If you have just installed SQL Server on Ubuntu Linux and you are trying to connect remotely you may have some difficulty connecting if port 1433 is not available.
Here is how you do it, using the UFW, or Uncomplicated Firewall on Ubuntu.
sudo ufw enable
sudo ufw allow 1433
While you are at it you may want to enable port 22 for SSH if that has not been allowed already. I also allowed 1434 for the dedicated admin console assuming that it is available on the Linux version of SQL Server v.next.
I hope this helps! Enjoy.