systemd timers instead of cron

For a job that runs once a night, a systemd timer is a service file plus a timer file. It is more typing than a crontab line, but you get logging and status for free.

The service

# /etc/systemd/system/cleanup.service
[Unit]
Description=Nightly cleanup

[Service]
Type=oneshot
ExecStart=/usr/local/bin/cleanup.sh

The timer

# /etc/systemd/system/cleanup.timer
[Unit]
Description=Run cleanup every night

[Timer]
OnCalendar=*-*-* 03:30:00
Persistent=true
RandomizedDelaySec=300

[Install]
WantedBy=timers.target

Enable it with systemctl enable --now cleanup.timer.

The two options worth knowing

• Persistent=true runs the job at the next boot if the machine was off at the scheduled time. Cron simply skips it.
• RandomizedDelaySec spreads start times, which is useful when many machines share the same schedule.

Looking at it

systemctl list-timers shows when each timer last ran and when it runs next. Output of the job goes to the journal: journalctl -u cleanup.service. To check a calendar expression before using it, run systemd-analyze calendar "*-*-* 03:30:00".

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