first day with docker

refer to:  https://docs.docker.com/engine/installation/linux/ubuntulinux

your Ubuntu: 16.04 LTS;

1.  $ sudo apt-get update

2.  $ sudo apt-get install apt-transport-https ca-certificates

3. $ sudo apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D

4. $ sudo vim /etc/apt/sources.list.d/docker.list        , with content: 

deb https://apt.dockerproject.org/repo ubuntu-xenial main

5. $ sudo apt-get update

6. $ sudo apt-get purge lxc-docker

7. $ sudo apt-cache policy docker-engine