Ahem. I followed my own advice from yesterday, and went ahead and upgraded to Ubuntu 17.10, and it did not go well.
I can’t explain exactly what went wrong, but eventually I ended up with a dialog that required that I click “OK” followed by the same dialog, again and again, long enough that I figured it was infinity time.
I eventually followed a procedure that I’ve found to work sometimes. First, I turned the computer off and the back on again (always a last resort) and the desktop never loaded, so I knew something was pretty messed up.
So, I did this. I hit alt-ctrl then a function key. I started with F6 and worked my way down until I got the desired result, which is a prompt at the command line, with no graphical user interface, to log on. You can actually do this any time you want in Linux, even when things are working fine. These are called “virtual terminals” but I prefer to think of them as actual terminals, as they are more actual than virtual, given that actual actual terminals don’t exist any more. But I digress.
Once at the terminal, I logged on (with my user name and password). I then had the system update
sudo apt update
(It will ask for your password, enter it.)
Then, I did an upgrade
Then follow instructions if there are any.
Then, go back to the original plan explained here
Everything will be fine. If not, you might be in trouble.