As root you want the machine to reboot in five minutes, with logged-in users warned now. Which command does that?
LPIC-1 Exam 101-500, objective 101. System architecture medium
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The options
Correct shutdown -r +5
Correct. -r requests a reboot, +5 schedules it five minutes from now, and shutdown broadcasts a wall message to logged-in users when it is scheduled.
Not correct shutdown -h +5
Wrong action: -h halts the system rather than rebooting it (on a systemd machine that means powering off). The timing part is right.
Not correct shutdown -c +5
Wrong. -c cancels a shutdown that has already been scheduled and takes no time argument, so this is not a way to schedule anything.
Not correct shutdown -k +5
Wrong. -k only sends the warning messages to logged-in users; it never halts or reboots the machine. It is the dress rehearsal option.
Why
shutdown takes a time (+m, hh:mm, or now) and an action: -h halt or power off, -r reboot, -P power off explicitly, -H halt explicitly, -c cancel a pending shutdown, -k warn only. Users are warned automatically, and you can append your own message after the time. Always give the time explicitly (shutdown -r now, shutdown -r +5): what a bare shutdown -r does when the time is omitted differs between the sysvinit and systemd implementations.
Where this comes from
- Cited
- LPI exam objective 101.3
- What it says
- Shutting down and rebooting the system, and warning users before it happens.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 101 and space the ones you get wrong.