How to trace what is causing WordPress error 500?

Question

Internal error 500 is such a general error and nothing shows up in the logs under /wordpress/error_log. Is there a way to get a stack trace of where the crash is occurring? In ASP.NET it is so easy because a stack trace, code snippet, and line number all show up in the error page. Any help would be greatly appreciated.

Solution

Turn on php errors in your php.ini or add this line to your .htacess file in your webroot:

php_flag display_errors on

Comments

[Bill]

Done both of these things and I still have no errors, just a default "Internal Server Error" page served up by my web browser.

[Mark]

@Bill (or anyone else coming along) - WordPress does funny stuff with error reporting based on constants. Look into the WP_DEBUG, WP_DEBUG_LOG, and WP_DEBUG_DISPLAY constants. For example in 4.7.3, WordPress will explicitly turn off display_errors, overriding your environment settings, if you have WP_DEBUG on but not WP_DEBUG_DISPLAY.

[Mark]

By contrast, WP_DEBUG_LOG = true will cause WordPress to clobber your error_log setting, pointing it to wp-content/debug.log instead, whereas WP_DEBUG_LOG = false (or omitted) will leave your error_log and log_errors alone.