How to Use Ubuntu Live CD to Rescue Grub Problem?

Background

While testing various options in Grub menu, the system broke – it booted into a blank black screen. I had to use an Ubuntu Live CD to rescue the system.

Steps to Use Ubuntu Live CD to Rescue Grub Problem

1. Boot up the computer with a live Ubuntu Desktop CD with option “Try Ubuntu without Installing…”
2. Open a Terminal window with CTRL-ATL-T or click on application -> terminal.
3. Use “sudo fdisk -l” command to figure out your drive designation. The hard drive on the messed up computer was sda5.
4. Mount the hard drive to mnt with command:  sudo mount /dev/sda5 /mnt
5. Mount other necessary directories:

   sudo mount --bind /dev /mnt/dev
   sudo mount --bind /sys /mnt/sys
   sudo mount --bind /proc /mnt/proc
   
   

6. Set root to new mnt directory: sudo chroot /mnt
7. Verify that the /boot directory is the working one by checking to see if there are lots of recent .mod files.
8. Now to you can modify the /etc/default/grub file as normal.
9. Update the grub configuration with command: sudo update-grub

That’s it. You can reboot the computer with updated grub files.

Reference

How do I run update-grub from a LiveCD?