Install openssh-server

sudo apt-get update
sudo apt-get upgrade

sudo apt-get purge openssh-server
sudo apt-get install openssh-server

/etc/ssh/sshd_config
Port 22
Protocol 2
PermitRootLogin no
AuthorizedKeysFile  .ssh/authorized_keys
PasswordAuthentication yes
PubkeyAuthentication yes
ChallengeResponseAuthentication no
X11Forwarding yes
UseDNS no

sudo service ssh --full-restart
sudo service ssh restart

ssh localhost