Re: Exim and hostname --fqdn, was Re: mutt attachment error
On Thu 12 May 2016 at 20:38:41 (+0100), Brian wrote:
> On Thu 12 May 2016 at 10:08:49 -0500, David Wright wrote:
> > On Thu 12 May 2016 at 11:33:10 (+0100), Brian wrote:
> > > On Wed 11 May 2016 at 14:51:31 -0500, David Wright wrote:
> > > > BTW when will dpkg-reconfigure exim4-config either stop saying
> > > > "hostname --fqdn did not return a fully qualified name, dc_minimaldns will not
> > > > work. Please fix your /etc/hosts setup." or suggest a reasonable fix?
> > > > Or IOW, why has bug #504427 never even received acknowledgment?
> > >
> > > It will stop, I suppose, when the user has a correct 127.0.1.1 line in
> > > /etc/hosts.
> >
> > That just begs the question as to what is correct. Refer to:
> > https://www.debian.org/doc/manuals/debian-reference/ch05.en.html#_the_hostname_resolution
>
> The -devel thread referred to in #719621 is worth reading. There was no
> consensus in it to support the suggestion that 127.0.0.1 is better than
> 127.0.1.1. The history of resolving local host/domainname goes back many
> years and what we have now does just work. For now, the "correct way" is
> the present way.
I'm quite happy to accept whatever Debian decides on in this regard
and presumably $ hostname is always going to make the appropriate
choice of source for the hostname. It's only the domainname that was
worrying me.
> My canonical hostname is "desktop.lan" and it has the alias "desktop",
> the hostname of the machine. 'hostname --fqdn' gives
>
> desktop.lan
>
> because the files method of nsswitch.conf matches the hostname with the
> canonical hostname.
But I would prefer not to have a domain tagged on the end if it's made
up. I don't want to use my own domain as the one thing it *doesn't* do
is resolve to my home network; it's even on a different continent.
With the expansion in TLDs, almost nothing is safe. The best I could
find was .localhost IF I'm interpreting RFCs 2606 and 6761 correctly.
So I might try setting that up at some time. Unlike the last change
you suggested (resolving hosts through avahi rather than /etc/hosts)
which I could do piecemeal, this probably has to be networkwide.
> For Exim and minimaldns the question is
>
> Does the hostname resolve to a fqdn (something with a dot in it)?
>
> 127.0.1.1 alum.anything_you_want alum
>
> would do this.
I haven't worked out why exim needs hostname --fqdn to resolve to a
dotty name. After all, it knows that your desktop.lan isn't really a
routable internet address just by its IP number.
> Having said this it as well to realise Exim will HELO to a remote host
> with "alum.anything_you_want". Some misguided hosts will deny contact
> because there is no reverse lookup which satisfies them. ISP smarthosts
> are generally very forgiving (they have to be!) so this is generally not
> a problem with sending mail through them.
That issue is covered by setting helo_data, which has the advantage
that it can be evaluated at the time it's used, so you can tailor it
to each and every host you use.
All that said, my beef is with the message. There doesn't appear to be
any deleterious effect, at least at present. I suspect there was, but
it's too long ago to remember; maybe a dozen years or more since
Starting MTA used to hang.
Cheers,
David.
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