Why ubuntu 19.10 can not find second monitor

Question

I recently installed ubuntu 19.10 and at the begining both monitors worked just fine. Now I boot ubuntu and the monitor connected to VGA 2 does not work. I tried to boot the system and then plug in the monitor. I changed the VGAs of monitors and still nothing. I used xrandr to check and I found out that only one monitor is connected. When I use Windows though both monitors work perfectly. I even downloaded additional drivers and updated the system and still nothing. Any advice apart from reinstalling ubuntu?

Answer 1

I had the same problem and after doing quite a lot of reading it seems that there are different reasons for this to happen.

So YMMV, but for me the problem was that the nvidia card was not enrolled in secure boot.

The quickest way to diagnose if this is the issue is to run the command from this answer:

andrew@desktop:~$ glxinfo|egrep "OpenGL vendor|OpenGL renderer*"
OpenGL vendor string: NVIDIA Corporation
OpenGL renderer string: GeForce RTX 2080 SUPER/PCIe/SSE2

Mine was not showing nvidia, it was showing some default thing. Now that it shows nvidia my second monitor lights up automagically, without touching the CLI.

So if yours is showing nvidia stuff in there, then ignore the rest of this answer.

Another diagnostic symptom was that running xrandr was giving this error: "xrandr: Failed to get size of gamma for output default"

I followed the advice on Ubuntu forums (here), but I think that is more aggressive than needed.

Really what I needed to do was get it enrolled in Secure Boot. So you could try:

sudo apt-get purge nvidia-driver-435
sudo apt-get install nvidia-driver-435

Note: You can find the correct number by looking in "additional drivers" in your settings.

When you reinstall the driver it asks you for a MOK password. I used a complicated one and it failed to match (not sure if this answer was helpful or not).

After the MOK password failed I decided to try using the most current version of the NVidia drivers, downloaded from their official page. Their installer handles all the MOK stuff and I used a six character english word password which I was able to match.

If you don't know which nvidia driver to select from their page try running lspci | grep -i nvidia

So, my 2c is to try:

1. Reinstalling the default driver to get it enrolled in secure boot
2. Use the nvidia installation from their site and get it enrolled in secure boot