title: GC Warning when running PDFTK command in PHP script
body: <p>My PHP script generates a PDF using <code>pdftk</code>. When it runs <code>pdftk</code> I get the error status <code>134</code> and the pdf is not generated. Weirdly if I run that exact same <code>pdftk</code> command in SSH shell it works. </p>
  
  <p>What does the status code <code>134</code> mean? And what could be going wrong? </p>
  
  <p>My command:</p>
  
  <pre><code>$output = '';
  $status = -1;
  $res = exec("cd /home/USER/public_html/app; pdftk mht1939-1-rp_spl_form_hba1c.pdf fill_form ./tmp/58c5e762113c0.fdf output ./tmp/58c5e76211451.pdf flatten verbose", $output, $status);
  
  print($status);
  var_dump($output);
  </code></pre>
  
  <p>The error output is:</p>
  
  <pre><code>134 
  array(3) { [0]=&gt; string(36) "GC Warning: Couldn't read /proc/stat" [1]=&gt; string(39) "GC Warning: GC_get_nprocs() returned -1" [2]=&gt; string(29) "Couldn't read /proc/self/stat" }
  </code></pre>
  
  <p>Note the folder <code>tmp</code> has permissions <code>777</code> and the server is a CentOS 6.8 VPS. </p>