BSD Unix machines hanging

[Brent W Baccala]

In <23407 at gwen.cs.purdue.edu>, you write:

>We have been experiencing a rather odd and intermittant problem with
>our Unix machines. It is not confined to a particular machine or Unix;
>it has happened with 4.2, 4.2 NFS, and 4.3 BSD on VAX 780, 785 and
>uVAX II machines.
>
>Symptoms: The machines appear to lock up, users cannot get characters
>echoed, console is hung. In short, the machine seems dead. The only
>way to recover is a reboot. 
>
>However, the machine is still running in a sense. One can ping the
>machine in question, and it responds. One can open a TCP connection to
>the machine, and the connection succeeds, but hangs at that point.

We had the EXACT same problem with a PDP-11/55 running 2.9 BSD. It was
much more consistant, though - ours would go down regularly every night
(after hours, of course).  I think fixed it this weekend (its been up
for more than two nights straight - a major achivement).

The problem appears to have been in a locally written version of
"syslogd".  I, too, suspected the network (though I'm far from a guru),
but only looked briefly at the networking code.  And since only one of
our programs (a port of phone) uses syslog, I didn't think tracking down
the bug justified the downtime that would be involved. Whether this
problem is peculiar to our local syslogd, I don't know.  Nor do I know
exactly what triggers the bug; it make not be peculiar to syslogd
either.

It's interesting, but my experience has been that whenever there's
a problem, turning off syslogd fixes it...maybe ours is just a broken
daemon.

Hope this helps (and let me know if you find the bug)

					-bwb

			- BRENT W. BACCALA -
			Aerospace Engineering Department
			U.S. Naval Academy
			Annapolis, MD

			<baccala at usna.arpa>

	"I do graphics work on an SGI Iris, fun work on a VAX 11/780,
		grunge work on an IBM XT"