How to change a machines hostname in Red Hat 6

There are several ways to change the hostname of a machine running Redhat 6.  These also works on CentOS, Fedora and older/other Redhat variants.

First: The "hostname" command.

You can use the hostname command to see the current host name of the system.

# hostname
bighat.putorius.net


You can also use the hostname command to change the host name of the machine.

# hostname smallhat.putorius.net

Then issue the hostname command again to see the changes.
# hostname
smallhat.putorius.net


This only makes a temporary or non-persistent change of hostname.

Second: The /etc/sysconfig/network configuration file. (preferred method)

In order for the change to survive a reboot, or to make it persistent, you must change it in the /etc/sysconfig/network file.

Open the file in your favorite editor and change the following line to reflect your desired hostname.

HOSTNAME=newname.putorius.net

After making changing to the configuration file you need to restart the network service in order to read that file.

/etc/init.d/network restart

NOTE: Do not do this remotely (via ssh) or you will lose your connection.

If you issue the hostname command now, you will see the hostname has changed. 

Third: The /proc/sys/kernel/hostname entry.

Another simple way to change the hostname is to echo the hostname into the /proc/sys/kernel/hostname file.

echo "bighat.putorius.net" > /proc/sys/kernel/hostname

NOTE: Using the /etc/sysconfig/network file is the preferred method to set the permanent hostname of a system.  Anything in the /proc/sys/kernel/hostname file will be overridden by the /etc/sysconfig/network file during a reboot. 

If you are using Red Hat 7 (RHEL7), CentOS 7 or newed versions of Fedora click below of instructions on changing your hostname.
http://www.putorius.net/2015/04/how-to-change-system-hostname-in-red.html