Step 1 - Check your Current Hostname

Check the Hostname with hostname Command.

$ hostname
oxygen

Step 2 - Change Hostname with hostnamectl Command

Change the Hostname from oxygen to hydrogen.

$ sudo hostnamectl set-hostname hydrogen

Step 3 - Update /etc/hosts

Use your favorite text editor to change any instances of your old hostname to the new hostname in /etc/hosts. If you have a DNS name pointed to this instance, it's a best practice to also set that name here.

$ sudo nano /etc/hosts

From:

127.0.0.1 localhost
127.0.1.1 oxygen

To:

127.0.0.1 localhost
127.0.1.1 hydrogen.example.com hydrogen

Step 4 - Confirm the Change

Reboot the Server.

Test your change with hostname.

$ hostname
hydrogen