When I first ran 'vagrant up' I got a message: "A Vagrant environment variable or target machine is required to run..."
Here's the full message.
"A Vagrant environment or target machine is required to run this
vagrant init to create a new Vagrant environment. Or,
get an ID of a target machine from
vagrant global-status to run
this command on. A final option is to change to a directory with a
Vagrantfile and to try again."
My bad, I was in the wrong directory.