systemd-timer¶

--- Managing Timers ---

To list all active timers (with next/last run times):

systemctl list-timers

To list all timers including inactive ones

systemctl list-timers --all

To start a timer

systemctl start <name>.timer

To stop a timer

systemctl stop <name>.timer

To check timer status

systemctl status <name>.timer

To enable a timer to start on boot

systemctl enable --now <name>.timer

To disable a timer

systemctl disable --now <name>.timer

To trigger the associated service immediately

systemctl start <name>.service

To reload systemd after creating or editing unit files

systemctl daemon-reload

--- Timer Unit File: /etc/systemd/system/.timer ---

[Unit] Description=Run backup daily at 2am

[Timer] OnCalendar=--* 02:00:00 Persistent=true

[Install] WantedBy=timers.target --- Service Unit File: /etc/systemd/system/.service --- [Unit] Description=Backup service

[Service] Type=oneshot ExecStart=/usr/local/bin/backup.sh --- OnCalendar expressions --- daily at midnight:

OnCalendar=daily

daily at 02:30

OnCalendar=*-*-* 02:30:00

weekdays at 09:00

OnCalendar=Mon..Fri *-*-* 09:00

every hour

OnCalendar=hourly

--- Other Timer Directives ---

Run once 15 minutes after boot:

OnBootSec=15min

Run every hour after last activation

OnUnitActiveSec=1h

Add random jitter (avoid thundering herd)

RandomizedDelaySec=5min

Catch up missed runs after downtime

Persistent=true

--- Debugging ---

To verify a calendar expression:

systemd-analyze calendar "<expression>"

To check the next 5 elapse times

systemd-analyze calendar --iterations=5 "<expression>"

To view timer logs

journalctl -u <name>.timer
journalctl -u <name>.service