Vagrant import an existing VM

 list your VMs to find the VM ID:

$ VBoxManage list vms
"UCS 4.1" {acef4c0a-35be-4640-a214-be135417f04d}
You can now package that VM as a Vagrant box:

$ vagrant package --base acef4c0a-35be-4640-a214-be135417f04d --output UCS.box                                                                                                                             
==> acef4c0a-35be-4640-a214-be135417f04d: Exporting VM...                                                                                                                                                
==> acef4c0a-35be-4640-a214-be135417f04d: Compressing package to: /home/crohr/dev/ucs/UCS.box                                                                                           
And add it to the list of your local Vagrant boxes:

$ vagrant box add UCS.box --name UCS
Finally, you can create a Vagrantfile to use this box:

Vagrant.configure("2") do |config|
  config.vm.box = "UCS"
  # ...
end