We're running a simple Symfony script, that at random returns a mistake 500. The machine administrator states he aren't able to find any trace of the Error 500 around the error logs, however using Curl or Firebug, it's apparent that the Error 500 has been came back.

The script simply parses a Publish request posted for an URL on our server. We already checked for performance, memory etc but nothing appears to become the issue.

How's this possible? We already enabled all debugging, logging, on Apache, PHP, etc and absolutely nothing.

The next testscript also will not generate any error messages/logs.

<?php
header($_SERVER['SERVER_PROTOCOL'].' 500 Internal server error');
echo 'Something went gaga';
?>

Nevertheless the access_log can have the "500" response code (presuming apache's default access_log configurations)

Search the code for "HTTP/1.1 500", "500" or "header(" and add:

trigger_error('Peep', E_USER_NOTICE);  // or error_log()

This can generate an entry within the errorlog (with filename and line-amounts)