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Date:      Mon, 3 Jun 2013 22:21:55 -0700
From:      Doug Hardie <bc979@lafn.org>
To:        staticsafe <me@staticsafe.ca>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: System Calls that do DNS
Message-ID:  <CC1F81CF-1107-4031-A72F-164D6E23E5B7@lafn.org>
In-Reply-To: <20130604033930.GA10393@uriel.asininetech.com>
References:  <F5EBDC53-CBA3-415D-B7CD-1EC873692348@lafn.org> <20130604033930.GA10393@uriel.asininetech.com>

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On 3 June 2013, at 20:39, staticsafe <me@staticsafe.ca> wrote:

> On Mon, Jun 03, 2013 at 07:57:07PM -0700, Doug Hardie wrote:
>> I have an unusual situation.  A program is doing a DNS lookup and =
often the IP address has no reverse DNS entries.  As a result the =
program hangs for several timeouts.  The call is not being made directly =
in its code, but is occurring in a system call.  There are no specific =
calls to DNS, its something else doing it.  I have been trying to track =
down which system call is doing it, but without success so far.  I have =
tried syslog calls around each of the system calls I thought might be =
the culprit, but my guessing is not very good.  How can I identify the =
system call that is calling DNS?  If I can find it, I hopefully can find =
another way to do whatever it does that does not involve a reverse DNS =
lookup.
>>=20
>>=20
>=20
> Use truss:
> http://www.freebsd.org/cgi/man.cgi?query=3Dtruss
>=20
> The truss utility traces the system calls called by the specified
> process or program.
> --=20
> staticsafe
> O< ascii ribbon campaign - stop html mail - www.asciiribbon.org
> Please don't top post - http://goo.gl/YrmAb
> Don't CC me! I'm subscribed to whatever list I just posted on.
>=20

Unfortunately truss does not show anything more than ktrace.  I know =
what is going out on the internet connection.  Its a plain old reverse =
DNS request.  The question is what library module (probably not a system =
call now that I think about it) is making that request.  Interestingly =
enough, adding the IP address with a dummy name in /etc/hosts causes the =
reverse request to succeed and there are no time delays.  So whatever =
module it is, is not using bind.  Bind doesn't check the hosts files as =
far as I can tell.=



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