[conspire] Upgrade Xubuntu 18.04 to 20.04 reboots to black screen

[Rick Moen]

Quoting rogerchrisman at gmail.com (rogerchrisman at gmail.com):

> Now I’ve done it. Last night I left my dual boot desktop computer to
> complete upgrading from Xubuntu 18.04 to 20.04. I had recently updated the
> 18.04. What could go wrong?
> 
> Now it is the next morning and the computer is stuck in black screen. No
> response to Cntr+Alt+F2 or mouse or keystrokes. Power button is
> illuminated. So pushed that. System appears to power down, power button and
> hard disk led are dark. Waited a moment. Pushed power button again. Power
> button lights up, hard disk led active for a bit. Black screen remains
> black.

Obvious first task is to determine whether your problem is hardware or software.
For this purpose, it's handy to have around a live distro (what we used
to call a 'live CD' or 'live DVD') of known-good characteristics.  Boot
that up, and see if everything appears to be normal.

It's also extremely useful to be acquainted with your hardware's entire
startup sequence, i.e., be familiar with what sounds you expect to hear,
what ought to appear on-screen at each step.  The early, hardware-only
part of startup is called POST, for power-on self-test.  This is where
some of your hardware components should be enumerated on-screen,
including a count of RAM, culminating to the point where the BIOS picks
a bootable device and transfers control to whatever is in its sector
zero, which by definition starts the software phase of startup.

Note:  This past decade or so, many desktop computers have defaulted in
their BIOS Setup configurations to a 'quiet' (or similar term) setting
for the display of POST information, whereby instead of showing the
details of hardware enumeration, the user is shown a pretty picture,
instead.  IMO, this setting should _always_ be disabled, so that you are
able to see the meaningful POST data.  (Many BIOSes also permit the user
to make the pretty picture go away during current boot, by pressing Esc
or something like that.)

Anyway, with luck, you already have 'quiet' POST mode disabled, and are
acquainted with your PC's normal hardware initialistion on-screen data,
hence can tell whether hardware init is proceeding normally or not.  If
not, hey, consider this a learning experience.


Attempting to boot from a known-good live distro sidesteps any possible
problem with your installed software.  Of course _booting to_ a live
distro requires picking during POST that device for booting.  So, once
again, it is strongly in your interest to know how to do so with your
motherboard and BIOS, e.g., what magic key to press to bring a 'boot
menu' to select current session's boot device.  Which magic key it is
differ by BIOS.  It could be F12, could be F10, could be various others.


I would strongly urge careful testing to disambiguate between hardware
nad software as root cause, before taking dramatic steps like blowing
away the contents with a fresh installation.  Even if that 'works', 
it's A Bad Thing to blow away everything with zero understanding of what
happened.


> Aha, found my Bionic Beaver Xubuntu 18.04 install dvd. Maybe I can startup
> with that and get past the black screen problem somehow? Without redoing
> the upgrade or a fresh install? 

If that's your known-good live distro, sure, do that.[1]  But it's also
_vital_ to know your boot sequence, starting with the sequence of what
happens during POST.

If you have no idea what happens during normal POST, if possible, try to 
learn.  (Of course, this is something better done when you aren't facing
a system failure of unknown nature.  File that fact away for future
action.)


[1] At any given time, there are various live distros that are good for
testing and diagnosis.  Desirable qualities include frequent ISO
refreshes with reasonably cutting-edge hardware support.  Your Xubuntu
thing as a 2018 ISO is, um, not cutting-edge, but presumably supports
_your_ hardware well enough, which is all you need for present purposes.