SSH

Overview

SSH is a protocol to connect to a remote system. Once a connection is made, you can execute commands to manage the remote system.

The local computer is also referred to as the client, the remote system as the host.

It is recommended to use keys to authenticate connections between the client and the host. There are 2 keys:

Key	File	Example
Private	*	id_rsa
Public	*.pub	id_rsa.pub

The client generates both of the keys. The public key is copied onto the host and stored under the home directory of a user account at ~/.ssh/authorized_keys.

Important

The private key is never be shared!

Once configured, you can run ssh account@host on the client to connect to the host, where account is a username account on the host and host is an ip address or FQDN.

sequenceDiagram
    participant client as Client:<br>Laptop
    participant remote  as Remote:<br>Server
    client->>remote: ssh account@host
    Note over remote: account:~/.ssh/authorized_keys
    par SSH Established
        client->>remote: $ <commands>
        client->>remote: $ exit
        remote->>client: Connection Closed
    end

Generating Keys

ssh-keygen

Disable Password Authentication

If you have a working key-based authentication set up, it is recommended to disable password authentication on the remote host system.

sudo nano /etc/ssh/sshd_config

Search for PasswordAuthentication and set it to no. Uncomment if necessary.

sshd_config

PasswordAuthentication no

Restart the ssh daemon.

sudo service ssh restart

Client Side Configuration

Aliases

Instead of running ssh demo@192.168.1.1 to connect to a remote system, you can create alias.

Edit/Create the config file at ./.ssh/config:

./.ssh/config

Host test
    HostName 192.168.1.1
    User demo

Now you can type ssh test to establish the SSH connection.