How to Fix: Permission denied (publickey) with error message: receive packet: type 51

The error 'Permission denied (publickey)' with the message 'receive packet: type 51' occurs when the SSH client is unable to verify the authenticity of the public key used for authentication. This issue affects users who have been granted administrative access to a specific Ubuntu instance, despite having successfully logged in to other instances using the same SSH keys.

This error can be frustrating as it prevents the user from accessing their instance, and it may take some time to troubleshoot the issue. However, by following the steps outlined below, you should be able to resolve the problem and regain access to your instance.

⚠️ Common Causes

• The primary reason for this error is that the SSH server on the target instance is not configured to accept public key authentication. This can occur if the SSH server configuration file (/etc/ssh/sshd_config) has been modified or if the SSH server is not properly installed.
• Another possible cause is that the user's public key has not been correctly registered with the SSH server. This may be due to a misconfiguration of the SSH client or server, or it could be a result of an issue with the user's SSH keys themselves.

🔧 Proven Troubleshooting Steps

💡 Conclusion

To resolve the 'Permission denied (publickey)' error with the message 'receive packet: type 51', first check and update the SSH server configuration to enable public key authentication. If that does not work, check and update the user's public key registration by adding the SSH key to the keyring and registering it with the SSH server. By following these steps, you should be able to regain access to your instance.