Во первых, не:
PHP код:
<?php
$filename = "/var/www/html/index.php";
$fp = fopen($filename, 'r');
$buf = fread($fp, filesize($filename));
fclose($fp);
echo $buf;
?>

а:
PHP код:
<?php
$buf = file_get_contents('/var/www/html/index.php');
echo $buf;
?>