System Calls that do DNS

[Mark Felder]

On Mon, 03 Jun 2013 21:57:07 -0500, Doug Hardie <bc979 at lafn.org> 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.
>
>

The system DNS lookups are handled by libc. Probably somewhere in the code  
here:

http://svnweb.freebsd.org/base/head/lib/libc/nameser/