Background / reason
In Ubuntu 18.04 I have a completely new problem that is not addressed by other questions about xinerama or xrandr. Suddenly, my 4K monitor is often treated as a 1440p monitor, with no option to reset the resolution to 4K. This issue is typically caused by reboots of the monitor or changes in resolution (for example, due to games). As soon as the problem occurs, either will be executed
xrandr -s 3840x2160
or bring the equivalent
gnome-settings Causes the screen to turn black for a few seconds before tacitly returning to the wrong one
2560x1440 Resolution. Especially not
dmesg It appears that error messages are displayed that are relevant to the problem. In addition, the problem persists after being triggered by a reboot: The resolution is still low, and
xrandr 3840x2160 still fails silently. It seems that the only way to solve the problem is to wait a considerable amount of time for the problem to resolve itself.
It's possible that the problem is a hardware issue, but I find that unlikely because:
4K works fine if the resolution problem is not triggered: still 60 Hz, soft, no distortion.
The problem does not occur on other operating systems or on the login screen of gdm (the text will be displayed in native resolution, as far as I can tell). The resolution will not be reset to 1440p until the X session is actually started.
You can also solve the problem by connecting a second 4K monitor and using both. However, the problem recurs as soon as the second 4K monitor has been removed!
I suspect that something strange has happened to the internal state of Xinerama – I do not understand why else I am suddenly plagued by these random changes in resolution, with the exception of hardware errors that I find unlikely. So I want to delete / reset all files that make up the internal state of xinerama.
I would like to know the location of xinerama's configuration files (or more generally the internal state) and forcibly reset them. You can try to solve xy problems with me, but first look at the failed solutions.
xrandr -s 0 – This command is often the answer to "How do I reset?" Ask. This had the same effect as
xrandr -s 3840x2160Nothing. I want to reset ALL status to fix the problem.
Reboot as mentioned.
3840x2160 as a new mode. The problem is not that the monitor does not report this as an option, but that
xrandr When this resolution is selected, nothing mysteriously happens:
Screen 0: minimum 320 x 200, current 2560 x 1440, maximum 16384 x 16384
DisplayPort-0 disconnected (normal left inverted right x axis y axis)
DisplayPort-1 disconnected (normal left inverted right x axis y axis)
HDMI-A-0 disconnected (normal left inverted right x axis y axis)
HDMI-A-1 connected primary 2560x1440+0+0 (normal left inverted right x axis y ax
is) 609mm x 349mm
3840x2160 60.00*+ 60.00 50.00 59.94 30.00 25.00 24.00
1920x1080 60.00 60.00 50.00 59.94 30.00 25.00 24.00
1280x1024 75.02 60.02
1280x720 60.00 50.00 59.94
1024x768 75.03 60.00
800x600 75.00 60.32
720x480 60.00 59.94
640x480 75.00 60.00 59.94
Hardware / software details
Kernel: 4.15.0-70 generic
Distribution: Ubuntu 18.04
CPU: AMD Ryzen 2700X
GPU: AMD Vega 64
EN: GNOME 3
Monitor: Dell U2718Q