Ubuntu SSH Server Refused Our Key: Troubleshooting Guide

🔍 Overview

If you are encountering “ssh server refused our key” error while trying to access your remote Ubuntu server, you are not alone. The error usually occurs when the SSH server doesn’t accept your authentication key, making it impossible to establish a connection between your local machine and the remote server. This error can be frustrating, especially if you need to access your server urgently.

In this comprehensive guide, we’ll walk you through the steps involved in troubleshooting the “ubuntu ssh server refused our key” error and explain the possible causes of the problem. We’ll also look at the advantages and disadvantages of using SSH key authentication and provide helpful tips on how to prevent the error from happening in the future.

👀 Opening

Welcome to our troubleshooting guide on ubuntu ssh server refused our key error. If you’re reading this, you’ve probably encountered the frustrating error while trying to access your remote server. Don’t worry; we’ve got you covered. In this guide, we’ll help you identify the problem and provide effective solutions that will help you regain access to your server in no time.

Before we dive into the troubleshooting steps, let’s first understand what SSH authentication is and how it works.

What is SSH Authentication?

SSH (Secure Shell) authentication is a method of securely logging into a remote computer over the internet or network. Instead of typing a username and password, SSH uses public-key cryptography to authenticate the user. The user generates a public and private key pair using a tool like ssh-keygen, and then shares the public key with the remote server. The user then uses their private key to authenticate themselves when logging in to the remote server.

The SSH authentication method is considered more secure than the traditional username and password method since it eliminates the risk of brute-force attacks, where an attacker can repeatedly attempt to log in with different password combinations. However, SSH authentication can also be prone to errors, such as the “ubuntu ssh server refused our key” error.

What Causes the “Ubuntu SSH Server Refused Our Key” Error?

The “ubuntu ssh server refused our key” error can occur due to various reasons, including:

🔎 Troubleshooting

Step 1: Check SSH Key Permissions

The first thing to check when you encounter the “ubuntu ssh server refused our key” error is the permissions on your SSH key file. Make sure that the file permissions are set to 600, which means that only you (the owner) can read and write the file.

To check the permissions, navigate to the directory where your SSH private key is stored and use the ls -l command to display the permissions. You should see something like:

-rw-------1 userstaff1.7K Jan1 20:00 id_rsa

If the permissions are set incorrectly, use the chmod command to change them. For example, to set the permissions to 600, you can run:

chmod 600 ~/.ssh/id_rsa

Step 2: Verify Public Key on Server

Another reason for the “ubuntu ssh server refused our key” error could be that the public key on the server doesn’t match the private key on your local machine. To fix this, you need to verify that the public key in your ~/.ssh/authorized_keys file on the server matches the public key in your local machine’s ~/.ssh/id_rsa.pub file.

You can do this by using the ssh-keygen command to generate the fingerprint of your local public key and compare it with the fingerprint of the public key on the server. The fingerprints should match exactly:

$ ssh-keygen -l -f ~/.ssh/id_rsa.pub2048 SHA256:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX user@local.machine (RSA)

$ ssh user@remote-server 'ssh-keygen -lf /dev/stdin' < ~/.ssh/authorized_keys2048 SHA256:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX user@local.machine (RSA)

If the fingerprints don’t match, you need to update the public key on the server with the one from your local machine. Copy the contents of ~/.ssh/id_rsa.pub from your local machine and add it to the end of the ~/.ssh/authorized_keys on the server.

Step 3: Check Username and Password

Make sure that you are using the correct username and password to log in to the remote server. If you are not sure about the username or password, you can check with your system administrator or refer to the server documentation.

Step 4: Disable Firewall

If you have a firewall running on your local machine or the remote server, try disabling it temporarily to see if it’s causing the problem. If the error disappears after disabling the firewall, you need to configure the firewall to allow SSH traffic on port 22.

Step 5: Restart SSH Server

If the “ubuntu ssh server refused our key” error persists after trying the above steps, you should try restarting the SSH server. To do this, connect to the server through another method, such as the console or physical access, and restart the SSH service:

$ sudo systemctl restart ssh

Step 6: Check SSH Server Configuration

If the error still occurs, it may be due to an error in the SSH server configuration file (sshd_config). Check the contents of the file to ensure that it’s configured correctly.

