title: How do I know whether "init" or "systemd" controls the docker?
body: <p>I follow the official <a href="https://docs.docker.com/engine/installation/linux/ubuntulinux/" rel="nofollow noreferrer">document</a> to install <code>Docker</code> on <code>Ubuntu 16.04 LTS</code>. Since my server works behind proxy, so I need to configure proxy for Docker. The processes running on my host like this:  </p>
  
  <pre><code># ps -aef | grep init
  root         1     0  0 03:05 ?        00:00:01 /sbin/init
  # ps -aef | grep docker
  root      3223     1  0 04:04 ?        00:00:00 /usr/bin/docker daemon -H fd://
  root      3230  3223  0 04:04 ?        00:00:00 docker-containerd -l /var/run/docker/libcontainerd/docker-containerd.sock --runtime docker-runc --start-timeout 2m
  </code></pre>
  
  <p>Since <code>docker</code>'s father process is <code>init</code>, I modify the <code>/etc/default/docker</code> file:  </p>
  
  <pre><code># cat /etc/default/docker
  # Docker Upstart and SysVinit configuration file
  
  #
  # THIS FILE DOES NOT APPLY TO SYSTEMD
  #
  #   Please see the documentation for "systemd drop-ins":
  #   https://docs.docker.com/engine/articles/systemd/
  #
  
  # Customize location of Docker binary (especially for development testing).
  #DOCKER="/usr/local/bin/docker"
  
  # Use DOCKER_OPTS to modify the daemon startup options.
  #DOCKER_OPTS="--dns 8.8.8.8 --dns 8.8.4.4"
  
  # If you need Docker to use an HTTP proxy, it can also be specified here.
  export http_proxy="http://web-proxy.corp.xxxxxx.com:8080/"
  export https_proxy="https://web-proxy.corp.xxxxxx.com:8080/"
  ......
  </code></pre>
  
  <p>But unfortunately, this change doesn't take effect. I doubt the <code>Docker</code> is controlled by <code>systemd</code>, so I check it:  </p>
  
  <pre><code># systemctl status docker
  ● docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: active (running) since Thu 2016-07-14 03:19:35 EDT; 2min 16s ago
       Docs: https://docs.docker.com
   Main PID: 3057 (docker)
      Tasks: 24
     Memory: 25.2M
        CPU: 531ms
     CGroup: /system.slice/docker.service
             ├─3057 /usr/bin/docker daemon -H fd://
             └─3064 docker-containerd -l /var/run/docker/libcontainerd/docker-containerd.sock --runtime docker-runc --start-timeout 2m
  ......
  </code></pre>
  
  <p>Then I follow this <a href="https://stackoverflow.com/questions/23111631/cannot-download-docker-images-behind-a-proxy">post</a> to set proxy, now it works!</p>
  
  <p>Per my understanding, since this <code>docker</code> process is spawned by <code>init</code>, it should be controlled by it. But in reality, it seems controlled by <code>systemd</code>. How do I know whether <code>init</code> or <code>systemd</code> controls the <code>docker</code>?</p>