From almost any GNU/Linux distribution, you can boot an entry that says
"recovery mode" and you will be presented a root terminal where you can fix
anything... or break things more!
Unfortunately, Trisquel uselessly makes your system harder to repair: you
have to fight to end up with a root terminal! You can, for instance, 'chroot'
from a Live system:
https://help.ubuntu.com/community/Grub2/Installing#via_ChRoot
To have a "recovery mode" entry in GRUB, comment the following line in
/etc/default/grub:
GRUB_DISABLE_RECOVERY="true"
Then execute:
$ sudo update-grub
To not have the useless GRUB password you faced, you can comment all lines in
/etc/grub.d/01_PASSWORD and then run 'sudo update-grub'.
When I write that the GRUB password is useless, I am actually repeating what
GRUB's developers state in their documentation (
https://www.gnu.org/software/grub/manual/grub.html#Security ):
By default, the boot loader interface is accessible to anyone with physical
access to the console: anyone can select and edit any menu entry, and anyone
can get direct access to a GRUB shell prompt. For most systems, this is
reasonable since anyone with direct physical access has a variety of other
ways to gain full access, and requiring authentication at the boot loader
level would only serve to make it difficult to recover broken systems.