Step 7: Contact System Administrator

If none of the above steps helps, you should contact your system administrator for further assistance. They should have more experience in troubleshooting SSH-related issues and will be able to provide you with more advanced support.

👍 Advantages and Disadvantages of Using SSH Authentication

Advantages of SSH Authentication

Using SSH authentication has several advantages over traditional username and password authentication:

• More secure: SSH authentication uses public-key cryptography, which eliminates the risk of brute-force attacks.
• Convenient: You don’t have to remember and type in a password every time you log in to the remote server.
• Automated: You can automate SSH authentication using tools like ssh-agent and ssh-add, which can save you time and effort.

Disadvantages of SSH Authentication

While SSH authentication has many advantages, it also has some drawbacks:

• Complex setup: Setting up SSH authentication requires more technical knowledge than traditional authentication.
• Key management: Managing SSH keys can be challenging, especially if you have multiple keys for different servers.
• Revoking access: If someone gains access to your private key, you need to revoke access manually by removing the public key from the authorized_keys file on all servers where it’s installed.

🙋‍♂️ FAQs

1. What is an SSH key?

An SSH key is a pair of cryptographic keys that are used for authentication when logging into a remote server.

2. How do I generate an SSH key?

You can generate an SSH key using the ssh-keygen command in the terminal. The command will create a public and private key pair that you can use for authentication.

3. What is the difference between a public key and a private key?

A public key is shared with the remote server, while the private key is kept on your local machine. The public key is used to authenticate you when logging in to the remote server.

4. How do I add my SSH key to the remote server?

You can add your SSH key to the remote server by appending the contents of your public key file to the ~/.ssh/authorized_keys file on the server.

5. Can I use the same SSH key for multiple servers?

Yes, you can use the same SSH key for multiple servers. However, it’s generally a good idea to use a different key for each server to minimize the risk of compromise.

6. What do I do if I lose my private key?

If you lose your private key, you need to generate a new one and remove the old public key from all servers where it’s installed.

7. How do I troubleshoot the “ubuntu ssh server refused our key” error?

To troubleshoot the “ubuntu ssh server refused our key” error, you need to check the permissions on your SSH key file, verify the public key on the server, check the username and password, disable the firewall, restart the SSH server, check the SSH server configuration, and contact your system administrator if the problem persists.

8. How do I prevent the “ubuntu ssh server refused our key” error from happening?

To prevent the “ubuntu ssh server refused our key” error from happening, you need to ensure that the permissions on your SSH key file are correct, use a strong passphrase to protect your private key, and keep your software up to date.

9. Can I use SSH authentication on Windows?

Yes, you can use SSH authentication on Windows by installing an SSH client, such as PuTTY or OpenSSH, and generating an SSH key pair.

10. Can I use SSH authentication with Git?

Yes, you can use SSH authentication with Git by adding your public key to your Git account and configuring your Git client to use SSH instead of HTTPS.

11. What is two-factor authentication (2FA) for SSH?

Two-factor authentication (2FA) for SSH adds an extra layer of security by requiring the user to provide a second authentication factor, such as a code from a mobile app, in addition to their SSH key.

12. What are some alternatives to SSH authentication?

Some alternatives to SSH authentication include passwordless login, LDAP authentication, and multi-factor authentication (MFA).

13. Is SSH authentication more secure than password authentication?

Yes, SSH authentication is generally considered more secure than password authentication because it eliminates the risk of brute-force attacks.

👉 Conclusion

In conclusion, the “ubuntu ssh server refused our key” error can be frustrating, but it’s relatively easy to fix if you follow the troubleshooting steps outlined in this guide. Remember to check the permissions on your SSH key file, verify the public key on the server, and make sure that you’re using the correct username and password. SSH authentication has many advantages over traditional authentication, but it also has some drawbacks. To prevent the error from happening, keep your software up to date and follow best practices for SSH key management.

💡 Disclaimer

The information in this article is provided “as is” and without warranties of any kind, either express or implied. The author and publisher disclaim any liability for any damages or losses incurred as a result of using the information in this article.

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