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Re: What is "pipe prediction wrong"? (router hangs)

On Tue, Mar 23, 2004 at 04:50:16AM -0500, Ambrose Li wrote:
> Hi,
> at my ZMailer installation at work, I just ran into a strange
> problem.
> The router seems to hang on anything that is in the aliases
> file (for example "root") or any user that has a .forward
> file. Email addresses with FQDN's don't hang the router, so
> only locally generated mail (e.g., those from cron) would
> hang the router, it seems.

  It is telling, that ZMailer's shell-script interpreter
  got confused with what would be next fd values for
  IO redirections inside the scripts.

  But why is it happening all the sudden in a system that has been
  stable until then ?

> z# router a
> <acli.interactive@>: address: a
> (((local a a@XXXXXX default_attributes)))
> z# router foo
> <acli.interactive@>: address: foo
> (((local foo foo@XXXXXX default_attributes)))
> z# router root
> <acli.interactive@>: address: root
> router: pipe prediction wrong: got 8|6 not 9|8
> <The router hangs at this point>

Running that last after issuing command:

z# rtrace
z# router root

will produce a lot longer report of what is going on.
It might tell what happens when that message appears.
(What happens just before, that is.)

> This causes processing of incoming mail to periodically
> suddenly stop because of cron jobs, and there is little I can
> do to make the mail flow again except to rm all the mails
> generated locally, and then restart the router.
> This is ZMailer 2.99.56. DBTYPE is btree, but it makes no
> difference if I change it to gdbm. I also tried to rm all
> the *.fc files, but it also didn't make any difference.

Sometimes I got it to appear, when I had modified something
deep inside the interpreter, and didn't do proper 'make clean'
before 'make' (e.g. compile).   But I don't think you would
encounter similar problem...

Or perhaps I just got it to fix itself all the sudden, but didn't
in reality find its reason in the first place.

> What does "pipe prediction wrong" mean? Why does this hang
> the router?

System is becoming confused about what file descriptor numbers
are really available and what are not.

> This is Linux 2.2.25, and ZMailer has been running without
> a problem (mostly) until yesterday.
> Thanks very much in advance.
> Best regards,
> -- 
> Ambrose LI Cheuk-Wing  <a.c.li@ieee.org>
> http://ada.dhs.org/~acli/

/Matti Aarnio	<mea@nic.funet.fi>
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