Work on the machine

All of our configuration and maintenance work
will be done by command line

So we need a convenient method to work
on the remote machine

Several providers give you access to a web console

But for ordinary work we need a better way to do that

Secure SHell

is the de-facto standard used
to connect to a remote shell (replacing old telnet)

It is composed by a daemon (listening on port TCP 22)
on the server and a client

SSH solves two main issues in remote connection

End to end encryption

All SSH connections are encrypted with
a symmetrical-(session)key algorithm

Connection authentication

Unlike (old standard) telnet,
all SSH connections are authenticated

The server requires the client to perform a secure authentication before starting the session

Almost every VPS distro is shipped with
openssh-server(ssh daemon) pre-installed

Otherwise

apt install openssh-server # for debian based

dnf install openssh-server # for fedora based

On our pc we need to install the ssh client

pacman -Syu ssh # for Arch based

apt install ssh # for debian based

dnf install ssh # for fedora based

then we can start a new connection
with the following command

ssh [<user>@]<host>

Password login is considered
a weak method of authentication

so ssh implements natively
an alternative way to trust connections...

Asymmetrical-key authentication

The client generates a pair of private and public keys

Then it shares the public key with the server
in a trusted way (not defined by ssh protocol)

During the login phase, ssh uses the private key on client and the public key on the server to ensure that the client is allowed to connect to the server

To generate the pair of public and private keys
you can use the following command

ssh-keygen [-t ed25519 | rsa | ...]

It will generate two files:
id_<name> and id_<name>.pub

To copy the public key on the remote server we can use a tool using an ssh connection with password authentication

ssh-copy-id -i /path/to/id_<name> [<user>@]<host>

Now we can use the private key to perform the ssh login

ssh -i /path/to/id_<name> [<user>@]<host>