KVM Child process has unexpectedly exited on DM (SDDM or lightDM)

[tjagh]

Describe the bug
desktop connect to fresh debian trixie pc does not work when not logged in.
a yellow "KVM Child process has unexpectedly exited" will appear in the desktop area after some seconds.

To Reproduce
Steps to reproduce the behavior:

1. desktop
2. click "Connect"
3. "KVM Child process has unexpectedly exited" in desktop area below Connect button

Expected behavior
client desktop login screen

Screenshots

Server Software (please complete the following information):

• OS: debian trixie 13.6
• Virtualization: Proxmox
• Network: behind nginx
• Version: 1.2.1
• Node: 20.19.2

Client Device (please complete the following information):

• Device: desktop pc
• OS: debian trixie 13.6
• Network: LAN
• Browser: FF 140.14.0esr

Remote Device (please complete the following information):

• Device: desktop pc
• OS: debian trixie 13.6
• Network: LAN
• Current Core Version (if known): Current Core: Feb 15 2026, 421355405
• pc has an intel "Battlemage G21 [Arc B570]"
• replaced SDDM with LightDM, didnt help

Your sanitized config.json file
Please sanitize your configuration (remove private or irrelevant values) before posting, using the community tool at https://sanitizer.meshcentraltools.com/

{
  "settings": {
    "cert": "meshcentral.domain-1.com",
    "WANonly": true,
    "sessionKey": "REDACTED",
    "port": 1029,
    "aliasPort": 443,
    "redirPort": 800,
    "AgentPong": 22,
    "webRTC": true,
    "webrtConfig": {
      "iceServers": [
        {
          "urls": "stun:turn.domain-1.com:3478"
        }
      ]
    }
  },
  "domains": {
    "": {
      "certUrl": "https://meshcentral.domain-1.com/"
    }
  }
}

[si458]

do you use wayland or x11 on the remote pc?
wayland is not supported at the moment.

[tjagh]

hmm. my impression was that lightDM itself always runs on X11 (didnt find a clear answer on that in the internets ...).

at least on this PC it seems to be that way:
root 49573 0.6 0.1 779276 108756 tty7 Ssl+ 11:27 0:14 \_ /usr/lib/xorg/Xorg :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch

also note:
when i try to connect to "Desktop" and the "KVM Child process ..." error appears the meshagent process spawns a new "--slave" process every second until the machine starts to lag and freeze (i counted 333 "--slave" subprocesses).
restarting the meshagent via "systemctl restart meshagent" then produces a lot of "[meshagent] " artefacts till the situation eventually resolves itself after some minutes.

[si458]

yeh thats a bug, needs looking into but we are snowed under at the moment (the community) we other issues

[tjagh]

apart from the "--slave" spawn thing - could you suggest a way to debug the "KVM Child ..." problem ?

i see no wrongs in the system logs, dmesg or the "events" tab in the mc UI ...

is there some debug log anywhere (i found nothing) or could i enable one ?