chmod.md

title	date	icon	background	tags	categories	intro
Chmod	2021-07-01 03:51:44 -0700	icon-permission	bg-emerald-600	permission	Linux Command	This quick reference cheat sheet provides a brief overview of file permissions, and the operation of the chmod command

Getting started {.cols-3}

Syntax

$ chmod [options] <permissions> <file> 

Example

$ chmod 755 foo.txt
$ chmod +x quickref.py
$ chmod u-x quickref.py
$ chmod u=rwx,g=rx,o= quickref.sh

Change files and directories recursively

$ chmod -R 755 my_directory

The chmod command stands for "change mode"

Chmod Generator

Chmod Generator allows you to quickly and visually generate permissions in numerical and symbolic.

Common Permissions

Command	s	Meaning
400	r--------	Readable by owner only
500	r-x------	Avoid Changing
600	rw-------	Changeable by user
644	rw-r--r--	Read and change by user
660	rw-rw----	Changeable by user and group
700	rwx------	Only user has full access
755	rwxr-xr-x	Only changeable by user
775	rwxrwxr-x	Sharing mode for a group
777	rwxrwxrwx	Everybody can do everything

Explains

$ ls -l
-rw-r--r--  1 root root 3 Jun 29 15:35 a.log
drwxr-xr-x  2 root root 2 Jun 30 18:06 dir

Permission analysis of "dir"

d  rwx  r-x  r-x
┬  ─┬─  ─┬─  ─┬─  
│   │    │    │  
│   │    │    └─ 4. Other｜5 (4+0+1)
│   │    └────── 3. Group｜5 (4+0+1)
│   └─────────── 2. User ｜7 (4+2+1)
└─────────────── 1. File Type | directory

Permission Modes {.col-span-2}

Permission	Description	Octal	Decimal
---	No Permission	000	0 (0+0+0)
--x	Execute	001	1 (0+0+1)
-w-	Write	010	2 (0+2+0)
-wx	Execute and Write	011	3 (0+2+1)
r--	Read	100	4 (4+0+0)
r-x	Read and Execute	101	5 (4+0+1)
rw-	Read and Write	110	6 (4+2+0)
rwx	Read, Write and Execute	111	7 (4+2+1)
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Objects

Who (abbr.)	Meaning
u	User
g	Group
o	Others
a	All, same as ugo
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Permissions

Abbreviation	Permission	Value
r	Read	4
w	Write	2
x	Execute	1
-	No permission	0
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File Types

Abbreviation	File Type
d	Directory
-	Regular file
l	Symbolic Link
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Chmod Examples {.cols-3}

Operators

Symbol	Description
+	Add
-	Remove
=	Set

chmod 600

$ chmod 600 example.txt
$ chmod u=rw,g=,o= example.txt
$ chmod a+rwx,u-x,g-rwx,o-rwx example.txt

chmod 664

$ chmod 664 example.txt
$ chmod u=rw,g=rw,o=r example.txt
$ chmod a+rwx,u-x,g-x,o-wx example.txt

chmod 777

$ chmod 777 example.txt
$ chmod u=rwx,g=rwx,o=rwx example.txt
$ chmod a=rwx example.txt

Symbolic mode {.row-span-3}

Deny execute permission to everyone.

$ chmod a-x chmodExampleFile.txt

Allow read permission to everyone.

$ chmod a+r chmodExampleFile.txt

Make a file readable and writable by the group and others.

$ chmod go+rw chmodExampleFile.txt

Make a shell script executable by the user/owner.

$ chmod u+x chmodExampleScript.sh

Allow everyone to read, write, and execute the file and turn on the set group-ID.

$ chmod =rwx,g+s chmodExampleScript.sh

Removing Permissions {.row-span-3}

In order to remove read write permissions given to a file, use the following syntax:

$ chmod o-rw example.txt

For our file example.txt, we can remove read write permissions using chmod for group by running the following command:

$ chmod  g-rx example.txt

To remove chmod read write permissions from the group while adding read write permission to public/others, we can use the following command:

$ chmod g-rx, o+rx example.txt

But, if you wish to remove all permissions for group and others, you can do so using the go= instead:

$ chmod go= example.txt

Executable

$ chmod +x ~/example.py
$ chmod u+x ~/example.py
$ chmod a+x ~/example.py

chmod 754

$ chmod 754 foo.sh
$ chmod u=rwx,g=rx,o=r foo.sh

Chmod Practices {.cols-3}

SSH Permissions

$ chmod 700 ~/.ssh
$ chmod 600 ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/id_rsa
$ chmod 600 ~/.ssh/id_rsa.pub
$ chmod 400 /path/to/access_key.pem

Web Permissions

$ chmod -R 644 /var/www/html/
$ chmod 644 .htaccess
$ chmod 644 robots.txt
$ chmod 755 /var/www/uploads/
$ find /var/www/html -type d -exec chmod 755 {} \;

Batch Change

$ chmod -R 644 /your_path
$ find /path -type d -exec chmod 755 {} \;
$ find /path -type f -exec chmod 644 {} \;

See: Command Substitution

Also see

• Modify File Permissions with chmod (linode.com)