Apache HTTP Server Error Code AH00558: How to Fix It

Easy 5-10 minutes Low Severity Verified June 2026
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Error Code
AH00558 Could Not Reliably Determine Server FQDN
Brand
Apache HTTP Server
Product Type
dev_tool
Severity
Low
DIY Difficulty
Easy
Estimated Fix Time
5-10 minutes
Apache HTTP Server error AH00558 occurs when the server cannot determine its Fully Qualified Domain Name (FQDN) because the ServerName directive is missing from the configuration file. This is a common configuration issue that prevents Apache from starting properly or causes warning messages during startup.
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Tools You'll Need

How to Fix Error Code AH00558 Could Not Reliably Determine Server FQDN

  1. Locate the Apache Configuration File

    Always backup your configuration file before making changes

  2. Open the Configuration File

  3. Find or Add the ServerName Directive

  4. Set the Correct Port Number

  5. Test the Configuration

  6. Restart Apache Service

  7. Verify the Fix

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When to Call a Professional

Contact a system administrator or web hosting provider if you don't have administrative access to the server, if the configuration file is missing or corrupted, or if you're working with a production server and are unfamiliar with Apache configuration management.

Frequently Asked Questions

What does Apache error AH00558 mean?
Apache error AH00558 means the server cannot reliably determine its Fully Qualified Domain Name (FQDN) because the ServerName directive is missing or incorrectly configured in the Apache configuration file.
Can I use localhost as the ServerName?
Yes, you can use 'ServerName localhost:80' for local development environments. For production servers, use your actual domain name like 'ServerName example.com:80'.
Will this error prevent my website from working?
The AH00558 error typically doesn't prevent websites from functioning, but it can cause warning messages during Apache startup and may lead to issues with certain features that rely on the server's FQDN.
Where should I place the ServerName directive?
Place the ServerName directive in the global server configuration section of your httpd.conf or apache2.conf file, outside of any VirtualHost blocks, typically near the top of the file after the Listen directives.
Do I need to restart Apache after fixing AH00558?
Yes, you must restart the Apache service after adding or modifying the ServerName directive for the changes to take effect and resolve the AH00558 error.

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