Arch Linux

Santo C01

Member

Registered: 2026-03-02

Posts: 19

SDDM black screen on boot (AMD iGPU + RTX 4090) — looking for opinions

Hi everyone,

I'm trying to understand an occasional boot issue before making any changes to my system.

System
Arch Linux
KDE Plasma 6 (Wayland session)
SDDM (X11 greeter)
Kernel: 7.1.4-arch1-1
NVIDIA Open Driver
RTX 4090 (primary GPU)
Ryzen 9 9950X3D (Raphael integrated GPU enabled)
Three monitors

The system is stable once Plasma starts.

Problem

Very occasionally, after booting, SDDM shows a black screen instead of the login screen.

A reboot usually fixes it immediately.

The issue is rare (not every boot).

What I've found

The journal shows SDDM starting normally, then the greeter crashes.

Older coredumps show:

sddm-greeter-qt6
SIGSEGV

Thread:
QSGRenderThread

Library:
libnvidia-glcore.so

On another occasion I found:

Xorg
SIGABRT

SDDM:
Failed to read display number from pipe

After retrying, SDDM starts normally.

I have not observed:

NVIDIA Xid errors
GPU hangs
kernel panics
filesystem errors
RAM related errors
Configuration

mkinitcpio.conf

HOOKS=(base udev autodetect microcode modconf kms keyboard keymap consolefont block filesystems fsck grub-btrfs-overlayfs)

NVIDIA DRM:

$ sudo cat /sys/module/nvidia_drm/parameters/modeset
Y

$ sudo cat /sys/module/nvidia_drm/parameters/fbdev
Y

The initramfs contains:

amdgpu.ko

but I could not find:

nvidia.ko
nvidia_modeset.ko
nvidia_uvm.ko
nvidia_drm.ko

inside the initramfs.

What I'm wondering

Someone suggested simply disabling the AMD iGPU.

I'd rather keep both GPUs enabled, since the integrated GPU is useful as a backup and for troubleshooting.

Instead, I'm considering configuring SDDM/Xorg to always use the RTX 4090 as the primary GPU while leaving the AMD iGPU enabled.

My questions
Has anyone seen similar intermittent SDDM greeter crashes with AMD + NVIDIA systems?
Would you recommend configuring SDDM/Xorg to explicitly use the NVIDIA GPU (PrimaryGPU) rather than disabling the AMD iGPU?
Is there any benefit to adding the NVIDIA kernel modules to MODULES=() in mkinitcpio.conf, or is that unnecessary on modern Arch with kms and nvidia_drm.modeset=Y?

I'm trying to solve this the "Arch way" with the smallest, most maintainable change rather than disabling hardware if it isn't necessary.

Thanks!

Santo C01

Member

Registered: 2026-03-02

Posts: 19

Re: SDDM black screen on boot (AMD iGPU + RTX 4090) — looking for opinions

Additional information: I checked the coredumps again and found that there have been two Xorg crashes:

2026-07-19 09:57:06 JST
2026-07-20 12:20:28 JST

The July 20 crash corresponds to the boot where one of my three monitors remained black at the SDDM login screen. The other monitor(s) worked, so I was still able to log in.

As soon as I logged into my Plasma (Wayland) session, the black monitor initialized correctly and all three monitors worked normally. The system was completely stable after login.

This seems to suggest the failure occurs during the SDDM/Xorg startup or monitor initialization phase rather than after the desktop session has started.

Santo C01

Member

Registered: 2026-03-02

Posts: 19

Re: SDDM black screen on boot (AMD iGPU + RTX 4090) — looking for opinions

Update: I checked the second Xorg coredump from July 19 and compared it with the July 20 crash. They appear to be the same failure.

Both Xorg instances were launched by sddm.service, both aborted with SIGABRT, and both have the same relevant stack:

modesetting_drv.so + 0x12877
InitOutput
FatalError
OsAbort
abort

The crashes occurred on:

2026-07-19 09:57:06 JST
2026-07-20 12:20:28 JST

On at least one of those boots, one monitor remained black at the SDDM screen, but I was still able to log in using another monitor. Once the Plasma Wayland session started, the black monitor initialized normally and all displays worked correctly.

This now looks reproducible as the same intermittent Xorg/SDDM output-initialization failure rather than two unrelated crashes. Could this be caused by Xorg choosing or probing the wrong DRM device in a mixed AMD iGPU + NVIDIA setup?

seth

Member

From: Won't reply 2 private help req

Registered: 2012-09-03

Posts: 76,983

Re: SDDM black screen on boot (AMD iGPU + RTX 4090) — looking for opinions

Very occasionally, after booting, SDDM shows a black screen instead of the login screen.

This is all over the place for various DMs, https://bbs.archlinux.org/viewtopic.php?id=314111
Delay SDDM or see whether https://wiki.archlinux.org/title/Kernel … _KMS_start suffices.

On a formal note, please use [code][/code] tags and please don't blog - edit your previous post to mend it if nobody has replied to not create a false sense of action on the thread.

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How to upload text · How to boot w/o GUI · Disable Windows Fast-Start! · Fix your xinitrc

Santo C01

Member

Registered: 2026-03-02

Posts: 19

Re: SDDM black screen on boot (AMD iGPU + RTX 4090) — looking for opinions

Thanks for the suggestion and for pointing me to the Early KMS section of the ArchWiki.

Sorry for editing my previous post. Next time I'll post all together.

I followed the ArchWiki and configured Early KMS by adding:

>>>MODULES=(nvidia nvidia_modeset nvidia_uvm nvidia_drm)<<<

I'll monitor the system over the next few days to see whether the intermittent SDDM/Xorg startup issue reappears. Thanks again for your help.