title: codeigniter sess_destroy() not working properly,what m i doing wrong?
body: <p>I am a newbie in codeigniter. I am using an an login form to login as an admin. When the admin logs in with the correct user name and password s/he is directed to the home page with a session variable.and then if he clicks the log out button the session is supposed to be destroyed and redirect the user to log in page i.e log in form page.</p>
  
  <p>The 1st controller is admin:</p>
  
  <pre><code>&lt;?php
  class Admin extends CI_Controller
  {
      function index()
      {
          $data['main_content'] = 'admin/log_in';
          $this -&gt; load -&gt; view('includes/admin/admin_template', $data);
      }
      function log_in()
      {
          $this-&gt;load-&gt;model('admin_model');
          $query = $this -&gt; admin_model -&gt; validate();
          if ($query)// if the user's credentials validated...
          {
              $data = array('user_name' =&gt; $this -&gt; input -&gt; post('user_name'), 'is_logged_in' =&gt; true);
              $this -&gt; session -&gt; set_userdata($data);
              redirect('admin/home/admin_home');
          } else// incorrect username or password
          {
              $this -&gt; index();
          }
      }
      function log_out()
      {
          $this-&gt;session-&gt;sess_destroy();
          redirect('/admin/admin','refresh');
      }
  }
  </code></pre>
  
  <p>The second controller is the home controller:</p>
  
  <pre><code>&lt;?php
  class Home extends CI_Controller
  {
      function __construct()
      {
          parent:: __construct();
          $this-&gt;is_logged_in();
      }
      function is_logged_in() 
      {
          $is_logged_in = $this -&gt; session -&gt; userdata('is_logged_in');
          if (!isset($is_logged_in) || $is_logged_in != true)
          {
              $this -&gt; load -&gt; view('admin/forbidden');
          }
      }
      function admin_home()
      {
          $data['main_content'] = 'home_view';
          $this-&gt;load-&gt;view('admin/home_view');
      }
  }
  </code></pre>
  
  <p>The model is admin_model:</p>
  
  <pre><code>&lt;?php
  class Admin_model extends CI_Model
  {
      function __construct()
      {
          parent:: __construct();
      }
      function validate()
      {
              $this-&gt;db-&gt;where('user_name',$this-&gt;input-&gt;post('user_name'));
              $this-&gt;db-&gt;where('password', $this-&gt;input-&gt;post('password'));
              $query = $this-&gt;db-&gt;get('user');
              if($query-&gt;num_rows==1)
              {
                  return true;
              }
      }
  }
  </code></pre>
  
  <p>Now, it supposed the user to logout and destroy the session, but if I click the back button of my browser I can get page back which was supposed not to be and the session is not destroyed.
  please tell me what I am doing wrong here. I am using codeigniter 2.1.0.</p>