https://blog.offline-net.com/2010/12/05/ubuntu-10-10%ef%bc%9avirtualbox%e3%81%ae%e5%85%b1%e6%9c%89%e3%83%95%e3%82%a9%e3%83%ab%e3%83%80%e3%82%92%e5%88%a9%e7%94%a8%e3%81%99%e3%82%8b/