CentOS RedHat啟動過程

標籤：

開啟PC的電源，BIOS開機自我測試 (POST)，按BIOS中設定的啟動裝置(通常是硬碟)啟動，接著啟動裝置上安裝的引導程式lilo或grub開始引導Linux，Linux首先進行核心的引導，接下來執行init程式，init程式調用了rc.sysinit和rc等程式，rc.sysinit和rc當完成系統初始化和運行服務的任務後，返回init；init啟動了mingetty後，開啟了終端供使用者登入系統，使用者登入成功後進入了Shell，這樣就完成了從開機到登入的整個啟動過程。

init進程起來後，系統啟動的控制權移交給init進程。

/sbin/init進程是所有進程的父進程，當init起來之後，它首先會讀取設定檔/etc/inittab，進行以下工作：

1）執行系統初始化指令碼(/etc/rc.d/rc.sysinit)，對系統進行基本的配置，以讀寫方式掛載根檔案系統及其它檔案系統，到此系統基本算運行起來了，後面需要進行運行層級的確定及相應服務的啟動；

2）確定啟動後進入的運行層級；

3)執行/etc/rc.d/rc，該檔案定義了服務啟動的順序是先K後S，而具體的每個運行層級的服務狀態是放在/etc/rc.d/rcn.d（n=0~6）目錄下，所有的檔案均連結至/etc/init.d下的相應檔案。

4）/etc/rc.d/rc$RUNLEVEL  # $RUNLEVEL為預設的運行模式

5) /etc/rc.d/rc.local

6）啟動虛擬終端/sbin/mingetty

7）在運行層級5上運行X

這時呈現給使用者的就是最終的登入介面。

至此，系統啟動過程完畢。

說明：

系統啟動運行層級的概念以及服務的定製方法；

當initrd 可以正常檢測和裝載之後，最後的工作就基本上由作業系統來進行了。當系統的init進程起來之後系統啟動的控制權移交給init進程。

/sbin/init 進程是所有進程的父進程，當init起來之後，它首先會讀取設定檔/etc/inittab，進行以下工作：

1）執行系統初始化指令碼(/etc/rc.d/rc.sysinit)，對系統進行基本的配置，以讀寫方式掛載根檔案系統及其它檔案系統，後面需要進行運行層級的確定及相應服務的啟動，（從這個角度可以看出如果要定義系統的init動作，需要修改/etc/rc.d/rc.sysinit指令碼）。它的主要工作有：配置selinux，系統時鐘，核心參數（/etc/sysctl.conf），hostname，啟用wap分區，根檔案系統的檢查和二次掛載（讀寫），啟用RAID和LVM裝置，啟用磁碟quota檢查並掛載其它檔案系統。

2）通過對/etc/inittab檔案

 

[[email protected] etc]# cat inittab# inittab is only used by upstart for the default runlevel.## ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.## System initialization is started by /etc/init/rcS.conf## Individual runlevels are started by /etc/init/rc.conf## Ctrl-Alt-Delete is handled by /etc/init/control-alt-delete.conf## Terminal gettys are handled by /etc/init/tty.conf and /etc/init/serial.conf,# with configuration in /etc/sysconfig/init.## For information on how to write upstart event handlers, or how# upstart works, see init(5), init(8), and initctl(8).## Default runlevel. The runlevels used are:#   0 - halt (Do NOT set initdefault to this)#   1 - Single user mode#   2 - Multiuser, without NFS (The same as 3, if you do not have networking)#   3 - Full multiuser mode#   4 - unused#   5 - X11#   6 - reboot (Do NOT set initdefault to this)#id:5:initdefault:

[[email protected] init]# cat rc.conf# rc - System V runlevel compatibility## This task runs the old sysv-rc runlevel scripts.  It# is usually started by the telinit compatibility wrapper.## Do not edit this file directly. If you want to change the behaviour,# please create a file rc.override and put your changes there.start on runlevel [0123456]stop on runlevel [!$RUNLEVEL]taskexport RUNLEVELconsole outputexec /etc/rc.d/rc $RUNLEVEL[[email protected] init]#

