DELUA technical manual, VAX diagnostic

Peter Coghlan cctech at
Wed Nov 19 10:03:35 CST 2014

>One thing, though.
>I don't think that the error code from the $QIO in the OPCOM log is a
>VMS exit code. But I might be wrong on that.
>But that could do with some more examining.

There is a poorly phrased entry in the CMU/IP FAQ which could give the
impression that CMU/IP uses it's own error codes that are entirely different
from VMS status codes.  What I think it is really trying to say is that like
many VMS applications, CMU/IP defines _additional_ status codes that VMS does
not already have suitable messages defined for and the text messages associated
with these are not available unless the appropriate CMU/IP provided message
files are loaded.

Low numbered error codes such as 1C (and another favourite - 0C which is
%SYSTEM-F-ACCVIO, access violation) come from system services and runtime
library functions that are part of VMS and the message texts are made available
automatically by VMS.  It is not the case that CMU/IP reporting an error code
of 1C means something different to some part of VMS reporting it.  They both
mean process quota exceeded.

Directly underneath that entry in the FAQ, I found the following:

>3.1.2 >>>> IPACP CRASH DUE TO QUOTA EXCEEDED                   [20-MAR-1995]
>For systems with a high IP load, IPACP may occasionally crash with a quota
>exceeded. This does not refer to disk quota, but to one of the process quota
>limits. Usually, the quota in question is BYTLM.
>The default BYTLM provided for IPACP (65536) is sufficient for only about 20
>connections. IPACP takes about 32000 for itself and each connection takes
>1872 bytes. This requirement is NOT currently documented.
>To increase the BYTLM for the IPACP, modify the IP_STARTUP.COM procedure and
>change the value of the /BUFFER_LIMIT qualifier on the RUN command that starts
>the IPACP process. Then shut down and restart IPACP.
>At the current time, there also appears to be a memory leak in IPACP which has
>the effect of gradually reducing the available BYTLM over time. When this gets
>close to zero, IPACP will hang (as it retries) and then crash soon afterwards.
>It is therefore desirable to give IPACP more BYTLM than the typical load might
>suggest. If this sort of crash is experienced, increase the BYTLM by 50% and
>restart it.
>                                                       <A.Harper at>

Looks like my pagefile quota guess was wrong and the culprit is BYTLM.  However,
I suspect the underlying cause of this problem has never been fully addressed
and increasing the quota will not help, or worse, will help for about a week
before the problem returns even more frequently.

I cannot overemphasise how much relief will be experienced on the replacement
of CMU/IP by something that works properly or even by something that doesn't
mess up as badly.  Problems that you didn't even know you had will go away,
even ones which seemed unrelated to networking.  On sunny days, the sun will
seem brighter and the sky bluer :-)

In my previous posting, I forgot to mention that you can also try:


if running DECnet.  This will give DECnet's view on any network media problems
including those relating to other protocols going through the same network
adapter.  It probably won't have much to say about hardware failures in the
network adapter though.  Remember that on a half duplex ethernet, collisions
are normal and expected but late collisions indicate a problem.

Peter Coghlan.

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