OpenSSH is a very popular SSH client/server solution, and as a result of its popularity has become the de facto standard for SSH servers.
From a terminal enter:
apt-get install openssh-server
This requires root permissions, so you may need to prepend sudo to the command in order for it to successfully execute.
And you're done! If you want to change any configuration just edit ”/etc/ssh/sshd_config”. It is suggested that you change the port (line 5) for security purposes. If you do make any changes, run this to restart the server:
/etc/init.d/ssh restart
If you are connected to your machine via SSH, the above command will disconnect all users currently logged in via SSH. You will need to log in to the host machine again.
From a terminal enter:
yum install openssh-server
This requires root permissions, so you may need to first run su - in order for it to successfully execute.