Originally Posted by maples
Disclaimer: I've only done this on Arch systems, but it should(tm) work on Ubuntu.
For an ubuntu install you have to:
# passwd -d root
# passwd root
But I've only tested that on linux-lite via the chroot mentioned. You should NOT do that as that's not how ubuntu is supposed to work. You can su to root after doing that. And I don't know of any way to UNDO that. If the user is in the adm and sudo groups it has root permissions by using sudo. And you can change the users password with passwd in the chroot without doing that. The user(s) should be discoverable by checking out the contents of /home/ and /etc/group.