devops-notes/05_Linux_SSH_Remote_Access.md

Linux – SSH & Remote Server Access (Day 5)

What is SSH?

SSH (Secure Shell) is used to securely connect to a remote server. DevOps engineers use SSH daily to manage cloud servers.

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Why SSH is Important for DevOps?

• Access cloud servers (AWS EC2, VPS)
• Deploy applications
• Debug production issues
• Manage configurations

No SSH = no DevOps work.

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Basic SSH Syntax

ssh user@server_ip

Example:

ssh ubuntu@13.234.56.78

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Default SSH Port

• Port 22

Custom port example:

ssh -p 2222 user@server_ip

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SSH First-Time Connection

You may see:

Are you sure you want to continue connecting (yes/no)?

Type:

yes

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SSH Key-Based Authentication (VERY IMPORTANT)

Instead of passwords, DevOps uses SSH keys.

Benefits:

• More secure
• No password typing
• Required by cloud providers

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Generate SSH Key

ssh-keygen

Press Enter for defaults.

This creates:

• private key → ~/.ssh/id_rsa
• public key → ~/.ssh/id_rsa.pub

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Copy SSH Key to Server

ssh-copy-id user@server_ip

Or manually copy:

cat ~/.ssh/id_rsa.pub

Paste into server:

~/.ssh/authorized_keys

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Login Using SSH Key

ssh user@server_ip

(No password needed)

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SSH Config File (PRO TIP)

Create:

~/.ssh/config

Example:

Host myserver
    HostName 13.234.56.78
    User ubuntu
    IdentityFile ~/.ssh/id_rsa

Now connect using:

ssh myserver

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Common SSH Commands

exit            # logout
whoami          # check user
hostname        # server name
uptime          # server running time

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Common SSH Errors

• Permission denied
• Wrong user
• Wrong key
• Port blocked by firewall

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DevOps Best Practices

• Disable password login
• Use key-based auth only
• Never share private key
• Use least privilege users

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Real DevOps Scenario

1. Create EC2 instance
2. SSH into server
3. Install Docker
4. Deploy application

SSH is the entry point.

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Summary

Today I learned SSH basics, key-based authentication, and how DevOps engineers securely connect to remote servers.