#!/bin/sh

 #------------------------------------

 #sysconfig/rc只定义了几个变量，内容如下：

 #rc_base=/etc/rc.d

 #rc_functions=${rc_base}/init.d/functions

 #network_devices=/etc/sysconfig/network-devices

 #----------------------------------------------

 . /etc/sysconfig/rc

 #由上面知rc_function为 "/etc/rc.d/init.d/functions"

 #文件只设置了一变量,如PATH="/bin:/usr/bin:/sbin:/usr/sbin".还有一些函数

 . ${rc_functions}

 # This sets a few default terminal options.

 stty sane

 # These  signals will not cause our script to exit

 trap "" INT QUIT TSTP

 #如果 ${}不为空,runlevel 为 ${}。${}是脚本的第一个参数

 [ "${1}" != "" ] && runlevel=${}

 #如果runlevel为空则退出.${}为脚本名字

 if [ "${runlevel}" = "" ]; then

 echo "Usage: ${0} " >&

 exit

 fi

 #当运行级变化时，PREVLEVEL存储当前runlevel变量.

 previous=${PREVLEVEL}

 #if previous is null, previous is setted N.

 #when boot system,the previous is null.

 [ "${previous}" = "" ] && previous=N

 #对应runlevel的目录不存在则退出。

 #boot_mesg为一个向屏幕输出字符串的函数

 if [ ! -d ${rc_base}/rc${runlevel}.d ]; then

 boot_mesg "${rc_base}/rc${runlevel}.d does not exist." ${WARNING}

 boot_mesg_flush

 exit

 fi

 # 停止前一个运行级的所有服务，退出这一runlevel

 # 当启动系统时，下面不会运行。不必细看

 if [ "${previous}" != "N" ]; then

 for i in $(ls -v ${rc_base}/rc${runlevel}.d/K* > /dev/null)

 do

 check_script_status

 suffix=${i#$rc_base/rc$runlevel.d/K[-][-]}

 prev_start=$rc_base/rc$previous.d/S[-][-]$suffix

 sysinit_start=$rc_base/rcsysinit.d/S[-][-]$suffix

 if [ "${runlevel}" != "" ] && [ "${runlevel}" != "" ]; then

 if [ ! -f ${prev_start} ] && [ ! -f ${sysinit_start} ]; then

 boot_mesg -n "WARNING:\n\n${i} can't be" ${WARNING}

 boot_mesg -n " executed because it was not"

 boot_mesg -n " not started in the previous"

 boot_mesg -n " runlevel (${previous})."

 boot_mesg "" ${NORMAL}

 boot_mesg_flush

 continue

 fi

 fi

 ${i} stop

 error_value=${?}

 if [ "${error_value}" != "" ]; then

 print_error_msg

 fi

 done

 fi

 #开启当前runlevel的所有服务，主要是这一段要明白。

 for i in $( ls -v ${rc_base}/rc${runlevel}.d/S* > /dev/null)

 do

 if [ "${previous}" != "N" ]; then #this if is false when booting.

 suffix=${i#$rc_base/rc$runlevel.d/S[-][-]}

 stop=$rc_base/rc$runlevel.d/K[-][-]$suffix

 prev_start=$rc_base/rc$previous.d/S[-][-]$suffix

 [ -f ${prev_start} ] && [ ! -f ${stop} ] && continue

 fi

 check_script_status #a function judgeing the file if is a file and executable.

 case ${runlevel} in

 |) #if runleve is 0 or 6, stop the service i.

 ${i} stop

 ;;

 *)

 ${i} start

 ;;

 esac

 error_value=${?}

 if [ "${error_value}" != "" ]; then

 print_error_msg

 fi

 done

 # End $rc_base/init.d/rc