I've noticed the port 55555 looks like it is already in use on Mac OS Big Sur.

If you run nc -l 55555 it shows an error. Address already in use

But nothing answers if you telnet it, and nothing shows up on lsof -i tcp:55555 too. Very odd behaviour.

Confirmed on several different machines.

Is there any way to figure out what is running and release it?

  • I faced the same issue and unfortunately have not been able to find a resolution. There is a discussion on Apple Developer Forum developer.apple.com/forums/thread/668506. Reaching out to Apple we got a response saying the port 55555 is now reserver for 1st party application; tho I'm hoping there will be a patch freeing this port coz we have 100k+ docker downloads depending on this port. I'd like to stay updated on this so if you hear anything about let us know. Thanks! – Tamimi Ahmad Jan 17 at 14:42

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