5:inittab
From Linux Man Pages
inittab - format of the inittab file used by the sysv-compatible init process
Contents |
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 com-
piled 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 termi-
nation.
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).
resume This process will be executed when init is told by the kernel that Software Suspend has resumed the
machine. This way you may specify userland programs what can restore hardware states the kernel cannot
(for example svgatextmode and hdparm).
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 com-
bination 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 fol-
lowing 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 mingettys 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:I:bootwait:/etc/init.d/boot
# Runlevel 0 is System halt (Never use this as initdefault!)
# Runlevel 1 is Single user mode
# Runlevel 2 is Local multiuser without remote network (e.g. NFS)
# Runlevel 3 is Full multiuser with network
# Runlevel 4 is Not used
# Runlevel 5 is Full multiuser with network and xdm
# Runlevel 6 is System reboot (Never use this as initdefault!)
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 in single-user mode
ls:S:wait:/etc/init.d/rc S
~~:S:respawn:/sbin/sulogin
# What to do at the "3 finger salute".
ca::ctrlaltdel:/sbin/shutdown -t5 -h now
# Runlevel 2 upto 5: mingetty on console.
# level 2, 3, and 5 also getty on serial port S0.
1:2345:respawn:/sbin/mingetty --noclear tty1
2:2345:respawn:/sbin/mingetty tty2
3:2345:respawn:/sbin/mingetty tty3
4:2345:respawn:/sbin/mingetty tty4
5:2345:respawn:/sbin/mingetty tty5
6:2345:respawn:/sbin/mingetty tty6
S0:235:respawn:/sbin/agetty -L 9600 ttyS0 vt102
# modem getty(s),
# /dev/modem is a link to the modem device.
#mo:235:respawn:/usr/sbin/mgetty -s 38400 modem
mo:235:respawn:/sbin/uugetty modem M19200
FILES
/etc/inittab
RELATED
init(8), telinit(8), init.d(7), agetty(8), mgetty(8)