https://blog.offline-net.com/2010/10/11/ubuntu-10-10%ef%bc%9avirtualboxintelmac%e7%89%88%e3%81%ab%e6%9c%80%e6%96%b0ubuntu64bit%e3%82%92%e3%82%a4%e3%83%b3%e3%82%b9%e3%83%88%e3%83%bc%e3%83%ab%e3%81%99%e3%82%8b/