title: Same Jupyter config, two different behaviors
body: <p>I used a working Jupyter configuration file on another machine, and got the following error. The configuration file parameters are basically those given in the <a href="https://jupyter-notebook.readthedocs.io/en/stable/public_server.html" rel="nofollow noreferrer">instructions for setting up a server</a>. Can anyone help diagnose?</p>
  
  <pre><code>ubuntu@ip:~$ jupyter lab
  Traceback (most recent call last):
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/traitlets/traitlets.py", line 528, in get
      value = obj._trait_values[self.name]
  KeyError: 'allow_remote_access'
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/notebook/notebookapp.py", line 869, in _default_allow_remote
      addr = ipaddress.ip_address(self.ip)
    File "/home/ubuntu/anaconda3/lib/python3.6/ipaddress.py", line 54, in ip_address
      address)
  ValueError: '' does not appear to be an IPv4 or IPv6 address
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "/home/ubuntu/anaconda3/bin/jupyter-lab", line 11, in &lt;module&gt;
      sys.exit(main())
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/jupyter_core/application.py", line 266, in launch_instance
      return super(JupyterApp, cls).launch_instance(argv=argv, **kwargs)
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/traitlets/config/application.py", line 657, in launch_instance
      app.initialize(argv)
    File "&lt;decorator-gen-7&gt;", line 2, in initialize
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/traitlets/config/application.py", line 87, in catch_config_error
      return method(app, *args, **kwargs)
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/notebook/notebookapp.py", line 1629, in initialize
      self.init_webapp()
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/jupyterlab/labapp.py", line 353, in init_webapp
      super().init_webapp(*args, **kwargs)
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/notebook/notebookapp.py", line 1379, in init_webapp
      self.jinja_environment_options,
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/notebook/notebookapp.py", line 158, in __init__
      default_url, settings_overrides, jinja_env_options)
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/notebook/notebookapp.py", line 251, in init_settings
      allow_remote_access=jupyter_app.allow_remote_access,
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/traitlets/traitlets.py", line 556, in __get__
      return self.get(obj, cls)
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/traitlets/traitlets.py", line 535, in get
      value = self._validate(obj, dynamic_default())
    File "/home/ubuntu/anaconda3/lib/python3.6/site-packages/notebook/notebookapp.py", line 872, in _default_allow_remote
      for info in socket.getaddrinfo(self.ip, self.port, 0, socket.SOCK_STREAM):
    File "/home/ubuntu/anaconda3/lib/python3.6/socket.py", line 745, in getaddrinfo
      for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
  socket.gaierror: [Errno -2] Name or service not known
  </code></pre>