Session Handling

Introduction

Session support in PHP consists of a way to preserve certain data across subsequent accesses.

A visitor accessing your web site is assigned a unique id, the so-called session id. This is either stored in a cookie on the user side or is propagated in the URL.

The session support allows you to store data between requests in the $_SESSION superglobal array. When a visitor accesses your site, PHP will check automatically (if session.auto_start is set to 1) or on your request (explicitly through session_start()) whether a specific session id has been sent with the request. If this is the case, the prior saved environment is recreated.

Caution

If you turn on session.auto_start then the only way to put objects into your sessions is to load its class definition using auto_prepend_file in which you load the class definition else you will have to serialize() your object and unserialize() it afterwards.

$_SESSION (and all registered variables) are serialized internally by PHP using the serialization handler specified by the session.serialize_handler ini setting, after the request finishes. Registered variables which are undefined are marked as being not defined. On subsequent accesses, these are not defined by the session module unless the user defines them later.

Warning

Because session data is serialized, resource variables cannot be stored in the session.

The php and php_binary serialize handlers place restrictions on root-level keys in $_SESSION. Nested keys inside arrays or objects stored in the session are not subject to these restrictions. The following root-level keys are not allowed:

Numeric keys (for example $_SESSION[0]). Such keys are skipped when the session is written, and a warning is emitted.
String keys that contain | when using the php serialize handler. Using such a key causes session write failure (and a warning as of PHP 8.5.0).

The php_serialize handler does not have these limitations, and may be used when numeric keys or keys containing | must be stored at the root of $_SESSION.

Note:
Please note when working with sessions that a record of a session is not created until a variable has been registered by adding a new key to the $_SESSION superglobal array. This holds true regardless of if a session has been started using the session_start() function.

Installing/Configuring
Predefined Constants
Examples
Session Upload Progress
Sessions and Security
- Session Management Basics
- Securing Session INI Settings
Session Functions
- session_abort — Discard session array changes and finish session
- session_cache_expire — Get and/or set current cache expire
- session_cache_limiter — Get and/or set the current cache limiter
- session_commit — Alias of session_write_close
- session_create_id — Create new session id
- session_decode — Decodes session data from a session encoded string
- session_destroy — Destroys all data registered to a session
- session_encode — Encodes the current session data as a session encoded string
- session_gc — Perform session data garbage collection
- session_get_cookie_params — Get the session cookie parameters
- session_id — Get and/or set the current session id
- session_module_name — Get and/or set the current session module
- session_name — Get and/or set the current session name
- session_regenerate_id — Update the current session id with a newly generated one
- session_register_shutdown — Session shutdown function
- session_reset — Re-initialize session array with original values
- session_save_path — Get and/or set the current session save path
- session_set_cookie_params — Set the session cookie parameters
- session_set_save_handler — Sets user-level session storage functions
- session_start — Start new or resume existing session
- session_status — Returns the current session status
- session_unset — Free all session variables
- session_write_close — Write session data and end session
SessionHandler — The SessionHandler class
- SessionHandler::close — Close the session
- SessionHandler::create_sid — Return a new session ID
- SessionHandler::destroy — Destroy a session
- SessionHandler::gc — Cleanup old sessions
- SessionHandler::open — Initialize session
- SessionHandler::read — Read session data
- SessionHandler::write — Write session data
SessionHandlerInterface — The SessionHandlerInterface class
- SessionHandlerInterface::close — Close the session
- SessionHandlerInterface::destroy — Destroy a session
- SessionHandlerInterface::gc — Cleanup old sessions
- SessionHandlerInterface::open — Initialize session
- SessionHandlerInterface::read — Read session data
- SessionHandlerInterface::write — Write session data
SessionIdInterface — The SessionIdInterface interface
- SessionIdInterface::create_sid — Create session ID
SessionUpdateTimestampHandlerInterface — The SessionUpdateTimestampHandlerInterface interface
- SessionUpdateTimestampHandlerInterface::updateTimestamp — Update timestamp
- SessionUpdateTimestampHandlerInterface::validateId — Validate ID