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I used to work with a dual screen setup (Lenovo P50 + external monitor). For an unknown reason, the external monitor stays black and seems not to be detected. When I use gdm3, only the builtin monitor is used, and when I switch to lightdm, only the external one is used, never both. I tried with several nvidia drivers (from 390 to 430), I also tried with the open-source one. I tried to purge then reinstall Nvidia drivers, manually install them, but the result is always the same, only one display at a time. I know that the GPU works as the two monitors are used when I dual boot on Windows.

Any idea on how to fix that ?

GuillaumeA
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  • Have you checked the screen settings in each case? –  Jul 22 '19 at 19:42
  • It used to work, but as soon as I tried to use NVidia drivers, it stopped working. Only one screen is detected. However I remove all NVidia drivers, remove the Nouveau one from blacklist and restore default driver and I recovered my two screens. – GuillaumeA Jul 23 '19 at 00:09

1 Answers1

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source gdm3 disables external monitors when options nvidia-drm modeset=1 is set. You can choose:

  • modeset=1: No screen tearing, can't use external monitors
  • modeset=0: Screen tearing, but can use External monitors

The fact it wouldn't work in lightdm still is a bit odd. I recall reading somewhere there's an issue with external monitors where it will try to output via VGA even if the monitor is connected by other means.

Riley Shea
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