title: Yii2: disable warning log message "Session is already started"
body: <p>There are a lot of messages in my <code>'app.log'</code> file with content:</p>
  
  <pre><code>2018-03-28 12:23:55 [66.70.168.171][-][-][warning][yii\web\Session::init] Session is already started
  </code></pre>
  
  <p><strong>Question:</strong> how to prevent this warning message from writing into log file?</p>
  
  <p>I've tried to add <code>'except'</code> element in <code>'targets'</code>:</p>
  
  <pre><code>'targets' =&gt; [
              [
                  'class' =&gt; 'yii\log\FileTarget',
                  'levels' =&gt; ['error', 'warning'],
                  'except' =&gt; [
                      'yii\web\Session', //here it is
                  ],
              ],
  </code></pre>
  
  <p>But no success.</p>