PHP Sessions

title: Sessions


Sessions are a feature in PHP that allow you to store data server side about a user. When a session is setup, a browser cookie is set which identifies the user to PHP so the PHP knows which server side variables to access.

Starting A Session

On every page you want to access the session you will need to start (or load) the session. To do so run the session_start() function which loads the PHP Session System.

<?php session_start();

Please note, that when using cookie-based sessions, session_start() must be called before outputing anything to the browser. anything else will result in an error.

Accessing And Setting Data In A Session

The $_SESSION['key'] variable is a special type of array (using a browser cookie to determine which session to access).

In the below example you see the user’s choice of theme is set to theme number one.

<?php session_start(); $_SESSION['themechoice'] = 1;

Accessing a session variable is similar to setting one. Simply include the variable where it needs to be accessed. For example echoing it out as shown in the code example below.

<?php session_start(); echo $_SESSION['themechoice'];

Removing A Session

To remove a session from the system run the following PHP code. It will unset the session variables and delete it from the system.

<?php session_unset(); session_destroy();

Here’s a full example to manually expire a user’s session:

<?php //Start our session. session_start(); //Expire the session if user is inactive for 30 //minutes or more. $expireAfter = 30; //Check to see if our "last action" session //variable has been set. if(isset($_SESSION['last_action'])){ //Figure out how many seconds have passed //since the user was last active. $secondsInactive = time() - $_SESSION['last_action']; //Convert our minutes into seconds. $expireAfterSeconds = $expireAfter * 60; //Check to see if they have been inactive for too long. if($secondsInactive >= $expireAfterSeconds){ //User has been inactive for too long. //Kill their session. session_unset(); session_destroy(); } } //Assign the current timestamp as the user's //latest activity $_SESSION['last_action'] = time();

Sessions Are Temporary

It is important to not treat a session as permanent storage. They get cleared from time to time by the developer, whenever the application is moved to a new host server, by the application itself (for example a logout button), and even during server maintenance. For long term storage of data make sure to use a database.


Last but not least it’s important to use php sessions securely. Read our article on Session Identifier Acquirement and Session Hijacking for more information.

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