/usr/sbin/shutdown [-bfhknr] time [warning-message ...]
The shutdown command provides an automated shutdown procedure. You must be root to use this command.
The time argument specifies when shutdown will bring the system down. You can use the word now (indicating an immediate shutdown) or specify a future time in one of two formats: +number or hhmm. The first form brings the system down in number minutes. The second form brings the system down at the hours and minutes specified. The hours and minutes in the second time format may be separated by a colon (:) for backward compatibility.
Any other arguments comprise the warning message that is broadcast to users currently logged into the system. Prior to shutdown, warning messages are displayed at the terminals of all users on the system. Messages are sent at intervals which get closer together as shutdown approaches.
Five minutes before shutdown (or immediately, if shutdown is in less than five minutes) logins are disabled by creating the /etc/nologin file and copying the warning message there. If this file exists when a user attempts to log in, the login program prints its contents and exits. The nologin file is removed just before shutdown exits. If the shutdown is canceled or aborted, the nologin file may remain, and then must then be removed by the superuser after determining that the system is safe for users. If you cancel the shutdown during the grace period by using the kill shutdown_process_id command, the shutdown is cancelled and the nologin file is removed. A shutdown process should not be aborted once the grace period ends and shutdown actually begins.
At shutdown time a message is written in the system log, containing the time of shutdown, who ran shutdown and the reason. A terminate signal is then sent to init to bring the system down to the single-user state. Alternatively, if you invoke shutdown with the -r, -h, or -k flag, the command executes the reboot command or the halt command, or avoids shutting the system down. Note that the -h and -r flags use a broadcast kill signal and not the run level transition scripts. To use the run level transition scripts, execute the shutdown command without the -h or -r flag. This will bring the system down to single user mode. From single user mode, execute shutdown with the -h or -r flag. Alternatively, you can execute init 0 which will bring the system from level 3 to the console prompt.
If you invoke the command with the -f flag, shutdown shuts down the system quickly (in the manner of the fastboot or the fasthalt program); the system halts or reboots without checking the file systems. For example, the shutdown -f time command brings the system to single user and creates the /fastboot file; when the system reboots to multiuser, it does not invoke fsck. The shutdown -f -r time command causes the system to shut down, create the /fastboot file, then immediately reboot. The shutdown -f -h time command causes the system to halt and create the /fastboot file.
The -n flag prevents the normal syncing of disks before stopping the system. The -n and -f flags together on the command line are incompatible.
The time of the shutdown and the warning message are placed in the nologin file and can be used to inform the users about when the system will be back up and why it is going down.
Commands: login(1), wall(1), fastboot(8), fasthalt(8), halt(8), reboot(8) delim off