Somehow the default MySQL admin account, which I believe was prepopulated by the installer, got blown away while I was deleting a Virtualhost. Fortunately I was able to reset things following these instructions: https://www.howtoforge.com/reset-forgotten-mysql-root-password
Is it possible I forgot to note the MySQL daemon credentials when I initially installed Virtualmin Pro? If so, is there anyway to recover them? I also have PostgreSQL running but like MySQL, I don't know the default credentials.