cron-like systemd unit notes

cron-like-systemd.md

cron-like systemd unit

1. Create myunit.service. Only [Service] is needed, with an ExecStart=

2. Create myunit.timer. It needs [Timer] with an OnCalendar= or similar. It needs [Install] with WantedBy=timers.target

3. Enable both units. The .service unit will issue a warning due to missing [Install]. This is not a problem

    systemctl --user enable $PWD/myunit.service
    systemctl --user enable $PWD/myunit.timer
   

Now you can start the timer when you want, for the .service to be executed according to schedule.

To verify the status of timers, use systemctl list-timers.

Starting on boot

At this point, the timer will only start once the user logs in (if installed for root it should start on boot). If you want the timer to start automatically on boot:

loginctl enable-linger [user]

No need for persistence

If you want to run a service on a schedule (or once) only temporarily (lose it after poweroff), you can use systemd-run. The .service and .timer units are created automatically for you. For example:

systemd-run --user [--unit=myunit] --on-calendar=hourly /bin/touch /tmp/test

myunit.service

[Unit]

[Service]
ExecStart="/bin/touch" "/tmp/test"

myunit.timer

[Unit]

[Timer]
OnCalendar=minutely

[Install]
WantedBy=timers.target