title: Dockerfile & installation -> Package 'openjdk-8-jre-headless' has no installation candidate
body: <p>I'm trying to install openjdk-8-jre vie DockerFile, as I build the docker images for my composer. But I'm hitting this error message. </p>
  
  <p>Error message:</p>
  
  <pre><code>Package openjdk-8-jre-headless is not available, but is referred to by another package.
  This may mean that the package is missing, has been obsoleted, or
  is only available from another source
  
  E: Package 'openjdk-8-jre-headless' has no installation candidate
  </code></pre>
  
  <p>Here is the part from Dockerfile:</p>
  
  <pre><code># Install openjdk and java cacerts
  RUN apt-get update &amp;&amp; apt-get install -y openjdk-8-jre-headless ca-certificates-java
  </code></pre>
  
  <p>If I install java directly from the console, by using exact same command without RUN, no problem with the package. But as I try installing it from the Dockerfile, I hit the error. I have understood that Docker uses same repos as the machine where docker is running? Ubuntu is version 16.04. </p>
  
  <p>Or how I check available installation packages on Dockerfile? java - v gives an error..</p>