Originally Posted by rickh
Rather than attempting to answer your question directly ...
I don't get why you couldn't just answer his question directly?
One time in Ubuntu I accidentally removed my user account out of the admin group. So, I lost all sudo access. I know the original poster doesn't use Ubuntu, but I had to boot into the recovery mode as mentioned. However, it kept asking me for the system recovery password. Of course I never recalled creating one during the Ubuntu installation, so I kept putting in bogus passwords. After a few attempts, it just put me right into the system as root. I was then able to add myself back into the admin group and regain my sudo access.