Permission Denied Publickey Gssapi Keyex Gssapi With Mic

Permission Denied: publickey, gssapi-keyex, gssapi-with-mic - Troubleshooting SSH Connection Errors

This article delves into the common SSH connection errors: "Permission denied (publickey)", "gssapi-keyex", and "gssapi-with-mic". These errors often indicate problems with SSH key authentication or GSSAPI configuration. We'll explore the causes, and provide troubleshooting steps to regain SSH access. Understanding these issues is crucial for maintaining secure remote access to your servers.

Understanding the Errors

• Permission denied (publickey): This classic error means the SSH server doesn't recognize your public key for authentication. Your server likely lacks your public key or there's a problem with the key's permissions or location.

• gssapi-keyex: This indicates an issue with the GSSAPI key exchange process. GSSAPI (Generic Security Service Application Program Interface) provides a secure method for key exchange and authentication, often using Kerberos. An error here points to a problem with your Kerberos configuration, network connectivity, or GSSAPI settings on either the client or server.

• gssapi-with-mic: Similar to gssapi-keyex, this error signifies a failure in the GSSAPI authentication process, specifically with the Message Integrity Code (MIC). The MIC verifies data integrity during authentication. Failures here usually stem from mismatched configurations or network issues.

Troubleshooting Steps

Here's a structured approach to troubleshoot these SSH connection errors:

1. Verify SSH Key Setup:

• Generate an SSH key pair (if you haven't already): Use the command ssh-keygen on your client machine. Choose a strong passphrase.
• Copy your public key: Locate your public key (usually ~/.ssh/id_rsa.pub or similar) and copy its contents.
• Authorize your public key on the server: Connect to the server (using password authentication if initially possible) and append your public key to the ~/.ssh/authorized_keys file on the server. Ensure the file has the correct permissions (e.g., chmod 600 ~/.ssh/authorized_keys). If the .ssh directory doesn't exist, create it with mkdir .ssh and set appropriate permissions (chmod 700 .ssh).

2. Check SSH Configuration Files:

• Client (~/.ssh/config): Check your client's config file for any incorrect settings that might interfere with key authentication or GSSAPI.
• Server (/etc/ssh/sshd_config): On the server, examine the sshd_config file. Ensure that PubkeyAuthentication is enabled (PubkeyAuthentication yes) and that GSSAPI authentication methods are correctly configured if needed. Consider relevant settings like GSSAPIAuthentication yes and GSSAPIKeyExchange yes. Restart the SSH daemon (sudo systemctl restart ssh) after making changes.

3. Investigate GSSAPI Configuration (if applicable):

• Kerberos: If using Kerberos, ensure that your Kerberos tickets are valid and that your client and server are properly configured to use Kerberos with SSH. Check Kerberos logs for errors. Verify network connectivity between your client and the Kerberos server.
• kinit: Before attempting to connect via GSSAPI, ensure you have a valid Kerberos ticket using kinit <username>.
• Firewall: Check firewalls on both client and server to ensure they are not blocking the necessary ports for SSH and Kerberos (if used).

4. Network Connectivity:

• DNS resolution: Ensure your client can correctly resolve the server's hostname.
• Network connectivity: Verify network connectivity between the client and the server using ping.

5. Check Server Logs:

Examine the server's SSH logs (/var/log/auth.log or a similar location depending on your Linux distribution) for any further error messages that might provide more clues.

6. Consider Other Authentication Methods:

If the above steps fail, temporarily revert to password authentication to rule out any key-related issues. This allows you to confirm if the network connectivity and server itself are functioning correctly. Remember to revert to public key authentication for enhanced security once the problem is resolved.

By systematically following these troubleshooting steps, you should be able to pinpoint the cause of the "Permission denied (publickey)", "gssapi-keyex", and "gssapi-with-mic" errors and restore your SSH connectivity. Remember to prioritize security and always use strong passwords and securely manage your SSH keys.