title: Getting "Unable to determine system type - response: 500 Unknow command" when listing files on ESP8266 with Apache Commons Net
body: <p>I try to connect to FTP server in <code>ESP8266</code>. Connection is successful, but I can't get list of files on the server. </p>
  
  <p>My code is:</p>
  
  <pre><code>FTPClient mFtpClient = new FTPClient();
  mFtpClient.setConnectTimeout(10000);
  mFtpClient.connect(InetAddress.getByName(ip));
  status = mFtpClient.login(userName, pass);
  Log.e("isFTPConnected", String.valueOf(status));
  if (FTPReply.isPositiveCompletion(mFtpClient.getReplyCode())) {
      mFtpClient.setFileType(FTP.BINARY_FILE_TYPE);
      mFtpClient.enterLocalPassiveMode();
      FTPFile[] mFileArray = mFtpClient.listFiles();
      Log.e("Size", String.valueOf(mFileArray.length));
  }
  </code></pre>
  
  <p><strong>In logical I get the error :</strong> </p>
  
  <blockquote>
    <p>java.io.IOException: Unable to determine system type - response: 500 Unknow command. </p>
  </blockquote>
  
  <p>I use Apache Commons Net FTP library. So what is wrong in my code? From <code>FileZilla</code> Windows client, I can connect. May be the reason is that in ESP is SPIFF file system? Or another one reason? </p>
  
  <p>Thanks for answers, and interest!</p>