How to Fix “Host Key Verification Failed” Error in Proxmox

The “Host key verification failed” error is a common issue when working with SSH-based systems like Proxmox. It occurs when SSH detects a mismatch between the host key of the remote server and the stored key in your known hosts file. This error is often triggered when a server’s host key changes, which can happen for various reasons, including server reinstallation, IP address changes, or security updates. In this guide, we’ll explain how to resolve this error and establish a secure SSH connection to your Proxmox nodes.

Prerequisites:

• Access to the Proxmox nodes or servers.
• Basic knowledge of the Linux command line.

Step 1: Identify the Cause

1.1. Attempt to connect to the remote server that triggered the error, e.g., ssh [email protected]. 1.2. Read the error message carefully to understand the cause, such as a host key mismatch.

Step 2: Remove the Old Host Key

2.1. If the host key has changed, you need to remove the old key from your known hosts file. Use the ssh-keygen command with the -R option followed by the server’s IP address or hostname:

ssh-keygen -R 192.168.1.110

This command removes the old entry for the remote server.

Step 3: Reconnect with the Updated Key

3.1. Try connecting to the remote server again, allowing SSH to retrieve and store the updated host key:

ssh [email protected]

You may be prompted to confirm the new host key. Type “yes” to proceed.

Step 4: Consider Automation (Optional)

4.1. To automate the process of updating known hosts files for multiple servers, you can use the following command to remove an old key and reconnect to the server, all in one step:

ssh-keygen -f "/etc/ssh/ssh_known_hosts" -R "hostname_or_ip" && ssh -o "HostKeyAlias=alias" username@hostname_or_ip

Replace “hostname_or_ip” with the server’s hostname or IP address, “alias” with a host key alias if needed, and “username” with your SSH username.

By following these steps, you can address the “Host key verification failed” error in Proxmox or any SSH-based system. It’s essential to keep your known hosts file up-to-date to ensure secure and reliable SSH connections.