INITTAB(5) Linux System Administrators 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, 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:
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 cor
responding tty, e.g. 1 for tty1. Some ancient login accounting
programs might expect this, though I cant 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 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
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 exe
cuted 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 con
nected to the computer. Init will wait for the process to fin
ish before continuing.
powerfail
As for powerwait, except that init does not wait for the pro
cesss completion.
powerokwait
This process will be executed as soon as init is informed 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 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.
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 follow
ing 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@cistron.nl). This
manual page was written by Sebastian Lederer (lederer@francium.infor
matik.uni-bonn.de) and modified by Michael Haardt (u31b3hs@pool.infor
matik.rwth-aachen.de).
SEE ALSO
init(8), telinit(8)
Dec 4, 2001 INITTAB(5)
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