Mac & Vagrant problem with setting up NFS? Could be your exports file

Suppose you get the following message when you're trying to provision a new vagrant instance:

NFS is reporting that your exports file is invalid. Vagrant does
this check before making any changes to the file. Please correct
the issues below and execute "vagrant reload":

exports:2: path contains non-directory or non-existent components: /path_to/something
exports:2: no usable directories in export entry
exports:2: using fallback (marked offline): /

This probably means that you had some older VM images kicking around, and now you've remove them, but the /etc/exports file wasn't cleaned up. Simply open the exports file and delete all lines associated with VMs that don't exist any more:

sudo rm /etc/exports
sudo touch /etc/exports

vagrant halt
vagrant up --provision