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:5: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
0:2345:respawn:/sbin/getty 115200 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 022 //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
1 # rc This file is responsible for starting/stopping 2 # services when the runlevel changes. 3 4 //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 0>&1
# Get first argument. Set new runlevel to this argument. [ "$1" != "" ] && runlevel=$1 if [ "$runlevel" = "" ] then echo "Usage: $0 <runlevel>" >&2 exit 1 fi //如果没有获取到运行级别就退出
previous=$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$runlevel.d ] then //rcS.d是目录 PROGRESS_STATE=0 //Split the remaining portion of the progress bar into thirds progress_size=$(((100 - $PROGRESS_STATE) / 3))//progress_size = 100/3 =33 case "$runlevel" in//runlevel=S 0|6) first_step=-100 progress_size=100 step_change=1 ;; S) //Begin where the initramfs left off and use 2/3of the remaining space first_step=$PROGRESS_STATE ///progress_size = 100/3 =33 progress_size=$(($progress_size * 2))//progress_size=66 step_change=1 ;; *) //Begin where rcS left off and use the final 1/3 ofthe space (by leaving progress_size unchanged) first_step=$(($progress_size * 2 + $PROGRESS_STATE)) step_change=1 ;; esac
num_steps=0 for s in /etc/rc$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 + 1))//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=0 # 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[0-9][0-9]* 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$runlevel.d/S[0-9][0-9]} stop=/etc/rc$runlevel.d/K[0-9][0-9]$suffix previous_start=/etc/rc$previous.d/S[0-9][0-9]$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 0|6) 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=$1 shift //shift 命令每执行一次，变量的个数($#)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" != "0" ]; 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 2>&1; 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