Those of us with busy servers may have run into bug 13729794, causing OEM 12c agents to eventually stop monitoring after raising a TOO_MANY_OPEN_FILES error. On 12cR1, patch 6895422 took care of this problem. Oracle’s bug database reports this bug as “fixed in 22.214.171.124.0” but in status 75 “Closed, Code fix resolution not verified.”
I had two 12cR2 agents bomb out over the weekend (nothing like logging into MOS on a day off) with TOO_MANY_OPEN_FILES. The OMS wouldn’t recognize either of them after bouncing the agent. I had to run an emctl clearstate on each of them with the agent down, then start it back up, before the 12cR2 OMS would report the agents as reachable again.
So it seems 12cR2 does not fix this bug, at least not on Linux x86-64. I should know in about two days whether or not this patch still fixes the problem.