https://zelkun.tistory.com/entry/Virtual-Box-Ubuntu-Server1404-%EB%B2%84%EC%B6%94%EC%96%BC%EB%B0%95%EC%8A%A4-%EC%9A%B0%EB%B6%84%ED%88%AC-%EC%84%9C%EB%B2%84-%ED%8F%B4%EB%8D%94%EA%B3%B5%EC%9C%A0