On Wed, Nov 29, 2006 at 02:20:03PM -0800, Ian Anderson enlightened us:
/etc/sysconfig/network is what assigns the hostname to your particular server. This is also where CentOS writes the hostname when you initially install the OS.
/etc/hosts provides a mechanism for mapping that hostname to an IP address. This is one of several ways to map ip's to hostnames.
I use /etc/sysconfig/network to "name" my machines and then enter that value into /etc/hosts. i.e.
/etc/sysconfig/network HOSTNAME="vpn-gateway"
/etc/hosts 127.0.0.1 localhost localhost.localdomain 10.0.0.1 vpn-gateway vpn-gateway.mydomain.com
the second entry is an "alias" to vpn-gateway. If you were to ping either one you would get a response from 10.0.0.1.
There is an order of operations that CentOS uses to resolve host names. By default the first attempt is in the hosts file. If it doesn't find anything there is will try DNS, if nothing is there it will try WINS, and so on. If you have a DNS server in your network you could add a record to resolve vpn-gateway.mydomain.com to 10.0.0.1 and not fill in a /etc/hosts value at all. (Providing /etc/resolv.conf is setup to look at that DNS server)
Someone correct me if I am wrong, but this is what I understand to be correct.
Not to pick nits, but according to the hosts manpage, you have your aliases and FQDN's backwards:
For each host a single line should be present with the following information:
IP_address canonical_hostname aliases
And it is /etc/nsswitch.conf that determines the order of search. By default this is files (e.g. /etc/hosts) then dns, and there may be others like ldap or nis depending on how you set up the machine.
Matt