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shutdown



SYNOPSIS

       /sbin/shutdown  [-t  sec]  [-arkhzncfF] time [warning-mes­
       sage]


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 process­
       ing 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 sys­
       tem, runlevel 6 is used to reboot the system, and runlevel
       1  is used to put to system into a state where administra­
       tive tasks can be performed; this is the default  if  nei­
       ther 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 mes­
              sages to everybody.

       -r     Reboot after shutdown.

       -h     Halt after shutdown.

       -z     Shutdown using software suspend. Using this  option
              will not kill processes but pass the control to the
              kernel what makes the proper steps to stop and save
              processes  to swaps. 'Software Suspend' needs to be
              compiled in.

       -n     [DEPRECATED] Don't call init(8) to do the  shutdown
              but  do it ourself.  The use of this option is dis­
              couraged, 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
       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  advi­
       sory  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  filesys­
       tems.


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 autho­
       rized 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 com­
       pares 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/shut­
       down.allow is one user name per line. Empty lines and com­
       ment lines (prefixed by a #) are allowed. Currently  there
       is a limit of 32 users in this file.
       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  Sys­
       tem,  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 envi­
       ronment.

       Shutdown wasn't designed  to  be  run  setuid.  /etc/shut­
       down.allow  is not used to find out who is executing shut­
       down, 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(1), halt(8), poweroff(8), reboot(8)

                          Juli 31, 2001               SHUTDOWN(8)
  

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