config.vm.provider "virtualbox" do |v|
  host = RbConfig::CONFIG['host_os']

  # Give VM 1/4 system memory & access to all cpu cores on the host
  if host =~ /darwin/
    cpus = `sysctl -n hw.ncpu`.to_i
    # sysctl returns Bytes and we need to convert to MB
    mem = `sysctl -n hw.memsize`.to_i / 1024 / 1024 / 4
  elsif host =~ /linux/
    cpus = `nproc`.to_i
    # meminfo shows KB and we need to convert to MB
    mem = `grep 'MemTotal' /proc/meminfo | sed -e 's/MemTotal://' -e 's/ kB//'`.to_i / 1024 / 4
  else # sorry Windows folks, I can't help you
    cpus = 2
    mem = 1024
  end

  v.customize ["modifyvm", :id, "--memory", mem]
  v.customize ["modifyvm", :id, "--cpus", cpus]
end