1. firewall (refer to https://help.ubuntu.com/lts/serverguide/firewall.html)
> sudo ufw enable
> sudo ufw allow 22
2. netstat
> sudo netstat -plant | grep ssh
3. install ssh (http://cooldragon.tistory.com/139)
> sudo apt-get install openssh-server
connection test from other terminal)
> ssh account@IP
> ssh cooldragon@192.168.56.102
