Let's start with the most useful server that, according to me, every administrator should install on their server, irrespective of the aim of this server and the services that need to be put on it. It is the OpenSSH server that allows you to remotely connect in a secure way to a server from a computer that can reach this server. The OpenSSH server is a set of tools that allow, besides the secure remote connection, a secure file transfer with the help of the scp protocol.
The OpenSSH server allows clients to connect using many authentication methods, such as a plain password, a public key, and kerberos tickets.
We can install only the OpenSSH server, but in general, we need both the OpenSSH tools—a server and a client. We need a server to connect to the Ubuntu Server that we are working on from a reachable computer. We require a client to connect it to another server or computer.
Installing OpenSSH (the server and client) is quite easy...