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How to restore GRUB2 using an Ubuntu Live CD or Thumb Drive 09/02/2010

Posted by muyiscoi in Guides.
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If you are a tinkerer like me, you will no doubt run into some problems with grub at one time or another.
Even though you do not tinker, you might still have a problem with grub especially if dual-boot your system with windows. In that case, the windows boot-loader overwrites GRUB in the Master boot record (MBR) (if you install Ubuntu first) thereby rendering your Linux partition not bootable. It has been a major bottleneck for a lot of Ubuntu users when they can no longer boot into their desktop and most times are forced to reinstall.

It is however, relatively easy to restore GRUB on your computer irrespective of how you lost it in the first place.
The only requirements are that you still have a healthy installation of Ubuntu on your machine and a ready live CD or a USB thumb drive with Ubuntu loaded on it.

I will assume that the readers of this post have some level of knowledge on how to get certain things done on Ubuntu so i will not be too specific in some areas. if anything is unclear, you can ask it in the comments and i will be glad to clarify.

First, you have to boot the live CD. If you are using a thumb drive, also boot from it.
After booting, you have to determine which of your hard-disk partitions is the root (/) partition. You can do this by typing

sudo fdisk -l

in the terminal.
Note: If you only have one partition or you already know the address of your root partition, you can skip this step.