Install (if it is not there anymore) the image of one of the kernels Trisquel
provides: "linux-image-lowlatency" (that is the one that was installed by
default) or "linux-image-generic" or...;
Remove the packages provided by linux-libre.fsfla.org (you can easily list
them with the "Origin" button in the bottom-left corner of the "Synaptic
Package Manager" in the "System Settings";
Optionally, remove the line "deb
https://linux-libre.fsfla.org/pub/linux-libre/freesh/ freesh main" from
/etc/apt/sources.list with a text editor (here GEdit):
$ gksu gedit /etc/apt/sources.list
I am actually not certain APT will let you remove the kernel you are
currently running. If not, reboot on Trisquel's kernel after installing it:
at GRUB's menu, choose the "Advanced options" and then Trisquel 7's kernel
(version 3.13). If you have not removed GRUB password, first learn it:
$ sudo cat /etc/grub.d/01_PASSWORD
It is the number at the very end of the output. The user is "grub".
