Adding a once off triggering of a systemd timer

I have a systemd timer which runs at 23:00 on Fridays in order to do some batch data processing once a week during low demand times. It is Tuesday, and I would like to test a change I have made, I would like it to start at 23:00 today, so that I can check it tomorrow, rather than having to wait until next Monday.

Is there an easy & build in way to schedule a once-off triggering of a systemd timer? e.g. systemd trigger-timer --timer whatever.timer --at 2021-06-22T23:00 or something? I want it only to start at this time, I don't want to add a new recurring rule. I want it to run as regular every Friday at 23:00 and today at 23:00.

I'm sure I could hack something together with sleep 10hr ; systemctl start whatever.service or maybe manually edit the /etc/systemd/system/whatever.timer file, but if there's is a proper way to do "once off" triggerings of a timer, I would prefer to use that.

This is on Ubuntu Linux 20.04 & 18.04, whatever version of systemd that is (245?)

Solution 1:

You could add a

OnCalendar=2021-06-22T23:00

to your timer unit file. Then remove it after you are done. Or if you just want to trigger the service, you could do:

systemd-run --on-calendar=2021-06-22T23:00 systemctl start example.service

Solution 2:

A one-off triggering of a timer is not a timer, and a one-off firing of the service can be achieved with at or using a cron.

at 23:00 <<<"systemctl start example.service" would be fairly equivalent to what you're looking for.