Downgrade Grub2 to Grub Legacy

1. Backup for Grub2 settings

$ sudo cp /etc/default/grub /etc/default/grub.old
$ sudo cp -R /etc/grub.d /etc/grub.d.old
$ sudo cp -R /boot/grub /boot/grub.old

2. Remove Grub2

$ sudo apt-get purge grub2 grub-pc

3. Install Grub Legacy

$ sudo apt-get install grub

4. Update Grub settings

$ sudo update-grub
$ sudo grub-install /dev/sdX

*sdX should be matched your machine state. Usually, it is /dev/sda.

5. Block the update of Grub Legacy

$ echo “grub hold” | sudo dpkg --set-selections