shutdown man page on Gentoo

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

       shutdown - bring the system down

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

       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 S 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.

       -a     Use /etc/shutdown.allow.

       -k     Don't  really shutdown; only send the warning messages to every‐

       -r     Reboot after shutdown.

       -h     Halt or power off after shutdown.

       -P     Halt action is to turn off the power.

       -H     Modifier to the -h flag.	Halt action is to halt	or  drop  into
	      boot  monitor on systems that support it.	 Must be used with the
	      -h flag.

       -f     Skip fsck on reboot.

       -F     Force fsck on reboot.

       -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.

       -c     Cancel a waiting shutdown. ("shutdown now" is  no	 longer	 wait‐
	      ing.)  With this option it is of course not possible to give the
	      time argument, but you can enter explanatory  message  arguments
	      on the command line that will be sent to all users.

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

       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 will create the advisory file
       /etc/nologin which causes programs such as login(1) to  not  allow  new
       user  logins.  This  file  is  created five minutes before the shutdown
       sequence starts. 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
       file systems get checked.  After that, the boot process	should	remove

       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 file systems.

       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 shut‐
       down is called with the -a argument (add	 this  to  the	invocation  of
       shutdown	 in  /etc/inittab),  it	 checks	 to see if the file /etc/shut‐
       down.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

       The -H option just sets the  init  environment  variable	 INIT_HALT  to
       HALT,  and the -P option just sets that variable to POWEROFF. The shut‐
       down script that calls halt(8)  as  the	last  thing  in	 the  shutdown
       sequence should check these environment variables and call halt(8) with
       the right options for  these  options  to  actually  have  any  effect.
       Debian 3.1 (sarge) supports this.


       A lot of users forget to give the time argument and are then puzzled by
       the error message shutdown produces. The time argument is mandatory; 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  processes
       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

       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  cur‐
       rently logged in on (one of the) console(s).

       Miquel van Smoorenburg,

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

			       November 12, 2003		   SHUTDOWN(8)

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