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I need to be able to use various custom resolutions starting from 800x600 and up to 4K with a step of 2x2. I was able to do that on a virtual box image with Ubuntu 16.04 running Xorg using

xrandr --size 800x600
xrandr --fb WidthxHeight --output VGA-0 --panning WidthxHeight

It also worked on a KVM image with Mint on another machine.

On another image with Ubuntu 16.04 on KVM on yet another machine this did not work. It used Cirrus Logic for graphics adapter (reported by lspci) and modesetting as Xorg driver (could be seen in Xorg log). After login in console and starting Xorg from terminal using

sudo Xorg :38 -ac -bs &
sleep 4
gnome-session --session=ubuntu &
sleep 1
unity &

I got a screen with UI but I couldn't change resolution from the default one which was 1024x768. Both xrandr --fb and xrandr --size failed with any resolution except the default one, giving BadMatch error for RRSetScreenSize. Running xrandr --verbose did not give EDID.

I also tried adding a custom mode (1920x1080) and using that which worked only partially. It still gave the same error after executing the command, but then xrandr output that current resolution remained the same while resolution for the output was set to that of the mode like so:

Screen 0: minimum 320 x 200, current 1024 x 768, maximum 4096 x 4096
VGA-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 0mm x 0mm

On images where resolution did change without error both numbers were changed.

What could possibly be causing this problem and how to make it work?

alerion
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  • I have always had troubles with the default cirrus video driver. I have had the best success using the vmvga video driver instead. here is how to change it in an existing definition file. And see also the notes section here for how to specify which editor to use. – Doug Smythies Aug 22 '17 at 23:33
  • @DougSmythies Using vmvga helped a bit: xrandr --size worked with all modes. Unfortunately xrandr --fb did not work, this time output was 
    Failed to get size of gamma for output default

    Can it be related to empty output of cat /proc/fb? I tried qxl on I hope similar machine and both commands worked.

     – alerion Aug 23 '17 at 13:51

0 Answers0