Restoring GRUB2 after installing Windows

This method of installation uses the chroot command to gain access to the broken system's files. Once the chroot command is issued, the LiveCD treats the broken system's / as its own. Commands run in a chroot environment will affect the broken systems filesystems and not those of the LiveCD.

1. Boot to the LiveCD Desktop (Ubuntu 9.10 or later).

2. Open a terminal - Applications, Accessories, Terminal.

3. Determine your normal system partition - (the switch is a lowercase "L")

   sudo fdisk -l

   • If you aren't sure, run

     df -Th. Look for the correct disk size and ext3 or ext4 format.

4. Mount your normal system partition:
   • Substitute the correct partition: sda1, sdb5, etc.

   sudo mount /dev/sdXX /mnt # Example: sudo mount /dev/sda1 /mnt

5. Only if you have a separate boot partition:

   • sdYY is the /boot partition designation (examply sdb3)

   • sudo mount /dev/sdYY /mnt/boot

6. Mount devices:

   sudo mount --bind /dev/ /mnt/dev

7. To ensure that only the grub utilities from the LiveCD get executed, mount /usr

   sudo mount --bind /usr/ /mnt/usr

8. mount proc filesystem

   sudo mount --bind /proc/ /mnt/proc

9. Chroot into your normal system device:

   sudo chroot /mnt

10. If there is no /boot/grub/grub.cfg or it's not correct, create one using

    update-grub

11. Reinstall GRUB 2:

    • Substitute the correct device - sda, sdb, etc. Do not specify a partition number.

    grub-install /dev/sdX

12. Verify the install (use the correct device, for example sda. Do not specify a partition): sudo grub-install --recheck /dev/sdX

13. Exit chroot: CTRL-D on keyboard

14. Unmount devices:

    sudo umount /mnt/dev

    • If you mounted a separate /boot partition:

      sudo umount /mnt/boot

15. Unmount last device:

    sudo umount /mnt

16. Reboot.

    reboot

Post-Restoration Commands

Once the user can boot to a working system, try to determine why the system failed to boot. The following commands may prove useful in locating and/or fixing the problem.

To refresh the available devices and settings in /boot/grub/grub.cfg

• sudo update-grub

To look for the bootloader location.

• grub-probe -t device /boot/grub

To install GRUB 2 to the sdX partition's MBR (sda, sdb, etc.)

• sudo grub-install /dev/sdX

To recheck the installation. (sda, sdb, etc.) sudo grub-install --recheck /dev/sdX

Please check the following link for further details.

https://help.ubuntu.com/community/Grub2#Reinstalling%20GRUB%202