[[email protected] ~]# cat /etc/rc.d/rc  #! /bin/bash## rc            This file is responsible for starting/stopping#               services when the runlevel changes.## Original Author:       #               Miquel van Smoorenburg, <[email protected]nl.mugnet.org>#set -m# check a file to be a correct runlevel scriptcheck_runlevel (){        # Check if the file exists at all.        [ -x "$1" ] || return 1        is_ignored_file "$1" && return 1        return 0}# Now find out what the current and what the previous runlevel are.argv1="$1"set $(/sbin/runlevel)runlevel=$2previous=$1export runlevel previous. /etc/init.d/functionsexport CONSOLETYPEdo_confirm="no"if [ -f /var/run/confirm ]; then        do_confirm="yes"fiUPSTART=[ -x /sbin/initctl ] && UPSTART=yes# See if we want to be in user confirmation modeif [ "$previous" = "N" ]; then        if [ "$do_confirm" = "yes" ]; then                echo $"Entering interactive startup"        else                echo $"Entering non-interactive startup"        fifi# Get first argument. Set new runlevel to this argument.[ -n "$argv1" ] && runlevel="$argv1"# Is there an rc directory for this new runlevel?[ -d /etc/rc$runlevel.d ] || exit 0# Set language, vc settings once to avoid doing it for every init script# through functionsif [ -f /etc/sysconfig/i18n -a -z "${NOLOCALE:-}" ] ; then  . /etc/profile.d/lang.sh 2>/dev/null  export LANGSH_SOURCED=1fi# First, run the KILL scripts.for i in /etc/rc$runlevel.d/K* ; do        # Check if the subsystem is already up.        subsys=${i#/etc/rc$runlevel.d/K??}        [ -f /var/lock/subsys/$subsys -o -f /var/lock/subsys/$subsys.init ] || continue        check_runlevel "$i" || continue        # Bring the subsystem down.        [ -n "$UPSTART" ] && initctl emit --quiet stopping JOB=$subsys        $i stop        [ -n "$UPSTART" ] && initctl emit --quiet stopped JOB=$subsysdone# Now run the START scripts.for i in /etc/rc$runlevel.d/S* ; do        # Check if the subsystem is already up.        subsys=${i#/etc/rc$runlevel.d/S??}        [ -f /var/lock/subsys/$subsys ] && continue        [ -f /var/lock/subsys/$subsys.init ] && continue        check_runlevel "$i" || continue                            # If we‘re in confirmation mode, get user confirmation        if [ "$do_confirm" = "yes" ]; then                confirm $subsys                rc=$?                if [ "$rc" = "1" ]; then                        continue                elif [ "$rc" = "2" ]; then                        do_confirm="no"                fi        fi        update_boot_stage "$subsys"        # Bring the subsystem up.        [ -n "$UPSTART" ] && initctl emit --quiet starting JOB=$subsys        if [ "$subsys" = "halt" -o "$subsys" = "reboot" ]; then                export LC_ALL=C                exec $i start        fi        $i start        [ -n "$UPSTART" ] && initctl emit --quiet started JOB=$subsysdone[ "$do_confirm" = "yes" ] && rm -f /var/run/confirmexit 0[[email protected] ~]#

[[email protected] rc5.d]# pwd/etc/rc5.d[[email protected] rc5.d]# lsK01smartd        K61nfs-rdma        K89netconsole    S10network         S24nfslock           S55sshdK02oddjobd       K69rpcsvcgssd      K89rdisc         S11auditd          S24rpcgssd           S70spice-vdagentdK05wdaemon       K73winbind         K92pppoe-server  S11portreserve     S25blk-availability  S80postfixK10psacct        K74ntpd            K95firstboot     S12rsyslog         S25cups              S82abrt-ccppK10saslauthd     K75ntpdate         K95rdma          S13cpuspeed        S25netfs             S82abrtdK15htcacheclean  K75quota_nld       K99rngd          S13irqbalance      S26acpid             S90crondK15httpd         K76ypbind          S01sysstat       S13rpcbind         S26haldaemon         S95atdK50dnsmasq       K84wpa_supplicant  S02lvm2-monitor  S15mdmonitor       S26udev-post         S99certmongerK50kdump         K87restorecond     S08ip6tables     S22messagebus      S28autofs            S99localK60nfs           K88sssd            S08iptables      S23NetworkManager  S50bluetooth[[email protected] rc5.d]#

CentOS RedHat啟動過程