poweroff(8) manual page

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. In order to use the shutdown command, the user must have root privileges or be a member of the operator group.

The following options are available:

-c

The system is power cycled (power turned off and then back on) at the specified time. If the hardware doesn't support power cycle, the system will be rebooted. At the present time, only systems with BMC supported by the ipmi(4) driver that implement this functionality support this flag. The amount of time the system is off is dependent on the device that implements this feature.

-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 -c, -h, -p or -r options are specified, shutdown will execute halt(8) or reboot(8) instead of sending a signal to init(8).

-n

If the -o option is specified, prevent the file system cache from being flushed by passing -n 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 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. The 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

Manual Pages — SHUTDOWN

NAME

CONTENTS

SYNOPSIS

DESCRIPTION

FILES

EXAMPLES

COMPATIBILITY

SEE ALSO

HISTORY

-c
	The system is power cycled (power turned off and then back on) at the specified time. If the hardware doesn't support power cycle, the system will be rebooted. At the present time, only systems with BMC supported by the ipmi(4) driver that implement this functionality support this flag. The amount of time the system is off is dependent on the device that implements this feature.
-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 -c, -h, -p or -r options are specified, shutdown will execute halt(8) or reboot(8) instead of sending a signal to init(8).
-n
	If the -o option is specified, prevent the file system cache from being flushed by passing -n 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 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.