shutdown may be used to halt, power-off or reboot the machine. The first argument may be a time string (which is usually “now”). Optionally, this may be followed by a wall message to be sent to all logged-in users before going down. The time string may either be in the format “hh:mm” for hour/minutes specifying the time to execute the shutdown at, specified in 24h clock format.
Alternatively it may be in the syntax “+m” referring to the specified number
of minutes m from now. “now” is an alias for “+0”, i.e. for triggering an immediate shutdown. If no time argument is specified, “+1” is implied.Note that to specify a wall message you must specify a time argument, too. If the time argument is used, 5 minutes before the system goes down the /run/nologin file is created to ensure that further logins shall not be allowed.
Shutdown A Server
shutdown -h nowThe Command is going to power off your system instantly without further delays. This is useful when you want to power off your machine
Rebooting Your Server
shutdown -r nowLike shutdown it will instantly restart your server without further delays.
Time Specified Reboot
shutdown -r +5It will trigger reboot after 5 minutes. Till then all users on the machine have option to safely close their work and message will be broadcasted for all users too.
Cancel Reboot or Shutdown
shutdown -cThis will cancel all pending shutdown or reboot task triggered on shell.