Start new or resume existing session

# session_start

(PHP 4, PHP 5, PHP 7, PHP 8)

session_start — Start new or resume existing session

### Description

session_start(array `$options` = []): bool

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.

### Parameters

`options`

  If provided, this is an associative array of options that will override the currently set session configuration directives. The keys should not include the `session.` prefix.

  In addition to the normal set of configuration directives, a `read_and_close` option may also be provided. If set to `true`, this will result in the session being closed immediately after being read, thereby avoiding unnecessary locking if the session data won't be changed.

### Return Values

This function returns `true` if a session was successfully started, otherwise `false`.

### Changelog

Version | Description
--- | ---
7.1.0 | session_start() now returns `false` and no longer initializes $_SESSION when it failed to start the session.

### Examples

#### A basic session example

Example #1 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 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>';
?>`

#### Providing options to session_start()

Example #3 Overriding the cookie lifetime

`<?php
// This sends a persistent cookie that lasts a day.
session_start([
'cookie_lifetime' => 86400,
]);
?>`

Example #4 Reading the session and closing it

`<?php
// If we know we don't need to change anything in the
// session, we can just read and close rightaway to avoid
// locking the session file and blocking other pages
session_start([
'cookie_lifetime' => 86400,
'read_and_close' => true,
]);`

### Notes

> Note:

> To use cookie-based sessions, session_start() must be called before outputting 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

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