[SOLVED] GUI not usable, Connection error - server offline?

[KappaSN]

Hello everyone,

since updating to 8.3.5, the GUI of my Proxmox server no longer really works. The GUI works for a few seconds, but as soon as there is interaction, connection error messages like “Connection error - server offline?” or “Connection error” appear. There are also messages in the browser with “ERR_ADDRESS_IN_USE”. This all points to network problems, but no errors could be detected. SSH and Ping also work perfectly.




pveproxy is also running and does not give any error messages:

● pveproxy.service - PVE API Proxy Server
Loaded: loaded (/lib/systemd/system/pveproxy.service; enabled; preset: enabled)
Active: active (running) since Tue 2025-03-25 15:31:33 CET; 44min ago
Process: 1927 ExecStartPre=/usr/bin/pvecm updatecerts --silent (code=exited, status=0/SUCCESS)
Process: 1929 ExecStart=/usr/bin/pveproxy start (code=exited, status=0/SUCCESS)
Main PID: 1931 (pveproxy)
Tasks: 4 (limit: 309021)
Memory: 228.0M
CPU: 39.296s
CGroup: /system.slice/pveproxy.service
├─1931 pveproxy
├─1932 "pveproxy worker"
├─1933 "pveproxy worker"
└─1934 "pveproxy worker"

There are no anomalies in journalctl either.

Thanks!

 

[bbgeek17]

ERR_ADDRESS_IN_USE indicates a client-side issue. Try a different browser, if using Windows - try to use the sandbox.
Check/disable any extensions, vpn clients, firewall additions.

Good luck

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Blockbridge : Ultra low latency all-NVME shared storage for Proxmox - https://www.blockbridge.com/proxmox

 

[KappaSN]

Hey bbgeek17,

thank you. I have already tried different clients and browsers (Chromium & Firefox), but the issue persists.
The server is at a remote location. I'll try connecting locally on Thursday, but I have already checked the firewall and the switch and didnt found any issues.

 

[bbgeek17]

Try something like this
putty.exe -ssh user@remote_host -L 8006:localhost:8006 (or equivalent via your favorite ssh client)

Then try to access PVE via: https://localhost:8006

This should bypass any middleware firewalls, etc.

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Blockbridge : Ultra low latency all-NVME shared storage for Proxmox - https://www.blockbridge.com/proxmox

 

[KappaSN]

Hello bbgeek17,

Thanks for the tip! I managed to solve the issue, and as it turns out, it wasn’t really a Proxmox problem, at least not directly.
The root cause was our environment setup. We use a terminal server agent that assigns port ranges to users and maps their requests to IP adresses on the firewall.

The fix was to adjust the HonorSrcPortRequest setting in the Registry. Setting this to 2 allowed applications to use specific local ports, even outside the assigned range. This resolved the port conflicts and eliminated the ERR_ADDRESS_IN_USE error.

 

[bbgeek17]

Thanks for sharing your find with the community!

I would say that this was not a PVE issue "directly" or "indirectly"

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Blockbridge : Ultra low latency all-NVME shared storage for Proxmox - https://www.blockbridge.com/proxmox