Permanent hostname change on RedHat based systems

From MDLog:/sysadmin:
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
/etc/sysconfig/network:

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NETWORKING=yes HOSTNAME="plain.domainname.com" GATEWAY="192.168.0.1" GATEWAYDEV="eth0" FORWARD_IPV4="yes"

So in order to preserve your change on system reboot edit this file and enter the appropriate name using the HOSTNAME variable.