SHUTDOWN(8)

NAME
shutdown, poweroff - close down the system at a given time

SYNOPSIS
shutdown [-] [ -h | -p | -r | -k] [ -o [-n]] time [warning-message ...]
poweroff

DESCRIPTION
The shutdown utility provides an automated shutdown procedure for super-users to nicely notify users when the system is shutting down, saving them from system administrators, hackers, and gurus, who would otherwise not bother with such niceties.

The following options are available:

-h  The system is halted at the specified time.

-p  The system is halted and the power is turned off (hardware support required, otherwise the system is halted) at the specified time.

-r  The system is rebooted at the specified time.

-k  Kick everybody off. The -k option does not actually halt the system, but leaves the system multi-user with logins disabled (for all but super-user).

-o  If one of the -h, -p or -r is specified, shutdown will execute halt(8) or reboot(8) instead of sending a signal to init(8).

-n  If the -o is specified, prevent the file system cache from being flushed by passing -n option to halt(8) or reboot(8). This option should probably not be used.

time
    Time is the time at which shutdown will bring the system down and may be the case-insensitive word now (indicating an immediate shutdown) or specify a future time in one of two formats: +number, or yymmddhhmm, where the year, month, and day may be defaulted to the current system values. The first form brings the system down in number minutes and the second at the absolute time specified. +number may be specified in units other than minutes by appending the corresponding suffix: “s”, “sec”, “m”, “min”, “h”, “hour”.

    If an absolute time is specified, but not a date, and that time today has already passed, shutdown will assume that the same time tomorrow was meant. (If a complete date is specified which has already passed, shutdown will print an error and exit without shutting the system down.)

warning-message
    Any other arguments comprise the warning message that is broadcast to users currently logged into the system.

-   If ‘-’ is supplied as an option, the warning message is read from the standard input.

At intervals, becoming more frequent as apocalypse approaches and starting at ten hours before shutdown, warning messages are displayed on the terminals of all users logged in. Five minutes before shutdown, or immediately if shutdown is in less than 5 minutes, logins are disabled by creating /var/run/nologin and copying the warning message there. If this file exists when a user attempts to log in, login(1) prints its contents and exits. The file is removed just before shutdown exits.

At shutdown time a message is written to the system log, containing the time of shutdown, the person who initiated the shutdown and the reason. Corresponding signal is then sent to init(8) to respectively halt, reboot or bring the system down to single-user state (depending on the above options). The time of the shutdown and the warning message are placed in /var/run/nologin and should be used to inform the users about when the system will be back up and why it is going down (or anything else).

A scheduled shutdown can be canceled by killing the shutdown process (a SIGTERM should suffice). The /var/run/nologin file that shutdown created will be removed automatically.

When run without options, the shutdown utility will place the system into single user mode at the time specified.

Calling “poweroff” is equivalent to running:

    shutdown -p now

FILES
/var/run/nologin
    tells login(1) not to let anyone log in

EXAMPLES
Reboot the system in 30 minutes and display a warning message on the terminals of all users currently logged in:

    # shutdown -r +30 "System will reboot"

BACKWARD COMPATIBILITY
The hours and minutes in the second time format may be separated by a colon (``:'') for backward compatibility.

SEE ALSO
kill(1), login(1), wall(1), nologin(5), halt(8), init(8), reboot(8)

HISTORY
A shutdown command was originally written by Ian Johnstone for UNSW's modified AT&T UNIX. It was modified and then incorporated in 4.1BSD.