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