Vagrant Config Error - "A box must be specified."

For someone that is having this issue now:

I had deleted my Vagrantfile before trying to destroy it. You need to run the vagrant destroy command from the right directory where the Vagrantfile for that process is.

Run vagrant ssh-config and look at the directory column.

If you, like me, deleted the file, do:

vagrant init

Then

vagrant destroy $id

P.S.: Use sudo if you have permission issues running those commands.

If you are getting this error with DigitalOcean, you may need their plugin:

vagrant plugin install vagrant-digitalocean
Installing the 'vagrant-digitalocean' plugin. This can take a few minutes...
Fetching: multipart-post-2.0.0.gem (100%)
Fetching: faraday-0.15.4.gem (100%)
Fetching: vagrant-digitalocean-0.9.3.gem (100%)

Inside of your machine definitions, you need to use the variable name of that machine, instead of config. Try this out:

In the file below, I've changed config.vm to either php5dot3.vm or php5dot6.vm:

Vagrant.configure("2") do |config|

    # Globally defined variables
    config.vm.synced_folder "./", "/var/www/public"

    # CentOS 6.5, Apache 2.2.15, MySQL 5.5.36 (-u root), PHP 5.3.28
    # Note: If PHP session keys don't work, set permissions to 777 (or other more restrictive, but this is guaranteed to work) on /var/lib/php/session
    config.vm.define "php5dot3", primary: true do |php5dot3|
        php5dot3.vm.box = "smallhadroncollider/centos-6.5-lamp"
        php5dot3.vm.network :forwarded_port, guest: 80, host: 4567
    end

    # Ubuntu 14.04 (SSH pw: vagrant), Apache 2.4.12, MySQL 5.5.43 (-u root -p root), PHP 5.6.10
    config.vm.define "php5dot6", autostart:false do |php5dot6|
        php5dot6.vm.box = "scotch/box"
        php5dot6.vm.network :forwarded_port, guest: 80, host: 4568
    end

end

I also added autostart:false to the definition of your php5dot6 box, which you can remove if you wish. (It just means that running vagrant up will only start the primary by default.