Troubleshooting Tip: Permission Denied (Public Key) Error on EC2 Instance

1. Introduction

If you are encountering a "Permission Denied (Public Key)" error on the EC2 instance, you are not alone. This common error can be frustrating and cause delays in your workflow. However, there are troubleshooting steps you can take to resolve this issue and regain access to your EC2 instance. In this blog, we will outline the possible causes of this error and provide step-by-step instructions on how to fix it. Whether you are a beginner or an experienced user, this guide will help you overcome the "Permission Denied (Public Key)" error and get back to work on your AWS instance.

2. Understanding the "Permission Denied (Public Key) Error"

The "Permission Denied (Public Key)" error is a common issue that users may encounter when trying to access their EC2 instance on AWS. This error occurs when the SSH key pair being used to authenticate the user is not properly set up or configured.

SSH (Secure Shell) is a cryptographic network protocol that allows secure communication between a client and a server. It is commonly used for remote login and executing commands on a remote machine. To authenticate the user and establish a secure connection, SSH uses public key cryptography.

How to Generate an SSH Key Pair (with Examples)

When setting up an EC2 instance on AWS, users are required to generate a key pair consisting of a public key and a private key. The public key is placed on the server, while the private key is kept securely on the user's local machine. When attempting to access the EC2 instance, the client's SSH client uses the private key to authenticate with the public key stored on the server.

The "Permission Denied (Public Key)" error commonly occurs when there is a mismatch between the public key stored on the server and the private key being used by the client. This can happen for several reasons, including:

1. Incorrect key pair: The user may be using a different key pair than the one associated with the EC2 instance. It is essential to ensure that the correct key pair is being used.

2. Incorrect permissions: The permissions for the private key file may be set incorrectly, preventing the SSH client from accessing it. The private key file should have permissions set to 400 (-r--------) to ensure that only the user has read access.

3. Key pair deleted or regenerated: If the key pair associated with the instance has been deleted or regenerated, the old private key will no longer work. In such cases, the user will need to generate a new key pair and associate it with the instance.

3. Troubleshooting Steps: Checking your Key Pair

3. Troubleshooting Steps: Checking Your Key Pair

When encountering the "Permission Denied (Public Key)" error on the EC2 instance, it is essential to check your key pair configuration. Follow these steps to troubleshoot and fix the issue:

1. Verify Correct Key Pair: Begin by confirming that the SSH key pair being used for authentication matches the key pair associated with the EC2 instance. Mistakenly using an incorrect key pair can result in the "Permission Denied (Public Key)" error. Ensure that you have the correct public and private key files.

2. Ensure Proper Permissions: Incorrect permissions on the private key file can also cause the error. The private key file should have permissions set to 400 (-r--------), allowing only the user to have read access. Ensure that the permissions are correctly set for the private key file.

3. Regenerated or Deleted Key Pair: If the key pair linked to the instance has been deleted or regenerated, the old private key will no longer function. In such cases, you need to generate a new key pair and associate it with the instance. Remember to update your SSH client configuration with the new private key.

4. Generate SSH key using keygen command: To generate an SSH key pair on your local system and associate the public key with your EC2 instance, follow these steps:

After generating this public key, go to the SSH folder on your PC. You can find it as C:\Users\User_name\.ssh. There will be a hidden file named "authorzied_keys". Replace the content of this file with the public key that you have generated using keygen. Save this file. After that, run :

ssh -i /path/to/your/private/key ubuntu@your-instance-public-dns

By following these troubleshooting steps and addressing any issues with your key pair configuration, you can resolve the "Permission Denied (Public Key)" error. In the next section, we will provide further guidance on troubleshooting and fixing the error.

4. Additional Troubleshooting Steps

If you have followed the previous steps and are still encountering issues with the "Permission Denied" error on the EC2 instance, here are some additional troubleshooting steps to help you identify and resolve the problem:

1. Restart Services: In some cases, restarting the relevant services can resolve permission issues. For example, if you are experiencing permission issues with a web server, try restarting the web server service using the appropriate command (e.g. sudo service apache2 restart).

2. Check Security Group Rules: If you are accessing EC2 instances through a network connection, verify that the security group rules associated with the instance are configured correctly. Ensure that the necessary inbound and outbound rules are configured to allow the desired network traffic.

3. Review System Logs: Examine system logs and error messages for any clues about the cause of the permission issues. System logs can provide valuable information to help troubleshoot and resolve the problem. Look for any error messages related to permissions or access.

By following these additional troubleshooting steps, you can further investigate and address permission issues on the EC2 instance. Remember to document any changes or steps taken during the troubleshooting process for future reference.

5. Conclusion and Final Thoughts

In conclusion, By following the steps outlined in this guide, you can effectively identify and resolve the problem. By implementing these strategies and persistently working through the troubleshooting steps, you can overcome the "Permission Denied" error and ensure a smooth operation on EC2 instances.

Remember, troubleshooting is an essential skill for any system administrator, and by applying the knowledge and techniques discussed in this guide, you can become more proficient in resolving permission-related issues and maintaining the stability and security of your systems.