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/rc, gettys...). Init distinguishes multiple runlevels, of which each can have its own set of processes that are started. Valid runlevels are 0-6 and 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 two-character-sequence which identifies an entry in inittab.

    Note: For gettys or other login processes, the id field should be the tty suffix of the corresponding tty, e.g. 1 for tty1. Otherwise, the login accounting will not work correctly. This is a bug in login and will be fixed.

runlevels
    describes in which runlevels 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.

Valid actions 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 runlevel field is ignored.

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

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.

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

powerwait
    The process will be executed when init receives the SIGPWR signal, indicating that there is something wrong with the power. Init will wait for the process to finish before continuing.

powerfail
    As powerwait, but init will not wait for the processes completion.

powerokwait
    The process will be executed when init receives the SIGPWR signal, provided there is a file called /etc/powerstatus containing the word OK. This means that the power has come back again.

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.

The runlevel-field may contain multiple characters for different runlevels, e.g. 123 if the process should be started in runlevels 1, 2 and 3. ondemand-entries may contain an A, B or C. The runlevel-field of sysinit, boot and bootwait entries are ignored.

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

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:4:initdefault:
    ud::boot:/etc/update
    rc::bootwait:/etc/rc
    cr::boot:/etc/crond
    #
    # level 1: getty on tty1
    # level 2: getty on tty1-4
    # level 3: tty1-4, dialin via modem(ttys2)
    # level 4: tty1-4, ttyb
    #
    mr:126:once:/usr/bin/nodialin
    mi:345:once:/usr/bin/dialin
    1:1234:respawn:/etc/getty 9600 tty1
    2:234:respawn:/etc/getty 9600 tty2
    3:234:respawn:/etc/getty 9600 tty3
    4:234:respawn:/etc/getty 9600 tty4
    s2:3:respawn:/etc/mgetty ttys2 19200
    b:4:respawn:/etc/getty 19200L ttyb
    ca::ctrlaltdel:/etc/shutdown -t3 -rf now

FILES
/etc/inittab

AUTHOR
Init was written by Miquel van Smoorenburg (miquels@drinkel.nl.mugnet.org), the 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)