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Systems & Data Center · Intermediate

systemd Timer

A systemd unit that activates another unit on a calendar schedule or after a time interval, as an alternative to cron.

Definition

Timers use OnCalendar= for wall-clock schedules or OnBootSec=/OnUnitActiveSec= for monotonic intervals and trigger a matching .service unit. Persistent=true runs missed jobs after downtime, and systemctl list-timers shows schedules.

Example

OnCalendar=*-*-* 02:00:00 runs the associated backup.service daily at 2 a.m.

Exam tip

Timers integrate with journald logging and dependencies, and Persistent=true catches up missed runs, unlike plain cron.

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