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On my Mac, I have a UDP port that is "already in use", but doesn't have an associated process:

sudo netstat -na | grep "udp.*\.500\>"


udp4       0      0     *.*                               
udp4       0      0     *.*                               

sudo lsof doesn't show a process on port 500 (ie sudo lsof -i:500 -P reports nothing).

Note I'm using 'sudo' on both commands so it should show all processes. (rebooting works, but looking for something less disruptive)

How can I unbind port 500 so I can use it again?

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Are you using sudo to run lsof as root? If not, it'll only be able to see files opened by processes you own, and this is probably a system process.

Port 500 is normally used for the isakmp, which is part of the IPSec suite. It'll generally show up on a Mac as a side effect of an IPSec-based VPN service.

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Yes, I'm using sudo on both commands. Yes, the actual problem is my vpn client won't start (fails with an "address already in use" error). – Chocohound Nov 12 '12 at 14:57

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