INITTAB(5) Linux System Administrator's Manual INITTAB(5)
NAME
inittab - format of the inittab file used by the sysv-com-
patible 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) distinguishes multi-
ple runlevels, each of which can have its own set of pro-
cesses 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 iden-
tifies 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.
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 pro-
cess 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 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:
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respawn
The process will be restarted whenever it termi-
nates (e.g. getty).
wait The process will be started once when the specified
runlevel is entered and init will wait for its ter-
mination.
once The process will be executed once when the speci-
fied 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 con-
sole. 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 init receives the
SIGPWR signal, indicating that there is something
wrong with the power. Init will wait for the pro-
cess to finish before continuing.
powerfail
As for powerwait, except that init does not wait
for the process's 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.
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ctrlaltdel
The process will be executed when init receives the
SIGINT signal. This means that someone on the sys-
tem console has pressed the CTRL-ALT-DEL key combi-
nation. 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):
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# Level to run in
id:2:initdefault:
# System initialization before anything else.
si::sysinit:/etc/rc.d/bcheckrc
# Runlevel 0,6 is halt and reboot, 1 is maintenance mode.
l0:0:wait:/etc/rc.d/rc.halt
l1:1:wait:/etc/rc.d/rc.single
l2:2345:wait:/etc/rc.d/rc.multi
l6:6:wait:/etc/rc.d/rc.reboot
# 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
FILES
/etc/inittab
AUTHOR
Init was written by Miquel van Smoorenburg
(miquels@cistron.nl). This 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)
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