A shutdown was scheduled earlier with `shutdown -h 23:00` and the maintenance has been called off. Which command cancels it?
LPIC-1 Exam 101-500, objective 101. System architecture easy
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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 shutdown -c
Correct. -c cancels a shutdown that is still waiting, and may be given a message that is broadcast to warn users that the shutdown is off.
Not correct shutdown -k
Wrong. -k sends the warning messages a real shutdown would send but never shuts the system down. It is a rehearsal, not a cancellation.
Not correct systemctl cancel
Wrong here, although the command exists. systemctl cancel cancels jobs queued in the manager's job queue; a timed shutdown is not one of those until its moment arrives.
Not correct wall 'shutdown cancelled'
Wrong. wall tells the users, which is worth doing, but the scheduled shutdown proceeds regardless.
Why
shutdown with a future time argument schedules the event and returns, leaving a pending shutdown that the systemd implementation records in /run/systemd/shutdown/scheduled; -c withdraws it. Two forms are not cancellable, because they are not scheduled: `shutdown now` and a time argument of +0. Remember the pairing of the flags by what they suppress: -k suppresses the shutdown but keeps the warnings, and -c withdraws a shutdown that was already announced.
Where this comes from
- Cited
- manual page shutdown(8)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 101 and space the ones you get wrong.
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