Warning message when you try to connect to a server using SSH

When connecting to your Ruachost server using SSH, you may sometimes see a warning message about the server’s host key. This article explains why this happens, what it means, and how to resolve it safely.

The Problem

When you attempt to connect to your server via SSH, you may see a warning message such as:

On macOS/Linux:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!         @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!

WARNING - POTENTIAL SECURITY BREACH!
The server's host key does not match the one PuTTY has cached.

This means the server’s RSA fingerprint has changed compared to what your computer has stored.

Cause

The most common reason is that the server’s SSH host key has legitimately changed — for example, after:

• A server rebuild or OS reinstall

• A new operating system template being applied

• A server migration

However, in rare cases, it could indicate a man-in-the-middle attack, where someone is impersonating your server to intercept your connection.

Resolution

On macOS and Linux

1. Review the warning message carefully.

2. Note the line that says something like:

   Offending RSA key in /path/.ssh/known_hosts:x
   

3. Open the known_hosts file in a text editor:

   nano /path/.ssh/known_hosts
   

4. Delete the line indicated by the warning (line x).

5. Save and exit the editor.

6. Reconnect to the server, you will be prompted to accept the new host key.

On Windows (PuTTY)

When PuTTY shows the warning, you have three options:

• Yes – If you know the server was recently reinstalled or updated, click Yes to update PuTTY’s cache with the new key.

• No – If you’re unsure, click No to connect without saving the new key. The warning will appear again next time.

• Cancel – If you suspect something malicious, click Cancel and do not proceed.

Important Security Note

• If you did not recently reinstall or change your server, and you see this warning, it may indicate a security risk.

• In that case, do not proceed with the connection.

• Instead, open a support ticket in your Ruachost Hosting Panel so our team can investigate.