Linux – What process does ‘own’ socket in ‘Time Wait’ state

Since you only do this manually, you may have to add another check.

netstat -p

and kill the pid associated with your open socket, even if it is bash or sh.

Also, you mentioned that most of the time SIGTERM works. If that's the case, your app should catch the SIGTERM and jump into some graceful exit code that RSTs all open connections and then closes the socket.

HTH

The last_ack state (if I recall my TCP stack correctly) is the state when you have received your FIN message to close the connection from your neighbour, but you still need to flush and shut down your connection. You send the final FIN yourself and wait for an ACK.

Typically hanging in last_ack means your application keeps a socket open even when the the other end has finished sending data. This can happen for multiple reasons. There might be a firewall or other load balancer which loses last ACK from the client, and leaves you stuck in the last_ack state. If the connections are not timed out after a few minutes (10 or so) you probably have a bug.

Have a look at the state diagram at http://tangentsoft.net/wskfaq/articles/debugging-tcp.html