SSH

SSH: The Secure Lifeline

The Instructor's Perspective

In the Army, we had “secure lines of communication.” In the Linux world, SSH (Secure Shell) is that line. If you are still using passwords to log into your servers, you are “walking point” without a weapon. Use keys. Every. Single. Time.

Why use it?

• Secure Remote Management: Encrypted access to your command line.
• Automation: The foundation for tools like Ansible.
• File Transfer: Using scp or sftp to move data securely.
• Tunneling: Securely “wrapping” other traffic (like VNC or web) through an SSH connection.

Remote Access Reliability (The PACE Plan)

Access Discipline

P (Primary): SSH Keys via LAN (Internal network). A (Alternate): SSH Keys via Wireguard or Tailscale VPN. C (Contingency): Proxmox Web Console (No-SSH fallback). E (Emergency): Physical KVM (Keyboard, Video, Mouse) at the server rack.

SOP: Managing SSH Keys

1. Generate: ssh-keygen -t ed25519 -C "your_email@example.com" (Ed25519 is faster and more secure than RSA).
2. Distribute: Use ssh-copy-id user@hostname to move your public key to the server.
3. Lock Down: Edit /etc/ssh/sshd_config to set PasswordAuthentication no.
4. The GitHub Trick: You can pull your public keys from GitHub to a new server using: curl https://github.com/your-username.keys >> ~/.ssh/authorized_keys

Check for Understanding

• Why is an Ed25519 key preferred over an RSA key in a modern environment?
• What happens to your Alternate plan if your Wireguard service fails?

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Related: The Stack, Shell, Ansible