title: Use docker build step plugin in Jenkins docker container
body: <p>I have a jenkins server inside a docker container:</p>
  
  <p>I've edited the base image so I'm able to mount the docker sockets to my container and use the sockets as jenkins user.</p>
  
  <pre><code>docker run -d -u jenkins --name jenkins \
    -p 50000:50000 \
    -p 8080:8080 \
    --volumes-from jenkins-volume \ 
    --restart=always \
    -v /var/run/docker.sock:/var/run/docker.sock \ 
    test/jenkins:1.0
  </code></pre>
  
  <p>So I'm able to run commands such as <code>docker version</code> and <code>docker ps</code> in my jenkins container (in a shell). </p>
  
  <p>Now I've installed the docker build step plugin.</p>
  
  <p>My question is how can I have to use and configure this plugin?</p>
  
  <p>In the global configuration I see:</p>
  
  <ul>
  <li>Docker installer (I would think I don't need that)</li>
  <li>Docker builder: Docker server REST API URL   </li>
  </ul>
  
  <p>So I don't know how to configure this.</p>
  
  <p>When I just try to perform a docker command using the plugin in a Jenkins Job I get an error; I'm not able to save the configuration of the docker command inside my job and I see the following error in my logs on jenkins:</p>
  
  <pre><code>Error while serving http://ip:8080/job/docker-test/configSubmit
  java.lang.reflect.InvocationTargetException
      at sun.reflect.GeneratedMethodAccessor648.invoke(Unknown Source)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  ...
  Caused by: javax.servlet.ServletException: This page expects a form submission but had only {}
  </code></pre>
  
  <p>How can I configure this plugin inside a jenkins-docker container in which the docker sockets are mounted?</p>