inittab详解

NAME
       inittab - format of the inittab file used by the sysv-compatible
       init process

       初始化表 - 一个整合初始化进程的表，初始化进程协调系统服务。inittab就是这样的文件格式。
 
DESCRIPTION （描述）
       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 run-
       levels, 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:

       inittab文件描述在系统引导之后，正常的操作下的启动之后的进程的启动。Init(8)辨别多重运行级别，每一个运行级别都启动她自己设定的一些进程。正常的运行级别按照所需条目输入0-6加上A ,B,C。在inittab文件中的条目有下面这样一些格式。
 
              id:runlevels:action:process
 
       Lines beginning with ‘#’ are ignored.忽略开头是#的行。
 
       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).

              id 是inittab里唯一的一个1-4个字符辨别一个条目。（系统收集服务的版本通过老的libc5（小于5.2.18版本）或者是a.out库限制两个字符、）
 
              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.
              注意：在传统上，对getty和其他的登录进程来说，id领域的值保持和相对应的tty后缀的值一样。比如：1对应着tty1，一些古老的账号程序可能预计会是这样，尽管我还没想到其他的。
 
       runlevels 运行级别
              lists the runlevels for which the specified action should
              be taken.
              列出运行级别，指定应该采取的动作。
             
       action 动作
              describes which action should be taken.
              
              描述应该采取的动作。             
 
       process 进程
              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 house-
              keeping.  This is also a historic bug.
              详细表述进程的执行。如果进程领域以+开始，init将不记录进程登录非登录的原因。这就需要gettys坚持做他们自己的utmp/wtmp房屋保持。这也是个历史bug。
----------------------------------------------------------------------------------
 
       The runlevels field may contain multiple characters for  differ-
       ent  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.

       不同的运行级别有着多重的特征。举个例子，1，2，3详细指定了进程应该在1，2，3的级别上运行。运行级别按照所需的条目包含A,B,C。运行级别忽略系统初始化，启动和启动等待。
 
       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.

       当系统运行级别发生变化，任何不再指定给新的运行级别的进程将被杀死，先发送SIGTERM信号，再发送SIGKILL信号。
 
       Valid actions for the action field are:动作领域里正常的动作是：
 
       respawn
              The process will  be  restarted  whenever  it  terminates
              (e.g. getty).
             在任何时候，进程在结束后自动重启。
 
       wait   The  process will be started once when the specified run-
              level is entered and init will wait for its  termination.
       等待   一旦当输入指定的运行级别，进程将被启动。init将等待进程结束。（不重新启动。）
 
       once   The process will be executed once when the specified run-
              level is entered.当指定运行级别之后，进程将被执行一次。
 
       boot   The process will be executed  during  system  boot.   The
              runlevels field is ignored.在系统启动期间，进程将被执行，忽略欲行级别的领域。
 
       bootwait
              The  process  will  be executed during system boot, while
              init waits for its termination (e.g. /etc/rc).  The  run-
              levels field is ignored.在系统启动期间，进程将被执行，当初始化等待结束。忽略运行级别。
 
       off    This does nothing.什么都不做。
 
       ondemand 按照请求
              A  process  marked with an ondemand runlevel will be exe-
              cuted whenever the specified ondemand runlevel is called.
              However,  no  runlevel  change  will occur (ondemand run-
              levels are ‘a’, ‘b’, and ‘c’).进程按照所需的请求被标记，当任何指定所需的运行级别被呼叫的时候，执行运行级别内的进程。然而，没有运行级别的改变将被执行。（所需的运行级别是‘a’，‘b’和‘c’）
 
       initdefault 默认运行级别
              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.
              默认运行级别指定了当系统启动之后应该执行的运行级别的条目。如果没有条目存在，初始化将在控制台请求一个运行级别，忽略进程领域。
 
       sysinit 系统初始化

              The  process will be executed during system boot. It will
              be executed before any boot or   bootwait  entries.   The
              runlevels field is ignored.
              进程将在系统启动的时候运行，进程将在任何boot或者是bootwait条目之前运行，忽略运行级别领域。
 
       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.
              当系统掉电的时候执行进程，init进程通常使用一个和电脑相连接的对话进程告知。init将在继续之前等待进程结束。
 
       powerfail
              As for powerwait, except that init does not wait for  the
              process’s completion.
             init进程不再等待进程结束。
 
       powerokwait
              This  process  will be executed as soon as init is infor-
              mormed that the power has been restored.一告知被恢复的电源，进程就被执行。
 
       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  moni-
              toring process are able to detect this condition).
 
       ctrlaltdel
              The  process will be executed when init receives the SIG-
              INT signal.  This means that someone on the  system  con-
              sole  has pressed the CTRL-ALT-DEL key combination. Typi-
              cally 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 com-
       ments 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