Troubleshooting SSH Key Authentication Errors

Learn how to resolve 'Permission denied (publickey)'

Troubleshooting SSH Key Authentication Errors


In the world of version control and secure data transmission, SSH keys are a fundamental component for authenticating connections between your local machine and remote servers. However, encountering errors like "Permission denied (publickey)" or "Could not open a connection to your authentication agent" can be frustrating. In this guide, we'll dive into common SSH key authentication errors, their causes, and step-by-step solutions to get you back on track.

Understanding SSH Key Authentication:

SSH (Secure Shell) keys provide a secure and convenient way to authenticate connections between your local and remote machines. They consist of a pair of keys: a private key stored on your local machine and a public key stored on the remote server.

Error 1: "Permission denied (publickey)":

This error often arises when the remote server rejects the public key provided by your local machine during the SSH handshake.

Common Causes:

  • Incorrect public key uploaded to your remote server.

  • Incorrect remote repository URL or username.

  • Private key not loaded into the SSH agent.


  1. Double-check your public key:

  2. Verify repository URL and username:

    • Confirm you're using the correct remote repository URL and username. Use git remote -v to check the URL.
  3. Load the private key into the SSH agent:

    • Start the agent: eval $(ssh-agent)

    • Add the private key: ssh-add ~/.ssh/id_ed25519

  4. Debug the connection using verbose mode:

    • Run: ssh -vT

    • This command provides detailed output, helping you pinpoint the issue if it persists.

Error 2: "Could not open a connection to your authentication agent":

This error occurs when the SSH agent isn't running or isn't properly configured.

Reasons for the Error:

  • SSH agent not started.

  • Incorrect environment variables.

Resolving the Issue:

  1. Start the SSH agent:

    • Run: eval $(ssh-agent)
  2. Add the private key to the agent:

    • Use: ssh-add ~/.ssh/id_ed25519

Best Practices for Managing SSH Keys:

  1. Generate a strong passphrase during key creation for added security.

  2. Regularly review and update your SSH keys.

  3. Use unique key pairs for different services or repositories.

  4. Keep your private keys secure and never share them.

  5. Consider using passphrase-protected keys for enhanced protection.


SSH key authentication is a crucial aspect of secure communication and version control. Understanding common errors like "Permission denied (publickey)" and "Could not open a connection to your authentication agent" can save valuable time and frustration. By following the solutions provided in this guide and adopting best practices for SSH key management, you'll ensure smooth and secure interactions between your local and remote systems.

Remember, troubleshooting SSH key issues is an essential skill for any developer or IT professional, and armed with this knowledge, you'll be better equipped to navigate these challenges effectively.

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