apt-get purge libx11*http://askubuntu.com/questions/484095/how-do-i-remove-all-desktop-related-packages-leaving-server-only

http://www.virment.com/iptables-setting-example/ http://qiita.com/Tocyuki/items/6d90a1ec4dd8e991a1ce

https://www.digitalocean.com/community/tutorials/how-to-setup-your-own-vpn-with-pptp