inittab

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,
       gettys...).  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
              corresponding 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
       bootwait 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
              runlevel 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
              (provided 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 example, 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@francium.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)