When $_SESSION doesn’t work

What to do when the following error occurs when trying to use $_SESSION.
Notice: Undefined variable: _SESSION in /private/var/www/localhost/application/controllers/StatusController.php on line 72

In the php.ini file of Apache, I heard that session.auto_start should be set to 1.

http://www.crystal-creation.com/web-appli/technical-information/programming/php/session/session/