Linux SSH Authentication | Engineering Notes

🎯 Objective

Configure SSH authentication in Linux to securely allow users to access a server remotely.

SSH authentication ensures that only authorized users can connect to the system.

🔐 What is SSH?

SSH (Secure Shell) is a protocol used to securely connect to remote systems over a network.

It provides:

Encrypted communication

Secure remote login

Secure command execution

Secure file transfer (SCP / SFTP)

Example connection:

bash

ssh user@server-ip

Example:

bash

ssh devops@192.168.1.10

🔑 Types of SSH Authentication

Linux supports two common authentication methods:

Key-based authentication is more secure and commonly used in DevOps environments.

🛠️ Step 1: Generate SSH Key Pair

Generate an SSH key on the client machine:

bash

ssh-keygen

Example output:

bash

Generating public/private rsa key pair.

Files created:

bash

~/.ssh/id_rsa
~/.ssh/id_rsa.pub

📤 Step 2: Copy Public Key to Server

Use the following command:

bash

ssh-copy-id user@server-ip

Example:

bash

ssh-copy-id devops@192.168.1.10

This copies the public key to:

bash

/home/user/.ssh/authorized_keys

🔍 Step 3: Test SSH Login

Now login without a password:

bash

ssh user@server-ip

Example:

bash

ssh devops@192.168.1.10

⚙️ Step 4: Configure SSH Server

Edit the SSH configuration file:

bash

sudo nano /etc/ssh/sshd_config

Important settings:

bash

PasswordAuthentication no
PubkeyAuthentication yes
PermitRootLogin no

Restart SSH service:

bash

sudo systemctl restart sshd

🔍 Step 5: Verify SSH Service

Check SSH service status:

bash

sudo systemctl status sshd

⚠️ Important Notes

Keep the private key secure

Do not share private keys

Disable password authentication in production

Restrict SSH access using firewalls or security groups

🎯 Result

SSH key authentication configured

Secure remote login enabled

Password-based access disabled for better security