Visvanath Ratnaweera

This is insightful.

> I've already thought about doing that with what I saw suggested about 'trying' ... 'just to see if...'. Harder to reverse engineer! Who wants to go one step forward just to go 2 steps back?

Wisely put.

> Thought moodle was about teaching and learning - not trial and error - but, then again, that's how some folks learn - but only the ones that have a high failure quotient.

Ha, ha, ha! A great qualification to be a pedagogic - in my eyes at least. And politically correct! 

> First, copying and pasting of bash commands you don't really understand depends on trusting what someone else has given you.

"Trust" I don't know. But again, there are many aspects.

> In particular, running under sudo can trash every application and even LInux itself in just 8 characters.

Yes, that is definitely one aspect. The command, especially run with superuser privileges, may cause damage.

Then there is the "Vanessa effect". The command writes "vanessa", where "jammy" is expected. That didn't damage the anything, but didn't give the expected result either. And for the audience these copy-and-paste commands are intended to, they wouldn't see top nor bottom! So back to Ken.

Sure - the Moodle Docs are open for everybody with an account on moodle.org to edit. As you yourself found out, every wiki page has a "talk page" like Talk:Moodle_migration. We can't be discussing every, thousands(?), of pages - each in 35 versions - in the forums!

Nobody took a shot. Here is the solution:

The problem was that impressive "echo "deb arch..." multi-like added to /etc/apt/sources.list.d/docker.list a line:

deb [arch=amd64 signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu vanessa stable

But vanessa should have been jammy. The Linux Mint added its code name there, but the Ubuntu Linux package expects its name, jammy.

Another peril of executing long shell commands one doesn't understand.