Diagnosing HTTP 500 / Internal Server Errors

Codebase Checks: PHP and WordPress

The most common cause of a 500 error is a fatal error within the website either due to a PHP error or a lack of PHP memory.

PHP errors can be caused by many things, including missing files and malware. The website Nginx/OpenLiteSpeed Error Logs are where you need to check.

1. Check the Nginx error log

You’ll find all of your website-specific error logs inside your website’s customizer. Head to the Sites page within your account and click on the name of the website you’re having trouble with to open the customizer. Next, click through to the logs tab:

You’ll find the Nginx error log at the bottom:

When checking the log, look for the errors that correspond to your timestamps.

2. Are there any Fatal Errors?

If yes, it will tell you whether it’s due to it being a PHP error or a lack of memory. If it’s a codebase error you will need to fix the error to resolve the issue. This may mean deactivating the plugin, or diving into PHP.

If the error is only happening on one page, or when doing something in the WordPress backend, also activate WordPress debug with the toggle at the top of the logs tab.

Check the following:

1. Check for Fatal PHP errors in the Nginx/OpenLiteSpeed Error Log (and WordPress debug log if it’s only happening on certain pages and not the whole website).
2. Check that WordPress core files aren’t in the wrong place – check for files that should be in /htdocs one level up where the wp-config.php lives.
3. Is there an additional wp-config.php file inside the /htdocs directory?
4. Is the PHP version is incompatible with the current codebase? Change the website’s PHP version to the previous version and check the error again.

A common cause is a lack of PHP memory, which you can increase directly inside your website’s customizer.

3. Did the 500 Error Occur after activating or deactivating a plugin?

If things went wrong after a plugin activation, deactivate the plugin (manually if necessary by connecting to your server over SFTP or SSH and renaming the plugins folder).

If things went wrong after a plugin deactivation, try restarting PHP.

4. Are all WordPress installation files OK?

Check that your website core files aren’t missing or corrupted – a missing or misplaced file can cause 500 errors.

You can run a check with the following command (replace site.url with your domain name):

gp wp site.url core verify-checksums

For example:

gp wp yourwebsite.com core verify-checksums

This will check your core WordPress installation files and let you know if there are any issues that need to be addressed. 

We rarely see 500 errors, but this is often the cause. A few examples we’ve seen are: 

1. wp-config.php was empty (unknown reason)
2. A wp-config.php was also inside the /htdocs directory
   More info: The wp-config.php Location at GridPane
3. index.php was missing (malware)
4. wp-settings.php was moved outside of the /htdocs directory (client mistake)