Permission Denied (publickey) With Error Message: Receive Packet: Type 51

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Understanding SSH Keys and Permission Issues

When working with SSH keys, it's not uncommon to encounter permission issues that prevent you from accessing your instances. In this article, we'll delve into the world of SSH keys and explore the common problem of "Permission denied (publickey)" with the error message "receive packet: type 51." We'll also discuss the specific scenario where you can log into all Ubuntu instances with GCP using the same SSH keys, except for one instance.

What are SSH Keys?

SSH keys are a way to authenticate users to a remote server without the need for a password. They consist of a public key and a private key. The public key is stored on the server, while the private key is stored on the client machine. When you try to connect to a server using SSH, the client machine sends the public key to the server, which then verifies it against the stored public key. If the keys match, the server grants access to the client machine.

Permission Denied (Publickey) Error

The "Permission denied (publickey)" error occurs when the SSH client is unable to authenticate with the server using the public key. This can happen due to various reasons, such as:

  • Incorrect key permissions: The private key file may not have the correct permissions, which prevents the SSH client from reading it.
  • Key not added to the authorized_keys file: The public key may not be added to the authorized_keys file on the server, which prevents the server from verifying the key.
  • Key format issues: The key format may be incorrect, which prevents the SSH client from reading it.

Receive Packet: Type 51 Error

The "receive packet: type 51" error is a more specific error that occurs when the SSH client is unable to authenticate with the server using the public key. This error is often seen in conjunction with the "Permission denied (publickey)" error.

Scenario: Logging into Ubuntu Instances with GCP

You can log into all Ubuntu instances with GCP using the same SSH keys, except for one instance. This instance was created by an Admin, who added a user for you, added you to the sudo and admin groups, and added your public key to the authorized_keys file.

Troubleshooting the Issue

To troubleshoot the issue, follow these steps:

  1. Check key permissions: Ensure that the private key file has the correct permissions. The file should be owned by the user and have read permissions for the user and group.
  2. Verify key format: Ensure that the key format is correct. The key should be in the OpenSSH format, which starts with ssh-rsa or ssh-dss.
  3. Check authorized_keys file: Ensure that the public key is added to the authorized_keys file on the server. You can check the file by running the command cat ~/.ssh/authorized_keys.
  4. Check SSH client configuration: Ensure that the SSH client is configured correctly. You can check the configuration by running the command ssh -v.

Resolving the Issue

To resolve the issue, follow these steps:

  1. Generate a new key pair: Generate a new key pair using the command ssh-keygen -t rsa.
  2. Add the new key to the authorized_keys file: Add the new public key to the authorized_keys file on the server.
  3. Update the SSH client configuration: Update the SSH client configuration to use the new key pair.

Conclusion

In conclusion, the "Permission denied (publickey)" error with the error message "receive packet: type 51" is a common issue that occurs when the SSH client is unable to authenticate with the server using the public key. By following the troubleshooting steps and resolving the issue, you should be able to access your instances using SSH keys.

Additional Tips and Resources

  • Use a key manager: Consider using a key manager like AWS Key Management Service (KMS) or Google Cloud Key Management Service (KMS) to manage your SSH keys.
  • Use a secure key format: Use a secure key format like OpenSSH format, which starts with ssh-rsa or ssh-dss.
  • Keep your keys up to date: Keep your keys up to date by regenerating them periodically.

References

Frequently Asked Questions

  • Q: What is the difference between a public key and a private key? A: The public key is stored on the server, while the private key is stored on the client machine.
  • Q: How do I generate a new key pair? A: You can generate a new key pair using the command ssh-keygen -t rsa.
  • Q: How do I add a new key to the authorized_keys file? A: You can add a new key to the authorized_keys file by running the command cat ~/.ssh/authorized_keys.
    Frequently Asked Questions (FAQs) about SSH Keys and Permission Issues ====================================================================

Q: What is the difference between a public key and a private key?

