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Newsgroups: comp.unix.sco.misc
From: Bela Lubkin <belal@sco.com>
Subject: Re: acctcom, at, OSR507
  by mail.ut.sco.com with SMTP; 2 Oct 2004 21:39:01 -0000
Date: Sat, 2 Oct 2004 21:38:45 GMT
Message-ID: <20041002213845.GU23239@sco.com>
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References: <415F16FE.4E38C1C5@tenzing.org>


Roger Cornelius wrote:

> On OSR507 with MP3 and UP3, why does acctcom produce no output when run
> by at?

This took a little longer to diagnose I thought you meant it was new
behavior in MP3/UP3.  I finally tried the same on an OSR505 system and
got the same results.

`acctcom` makes a guess about whether you mean to process stdin or the
default file, /usr/adm/pacct.  If stdin is a tty or /dev/null, it
assumes you want /usr/adm/pacct; otherwise, you want stdin.  stdin of a
process run by `at` is the shell script containing the commands you told
it to run.  `acctcom` attempts to process that as accounting records,
doesn't see anything sensible, and produces no output.

Workaround: tell it either `acctcom /usr/adm/pacct` or `acctcom <
/dev/null`.

Hmmm, now that I've written this, I see that acctcom(ADM) itself says
the same thing:

"  If no files are specified, and if the standard input is
"  associated with a terminal or /dev/null (as is the case when
"  using ``&'' in the shell), acctcom reads /usr/adm/pacct;
"  otherwise, it reads the standard input.

Another way to look at this problem is that when you run `acctcom` from
the command line, with no arguments, you're really committing a semantic
error.  You are actually telling it that you intend to manually type in
accounting records (binary gibberish).  Someone long ago noticed that
this wasn't a useful behavior, so they made the program guess your real
intentions.  So `acctcom` abets your semantic error.  Everything's fine
until you present it with different conditions where the sematic error
becomes significant.

The heuristic could probably be improved.  e.g. if stdin is a file, but
either its total size or its current seek offset isn't a multiple of the
accounting record size, it could guess that you didn't mean stdin.  But
that would only work _most_ of the time; occasionally you would again
hit the conditions (e.g. you'd submit an `at` job whose resulting script
was an exact multiple of 32 bytes -- a 1-in-32 chance), and it would
misbehave again.  Only now it would be 32x more mysterious.  The real
chance is more like 1-in-32^2, so now it would screw up one in a
thousand runs.  I would rather have it fail consistently, so you
immediately notice the problem and deal with it...

>Bela<

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