In some case you should need to change your exsisting hostname on your linuxYou need to edit below files(you can use vi editor)  than you need to reebot your system to can change your hostname permanently

1. /etc/hosts

2. /etc/sysconfig/network

3. /etc/sysconfig/network-scripts/ifcfg-eth0 (depends on NIC name)

then reboot.

Ps: If you have Oracle E-Business Suite and if you want to change hostname you need to follow below metalink documents:

How to change the hostname and/or port of the Database Tier using AutoConfig [ID 338003.1]
How to change the hostname of an Applications Tier using AutoConfig [ID 341322.1]