session_start — Starting a New Session or Reusing an Existing Session (PHP)

session_start() creates a new session or reuses an existing one. If a session ID is submitted via GET, POST, or a cookie, the existing session is reused.

When a session starts automatically or manually via session_start(), PHP calls the session manager's open and read callbacks. The manager may be the default, an extension (e.g., SQLite or Memcached), or a user‑defined handler set with session_set_save_handler(). The read callback returns serialized session data, which PHP automatically unserializes into the $_SESSION superglobal.

Parameters

options – an associative array that, if provided, overrides configuration directives; keys need not include the session. prefix.

Return value

On success, the function returns TRUE; otherwise it returns FALSE.

Example

<?php
// page1.php
session_start();
echo 'Welcome to page #1';
$_SESSION['favcolor'] = 'green';
$_SESSION['animal'] = 'cat';
$_SESSION['time'] = time();
// If using cookie to transmit the session ID
echo '<br /><a href="page2.php">page 2</a>';
// If not using cookie, transmit the session ID via URL rewriting
echo '<br /><a href="page2.php?' . SID . '">page 2</a>';
?>