3 step for change hostname to RHEL Linux:
1. edit: /etc/hosts
127.0.0.1 srv03.mil1.wide-net.org localhost.localdomain localhost
2. edit: /etc/sysconfig/network
HOSTNAME=srv03.mil11.wide-net.org
3. past into kernel new hostname
echo "srv03.mil1.wide-net.org" > /proc/sys/kernel/hostname
Or
sysctl kernel.hostname=srv03.mil1.wide-net.org
Consider a restart net services /etc/init.d/network restart but is not strictly required.