Won't recognize monitor/Gnome shell crashes

[Larry Reid]

Previously, I was using a Startech USB hub with an HDMI port to connect to an LG monitor, and connecting to my Slimbook laptop on one of the USB-C ports. I had to switch between a Mac for work and my Slimbook for personal use, and this was a convenient configuration.

Since I no longer needed to connect to the Mac, I removed the USB hub and connected the monitor directly to the HDMI port on my laptop.

Expected:

The external LG monitor should display output.

Actual:

The monitor said, "No signal detected", and nothing would appear on the monitor. Unplugging the HDMI cable would cause Gnome shell (`gdm`?) to crash and log me out.

Before crashing, system settings would recognize both monitors and allow me to change the configuration of the external monitor, but nothing would ever appear on the external monitor.

Work-around:

1. I disconnected the external monitor from the USB hub.
2. `mv .config/monitors.xml .config/monitors.xml.crashing-a`.
3. Connect the monitor to the laptop's USB port (caused the crash for Gnome shell).
4. Log back in.
5. The external monitor was now recognized. No `.config/monitors.xml` yet.
6. Open system settings and change the external monitor configuration (e.g. layout, resolution). Image/layout changed and a `.config/monitors.xml` was created.
7. Haven't had a crash of Gnome shell yet.

I'm running X11 (because I have Nvidia video):

```
echo $XDG_SESSION_TYPE
x11
```

Some symptoms were similar to bugs such as: https://bugs.launchpad.net/ubuntu/+source/mutter/+bug/2050865, but I have the latest `mutter`, and many of the similar bugs were for Wayland.

The `monitors.xml` that fails/caused crashes:

```
<monitors version="2">
  <configuration>
    <logicalmonitor>
      <x>0</x>
      <y>0</y>
      <scale>1</scale>
      <primary>yes</primary>
      <monitor>
        <monitorspec>
          <connector>eDP-1</connector>
          <vendor>BOE</vendor>
          <product>0x0aca</product>
          <serial>0x00000000</serial>
        </monitorspec>
        <mode>
          <width>2560</width>
          <height>1600</height>
          <rate>90.003</rate>
        </mode>
      </monitor>
    </logicalmonitor>
    <disabled>
      <monitorspec>
        <connector>HDMI-1</connector>
        <vendor>GSM</vendor>
        <product>LG HDR 4K</product>
        <serial>0x00040902</serial>
      </monitorspec>
    </disabled>
  </configuration>
  <configuration>
    <logicalmonitor>
      <x>0</x>
      <y>441</y>
      <scale>1</scale>
      <monitor>
        <monitorspec>
          <connector>eDP-1</connector>
          <vendor>BOE</vendor>
          <product>0x0aca</product>
          <serial>0x00000000</serial>
        </monitorspec>
        <mode>
          <width>2560</width>
          <height>1600</height>
          <rate>90.003</rate>
        </mode>
      </monitor>
    </logicalmonitor>
    <logicalmonitor>
      <x>2560</x>
      <y>0</y>
      <scale>1</scale>
      <primary>yes</primary>
      <monitor>
        <monitorspec>
          <connector>DP-3</connector>
          <vendor>AUS</vendor>
          <product>ASUS VA24E</product>
          <serial>N1LMTF161279</serial>
        </monitorspec>
        <mode>
          <width>1920</width>
          <height>1080</height>
          <rate>60.000</rate>
        </mode>
      </monitor>
    </logicalmonitor>
  </configuration>
  <configuration>
    <logicalmonitor>
      <x>2560</x>
      <y>0</y>
      <scale>1</scale>
      <primary>yes</primary>
      <monitor>
        <monitorspec>
          <connector>HDMI-1</connector>
          <vendor>AUS</vendor>
          <product>ASUS VA24E</product>
          <serial>N1LMTF161279</serial>
        </monitorspec>
        <mode>
          <width>1920</width>
          <height>1080</height>
          <rate>60.000</rate>
        </mode>
      </monitor>
    </logicalmonitor>
    <logicalmonitor>
      <x>0</x>
      <y>233</y>
      <scale>1</scale>
      <monitor>
        <monitorspec>
          <connector>eDP-1</connector>
          <vendor>BOE</vendor>
          <product>0x0aca</product>
          <serial>0x00000000</serial>
        </monitorspec>
        <mode>
          <width>2560</width>
          <height>1600</height>
          <rate>90.003</rate>
        </mode>
      </monitor>
    </logicalmonitor>
  </configuration>
  <configuration>
    <logicalmonitor>
      <x>2560</x>
      <y>261</y>
      <scale>1</scale>
      <monitor>
        <monitorspec>
          <connector>eDP-1</connector>
          <vendor>BOE</vendor>
          <product>0x0aca</product>
          <serial>0x00000000</serial>
        </monitorspec>
        <mode>
          <width>2560</width>
          <height>1600</height>
          <rate>90.003</rate>
        </mode>
      </monitor>
    </logicalmonitor>
    <logicalmonitor>
      <x>0</x>
      <y>0</y>
      <scale>1</scale>
      <primary>yes</primary>
      <monitor>
        <monitorspec>
          <connector>DP-3</connector>
          <vendor>GSM</vendor>
          <product>LG HDR 4K</product>
          <serial>0x00040902</serial>
        </monitorspec>
        <mode>
          <width>2560</width>
          <height>1440</height>
          <rate>59.951</rate>
        </mode>
      </monitor>
    </logicalmonitor>
  </configuration>
</monitors>
```

The one that works now:

```
<monitors version="2">
  <configuration>
    <logicalmonitor>
      <x>2560</x>
      <y>0</y>
      <scale>1</scale>
      <monitor>
        <monitorspec>
          <connector>eDP-1</connector>
          <vendor>BOE</vendor>
          <product>0x0aca</product>
          <serial>0x00000000</serial>
        </monitorspec>
        <mode>
          <width>2560</width>
          <height>1600</height>
          <rate>90.003</rate>
        </mode>
      </monitor>
    </logicalmonitor>
    <logicalmonitor>
      <x>0</x>
      <y>0</y>
      <scale>1</scale>
      <primary>yes</primary>
      <monitor>
        <monitorspec>
          <connector>HDMI-1</connector>
          <vendor>GSM</vendor>
          <product>LG HDR 4K</product>
          <serial>0x00040902</serial>
        </monitorspec>
        <mode>
          <width>2560</width>
          <height>1440</height>
          <rate>59.951</rate>
        </mode>
      </monitor>
    </logicalmonitor>
  </configuration>
</monitors>
```

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: gnome (not installed)
ProcVersionSignature: Ubuntu 6.8.0-57.59-generic 6.8.12
Uname: Linux 6.8.0-57-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.28.1-0ubuntu3.5
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Thu Apr 10 10:56:16 2025
InstallationDate: Installed on 2022-08-26 (958 days ago)
InstallationMedia: Ubuntu 22.04 LTS "Jammy Jellyfish" - Release amd64 (20220419)
SourcePackage: meta-gnome3
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.default.apport:
 # set this to 0 to disable apport, or to 1 to enable it
 # you can temporarily override this with
 # sudo service apport start force_start=1
 enabled=0
mtime.conffile..etc.default.apport: 2022-08-26T02:00:13.746746

[Larry Reid (lcreid)]

FWIW, I just wanted to highlight that the `monitors.xml` that causes the crash, has two entries for the same serial number, on different connectors.