What causes Dolphin to listen on port 3321?

I’ve run into an occasional port conflict where Dolphin will start listening on Does anyone know what triggers Dolphin to start listening for connections on that port or any other port?

At the time there were several tabs open to local folders, folders that were actually NFS mounts, and a USB drive. Closing the tabs didn’t stop Dolphin from listening on the port. I had to close Dolphin.

I tried to re-open the same items and Dolphin didn’t start listening on any ports at all.

This was on Ubuntu 22.04 that originally had Gnome installed, then KDE was installed.

Any leads would be appreciated.


Probably not what you’re seeing, but Dolphin supports the freedesktop.org file manager D-Bus specification and has a daemon version of itself listen for incoming requests. Like notifications you sometimes get: “XYZ.pdf finished downloading. [Open containing folder]”

But I’m not sure right now if D-Bus services even use TCP sockets or just randomly named Unix socket files. Probably the latter tbh. You wanted possible leads though, so here you go.

Thank you for the response, @jpetso

I can’t find anything related to d-bus and port 3321. All I’ve been able to find out is that 3321 is registered to the IANA as “VNSSTR”. I can’t find any other enlightening detail about the term VNSSTR. There might be a paper by the person who registered the port, but I can’t read it.


In any case, I’m no closer to figuring out what triggers Dolphin to start listening on port 3321.

I just searched my locally downloaded set of all KDE components (at least including the hard requirements of Dolphin, maybe there are some more optional plugins out there that I missed) for the number 3321. No source code in Dolphin and the combined KDE codebase seems to use that number for anything networking-related.

So it seems likely that this comes from a non-KDE dependency somehow. Hard to tell what it is exactly.

Thanks again. I’ve searched dolphin plugins, and didn’t see anything there either. I don’t know the structure of the code well enough to really guess where to look other than the obvious dolphin code and dolphin plugin code.

It may be one of the NFS services which has requested a free port to the portmapper. rpcinfo -p shows the assigned ports.

ubuntu - Which ports do I need to open in the firewall to use NFS? - Server Fault has some info on configuring some services to use static ports.