On a systemd system you have created /etc/systemd/system/backup.timer containing a [Timer] section with `OnCalendar=*-*-* 03:30:00`. What else is required, and what does that OnCalendar value mean?
LPIC-1 Exam 102-500, objective 107. Administrative tasks hard
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The options
Not correct Nothing else; the command to run is written in the [Timer] section itself
Wrong. A .timer unit has no ExecStart. It carries only the schedule; the work always lives in a separate unit, normally a .service.
Not correct A matching backup.service must exist; the timer fires it 3 hours 30 minutes after boot
Wrong on the schedule. A delay relative to boot is expressed with OnBootSec=, and one relative to the unit's activation with OnUnitActiveSec=. OnCalendar= is absolute wall-clock time.
Not correct An entry in /etc/crontab is still needed, because systemd timers only wake the machine
Wrong. systemd timers are a full replacement for cron entries and do not depend on cron at all. Waking a suspended machine is a separate opt-in setting, WakeSystem=true.
Correct A matching backup.service unit must exist; the timer fires it at 03:30 every day
Correct. A timer activates a unit; by default that is the unit of the same name with a .service suffix (overridable with Unit= in the [Timer] section). The calendar expression is year-month-day hour:minute:second with * as a wildcard, so this matches 03:30:00 on every date.
Why
A timer must be enabled and started (`systemctl enable --now backup.timer`) to have any effect; enabling the .service instead is the usual mistake. `systemctl list-timers` shows the next and last elapse of every active timer, and `systemd-analyze calendar '*-*-* 03:30:00'` expands an expression so you can check it before deploying. Persistent=true makes a timer catch up a run missed while the machine was off, which is systemd's answer to anacron.
Where this comes from
- Cited
- LPI exam objective 107.2
- What it says
- Understand systemd timer units as an alternative to cron.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 107 and space the ones you get wrong.