devops-basics

SSH

1. What is SSH?

Overview

• SSH (Secure Shell) is a network protocol that allows secure, encrypted communication between two systems over an unsecured network.
• It is most commonly used to remotely log into servers, execute commands, and transfer files (via SCP/SFTP), replacing older insecure protocols like Telnet and rlogin.
• SSH uses public-key cryptography to authenticate the remote computer and, optionally, to authenticate the user.

Official website documentation of SSH

• https://www.openssh.com/
• https://www.ssh.com/academy/ssh/protocol

2. Prerequisites

• Basic Linux command line usage
• Basic understanding of networking (client-server model, ports)

3. Installation

How to install SSH?

On most Linux distributions, the SSH client is installed by default. To install the SSH server:

# Debian/Ubuntu
sudo apt update
sudo apt install openssh-server -y
sudo systemctl enable ssh
sudo systemctl start ssh

# RHEL/CentOS
sudo yum install openssh-server -y
sudo systemctl enable sshd
sudo systemctl start sshd

Verify it’s running:

sudo systemctl status ssh

4. Basics of SSH

Getting started with SSH

• To get started visit topics/ssh/basics

5. Beyond the Basics

Exploring Advanced Examples

• To get more advanced examples/hands on visit topics/ssh/advanced

6. More…

Cheatsheet

• ssh user@host — connect to a remote host
• ssh -p 2222 user@host — connect on a custom port
• ssh-keygen -t ed25519 — generate a new key pair
• ssh-copy-id user@host — copy your public key to a remote host
• scp file.txt user@host:/path/ — copy a file to a remote host
• ssh -L 8080:localhost:80 user@host — local port forwarding

Recommended Books

• “SSH Mastery” by Michael W Lucas

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