Php sessions being lost - php

Question

I do the following to set my session, this works because the echo appears. but when I go to the next page or another the session is not there? what am I doing wrong?
$session_start();
if ($username==$dbusername&&$password==$dbpassword)
{
echo"<b>Login Successful</b><br><a href='systemadmin.html'><br>Click here to access the <strong>System Admin Page</strong></a>";
$_session['username']=$dbusername;
if($username == "admin")
{
$_session['admin'] = true;
}
I am trying to get the following to work with these sessions:
<?php
session_start();
if($_session['admin'] == true)
{
// do nothing
}else{
header( 'Location: home.html' ) ;
}
?>
Update:
the uppercase sessions work but now the sessions arent destroying when i use the logout.php
<?php
session_start();
session_destroy();
header("location: home.html");
?>

Answer 1

$_session should be => $_SESSION.
http://php.net/manual/en/reserved.variables.session.php
The first works because you are setting a 'normal' variable (which is available for the request).
UPDATE
To destroy the session:
<?php
// Initialize the session.
// If you are using session_name("something"), don't forget it now!
session_start();
// Unset all of the session variables.
$_SESSION = array();
// If it's desired to kill the session, also delete the session cookie.
// Note: This will destroy the session, and not just the session data!
if (ini_get("session.use_cookies")) {
$params = session_get_cookie_params();
setcookie(session_name(), '', time() - 42000,
$params["path"], $params["domain"],
$params["secure"], $params["httponly"]
);
}
// Finally, destroy the session.
session_destroy();
?>
http://php.net/manual/en/function.session-destroy.php#example-4368
Additionaly you should always use exit(); after you do a redirect to prevent further execution of the script.

Answer 2

PHP Server/Session/Global variables are case sensitive. To PHP, $_SESSION is NOT the same variable as $_session, even though to you in English, they seem to be. You must use $_SESSION, not $_session in order to access the PHP Session variables as you are expecting.

Answer 3

You have to use exit(); after the header(); because the script doesn't always end right after the user redirects to a new page.

Answer 4

The name of the superglobal is $_SESSION in uppercase letters. Try changing that and see if it helps.