sudo grub-mkpasswd-pbkdf2
Output:
grub.pbkdf2.sha512.10000.EXAMPLE000EXAMPLE000
sudo vim /etc/grub.d/40_custom
Add to end of file:
set superusers="titus"
password_pbkdf2 titus grub.pbkdf2.sha512.10000.EXAMPLE000EXAMPLE000
sudo update-grub