Section: Linux System Administrator's Manual (5)
Updated: Dec 4, 2001
inittab - format of the inittab file used by the sysv-compatible init
file describes which processes are started at bootup and
during normal operation (e.g. /etc/init.d/boot, /etc/init.d/rc, gettys...).
distinguishes multiple runlevels
, each of which can have its own set of
processes that are started. Valid runlevels are 0
, and C
entries. An entry in the
file has the following format:
Lines beginning with `#' are ignored.
is a unique sequence of 1-4 characters which identifies an entry in
(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.
lists the runlevels for which the specified action should be taken.
describes which action should be taken.
specifies the process to be executed. If the process field starts with
a `+' character,
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 length of this field is limited to 127 characters.
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:
The process will be restarted whenever it terminates (e.g. getty).
The process will be started once when the specified runlevel is entered and
will wait for its termination.
The process will be executed once when the specified runlevel is
The process will be executed during system boot. The runlevels
field is ignored.
The process will be executed during system boot, while
waits for its termination (e.g. /etc/rc).
The runlevels field is ignored.
This does nothing.
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',
An initdefault entry specifies the runlevel which should be
entered after system boot. If none exists,
will ask for a runlevel on the console. The process field is ignored.
The process will be executed during system boot. It will be
executed before any boot or bootwait entries.
The runlevels field is ignored.
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.
As for powerwait, except that init does not wait for the process's
This process will be executed as soon as init is informed that the
power has been restored.
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).
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 process will be executed when init receives a signal from the
keyboard handler that a special key combination was pressed on the
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
This is an example of a inittab which resembles the old Linux inittab:
# inittab for linux
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
A more elaborate inittab with different runlevels (see the comments
# Level to run in
# Boot-time system configuration/initialization script.
# What to do in single-user mode.
# /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.
# 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
was written by Miquel van Smoorenburg
). This manual page was written by
Sebastian Lederer (email@example.com
) and modified
by Michael Haardt (firstname.lastname@example.org