second monitor suddenly not detected

[Liam Proven]

On Sat, 26 Sep 2020 at 10:49, Karl Auer <kauer at biplane.com.au> wrote:
>
> This is a new one on me. For no apparent reason, the display manager
> (Wayland/Ubuntu on 20.04) exited. I still had a console, so I logged in
> and powered off the laptop gracefully.

By "display manager exited" you mean the GUI crashed?

Yes, that is not unheard of. Ctrl-Alt-Del will do a quick clean reboot.

> Upon powering up, Ubuntu did not detect my second HDMI-connected
> monitor. There are a couple of other niggles, such as a Gnome shell
> extension having vanished. And the gnome tweaks tool doesn't show 90%
> of the tweaks it used to. Butthe display looks OK otherwise.

Hmmm. It could be some kind of config file damage or corruption.

HDMI depends on a lot of fancy device detection -- designed in to
maintain copyright protection. Sadly, I kid you not.

Disconnect the cable, both ends, and reconnect it. If it's HDMI to
HDMI, try reversing the cable.

(On 1 of my machines -- not Linux, but still -- I could only get a
reliable picture by converting the signal from Displayport to HDMI to
DVI. I wish I were joking. This worked 100% of the time, instantly;
Displayport worked about 66% of the time after 1-2min of trying to
detect the screen.)

> I've looked for answers in google, but the answers don't seem to apply
> (and are almost all regarding 18.04). I tried switching from Ubuntu to
> Gnome and back at login, no change.

So does that mean switching from Wayland to X.org? (I am sorry, I
don't use GNOME and don't have an Ubuntu GNOME machine installed
anywhere any more. I have tried, at length, but I just can't stand
it.)

> Tried update/upgrade and it
> upgraded a surprising number of packages in icluding Nvidia libraries
> and suchlike, but no change.

Silly question: did you reboot?

> Ran "sudo dpkg-reconfigure gdm3", no
> output and no change.

> Short of re-installing Ubuntu, is it possible to reinstall or
> reconfigure the graphics subsystem? This is a Lenovo Y540 with Nvidia
> graphics hardware, and currently the nouveau driver is active.

Well, you could try the nVidia drivers. That would be my preference.

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