Boot2docker parallels image managed by vagrant with NFS sharing and SSH agent forwarding

Vagrantfile

VAGRANTFILE_API_VERSION = '2'
Vagrant.require_version '>= 1.6.3'

def require_plugin(name)
  unless Vagrant.has_plugin?(name)
    raise <<-EOT.strip
      #{name} plugin required. Please run: "vagrant plugin install #{name}"
    EOT
  end
end

require_plugin 'vagrant-parallels'
require_plugin 'vagrant-triggers'

Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
  config.vm.define 'boot2docker'
  config.vm.box = 'parallels/boot2docker'

  config.vm.provider 'parallels' do |v|
    v.name = 'boot2docker'
    v.check_guest_tools = false
    v.memory = (`sysctl -n hw.memsize`).to_i / 2**20 * 2 / 3 / 4 * 4
    v.cpus = (`sysctl -n hw.ncpu`).to_i * 2 / 3
    v.optimize_power_consumption = false
    unless `prlctl list --info boot2docker | grep hdd0`
      v.customize ['set', :id, '--device-add', 'hdd']
    end
  end

  config.vm.network 'private_network', ip: '10.109.20.70'

  config.ssh.forward_agent = true

  {
       80 =>    80  # web
       # ... other ports
  }.each do |guest, host|
    config.vm.network :forwarded_port, guest: guest, host: host
  end

  config.vm.synced_folder(
    ENV['HOME'], ENV['HOME'],
    type: 'nfs',
    nfs_udp: true,
    mount_options: %w[actimeo=2],
    bsd__nfs_options: %w[alldirs maproot=root:wheel]
  )

  # fix busybox/udhcpc issue
  config.vm.provision :shell do |s|
    s.inline = <<-EOT
      if ! grep -qs ^nameserver /etc/resolv.conf; then
        sudo /sbin/udhcpc
      fi
      cat /etc/resolv.conf
    EOT
  end

  # adjust datetime after suspend and resume
  config.vm.provision :shell do |s|
    s.inline = <<-EOT
      sudo /usr/local/bin/ntpclient -s -h pool.ntp.org
      date
    EOT
  end

  # ssh connection for agent forwarding
  config.trigger.after [:up, :reload] do
    command = %Q(vagrant ssh -- -t 'ln -sf `ls -d /tmp/ssh*/* | head -n 1` /tmp/authsock; sh')
    pid = Process.spawn(command, out: '/dev/null', err: '/dev/null')
    Process.detach(pid)
  end
end