How do I get my user back on the sudoers list? I've tried How do I add myself back as a sudo user? but with the left SHIFT key pressed all the way from the moment the reboot is pressed until the end, but it is not working.
I'm using Ubuntu 16.04.2 LTS, on a DELL E7440. This uses EFI (not sure whether this makes any difference at all).
The last option is reinstalling my system from scratch, which I'm avoiding.