來CSDN一年多兩年了，也是我工作年齡，哈哈~~每天都會來逛，現在，終於想到要寫部落格了。主要是自己比較懶，哈哈~~因為有些東西自己總是重複去網上查，還是寫自己的部落格好，可以經常檢視，也能幫助下其他人。

       最近系統學習linux各個方面，主要是系統管理和網路程式設計。

===================================================================================================================================

       在開機時，首先進行核心引導，嘩啦嘩啦的資訊一滾而過，想要再次看看？可以。不過，這個資訊接近300行，可以重定向到一個檔案再去看看。

       dmesg > startup_info.txt

       注意了，dmesg檢視的引導資訊是最近一次開機的，重新開機會被重置。而Soralis則相反。

       好了，引導完了，到init程序上場了。學過Linux的都知道，和Unix一樣，所有程序的老大都是init程序，它負責所有核心繫統功能的有序啟動(和關閉)，而且，它還為程序賦予許可權。我們可以控制Linux在核心啟動後，進入哪一個執行級別。

        我用的是Red Hat Enterprise 5版本，用命令看看inittab下是什麼內容：< cat -n /etc/inittab >

     1  #
     2  # inittab       This file describes how the INIT process should set up
     3  #               the system in a certain run-level.
     4  #
     5  # Author:       Miquel van Smoorenburg, <
 
[email protected]>
     6  #               Modified for RHS Linux by Marc Ewing and Donnie Barnes
     7  #
     8
     9  # Default runlevel. The runlevels used by RHS are:
    10  #   0 - halt (Do NOT set initdefault to this)
    11  #   1 - Single user mode
    12  #   2 - Multiuser, without NFS (The same as 3, if you do not have networking)
    13  #   3 - Full multiuser mode
    14  #   4 - unused
    15  #   5 - X11
    16  #   6 - reboot (Do NOT set initdefault to this)
    17  #
    18  id:3:initdefault:
    19
    20  # System initialization.
    21  si::sysinit:/etc/rc.d/rc.sysinit
    22
    23  l0:0:wait:/etc/rc.d/rc 0
    24  l1:1:wait:/etc/rc.d/rc 1
    25  l2:2:wait:/etc/rc.d/rc 2
    26  l3:3:wait:/etc/rc.d/rc 3
    27  l4:4:wait:/etc/rc.d/rc 4
    28  l5:5:wait:/etc/rc.d/rc 5
    29  l6:6:wait:/etc/rc.d/rc 6
    30
    31  # Trap CTRL-ALT-DELETE
    32  ca::ctrlaltdel:/sbin/shutdown -t3 -r now
    33
    34  # When our UPS tells us power has failed, assume we have a few minutes
    35  # of power left.  Schedule a shutdown for 2 minutes from now.
    36  # This does, of course, assume you have powerd installed and your
    37  # UPS connected and working correctly.
    38  pf::powerfail:/sbin/shutdown -f -h +2 "Power Failure; System Shutting Down"
    39
    40  # If power was restored before the shutdown kicked in, cancel it.
    41  pr:12345:powerokwait:/sbin/shutdown -c "Power Restored; Shutdown Cancelled"
    42
    43
    44  # Run gettys in standard runlevels
    45  1:2345:respawn:/sbin/mingetty tty1
    46  2:2345:respawn:/sbin/mingetty tty2
    47  3:2345:respawn:/sbin/mingetty tty3
    48  4:2345:respawn:/sbin/mingetty tty4
    49  5:2345:respawn:/sbin/mingetty tty5
    50  6:2345:respawn:/sbin/mingetty tty6
    51
    52  # Run xdm in runlevel 5
    53  x:5:respawn:/etc/X11/prefdm -nodaemon
 

