session_dureedevie

<?php

//Déclaration de la session
session_start();


//test si la variable existe
if(!isset($_SESSION['time'])){


//elle n' existe pas on la déclare
$_SESSION['time'] = time()+1200;


}

//test de la durée
if($_SESSION['time'] < time()){

        //destruction de la session
        session_unset();
	    session_destroy();

        //redirection
	    header("Location: ./index.php");
        exit();


}else{

//reste de ton code


}

?>

<?php
if( isset( $_REQUEST[session_name()] ) ) {
  session_start();
  if( ! isset( $_SESSION['logged'] ) ) {
    header('Location: http://' . $_SERVER['SERVER_NAME'] . '/' );
    exit;
  }
}
?>

<?php
require 'prepend.inc.php';
// .... le reste
?>

<?php
<?php
session_start();
$_SESSION['logged'] = true;
// la suite ...
?>