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Use SSH keys on Linux for password-less authentication

Updated:
ssh , ssh key , authentication

To use SSH keys on Linux for secure, password-less authentication, follow these steps:

1. Generate an SSH Key Pair

Terminal window
ssh-keygen -t ed25519 -C "[email protected]"  # Recommended (Ed25519)

Or for RSA:

Terminal window
ssh-keygen -t rsa -b 4096 -C "[email protected]"

Output: Two files created:

  • Private key: ~/.ssh/id_ed25519 (keep this secure; never share it).
  • Public key: ~/.ssh/id_ed25519.pub (copy to servers).

2. Copy the Public Key to the Server

Method 1: Use ssh-copy-id:

Terminal window
ssh-copy-id -i ~/.ssh/id_ed25519.pub username@server_ip
  • Enter your server password when prompted.
  • This appends your public key to ~/.ssh/authorized_keys on the server.

Method 2: Manual Copy:

Display your public key:

Terminal window
cat ~/.ssh/id_ed25519.pub

Log in to the server and paste the key into ~/.ssh/authorized_keys:

Terminal window
mkdir -p ~/.ssh
echo "public_key_string" >> ~/.ssh/authorized_keys
chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

3. Connect via SSH

Terminal window
ssh -i ~/.ssh/custom_key_name username@server_ip

Troubleshooting

Terminal window
chmod 700 ~/.ssh && chmod 600 ~/.ssh/id_ed25519*