Arch Linux

odror

Member

Registered: 2015-03-17

Posts: 168

How to force one monitor off in GDM

I have an i9-13900k system using X11 with latest arch packages

The iGPU is connected to one monitor and the Nvidia card is connected to 4 additional monitors. All at 4k resolution. (The nvidia monitors are need  for a VM and the 5th monitor is for the host)
When the VM is not running GDM fails with a large white screen. Apparently it cannot handle 5 screens.

When disconnecting any one of the monitors GDM is back to normal.

Issue number 1: Why GDM cannot handle more than 4 monitors. Can that be fixed? is there a setup for it.
Issue number 2: How can I Automatically disable one specific  monitor (when all 5 are available)
Issue number 3: I cannot use xrandr because I have no access to the gdm display environment. Even when using sudo and setting the DISPLAY variable to :0, xrandr fails.

Any help will be appreciated

seth

Member

From: Won't reply 2 private help req

Registered: 2012-09-03

Posts: 76,691

Re: How to force one monitor off in GDM

https://wiki.archlinux.org/title/GDM#Se … r_settings
Unless GDM is too creative, you can also try https://wiki.archlinux.org/title/Multih … _xorg.conf
All present outputs are enabled by default, but you can

Option  "Enable"        "False"

one of them.

Are the outputs in cloning mode (all show the same) or arranged in a grid/strip?
5 4k outputs in a row might exceed some texture size limits.

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odror

Member

Registered: 2015-03-17

Posts: 168

Re: How to force one monitor off in GDM

I was able to resolve issue 2 buy blocking the specific monitor by name by adding a config in /usr/share/X11/xorg.conf.d

https://wiki.archlinux.org/title/GDM#Se … r_settings
Are the outputs in cloning mode (all show the same) or arranged in a grid/strip?
5 4k outputs in a row might exceed some texture size limits.

No every monitor have a different name.  For example one of the ports of the igpu is HDMI-0, The nvidia one is HDMI-1-0. There is a "-1" added to the nvidia names.

Regarding issue #1
Is it possible that I am exceeding a resource limit by GDM. For example is there a memory limit for GDM. If so how can I change that.

seth

Member

From: Won't reply 2 private help req

Registered: 2012-09-03

Posts: 76,691

Re: How to force one monitor off in GDM

No every monitor have a different name.

That's irrelevnat. The question is about size of the final resolution.
3840*4=15360, 3840*4=19200 which crosses 2^14

glxinfo -l | grep -i max

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odror

Member

Registered: 2015-03-17

Posts: 168

Re: How to force one monitor off in GDM

No every monitor have a different name.

That's irrelevnat. The question is about size of the final resolution.
3840*4=15360, 3840*4=19200 which crosses 2^14

glxinfo -l | grep -i max

I though that each video card has its own Maximum. I use only 4 nvidia monitors. If it is a system wide maximum. Can that be changed.
One more thing My nvidia card is RTX 4070ti Which supports 4 8k monitors at 60Hz.

Is it possible that the intel iGPU is setting up a system wide maximum through mutter.

seth

Member

From: Won't reply 2 private help req

Registered: 2012-09-03

Posts: 76,691

Re: How to force one monitor off in GDM

How about we first start to figure whether that's the problem by you elaborating the present configuration and whether it's relevant.
The image is rendered by *one* GPU, no matter where it's then copied for further output and the relevant limitation w/ GDM will be some 3D/texture/buffer size, not the crtc capacity.

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