Linux系统管理—修复MBR扇区故障、修复GRUB引导故障、清除Linux各种密码

【centos6.5】

修复MBR扇区故障

1、挂载/dev/sdb1到/backup，将MBR扇区备份至此，毁坏MBR扇区，重启

[root@localhost ~]# init 3

[root@localhost ~]# fdisk /dev/sdb

Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel

Building a new DOS disklabel with disk identifier 0xc4d08778.

Changes will remain in memory only, until you decide to write them.

After that, of course, the previous content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to

         switch off the mode (command 'c') and change display units to

         sectors (command 'u').

Command (m for help): n

Command action

   e   extended

   p   primary partition (1-4)

p

Partition number (1-4): 1

First cylinder (1-130, default 1):

Using default value 1

Last cylinder, +cylinders or +size{K,M,G} (1-130, default 130):

Using default value 130

Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.

Syncing disks.

[root@localhost ~]# fdisk -l

Disk /dev/sda: 42.9 GB, 42949672960 bytes

255 heads, 63 sectors/track, 5221 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x00058c62

   Device Boot      Start         End      Blocks   Id  System

/dev/sda1   *           1          64      512000   83  Linux

Partition 1 does not end on cylinder boundary.

/dev/sda2              64        5222    41430016   8e  Linux LVM

Disk /dev/sdb: 1073 MB, 1073741824 bytes

255 heads, 63 sectors/track, 130 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0xc4d08778

   Device Boot      Start         End      Blocks   Id  System

/dev/sdb1               1         130     1044193+  83  Linux

Disk /dev/mapper/VolGroup-lv_root: 40.3 GB, 40340815872 bytes

255 heads, 63 sectors/track, 4904 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x00000000

Disk /dev/mapper/VolGroup-lv_swap: 2080 MB, 2080374784 bytes

255 heads, 63 sectors/track, 252 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x00000000

root@localhost ~]# mkfs.ext4 /dev/sdb1

mke2fs 1.41.12 (17-May-2010)

文件系统标签=

操作系统:Linux

块大小=4096 (log=2)

分块大小=4096 (log=2)

Stride=0 blocks, Stripe width=0 blocks

65280 inodes, 261048 blocks

13052 blocks (5.00%) reserved for the super user

第一个数据块=0

Maximum filesystem blocks=268435456

8 block groups

32768 blocks per group, 32768 fragments per group

8160 inodes per group

Superblock backups stored on blocks:

         32768, 98304, 163840, 229376

正在写入inode表: 完成                           

Creating journal (4096 blocks): 完成

Writing superblocks and filesystem accounting information: 完成

This filesystem will be automatically checked every 38 mounts or

180 days, whichever comes first.  Use tune2fs -c or -i to override.

[root@localhost ~]# mkdir /backup

[root@localhost ~]# mount /dev/sdb1 /backup

[root@localhost ~]# dd if=/dev/sda  of=/backup/sda.mbr.bak  bs=512  count=1

记录了1+0 的读入

记录了1+0 的写出

512字节(512 B)已复制，0.0242714 秒，21.1 kB/秒

[root@localhost ~]# du -sh /backup/sda.mbr.bak

4.0K /backup/sda.mbr.bak

[root@localhost ~]# ls -l /backup/sda.mbr.bak

-rw-r--r--. 1 root root 512 3月  20 04:35 /backup/sda.mbr.bak

[root@localhost ~]# dd  if=/dev/zero  of=/dev/sda  bs=512  count=1

记录了1+0 的读入

记录了1+0 的写出

512字节(512 B)已复制，0.00116769 秒，438 kB/秒

[root@localhost ~]#reboot

2、挂载系统光盘，从光盘引导进入安全模式

选择语言：英语

选择键盘：美式键盘

 

是否开启网络访问，选择no

选择“Continue”

选择OK

开始shell

运行诊断

重启

选择shell

在shell界面将/dev/sdb1/挂载使用，将里面的备份写入/dev/sda,重启

至此可以重新进入系统，MBR分区修复成功

二、修复GRUB引导故障

1、方法一，尝试手动输入【针对配置文件和有备份的情况】

[root@localhost ~]# cat /boot/grub/grub.conf

# grub.conf generated by anaconda

#

# Note that you do not have to rerun grub after making changes to this file

# NOTICE:  You have a /boot partition.  This means that

#          all kernel and initrd paths are relative to /boot/, eg.

#          root (hd0,0)

#          kernel /vmlinuz-version ro root=/dev/mapper/VolGroup-lv_root

#          initrd /initrd-[generic-]version.img

#boot=/dev/sda

default=0

timeout=5

splashimage=(hd0,0)/grub/splash.xpm.gz

hiddenmenu

title CentOS (2.6.32-431.el6.x86_64)

            root (hd0,0)

            kernel /vmlinuz-2.6.32-431.el6.x86_64 ro root=/dev/mapper/VolGroup-lv_root         rd_NO_LUKS rd_NO_MD rd_LVM_LV=VolGroup/lv_swap crashkernel=auto LANG=zh_CN.UTF-8 rd_LVM_LV=VolGroup/lv_root  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM  rhgb quiet

