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 now
The 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 now
Like shutdown it will instantly restart your server without further delays.
Time Specified Reboot
shutdown -r +5
It 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
This will cancel all pending shutdown or reboot task triggered on shell.