在Cloud9上启动一个简单的DerbyJS项目

我正在尝试在Cloud9上部署一个简单的derby项目。

我使用Node.js创建了一个工作区，并添加了以下4个文件的内容:

index . html:

<Body:>
  <!--Templates define both HTML and model-view bindings-->
  Holler: <input value="{{hello.message}}">
  <h2>{{hello.message}}</h2>

index.js:

var app = module.exports = require('derby').createApp('hello', __filename);
app.loadViews(__dirname);
// Routes render on client as well as server
app.get('/', function(page, model) {
  // Subscribe specifies the data to sync
  model.subscribe('hello.message', function() {
    page.render();
  });
});

server.js:

require('derby-starter').run(__dirname, {port: process.env.PORT});

package.json:

{
  "name": "derby-examples",
  "description": "Example applications for the Derby framework",
  "version": "0.6.0",
  "repository": "",
  "main": "server.js",
  "dependencies": {
    "derby": "0.6.0-alpha41",
    "derby-starter": "^0.2.6",
    "derby-stylus": "~0.1.0",
    "express": "~3.18.0",
    "d-connection-alert": "~0.1.0",
    "d-before-unload": "~0.1.0",
    "d-bootstrap": "~0.1.0",
    "d-codemirror": "~0.2.0",
    "d-showdown": "~0.1.0",
    "derby-debug": "^0.1.0"
  },
  "optionalDependencies": {},
  "devDependencies": {},
  "engines": {
    "node": "0.10.x"
  }
}

当我启动服务器时，它一直在说

Important: use process.env.PORT as the port and process.env.IP as the host in your scripts!                                                                                             
debugger listening on port 15454                                                                                                                                                        
Master pid  27985                                                                                                                                                                       
debugger listening on port 15454                                                                                                                                                        
Failed to open socket on port 15454, waiting 1000 ms before retrying                                                                                                                    

，接着是

Failed to open socket on port 15454, waiting 1000 ms before retrying                                                                                                                    

如何才能正常启动服务器?