how to install docker Ubuntu Xenial 16.04 (LTS)

install Docker Community Edition (Docker CE) on Ubuntu  Xenial 16.04 (LTS)

 To install Docker CE, you need the 64-bit version

 Uninstall old versions
 sudo apt-get remove docker docker-engine docker.io
 The contents of /var/lib/docker/

 The Docker CE package is now called docker-ce.

 Some users download the DEB package
 Most users set up Docker’s repositories and install from them, for ease of installation and upgrade tasks. This is the recommended approach.
 Some users download the DEB package and install it manually and manage upgrades completely manually. This is useful in situations such as installing Docker on air-gapped systems with no access to the internet.
 In testing and development environments, some users choose to use automated convenience scripts to install Docker.

Update the apt package index
$sudo apt-get update

Requirements

$sudo apt-get install apt-transport-https
$sudo apt-get install ca-certificates
$sudo apt-get install curl
$sudo apt-get install software-properties-common

Add Docker’s official GPG key
$curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

Verify  key
$sudo apt-key fingerprint 0EBFCD88

set up the stable repository
$sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"

Update the apt package index
$sudo apt-get update

Install the latest version of Docker CE
$sudo apt-get install docker-ce

$docker version

OS requirements
To install Docker CE, you need the 64-bit version of one of these Ubuntu versions:
    Zesty 17.04
    Xenial 16.04 (LTS)
    Trusty 14.04 (LTS)

Verify old versions are removed.
$sudo apt-get remove docker docker-engine docker.io