A bit of background in hopes that I can have the rest of this make any sense to other folks here:
I actually provide the support for a bunch of former windows users after setting them up with U/M.
They are very content with their PCs & generally speaking I am able to find whatever info I need if/when any problem may arise (seldom !!) - thus I post here ONLY if I am totally lost for finding workable answers.
Lately I've completed a bunch of upgrades from 18.04.x to 20.04.2 for other folks' PCs.
Most went along just fine despite being quite time consuming & with good results.
I did run into a couple of instances which got very sticky as well, so I used alternate methods - the worst of which was actually wiping & totally starting over with a fresh installation of 20.04.2.
Tonight however was absolutely THE WORST experience of them all, sadly.
Given that today was a holiday here, I cleared all my earlier work & finally did this upgrade for my own desktop...and it failed to fully boot up afterwards.
It only got as far as the desktop wallpaper with a mouse arrow that alternated with the spinny cursor & there it stayed no matter for how long - and was otherwise totally unresponsive.
Fortunately - since I was aware that it could go fubar like those couple of others did, I had used an identically sized HDD beforehand & totally cloned my daily driver PC's entire OS & data - then tested it on my spare box to be 100% sure it was as it should be - which it was.
So, when my own PC's upgrade went totally fubar, I just deleted & re-copied in /boot & / and here I am, right back where I began before I'd wasted far too many hours on this absurdity of an attempted upgrade.
Yes - I have many apps & have made this PC's OS very much my own;
Up 'till this botch it was working perfectly each & every single day, so:
It can stay as it is so that I don't get stuck like that again - and...
Later I'll re-create my preferred configuration on my spare box as time allows with 20.04.2 then freshly installed as its base.
All that having been said - after doing lots of these upgrades - and after looking for any simpler ways to go about it - I have some questions which I have not found helpful answers for, please:
1 - Knowing I might need it, I got the 20.04.2 ISO & had it near to hand - so just for yuks (as the answer was already in mind...) I did a live boot of it with another 18.04 setup connected to see what it might offer.
No direct route from that session to any upgrading was obvious - just as I expected.
I had read before that it could be done by doing an over-install whilst preserving /home & then reinstalling needed apps - so I tried that - and frankly saw zero advantages after the efforts needed in doing it that way !!
Short of making some local server with the repos, etc. in it - it there any method to do multiple upgrades SIMPLY & EASILY via some local media so as to avoid doing the downloading process for EVERY upgrade over & over & over ??
Is there some sort of upgrade data or media that can be gotten that is intended JUST for upgrading an existing system ??
Short of doing all the careful preparation & steps that I did for this roll-back, is there some better method for recovering from a botched upgrade that refuses to boot fully and is totally unresponsive ??
I did consider entering recovery mode and playing around with that & DPKG, etc. - but since I actually needed to get back to work tonight I had already wasted FAR more time on the botch than it deserved, so I did not try any of that sort of stuff.
My closing comment:
This result is the sort of thing that has folks pointing to Linux in general as being too fiddly and/or techie.
Even with my years of being a very happy & satisfied Linux user this seriously messed with me 'cuz it SHOULD have gone flawlessly - but did not even come close to that after I wasted too much of my day patiently trying to get through the process.
Thanks for any helpful pointers in reply !!