fdisk -l
mount /dev/sdaX /mnt
for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; don
chroot /mnt
update-grub
grub-install /dev/sda
for i in /sys /proc /dev/pts /dev; do sudo umount /mnt$i; done
umount /mnt
reboot