Host Key for Server Does Not Match: Understanding the Issue and How to Solve It

Hello Dev, have you ever come across the error message “host key for server does not match” while trying to access a remote machine or server through SSH? If yes, then you are not alone. This is a common issue that often occurs when you try to connect to a server that you have connected to before but with a different key. In this journal article, we will explore this issue in detail and guide you on how to solve it effectively.

Understanding the Host Key for Server Does Not Match Error

When you connect to a remote machine or server through SSH, your computer stores the server’s public key in its known_hosts file. This key is used to verify the identity of the server when you connect to it. However, if the server’s key changes for any reason, your computer will not be able to verify the new key against the old one stored in the known_hosts file. This will result in the “host key for server does not match” error message.

The error message can be caused by various reasons, including:

1. The server’s key has been regenerated
2. The server has been reinstalled
3. The server’s IP address has changed
4. The server’s hostname has changed
5. The server’s DNS entry has changed

Now, let us dive into the ways you can solve this issue.

Solving the Host Key for Server Does Not Match Error

Method 1: Remove the Old Key

The first and most straightforward method to solve this issue is to remove the old key from your computer’s known_hosts file. Here is how to do it:

1. Open your terminal application
2. Type the following command: ssh-keygen -R remote_host_name_or_ip
3. Replace remote_host_name_or_ip with the hostname or IP address of the remote server you are trying to connect to
4. Press Enter

This command will remove the old key from your known_hosts file, and the next time you connect to the remote server, your computer will store the new key in the known_hosts file.

Method 2: Update the Known Hosts File

If you do not want to remove the old key from your known_hosts file, you can update it with the new key by following these steps:

1. Open your terminal application
2. Type the following command: ssh-keyscan -t rsa remote_host_name_or_ip >> ~/.ssh/known_hosts
3. Replace remote_host_name_or_ip with the hostname or IP address of the remote server you are trying to connect to
4. Press Enter

This command will scan the remote server for its public key and append it to your known_hosts file. The next time you connect to the remote server, your computer will use the new key to verify the server’s identity.

Method 3: Verify the Server’s Key

If you are still unable to connect to the remote server after trying the above methods, you may want to verify the server’s key manually. Here is how to do it:

1. Open your terminal application
2. Type the following command: ssh-keygen -lf /etc/ssh/ssh_host_rsa_key.pub
3. Press Enter

This command will display the fingerprint of the server’s public key. Verify that it matches the fingerprint of the key provided by the server administrator. If the fingerprints do not match, it is likely that the server has been compromised, and you should contact the server administrator immediately.

FAQ About Host Key for Server Does Not Match

In conclusion, the host key for server does not match error can be frustrating and confusing, but it is a simple issue to solve once you understand the cause. Use the methods we have discussed in this article to solve the issue and ensure a secure connection to your remote server.