Ошибка xdebug_debug_zval: как исправить?

Question

[MakPET]

lamp-server
php7
ubuntu 14.04

<?php

$a = "new string";

xdebug_debug_zval($a);

Fatal error: Uncaught Error: Call to undefined function xdebug_debug_zval() in /var/www/html/test/index.php:5 Stack trace: #0 {main} thrown in /var/www/html/test/index.php on line 5