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So last night (April 13th), I installed an update from Canonical that popped up in a GUI, it said something about a security update (I didn't look at it too hard). Since then I've rebooted my machine and now the display is the wrong resolution (it ought to be 3840 x 2160, 597mm x 336mm, 60fps monitor). I'm presently on Ubuntu 20.04.2 LTS.

$ xrandr
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 1024 x 768, current 1024 x 768, maximum 1024 x 768
default connected primary 1024x768+0+0 0mm x 0mm
   1024x768      76.00*

$ inxi -G
Graphics:
  Device-1: NVIDIA GM107GL [Quadro K2200] driver: N/A 
  Display: x11 server: X.Org 1.20.9 driver: fbdev,nouveau 
  unloaded: modesetting,vesa resolution: 1024x768~76Hz 
  OpenGL: renderer: llvmpipe (LLVM 11.0.0 256 bits) v: 4.5 Mesa 20.2.6

I've tried unplugging and replugging the monitor, rebooting several times, adding an xrandr modeline, and changing /etc/default/grub to have GRUB_CMDLINE_LINUX_DEFAULT="quiet splash i915.alpha_support=1" (where it was "quiet splash" before). None of these have led to any success.

My feeling is that there's some graphics driver issue (that the renderer is llvmpipe doesn't seem right).

I guess there's also a confounding factor in that I'm running the display through a KVM switch, but I really hope that's not the problem. I've been using it for a while anyway with no issue, the Windows 10 partition of this machine renders fine, and I have another machine running 18.04 that gets the resolution just fine.

Update:

I tried booting into recovery mode, which was no dice (also tried cleaning up dpkg through the recovery interface). While I was in the GRUB menu, I noticed that it defaults to the kernel version 5.8.0-49, but that I also had 5.8.0-48 installed. Booted into the older kernel, and everything works. Curious, I checked the logs.

$ cat /var/log/dpkg.log | grep linux-image
2021-04-13 23:15:01 install linux-image-5.8.0-49-generic:amd64 <none> 5.8.0-49.55~20.04.1

And that lines up with when I did that update. So it seems that a kernel update messed up display detection somehow.

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1 Answer 1

Reset to default
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It's a temporary solution but I recommend you try booting Ubuntu in safe mode and see if it helps

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  • Thanks for the tip. This didn't end up being the solution, but put me on the path to finding a different kernel in the GRUB menu.
    – fp.monkey
    Apr 15, 2021 at 0:14
  • Did the different kernel help?
    – ie8yq
    Apr 15, 2021 at 0:15
  • yeah it did. I'll submit an issue to canonical, not sure if something's configured weird on my machine or they messed up
    – fp.monkey
    Apr 15, 2021 at 0:25

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