shutdown



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 pro-
       cess, 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  per-
       formed;  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 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  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.


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, miquels@cistron.nl


SEE ALSO

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



                                 Juli 31, 2001                     SHUTDOWN(8)

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