Starting with Ubuntu Karmic, Grub2 is used (for clean installs for now), so THIS how-to on recovering the GRUB no longer works for the new GRUB2.

But recovering GRUB2 (after breaking the GRUB2 or installing Windows – which breaks GRUB2, etc.) is just as easy. Here is what you need to do

Note: This tutorial should work for any Linux distribution which uses GRUB2, not just Ubuntu.

You need a live CD of Ubuntu Karmic (Lucid will work too – or any other Linux distribution which uses Grub2) from which you need to boot. Once you boot to the LIVE CD, open a terminal an and type these commands:

a) Firstly, you need to find out on which partition your Linux system is installed:

sudo fdisk -l

(in my case, it’s “sda1″)

b) Now, we must mount this partition:

sudo mount /dev/sda1 /mnt

Where “sda1″ is the partition where you installed Ubuntu (or any other Linux distro). It could be “sda5″, “sda6″, etc. for you.

c) Install grub to the partition you’ve mounted:

sudo grub-install -–root-directory=/mnt/ /dev/sda

Important: Please notice that it’s “/dev/sda”, not “/dev/sda1″. “sda” is the hard disk on which your Linux distribution is installed!

d) Restart your computer. As previous Grub2 entries are removed, run the following command to restore them:

sudo update-grub

Here is all the process (without step “d)” which takes place after restart) in a single screenshot:

And a final note: I have tested this in VirtualBox by breaking my GRUB2 and then mounting a Live Ubuntu CD and it all went very smooth.

[via mundogeek]