sudo grub-install --root-directory=/mnt/ /dev/sda
sudo grub-install --root-directory=/mnt /dev/sda
http://liveusb.info/dotclear/index.php?pages/install
For GRUB 2 version 1.98 and earlier (Ubuntu 10.04), the installation command is slightly different. Rather than designating the --boot-directory, the switch is --root-directory. In this case, the location changes to /mnt sudo grub-install --root-directory=/mnt /dev/sdX