What does Ubuntu Linux do with GRUB during a new installation?

Question

I've been messing around with a cheap PC lately and now I have some questions about GRUB; what exactly does Ubuntu do with GRUB during a new install? Several times I've modified my partitions (moved the Linux partition left - namely) and not been able to get GRUB back and working. I've read online about both "grub" and "grub-install" from a Ubuntu Live CD, but can never manage to recover my computer to a working state.

Several times I've just wiped a partition and did a new install of Ubuntu on it just to get GRUB back to where I can boot ALL of my partitions.

So, I'd like to know, how can I accomplish that WITHOUT going through the entire install process?

Answer 1

To my recollection, Ubuntu uses GRUB2, not GRUB (now, GRUB Legacy) - this might help your search for answers. The way I would go about making my system bootable again after shuffling partitions around (presumably, using something like PartitionMagic) is to boot from a LiveCD, get my Linux partitions mounted, then chroot into the Linux system. From there, make a backup copy of your GRUB2 configuration, then run

grub-mkconfig -o /boot/grub/grub.cfg
grub-install

That should get you back up and running.