Change your Hostname without Rebooting in RedHat Linux

cd /etc/sysconfig
vi network

Look for the HOSTNAME line and replace it with the new hostname you want to use. In this example I want to replace localhost with redhat9.

HOSTNAME=redhat9

When you are done, save your changes and exit vi. Next we will edit the /etc/hosts file and set the new hostname.
vi /etc/hosts

In hosts, edit the line that has the old hostname and replace it with your new one.

192.168.1.110  redhat9

Save your changes and exit vi. The changes to /etc/hosts and /etc/sysconfig/network are necessary to make your changes persistent (in the event of an unscheduled reboot).
Now we use the hostname program to change the hostname that is currently set.
hostname redhat9
And run it again without any parameters to see if the hostname changed.
hostname

Finally we will restart the network to apply the changes we made to /etc/hosts and /etc/sysconfig/network.
service network restart

To verify the hostname has been fully changed, logout of your system and you should see your new hostname being used at the login prompt and after you've logged back in.

Quick, painless, and you won't lose your server's uptime.

Step # 1: Change Hostname

You need to update two files:

1. Linux Distribution specific file. Edit appropriate file as per your distribution as follows.
2. /etc/hosts

Redhat / CentOS / Fedora: Change Hostname

Edit /etc/sysconfig/network, enter:

vi /etc/sysconfig/network

Set HOSTNAME=newhost.example.com, enter:

HOSTNAME=server2.nixcraft.com

Save and close the file. Type the following command:

hostname server2.nixcraft.com
hostname

Now, proceed to step # 2.

Step #2: Update /etc/hosts

Now, you need to edit /etc/hosts file, enteR:

vi /etc/hosts

127.0.0.1       localhost.localdomain   localhost
::1     localhost6.localdomain6 localhost6
192.168.67.129  server2.nixcraft.com server2