INITTAB详解

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INITTAB

This document was created by using the manual pages.

Section: Linux System Administrator's Manual (5)

Updated: May 19, 1998

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, gettys...).

(8) distinguishes multiple

runlevels, each of which can have its own set of processes that are started. Valid runlevels are

6 plus

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.

is a unique sequence of 1-4 characters which identifies 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 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. Therunlevels 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

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 linuxid:1:initdefault:rc::bootwait:/etc/rc1:1:respawn:/etc/getty 9600 tty12:1:respawn:/etc/getty 9600 tty23:1:respawn:/etc/getty 9600 tty34:1: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 inid: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.haltl1:1:wait:/etc/rc.d/rc.singlel2:2345:wait:/etc/rc.d/rc.multil6:6: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 linux2:23:respawn:/sbin/getty tty2 VC linux3:23:respawn:/sbin/getty tty3 VC linux4:23:respawn:/sbin/getty tty4 VC linuxS2:3:respawn:/sbin/uugetty ttyS2 M19200