linux 文件系统sysvinit 流程分析

参考网上许多的教程。

然后有一下相关的笔记：

kernel 在挂载完文件系统后，会执行第一个进程init

这个进程的PID为1

这个进程是所有进程的父进程

init 进程，首先要去读取inittab中的数据，根据这里面的数据去执行相关的初始化。

在inittab  可以指定默认的运行级别

　　

id::initdefault:

还会规定第一个执行的程序

si::sysinit:/etc/init.d/rcS

//指定单用户模式

~~:S:wait:/sbin/sulogin

在TI的板子上还规定终端的显示的开关

::respawn:/sbin/getty  ttyO0

这里提到，他规定下一个执行的是/etc/init.d/rcS

在/etc/init.d/rcS 内又做了哪些工作呢？

PATH=/sbin:/bin:/usr/sbin:/usr/bin                                 //设置环境变量

runlevel=S                                                                      //设置运行级别

prevlevel=N

umask                                                                        //设置默认权限补码

export PATH runlevel prevlevel                                          //对外发布这些变量

trap ":" INT QUIT TSTP

 //这里话的含义是忽略ctrl + c中断信号

exec /etc/init.d/rc S    //运行/etc/init.d/rc    并加一个参数S

下面进入rc文件分析

 # rc        This file is responsible for starting/stopping

 #       services when the runlevel changes.

 //在文件一开始，就说明了这个文件是当运行级别改变就要更改相关的服务

//设置终端,将 CR 字符映射为 NL 字符,避免阶梯效应

  stty onlcr >&

  # Get first argument. Set new runlevel to this argument.

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

  if [ "$runlevel" = "" ]

  then

    echo "Usage: $0 <runlevel>" >&

    exit

  fi

//如果没有获取到运行级别就退出

previous=$PREVLEVEL

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

    //传入参数是S的话，则$runleve=S $previous=N

  export runlevel previous

//若$runlevel=“S”，即检查rcS.d是否为目录。

  if [ -d /etc/rc$runlevel.d ]

  then

    //rcS.d是目录

    PROGRESS_STATE=

    //Split the remaining portion of the progress bar into thirds

    progress_size=$((( - $PROGRESS_STATE) / ))//progress_size = 100/3 =33

    case "$runlevel" in//runlevel=S

        |)

            first_step=-

            progress_size=

            step_change=

            ;;

     S)

            //Begin where the initramfs left off and use 2/3of the remaining space

            first_step=$PROGRESS_STATE ///progress_size = 100/3 =33

            progress_size=$(($progress_size * ))//progress_size=66

            step_change=

            ;;

        *)

            //Begin where rcS left off and use the final 1/3 ofthe space (by leaving progress_size unchanged)

            first_step=$(($progress_size *  + $PROGRESS_STATE))

            step_change=

            ;;

    esac

num_steps=

    for s in /etc/rc$runlevel.d/[SK]*; //s取/etc/rcS.d目录下以S或K开头的文件名

    do

        //这句话的含义去掉变量s中所有的/etc/rcS.d/S??的部分

        //例：s=/etc/rc$runlevel.d/S10checkroot，那么去掉/etc/rc$runlevel.d/K??部分后，s为checkroot

    case "${s##/etc/rc$runlevel.d/S??}" in

        gdm|xdm|kdm|reboot|halt)//若s剩下的文件名中为这五个则跳出for语句

            break

            ;;

    esac

    num_steps=$(($num_steps + ))//num_steps递加，表示查找到此目录下/etc/rcS.d有多少个脚本

  done//for语句结束

        step=

 # First, run the KILL scripts.       首先运行KILL

    if [ $previous != N ]                                    //由于previous = N ,所以一下不执行

    then

        for i in /etc/rc$runlevel.d/K[-][-]*

        do

            # Check if the script is there.

            [ ! -f $i ] && continue

            # Stop the service.

            startup $i stop

        done

    fi
                                                              

    # Now run the START scripts for this runlevel.

    for i in /etc/rc$runlevel.d/S*

    do

        [ ! -f $i ] && continue

        if [ $previous != N ] && [ $previous != S ]     //由于previous为N所以跳过

        then

            #

            # Find start script in previous runlevel and

            # stop script in this runlevel.

            #

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

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

            previous_start=/etc/rc$previous.d/S[-][-]$suffix

            #

            # If there is a start script in the previous level

            # and _no_ stop script in this level, we don't

            # have to re-start the service.

            #

            [ -f $previous_start ] && [ ! -f $stop ] && continue

        fi

        case "$runlevel" in

            |)

                startup $i stop

                ;;

            *)

                startup $i start            //然后启动了相关的服务   运行在文件前面定义的 startup 函数

                ;;

        esac

    done

  fi                                                                            

startup函数有如下定义：

#

# Start script or program.

#

startup() {

  # Handle verbosity

  [ "$VERBOSE" = very ] && echo "INIT: Running $@..."

  case "$1" in             //判断第一个参数，如果是一个脚本，执行第一个

    *.sh)

        # Source shell script for speed.

        (

            trap - INT QUIT TSTP

            scriptname=$

            shift                               //shift 命令每执行一次，变量的个数($#)减一，而变                    量值提前一位

            . $scriptname                  //在执行第一个参数

        )

        ;;

    *)                            //如果不是一个脚本，那么认为是一个服务

        "$@"

        ;;

  esac

  startup_progress             //再运行前一个函数

}
                                

startup_progress 函数详解

startup_progress() {

    step=$(($step + $step_change))

    if [ "$num_steps" != "" ]; then

        progress=$((($step * $progress_size / $num_steps) + $first_step))

    else

        progress=$progress_size

    fi

    #echo "PROGRESS is $progress $runlevel $first_step + ($step of $num_steps) $step_change $progress_size"

    #if type psplash-write >/dev/null 2>&1; then

    #    TMPDIR=/mnt/.psplash psplash-write "PROGRESS $progress" || true

    #fi

    if [ -e /mnt/.psplash/psplash_fifo ]; then

        echo "PROGRESS $progress" > /mnt/.psplash/psplash_fifo

    fi

    echo progress over...

}
                                                                

最后，执行qt.sh

#Uncomment to cause psplash to exit manually, otherwise it exits when it sees a VC switch

if [ "x$runlevel" != "xS" ] && [ ! -x /etc/init.d/xserver-nodm ]; then

    . /etc/init.d/qt.sh

#    if type psplash-write >/dev/null >&; then

#        TMPDIR=/mnt/.psplash psplash-write "QUIT" || true

#       umount /mnt/.psplash

#    fi

fi                                                                           

参考：

http://www.cnblogs.com/cnland/archive/2013/03/26/2981967.html

https://wiki.archlinux.org/index.php/Arch_boot_process_(%E7%AE%80%E4%BD%93%E4%B8%AD%E6%96%87)#Init_.E6.B5.81.E7.A8.8B

http://blog.chinaunix.net/uid-17188120-id-4073497.html