linux-display-setup

name	linux-display-setup
title	Linux Display Setup
description	Fix Linux display issues: broken EDID, custom modelines, multi-monitor setup, GPU driver diagnosis, and refresh rate configuration. Covers xrandr workflows, autostart persistence, and NVIDIA G-Sync activation.
triggers	["User says monitor is \"unknown display\" / not detected","User wants custom resolution or refresh rate (e.g. 144Hz)","EDID-related display issues (0mm x 0mm in xrandr)","Multi-monitor layout configuration","GPU driver check (NVIDIA, AMD, Intel)","G-Sync / VRR setup","Second monitor detected at wrong resolution"]
version	1.0.0
author	Hermes Agent
license	MIT

Linux Display Setup

Diagnostic Workflow

When a monitor shows wrong resolution or is detected as "unknown display", work through this checklist before proposing fixes:

1. Identify GPU and current driver

   lspci | grep -E "VGA|3D|Display"
   nvidia-smi 2>/dev/null || echo "No NVIDIA GPU detected"
   

2. List all displays and current modes

   xrandr --query
   

   • * = currently active mode
   • + = preferred mode (from EDID)
   • Look for monitors reporting 0mm x 0mm — hallmark of broken EDID

3. Get detailed monitor info (especially for "unknown display")

   xrandr --verbose | grep -A30 "^<PORT>"
   

   Check: vrr_capable, max bpc, connection type (subconnector: Native)

4. Calculate correct modeline

   cvt 1920 1080 144            # Standard CVT timing
   # Output: Modeline "1920x1080_144.00"  452.50  1920 2088 2296 2672  1080 1083 1088 1177 -hsync +vsync
   

   • cvt <width> <height> <refresh> for standard timing
   • cvt -r <width> <height> <refresh> for reduced blanking (some monitors prefer this)
   • If both fail, try known-working GTF timings from monitor forums

EDID Repair — Custom Modeline

When EDID is broken, the monitor reports no physical size (0mm x 0mm) and only shows basic resolutions like 1024x768 or 640x480. The fix is to manually add a custom modeline.

Step 1: Create the new mode

xrandr --newmode "1920x1080_cvt144"  452.50  1920 2088 2296 2672  1080 1083 1088 1177 -hsync +vsync

The name (e.g. 1920x1080_cvt144) is free-form — use something descriptive.

Step 2: Add mode to the correct output port

xrandr --addmode DP-1-1 "1920x1080_cvt144"

Find the port from xrandr --query: look for connected entries (DP-0, HDMI-0, DP-1-1, etc.).

Step 3: Activate the mode

xrandr --output DP-1-1 --mode "1920x1080_cvt144" --rate 144 --right-of eDP-1-1

Position options: --right-of, --left-of, --above, --below, or --same-as.

Step 4: Verify

xrandr --query | grep -A5 "DP-1-1"

Look for the new mode with * (active marker). Example output:

DP-1-1 connected 1920x1080+1920+0
   1920x1080_cvt144 143.88*       # ← 144Hz aktiv!

Important: xrandr vs NVIDIA MetaMode

Modes added via xrandr --newmode + --addmode are NOT managed by nvidia-settings. Attempting to set CurrentMetaMode with ForceCompositionPipeline or AllowGSYNCCompatible via nvidia-settings on an xrandr-created mode will fail with Attribute not available.

To get G-Sync working on custom modelines, use xrandr to set vrr_capable:

xrandr --output DP-1-1 --set "vrr_capable" 1

But note: G-Sync via nvidia-settings requires modes to be set through NVIDIA's own MetaMode system (via nvidia-xconfig or nvidia-settings GUI), not through raw xrandr.

Persistence (Autostart)

Custom modelines do not survive a reboot because the EDID is still broken. Three persistence strategies:

A. xrandr Autostart Script (Recommended, simple)

1. Create a script in ~/bin/:

   mkdir -p ~/bin
   cat > ~/bin/monitor-setup.sh << 'SCRIPT'
   #!/bin/bash
   xrandr --newmode "1920x1080_cvt144"  452.50  1920 2088 2296 2672  1080 1083 1088 1177 -hsync +vsync 2>/dev/null
   xrandr --addmode DP-1-1 "1920x1080_cvt144" 2>/dev/null
   xrandr --output DP-1-1 --mode "1920x1080_cvt144" --rate 144 --right-of eDP-1-1
   SCRIPT
   chmod +x ~/bin/monitor-setup.sh
   

2. Add to Gnome/KDE autostart:

   mkdir -p ~/.config/autostart
   cat > ~/.config/autostart/monitor-setup.desktop << 'EOF'
   [Desktop Entry]
   Type=Application
   Name=Monitor Setup
   Exec=/home/bratan/bin/monitor-setup.sh
   X-GNOME-Autostart-enabled=true
   NoDisplay=true
   EOF
   

B. xorg.conf (Advanced, NVIDIA only)

Add to /etc/X11/xorg.conf:

Section "Monitor"
    Identifier  "DP-1-1"
    Modeline    "1920x1080_144" 452.50 1920 2088 2296 2672 1080 1083 1088 1177 -hsync +vsync
    Option      "PreferredMode" "1920x1080_144"
EndSection

C. Kernel boot parameter (EDID override)

Add video=DP-1-1:1920x1080@144 to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub. This works for simple resolutions but not for custom timings.

G-Sync / VRR on Custom Modes

G-Sync with custom xrandr modelines is limited:

1. Check if VRR is supported on the port:

   xrandr --props | grep -A5 "DP-1-1" | grep vrr_capable
   

   vrr_capable: 0 means disabled.

2. Enable VRR via xrandr (partial):

   xrandr --output DP-1-1 --set "vrr_capable" 1
   

   This may enable variable refresh at the driver level.

3. Full G-Sync with nvidia-settings requires the mode to be set through NVIDIA's MetaMode system, not xrandr. Steps:

   • Generate xorg.conf: sudo nvidia-xconfig
   • Add custom modeline to xorg.conf
   • Set AllowGSYNCCompatible=On in the Display Device section
   • Reboot

Multi-Monitor Layout Quick Reference

Command	Effect
--right-of eDP-1-1	External right of laptop
--left-of eDP-1-1	External left of laptop
--above eDP-1-1	External above laptop
--same-as eDP-1-1	Mirror (clone) mode
--primary	Set as primary display

Pitfalls

1. cvt pixel clock may exceed DisplayPort bandwidth. DP 1.2 max: 540 MHz. CVT 1920x1080@144 = 452.50 MHz — fine. CVT 2560x1440@144 = 596.50 MHz — exceeds DP 1.2 limit! Use cvt -r for reduced blanking.

2. Custom modes vanish on display sleep/wake. The autostart script may not re-run. Workaround: create a udev rule or use xrandr in a systemd user service that watches for DP-1-1 reconnect.

3. xrandr --newmode fails if mode name already exists. Always use unique names (e.g. include refresh rate in the name) and redirect stderr: 2>/dev/null.

4. nvidia-settings --assign CurrentMetaMode fails on xrandr-created modes. The error is Attribute not available — NVIDIA's MetaMode system only recognizes modes configured through nvidia-settings or xorg.conf.

5. EDID works fine on Windows but not Linux. This is common with certain monitor firmware/GPU combinations. The fix is always the same (xrandr custom modeline), regardless of the root cause.

Reference Files

• references/edid-modeline-recipes.md — Known-working modelines for specific monitors