How to Set Up SSH Key Authentication and Disable Password Login on Ubuntu Server

ByAkensai

Learning how to set up SSH key authentication and disable password login on Ubuntu Server is one of the most important security steps you can take. Password-based logins are vulnerable to brute-force attacks. Hackers run automated scripts that try thousands of password combinations every minute. SSH key authentication stops that cold. Instead of a password, you use a cryptographic key pair , a private key you keep on your machine and a public key stored on the server. Only someone with the matching private key can log in. This tutorial walks you through generating your SSH key pair, copying it to your Ubuntu server, and disabling password login entirely. By the end, your server will be significantly more secure. This guide assumes you have basic Linux command-line experience and an existing Ubuntu server you can access.

Prerequisites for Setting Up SSH Key Authentication and Disabling Password Login on Ubuntu Server

Before you start, make sure you have the following in place.

What you need:

– An Ubuntu server (18.04, 20.04, or 22.04 LTS recommended)
– A local machine running Linux, macOS, or Windows with OpenSSH installed
– An existing user account with sudo privileges on the server
– Current SSH password access to the server (you’ll need this before switching)

Assumed knowledge:

– Basic terminal and command-line usage
– How to connect to a remote server via SSH
– Familiarity with a text editor like nano or vim

Estimated time: 15–30 minutes

Important warning: Don’t close your current SSH session until you’ve confirmed key-based login works. Locking yourself out of your own server is a real risk if you skip that step.

For reference, the official Ubuntu OpenSSH documentation covers additional configuration options you may find useful.

Step-by-Step Guide to Set Up SSH Key Authentication and Disable Password Login on Ubuntu Server

Related article: How to Set Up Nginx as a Reverse Proxy for Docker Containers with Ssl and Load Balancing

Follow these steps carefully and in order.

Step 1: Generate an SSH key pair on your local machine

Open a terminal on your local computer. Run this command:

ssh-keygen -t ed25519 -C "[email protected]"

The -t ed25519 flag creates a modern, secure key type. When prompted, choose a save location (the default ~/.ssh/id_ed25519 is fine). Set a strong passphrase when asked. This passphrase protects your private key if someone gains access to your local machine.

Step 2: Copy your public key to the server

Use the ssh-copy-id command to transfer your public key:

ssh-copy-id -i ~/.ssh/id_ed25519.pub your_username@your_server_ip

Replace your_username and your_server_ip with your actual values. You’ll be asked for your password one last time. The command automatically adds your public key to ~/.ssh/authorized_keys on the server.

If you’re on Windows and ssh-copy-id isn’t available, run this instead:

type $env:USERPROFILE.sshid_ed25519.pub | ssh your_username@your_server_ip "cat >> ~/.ssh/authorized_keys"

Step 3: Test key-based login before changing anything

Open a new terminal window. Don’t close your current session yet. Connect to your server:

ssh -i ~/.ssh/id_ed25519 your_username@your_server_ip

If you log in successfully without entering a password (only your key passphrase if set), you’re ready to proceed. If it fails, stop here and check Step 2 again.

Step 4: Set correct permissions on the server

SSH is strict about file permissions. If they’re wrong, key authentication silently fails. On the server, run:

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

These commands ensure only your user can read or write those files.

Step 5: Edit the SSH daemon configuration

Now you’ll disable password login. On the server, open the SSH config file:

sudo nano /etc/ssh/sshd_config

Find and update these lines. Change them to match exactly:

PasswordAuthentication no
PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys
PermitRootLogin no
ChallengeResponseAuthentication no

Setting PermitRootLogin no prevents direct root logins. That’s an extra layer of protection. Save the file with Ctrl+O, then exit with Ctrl+X.

Step 6: Restart the SSH service

Apply your changes by restarting SSH:

sudo systemctl restart sshd

Check that the service is running properly:

sudo systemctl status sshd

You should see active (running) in the output.

Step 7: Verify password login is disabled

Open yet another new terminal window. Try connecting with a password explicitly:

ssh -o PreferredAuthentications=password your_username@your_server_ip

You should get a “Permission denied” error. That means it’s working. Your server now only accepts key-based logins.

Troubleshooting SSH Key Authentication Issues on Ubuntu Server

Things don’t always go smoothly. Here are the most common problems and how to fix them.

Problem: “Permission denied (publickey)” error

This usually means the server can’t find your key. Check these things:

– Confirm ~/.ssh/authorized_keys on the server contains your public key
– Run chmod 700 ~/.ssh and chmod 600 ~/.ssh/authorized_keys again
– Make sure you’re specifying the right key with -i ~/.ssh/id_ed25519

Problem: SSH service won’t restart after config changes

Check your config file for typos:

sudo sshd -t

This command tests the configuration without restarting. It will point out any syntax errors.

Problem: Locked out of the server

If you’re on a VPS, use your provider’s web console or rescue mode to access the server. From there, you can revert sshd_config changes. This is why keeping your original SSH session open during testing is so important.

Problem: Windows users can’t connect with their key

Make sure your ~/.ssh/config file on Windows points to the right key:

Host your_server_ip
    IdentityFile C:UsersYourName.sshid_ed25519

For more detail on managing SSH keys, the OpenSSH official manual is an excellent reference.

Tip: Use an SSH config file for convenience

On your local machine, create or edit ~/.ssh/config:

Host myserver
    HostName your_server_ip
    User your_username
    IdentityFile ~/.ssh/id_ed25519

Now you can connect with just ssh myserver. Much faster.

Conclusion

You now know how to set up SSH key authentication and disable password login on Ubuntu Server. Your server no longer accepts password-based logins. Brute-force attacks will fail instantly. You’ve generated a secure key pair, deployed the public key, hardened your SSH config, and verified everything works. These steps form the foundation of a secure server setup. From here, consider setting up a firewall with ufw, enabling automatic security updates, or configuring fail2ban for additional protection. If you manage a WordPress site on this server, securing SSH access is one of the first things you should do before anything else. Good security habits compound over time. Start with SSH, and build from there.

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