         initrd /initramfs-2.6.32-431.el6.x86_64.img

[root@localhost ~]# mount  /dev/sdb1  /backup

[root@localhost ~]# cd  /boot/grub

[root@localhost grub]# ls

device.map     grub.conf         minix_stage1_5     stage2

e2fs_stage1_5  iso9660_stage1_5  reiserfs_stage1_5  ufs2_stage1_5

fat_stage1_5   jfs_stage1_5      splash.xpm.gz      vstafs_stage1_5

ffs_stage1_5   menu.lst          stage1             xfs_stage1_5

[root@localhost grub]# mv grub.conf  grub.conf.bak

[root@localhost grub]# ls

device.map     grub.conf.bak     minix_stage1_5     stage2

e2fs_stage1_5  iso9660_stage1_5  reiserfs_stage1_5  ufs2_stage1_5

fat_stage1_5   jfs_stage1_5      splash.xpm.gz      vstafs_stage1_5

ffs_stage1_5   menu.lst          stage1             xfs_stage1_5

 [root@localhost grub]# reboot

引导停滞，出现“grub>”提示符

进行手动输入，注意：内核信息无法tab补全，需查看之前备份（输入自己主机备份的内核信息）

重新登录进去，修改grub。conf文件 【如果不修改重启之后会进入grub界面出现死循环】

2、方法二：进入急救模式，重建grub程序。需要提前备份MBR前446字节  【针对有备份的情况】

 [root@localhost ~]# dd  if=/dev/sda  of=/backup/sda.mbr.bak  bs=446  count=1

[root@localhost ~]# ls /backup

[root@localhost ~]# mount /dev/sdb1 /backup

[root@localhost ~]# ls /backup

grub.conf  lost+found  sda.mbr.bak

[root@localhost ~]# ls /boot/grub

device.map     grub.conf         minix_stage1_5     stage2

e2fs_stage1_5  iso9660_stage1_5  reiserfs_stage1_5  ufs2_stage1_5

fat_stage1_5   jfs_stage1_5      splash.xpm.gz      vstafs_stage1_5

ffs_stage1_5   menu.lst          stage1             xfs_stage1_5

[root@localhost ~]# cd /boot/grub

[root@localhost grub]# ls

device.map     grub.conf         minix_stage1_5     stage2

e2fs_stage1_5  iso9660_stage1_5  reiserfs_stage1_5  ufs2_stage1_5

fat_stage1_5   jfs_stage1_5      splash.xpm.gz      vstafs_stage1_5

ffs_stage1_5   menu.lst          stage1             xfs_stage1_5

[root@localhost grub]# mv grub.conf grub.conf.bak  【bak表示备份文件】

[root@localhost grub]# ls

device.map     grub.conf.bak     minix_stage1_5     stage2

e2fs_stage1_5  iso9660_stage1_5  reiserfs_stage1_5  ufs2_stage1_5

fat_stage1_5   jfs_stage1_5      splash.xpm.gz      vstafs_stage1_5

ffs_stage1_5   menu.lst          stage1             xfs_stage1_5

[root@localhost grub]# dd if=/dev/zero of=/dev/sda bs=446 count=1

记录了1+0 的读入

记录了1+0 的写出

446字节(446 B)已复制，0.0424687 秒，10.5 kB/秒

[root@localhost grub]# reboot

进去急求模式shell

 

进去shell后，将根路径修改为/mnt/sysimage  (chroot/mnt/sysimage)

命令“-l|grep”中间是通道号

3、方法三：若无MBR备份，进去急救模式，重新安装grub程序  【只针对扇区修复，不会修复配置文件，除非编辑文本】

进入安全模式shell同方法二

改变磁盘根目录到/mnt/sysimage

重新安装grub引导程序

退出重启

Chroot挂载的意思 挂载到伪目录

关机

从“打开电源时进入固件”进入

进入boot界面把“Hard Drive（硬盘）”放入第一位

进入Exit界面 选Exit Saving Changes（保存并退出）选yes

向上：shift键++键

三、清除Linux各种密码

3.1方法一

重启主机按“↑”进入字符界面

按e键

按“下键”

按e键

按“空格 1”

回车再按b

输入paasswd

输入新密码，回车，再输一遍，再输入reboot，回车

密码修改成功

3.2方法二、密码修改

进入急救模式的方法

从电源固件进入 boot里选

 

保存退出，再重启进入急救模式

进入伪根目录chroot  /mnt/sysimage

3.3方法三

按“x键删除单个字符‘

删除密文前

删除密文后，保存退出

实验补充：

1、init（0-7）表示runlevels的运行级别

2、进行修复GRUB引导故障，需提前记下内核的UUID或者存储的绝对路径，此处数据出错任何一个都会导致修复失败

（1）内核信息如果忘了备份，可以找台好的机器手抄其内核信息（之前做实验用的老师机子内核信息就会失败）

(2)直接把/boot/geub/grub.conf改为grub.conf.bak重启后出现以下问题，一直循环在这个界面

无论按什么命令都显示无法找到命令

（3）如果一直在grub界面循环并且输任何命令都显示无此命令，把配置文件修改过来，用第3种方案可以急救

（3）伪目录chroot  /mnt/sysimage