/etc/inittab 分析

文件格式：

:::

各标号的意思：

标号	说明
Id	表示这个进程要使用的控制台，省略默与init进程相同
Runlevels	运行级别
Action	Init进程如何控制此进程
process	要执行的程序（可执行程序或脚本）

Action名称	执行条件	说明
Sysinit	系统启动后最先执行	只执行一次，init进程等待它结束才继续执行其他动作
Wait	系统执行完sysinit进程后，执行	只执行一次，init进程等待它结束才继续执行其他动作
Once	系统执行完wait进程后执行	只执行一次，init进程不等待它结束
Respawn	启动完once进程后	Init进程监测发现子进程退出时，重新启动它
Askfirst	启动完respawn进程后	与respawn进程类似，不过init进程先输出Please press Enter to active this console,等待用户输入回车键后才启动
Shutdown	当系统关机时	即重启、关闭系统时
Restart	当init进程收到SIGHUP（挂断控制终端）信号时	先重新读取，解析/etc/inittab文件，在执行restart程序
Ctrlatldel	按下ctrl+alt+del 时

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 ondemandentries. 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 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, 123specifies that the process should be started in runlevels 1, 2, and 3. The runlevels forondemand entries may contain an A, B, or C. The runlevels field of sysinit, boot, and bootwaitentries 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 ( ondemandrunlevels 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.

最先执行

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:

# 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