從LIVE CD恢複GRUB2

How To Re-install GRUB 2 From A Live CD
without the need to chroot.

1)Boot your Ubuntu Karmic Koala or later 'Desktop' Live CD, or anotherKarmic installation such as an operating system in a USB device orwhateveryou have to use as a as a rescue disk.

Tip: It will make your Ubuntu life alot easier if you take a few minutes to set a nice user-freindly filesystem label in your linux file systems,

How To Set File System Labels With GParted.

2) The operating system you want to fix needs to be mounted.

Just go'Places'-->'Removable Media' or just 'Places' and look under'Computer' for the disk or partition you want to mount and click on it.- also see
Click-Icon Mounting.
Youshould see an icon for it on your desktop, but what you may not see isthe 'mount point', which will normally be located in your /mediadirectory. We will need to know the file path and name of the mount point.

3) Find the name of the mount point,

ls /media

Thefile path that is returned from theabove command will be needed for making up the next command. The nameof the mount point might be a file system LABEL or UUID number. Formy example I'll just usethe word 'disk' for short.

4)  Run the grub-setup command, inserting the -d option and specifying thepath to the /boot/grub directory of the operating system you're tryingto fix,

sudo grub-setup -d /media/disk/boot/grub /dev/sda

The -d option tells GRUB to use files from the specified directory.
Please substitute the word 'disk' with the name of your own mount point as found in step 3)
The '/dev/sda' part tells grub-setup to install GRUB to MBR in the first hard disk, which is called '/dev/sda'.
You may use the same command to install GRUB in any other disks in yourcomputer by replacing the /dev/sda part of the command with /dev/sdb or/dev/sdc and so on.

- Ifthe command fails with feedback about not being able to access adevice.map file, you might need to try again and specify the exactdevice.map file to use with the -m option.

sudo grub-setup -d /media/disk/boot/grub -m /media/disk/boot/grub/device.map /dev/sda

The -m option tells GRUB what device.map you want to use.