Trying to understand FQDN's

I am struggling to understand the FQDN for servers.

At the moment mine is just localhost if i type hostname in to my server terminal it just says localhost.

I understand you need a different one from this if you want to set up cpanel, or postfix or anything really.

As i know its comprised of two parts:

hostname.domainname

can domain name be made up, or does it have to be one of your domains that is set up for use on your server?

and host name can be anything, or it has to be the servername? and does it have to be set up as a sub domain of the domain?

I hope you understand my issues.

Thanks

Solution

Try typing

hostname --fqdn

FQDN means Fully Qualified Domain Name, composed mainly of two parts:

Your hostname
The domain name where your hostname is located.

It can be as easy as mycomputername.myfamilydomainname.tld, or as complex as cor-th3-1.par.fr.eu.mynetwork.net.

All of this can technically be made up, though, if you use for example, google.com as local domain, your local resolver may use this info and believe you're in the google.com DNS zone, you may then have problems resolving entries that are in the google.com DNS zone.

More info at: http://en.wikipedia.org/wiki/Hostname