Very much like:
Ubuntu 18.04 is stuck at loading screen after new installation
Except for being Ubuntu 18.10
The only way to interrupt a hung system like this, which simply never completes the boot process, is to use REISUB
?
It's booted fine more than a few times.
see also:
enable ctrl+alt+F1 virtual consoles in ubuntu gnome
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I wasn't able to get a virtual to a virtual console, unfortunately.
For practical purposes, yes, "solved" problem in that I haven't had the problem since. Either the underlying problem was resolved or it's just intermittent.
The only reason I haven't accepted the answer, which is an excellent answer, is that, should someone come here with the exact same problem, I'm not convinced they'll be able to get to a virtual console. Which was rather the point of the question, being as other aspects were answered in the linked question, I believe.
Again, it's an excellent answer. Not looking to detract from the answer. I think I was correctly trying to access virtual consoles and it just wasn't working, but I can't say absolutely. Which was the crux of the problem.