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Question re: gdm3 and Ubuntu with eGPU  

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rstrube
(@rstrube)
Active Member
Joined: 7 months ago
Posts: 16
April 24, 2019 3:01 pm  

Hello Everyone,

Thanks to the fine people on this forum I've been running my RTX 2070 as an eGPU for the past 8 months with no problems (using the xorg.conf technique).  The one thing I've had to do (which other folks haven't mentioned) is switch from gdm3 to lightdm.

With gdm3 running with stock settings (using a Wayland backend), at login time an image appears on my both my internal laptop display and my external display, but when I login to my Gnome session running on Xorg, I only get a display output on my internal laptop display.  In Gnome settings, I see the Thunderbolt enclosure, but I do not see the external display.

With gdm3 running with an Xorg backend (modified the /etc/gdm3/custom.conf file), I only see display output on the laptop display, and logging in has the same problems (only the laptop display is available).

My understanding is that gdm3 *does not honor* the xorg.conf file when running with an Xorg backend - so this might be the issue?

Switching to lightdm resolves these issues entirely, but I have to make some compromises within Gnome (display blanking doesn't work, etc.).

Is anyone else having these issues with gdm3?  If so how have you been able to work around them?

Thanks for any help you might be able to provide!

Pending: Add my system information and expected eGPU configuration to my signature to give context to my posts


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(@tim_richardson)
New Member
Joined: 5 days ago
Posts: 1
May 20, 2019 4:08 am  

See https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/1716857

The solution to this is to run X11 as root, so it can use VGA arbiter and detect displays on both the NVIDIA and modesetting drivers.

Add this to /etc/X11/Xwrapper.config :
needs_root_rights = yes

Pending: Add my system information and expected eGPU configuration to my signature to give context to my posts


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