SSH Passwordless Authentication Setup

Set up SSH key-based authentication to connect from your local machine to a remote server without entering a password each time.

Prerequisites

• Access to both local and remote machines
• SSH server running on remote machine
• Terminal/command-line access

Setup Steps

1. Generate SSH Key Pair

ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519

• Press Enter twice when prompted for passphrase (or set one for added security)
• Skip this step if you already have an SSH key
• Creates two files: id_ed25519 (private key) and id_ed25519.pub (public key)

2. Copy Public Key to Remote Server

ssh-copy-id username@remote-server-ip

Replace:

• username with your remote username
• remote-server-ip with the server's IP address or hostname

Example:

ssh-copy-id john@192.168.1.100

• Enter your remote server password when prompted
• This is the last time you'll need to enter the password

3. Test the Connection

ssh username@remote-server-ip

Success: You connect without a password prompt
Failure: You're still asked for a password (troubleshoot below)

Troubleshooting

Still Asking for Password?

Check permissions on remote server:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

Verify SSH server configuration (/etc/ssh/sshd_config):

PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys

Restart SSH service (on remote server):

sudo systemctl restart sshd

Key Not Found?

Manually copy the key:

cat ~/.ssh/id_ed25519.pub | ssh username@remote-server-ip "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"

Security Best Practices

1. Protect your private key

   • Never share ~/.ssh/id_ed25519
   • Set appropriate permissions: chmod 600 ~/.ssh/id_ed25519

2. Use a passphrase (recommended)

   • Adds extra security layer
   • Use ssh-agent to avoid typing it repeatedly

3. Disable password authentication (after key setup works)

   • Edit /etc/ssh/sshd_config on remote server
   • Set: PasswordAuthentication no
   • Restart SSH: sudo systemctl restart sshd

Platform-Specific Notes

macOS

• Open Terminal (Spotlight → "Terminal")
• SSH client pre-installed

Linux

• Use default terminal emulator
• SSH client typically pre-installed

Windows

• Use PowerShell, Command Prompt, or Git Bash
• Windows 10/11 has built-in SSH client
• Alternative: Use PuTTY with PuTTYgen for key generation

Common Use Cases

• Remote server administration
• Git operations (GitHub, GitLab, etc.)
• Automated scripts and deployments
• Development environment access
• File transfers with scp or rsync

Additional Resources

Test key authentication:

ssh -v username@remote-server-ip

The -v flag shows verbose output for debugging

Use specific key file:

ssh -i ~/.ssh/custom_key username@remote-server-ip

Add key to SSH agent (avoid passphrase prompts):

ssh-add ~/.ssh/id_ed25519

Summary

Once configured, you can connect to your remote server securely without typing passwords, making workflows faster and enabling automation.