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CentOS 6 启动管理

CentOS 启动流程

• POST加电自检
• MBR引导
• GRUB引导
• 加载内核

GRUB启动阶段

GRUB是硬件加载操作系统的中介
第一阶段是直接以二进制的形式放在磁盘上

• primary boot loader:
  1st stage:MBR的第446个字节
  1.5st: mbr之后，加载文件系统驱动
• secondary boot loader:加载内核
  GRUB定义了内核的位置
  /boot/grub/grub.conf 中写了内核位置

[root@C6-56 ~]# hexdump -C -n 512 /dev/sda00000000  eb 48 90 10 8e d0 bc 00  b0 b8 00 00 8e d8 8e c0  |.H..............|00000010  fb be 00 7c bf 00 06 b9  00 02 f3 a4 ea 21 06 00  |...|.........!..|00000020  00 be be 07 38 04 75 0b  83 c6 10 81 fe fe 07 75  |....8.u........u|00000030  f3 eb 16 b4 02 b0 01 bb  00 7c b2 80 8a 74 03 02  |.........|...t..|00000040  80 00 00 80 fe 89 04 00  00 08 fa 90 90 f6 c2 80  |................|00000050  75 02 b2 80 ea 59 7c 00  00 31 c0 8e d8 8e d0 bc  |u....Y|..1......|00000060  00 20 fb a0 40 7c 3c ff  74 02 88 c2 52 f6 c2 80  |. ..@|<.t...R...|00000070  74 54 b4 41 bb aa 55 cd  13 5a 52 72 49 81 fb 55  |tT.A..U..ZRrI..U|00000080  aa 75 43 a0 41 7c 84 c0  75 05 83 e1 01 74 37 66  |.uC.A|..u....t7f|00000090  8b 4c 10 be 05 7c c6 44  ff 01 66 8b 1e 44 7c c7  |.L...|.D..f..D|.|000000a0  04 10 00 c7 44 02 01 00  66 89 5c 08 c7 44 06 00  |....D...f.\..D..|000000b0  70 66 31 c0 89 44 04 66  89 44 0c b4 42 cd 13 72  |pf1..D.f.D..B..r|000000c0  05 bb 00 70 eb 7d b4 08  cd 13 73 0a f6 c2 80 0f  |...p.}....s.....|000000d0  84 f0 00 e9 8d 00 be 05  7c c6 44 ff 00 66 31 c0  |........|.D..f1.|000000e0  88 f0 40 66 89 44 04 31  d2 88 ca c1 e2 02 88 e8  |..@f.D.1........|000000f0  88 f4 40 89 44 08 31 c0  88 d0 c0 e8 02 66 89 04  |..@.D.1......f..|00000100  66 a1 44 7c 66 31 d2 66  f7 34 88 54 0a 66 31 d2  |f.D|f1.f.4.T.f1.|00000110  66 f7 74 04 88 54 0b 89  44 0c 3b 44 08 7d 3c 8a  |f.t..T..D.;D.}<.|00000120  54 0d c0 e2 06 8a 4c 0a  fe c1 08 d1 8a 6c 0c 5a  |T.....L......l.Z|00000130  8a 74 0b bb 00 70 8e c3  31 db b8 01 02 cd 13 72  |.t...p..1......r|00000140  2a 8c c3 8e 06 48 7c 60  1e b9 00 01 8e db 31 f6  |*....H|`......1.|00000150  31 ff fc f3 a5 1f 61 ff  26 42 7c be 7f 7d e8 40  |1.....a.&B|..}.@|00000160  00 eb 0e be 84 7d e8 38  00 eb 06 be 8e 7d e8 30  |.....}.8.....}.0|00000170  00 be 93 7d e8 2a 00 eb  fe 47 52 55 42 20 00 47  |...}.*...GRUB .G|00000180  65 6f 6d 00 48 61 72 64  20 44 69 73 6b 00 52 65  |eom.Hard Disk.Re|00000190  61 64 00 20 45 72 72 6f  72 00 bb 01 00 b4 0e cd  |ad. Error.......|000001a0  10 ac 3c 00 75 f4 c3 00  00 00 00 00 00 00 00 00  |..<.u...........|000001b0  00 00 00 00 00 00 00 00  7f 83 03 00 00 00 80 20  |............... |000001c0  21 00 83 5e 38 26 00 08  00 00 00 60 09 00 00 5e  |!..^8&.....`...^|000001d0  39 26 83 fe ff ff 00 68  09 00 00 98 38 02 00 fe  |9&.....h....8...|000001e0  ff ff 82 fe ff ff 00 00  42 02 00 00 3e 00 00 00  |........B...>...|000001f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 55 aa  |..............U.|00000200

grub.conf 菜单文件

• grub提供了开机引导菜单选项
• grub配置文件grub.conf记录了内核的路径

default=0 ## 默认选在第一个内核timeout=5 ## 选择延时splashimage=(hd0,0)/grub/splash.xpm.gz ##背景图片hiddenmenu ##默认隐藏title CentOS 6 (2.6.32-754.el6.x86_64)	root (hd0,0) ##指boot所在硬盘，分区，这里指sda1	kernel /vmlinuz-2.6.32-754.el6.x86_64 ro root=UUID=6a0b88e9-b88a-498c-b1b9-e5caae44c8d1 rd_NO_LUKS rd_NO_LVM LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet ## /vmlinuz 前是将/boot/当作根；root=是真正的根	initrd /initramfs-2.6.32-754.el6.x86_64.img ##微型的linux，包含了驱动

CentOS6 破解口令

CentOS6由grub引导，在开机引导时对加载内核选项进行编辑，从而可以无需密码进入单用户模式下修改密码

步骤：

• 开机后按任意键进入grub菜单
  
• 在grub菜单按a键进行编辑
  
• 在内核选项后输入1|s|S|single 回车确认
  
• 不用输入密码进入单用户模式
  
• 使用passwd修改root密码

echo '密码' | passwd --stdin 用户 ##非交互式修改密码

passwd root ## 交互式修改密码

• 或者编辑/etc/shadow文件，清空密码部分的内容

vi /etc/shadow