        在23到29行，分別有對應各種不同啟動模式的啟動指令碼，對於系統管理員可以去看看裡面的指令碼，裡面配置了進入對應級別啟動和禁止的服務等。

        我們試著進入這個目錄看看：cd /etc/rc.d/rc3.d ，然後看看裡面有什麼：ll

lrwxrwxrwx 1 root root 24 Jul 22 22:13 K02avahi-dnsconfd -> ../init.d/avahi-dnsconfd
lrwxrwxrwx 1 root root 16 Jul 22 22:13 K02dhcdbd -> ../init.d/dhcdbd
lrwxrwxrwx 1 root root 24 Jul 22 22:15 K02NetworkManager -> ../init.d/NetworkManager
lrwxrwxrwx 1 root root 34 Jul 22 22:15 K02NetworkManagerDispatcher -> ../init.d/NetworkManagerDispatcher
lrwxrwxrwx 1 root root 16 Jul 22 22:14 K05conman -> ../init.d/conman
lrwxrwxrwx 1 root root 19 Jul 22 22:13 K05saslauthd -> ../init.d/saslauthd
lrwxrwxrwx 1 root root 19 Jul 22 22:16 K10dc_server -> ../init.d/dc_server
lrwxrwxrwx 1 root root 16 Jul 22 22:14 K10psacct -> ../init.d/psacct
lrwxrwxrwx 1 root root 19 Jul 22 22:16 K12dc_client -> ../init.d/dc_client
lrwxrwxrwx 1 root root 15 Jul 22 22:16 K15httpd -> ../init.d/httpd
lrwxrwxrwx 1 root root 13 Jul 22 22:14 K20nfs -> ../init.d/nfs
lrwxrwxrwx 1 root root 15 Jul 22 22:15 K20rwhod -> ../init.d/rwhod
lrwxrwxrwx 1 root root 14 Jul 22 22:14 K24irda -> ../init.d/irda
lrwxrwxrwx 1 root root 15 Jul 22 22:16 K25squid -> ../init.d/squid
lrwxrwxrwx 1 root root 13 Jul 22 22:16 K35smb -> ../init.d/smb
lrwxrwxrwx 1 root root 19 Jul 22 22:18 K35vncserver -> ../init.d/vncserver
lrwxrwxrwx 1 root root 17 Jul 22 22:20 K35winbind -> ../init.d/winbind
lrwxrwxrwx 1 root root 16 Jul 22 22:16 K36mysqld -> ../init.d/mysqld
lrwxrwxrwx 1 root root 20 Jul 22 22:13 K50netconsole -> ../init.d/netconsole
lrwxrwxrwx 1 root root 13 Jul 22 22:16 K50tux -> ../init.d/tux
................................
................................
 
lrwxrwxrwx 1 root root 16 Jul 22 22:14 S28autofs -> ../init.d/autofs
lrwxrwxrwx 1 root root 15 Jul 22 22:14 S44acpid -> ../init.d/acpid
lrwxrwxrwx 1 root root 15 Jul 22 22:14 S50hplip -> ../init.d/hplip
lrwxrwxrwx 1 root root 14 Jul 22 22:14 S55sshd -> ../init.d/sshd
lrwxrwxrwx 1 root root 14 Jul 22 22:13 S56cups -> ../init.d/cups
lrwxrwxrwx 1 root root 16 Jul 22 22:16 S56xinetd -> ../init.d/xinetd
lrwxrwxrwx 1 root root 18 Jul 22 22:13 S80sendmail -> ../init.d/sendmail
lrwxrwxrwx 1 root root 13 Jul 22 22:12 S85gpm -> ../init.d/gpm
lrwxrwxrwx 1 root root 15 Jul 22 22:13 S90crond -> ../init.d/crond
lrwxrwxrwx 1 root root 13 Jul 22 22:18 S90xfs -> ../init.d/xfs
lrwxrwxrwx 1 root root 17 Jul 22 22:12 S95anacron -> ../init.d/anacron
lrwxrwxrwx 1 root root 13 Jul 22 22:13 S95atd -> ../init.d/atd
lrwxrwxrwx 1 root root 15 Jul 22 22:15 S97rhnsd -> ../init.d/rhnsd
lrwxrwxrwx 1 root root 22 Jul 22 22:14 S97yum-updatesd -> ../init.d/yum-updatesd
lrwxrwxrwx 1 root root 22 Jul 22 22:13 S98avahi-daemon -> ../init.d/avahi-daemon
lrwxrwxrwx 1 root root 19 Jul 22 22:15 S98haldaemon -> ../init.d/haldaemon
lrwxrwxrwx 1 root root 19 Jul 22 22:15 S99firstboot -> ../init.d/firstboot
lrwxrwxrwx 1 root root 11 Jul 22 22:13 S99local -> ../rc.local
lrwxrwxrwx 1 root root 16 Jul 22 22:15 S99smartd -> ../init.d/smartd

        Start with "K"：同進程相關的指令碼在進入指定的執行模式時候終止，以stop引數呼叫

        Start with "S"：同進程相關的指令碼在進入指定的執行模式時候終止，以start引數呼叫

         注意到，它們都是連結檔案，為什麼這麼做呢？假如我們不小心刪除了rc.d目錄下的檔案，在init.d目錄下的檔案還在，這樣可以避免誤操作。因此，假如我們自己建立執行shell指令碼的話，也應該首先在init.d目錄下寫好shell指令碼，再在rc.d對應執行級別上建立連結檔案。