If you look at this page here in the Superuser & Password Designation section, you will see that it specifically states that:
Note: GRUB 2 1.99 in 12.04 LTS doesn't protect submenu, ie. command
line, entry editing and access to entries is not protected! See bug
However, they claim that the work around would be to add
export superusers to the
/etc/grub.d/00_header file. The example looks like the following lines added to the bottom of the file:
cat << EOF
password user1 password1
after those lines are added to your user information, update the grub so the settings take effect:
I just tested this on my own system, and as soon as I selected
Advanced Options it asked for a username and password. However, once you type it in, it is stored for that session and you can edit all lines, even the main Ubuntu entry. If I rebooted the system, then pressed
e on the first entry of Ubuntu, it asked for the username and password.
NOTE: this does not protect if someone boots the host to Live media. The only way to protect against that would be to use full drive encryption, but that is for a whole other topic.
Hope this helps!