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 opera-
tion (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 run-
levels 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 '+' char-
acter, 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 termina-
tion (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 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. Typi-
cally 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 writ-
ing). 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 (). This manual page was
written by Sebastian Lederer () and modified by
Michael Haardt ().
SEE ALSO
init(8), telinit(8)
Dec 4, 2001 INITTAB(5)
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