Actually the grub-install command is a terminal command to be issued inside the installed Linux and will not work without prior connection with the installed version. As such Grub need to know where the Grub comes from by the use of the "root" statement.
If the Ubuntu has been installed in say (hd0,1) or the 2nd partition of the 1st disk (or sda2 to Ubuntu Linux) then the commands in a Grub shell are
Code:
sudo grub
root (hd0,1)
setup (hd0)
will instruct Grub to "source" the Grub files from (hd0,1) and install itself in the MBR or the whole of the disk sda.
Alternatively without a Grub shell but grub-install one needs to mount the partition first like
Code:
sudo mkdir /mnt/sda2
sudo mount /dev/sda2 /mnt/sda2
sudo chroot /mnt/sda2
grub-install /dev/sda
exit
The
red commands above change root from the boot-up CD Linux into the unbootable Ubuntu inside partition sda2. Therefore grub-install is issued "inside" the unbootable Linux.
Both methods work satisfactorily. The latter does not need the original Ubuntu installation CD but any Live CD will do because one boots up the kernel of the Live CD but is actually using the Bash shell of the unbottable Linux. Therefore the same method of using any Live CD can be used to rescue a Lilo whose equivalent command to "grub-install /dev/sda" is just "lilo -b /dev/sda" at the terminal.
