Software & AppsOperating SystemLinux

How To Fix “Host key verification failed” SSH Connection Error

Ubuntu 15

SSH (Secure Shell) is a secure protocol used to remotely connect to a server. However, sometimes when trying to establish a connection, you may encounter the error “Host key verification failed”. This typically means that the host key of the remote machine has changed. This can happen if the remote machine has been reinstalled or if the SSH configuration has been modified.

In this article, we will walk you through several methods to fix this issue.

Quick Answer

To fix the "Host key verification failed" SSH connection error, you can try editing the known_hosts file manually and removing the line corresponding to the remote machine. Alternatively, you can use the ssh-keygen command to remove the old host key from the known_hosts file. Another option is to temporarily disable host key checking, but this is not recommended for regular use due to security reasons. If none of these solutions work, there may be other SSH configuration issues causing the problem.

Understanding the Error

Before we dive into the solutions, it’s important to understand what this error message means. SSH uses a mechanism known as host key verification to ensure that you are connecting to the correct remote machine. The host keys of remote machines are stored in a file on your local machine called known_hosts, located in the ~/.ssh/ directory.

When you see the “Host key verification failed” error, it means that the host key of the remote machine you are trying to connect to does not match the key stored in your known_hosts file.

Method 1: Edit the known_hosts File Manually

The most straightforward method to resolve this issue is to edit the known_hosts file manually and remove the line corresponding to the remote machine you are trying to connect to. The line number is usually specified in the error message.

To open the known_hosts file, you can use a text editor such as vim or nano. Here is an example using nano:

nano ~/.ssh/known_hosts

After removing the line, save the file and exit. Then, try connecting to the remote machine again.

Method 2: Use the ssh-keygen Command

If you prefer to use a command-line solution, you can use the ssh-keygen command to remove the old host key from the known_hosts file. The -R option is used to remove keys:

ssh-keygen -R hostname

In this command, replace hostname with the actual hostname or IP address of the remote machine. This command will remove all keys belonging to the specified hostname from the known_hosts file.

Method 3: Disable Host Key Checking

In some cases, you might not have interactive access to confirm the host key. In such situations, you can temporarily disable host key checking by adding the -o StrictHostKeyChecking=no option to the ssh command:

ssh -o StrictHostKeyChecking=no user@hostname

However, this method is not recommended for regular use due to security reasons. Disabling host key checking opens you up to potential man-in-the-middle attacks.

Method 4: Confirm the Connection

Sometimes, the error message may be asking you to confirm the connection by typing “yes” when prompted. Make sure to read the error message carefully and follow the instructions provided.

Method 5: Check for Other SSH Configuration Issues

If none of the above solutions work, there may be other SSH configuration issues causing the problem. You can add the -v option to the ssh command to enable verbose mode, which provides more detailed information about the connection process:

ssh -v user@hostname

This can help in identifying and resolving any other issues.

Conclusion

Fixing the “Host key verification failed” SSH connection error involves understanding how SSH host key verification works and how to manage the known_hosts file. It’s important to be cautious when modifying SSH configurations and to ensure that you are connecting to the correct remote machine to avoid security risks.

Remember to replace user and hostname with the appropriate values for your setup. If you’re still having trouble, consider reaching out to your network administrator or the owner of the remote machine for assistance.

What is SSH?

SSH (Secure Shell) is a secure protocol used to remotely connect to a server. It provides a secure way to access and manage remote machines over an unsecured network.

What causes the “Host key verification failed” SSH connection error?

The "Host key verification failed" error typically occurs when the host key of the remote machine you are trying to connect to does not match the key stored in your known_hosts file. This can happen if the remote machine has been reinstalled or if the SSH configuration has been modified.

How can I fix the “Host key verification failed” SSH connection error?

There are several methods to fix this issue. You can manually edit the known_hosts file and remove the line corresponding to the remote machine. Alternatively, you can use the ssh-keygen command to remove the old host key from the known_hosts file. Another option is to temporarily disable host key checking, but this is not recommended for regular use due to security reasons. It’s also important to carefully read the error message and follow any instructions provided, as sometimes you may be asked to confirm the connection. If none of these solutions work, there may be other SSH configuration issues causing the problem, and you can enable verbose mode with the -v option to get more detailed information about the connection process.

Is it safe to disable host key checking?

Disabling host key checking, even temporarily, is not recommended for regular use due to security reasons. It opens you up to potential man-in-the-middle attacks. It’s always best to confirm the host key and ensure that you are connecting to the correct remote machine to maintain a secure connection.

What should I do if none of the provided solutions work?

If none of the provided solutions work, there may be other SSH configuration issues causing the problem. In such cases, you can add the -v option to the ssh command to enable verbose mode, which provides more detailed information about the connection process. If you’re still having trouble, consider reaching out to your network administrator or the owner of the remote machine for assistance.

Leave a Comment

Your email address will not be published. Required fields are marked *