As asked very clearly by this poster:
Fresh 18.04.1 LTS install, can't login, multiple re-installs.. same result
When you install a fresh server from the 18.04.1 install media, you may find that you cannot log into the system (at all). During install it asks for your user info, but it does not create that user, at least not always, apparently.
The resolution to this problem is to boot into rescue mode (after BIOS POST, press esc or shift until you get the grub boot menu, then choose a rescue mode, and then choose the root console). Then you can verify that the user does not exist and create one. IE: adduser WHATEVERUSER; adduser WHATEVERUSER sudo. Once that is done, reboot to regular mode and you will be able to log in. The linked question was perfectly clear and deserves an answer but I can't answer it since it is closed. I'm sure there are other people besides myself and Curtis who run into that problem after install. I think I've used the same install media on different hardware without that issue so I don't know what causes it.
References:
How do I rescue my Ubuntu server from the sever ISO ubuntu-18.04.1-live-server-amd64.ISO?
https://websiteforstudents.com/reset-forgotten-ubuntu-user-password-on-ubuntu-16-04-17-10-18-04/