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If Fetch displays a message similar to "Warning: the RSA host key for 'ftp.example.com' differs from the key for the IP address '192.0.34.166'" when you are opening a connection to an SFTP server, there may be a security problem with the server you are trying to connect to. The warning may also indicate that the host has legitimately changed its host key.

Each SFTP server has an SSH host key that enables secure transfers. When you connect to an SFTP server, Mac OS X stores that server's key for future use. This warning occurs when two different host keys for the same server have been stored in your known_hosts key file — one under the server's hostname, and one under the server's IP address.

While your server probably changed keys legitimately, this warning could indicate a security problem, and you should check with your server administrator or computing helpdesk before continuing with your connection. Click the Cancel button to stop connecting, or click Connect to go ahead and connect.

You cannot disable this warning in Fetch. If you repeatedly receive this warning when connecting to a server even after your server administrator or computing helpdesk verifies that there isn't a problem (or fixes the problem), the best way to stop receiving the warning is to delete your ~/.ssh/known_hosts file.

Important: Consult your server administrator or computing helpdesk for assistance before deleting this file if you If you are not comfortable with these instructions.

To delete the known_hosts file, click on this link:

Delete the known_hosts file for me

Or you can follow these steps:

  1. In the Finder, choose Go > Go to Folder. The Finder will display a prompt.
  2. Type "~/.ssh" (without the quotes) into the prompt, and click the Go button. The Finder will display a window showing the contents of the .ssh folder.
  3. Select the known_hosts file, and drag it to the Trash.
  4. Close the window.

The next time you try to connect to the server, you should not get a warning.

After deleting the known_hosts file, the first time you connect to a server you may be warned that the authenticity of the host cannot be established. This is normal if you have checked the SFTP: Ask before accepting unknown host keys preference in the Security Preferences pane. See the Host Authenticity topic for more information.

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