Maybe this helps
<?php
/ set the cache limiter to 'private' /
session_cache_limiter('private');
$cache_limiter = session_cache_limiter();
/ set the cache expire to 30 minutes /
session_cache_expire(30);
$cache_expire = session_cache_expire();
/ start the session /
session_start();
echo "The cache limiter is now set to $cache_limiter<br />";
echo "The cached session pages expire after $cache_expire minutes";
?>