How to create and save a unique session ID?

Question

PHP

Hello.
Please tell me how it is possible to generate a unique ID for each visitor when entering the site (a number, a set of numbers, for example), write this ID into the session $_SESSION['newid'] = 12345and so that this session lives until either the cache in the browser is reset or unset occurs.
$_SESSION['id']- does not fit, you need your own.