second monitor suddenly not detected

[Karl Auer]

On Mon, 2020-09-28 at 08:41 +0100, Colin Law wrote:
> Another thing that could be looked at is to unplug it, reboot monitor
> the log (sudo journalctl -f, or tail -f syslog if  you prefer) plug
> it in and see what appears.

Well, I have two monitors again. I installed the latest NVidia drivers
(450.66) power cycled the thing, and the second monitor came back.

The weird thing is I never *chose* to install the NVidia drivers, they
appeared as an update. They seem to have replaced nouveau unbidden. So
I remain pretty confused. I don't like operating my computers on
hopefulness, I prefer to know what's going on.

The success was after quite a few tantalising failures. Switched the
BIOS to "switchable graphics" and the distro USB booted without me
having to select "safe graphics", so that was good. The distro USB
seemed to know about the second monitor but was unable to use it. If I
selected "join displays" the "Revert/Keep" dialog disappeared; I guess
it was on the second monitor, so I just pressed escape to revert.

I put the BIOS back to discrete graphics, ran apt update and apt
upgrade and saw a bunch of nvidia stuff being held back. So I did a
dist-upgrade, power cycled, and lo! Two screens again. No real idea
why, and most importantly no idea why it went away in the first place.
My suspicion is that the new NVidia stff was not actually necessary,
but the process of installing it fixed up whatever was broken.

My thanks to all who contributed ideas; clearly display management
remains the black art it has always been. My boundless gratitude goes
to that band of geniuses that keep it all working.

Regards, K.

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Karl Auer (kauer at biplane.com.au)
http://www.biplane.com.au/kauer

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