linux系统初始化——sysinit文件写法详解

sysinit文件写法详解

sysinit文件是linux初始化文件系统时执行的第一个脚本文件。它主要做在各个运行级别中进行初始化工作,包括: 启动交换分区;检查磁盘;设置主机名;检查并挂载文件系统;加载并初始化硬件模块.

具体执行的脚本由inittab文件中的action为sysinit的一行确定。如LFS中为如下一行：
si::sysinit:/etc/rc.d/init.d/rc sysinit
这代表init初始化程序执行的第一个脚本为/etc/rc.d/init.d/rc，并传入sysinit参数。一般linux传入的参数为一数字，代表运行级别。rc会用参数合成/etc/init.d/rcsysinit.d目录，并执行其中的文件完成服务初始化。

下面是/etc/init.d/rcsysinit.d目录中的文件。
│ └── rcsysinit.d
│ ├── S00mountkernfs -> ../init.d/mountkernfs
│ ├── S02consolelog -> ../init.d/consolelog
│ ├── S05modules -> ../init.d/modules
│ ├── S10udev -> ../init.d/udev
│ ├── S20swap -> ../init.d/swap
│ ├── S30checkfs -> ../init.d/checkfs
│ ├── S40mountfs -> ../init.d/mountfs
│ ├── S45cleanfs -> ../init.d/cleanfs
│ ├── S50udev_retry -> ../init.d/udev_retry
│ ├── S70console -> ../init.d/console
│ ├── S80localnet -> ../init.d/localnet
│ └── S90sysctl -> ../init.d/sysctl

下面我们来看一下LFS中rc文件的写法。

 #!/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