How to Generate and Utilize SSH Keys on Linux

Generating and Using SSH Keys on Linux (Step-by-Step)

SSH keys provide a secure and convenient way to authenticate to remote servers without relying on passwords. They offer stronger security and greatly reduce the risk of brute-force attacks.

Step 1 — Check for Existing SSH Keys

Before generating a new key pair, check whether you already have SSH keys:

ls ~/.ssh

If you see files such as id_rsa and id_rsa.pub, you already have an SSH key pair and can use it immediately.

Step 2 — Generate a New SSH Key Pair

If you need a new key pair, run the following command:

ssh-keygen -t rsa -b 2048

• -t rsa: Specifies the key type
• -b 2048: Sets the key size

You will be prompted to choose a location for the new key:

~/.ssh/id_rsa

You can also set an optional passphrase for additional protection.

Step 3 — Copy the Public Key to the Remote Server

To enable key-based access, copy your public key to the remote server:

ssh-copy-id username@remote_server

Replace username with your remote account name and remote_server with the server’s address.

Step 4 — Test SSH Key Login

After copying the key, test your connection:

ssh username@remote_server

If you set a passphrase, you will be prompted to enter it.

Additional Tips

• Use SSH Agent
  • Start the SSH agent:

  eval "$(ssh-agent -s)"

  • Add your key:

  ssh-add ~/.ssh/id_rsa

• Configure SSH
  • You can configure per-host settings in:

  ~/.ssh/config

• Revoke Access
  • If your private key is compromised, remove the corresponding public key from authorized_keys on the server.
• Use Separate Keys
  • Consider using different SSH keys for different servers or services.

Frequently Asked Questions

What is an SSH key?

An SSH key is a cryptographic authentication method that allows secure access to a server without using a password.

Do I need a passphrase?

A passphrase adds an extra layer of security by encrypting your private key. It is recommended, especially for sensitive environments.

Can I use the same SSH key on multiple servers?

Yes. You can add the same public key to the authorized_keys file on different servers and use one private key to connect.

What happens if I lose my private key?

If you lose your private key, you will not be able to access servers that rely on it. You must generate a new key and update access.