What is SHUTDOWN command?

What is SHUTDOWN command?

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The SHUTDOWN command brings a Linux server down in a secure way. Using this command notifies all logged-in users that a server is going down. The SHUTDOWN command signals the INIT daemon to change the run level.

Syntax:

SHUTDOWN [-t sec] [options] time [warning message]

where, time argument tells the command when to shutdown, and warning message is a message that the command sends to all logged-in users on the server.

Several options are used with the SHUTDOWN command. Following is a list of some important options:

Option	Description
-a	Uses the /etc/shutdown.allow file to verify user permission.
-t	Tells the INIT daemon to wait for a specified number of seconds to change the system to another run level after sending the processes the warning.
-k	Sends only warning messages to users.
-r	Reboots the server after shutdown.
-h	Halts the server after shutdown.
-c	Cancels an already running SHUTDOWN process.

Note: If -a option is specified in the command (can be added to the invocation of the SHUTDOWN command in the /etc/inittab file), the command checks the logged-in user account in the /etc/shutdown.allow file. The command will proceed only if the user is authorized or he is a root user.

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