Upgrading Mythbuntu from Trusty to Xenial

Yesterday I took the plunge and upgraded my Mythbuntu install from Trusty to Xenial. Except for a few heart-stopping moments, it went smoothly.

Things I wish I’d known about the upgrade

There’s a bug with upgrading MySQL when you have the Mythbuntu tweaks installed. As a result, the upgrade fails to install MySQL properly - and then everything looks broken. Ouch. You can find out more about the defect here. The symptom is the message “[ERROR] unknown variable ‘table_cache=128’ ” which scrolls off the screen when you do an upgrade (or dpkg —configure -a). The fix is to change

table_cache = 128

table_open_cache = 128

in /etc/mysql/conf.d/mythtv-tweaks.cnf.

During the upgrade, I got prompted for which user to use for the database. (With the recommendation to use “root” if you don’t thoroughly understand the permissions models.) But of course “root” didn’t work. What did work was the default, debian-sys-maint.
After install, lirc didn’t work. I uninstalled lirc using Mythbuntu Control Center and rebooted; that appeared to fix things and now my Streamzap remote is being detected as a keyboard device with the appropriate mappings. (I get a warning about a plugin using MCC, but hey, it seems to work.)
Next, I got warnings using apt. Probably due to the upgrade failure, I had a file called 50unattended-upgrades.ucf-old left over in /etc/apt/apt.conf.d. Nuking that fixed things.
It looks as if mythfrontend and mythbackend are using different users now. I’m not sure why, but some day I’ll need to go through and fix permissions / unify those two users.
I had to go into mythtv-setup and assign directories for music and music art. (Since I didn’t have an art directory, I created one under my music directory. That seems to work.)
Probably as a result of the botched upgrade, mythweb was broken. I installed php7.0-mysql, then removed/installed mythweb and it was working again.
Finally, I tried to look into mythconverg. In this release the admin user is debian-sys-maint, and the password for that user is stored in /etc/mysql/debian.cnf.