安装增强工具:http://mikemainguy.blogspot.jp/2015/03/installing-virtualbox-guest-additions.html
安装ssh:https://www.rosehosting.com/blog/how-to-configure-and-use-openssh-on-centos-7/
安装网络工具:https://www.unixmen.com/ifconfig-command-found-centos-7-minimal-installation-quick-tip-fix/
互访:http://www.cnblogs.com/wynn0123/p/6286532.html
https://hk.saowen.com/a/daf7a205d315b09e7a8e3d472bc175f299af23ece13a038ac3984754ca65d6bd