INITTAB(5)                                              Linux System Administrator's Manual                                             INITTAB(5)

NAME

       inittab - format of the inittab file used by the sysv-compatible init process

DESCRIPTION

       The  inittab  file describes which processes are started at bootup and during normal operation (e.g. /etc/init.d/boot, /etc/init.d/rc, get-
       tys...).  Init(8) distinguishes multiple runlevels, each of which can have its own set of processes that are started.  Valid runlevels  are
       0-6 plus A, B, and C for ondemand entries.  An entry in the inittab file has the following format:

              id:runlevels:action:process

       Lines beginning with `#' are ignored.

       id     is a unique sequence of 1-4 characters which identifies an entry in inittab (for versions of sysvinit compiled with the old libc5 (<
              5.2.18) or a.out libraries the limit is 2 characters).

              Note: traditionally, for getty and other login processes, the value of the id field is kept the same as the  suffix  of  the  corre-
              sponding tty, e.g. 1 for tty1. Some ancient login accounting programs might expect this, though I can't think of any.

       runlevels
              lists the runlevels for which the specified action should be taken.

       action describes which action should be taken.

       process
              specifies  the  process to be executed.  If the process field starts with a `+' character, init will not do utmp and wtmp accounting
              for that process.  This is needed for gettys that insist on doing their own utmp/wtmp housekeeping.  This is also a historic bug.

       The runlevels field may contain multiple characters for different runlevels.  For example, 123 specifies that the process should be started
       in  runlevels  1, 2, and 3.  The runlevels for ondemand entries may contain an A, B, or C.  The runlevels field of sysinit, boot, and boot-
       wait entries are ignored.

       When the system runlevel is changed, any running processes that are not specified for the new runlevel are killed, first with SIGTERM, then
       with SIGKILL.

       Valid actions for the action field are:

       respawn
              The process will be restarted whenever it terminates (e.g. getty).

       wait   The process will be started once when the specified runlevel is entered and init will wait for its termination.

       once   The process will be executed once when the specified runlevel is entered.

       boot   The process will be executed during system boot.  The runlevels field is ignored.

       bootwait
              The  process  will  be  executed  during  system  boot, while init waits for its termination (e.g. /etc/rc).  The runlevels field is
              ignored.

       off    This does nothing.

       ondemand
              A process marked with an ondemand runlevel will be executed whenever the specified ondemand runlevel is called.   However,  no  run-
              level change will occur (ondemand runlevels are `a', `b', and `c').

       initdefault
              An initdefault entry specifies the runlevel which should be entered after system boot.  If none exists, init will ask for a runlevel
              on the console. The process field is ignored.

       sysinit
              The process will be executed during system boot. It will be executed before any boot or  bootwait entries.  The runlevels  field  is
              ignored.

       powerwait
              The  process  will be executed when the power goes down. Init is usually informed about this by a process talking to a UPS connected
              to the computer.  Init will wait for the process to finish before continuing.

       powerfail
              As for powerwait, except that init does not wait for the process's completion.

       powerokwait
              This process will be executed as soon as init is informed that the power has been restored.

       powerfailnow
              This process will be executed when init is told that the battery of the external UPS is almost empty and the power is failing  (pro-
              vided that the external UPS and the monitoring process are able to detect this condition).

       ctrlaltdel
              The  process  will  be executed when init receives the SIGINT signal.  This means that someone on the system console has pressed the
              CTRL-ALT-DEL key combination. Typically one wants to execute some sort of shutdown either to get into single-user level or to reboot
              the machine.

       kbrequest
              The process will be executed when init receives a signal from the keyboard handler that a special key combination was pressed on the
              console keyboard.

              The documentation for this function is not complete yet; more documentation can be found in the kbd-x.xx packages (most  recent  was
              kbd-0.94 at the time of this writing). Basically you want to map some keyboard combination to the "KeyboardSignal" action. For exam-
              ple, to map Alt-Uparrow for this purpose use the following in your keymaps file:

              alt keycode 103 = KeyboardSignal

EXAMPLES

       This is an example of a inittab which resembles the old Linux inittab:

              # inittab for linux
              id:1:initdefault:
              rc::bootwait:/etc/rc
              1:1:respawn:/etc/getty 9600 tty1
              2:1:respawn:/etc/getty 9600 tty2
              3:1:respawn:/etc/getty 9600 tty3
              4:1:respawn:/etc/getty 9600 tty4

       This inittab file executes /etc/rc during boot and starts gettys on tty1-tty4.

       A more elaborate inittab with different runlevels (see the comments inside):

              # Level to run in
              id:2:initdefault:

              # Boot-time system configuration/initialization script.
              si::sysinit:/etc/init.d/rcS

              # What to do in single-user mode.
              ~:S:wait:/sbin/sulogin

              # /etc/init.d executes the S and K scripts upon change
              # of runlevel.
              #
              # Runlevel 0 is halt.
              # Runlevel 1 is single-user.
              # Runlevels 2-5 are multi-user.
              # Runlevel 6 is reboot.

              l0:0:wait:/etc/init.d/rc 0
              l1:1:wait:/etc/init.d/rc 1
              l2:2:wait:/etc/init.d/rc 2
              l3:3:wait:/etc/init.d/rc 3
              l4:4:wait:/etc/init.d/rc 4
              l5:5:wait:/etc/init.d/rc 5
              l6:6:wait:/etc/init.d/rc 6

              # What to do at the "3 finger salute".
              ca::ctrlaltdel:/sbin/shutdown -t1 -h now

              # Runlevel 2,3: getty on virtual consoles
              # Runlevel   3: getty on terminal (ttyS0) and modem (ttyS1)
              1:23:respawn:/sbin/getty tty1 VC linux
              2:23:respawn:/sbin/getty tty2 VC linux
              3:23:respawn:/sbin/getty tty3 VC linux
              4:23:respawn:/sbin/getty tty4 VC linux
              S0:3:respawn:/sbin/getty -L 9600 ttyS0 vt320
              S1:3:respawn:/sbin/mgetty -x0 -D ttyS1

FILES

       /etc/inittab

AUTHOR

       Init was written by Miquel van Smoorenburg (miquels@cistron.nl).   This  manual  page  was  written  by  Sebastian  Lederer  (lederer@fran-
       cium.informatik.uni-bonn.de) and modified by Michael Haardt (u31b3hs@pool.informatik.rwth-aachen.de).

SEE ALSO

       init(8), telinit(8)

                                                                    Dec 4, 2001                                                         INITTAB(5)