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Linux系统灾难恢复技术和方法-[3]
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系统 /boot 分区损坏
一般来说系统 /boot 分区损坏，我们会先尝试修复文件系统。如果文件系统损坏不能修复，那么我们可以参照前述的方法来依次新建 /boot 分区，重新安装内核和镜像，然后安装 GURB 再手工编辑引导菜单，以最终来恢复系统可正常引导。通常我们需要按照如下的步骤来恢复。
创建分区
碰到比较严重的情况就是 /boot 分区已经完全损坏，启动时会提示找不到引导设备。
图 8. 引导分区损坏
挂载安装盘后进入援救模式，查看分区情况，发现分区 /dev/sda1 不存在。
bash-4.1# Disk /dev/sda: 43.0 GB, 42991616000 bytes 255 heads, 63 sectors/track, 5226 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 Device Boot Start End Blocks Id System /dev/sda2 17 147 1048576 82 Linux swap / Solaris Partition 2 does not end on cylinder boundary. /dev/sda3 147 5227 40803328 83 Linux Disk /dev/sdb: 2147 MB, 2147483648 bytes 255 heads, 63 sectors/track, 261 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: 0xcdd48395 Device Boot Start End Blocks Id System /dev/sdb1 1 261 2096451 83 Linux 新建一个分区并且设置它为启动分区。
bash-4.1# fdisk /dev/sda 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 (1-5226, default 1): Using default value 1 Last cylinder, +cylinders or +size{K,M,G} (1-16, default 16): Using default value 16 Command (m for help): a Partition number (1-4): 1 Command (m for help): p Disk /dev/sda: 43.0 GB, 42991616000 bytes 255 heads, 63 sectors/track, 5226 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 Device Boot Start End Blocks Id System /dev/sda1 * 1 16 128488+ 83 Linux /dev/sda2 17 147 1048576 82 Linux swap / Solaris Partition 2 does not end on cylinder boundary. /dev/sda3 147 5227 40803328 83 Linux Command (m for help): w The partition table has been altered! 重启主机以更新分区表，然后进入援救模式，并在我们新创建的分区上创建文件系统。
bash-4.1# mkfs.ext4 /dev/sda1 Filesystem label= OS type: Linux Block size=1024 (log=0) Fragment size=1024 (log=0) Stride=0 blocks, Stripe width=0 blocks 32128 inodes, 128488 blocks 6424 blocks (5.00%) reserved for the super user First data block=1 Maximum filesystem blocks=67371008 16 block groups 8192 blocks per group, 8192 fragments per group 2008 inodes per group Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729 Writing inode tables: done Creating journal (4096 blocks): done Writing superblocks and filesystem accounting information: done This filesystem will be automatically checked every 38 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override. 安装内核镜像文件
通过前述的方法我们安装内核和镜像文件。
bash-4.1# chroot /mnt/sysp_w_picpath sh-4.1# mount /dev/sda1 /boot sh-4.1# mount – o loop /dev/sr0 /media sh-4.1# cd /media/Server/Packages sh-4.1# rpm -ivh --force kernel-2.6.32-71.el6.x86_64.rpm warning: kernel-2.6.32-71.el6.x86_64.rpm: \ Header V3 RSA/SHA256 Signature, key ID fd431d51: NOKEY Preparing... ########################################### [100%] 1:kernel ########################################### [100%] 安装 GRUB
我们安装 GRUB 到硬盘设备 sda 上。
sh-4.1# grub-install /dev/sda Installation finished. No error reported. This is the contents of the device map /boot/grub/device.map. Check if this is correct or not. If any of the lines is incorrect, fix it and re-run the script `grub-install'. (fd0) /dev/fd0 (hd0) /dev/sda (hd1) /dev/sdb 编辑引导菜单
由于我们创建了新的分区，其对应的 UUID 会发生变化，可以通过命令 blkid 来查询分区的 UUID。
bash-4.1# blkid /dev/loop0: TYPE="squashfs" /dev/sda2: UUID="7b1e0fac-ff06-492c-848d-497e2a38c54e" TYPE="swap" /dev/sda3: UUID="ef89764e-04ff-4f26-ae82-dcab267ecc66" TYPE="ext4" /dev/sdb1: UUID="2b824352-df2a-44c6-a547-838d46f526fa" SEC_TYPE="ext2" TYPE="ext3" /dev/loop1: LABEL="RHEL_6.0 x86_64 Disc 1" TYPE="iso9660" /dev/sda1: UUID="cec964af-1618-48ff-ac33-4ef71b9d3265" TYPE="ext4" 上述的 sda3 为根分区，编辑 /boot/grub/grub.conf 文件更新其对应的 UUID，其内容如下。
title Red Hat Enterprise Linux 6 root (hd0,0) kernel /vmlinuz-2.6.32-71.el6.x86_64 \ root=UUID=ef89764e-04ff-4f26-ae82-dcab267ecc66 rhgb quiet initrd /initramfs-2.6.32-71.el6.x86_64.img 更新 /etc/fstab
类似的我们也需要更新 /etc/fstab 里 /boot 分区对应的新 UUID，其内容如下。
# # /etc/fstab # Created by anaconda on Sun Mar 18 04:35:07 2012 # # Accessible filesystems, by reference, are maintained under '/dev/disk' # See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info # UUID=ef89764e-04ff-4f26-ae82-dcab267ecc66 / ext4 defaults 1 1 UUID=cec964af-1618-48ff-ac33-4ef71b9d3265 /boot ext4 defaults 1 2 UUID=7b1e0fac-ff06-492c-848d-497e2a38c54e swap swap defaults 0 0 tmpfs /dev/shm tmpfs defaults 0 0 devpts /dev/pts devpts gid=5,mode=620 0 0 sysfs /sys sysfs defaults 0 0 proc /proc proc defaults 0 0 现在我们的恢复步骤已经完成，重启主机后 GRUB 中可见我们配置的系统列表。
图 9. GRUB 菜单
至此 /boot 分区已恢复，系统可正常引导启动。
图 10. 系统启动
总结
本文阐述了常见的 Linux 灾难恢复技术和方法，及其出现严重灾难时应注意的恢复顺序，以确保 Linux 系统在出现灾难时得以安全恢复。
转载于:https://blog.51cto.com/redkey/1179089
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