[ltp] Getting full hostname from DHCP

Tino Keitel linux-thinkpad@www.bm-soft.com
Fri, 21 Jun 2002 08:43:03 +0200

On Fri, Jun 21, 2002 at 00:03:58 +0200, Edi Weitz wrote:
> Eric Jorgensen <alhaz@xmission.com> writes:
> > On 13 Jun 2002 00:36:35 +0200 Edi Weitz <edi@agharta.de> wrote:
> > > I'm using DHCP at home as well as when I'm visiting customers of
> > > mine and it is started with the -H option to set the hostname of
> > > my laptop. However, no matter where I am I only get the first part
> > > of the hostname, i.e. 'bird' instead of the FQDN 'bird.agharta.de'
> > > for example.
> > 
> > 	This behavior is correct. That is to say, it is standards compliant. 
> > 
> > > This isn't a problem at home because my domain is in
> > > /etc/resolv.conf, but it is a problem when I'm not at home,
> > > especially for apps like Apache or Postfix which seem to rely on
> > > fully qualified hostnames.
> > > 
> > > Any ideas how to fix this? Is this a problem of the DHCP server(s)
> > > or is it related to my set-up?
> > 
> > 	You can fix this symptom by defining the domain name on the
> > DHCP server. Of course, at work you will probably have to ask your
> > kind network administrators to make the change for you.
> > 
> > 	In ISC DHCPD, you would define something like this: 
> > 
> > option domain-name "areb.org";
> > option domain-name-servers,,;
> > 
> > 	And then, most DHCP clients will apply this information to
> > your local resolv.conf. Certainly dhclient does for me on
> > debian/woody, not sure about others. Other popular possibilities are
> > isc-dhcpcd and pumpd, not to mention udhcpc, etc.
> [Sorry, I wasn't able to answer earlier.]
> Thanks for your reply. It turns out that I didn't look into the
> problem exactly enough. Fact is that even when I'm not at home my
> /etc/resolv.conf is modified so that it reflects the network I'm
> currently in. Nevertheless there is a problem with apps like Apache
> and Postfix. It goes like this:
> The distro that I'm using (Gentoo) has an init script that sets the
> hostname statically before any of the network init scripts have been
> started. Thus, the hostname is set to 'bird.agharta.de' (which is my
> laptop's name when I'm at home). If I'm at home this is fine, but if
> I'm "on the road" this doesn't work: The DHCP server sets my hostname
> to, say, 'dyn164' and modifies my resolv.conf to include the line
> 'search dbdmedia.de', i.e. my FQDN would be 'dyn164.dbdmedia.de'. But
> /bin/hostname will still answer with 'dyn164' and this is what Postfix
> is complaining about:
>   Jun 20 16:24:51 dyn164 postfix[6044]: warning: My hostname dyn164 is not a fully qualified name - set myhostname or mydomain in /etc/postfix/main.cf
> Am I supposed to write a hostname init script that starts after the
> network has been initialized and calls /bin/hostname with a fully
> qualified hostname determined from /etc/resolv.conf, something like
> this:
>   #!/bin/sh
>   FIRST=`/bin/hostname`
>   REST=`perl -n -e 'print $1 if /^search (.*)/' /etc/resolv.conf`
>   hostname "$FIRST.$REST"
> I think that would the trick, but I wonder if this is the correct way
> to do it.

It seems like your DHCP client expects the DHCP server to supply a host
name as a FQDN, but the server doesn't. What DHCP client are you using?


dipl.-inf.                        Innominate Security Technologies AG
software engineer                                   networking people
tel: +49.30.6392-3308                      http://www.innominate.com/

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