#faq-smb-shares +* http://www.karlrunge.com/x11vnc/faq.html#faq-cups +* http://www.karlrunge.com/x11vnc/faq.html#faq-sound + +--- + +## Downloading + +Downloads for this project are hosted at Sourceforge.net. + +Choose the archive file bundle that best suits you (e.g. no source +code, windows only, unix only, zip, tar etc). + +A quick guide: + +* On some flavor of Unix, e.g. Linux or Solaris? Use "ssvnc_unix_only" (or "ssvnc_no_windows" to recompile). +* On Mac OS X? Use "ssvnc_no_windows". +* On Windows? Use "ssvnc_windows_only". + +``` +ssvnc_windows_only-1.0.28.zip Windows Binaries Only. No source included (6.2MB) +ssvnc_no_windows-1.0.28.tar.gz Unix and Mac OS X Only. No Windows binaries. Source included. (10.1MB) +ssvnc_unix_only-1.0.28.tar.gz Unix Binaries Only. No source included. (7.2MB) +ssvnc_unix_minimal-1.0.28.tar.gz Unix Minimal. You must supply your own vncviewer and stunnel. (0.2MB) + +ssvnc-1.0.28.tar.gz All Unix, Mac OS X, and Windows binaries and source TGZ. (16.1MB) +ssvnc-1.0.28.zip All Unix, Mac OS X, and Windows binaries and source ZIP. (16.4MB) +ssvnc_all-1.0.28.zip All Unix, Mac OS X, and Windows binaries and source AND full archives in the zip dir. (19.2MB) +``` + +Here is a conventional source tarball: + +``` +ssvnc-1.0.28.src.tar.gz Conventional Source for SSVNC GUI and Unix VNCviewer (0.5MB) +``` + +it will be of use to those who do not want the SSVNC +"one-size-fits-all" bundles. For example, package/distro maintainers +will find this more familiar and useful to them (i.e. they run: "make +config; make all; make install"). Note that it does not include the +stunnel source, and so has a dependency that the system stunnel is +installed. + +Read the README.src file for more information on using the +conventional source tarball. + + +Note: even with the Unix bundles, e.g. "ssvnc_no_windows" or +"ssvnc_all", you may need to run the "./build.unix" script in the top +directory to recompile for your operating system. + +Here are the corresponding 1.0.29 development bundles (Please help +test them): + +``` +ssvnc_windows_only-1.0.29.zip +ssvnc_no_windows-1.0.29.tar.gz +ssvnc_unix_only-1.0.29.tar.gz +ssvnc_unix_minimal-1.0.29.tar.gz + +ssvnc-1.0.29.tar.gz +ssvnc-1.0.29.zip +ssvnc_all-1.0.29.zip + +ssvnc-1.0.29.src.tar.gz Conventional Source for SSVNC GUI and Unix VNCviewer (0.5MB) +``` + +For any Unix system, a self-extracting and running file for the +"ssvnc_unix_minimal" package is here: ssvnc. Save it as filename +"ssvnc", type "chmod 755 ./ssvnc", and then launch the GUI via typing +"./ssvnc". Note that this "ssvnc_unix_minimal" mode requires you +install the "stunnel" and "vncviewer" programs externally (for +example, install your distros' versions, e.g. on debian: "apt-get +install stunnel4 xtightvncviewer".) It will work, but many of the +SSVNC features will be missing. + +## Previous releases + +* Release 1.0.18 at Sourceforge.net +* Release 1.0.19 at Sourceforge.net +* Release 1.0.20 at Sourceforge.net +* Release 1.0.21 at Sourceforge.net +* Release 1.0.22 at Sourceforge.net +* Release 1.0.23 at Sourceforge.net +* Release 1.0.24 at Sourceforge.net +* Release 1.0.25 at Sourceforge.net +* Release 1.0.26 at Sourceforge.net +* Release 1.0.27 at Sourceforge.net +* Release 1.0.28 at Sourceforge.net + + +Please help test the UltraVNC File Transfer support in the native Unix +VNC viewer! Let us know how it went. + +Current Unix binaries in the archives: + +``` +Linux.i686 +Linux.x86_64 +Linux.ppc64 X (removed) +Linux.alpha X (removed) +SunOS.sun4u +SunOS.sun4m +SunOS.i86pc +Darwin.Power.Macintosh +Darwin.i386 +HP-UX.9000 X (removed) +FreeBSD.i386 X (removed) +NetBSD.i386 X (removed) +OpenBSD.i386 X (removed) +``` + +(some of these are out of date, marked with 'X' above, because I no +longer have access to machines running those OS's. Use the +"build.unix" script to recompile on your system). + +Note: some of the above binaries depend on libssl.so.0.9.7, whereas +some recent distros only provide libssl.so.0.9.8 by default (for +compatibility reasons they should install both by default but not all +do). So you may need to instruct your distro to install the 0.9.7 +library (it is fine to have both runtimes installed simultaneously +since the libraries have different names). Update: I now try