A systemd host has no atd installed and no package installation is permitted. You must run /usr/local/bin/report.sh exactly once, fifteen minutes from now, without writing any unit files. Which command does it?
LPIC-1 Exam 102-500, objective 107. Administrative tasks hard
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Correct systemd-run --on-active=15m /usr/local/bin/report.sh
Correct. --on-active creates a transient timer unit plus a transient service unit, with the timer set to elapse the given interval after it is started.
Not correct systemd-run --on-calendar=15m /usr/local/bin/report.sh
Wrong. --on-calendar expects a calendar event expression such as `*-*-* 02:00:00` or `Mon *-*-* 09:00`, not a relative delay, so this is rejected as an invalid specification.
Not correct systemctl start --timer=15m /usr/local/bin/report.sh
Wrong. systemctl start activates an existing unit by name; it has no --timer option and takes no executable paths.
Not correct echo /usr/local/bin/report.sh | at now + 15 minutes
Wrong under the stated constraints. This is the correct classic answer, but at is a client for the atd daemon, and the scenario says atd is not present, so the job would never be executed.
Why
systemd-run runs a command inside a transient unit created on the fly. With no timer option it starts immediately; with --on-active=, --on-boot=, --on-startup=, --on-unit-active= or --on-calendar= it instead creates a transient .timer that activates the transient service. Monotonic options take a time span such as 15m or 90s, while --on-calendar takes systemd calendar syntax, and confusing the two is the usual mistake.
Where this comes from
- Cited
- manual page systemd-run(1)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 107 and space the ones you get wrong.
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