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 3 signals will not cause our script to exit

trap "" INT QUIT TSTP

#如果 ${1}不为空,runlevel 为 ${1}。${1}是脚本的第一个参数

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

#如果runlevel为空则退出.${0}为脚本名字

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

echo "Usage: ${0} " >&2

exit 1

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 1

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* 2> /dev/null)

do

check_script_status

suffix=${i#$rc_base/rc$runlevel.d/K[0-9][0-9]}

prev_start=$rc_base/rc$previous.d/S[0-9][0-9]$suffix

sysinit_start=$rc_base/rcsysinit.d/S[0-9][0-9]$suffix

if [ "${runlevel}" != "0" ] && [ "${runlevel}" != "6" ]; then

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

boot_mesg -n "WARNING:nn${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}" != "0" ]; 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* 2> /dev/null)

do

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

suffix=${i#$rc_base/rc$runlevel.d/S[0-9][0-9]}

stop=$rc_base/rc$runlevel.d/K[0-9][0-9]$suffix

prev_start=$rc_base/rc$previous.d/S[0-9][0-9]$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

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

${i} stop

;;

*)

${i} start

;;

esac

error_value=${?}

if [ "${error_value}" != "0" ]; then

print_error_msg

fi

done

# End $rc_base/init.d/rc