who has ever tried following this tutorial about Docker Swarm?

https://docs.docker.com/get-started/part4/

There is a section called : Create a cluster. What I wanted to do was to create a couple of VMs using docker-machine. Since I use ubuntu16.0.4 so I used following commands to get VirtualBox.

sudo apt-get update
sudo apt-get install virtualbox-5.2

After I installed VirtualBox, typed a command like :

docker-machine create --driver virtualbox myvm1

But it says : sudo: docker-machine: command not found

So I typed another command to check if I have installed VirtualBox correctly.

sudo virtualbox version

This opens the Oracle VM VirtualBox Manager, which means I did install VirtualBox correctly , but not sure.

Could anyone help me with a proper solution? Any help would be appreciated.

You need to install Docker Machine first on your local machine. If you use Ubuntu, just use this snippet (Update the version from the Official Repository Releases if needed) :

$ curl -L https://github.com/docker/machine/releases/download/v0.16.0/docker-machine-`uname -s`-`uname -m` >/tmp/docker-machine &&
chmod +x /tmp/docker-machine &&
sudo cp /tmp/docker-machine /usr/local/bin/docker-machine