vagrant 1.8.1 在 ansible_local 中指定时似乎没有安装 ansible

我的供应商是这样的：

config.vm.provision :ansible_local do |ansible|
  ansible.playbook = '/home/deploy/sosd/local/ansible/sosd.yml'
  ansible.install = true
end

但vagrant up它似乎没有安装：

==> default: Running provisioner: ansible_local...
    default: Installing Ansible...
The Ansible software could not be found! Please verify
that Ansible is correctly installed on your guest system.

If you haven't installed Ansible yet, please install Ansible
on your Vagrant basebox, or enable the automated setup with the
`install` option of this provisioner. Please check
https://docs.vagrantup.com/v2/provisioning/ansible_local.html
for more information.

我究竟做错了什么？