ORCID iDI had a problem with my Tor relay last night. For some reason, the application (daemon) started but then after about 5 seconds it stopped listening. The Tor Metrics site was displaying a red button saying my node was unreachable and when I did “sudo ss -ltp” I got nothing. The application literally wasn’t “listening” (in network socket terms).
The answer was actually embarrassingly simple. If your Tor daemon stops listening, even if you can’t find a log entry saying why, it could be because you have burned through your entire traffic allocation for the accounting period. Increase the limit and try restarting it to avoid a red face.