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