The “Host key verification failed” error can stop you from connecting to remote servers via SSH. While frustrating, this error actually helps protect against potential security threats. Let’s explore how to fix this issue and why it occurs in the first place.
Removing the Problematic Host Key
The quickest way to resolve a host key verification error is to remove the incorrect key from your SSH client’s known_hosts file:
Step 1: Open a terminal window on your local machine.
Step 2: Run the following command, replacing hostname with the remote server’s domain name or IP address:
ssh-keygen -R hostname
Step 3: Attempt to reconnect to the server using:
ssh username@hostname
You’ll likely see a warning about the host’s authenticity. Type yes to accept the new key and connect.
Manual Removal of the Host Key
If you prefer a more hands-on approach:
Step 1: Open your known_hosts file in a text editor:
sudo nano ~/.ssh/known_hosts
Step 2: Locate the line containing the problematic host key. The SSH error message usually specifies the line number.
Step 3: Delete that entire line.
Step 4: Save the file and exit the editor.
Step 5: Try reconnecting to your server.
Understanding Host Key Verification
SSH uses cryptographic keys to verify server identities. When you first connect to a server, its public key is stored in your known_hosts file. On subsequent connections, SSH compares the server’s current key to the stored one.
The “Host key verification failed” error occurs when these keys don’t match. This mismatch can happen for several reasons:
- The server’s operating system was reinstalled
- The server’s IP address changed
- The SSH service on the server was reconfigured
- In rare cases, it could indicate a potential security threat
Why Host Key Verification Matters
This verification process is crucial for maintaining SSH security. It helps prevent man-in-the-middle attacks, where an attacker might try to impersonate a legitimate server.
When you receive this error, it’s important to verify that the change in the host key is expected. If you’re unsure, contact your server administrator or hosting provider to confirm any recent changes.
SSH host key verification errors can be quickly resolved once you understand their purpose. By following these steps, you can maintain secure connections to your remote servers while staying alert to potential security issues.