摘要
这段时间在搞一个微型的Linux,将它作为一个项目的平台，这个过程中，看了研究了一下Linux的启动过程，同时把启动配置文件看了一下，作了一下注释，同时和大家共享一下:)。我使用的Linux平台是Red Hat Linux 7.3
#
# inittab This file describes how the INIT process should set up
# the system in a certain run-level.
#
# Author: Miquel van Smoorenburg,
# Modified for RHS Linux by Marc Ewing and Donnie Barnes
#
# Default runlevel. The runlevels used by RHS are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
id:3:initdefault:
##这是init进程启动以后读取的第一条内容,用来确定运行级别.
##这条内容读入以后,runlevel这个工具就可以正常显示运行级别了
##在rc这个脚本文件中将用到runlevel这个工具
# System initialization.
si::sysinit:/etc/rc.d/rc.sysin
l0:0:wait:/etc/rc.d/rc 0
l1:1:wait:/etc/rc.d/rc 1
l2:2:wait:/etc/rc.d/rc 2
l3:3:wait:/etc/rc.d/rc 3
l4:4:wait:/etc/rc.d/rc 4
l5:5:wait:/etc/rc.d/rc 5
l6:6:wait:/etc/rc.d/rc 6
##第三个域中的wait表示init进程在启动的时候运行一次后边的内容
##而且，init进程会等待这个运行的部分正常返回以后才往下运行其它内容。
# Things to run in every runlevel.
ud::once:/sbin/update
##这个update使用来自动让你缓存中的数据写回磁盘。
# Trap CTRL-ALT-DELETE
ca::ctrlaltdel:/sbin/shutdown -t3 -r now
##定义当用户按下Ctrl+Alt+Delete这三个组合键后init进程做的动作。
# When our UPS tells us power has failed, assume we have a few minutes
# of power left. Schedule a shutdown for 2 minutes from now.
# This does, of course, assume you have powerd installed and your
# UPS connected and working correctly.
pf::powerfail:/sbin/shutdown -f -h +2 "Power Failure; System Shutting Down"
# If power was restored before the shutdown kicked in, cancel it.
pr:12345:powerokwait:/sbin/shutdown -c "Power Restored; Shutdown Cancelled"
# Run gettys in standard runlevels
1:2345:respawn:/sbin/mingetty 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
##第三个域中间的respawn意思是让init进程一直监视后面的进程，
##如果后面的进程结束了，马上重新启动
# Run xdm in runlevel 5
# xdm is now a separate service
x:5:respawn:/etc/X11/prefdm -nodaemon
