The Server’s Host Key Failed to Verify: Understanding and Troubleshooting

Hey Dev, have you ever experienced receiving an error message “The server’s host key failed to verify” while connecting to a remote server through SSH? This error can be frustrating and confusing, especially if you’re not familiar with SSH and its workings. In this article, we’ll explore the root causes of this error and provide you with effective methods to troubleshoot it.

Understanding the Error Message

When you connect to a remote server using SSH, your computer checks the server’s host key to verify its identity. The host key is a unique cryptographic key that identifies the server, and it helps ensure that the server you’re connecting to is the one you intended to. The error message “The server’s host key failed to verify” indicates that your computer failed to verify the server’s host key.

There are several reasons why your computer might fail to verify the server’s host key, including:

• The server’s host key has changed since the last time you connected to it
• Your SSH client is configured to not automatically trust new host keys
• Your SSH client is configured to only use a specific type of host key
• The server’s hostname or IP address has changed
• The server’s clock is not synchronized with your computer’s clock

Troubleshooting the Server’s Host Key Verification Error

Method 1: Verify the Server’s Host Key

The first step in troubleshooting the error message “The server’s host key failed to verify” is to verify the server’s host key manually. You can use the ssh-keygen command to compare the server’s host key with the one stored on your computer. Here’s how you can do it:

1. Open your terminal or SSH client.
2. Type the command: ssh-keygen -F [server hostname or IP address]. This command will list the stored host keys for the server.
3. Compare the output with the server’s current host key. You can obtain the current host key from the server administrator or by logging into the server manually.
4. If the host key stored on your computer doesn’t match the server’s current host key, delete the invalid key with command: ssh-keygen -R [server hostname or IP address].

Method 2: Configure Your SSH Client to Trust New Host Keys

If your SSH client is configured to not automatically trust new host keys, you will see the error message “The server’s host key failed to verify” whenever you connect to a server for the first time. You can configure your SSH client to trust new host keys by adding them to the known_hosts file. Here’s how you can do it:

1. Open your terminal or SSH client.
2. Type the command: ssh-keyscan [server hostname or IP address] >> ~/.ssh/known_hosts. This command will append the server’s host key to the known_hosts file.
3. If you’re not logged in as the current user, replace ~/.ssh/known_hosts with the path to the known_hosts file for the specific user.

Method 3: Configure Your SSH Client to Use All Types of Host Keys

If your SSH client is configured to only use a specific type of host key, it might fail to verify the server’s host key if the server uses a different type of key. You can configure your SSH client to use all types of host keys by adding the following line to your ~/.ssh/config file:

Host *
HostkeyAlgorithms +ssh-dss

This configuration will allow your SSH client to use all host key types, including ones that might not be supported by default.

Frequently Asked Questions (FAQ)

Q: What is a host key?

A: A host key is a cryptographic key that identifies a server. It helps ensure that the server you’re connecting to is the one you intended to.

Q: Why did the server’s host key fail to verify?

A: There are several reasons why your computer might fail to verify the server’s host key, including changes in the server’s host key, configuration issues with your SSH client, or changes in the server’s hostname or IP address.

Q: How do I verify the server’s host key manually?

A: You can use the ssh-keygen command to list the stored host keys for the server and compare them with the server’s current host key. If they don’t match, delete the invalid key and try connecting to the server again.

Q: How do I configure my SSH client to trust new host keys?

A: You can add new host keys to the known_hosts file by using the ssh-keyscan command. This will allow your SSH client to automatically trust new host keys.

Q: How do I configure my SSH client to use all types of host keys?

A: You can configure your SSH client to use all types of host keys by adding the HostkeyAlgorithms option to your ~/.ssh/config file.

Conclusion

The error message “The server’s host key failed to verify” can be frustrating, but it doesn’t have to be. By understanding the root causes of the error and following the troubleshooting methods we’ve outlined in this article, you can quickly resolve any host key verification issues and get back to working on your remote server.