How to Fix WordPress 500 Internal Server Error

1. The Immediate Diagnostic: Enable WP_DEBUG

Since a 500 error hides the actual PHP failure, you must force WordPress to reveal it.

• The Action: Edit your wp-config.php file and find the line define( 'WP_DEBUG', false );.
• The Fix: Change it to:PHPdefine( 'WP_DEBUG', true ); define( 'WP_DEBUG_LOG', true ); define( 'WP_DEBUG_DISPLAY', false );
• Result: This creates a debug.log file inside the /wp-content/ folder. Check this file immediately; it will tell you exactly which file and which line of code triggered the fatal error.

2. Check the .htaccess File for Corruption

A common cause of 500 errors is a syntax error in your server configuration file, often caused by a redirection or security plugin.

• The Action: Connect via FTP or File Manager and rename your .htaccess file to .htaccess_old.
• The Fix: Try loading your site. If it works, the issue was in that file. Go to Settings > Permalinks in your dashboard and click “Save Changes” to generate a fresh, clean .htaccess file.

3. Increase the PHP Memory Limit

If the error occurs only when you try to perform a specific task (like uploading a large image or accessing the dashboard), you are likely hitting the memory ceiling.

• The Action: Add the following line to your wp-config.php file, just before the “That’s all, stop editing” message:define( 'WP_MEMORY_LIMIT', '256M' );
• Server Level: You may also need to increase the memory_limit in your php.ini file on the VPS.

4. Deactivate All Plugins (The “Binary Search” Method)

If the logs didn’t point to a specific file, a plugin conflict is the most likely culprit.

• The Action: Rename the /wp-content/plugins/ folder to /plugins_old/.
• The Fix: If the site loads, rename the folder back to plugins and reactivate them one by one until the site breaks again. This identifies the specific “poisoned” plugin.

5. Re-upload Core Files

Sometimes, a failed update or a server glitch can corrupt the core WordPress files themselves.

• The Action: Download a fresh copy of WordPress from WordPress.org.
• The Fix: Upload the /wp-admin/ and /wp-includes/ folders to your server, overwriting the old ones. Do not touch the wp-content folder or wp-config.php.

6. Check Server Error Logs

If none of the above works, the issue is likely at the server level (NGINX/Apache), not the application level.

• The Action: Check your NGINX or Apache error logs (usually located in /var/log/nginx/error.log or /var/log/apache2/error.log).
• What to Look For: Look for “mod_rewrite” errors or “Permission denied” messages. If you see “Permission denied,” reset your ownership with:sudo chown -R www-data:www-data /var/www/html