start_dependent_systemd_service

#!/bin/bash
#
# TODO: Maybe reread https://unix.stackexchange.com/questions/326181/systemd-unit-service-restart-if-another-service-start-or-reload

help() {
   echo 'usage: start_dependent_systemd_service serviceA serviceB'
   echo '       start_dependent_systemd_service serviceA serviceB --help'
   echo
   echo '   Will watch/monitor dbus for systemd events and will start'
   echo '   serviceB when it sees that serviceA has started.'
   echo
   echo '   ATTENTION: this script will NOT sanitize the serviceA'
   echo '              or serviceB parameters and pass them straight'
   echo '              to awk and the shell!!! YOU HAVE BEEN WARNED!!!'
   echo
   echo '   Dependencies: gdbus, awk'
   echo
   echo '   Note: this script was originally created to solve the'
   echo '         following problem:'
   echo '         * you start some containers with `docker-compose`'
   echo '         * you (or something) does'
   echo '          `systemctl stop docker; systemctl stop docker`'
   echo '         * your "docker-compose containers" will not get'
   echo '           started...'
   echo '         To solve this particular problem you better use'
   echo '         `restart: until-stopped`.'
   echo
   exit 1
}

[ "$1" == "--help" ] && help
[ "$1" == "" ] && echo "You have to pass the name of serviceA to the script" >&2 && exit 1
[ "$2" == "" ] && echo "You have to pass the name of serviceB to the script" >&2 && exit 2

set -e          # stop on error
set -u          # stop on undefined variable
set -o pipefail # stop part of pipeline failing

SERVICE_A="$1"
SERVICE_B="$2"

# gdbus will output something like this, that is interesting for us:
#
#     /org/freedesktop/systemd1: org.freedesktop.systemd1.Manager.JobRemoved (uint32 12045, objectpath '/org/freedesktop/systemd1/job/12045', 'testing.service', 'done')
#
gdbus monitor --system \
              --dest org.freedesktop.systemd1 \
              --object-path /org/freedesktop/systemd1 \
| awk "/^\/org\/freedesktop\/systemd1: org.freedesktop.systemd1.Manager.JobRemoved \(uint32.* '${SERVICE_A}.service', 'done'\)$/ { system(\"systemctl is-active ${SERVICE_A} && systemctl start ${SERVICE_B}.service\") }"