title: Why is docker-machine displaying an empty list?
body: <p>Docker newbie here. I am using <a href="http://coding.jandavid.de/2016/01/22/dockerizing-sinatra/" rel="noreferrer">this tutorial</a> as an example.</p>
  
  <p>I am on a Mac running El Cap. Running the latest Docker for mac.</p>
  
  <p>I created a docker image</p>
  
  <pre><code>$ docker build -t pitosalas/sinatra-example .
  Sending build context to Docker daemon 9.728 kB
  Step 1 : FROM phusion/passenger-ruby23:0.9.19
   ---&gt; 6841e494987f
  Step 2 : ENV HOME /root
   ---&gt; Using cache
   ---&gt; 94013634dd29
  Step 3 : CMD /sbin/my_init
   ---&gt; Using cache
   ---&gt; 545db4245647
  Step 4 : RUN rm -f /etc/service/nginx/down
   ---&gt; Using cache
   ---&gt; 1a5361bf707b
  Step 5 : RUN rm /etc/nginx/sites-enabled/default
   ---&gt; Using cache
   ---&gt; 6d884a990bd7
  Step 6 : ADD docker/vhost.conf /etc/nginx/sites-enabled/app.conf
   ---&gt; Using cache
   ---&gt; 471fcf124466
  Step 7 : RUN mkdir /home/app/webapp
   ---&gt; Using cache
   ---&gt; a0336183d1f0
  Step 8 : WORKDIR /tmp
   ---&gt; Using cache
   ---&gt; 38b834783e4f
  Step 9 : COPY app/Gemfile /tmp/
   ---&gt; Using cache
   ---&gt; 6541c0cbf6eb
  Step 10 : COPY app/Gemfile.lock /tmp/
   ---&gt; Using cache
   ---&gt; 1be89d7bd57b
  Step 11 : RUN bundle install
   ---&gt; Using cache
   ---&gt; 3b21f88e6bcf
  Step 12 : COPY app /home/app/webapp
   ---&gt; Using cache
   ---&gt; 8bc0cb084d99
  Step 13 : RUN chown -R app:app /home/app
   ---&gt; Using cache
   ---&gt; 4bba23481f1f
  Step 14 : RUN apt-get clean &amp;&amp; rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
   ---&gt; Using cache
   ---&gt; d85a89da09c2
  Successfully built d85a89da09c2
  </code></pre>
  
  <p>Then I checked for running containers. None. As expected:</p>
  
  <pre><code>$ docker-machine ls
  NAME   ACTIVE   DRIVER   STATE   URL   SWARM   DOCKER   ERRORS
  $ 
  </code></pre>
  
  <p>Next I run the container:</p>
  
  <pre><code>docker run -p 4567:80 pitosalas/sinatra-example
  *** Running /etc/my_init.d/00_regen_ssh_host_keys.sh...
  *** Running /etc/my_init.d/30_presetup_nginx.sh...
  *** Running /etc/rc.local...
  *** Booting runit daemon...
  *** Runit started as PID 8
  Aug 22 02:07:22 dd3474178cd5 syslog-ng[18]: syslog-ng starting up; version='3.5.6'
  ok: run: /etc/service/nginx-log-forwarder: (pid 27) 0s
  [ 2016-08-22 02:07:23.8489 28/7fc94dfd9780 age/Wat/WatchdogMain.cpp:1291 ]: Starting Passenger watchdog...
  [ 2016-08-22 02:07:23.8769 31/7f07e849d780 age/Cor/CoreMain.cpp:982 ]: Starting Passenger core...
  [ 2016-08-22 02:07:23.8770 31/7f07e849d780 age/Cor/CoreMain.cpp:235 ]: Passenger core running in multi-application mode.
  [ 2016-08-22 02:07:23.8842 31/7f07e849d780 age/Cor/CoreMain.cpp:732 ]: Passenger core online, PID 31
  [ 2016-08-22 02:07:23.9104 42/7f66f0bb5780 age/Ust/UstRouterMain.cpp:529 ]: Starting Passenger UstRouter...
  [ 2016-08-22 02:07:23.9155 42/7f66f0bb5780 age/Ust/UstRouterMain.cpp:342 ]: Passenger UstRouter online, PID 42
  </code></pre>
  
  <p>Looks ok, but:</p>
  
  <pre><code>$ docker-machine ls
  NAME   ACTIVE   DRIVER   STATE   URL   SWARM   DOCKER   ERRORS
  $
  </code></pre>
  
  <p>Still no containers. Here are some more files:</p>
  
  <pre><code>[Dockerfile]
  FROM phusion/passenger-ruby23:0.9.19
  
  # Set correct environment variables.
  ENV HOME /root
  
  # Use baseimage-docker's init process.
  CMD ["/sbin/my_init"]
  
  # Enable nginx and Passenger
  RUN rm -f /etc/service/nginx/down
  
  # Remove the default site
  RUN rm /etc/nginx/sites-enabled/default
  
  # Create virtual host
  ADD docker/vhost.conf /etc/nginx/sites-enabled/app.conf
  
  # Prepare folders
  RUN mkdir /home/app/webapp
  
  # Run Bundle in a cache efficient way
  WORKDIR /tmp
  COPY app/Gemfile /tmp/
  COPY app/Gemfile.lock /tmp/
  RUN bundle install
  
  # Add our app
  COPY app /home/app/webapp
  RUN chown -R app:app /home/app
  
  # Clean up when done.
  RUN apt-get clean &amp;&amp; rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
  </code></pre>
  
  <p>Also</p>
  
  <pre><code>[vhost.conf]
  server {
      listen 80;
      server_name localhost;
      root /home/app/webapp/public;
  
      passenger_enabled on;
      passenger_user app;
  
      passenger_ruby /usr/bin/ruby2.3;
  }
  </code></pre>
  
  <p>Here's the directory tree I am working with:</p>
  
  <pre><code>$ tree
  .
  ├── Dockerfile
  ├── app
  │   ├── Gemfile
  │   ├── Gemfile.lock
  │   ├── app.rb
  │   └── config.ru
  ├── docker
  │   └── vhost.conf
  └── tmp
  
  3 directories, 6 files
  $
  </code></pre>
  
  <p>Why am I not showing a running container? </p>