启动关机的流程和加载程序

启动时候,如何获取系统运行等级?/etc/inittab文件中
#
# 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) 系统直接关机
#   1 - Single user mode 单用户模式
#   2 - Multiuser, without NFS (The same as 3, if you do not have networking)
#   3 - Full multiuser mode 纯文本模式
#   4 - unused 系统保留功能
#   5 - X11 与等级3类似,但使用X Windows
#   6 - reboot (Do NOT set initdefault to this)
#
#系统默认启动的等级设置
id:5:initdefault:
#开始启动运行等级的服务前,使用检测与初始化系统的环境的设置文件
# System initialization.
si::sysinit:/etc/rc.d/rc.sysinit
#7个不同运行等级需要启动的服务的脚本的放置路径
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

# Trap CTRL-ALT-DELETE
#是否按下ctrl+del+alt键就重新启动的设置项目
ca::ctrlaltdel:/sbin/shutdown -t3 -r now

# 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
#本机终端的启动个数
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

# Run xdm in runlevel 5
#在x window(运行等级5)环境下的启动脚本设置项目
x:5:respawn:/etc/X11/prefdm -nodaemon

我们开始加载各项系统服务之前,先做好整个系统环境,主要在/etc/rc.d/rc.sysinit
查看当前运行等级runlevel即可