As a brief note to self, if you forget the MySQL root password again, these are the steps you followed to create a new MySQL root password on an existing MySQL server running on Ubuntu 16.x:
Wow, I thought I'd get really secure when I took my MacBook Pro on vacation recently. So secure that I managed to forget the root password after I changed it. (duh) Fortunately I found an easy way to change it after I lost it.
I was lucky enough that I created one of my login accounts as an administrator ("Admin") account, and that's all I needed. Well, that, a Terminal, and the
sudo command. :) Here's what I did.