I have one instance that does that, about every twelve hours, and I haven't had enough aolserver-fu to have been able to diagnose it.
Like you, many other aolserver instances run just fine, and it happens that the one that does this is a very strangely modified aolserver. AOLserver 3.3+ad13 & OpenACS 3.2.5 + ACS 3.4 + ACS 4 code + a bunch of other stuff I felt compelled to agglomerate into the mix. And it's doing this on PG 7.3, (or whichever the latest PG is that OpenACS 3.2.5 isn't supposed to support.)
So I've always suspected it was some of my own brain damage.
On the otherhand, this is a very lightly used aolserver instance, and the roughly twelve hour period make me feel it is some scheduled proc or cron job screwing around with my head.
I haven't checked /proc/sys/fs/file-max, maybe I should....
