双系统重装windows后，修复grub启动

xp+ubuntu 12.04双系统，重装xp为win7，装好win7后恢复ubuntu的启动项。

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应用LiveCD启动光盘选择“试用而不安装”，进入后打开终端：

1、sudo fdisk -l

找到 id=83 选项，获取ubuntu的分区。

 

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x91c6943c

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          63   102414374    51207156    7  HPFS/NTFS/exFAT
Partition 1 does not start on physical sector boundary.
/dev/sda2       102414436   597938175   247761870    f  W95 Ext'd (LBA)
Partition 2 does not start on physical sector boundary.
/dev/sda3       597938176   776771583    89416704   83  Linux
/dev/sda4       776774880   976768064    99996592+  83  Linux
/dev/sda5       102414438   348176744   122881153+   7  HPFS/NTFS/exFAT
Partition 5 does not start on physical sector boundary.
/dev/sda6       348176808   593939114   122881153+   7  HPFS/NTFS/exFAT
/dev/sda7       593940480   597938175     1998848   82  Linux swap / Solaris

2、sudo -i 

3、mount /dev/sda2 /mnt

4、mount /dev/sda2 /mnt/boot   这一步是有给 /boot 单独分区的命令，若没单独分区跳过这步

5、grub-install --root-directory=/mnt /dev/sda

6、重启