Vagrant provisioning not working - adding docker to the VM

OK.

So I have a Vagrant file - and I can

vagrant up

and

vagrant halt

and

vagrant up

etc and all is fine.

But then I want to add docker to my VM - just Docker - no docker images/containers etc - just the docker tool.

So in my Vagrant file I add in:

config.vm.provision "docker"

in the main block in between

Vagrant.configure(2) do |config|

and

end

I then halt the machine and then 'vagrant up' it again - log in - but - no docker command!

Turns out that provisioning only runs on the 'up' command when it is run for the first time - after that provisioning is ignored (which makes sense I suppose). To get it to run the provision stuff you need to call:

$ vagrant up --provision

It's all explained here:

http://docs.vagrantup.com/v2/provisioning/