This script lists the grub2 menu entries (including submenus) 
and allows you to select which one to boot by default. It sets 
the menu (and submenu) number in GRUB_DEFAULT in 
/etc/default/grub, and then (by default) runs update-grub.

The script was written after spending some time trying to 
google a solution to what should be an easy task. The default 
method of using grub-set-default didn't work for me, so I 
worked out a way to set the default entry without having to 
look through grub.cfg and figuring out which numbers or 
titles to use.

The number method I used seems to work reliably and should 
hopefully work on other setups, but no guarantees. The script 
has been made to be as portable as possible.