systemd: execute bash script on start

Source

systemd is a not so new Linux init system. It's default on Debian systems. This is the very first process to start when Linux boots - it's PID is 1:

$ ps aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.1 139092  6876 ?        Ss   14:03   0:01 /sbin/init

$ file /sbin/init
/sbin/init: symbolic link to /lib/systemd/systemd

I've been running systemd for a while. But thanks to it's System V init script compatibility I've never actually written any scripts for it.

I wanted to start a simple bash script after linux booted and I decided it's time to use systemd to take care of business.

Unit file

Unit files describe the services systemd manages. Very simple unit file that starts a bash script could be:

[Unit]
Description=Starts some bash script

[Service]
WorkingDirectory=/home/povilas/
Type=forking
ExecStart=/bin/bash my_script.sh
KillMode=process

[Install]
WantedBy=multi-user.target

WantedBy option in the Install section means that this unit is wanted by multi-user.target unit. Meaning this unit becomes a dependency of multi-user.target unit.

Install unit file

Save the unit file to /etc/systemd/system/my_unit.service and enable it with:

# systemctl enable my_unit.service

Next time the OS boots, bash script will be executed.

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