title: chdir in php can't work
body: <p>I want to change directory using <code>chdir</code> in php, because i need to execute command in Linux.
  My current directory is <code>/var/www/httpdocs/website/admin</code>,I want to go to httpdocs's sub_directory <code>docs</code>.I use absolute path like:<br></p>
  
  <pre><code>chdir("/var/www/httpdocs/docs");
  </code></pre>
  
  <p>but it does't work.</p>
  
  <p>I only can get website using : <code>chdir("../");</code>
  or get admin's sub_directory <code>images</code> using : <code>chdir("/var/www/httpdocs/website/admin/images");</code></p>
  
  <p>but I can't get <code>httpdocs</code>.
  what's wrong?</p>
  
  <p>Any tips would be appreciated.</p>