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, gettys...).
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 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 `+' 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:
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
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. 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):
# Level to run in
id:2:initdefault:
# Boot-time system configuration/initialization script.
si::sysinit:/etc/rc.sysinit
# 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/rc 0
l1:1:wait:/etc/rc 1
l2:2:wait:/etc/rc 2
l3:3:wait:/etc/rc 3
l4:4:wait:/etc/rc 4
l5:5:wait:/etc/rc 5
l6:6:wait:/etc/rc 6
# What to do at the "3 finger salute".
ca::ctrlaltdel:/sbin/shutdown -t3 -r now
# Runlevel 2,3: getty on virtual consoles
# Runlevel 3: mgetty on terminal (ttyS0) and modem (ttyS1)
1:23:respawn:/sbin/mingetty tty1
2:23:respawn:/sbin/mingetty tty2
3:23:respawn:/sbin/mingetty tty3
4:23:respawn:/sbin/mingetty tty4
S0:3:respawn:/sbin/agetty ttyS0 9600 vt100-nav
S1:3:respawn:/sbin/mgetty -x0 -D ttyS1
