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Terminal Commands:

Mount the partition your Ubuntu Installation is on. If you are not sure which it is, launch GParted (included in the Live CD) and find out. It is usually a EXT4 Partition.

Replace the XY with the drive letter, and partition number, for example:sudo mount /dev/sda5 /mnt.

sudo mount /dev/sdXY /mnt

Now bind the directories that grub needs access to to detect other operating systems, like so:

sudo mount --bind /dev /mnt/dev && sudo mount --bind /dev/pts /mnt/dev/pts && sudo mount --bind /proc /mnt/proc && sudo mount --bind /sys /mnt/sys

Now we jump into that using chroot.

sudo chroot /mnt

Now install, check, and update grub.

This time you only need to add the drive letter (usually a) to replace X, for example: grub-install /dev/sda, grub-install –recheck /dev/sda.

grub-install /dev/sdX

grub-install --recheck /dev/sdX

update-grub

update-grub2

Now grub is back, all that is left is to exit the chrooted system and unmount everything.

exit && sudo umount /mnt/dev && sudo umount /mnt/dev/pts && sudo umount /mnt/proc && sudo umount /mnt/sys && sudo umount /mnt

Shut down and turn your computer back on, and you will be met with the default Grub2 screen.

You may want to update grub or re-install burg however you like it.

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