title: Ubuntu 16.04 - Docker installed but not available
body: <p>I am trying to install <code>docker</code> on an Ubuntu-16.04 server.
  When I execute <code>sudo apt-get install -y docker-ce</code> the system tells me that docker is already installed:</p>
  
  <pre><code>$ sudo apt-get install -y docker-ce
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done
  docker-ce is already the newest version (5:19.03.1~3-0~ubuntu-xenial).
  0 upgraded, 0 newly installed, 0 to remove and 133 not upgraded.
  </code></pre>
  
  <p>And running <code>sudo systemctl status docker</code> looks like it's already running:</p>
  
  <pre><code>$ sudo systemctl status docker
  ● docker.service - Docker Application Container Engine
     Loaded: loaded (/etc/systemd/system/docker.service; enabled; vendor     preset: enabled)
     Active: active (running) since Wed 2019-08-21 17:26:02 PDT; 24min ago
       Docs: http://docs.docker.com
   Main PID: 14283 (dockerd)
      Tasks: 28
     Memory: 64.7M
        CPU: 1.128s
     CGroup: /system.slice/docker.service
         └─14283 /usr/bin/dockerd
  
  Aug 21 17:26:02 node1 dockerd[14283]: time="2019-08-21T17:26:02.137366865-07:00" level=warning msg="Your kernel does not support cgroup rt period"
  Aug 21 17:26:02 node1 dockerd[14283]: time="2019-08-21T17:26:02.137381329-07:00" level=warning msg="Your kernel does not support cgroup rt runtime"
  Aug 21 17:26:02 node1 dockerd[14283]: time="2019-08-21T17:26:02.139558576-07:00" level=info msg="Loading containers: start."
  Aug 21 17:26:02 node1 dockerd[14283]: time="2019-08-21T17:26:02.229011852-07:00" level=info msg="Default bridge (docker0) is assigned with an IP address 172.17.0.0/16. Daemon option --bip can be used to set a preferred IP address"
  Aug 21 17:26:02 node1 dockerd[14283]: time="2019-08-21T17:26:02.264094521-07:00" level=info msg="Loading containers: done."
  Aug 21 17:26:02 node1 dockerd[14283]: time="2019-08-21T17:26:02.317824839-07:00" level=warning msg="Not using native diff for overlay2, this may cause degraded performance for building images: opaque flag erroneously copied up, consider u
  Aug 21 17:26:02 node1 dockerd[14283]: time="2019-08-21T17:26:02.318092298-07:00" level=info msg="Docker daemon" commit=74b1e89e8a graphdriver(s)=overlay2 version=19.03.1
  Aug 21 17:26:02 node1 dockerd[14283]: time="2019-08-21T17:26:02.318144708-07:00" level=info msg="Daemon has completed initialization"
  Aug 21 17:26:02 node1 dockerd[14283]: time="2019-08-21T17:26:02.333727950-07:00" level=info msg="API listen on /var/run/docker.sock"
  Aug 21 17:26:02 node1 systemd[1]: Started Docker Application Container Engine.
  </code></pre>
  
  <p>But when I try to run <code>docker-ps</code> I get this error:</p>
  
  <pre><code>$ docker ps
  The program 'docker' is currently not installed. You can install it by typing:
  sudo apt install docker.io
  </code></pre>
  
  <p>Also <code>which docker</code> doesn't return anything...</p>
  
  <p>Any idea of what can be going on here? How can I debug this further?</p>
  
  <p>Thanks in advance</p>
  
  <h2>UPDATE</h2>
  
  <p><code>docker-cli</code> appears to be installed to:</p>
  
  <pre><code>sudo apt-get install docker-ce-cli
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done
  docker-ce-cli is already the newest version (5:19.03.1~3-0~ubuntu-xenial).
  0 upgraded, 0 newly installed, 0 to remove and 133 not upgraded.
  cord@node1:~$ which docker
  </code></pre>
  
  <p>But still the <code>docker</code> command is not there.</p>
  
  <p>Here is the output of <code>dpkg -L docker-ce</code>:</p>
  
  <pre><code>$ dpkg -L docker-ce
  /.
  /etc
  /etc/default
  /etc/default/docker
  /etc/init.d
  /etc/init.d/docker
  /etc/init
  /etc/init/docker.conf
  /lib
  /lib/systemd
  /lib/systemd/system
  /lib/systemd/system/docker.socket
  /lib/systemd/system/docker.service
  /usr
  /usr/bin
  /usr/bin/dockerd
  /usr/bin/docker-init
  /usr/bin/docker-proxy
  /usr/share
  /usr/share/doc
  /usr/share/doc/docker-ce
  /usr/share/doc/docker-ce/changelog.Debian.gz
  /usr/share/doc/docker-ce/README.md
  /var
  /var/lib
  /var/lib/docker-engine
  /var/lib/docker-engine/distribution_based_engine.json
  </code></pre>