Configuring your host name and fully qualified domain name (FQDN) can be challenging. Many tutorials on the Internet are outdated and refer us to all kinds of different files. In this tutorial, I will show you how to permanently configure your hostname and FQDN on CentOS so that the following commands work as expected: This should return the hostname
. This should return the fully qualified domain name.
This should return
the domain name.
Quick explanation of terms
Just to make us clear about what we’re talking about, the FQDN (fully qualified
domain
name) looks like a subdomain address.
The hostname is the first part, followed by the domain name and a “.com” or “.net” or whatever. So, if we have the string:
it means that the hostname is “newhostname”, the domain is “dummyserver.com”, and the FQDN is “newhostname.dummyserver.com”. Note that the hostname is only a convention. There’s nothing stopping us from having the hostname the same as the FQDN itself (more on that later).
We
want to configure CentOS so that these values are returned by the regular
commands: hostname hostname -f hostname
- –
- d
Hostname configuration
We can get our current hostname by simply typing the command
:
On a new server like mine, all three commands return the following:
You can see that I have neither a domain name configured nor an FQDN. The host name value is stored in a file called
:
Here is the contents of that file as expected
:
Temporary hostname
change
We can temporarily change the hostname (transient hostname) using the command:
This will change the host name to “newname”, but the changes will not persist after a reboot. It also does not allow us to change the domain name, or obtain the FQDN. Here’s a screenshot of what it looks like after running the command
: 
This transient hostname does not persist after a reboot as shown here:
<img src="https://webhostinghero.org/wp-content/uploads/2017/07/after-reboot-hostname-reverted.jpg" alt=
“
” />
We return to where we started. So how do we make this change permanent?
Permanently
change the hostname
To make sure our hostname remains changed
, we use the following command:
When we run this command, it makes the change directly in /etc/hostname. You can see that the value has changed in the file
: 
We also see that it persists after a reboot:
<img src
=”https://webhostinghero.org/wp-content/uploads/2017/07/hostname-changes-are-permanent.jpg”
alt=”” />
Now we will see how to configure the domain name
and FQDN.
RedHat/RHEL recommendations regarding hostnames and FQDNs
It turns out that RedHat wants to eliminate the practice of having a host name separate from the FQDN. In your documentation, here’s what you have to say:
A hostname can be a freeform string up to 64 characters in length. However, Red Hat recommends that both static and transient names match the fully qualified domain name (FQDN) used for the machine in DNS, such as host.example.com.
It means that RedHat wants
your hostname to be something like:
instead of If you want to go ahead with your recommendations, you can simply set the hostname as FQDN and be done with it. However, note that the “hostname -d” and “hostname -f” commands will not work as expected. If, on the other hand, you want a separate domain name and FQDN, read on!
Configuring the
domain
name through the /etc/hosts file
Now that you have configured the hostname through the /etc/hostname file, we need to use the following file to set the FQDN
:
Open this using an editor like “vi” and add the following line at the end:
For a local test server like mine, Here is my entry /etc/hosts:
Save your changes. Now, when you run the “hostname -d” command, the system will parse the FQDN and return the domain name as expected. Here is the result of “hostname -f” and “hostname -d” after making the above changes in /etc/hosts:
And we’ve done it! These changes will persist after boot. We have managed to change our hostname, configure our FQDN and identify our domain name on CentOS/RHEL.