But what if GRUB was Locked By password and you forget Root Password, There’s always away to do it but you need the same media for Operating system ( Never tried to use different distribution ) after boot :
In the above screen Type ” linux rescue ” and then Press enter
After follow the instruction and Enter Bash
chroot /mnt/sysimage [Enter]
cd /boot/grub [Enter]
Now In that file you see word “Password” Remove Line, This will remove Grub password after save it the OS will Reboot but this time Grub will be UN-Protected , Remove CD and follow the normal instruction in Article Number one Here.