Sonarr sometimes decides to start working for a day or a few weeks. It’s web page won’t load and the log file complains about the disk being full, so it can’t write the PID file. All four mechanical disks in the array have space, the cache has space and so does the flash key Unraid runs from. So this message is bogus.
Where does /config actually exist? Can you check the free space there when it happens?
The error comes from mono, I doubt it’s a mono bug, but something with mono telling the system to create the file is leading to the out of space error.
No, Sonarr is written in C# for .net), mono is an interpretation of .net for Linux/macOS. Python would require the entirety of Sonarr to be rewritten.
Could this be a virtual filesystem thing?
Sounds like it, but not sure if it’s an issue with the contain filesystem being full or with the mapping to the host.
Have you mapped /config for the container to the unRAID cache drive?