inittab - phpMan

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) distin-
guishes 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 house-
keeping. 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 comple-
tion.

powerokwait
This process will be executed as soon as init is informormed 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 AT cistron.nl). This manual page
was written by Sebastian Lederer (lederer AT francium.de) and mod-
ified by Michael Haardt (u31b3hs AT pool.de).