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Linux in a Nutshell

This directory of Linux commands is from Linux in a Nutshell, 5th Edition.

Click on any of the 687 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Bookshelf.

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shutdown [options] when [message]

System administration command. Terminate all processing. when may be a specific time (in hh:mm format), a number of minutes to wait (in +m format), or now. A broadcast message notifies all users to log off the system. Processes are signaled with SIGTERM to allow them to exit gracefully. /etc/init is called to perform the actual shutdown, which consists of placing the system in runlevel 1. Only privileged users can execute the shutdown command, although init may call shutdown with root privileges when the Ctrl-Alt-Del key combination is pressed from the console keyboard. Broadcast messages, default or defined, are displayed at regular intervals during the grace period; the closer the shutdown time, the more frequent the message.



When called from init, shut down only if one of the users listed in the file /etc/shutdown.allow is currently logged in.


Cancel a shutdown that is in progress.


Reboot fast, by suppressing the normal call to fsck when rebooting.


Force a filesystem check (fsck) on reboot.


Halt the system when shutdown is complete.


Print the warning message, but suppress actual shutdown.


Reboot the system when shutdown is complete.

-t num

Ensure a num-second delay between killing processes and changing the runlevel.

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