note 18940 deleted from function.session-id by nicos

It isn't a good idea to call session_id(SID) as suggested above, because the SID contains not only the session id but also the session name and equal sign, for instance it may have something like "PHPSESSION=0adaf898da38c8c2066386dfd1eeb08astant ". OTOH, if you want to use a session id that comes from an URL, and you want to override any session id that could stored as a cookie, what you should do is something like : session_id($HTTP_GET_VARS[session_name()]) (provided you have track_vars enabled)