title: How does Java application know it is running within a Docker container
body: <p>I have written a DockerFile for my application primarily  to allow it to be run within a NAS machine (via Docker). The web interface allows the user to traverse the filesystem tree  looking for Music files, but when using Docker the filesystem tree is irrelevant except for the /Music volume which is the mount point for the users actual Music folder on the NAS. </p>
  
  <p>So I only want to display the /Music folder instead of the whole filesystem tree and to do that the application needs to be aware it is actually running within a Docker rather than an actual native Linux OS.</p>
  
  <p>What is the correct way for the application to know it is in docker, the application is written in Java.</p>