to +statically link libssl.a for all of the binaries in the archive. + +You can also run the included build.unix script to try to +automatically build the binaries if your OS is not in the above list +or the included binary does not run properly on your system. Let me +know how that goes. + +--- + +## IMPORTANT + +there may be restrictions for you to download, use, or +redistribute the above because of cryptographic software they contain +or for other reasons. Please check out your situation and information +at the following and related sites: + +``` +http://stunnel.mirt.net +http://www.stunnel.org +http://www.openssl.org +http://www.chiark.greenend.org.uk/~sgtatham/putty/ +http://www.tightvnc.com +http://www.realvnc.com +http://sourceforge.net/projects/cotvnc/ +``` diff --git a/doc/SUNRAY.md b/doc/SUNRAY.md new file mode 100644 index 0000000..b01b07a --- /dev/null +++ b/doc/SUNRAY.md @@ -0,0 +1,364 @@ +# Sun Ray Notes + +You can run x11vnc on your (connected or disconnected) SunRay session +(Please remember to use settings like -wait 200, -sb 15, and not +running a screensaver animation (blank instead) to avoid being a +resource hog! x11vnc does induce a lot of memory I/O from polling the +X server. It also helps to have a solid background color, e.g. +-solid). + +News: Sun Ray Remote Control Toolkit: See the nice set of tools in the +Sun Ray Remote Control Toolkit that launch x11vnc automatically for +you for certain usage modes. + +You have to know the name of the machine your SunRay session X server +is running on (so you can ssh into it and start x11vnc). You also need +to know the X11 DISPLAY number for the session: on a SunRay it could +be a large number, e.g. :137, since there are many people with X +sessions (Xsun processes) on the same machine. If you don't know it, +you can get it by running who(1) in a shell on the SunRay server and +looking for the dtlocal entry with your username (and if you don't +even know which server machine has your session, you could login to +all possible ones looking at the who output for your username...). + +I put some code in my ~/.dtprofile script that stores $DISPLAY +(including the hostname) in a ~/.sunray_current file at session +startup (and deletes it when the X session ends) to make it easy to +get at the hostname and X11 display number info for my current X +sessions when I ssh in and am about to start x11vnc. + +SunRay Gotcha #1: Note that even though your SunRay X11 DISPLAY is +something like :137, x11vnc still tries for port 5900 as its listening +port if it can get it, in which case the VNC display (i.e. the +information you supply to the VNC viewer) is something like +sunray-server:0 (note the :0 corresponding to port 5900, it is not +:137). If it cannot get 5900, it tries for 5901, and so on. You can +also try to force the port (and thereby the VNC display) using the +-rfbport NNNN option. + +Especially on a busy Sun Ray server it is often difficult to find free +ports for both VNC and the HTTP Java applet server to listen on. This +script, vnc_findports may be of use for doing this automatically. It +suggests x11vnc command line options based on netstat output that +lists the occupied ports. It is even more difficult to start +vncserver/Xvnc on a busy Sun Ray because then 3 ports (HTTP, VNC, and +X11), all separated by 100 are needed! This script, findvncports may +be helpful as well. Both scripts start at VNC display :10 and work +their way up. + + SunRay Gotcha #2: If you get an error like: + +``` +shmget(tile) failed. +shmget: No space left on device +``` + +when starting up x11vnc that most likely means all the shared memory +(shm) slots are filled up on your machine. The Solaris default is only +100, and that can get filled up in a week or so on a SunRay server +with lots of users. If the shm slot is orphaned (e.g. creator process +dies) the slot is not reclaimed. You can view the shm slots with the +"ipcs -mA" command. If there are about 100 then you've probably hit +this problem. They can be cleaned out (by the owner or by root) using +the ipcrm command. I wrote a script shm_clear that finds the orphans +and lists or removes them. Longer term, have your SunRay sysadmin add +something like this to /etc/system: + +``` +set shmsys:shminfo_shmmax = 0x2000000 +set shmsys:shminfo_shmmni = 0x1000 +``` + +SunRay Gotcha #3: Some SunRay installations have implemented +suspending certain applications when a SunRay session is in a +disconnected state (e.g. Java Badge pulled out, utdetach, etc). This +is a good thing because it limits hoggy or runaway apps from wasting +the shared CPU resource. Think how much CPU and memory I/O is wasted +by a bunch of Firefox windows running worthless Flash animations while +your session is disconnected! + +So some sites have implemented scripts to suspend (e.g. kill -STOP) +certain apps when your badge is removed from the SunRay terminal. When +you reattach, it kill -CONT them. This causes problems for viewing the +detached SunRay session via x11vnc: those suspended apps will not +respond (their windows will be blank or otherwise inactive). + +What to do? Well, since you are going to be using the application you +might as well unfreeze it rather than starting up a 2nd instance. Here +is one way to do it using the kill -CONT mechanism: +kill -CONT `ps -ealf | grep ' T ' | grep $LOGNAME | awk '{print $4}'` + +If you want to be a good citizen and re-freeze them before you exit +x11vnc this script could be of use: + +``` +#!/bin/sh +# +# kill -STOP/-CONT script for x11vnc (or other) SunRay usage ("freezes" +# certain apps from hogging resources when disconnected). +# +# Put here a pattern that matches the apps that are frozen: +# +appmatch="java_vm|jre|netscape-bin|firefox-bin|realplay|acroread|mozilla-bin" + +if [ "X$1" = "Xfreeze" ]; then + pkill -STOP -U $LOGNAME "$appmatch" +elif [ "X$1" = "Xthaw" ]; then + pkill -CONT -U $LOGNAME "$appmatch" + +elif [ "$RFB_MODE" = "afteraccept" -a "$RFB_STATE" = "NORMAL" ]; then + # a valid x11vnc login. + if [ "$RFB_CLIENT_COUNT" = "1" ]; then + # only one client present. + pkill -CONT -U $LOGNAME "$appmatch" + fi +elif [ "$RFB_MODE" = "gone" -a "$RFB_STATE" = "NORMAL" ]; then + # a valid x11vnc login. + if [ "$RFB_CLIENT_COUNT" = "0" ]; then + # last client present has just left. + pkill -STOP -U $LOGNAME "$appmatch" + fi +fi +exit 0 +``` + +If you called the script "goodcitizen" you could type "goodcitizen +thaw" to unfreeze them, and then "goodcitizen freeze" to refreeze +them. One could also use these x11vnc options "-afteraccept +goodcitizen -gone goodcitizen" to do it automatically. + +SunRay Gotcha #4: Recent versions of the Sun Ray Server Software +SRSS (seems to be version 3.0 or 3.1) have a "misfeature" that when +the session is disconnected (i.e. badge/smartcard out) the screen +locker (xscreensaver) will freeze the X server just when the "Enter +Password" dialog box appears. So you cannot unlock the screen remotely +via x11vnc! + +Update: please see Bob Doolittle's detailed description of the this +issue at the bottom of this section. + +Here "freeze" means "stop other X clients from inserting keyboard and +mouse input and from viewing the current contents of the screen". Or +something like that; the upshot is x11vnc can't do its normal thing. + +There are several workarounds for this. + +1. The easiest one by far is to put these lines in your +$HOME/.dtprofile file: + + ``` + SUN_SUNRAY_UTXLOCK_PREF="/usr/openwin/bin/xlock -mode blank" + export SUN_SUNRAY_UTXLOCK_PREF + ``` + + One might argue that xlock isn't particularly "pretty". (Just IMHO, + but if something like this not being pretty actually gets in the way + of your work I think some introspection may be in order. :-) + +2. The problem has been traced to the pam_sunray.so PAM module. +Evidently xscreensaver invokes this pam module and it communicates +with utsessiond who in turn instructs the Xsun server to not process +any synthetic mouse/keyboard input or to update the screen +framebuffer. It is not clear if this is by design (security?) or +something else. + + In any event, the problem can be avoided, somewhat drastically, by + commenting out the corresponding line in /etc/pam.conf: + + ``` + #xscreensaver auth sufficient /opt/SUNWut/lib/pam_sunray.so syncondisplay + ``` + + Leave the other xscreensaver pam authentication lines unchanged. The + dtsession-SunRay line may also need to be commented out to avoid the + problem for CDE sessions. N.B. it is possible the application of a + SSRS patch, etc, may re-enable