So here's something not to do: don't 
blindly flail at a system upgrade on 
your server!

A couple of nights ago, I decided to 
upgrade gopher.visiblink.ca. It runs 
Raspberry Pi OS on a Pi Zero W. 
Raspberry Pi OS is based on Debian and 
the /etc/apt/sources.list file uses 
the same codenames as Debian.

So, without going to the Raspberry Pi 
OS homepage to check on the latest 
version, I just assumed that it was 
Debian 12 "Bookworm" and went ahead 
with the regular steps toward a 
dist-upgrade. It turns out that the 
latest version of Raspberry Pi OS is 
Debian 11 "Bullseye." Ouch.

Oddly, the system pulled the 
"Bookworm" packages and went through 
the whole process. But when I 
rebooted, I had a broken mess that 
wouldn't let me log in. 

Fortunately, I had a relatively recent 
backup of the important directories 
and was able to grab a few more 
recently changed files from the SD 
card. Even so, reinstalling the OS and 
setting everything up again took 
several hours.

Lesson learned? I hope so. 

On the positive side, the server is up 
and running with the latest version of 
Raspberry Pi OS and a very lean setup.