Today I ran into a funny issue with my ubuntu test environment. Somehow I removed my only user from the admin group.

After the next reboot (I am running this in VirtualBox), I was not able to sudo any more, due to not being in the sudoers list any more!

I managed to recover (re-adding myself to the admin group) by following instructions from this post about recovering the root password. having more than one kernel in GRUB, the instructions weren’t exactly right, but close enough to get me going.

The important bit was to add

rw init=/bin/bash

to the kernel line of the selected boot configuration.

Phewww!