"There appears to be another process already listening on socket"

[SleepyCatten]

• OS and version: Windows 11 Pro, 64-bit, 24H2, build 26100.6899
• BiglyBT Version Number: 4.0.0.0 (2025-12-19)

Hello there. Been trying to determine the cause of an issue that's been intermittently affecting users for years with seemingly no solution. All prior tickets have been closed. However, the issue still remains and there's no viable workaround for the issue, which seems to be undetermined.

For unknown reasons, BiglyBY recently-ish decided that after accepting a single magnet link, it would start producing the below error. Screenshotted an example.

For accessibility, text reads:

Error:
There appears to be another process already listening on socket [127.0.0.1:16889]
Locate and terminate the other program or change the control port
See the wiki for details, http://wiki.biglybt.com/w/Commandline_options#Changing-the-Control-Port

By default, without any additional command line options added to it, such as adding -Dazureus.instance.port=16889 to the java.vmoptions file, the port show will be 6800.

Anyway, closing BiglyBT, updating the control port, and then relaunching BiglyBT, will allow it to work for exactly one magent link before the error message changes to the new control port. Restarting Windows / the PC also works. Users can copy the magnet link and paste (via CTRL + V) into BiglyBT, but this is just skirting around the issue, rather than a workaround.

Thought it might be a Mozilla Firefox issue, so tested it in Microsoft Edge too: same issue. Both latest versions. In case it's relevant, the system on which this is occuring is using a VPN with split tunnelling. Firefox is not going through the VPN, but Edge and BiglyBT are. Happy to share further details as requested.

Please don't close this one down without at least trying to find the root cause, as clearly the issue keeps coming up 🥺

At the very least, don't suppose somebody could update the link in the error message to the correct one in the GitHub please, rather than relying on a redirect?

[parg]

All our wiki links redirect from wiki.biglybt.com in order to allow us to move the wiki without having to update the existing clients although I can see that in this case it is a pain as it can't be clicked.

The issue is no doubt to do with your VPN.

When a browser .torrent/magnet link is clicked on BiglyBT's protocol handler registration with the browser causes the following command (or equivalent) to be executed:

c:\program files\BiglyBT\BiglyBT.exe <X>

Assuming that BiglyBT isn't currently running this will result in BiglyBT starting up and processing the to add the torrent/magnet. It will also start listening on TCP port 127.0.0.1:6880 (the instance port default if not explicitly set) so that future magnet/torrent links can be passed to the already running procress.

The second time you click on a link BiglyBT.exe starts running and uinder normal circumstances will find that something is already listening on port 6880 - it will then connect to that port and send the to the existing BiglyBT process in order to add it and close down.

If something prevents that connection (e.g. your VPN) then you end up with that error message.

[SleepyCatten]

The issue is no doubt to do with your VPN.

Been using this VPN and a previous one with split tunnelling for years without any issues. Also, wife uses the exact same VPN and BiglyBT on a different PC (with the same VPN set up) but doesn't encounter this issue.

There's got to be more to it than just that.

[parg]

If you say so but I can't diagnose it from here...

[parg]

Can you perform a test with the VPN disconnected? You could create a separate instance of BiglyBT by following

https://github.com/BiglySoftware/BiglyBT/wiki/Command-Line-Options#running-multiple-biglybt-instances

to avoid running your existing one with the VPN disconnected