Permission Denied Publickey Gssapi Keyex Gssapi With Mic Password

Permission Denied (publickey, gssapi-keyex, gssapi-with-mic): Troubleshooting SSH Connection Issues

Getting a "Permission denied (publickey, gssapi-keyex, gssapi-with-mic)" error when trying to connect via SSH is frustrating, but thankfully solvable. This error means your SSH client couldn't authenticate to the server using any of the methods it tried: publickey, GSSAPI key exchange, or GSSAPI with message integrity check. This comprehensive guide will walk you through the most common causes and solutions. We'll cover troubleshooting steps for both the client and server sides.

Understanding the Error Message

The error message itself points to authentication failures. Let's break down each part:

• publickey: This refers to SSH key authentication, the most secure method. The server couldn't find your public key in its authorized_keys file.
• gssapi-keyex: This uses Kerberos for authentication, a common method within enterprise networks. The authentication failed due to Kerberos configuration issues.
• gssapi-with-mic: Similar to gssapi-keyex, but adds a message integrity check for enhanced security. Failure here also points to Kerberos configuration problems.

Troubleshooting Steps

We'll tackle this systematically, focusing on potential problems on both the client (your computer) and the server (the remote machine).

1. Client-Side Troubleshooting:

• Check SSH Keys:
  • Generate a key pair (if you don't have one): If you've never connected to this server before, you'll need an SSH key pair. Use ssh-keygen to generate one. Choose a strong passphrase.
  • Copy your public key: Use ssh-copy-id username@server_ip to securely copy your public key to the authorized_keys file on the server. This command simplifies the process.
  • Verify key location: Your private key should be in ~/.ssh/id_rsa (or a similar location, depending on the key type you generated). Ensure its permissions are restrictive (e.g., chmod 600 ~/.ssh/id_rsa).
• Check SSH Configuration: The ~/.ssh/config file allows you to specify connection parameters. Ensure that the HostName, User, and IdentityFile settings are correct. Incorrect settings here can lead to authentication issues.
• Restart SSH Agent: If you're using an SSH agent (like ssh-agent), try restarting it. This can resolve issues with cached credentials.
• Check Network Connectivity: Ensure you can ping the server. Network problems can prevent SSH connections.

2. Server-Side Troubleshooting:

• Check SSH Server Configuration: The SSH server on the remote machine needs to be properly configured to allow the authentication methods you're using. Verify that publickey authentication is enabled in the SSH server configuration file (usually /etc/ssh/sshd_config).
• Verify Authorized Keys File: Ensure the authorized_keys file exists in the .ssh directory of the user's home directory and has the correct permissions (600). A typo in the file can also prevent authentication.
• Check Kerberos Configuration (for gssapi methods): If you're using GSSAPI, the Kerberos setup on both the client and server needs to be correctly configured. This often involves verifying Kerberos tickets, checking the KDC (Key Distribution Center) settings, and ensuring proper hostname resolution. This is a more complex area requiring familiarity with Kerberos.
• Firewall Rules: Check if the server's firewall is blocking SSH connections on port 22. You might need to open this port.
• Restart SSH Service: Restarting the SSH daemon (sshd) on the server can clear any transient issues.

3. Password Authentication (Last Resort):

If all else fails, you can try enabling password authentication, but this is generally less secure than key-based authentication. Locate the /etc/ssh/sshd_config file on the server and temporarily change PasswordAuthentication from no to yes. Remember to change it back to no for enhanced security after resolving the issue.

By systematically working through these steps, checking both client and server configurations, you should be able to resolve the "Permission denied" error and successfully establish your SSH connection. Remember to prioritize security best practices and use SSH keys whenever possible.