Many thanks for your explanation. It makes sense now.

One thing I've learned is that I need to get rid of the resource trackers for shared memory, so I've applied the monkey patch fix mentioned in https://bugs.python.org/issue38119

The issue is that you need shared memory in a multi processing environment, but the resource tracker can hardly know about other processes using the shared memory unless you tell it explicitly.

It looks like the resource tracker is guessing that all users of a shared memory are somehow forked from the same main process but I'm using spawn and not fork because my software should run on Windows as well.

Regarding /dev/shm on Linux: As far as I know there's an option 'RemoveIPC' to the systemd daemon that will delete shared memory on logout of the user which is turned on by default. I also remember seeing cronjobs for cleaning up /dev/shm on Debian, but not sure if that is the current approach anymore.