title: Mount a volume without deleting files
body: <p>I am trying to use a folder named <em>tmp</em> as a volume in docker container in order to do it I am using the following <em>docker-compose.yml</em> file</p>
  
  <pre><code>version: "3"
  
  services:
    master:
      image: singularities/spark
      command: start-spark master
      hostname: master
      ports:
        - "6066:6066"
        - "7070:7070"
        - "8080:8080"
        - "50070:50070"
        - "7077:7077"
      volumes:
        - "../data:/tmp/"
      deploy:
        placement:
          constraints:
            - node.role == manager
    worker:
      image: singularities/spark
      command: start-spark worker master
      environment:
        SPARK_WORKER_CORES: 1
        SPARK_WORKER_MEMORY: 4g
      links:
        - master
      volumes:
        - "../data:/tmp/"
  </code></pre>
  
  <p><em>tmp</em> folder exist in singularities/spark image. After I run following command, folders and files under tmp folder are deleted.</p>
  
  <pre><code>docker-compose up -d
  </code></pre>