Search the initialize.php . Special feature for symlinks.

gistfile1.php

<?php 

/**
 * Initialize the system
 */
$dir = dirname(isset($_SERVER['SCRIPT_FILENAME']) ? $_SERVER['SCRIPT_FILENAME'] : __FILE__);

while ($dir && $dir != '.' && $dir != '/' && !is_file($dir . '/system/initialize.php')) {
	$dir = dirname($dir);
}

if (!is_file($dir . '/system/initialize.php')) {
	header("HTTP/1.0 500 Internal Server Error");
	header('Content-Type: text/html; charset=utf-8');
	echo '<h1>500 Internal Server Error</h1>';
	echo '<p>Could not find initialize.php!</p>';
	exit(1);
}

define('TL_MODE', 'BE');
require($dir . '/system/initialize.php');