PHP 4, PHP 5, PHP 7, PHP 8
session_start - Start new or resume existing session
Code Examples

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.



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.



To use cookie-based sessions, session_start must be called before outputting anything to the browser.


Use of zlib.output_compression is recommended instead of ob_gzhandler


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


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

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