Tracking down "kern.ipc.maxpipekva exceeded"

[Ewald Jenisch]

Hi,

For some time one of my machines in plaged be becoming completely
unresponsive after different amounts of time (several hours up to
several days).

Symptoms:
Machine is PINGable, but no access over the network is possible
(neither ssh-login nor http-access). 

/var/log/messages:
May 11 12:11:00 io kernel: kern.ipc.maxpipekva exceeded; see tuning(7)
maxproc limit exceeded by uid 0, please see tuning(7) and login.conf(5).
(tons of both)
and finally 
May 11 12:42:03 io kernel: maxproc
May 11 12:42:03 io kernel: limit exceede
May 11 12:42:03 io kernel: d by uid
May 11 12:42:03 io kernel: 0, ple
May 11 12:42:03 io kernel: se see tun
May 11 12:42:03 io kernel: ng(7) and l
May 11 12:42:03 io kernel: ogin.conf
May 11 12:42:03 io kernel: (5).
May 11 12:42:03 io kernel: 

>From that time on I can't log in any more, not even from the console.

When rebooting the box via ctl-alt-del, before shutdown, it fails to
sync buffers on shutdown (counts down to 1 and stays there) and
finally gives up - requiring an fsck on reboot.

Please note that the box does *not* crash completely, nor do I get a
kernel panic though.

The system is running "5.4-STABLE FreeBSD 5.4-STABLE #0: Sat Apr 16
10:19:26 CEST 2005" but this problem has been there since I first
installed 5.3 on the box.

So my primary question is:

How do I track down the cause of the problem, i.e. which
program/process is responsible for "kern.ipc.maxpipekva" to be
exceeded?

Thanks much in advance for any clue,
-ewald