Does anyone have any experience or tools for tracking down unclosed file
descriptors? From what I understand unclosed FD's occur when "the remote peer
has closed the connection (sent a FIN) but the local application hasn’t yet
closed its end."

So I'm guessing this either from a db call, http request or websocket. But I've
been going through my code and can't seem to find any instances of unclosed
sockets.

Are there any tools for further investigation?