"FD_SET() has a hidden limit of 256 descriptors" qmail big-concurrency issue

From: Scott Fultz <scott(at)mountainmedia.com>
Date: Tue Dec 17 2002 - 13:19:36 EST

I've been googling and have checked this list archive and can find no answers, please help.

I am setting up a mail server with OpenBSD 3.2, qmail 1.03 with big-concurrency patch, ezmlm, vpopmail, courier-imap.

When I try to compile qmail with the big-concurrency patch, I get the error:

---

./chkspawn
Oops. Your system's FD_SET() has a hidden limit of 256 descriptors. This means that the qmail daemons could crash if you set the run-time concurrency higher than 125. So I'm going to insist that the concurrency limit in conf-spawn be at most 125. Right now it's 1000. *** Error code 1

Stop in /usr/local/src/mail/qmail-1.03 (line 1903 of Makefile).

---

I have tried many things to increase this "hidden" limit. It does indeed seem hidden. ;-(

My plan is to run with a concurrencyremote setting of 500 to start with, and tune from there. But I can't get qmail to compile. I've tried modified settings in login.conf (openfiles-max and openfiles-cur) setting them to 1024. I've tried recompiling my kernel after setting FD_SETSIZE in /usr/src/sys/sys/types.h to 2048. Nothing seems to help. I've tried modifying /usr/src/sys/sys/syslimits.h.

Does anyone know a way to over-ride the FD_SET() hidden limit? Received on Tue Dec 17 13:22:25 2002