title: VCHI initialization failed screen error when executing sh script from php
body: <p>I want to trigger the screen power on a raspberry pi from an simple <code>php</code> site.</p>
  
  <p>I'm using <code>apache 2</code> and <code>php7</code> on <code>raspbian</code> and the files are stored on <code>/var/www/html/controller</code> and all have chmod 777 set.</p>
  
  <p>this is how my php site looks:</p>
  
  <pre><code>&lt;?php
  if ($_GET['on']) {
      shell_exec("/var/www/html/controller/on.sh");
  }
  ?&gt;
  &lt;a href="?on=true"&gt;turn on&lt;/a&gt; 
  </code></pre>
  
  <p>and my <code>on.sh</code> file like this:</p>
  
  <pre><code>#!/bin/bash
  vcgencmd display_power 1
  </code></pre>
  
  <p>when I click the link I get the following error:</p>
  
  <blockquote>
    <p>VCHI initialization failed screen </p>
  </blockquote>
  
  <p>Any suggestions how to fix this?</p>