How to fix "Could not reliably determine the server’s fully qualified domain name" warning in Apache

When starting or restarting the Apache web server, you might see a warning message about the server’s fully qualified domain name (FQDN). This warning occurs because Apache tries to identify the FQDN but fails, defaulting to an IP address like 127.0.1.1 instead. The warning doesn’t affect Apache's functionality but can be undesirable for system administrators.

Could not reliably determine the server’s fully qualified domain name, using 127.0.1.1 for ServerName.

The FQDN is important for identifying the server on a network. Without a proper FQDN, Apache cannot correctly associate the server with its intended domain name. This leads to a fallback on a loopback address, which isn’t optimal for production environments.

To fix this issue, you need to set the ServerName directive in the Apache configuration file. This ensures that Apache uses the correct FQDN or IP address, eliminating the warning and ensuring proper server behavior.

1. Open the Apache main configuration file using your preferred text editor.

   $ sudo vi /etc/apache2/apache2.conf
   Password:

   Related: Location for Apache main configuration file

2. Add the ServerName directive, followed by the FQDN or IP address of your server.

   ServerName your-server-name

3. Save and close the file.
4. Test the configuration to ensure there are no syntax errors.

   $ sudo apache2ctl configtest

5. If the output displays “Syntax OK”, proceed to the next step. Otherwise, correct any indicated errors and retest.
6. Restart or reload the Apache service to apply the changes.

   $ sudo systemctl restart apache2 #Ubuntu, Debian, openSUSE, and SLES
   $ sudo systemctl restart httpd #CentOS and Red Hat

   Related: How to manage the Apache web server service

7. Start or restart the Apache service again and ensure the warning message no longer appears.

   $ sudo systemctl start apache2