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Passwordless SSH on Ubuntu: Secure Setup Guide

·365 words·2 mins
Linux SSH Ubuntu Security DevOps

Passwordless SSH on Ubuntu: Secure Setup Guide

Configuring password-free SSH login on an Ubuntu server is a foundational practice for improving both security and operational efficiency.

By leveraging asymmetric cryptography, you eliminate password-based attacks while enabling seamless automation and remote access.

🔐 Core Concept: Asymmetric Encryption
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SSH key authentication is based on a key pair:

  • Public Key (id_rsa.pub)
    Stored on the server — acts like a lock

  • Private Key (id_rsa)
    Kept securely on your local machine — acts like the key

Only a matching private key can unlock access, making brute-force attacks virtually ineffective.

⚙️ Step-by-Step Setup
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Step 1: Create a Dedicated User (Server-Side)
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Use adduser for a complete and interactive setup:

server$ sudo adduser vxbus
  • Automatically creates home directory
  • Sets default shell and environment

Step 2: Generate SSH Key Pair (Local Machine)
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If you don’t already have a key pair:

PC$ ssh-keygen -t rsa -b 4096
  • Keys stored in ~/.ssh/
  • Optional: add a passphrase for extra protection

💡 Modern alternative: ed25519 keys offer better performance and security.

Step 3: Copy Public Key to Server
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Use the recommended method:

PC$ ssh-copy-id -i ~/.ssh/id_rsa.pub vxbus@192.168.1.123

This ensures proper setup without manual errors.

🔍 What Happens Behind the Scenes
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Running ssh-copy-id performs several critical actions:

  1. Creates /home/vxbus/.ssh/ if it doesn’t exist
  2. Appends your public key to authorized_keys
  3. Sets strict permissions:
~/.ssh            → 700
authorized_keys   → 600

⚠️ SSH will reject login if permissions are too open.

🛡️ Advanced Security Hardening
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Once key-based login works, disable password authentication:

Step 1: Edit SSH config
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sudo nano /etc/ssh/sshd_config

Step 2: Update setting
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PasswordAuthentication no

Step 3: Restart SSH service
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sudo systemctl restart ssh

This prevents attackers from even attempting password-based access.

✅ Summary Checklist
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  • User Created Home directory and shell environment configured

  • Key Pair Generated id_rsa and id_rsa.pub available

  • Public Key Installed Present in ~/.ssh/authorized_keys

  • Permissions Secured .ssh = 700, authorized_keys = 600

🧠 Key Takeaway
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Passwordless SSH is not just a convenience—it’s a security baseline for modern systems.

It enables:

  • Safer remote access
  • Automation (CI/CD, scripts, orchestration)
  • Reduced attack surface

For larger environments, this setup becomes the foundation for tools like Ansible and other configuration management systems.

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