RedHat based systems 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.
Here is a sample:
/etc/sysconfig/network
NETWORKING=yes
HOSTNAME=myhost.mydomain.com
FORWARD_IPV4=yes
In order to preserve your change on system reboot, edit this file and enter the appropriate name using the HOSTNAME variable.