4.5. Check DNS

All hosts in your system must be configured for DNS and Reverse DNS.

If you are unable to configure DNS and Reverse DNS, you must edit the hosts file on every host in your cluster to contain the address of each of your hosts and to set the Fully Qualified Domain Name hostname of each of those hosts. The following instructions cover basic hostname network setup for generic Linux hosts. Different versions and flavors of Linux might require slightly different commands. Please refer to your specific operating system documentation for the specific details for your system.

4.5.1. Edit the Host File

Using a text editor, open the hosts file on every host in your cluster. For example:
```
vi /etc/hosts
```

Add a line for each host in your cluster. The line should consist of the IP address and the FQDN. For example:

1.2.3.4 fully.qualified.domain.name

	Note
Do not remove the following two lines from your host file, or various programs that require network functionality may fail. 127.0.0.1 localhost.localdomain localhost ::1 localhost6.localdomain6 localhost6

Note

Do not remove the following two lines from your host file, or various programs that require network functionality may fail.

127.0.0.1 localhost.localdomain localhost 
::1 localhost6.localdomain6 localhost6

4.5.2. Set the Hostname

Use the "hostname" command to set the hostname on each host in your cluster. For example:
```
hostname fully.qualified.domain.name
```
Confirm that the hostname is set by running the following command:
```
hostname -f
```
This should return the name you just set.

4.5.3. Edit the Network Configuration File

Using a text editor, open the network configuration file on every host. This file is used to set the desired network configuration for each host. For example:
```
vi /etc/sysconfig/network
```

Modify the HOSTNAME property to set the fully.qualified.domain.name.

NETWORKING=yes
NETWORKING_IPV6=yes
HOSTNAME=fully.qualified.domain.name

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