How to fix the “Warning: Remote host identification has changed” SSH error

In this post, we have seen that the “Warning: Remote host identification has changed” error is an important security mechanism that is doing its job. By following the steps in this article, you can confidently handle this common issue while ensuring your connections remain secure. If you ignore this warning and proceed, you will send your password or other credentials directly to the attacker’s machine, completely compromising your account. This is why you must verify the cause before you implement any fix.ssh-keygen -R your-server-hostname

# Run these on the remote server you're trying to connect TO (not on your personal laptop)
ssh-keygen -lf /etc/ssh/ssh_host_rsa_key.pub
ssh-keygen -lf /etc/ssh/ssh_host_ecdsa_key.pub
ssh-keygen -lf /etc/ssh/ssh_host_ed25519_key.pub

This means your computer’s security system no longer recognizes your server. The first time you connected, your laptop saved a unique “fingerprint” for that server. Now, the server shows a different fingerprint.
With RunCloud, you rarely need to connect to your server with SSH to manage your web applications, databases, or firewall. The RunCloud dashboard provides a secure, visual interface for all these tasks so that you can sidestep this error completely.

What Does This Error Mean?

More often than not, this error is caused by routine server administration, not a malicious attack. Here are the most common legitimate reasons:Follow these steps to resolve the issue without compromising your security.From that point on, every time you connect, the server presents its key again. Your SSH client checks its known_hosts file and says, “Does the key this server is showing me match the key I saved for it last time?”This is very common, especially in cloud hosting environments. Here are a few reasons it can happen:
The server’s operating system was reinstalled or upgraded.
You moved your site to a new server with the same IP address as the old one.
Your cloud provider (like AWS, DigitalOcean, etc.) replaced the underlying virtual machine.

Why Did the Host Key Change?

Although this is usually a benign warning, the error’s primary purpose is to protect you from a Man-in-the-Middle (MITM) attack. Here’s how an MITM attack works in this context:

1. Server OS Reinstallation: If the server’s operating system (e.g., Ubuntu, CentOS) was reinstalled from scratch, the SSH service would have generated a new set of unique host keys. The old ones will have been wiped out with the old OS. This is the most frequent cause.
2. Server Migration or Re-IP: The IP address you are connecting to may have been reassigned. For example, the old server 123.45.67.89 was decommissioned, and a brand new server was spun up and given the same IP address.
3. Cloud/Virtualization Environments: In cloud environments like AWS, GCP, or Azure, virtual server instances can be terminated and replaced. The new instance will have a different host key, even if it has the same IP address or hostname.
4. Load Balancers: If you connect to a hostname behind a load balancer, your connection might be routed to a different server in the pool from the one you connected to last time. You’ll see this error if the servers don’t share the same host key.
5. Deliberate Key Regeneration: A system administrator may have intentionally regenerated the server’s SSH keys for security policy reasons.

The Man-in-the-Middle (MITM) Attack

To understand the error, you need to know how SSH establishes trust. The first time you connect to a new server, it presents its “public host key”, which is a unique identifier for that server. Your SSH client asks you if you trust this key.

1. You try to connect to your legitimate server.
2. An attacker, positioned somewhere on the network between you and the server (e.g., on the same public Wi-Fi), intercepts your connection request.
3. The attacker blocks your connection to the real server and instead presents their own fake SSH server to you.
4. Your SSH client sees a new, unexpected host key and throws the “REMOTE HOST IDENTIFICATION HAS CHANGED” error.

Once you’ve verified the new key’s authenticity, you can safely remove the old, conflicting key from your local ~/.ssh/known_hosts file. The ssh-keygen command has a specific function for removing hosts.

How to Safely Fix the Error: The “Verify, Then Remove” Protocol

This security check matters, but it can be frustrating when you just need to get back to work. The key is knowing when the error signals a real problem versus routine server maintenance.

Step 1: VERIFY the New Host Key

With RunCloud, you can deploy and manage your web applications, databases, and firewalls directly from an intuitive dashboard, completely sidestepping common issues like the “Remote Host Identification Has Changed” error.

• If you are not the server administrator: Contact the person or team that is and ask them if the server’s host key was recently changed. They should be able to confirm if this is the case, and even provide you with the new key’s fingerprint.
• If you are the server administrator: You must get the new key’s fingerprint directly from the server console.
  • Log in to the server using an alternative method (e.g., the web console provided by your cloud provider, like AWS EC2 Connect, GCP Console, or a direct KVM/IPMI connection in a data center).
  • Once logged in, run the following commands to display the fingerprints of the server’s host keys. A server usually has several key types (RSA, ECDSA, ED25519).

If you’re sure the server is safe, the fastest fix is to tell your computer to forget the old fingerprint. You can do this by running a single command on your local machine (not the server):
ssh-keygen -R your-server-ip-or-hostname   
Replace your-server-ip-or-hostname with your server’s actual address. After you run this, you can connect again and be asked to approve the new fingerprint.

Step 2: REMOVE the Old Host Key from known_hosts

That’s why we built RunCloud.This is the most important step. Do not proceed until you have confirmed the new key is legitimate.Now that the old key is gone, try your SSH connection again. You will be prompted to accept the new key as if you were connecting for the first time. Since you have already verified its fingerprint, you can confidently type ‘yes’.When you type ‘yes’, your computer saves this key and its associated hostname/IP address in a file located at ~/.ssh/known_hosts. This file acts as your personal “phonebook” of trusted servers.

Step 3: Reconnect and Accept the New Key

Already certain this error came from recent server changes? Remove the old host key with this command:

Conclusion

The “Remote Host Identification Has Changed” error occurs when the answer is NO. The server is presenting a key your computer has never seen before.Managing servers and deploying new web applications can be challenging, especially if you are unfamiliar with Linux and the command line.Sign up for RunCloud today and experience hassle-free web server management.ssh-keygen -R your-server-hostname

nano ~/.ssh/known_hosts

This guide covers everything you need to know: what causes the warning, how to tell if it’s dangerous, and how to fix it without compromising your server’s security. You’ll be able to handle this error confidently, whether you’re managing one server or dozens.