ssh, short for “secure shell”, is a protocol to make an encrypted connection to a remote server. Per the name, the most common use case is to connect via shell, but it is also used by applications like git, scp, etc. to make secure connections and transfer data.

Using SSH

You initiate a connection to a server over ssh by opening a terminal and running

ssh <username>@<server>

for example

ssh mike@example.com

Depending on the server configuration, you will be prompted for your password for the account you have on the server. Upon successfuly authentication, a shell session on the remote server will appear in your terminal, and you can interact as you would in a normal terminal session.

To exit an ssh session, simply type

exit

Generating a Key

ssh uses public key cryptography. Generating an ssh key is as simple as running

ssh-keygen

This will put a public key at ~/.ssh/id_rsa.pub and a private key under ~/.ssh/id_rsa. You can choose when you create the key to add a passphrase. The public key is the one shared with the server you want to connect to. The private key should always remain private.

Connecting to a Server Using Your Key

To connect to a server with an ssh key for the first time, run

ssh-copy-id <username>@<server> 

e.g.

ssh-copy-id mike@example.com

This will log you into the remote server and put your public key fingerprint in ~/.ssh/authorized_keys. From then on, you can simply log in without being prompted for a password.

To remove a known host, simply run ssh-keygen -R <domain>.