When the shutdown command is initiated, a warning followed by a final shutdown message is broadcast to all users who are currently logged in to the system and all systems that are mounting resources from the affected system.
For this reason, the shutdown command is preferred instead of the init command when you need to shut down a server. When you use either command, you might want to give users more notice by sending them a mail message about any scheduled system shutdown.
Use the who command to determine which users on the system need to be notified. This command is also useful for determining a system's current run level. For more information, see Determining a System's Run Level and the who(1) man page.