dhclient and automatic fqdn.fqdn generation

[Ted Lemon]

> I'm setting this all up in the DHCP client (dhclient.conf file).
> My dhclient.conf file contains a host-name setting and I want to
> concatenate this host-name with the domain-name from the DHCP
> server (from the DHCPACK packet).

> Though from the first paragraph of your reply, it seems to make
> sense that this isn't possible because DHCP (dhclient) has no way
> of evaluating the value of domain-name because it hasn't received
> an ACK in the first place.

The only reason to ever use an fqdn option is if you want the DHCP server to do a DNS update for you.   If you want the server to do a DNS update using a hostname provided by the client, and you do not want the client to provide a domain name, use the host-name option.   If you want the server to do its dns update using a hostname configured on the server, that's a server configuration issue, and requires no configuration on the client.   There is no reason why a client should ever take a hostname provided by the server and send it back to the server to make an update happen.

If what you are trying to do is configure the client's hostname based on what the server sent, that's a completely different thing, and isn't done through the configuration file, but rather through the client script.