Почему не работают сессии?

[02-Dec-2018 14:29:28 UTC] PHP Warning:  ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home/****/public_html/index.php on line 4
[02-Dec-2018 14:29:28 UTC] PHP Warning:  session_start(): Cannot start session when headers already sent in /home/****/public_html/index.php on line 5

<?php
if(!session_id())
{
	ini_set('session.cookie_lifetime', 365 * 60 * 60 * 24);
	session_start();
}