that /etc/pam.conf line. It may be + difficult to convince a sysadmin to make this change. + +3. A more forceful way is to kill the xscreensaver process from a +shell prompt whenever you connect via x11vnc and the screen is in a +locked state: + + ``` + pkill -U $LOGNAME '^xscreensaver$' + ``` + + And then after you are in be sure to restart it by typing something + like: + + ``` + xscreensaver & + ``` + + You may want to avoid restarting it until you are about to disconnect + your VNC viewer (since if it locks the screen while you are working + you'll be stuck again). + + 3') The above idea can be done a bit more cleanly by having x11vnc do + it. Suppose we called the following script xss_killer: + + ``` + #!/bin/sh + # + # xss_killer: kill xscreensaver after a valid x11vnc client logs in. + # Restart xscreensaver and lock it when the last client + # disconnects. + + PATH=/usr/openwin/bin:/usr/bin:$PATH + export PATH + + if [ "$RFB_MODE" = "afteraccept" -a "$RFB_STATE" = "NORMAL" ]; then + # a valid x11vnc login. + if [ "$RFB_CLIENT_COUNT" = "1" ]; then + # only one client present. + pkill -U $LOGNAME '^xscreensaver$' + pkill -KILL -U $LOGNAME -f xscreensaver/hacks + fi + elif [ "$RFB_MODE" = "gone" -a "$RFB_STATE" = "NORMAL" ]; then + # a valid x11vnc login. + if [ "$RFB_CLIENT_COUNT" = "0" ]; then + # last client present has just left. + xscreensaver -nosplash & + sleep 1 + xscreensaver-command -lock & + fi + fi + ``` + + Then we would run x11vnc with these options: "-afteraccept xss_killer + -gone xss_killer". The -afteraccept option (introduced in version 0.8) + is used to run a command after a vncviewer has successfully logged in + (note that this is a VNC login, not a Unix login, so you may not want + to do this if you are really paranoid...) + + Note if you use the above script and also plan to Ctrl-C (SIGINT) + x11vnc you have to run the xscreensaver in a new process group to + avoid killing it as well. One way to do this is via this kludge: + + ``` + perl -e 'setpgrp(0,0); exec "xscreensaver -nosplash &"' + ``` + + in the above script. + +4. There appears to be a bug in pam_sunray.so in that it doesn't seem +to honor the convention that, say, DISPLAY=unix:3 means to use Unix +sockets to connect to display 3 on the local machine (this is a bit +faster than TCP sockets). Rather, it thinks the display is a non-local +one to a machine named "unix" (that usually does not resolve to an IP +address). + + Amusingly, this can be used to bypass the pam_sunray.so blocking of + Xsun that prevents one from unlocking the screen remotely via x11vnc. + One could put something like this in $HOME/.dtprofile to kill any + existing xscreensavers and then start up a fresh xscreensaver using + DISPLAY=unix:N + + ``` + # stop/kill any running xscreensavers (probably not running yet, but to be sure) + xscreensaver-command -exit + pkill -U $LOGNAME '^xscreensaver$' + env DISPLAY=`echo $DISPLAY | sed -e 's/^.*:/unix:/'` xscreensaver & + ``` + +Important: Note that all of the above workarounds side-step the +pam_sunray.so PAM module in one way or another. You'll need to see if +that is appropriate for your site's SunRay / smartcard usage. Also, +these hacks may break other things and so you may want to test various +scenarios carefully. E.g. check corner cases like XDMCP/dtremote, +NSCM, etc. + +Update May 2008: Here is a useful description of this issue from Bob +Doolittle who is a developer for Sun Ray at Sun. I don't have the time +to digest and distill it and then adjust the above methods to provide +a clearer description, so I just include below the description he sent +me with the hope that it will help some users: + +> In SRSS 4.0 and earlier, the purpose of pam_sunray.so in the "auth" +> PAM stack of screensavers is to enable NSCM (and, although this is +> much less commonly used, "SC", which is configured when 3rd-party +> software is installed to allow smartcards to be used as part of the +> authentication process) to work. It should have no effect with +> smartcards. Currently, however, it does block the PAM stack for all +> sessions, which causes xscreensaver, when it locks a disconnected +> session, to not process any mouse or keyboard events as you +> describe (unless xscreensaver does an X server grab, however, other +> applications should still be able to draw in the session although +> xscreensaver may be playing tricks like putting a black window on +> top of everything). In both of the NSCM and SC models, +> authentication occurs in a separate session before SRSS will +> reconnect to the user session, in which case pam_sunray.so causes +> xscreensaver to just unlock the screen without prompting the user +> to enter their password again. To do this, pam_sunray.so has to +> block until the session becomes reconnected, so it can query SRSS +> at that time to determine whether the user has already +> authenticated or not. In SRSS 4.0 and earlier releases, +> pam_sunray.so could have been optimized to not block smartcard +> sessions, although since the session is disconnected this typically +> isn't important (except in the x11vnc case, as you've observed). +> +> In SRSS 4.1, however, for increased security the out-of-session +> authentication model has been extended to *all* session types, so +> pam_sunray.so will be required in all cases unless users are +> willing to authenticate twice upon hotdesking (e.g. when their card +> is inserted). In future, we may do away with pam_sunray.so, and in +> fact with any traditional screen locker in the user session, since +> SRSS itself will be providing better security than a screen locker +> running entirely within the user's X session is capable of +> providing. +> +> Your trick of setting DISPLAY to unix:DPY will effectively disable +> pam_sunray.so (I'm not sure I'd call that a bug - you're going out +> of your way to do something that wouldn't occur in the normal +> course of events, and really provides no useful value other than to +> tickle this behavior in pam_sunray.so). This will mean that, in +> SRSS 4.0 and earlier releases, users will be prompted for their +> passwords twice when reconnecting to their sessions for NSCM and SC +> session types. In 4.1, disabling pam_sunray.so in this way will +> cause this double-authentication to occur for *all* sessions, +> including simple smartcard sessions. Users may be willing to pay +> that price in order to be able to use x11vnc in disconnected +> sessions. I like this hack, personally. It's a little less +> convenient than some of the other approaches you describe, but it's +> lighter-weight and more secure than most of the other approaches, +> and provides the value of being able to use x11vnc in locked +> sessions. +> +> Here are some other minor notes: - I wouldn't recommend storing +> your display in your .dtprofile, unless you're willing to live with +> a single session at a time. Personally, I often find myself using +> several sessions, in several FoGs, for short periods of time so +> this would certainly break. IMO it's pretty easy to use $DISPLAY to +> do what you want on the fly, as needed, so I don't think the price +> of breaking multiple-session functionality would be worth the +> convenience, to me at least. Here's some ksh/bash syntax to extract +> the hostname and display number on the fly which you may find +> useful: +> +> ``` +> HOSTNAME=${DISPLAY%:*} +> FULLDPY=${DISPLAY#*:} +> DPYNUM=${FULLDPY%.*} +> ``` +> +> A final note may give you some insight into other clever hacks in +> this area: - Check out utaction. It's a very handy little utility +> that can be run as a daemon in the user session which will invoke a +> specified command upon session connects and/or disconnects. +> Personally, I start one up in my .dtprofile as follows: +> +> ``` +> utaction -c $HOME/.srconnectrc -d $HOME/.srdisconnectrc & +> ``` +> +> This then allows me to construct a .srconnectrc script containing +> useful commands I'd like to have run every time I insert my +> smartcard, and a .srdisconnectrc script of commands to be run every +> time I remove my smartcard (or, connect/disconnect to my session +> via NSCM or SC). This can be used for things like notifying a chat +> client of away status, as well as some of the hacks you've +> described on your page such as freeze/unfreeze, or perhaps to +> terminate an xscreensaver and start up a new one with the unix:DPY +> $DISPLAY specification as you describe (although it probably makes +> most sense to do this at login time, as opposed to every connect or +> disconnect event).