I don’t recall why but I installed brew’s verison of openssh using the instructions here on my OSX 10.8.5.   10.8.5 is Mountain Lion.

Ssh stopped working.  ssh -v revealed it would hang at “debug1: SSH2_MSG_SERVICE_ACCEPT received” which after I while I traced down to a hint that ssh-agent might be wedged.

Sure enough launchd’s org.openbsd.ssh-agent was failing.   Console was reporting: ” (org.openbsd.ssh-agent) Throttling respawn: Will start in 10 seconds”, a lot.

This failure arises because the org.openbsd.ssh-agent plist passes a -l switch to ssh-agent, and the one brew provided doesn’t have this undocumented switch.  You can see the switch in apple’s variant, just look for l_switch.

There are assorted pages complaining about this problem, but no solution.  My solution was to change the org.openbsd.ssh-agent plist to use the apple version of ssh-agent that resides in /usr/bin/ssh-agent.

I think I’m happy now.