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



NAME
       shutdown - bring the system down

SYNOPSIS
       /sbin/shutdown [-t sec] [-arkhncfFHP] 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  run-
              level.

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

       -r     Reboot after shutdown.

       -h     Halt or poweroff after shutdown.

       -H     Halt action is to halt or drop into boot monitor on systems that
              support it.

       -P     Halt action is to turn off the power.

       -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 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
       ignored.

HALT OR POWEROFF
       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.

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

AUTHOR
       Miquel van Smoorenburg, miquelsATcistron.nl

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



                               November 12, 2003                   SHUTDOWN(8)