GRUB
Notes on grub, because it's useful :)
To apply any of these changes, make sure to run the following command after saving the configurations.
sudo update-grub
/etc/defaults/grub
Create a backup of your configuration before making any edits, so you can restore the original configuration if things get out of hand.
sudo cp /etc/defaults/grub /etc/defaults/grub.bak
Saves last selected boot option as the default for next boot. To override it, simply reboot and select a different option.
GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true