Ubuntu Xenial with Ruby installed via rbenv

Vagrantfile

PROVISION_SYSTEM = <<~EOS
  set -e
  apt-get update --yes
  apt-get install --yes gcc
  apt-get install --yes make
EOS

PROVISION_USER = <<~EOS
  set -e
  mkdir -p ~/.rbenv
  cd ~/.rbenv
  git init
  git remote add -f -t master origin https://github.com/rbenv/rbenv.git
  git checkout -b master origin/master
  mkdir -p ~/.rbenv/plugins
  git clone https://github.com/rbenv/ruby-build.git ~/.rbenv/plugins/ruby-build
  echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
  echo 'eval "$(rbenv init -)"' >> ~/.bashrc
  export PATH="$HOME/.rbenv/bin:$PATH"
  eval "$(rbenv init -)"
  rbenv install ruby-2.6.3
  rbenv global ruby-2.6.3
EOS

Vagrant.configure('2') do |config|
  config.vm.box = 'ubuntu/xenial64'
  config.vm.box_version = '20170914.2.0'
  config.vm.provision :shell, inline: PROVISION_SYSTEM
  config.vm.provision :shell, privileged: false, inline: PROVISION_USER
end