Xenial vagrant (ubuntu 16.04)

Vagrantfile

# -*- mode: ruby -*-
# vi: set ft=ruby :
Vagrant.configure(2) do |config|
  config.vm.box = "ubuntu/xenial64"
  config.vm.hostname = "ubuntu-xenial"
  config.vm.network "public_network", ip: "192.168.0.131"
  config.vm.synced_folder "/Volumes/Data/Shares", "/home/ubuntu/Shares", create: true   
  
  config.vm.provider "virtualbox" do |vb|
    vb.name = "ubuntu-xenial64"
    vb.gui = false
    vb.memory = "2048"
    vb.cpus = 2
  end

  config.vm.provision "shell", inline: <<-SHELL
     sudo apt-get update
     sudo apt-get install -y whois git htop
     sudo useradd -m -p `mkpasswd password_here` -s /bin/bash user_here
     sudo usermod -a -G sudo user_here
  SHELL

end

You want to fix the 'sync_folder' error, You should install plugin vbguest for vagrant before run "vagrant up".
That command below:

$ vagrant plugin install vagrant-vbguest

Vagrant:
https://www.vagrantup.com/downloads.html

Just spent a couple hours banging my head against this myself today.

Another horrible workaround if you're using git bash:

cp /mingw64/bin/curl.exe /c/HashiCorp/Vagrant/embedded/bin/curl.exe

I hope there will be a better solution in the actual installer in a future release.