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:
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.
