The shutdown utility provides an automated shutdown procedure for super-users to nicely notify users when the system is shutting down, saving them from system administrators, hackers, and gurus, who would otherwise not bother with such niceties.
# To power off (halt) immediately:
shutdown -h now
# To reboot immediately:
shutdown -r now
# To reboot in 5 minutes:
shutdown -r +5 &
# To shutdown at 1:00 pm (Uses 24h clock):
shutdown -h 13:00
# To cancel a pending shutdown/reboot operation:
shutdown -c