*auto repair: https://help.ubuntu.com/community/Boot-Repair
*manual repair: http://ubuntuforums.org/showthread.php?t=224351


==steps==
<pre>
/mnt/etc/default/grub:
GRUB_DISABLE_LINUX_UUID=true
GRUB_DISABLE_RECOVERY="true"

grub-install --boot-directory=/mnt/boot /dev/sdb
mount --bind /dev /mnt/dev
mount --bind /sys /mnt/sys
mount --bind /proc /mnt/proc
chroot /mnt /usr/sbin/grub-mkconfig -o /boot/grub/grub.cfg
umount /mnt/dev
umount /mnt/sys
umount /mnt/proc

/etc/fstab:
Use device path instead of UUID.

/boot/grub/grub.cfg:
set root='hd?,modos?' -> set root='hd0,msdos1'
root=/dev/sd?? -> root=/dev/sda1

</pre>