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?