shutdown : power off or reboot the machine
[SYNOPSIS] shutdown OPTION TIME WALL
OPTION
-H
Halt the machine
-P
Power-off the machine
# shutdown -P
Turn off the computer after one minute
# shutdown -P +10
Turn off the computer after 10 minutes
-r
Reboot the machine
# shutdown -r now
Restart your computer now
-h
Equivalent to --poweroff, overridden by --halt
-k
Don't halt/power-off/reboot, just send warnings
-c
Cancel a pending shutdown