$ man shutdown
SHUTDOWN( 8 )             FreeBSD System Manager's Manual            SHUTDOWN(8)

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

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

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 sup-
             port required) 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 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 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.

     warning-message
             Any other arguments comprise the warning message that is broad-
             cast 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 start-
     ing at ten hours before shutdown, warning messages are displayed on the
     terminals of all users logged in.  Five minutes before shutdown, or imme-
     diately 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.

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

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

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

HISTORY
     The shutdown utility appeared in  4 .0BSD.

FreeBSD  4 . 9                     December  11 ,  1998                    FreeBSD  4 . 9