Re: exim HELO=fully qualified host name?
From: David Clymer (david_at_zettazebra.com)
To: Debian-User <firstname.lastname@example.org> Date: Fri, 06 Feb 2004 17:31:21 -0500
On Fri, 2004-02-06 at 14:32, Derrick 'dman' Hudson wrote:
> On Fri, Feb 06, 2004 at 01:26:10PM -0500, David Clymer wrote:
> | On Fri, 2004-02-06 at 12:11, Monique Y. Herman wrote:
> | > On 2004-02-06, David Clymer penned:
> | > > On Fri, 2004-02-06 at 09:07, davis wrote:
> | > >> I can not subscribe to the pcmcia-cs mailing list on source forge
> | > >> because my helo only gives my host name and not my fully qualified
> | > >> hostname. How do I resolve this problem?
> | > >
> | > > You need to set exim's primary_hostname to your FQDN (or the
> | > > equivilant configuration variable for your choice of MTA).
> | >
> | > I believe that exim will, by default, report the first entry in your
> | > /etc/hosts file. So if you have
> | >
> | > 22.214.171.124 booger yoda www.sticky.net
> | >
> | > I believe exim will report the machine as booger.
> | >
> | > Just move the FQDN into the first slot and you should be fine.
> | >
> | > My understanding is that exim's primary_hostname setting is considered a
> | > kludge and that it's "better" to use the above method.
> Basically correct.
> | I learn something new every day, it seems. I suppose I should modify my
> | own server, if thats the case. Could you expound apon the "kludge-ness"
> | of primary_hostname?
> primary_hostname only affects exim. Nothing else on your system will
> know about that setting, in exim's config file. By default exim uses
> the gethostbyaddr() system call to ask the system what the host name
> is. glibc uses the hosts file, if an appropriate entry is available
> and the nssswitch.conf file tells it to look there, to determine what
> the machine's full name is.
> You can test the system's idea of your host name either by running the
> 'hostname' command or using this snippet of python code :
> python -c "import socket; print socket.gethostbyaddr(socket.gethostname())"
> In short, it is best to have the system correctly know what its name
> is than to explicitly tell exim what it is.
I just assumed that the /etc/hosts file was, for the most part, obviated
by DNS, and now only really good for making aliases for the localhost
(since one can't generally resolve the loopback address via DNS). I
suppose its less expensive than a DNS query, but specifying a hostname
in /etc/hosts seems to differ in kludgyness from primary_hostname by
degree rather than method.
for instance, when communicating with a remote host, it would seem to me
that the logical hostname to supply (as a self reference) would be a
hostname which is resolvable via DNS rather than an /etc/hosts alias
which is inaccessable to the remote host and can contain (and rightly
so) a hostname resolving to 127.0.0.1.
am I way off base in thinking this?
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