When making multi-boot systems or re-organizing your disks you may be unlucky to find your grub install is either partially or completely removed.
The simplest way to fix this is to boot a livecd but what should you do once the live cd is loaded, especially if you enter grub-install or grub and then find /boot/grub/stage1 and all you get is
Fatal: Error 15
The following are a few quick steps to fix grub using chroot
First make your life easier by getting into a full root session
ubuntu@ubuntu:~$ sudo su
now mount your ubuntu install
root@ubuntu:/home/ubuntu# mount /dev/hda5 /mnt
Next bind your real devices so that the grub command can work
root@ubuntu:/home/ubuntu# mount -o bind /dev /mnt/dev
root@ubuntu:/home/ubuntu# mount -o bind /proc /mnt/proc
Enter the chroot session
root@ubuntu:/home/ubuntu# chroot /mnt
root@ubuntu:/# grub
grub> find /boot/grub/stage1
find /boot/grub/stage1
(hd0,1)
(hd0,4)
My root disk was installed on partition 5 so now set that as root
grub> root (hd0,4) root (hd0,4)
install grub
grub> setup (hd0)
setup (hd0)
Checking if "/boot/grub/stage1" exists... yes
Checking if "/boot/grub/stage2" exists... yes
Checking if "/boot/grub/e2fs_stage1_5" exists... yes
Running "embed /boot/grub/e2fs_stage1_5 (hd0)"... 16 sectors are embedded.
succeeded
Running "install /boot/grub/stage1 (hd0) (hd0)1+16 p (hd0,4)/boot/grub/stage2 /boot/grub/menu.lst"... succeeded
Done.
Now quit and restart your machine
grub> quit
exit
reboot