A: The public key is stored on the server, while the private key is stored on the client machine. The public key is used to verify the identity of the client machine, while the private key is used to authenticate the client machine.

Q: How do I generate a new key pair?

A: You can generate a new key pair using the command ssh-keygen -t rsa. This will create a new pair of keys, one public and one private, in the default location.

Q: How do I add a new key to the authorized_keys file?

A: You can add a new key to the authorized_keys file by running the command cat ~/.ssh/authorized_keys. This will display the contents of the file, and you can add the new key to the end of the file.

Q: What is the authorized_keys file?

A: The authorized_keys file is a file on the server that contains a list of public keys that are allowed to access the server. When a client machine tries to connect to the server using SSH, the server checks the client's public key against the list of keys in the authorized_keys file.

Q: How do I check the permissions of my private key file?

A: You can check the permissions of your private key file by running the command ls -l ~/.ssh/id_rsa. This will display the permissions of the file, and you can adjust them as needed.

Q: What is the difference between SSHv1 and SSHv2?

A: SSHv1 is an older version of the SSH protocol that is no longer supported. SSHv2 is the current version of the protocol, and it is more secure than SSHv1.

Q: How do I upgrade from SSHv1 to SSHv2?

A: To upgrade from SSHv1 to SSHv2, you will need to generate a new key pair using the command ssh-keygen -t rsa. You will also need to update your SSH client to use the new key pair.

Q: What is the difference between a key pair and a certificate?

A: A key pair is a pair of keys, one public and one private, that are used to authenticate a client machine. A certificate is a digital document that contains information about a client machine, including its public key.

Q: How do I obtain a certificate?

A: You can obtain a certificate by submitting a request to a certificate authority (CA). The CA will verify your identity and issue a certificate that contains your public key.

Q: What is the difference between a CA and a RA?

A: A CA (Certificate Authority) is an organization that issues certificates to clients. A RA (Registration Authority) is an organization that verifies the identity of clients and issues certificates on behalf of the CA.

Q: How do I configure my SSH client to use a certificate?

A: To configure your SSH client to use a certificate, you will need to add the certificate to your SSH client's configuration file. The exact steps will depend on your SSH client and operating system.

Q: What is the difference between a key pair and a password?

A: A key pair is a pair of keys, one public and one private, that are used to authenticate a client machine. A password is a secret word or phrase that is used to authenticate a client machine.

Q: How do I secure my SSH keys?

A: To secure your SSH keys, you should store them in a secure location, such as a encrypted file or a hardware security module. You should also limit access to your SSH keys to only those who need to use them.

Q: What is the difference between SSH and SFTP?

A: SSH (Secure Shell) is a protocol that allows you to securely access a remote server. SFTP (Secure File Transfer Protocol) is a protocol that allows you to securely transfer files between a local machine and a remote server.

Q: How do I use SFTP to transfer files?

A: To use SFTP to transfer files, you will need to install an SFTP client on your local machine. You will then need to connect to the remote server using the SFTP client and transfer the files as needed.

Q: What is the difference between SSH and SCP?

A: SSH (Secure Shell) is a protocol that allows you to securely access a remote server. SCP (Secure Copy) is a protocol that allows you to securely copy files between a local machine and a remote server.

Q: How do I use SCP to transfer files?

A: To use SCP to transfer files, you will need to install an SCP client on your local machine. You will then need to connect to the remote server using the SCP client and transfer the files as needed.

Q: What is the difference between SSH and RDP?

A: SSH (Secure Shell) is a protocol that allows you to securely access a remote server. RDP (Remote Desktop Protocol) is a protocol that allows you to remotely access a Windows machine.

Q: How do I use RDP to access a Windows machine?

A: To use RDP to access a Windows machine, you will need to install an RDP client on your local machine. You will then need to connect to the remote Windows machine using the RDP client and access the machine as needed.