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Installer displays on disconnected DP-1 instead of the only connected monitor on DP-3 #152

Description

@btownsend

System details

  • Omarchy ISO versions: 4.0.1 and 4.0.2 (reproduced on both)
  • Motherboard: ASRock B650M Pro RS WiFi
  • GPU: NVIDIA GeForce RTX 4080 SUPER
  • Current NVIDIA driver: nvidia-open-dkms 610.57.04-1
  • Current kernel: 7.1.9-arch1-2
  • Display setup: one monitor connected over DisplayPort

What's wrong?

When booting the Omarchy ISO, the machine appeared to boot to a completely
black screen every time.

After trying several USB drives and numerous suggested UEFI/BIOS changes, I
discovered that the live installer was displaying through DP-1 even though my
only monitor was connected to DP-3. There was no monitor connected to DP-1 and
no visible indication that the ISO had booted successfully.

Moving the DisplayPort cable from DP-3 to DP-1 immediately revealed the running
installer and allowed installation to continue.

Steps to reproduce

  1. Connect a single monitor to DP-3 on the NVIDIA GPU.
  2. Leave DP-1 disconnected.
  3. Boot the Omarchy installation ISO.
  4. Observe that the connected monitor remains black.
  5. Move the same cable from DP-3 to DP-1.
  6. Observe that the already-running installer becomes visible.

Expected behavior

The live environment should detect which output has a connected monitor and
display the installer there. With only one monitor connected, the installer
should not select an unconnected output.

Actual behavior

The installer selected DP-1 while the only monitor was connected to DP-3,
making a successfully booted ISO appear to have failed with a black screen.

Additional comparison

The same computer and display connection work correctly with other installer
ISOs, including CachyOS. CachyOS detects the single monitor on DP-3 and displays
its installer there without requiring the cable to be moved.

Impact

This failure is indistinguishable from an ISO, USB-drive, firmware, or GPU boot
problem. It led to hours of unnecessary troubleshooting and repeated USB-media
creation before the output-selection issue was discovered.

Filed by GPT-5 via Codex.

Activity

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