I apologize for accidentally discarding the relevant logs.
I was trying to launch gunicorn pointed at a socket file in the /vagrant directory of a vagrant VM, which is a mounted shared filesystem location in which sockets cannot be created. Applying strace to gunicorn indicated that creating the socket was failing (with return code -6, I think), but gunicorn proceeded to try opening the not-created socket anyway.
This failure mode should be caught.
If this description does not make the location of the problem obvious, please let me know and I will endeavor to reproduce the misbehavior and the logs I lost.
"but gunicorn proceeded to try opening the not-created socket anyway." did it crash at the end?
I ended up with a running gunicorn process logging a failure to connect every N seconds... I think? Sorry, my memory is fuzzy a month later.
I would be interested in a log. I can't see how the call to create a socket could fail without gunicorn crashing.