Running update-grub from chroot (e.g., recovering via livecd)

http://askubuntu.com/questions/145241/how-do-i-run-update-grub-from-a-livecd

and much the same information but a bit prettier here:

http://howtoubuntu.org/how-to-repair-restore-reinstall-grub-2-with-a-ubuntu-live-cd