Why does virtual box vboxheadless process using Vagrant use 100% of my cpu?

EngineerCoder’s answer only applies if you’re using CoreOS.

I’ve run into problems if the VirtualBox Extensions pack version differs from the version of VirtualBox. Also, install the Vagrant VirtualBox guest plugin:

vagrant plugin install vagrant-vbguest

And make sure to update the plugin when you update Virtualbox and the extension pack:

vagrant plugin update vagrant-vbguest