inittab - format of the inittab file used by the sysv-compatible init
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:
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 libraries <
5.2.18 or a.out libraries the limit is 2 characters).
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 might not work correctly.
lists the runlevels for which the specified action should be
action describes which action should be taken.
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 run-
levels. For example, 123 specifies that the process should be started
in runlevels 1, 2, and 3. The runlevels for ondemand entries may con-
tain 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
Valid actions for the action field are:
The process will be restarted whenever it terminates (e.g.
wait The process will be started once when the specified runlevel is
entered and init will wait for its termination.
waits for its termination (e.g. /etc/rc). The runlevels field
off 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', and
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.
The process will be executed during system boot. It will be exe-
cuted before any boot or bootwait entries. The runlevels field
The process will be executed when the power goes down. Init is
usually informed about this by a process talking to a UPS con-
nected to the computer. Init will wait for the process to fin-
ish before continuing.
As for powerwait, except that init does not wait for the pro-
This process will be executed as soon as init is informormed
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 sig-
nal. 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 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.
# 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 on
A more elaborate inittab with different runlevels (see the comments
# Level to run in
# System initialization before anything else.
# Runlevel 0,6 is halt and reboot, 1 is maintenance mode.
# What to do at the "3 finger salute".
ca::ctrlaltdel:/sbin/shutdown -t5 -rf now
# Runlevel 2&3: getty on console, level 3 also getty on modem port.
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
S2:3:respawn:/sbin/uugetty ttyS2 M19200
Init was written by Miquel van Smoorenburg (firstname.lastname@example.org). This
manual page was written by Sebastian Lederer (email@example.com-
matik.uni-bonn.de) and modified by Michael Haardt (firstname.lastname@example.org-
May 19, 1998 inittab(5)