Hi, i made i minecraft server following this tutorial, but nobody can connect to it. When i'm not connected to the server through PuTTy i can't connect either. What am i doing wrong?

Im running it on ubuntu 14.04. I tryed turning of the firewall through '$ sudo ufw disable', which did turn the firewall off but i still couldn't connect, neither could my friends. I also tryed opening the specific ports for the server.

I also tryed following this tutorial but that didnt work either. I then reset my system, tryed the first tutorial again, but still nothing.