[PHP] how to see all sessions sets in server

[Farzan Dalaee]

hi
i want to write online user module for my site and i want to check
$_SESSION['userID'] to find all users id who loged in
but when i echo this code its return only current user detail
how i can see all sessions?

foreach($_SESSION as $k => $v)
{
echo $k."----------".$v;
}
 or how i handle online users?