When starting the Apache HTTP server on CentOS 7, you might encounter the error message "AH00558: httpd: Could not reliably determine the server's fully qualified domain name." This message indicates that Apache is unable to reliably determine the fully qualified domain name (FQDN) of the server. This issue often arises when the server's hostname is not properly configured or when the network is misconfigured. In this article, we'll discuss how to resolve this problem.

Causes of the Error

The error message "AH00558" indicates that Apache is attempting to identify the server's fully qualified domain name but is failing to do so. This could be due to several reasons:

• Unconfigured hostname: If the server lacks a configured hostname or if it's configured incorrectly.

• Missing or incorrect Apache configuration: Apache requires proper configuration to determine the FQDN.

Resolving the Issue

Step 1: Set the Server's Hostname

1. Check the current hostname using the command:

   hostnamectl
   ​

2. If the hostname needs to be changed, use:

   sudo hostnamectl set-hostname your_fully_qualified_domain_name
   ​

3. Replace your_fully_qualified_domain_name with the actual name you wish to use.

4. Edit the /etc/hosts file and add a record for the hostname if it's not already present. For example:

   127.0.0.1   localhost localhost.localdomain your_hostname
   ::1         localhost localhost.localdomain your_hostname
   ​

Here, replace your_hostname with the actual server name.

 

Step 2: Apache Configuration

1. Open the main Apache configuration file, usually located at /etc/httpd/conf/httpd.conf.

2. Add or modify the ServerName directive and set it to your FQDN or IP address so that Apache knows how to identify itself. For example:

   ServerName your_fqdn:80
   

 

Replace your_fqdn with the actual fully qualified domain name or IP address of the server.

3. After making changes, save the file and restart Apache to apply the new configuration:

   sudo systemctl restart httpd
   ​

Step 3: Verify Functionality

To verify that Apache no longer reports the error, you can run:

sudo apachectl configtest

If everything is configured correctly, you should see the message Syntax OK, indicating that Apache is properly configured and the error has been resolved.

 

The "AH00558" error during Apache startup on CentOS 7 is typically caused by an incorrectly set hostname or missing Apache configuration. Follow the above steps to correctly set the hostname and Apache configuration, which should resolve the issue. If the problem persists even after performing these steps, we recommend further diagnostics or consulting with an expert.