Setup (and secure) an SSH server on Ubuntu

Install OpenSSH Server:

sudo apt-get install openssh-server

To check if the server is running you should get no error when you restart it:

sudo /etc/init.d/ssh restart

Now your ssh server is ready to use.

To add additional security edit your sshd_config (gksudo gedit /etc/ssh/sshd_config):

# Deny root login:
PermitRootLogin no

# To whitelist users:
AllowUsers USERNAME1 USERNAME2

# To disable interactive authentication (without SSH key)
PasswordAuthentication no

Don't forget to restart after editing the sshd_config:

sudo service ssh restart

(Tested on Ubuntu 14.04)