Where are user session data usually stored?

User session data in PHP is usually stored on the server as files in a special directory (by default — the folder specified in the session.save_path setting).

When a user opens a session, PHP creates a unique session identifier (session ID), which is transmitted to the client as a cookie. On the server, all session data is stored under this ID.

It is also possible to store session data in a database or in memory (for example, Redis), if scalability or more flexible management is required.

Example of standard session usage in PHP:

session_start();
$_SESSION['user_id'] = 123;
// Data is stored on the server, the client only keeps the session ID