Port 55555 in use on Mac OS Big Sur

Question

Created Jan ’21

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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.

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Answer 1

Etresoft OP

Jan ’21

This is apparently a known problem: https://developer.apple.com/forums/thread/659864

The solution is to use some other port.

1

Answer 2

omg_it_burns OP

Jan ’21

This is extremely irritating. It's not even documented, https://support.apple.com/en-gb/HT202944

1

Answer 3

cosmozhang OP

Mar ’21

I also met this problem after I upgraded to Big Sur. It seems the "well-known" problem is about iOS 14. I didn't find any official posts about this problem on Mac OS. I have started a question on stackoverflow.

0