SHUTDOWN(8)						Linux System Administrator's Manual					       SHUTDOWN(8)

NAME

       shutdown - bring the system down

SYNOPSIS

       /sbin/shutdown [-t sec] [-arkhncfF] time [warning-message]

DESCRIPTION

       shutdown  brings the system down in a secure way.  All logged-in users are notified that the system is going down, and login(1) is blocked.
       It is possible to shut the system down immediately or after a specified delay.  All processes are first notified that the system  is  going
       down  by  the  signal  SIGTERM.	This gives programs like vi(1) the time to save the file being edited, mail and news processing programs a
       chance to exit cleanly, etc.  shutdown does its job by signalling the init process, asking it to change the runlevel.  Runlevel 0  is  used
       to  halt  the  system,  runlevel  6 is used to reboot the system, and runlevel 1 is used to put to system into a state where administrative
       tasks can be performed; this is the default if neither the -h or -r flag is given to shutdown.  To see which actions are taken on  halt	or
       reboot see the appropriate entries for these runlevels in the file /etc/inittab.

OPTIONS

       -a     Use /etc/shutdown.allow.

       -t sec Tell init(8) to wait sec seconds between sending processes the warning and the kill signal, before changing to another runlevel.

       -k     Don't really shutdown; only send the warning messages to everybody.

       -r     Reboot after shutdown.

       -h     Halt after shutdown.

       -n     [DEPRECATED]  Don't  call  init(8) to do the shutdown but do it ourself.	The use of this option is discouraged, and its results are
	      not always what you'd expect.

       -f     Skip fsck on reboot.

       -F     Force fsck on reboot.

       -c     Cancel an already running shutdown. With this option it is of course not possible to give the time argument, but	you  can  enter  a
	      explanatory message on the command line that will be sent to all users.

       time   When to shutdown.

       warning-message
	      Message to send to all users.

       The  time argument can have different formats.  First, it can be an absolute time in the format hh:mm, in which hh is the hour (1 or 2 dig-
       its) and mm is the minute of the hour (in two digits).  Second, it can be in the format +m, in which m is the number of	minutes  to  wait.
       The word now is an alias for +0.

       If  shutdown is called with a delay, it creates the advisory file /etc/nologin which causes programs such as login(1) to not allow new user
       logins. Shutdown removes this file if it is stopped before it can signal init (i.e. it is cancelled or  something  goes	wrong).   It  also
       removes it before calling init to change the runlevel.

       The  -f	flag  means `reboot fast'.  This only creates an advisory file /fastboot which can be tested by the system when it comes up again.
       The boot rc file can test if this file is present, and decide not to run fsck(1) since the system has been shut down  in  the  proper  way.
       After that, the boot process should remove /fastboot.

       The  -F	flag  means `force fsck'.  This only creates an advisory file /forcefsck which can be tested by the system when it comes up again.
       The boot rc file can test if this file is present, and decide to run fsck(1) with a special `force' flag so that  even  properly  unmounted
       filesystems get checked.  After that, the boot process should remove /forcefsck.

       The -n flag causes shutdown not to call init, but to kill all running processes itself.	shutdown will then turn off quota, accounting, and
       swapping and unmount all filesystems.

ACCESS CONTROL

       shutdown can be called from init(8) when the magic keys CTRL-ALT-DEL are pressed, by creating an appropriate entry  in  /etc/inittab.  This
       means that everyone who has physical access to the console keyboard can shut the system down. To prevent this, shutdown can check to see if
       an authorized user is logged in on one of the virtual consoles. If shutdown is called with the -a argument (add this to the  invocation	of
       shutdown in /etc/inittab), it checks to see if the file /etc/shutdown.allow is present.	It then compares the login names in that file with
       the list of people that are logged in on a virtual console (from /var/run/utmp). Only if one of those authorized users or  root	is  logged
       in, it will proceed. Otherwise it will write the message

       shutdown: no authorized users logged in

       to the (physical) system console. The format of /etc/shutdown.allow is one user name per line. Empty lines and comment lines (prefixed by a
       #) are allowed. Currently there is a limit of 32 users in this file.

       Note that if /etc/shutdown.allow is not present, the -a argument is ignored.

FILES

       /fastboot
       /etc/inittab
       /etc/init.d/halt
       /etc/init.d/reboot
       /etc/shutdown.allow

NOTES

       A lot of users forget to give the time argument and are then puzzled by the error message shutdown produces. The time  argument	is  manda-
       tory; in 90 percent of all cases this argument will be the word now.

       Init  can  only	capture  CTRL-ALT-DEL and start shutdown in console mode.  If the system is running the X window System, the X server pro-
       cesses all key strokes. Some X11 environments make it possible to capture CTRL-ALT-DEL, but what exactly is done with that event depends on
       that environment.

       Shutdown  wasn't  designed  to  be run setuid. /etc/shutdown.allow is not used to find out who is executing shutdown, it ONLY checks who is
       currently logged in on (one of the) console(s).

AUTHOR

       Miquel van Smoorenburg, miquels@cistron.nl

SEE ALSO

       fsck(8), init(8), halt(8), poweroff(8), reboot(8)

								   Juli 31, 2001						       SHUTDOWN(8)