session_set_save_handler
session_status
Session Functions
PHP Manual

# session_start

(PHP 4, PHP 5)

session_start — Start new or resume existing session

### Description

bool session_start ( void )

session_start() creates a session or resumes the current one based on a session identifier passed via a GET or POST request, or passed via a cookie.

When session_start() is called or when a session auto starts, PHP will call the open and read session save handlers. These will either be a built-in save handler provided by default or by PHP extensions (such as SQLite or Memcached); or can be custom handler as defined by session_set_save_handler(). The read callback will retrieve any existing session data (stored in a special serialized format) and will be unserialized and used to automatically populate the $_SESSION superglobal when the read callback returns the saved session data back to PHP session handling.

To use a named session, call session_name() before calling session_start().

When session.use_trans_sid is enabled, the session_start() function will register an internal output handler for URL rewriting.

If a user uses ob_gzhandler or similar with ob_start(), the function order is important for proper output. For example, ob_gzhandler must be registered before starting the session.

### Return Values

This function returns `TRUE` if a session was successfully started, otherwise `FALSE`.

### Changelog

Version | Description
--- | ---
5.3.0 | If a session fails to start, then `FALSE` is returned. Previously `TRUE` was returned.
4.3.3 | As of PHP 4.3.3, calling session_start() after the session was previously started will result in an error of level `E_NOTICE`. Also, the second session start will simply be ignored.

### Examples

Example #1 A session example: page1.php

`<?php
// page1.php
session_start();
echo 'Welcome to page #1';
$_SESSION['favcolor'] = 'green';
$_SESSION['animal'] = 'cat';
$_SESSION['time'] = time();
// Works if session cookie was accepted
echo '<br /><a href="page2.php">page 2</a>';
// Or maybe pass along the session id, if needed
echo '<br /><a href="page2.php?' . SID . '">page 2</a>';
?>`

After viewing page1.php, the second page page2.php will magically contain the session data. Read the session reference for information on propagating session ids as it, for example, explains what the constant `SID` is all about.

Example #2 A session example: page2.php

`<?php
// page2.php
session_start();
echo 'Welcome to page #2<br />';
echo $_SESSION['favcolor']; // green
echo $_SESSION['animal']; // cat
echo date('Y m d H:i:s', $_SESSION['time']);
// You may want to use SID here, like we did in page1.php
echo '<br /><a href="page1.php">page 1</a>';
?>`

### Notes

> Note:

> To use cookie-based sessions, session_start() must be called before outputing anything to the browser.

> Note:

> Use of zlib.output_compression is recommended instead of ob_gzhandler()

> Note:

> This function sends out several HTTP headers depending on the configuration. See session_cache_limiter() to customize these headers.

### See Also

- $_SESSION
- The session.auto_start configuration directive
- session_id() - Get and/or set the current session id

session_set_save_handler
session_status
Session Functions
PHP Manual