UPDATE 2017-03-21 CentOS 7 come with hostnamectl command, that allow you to easily set server hostname with out manually editing any of these files.
RedHat based system use the file /etc/sysconfig/network to read the saved hostname at system boot. This is set using the init script /etc/rc.d/rc.sysinit
NETWORKING=yes HOSTNAME="plain.domainname.com" GATEWAY="111.222.333.1" GATEWAYDEV="eth0" FORWARD_IPV4="yes"
TCP/IP Network Configuration Files
This configures Linux so that it knows which DNS server will be resolving domain names into IP addresses
search name-of-domain.com - Name of your domain or ISP's domain if using their name server nameserver XXX.XXX.XXX.XXX - IP address of primary name server nameserver XXX.XXX.XXX.XXX - IP address of secondary name server
Locally resolve node names to IP addresses
::1 localhost6.localdomain6 localhost6 # Do not remove the following line, or various programs # that require network functionality will fail. 111.222.333.444 yourname.server.com yourname 127.0.0.1 localhost
Configuration settings for your first ethernet port
DEVICE=eth0 BOOTPROTO=static BROADCAST=111.222.333.255 IPADDR=111.222.333.444 NETMASK=255.255.255.0 NETWORK=111.222.333.0 ONBOOT=yes
And to finalize , you need to restart your network
service network restart