A reference guide to the most common Apache errors and their direct fixes, including Apache's distinctive "AH" (Apache HTTP) error codes.
500 Internal Server Error
Usually caused by a broken .htaccess file, a PHP fatal error, or incorrect file permissions.
sudo tail -f /var/log/apache2/error.logTest if the issue is .htaccess by temporarily renaming it:
mv .htaccess .htaccess.bak403 Forbidden
sudo chown -R www-data:www-data /var/www/yoursite
sudo chmod -R 755 /var/www/yoursiteAlso verify the <Directory> block includes:
Require all grantedAH00558: Could Not Reliably Determine the Server's Fully Qualified Domain Name
Harmless startup warning — set a global ServerName to silence it:
sudo nano /etc/apache2/apache2.confServerName localhostAH00013: Pre-configuration Failed / Syntax Error
Always validate before restarting:
sudo apache2ctl configtestThis reports the exact file and line number of the syntax error.
AH00526: Invalid Command (Module Not Loaded)
A directive from a module that isn't enabled. Enable it:
sudo a2enmod MODULE_NAME
sudo systemctl restart apache2Port 80 Already in Use
sudo ss -tulpn | grep :80Usually another web server (Nginx) is already bound to the port.
.htaccess Rules Not Working
Confirm AllowOverride All is set in the site's <Directory> block and that mod_rewrite is enabled:
sudo a2enmod rewrite
sudo systemctl restart apache2PHP Files Download Instead of Executing
sudo apt install libapache2-mod-php -y
sudo a2enmod php8.3
sudo systemctl restart apache2Adjust the PHP version to match what's installed.
Diagnostic Checklist
sudo apache2ctl configtest— validate config syntax firstsudo systemctl status apache2— confirm the service is actually runningsudo tail -f /var/log/apache2/error.log— the fastest path to the real cause- Check file/directory ownership and permissions for 403/500 errors
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- How to Install Apache on Ubuntu & Debian
- Apache Virtual Hosts: Hosting Multiple Websites
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