[CentOS] 6.2 How to change hostname for each individual IP

[Lamar Owen]

On Friday, April 06, 2012 09:18:27 AM Jonathan Vomacka wrote:
> No matter what I do when I connect to the application it read 
> "example.example.org" which is the hostname of the machine rather then 
> the hostname I want it to read on a particular IP. Is this possible to 
> change?

Well, it probably isn't.  Hostnames should not be confused with FQDN's that map to IP addresses; they are different (even though CentOS will by default grab its hostname from reverse DNS if it gets its main interface's IP address by DHCP (in the case of multiple interfaces, there is a preferred interface that will assign the hostname)).

Hostnames belong to the host OS.  FQDN's belong to their respective IP addresses; and IP addresses belong to their respective interfaces, not to the host.  I know that's splitting hairs, but you're hitting the very corner case that splits this particular hair.  The host itself does not have an IP address.  Even in the case of a non-localhost-addressed loopback, the IP address belongs to the loopback interface, not to the host.

This has been true for a very long time;  I've run multiple alias interfaces since kernel 2.0 days on Red Hat Linux 4.1 (not RHEL, but old RHL), and this has been the behavior for at least that long.

A host can only have one name (this is true for basically any IP host, whether it's a Linux system, a BSD system, a Windows system, or a Cisco router.  Especially on a router with a lot of interfaces (broadband aggregation routers, for instance, can have thousands of interfaces with each one having a unique IP) you don't want the name of the IP associated with the interface to override the hostname.  And the hostname does not have to match what DNS says about the FQDN that belongs to any interface on the system (I have a few of those, too).

Now, I can't quote RFC 'chapter and verse' on this, but I have never seen a system where you could do what you're describing.  (that doesn't mean they don't exist, just that I've not seen one in my limited experience of AT&T Unix SVR2, Xenix V7 and SIII, Apollo DomainOS, and Solaris).