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Updating SSH Keys

As the department's servers are upgraded, there is a possibility that the servers' host keys will change. If your computer has a cached copy of a server's old host key, your SSH client may refuse the connection when you try to connect to that server.

To remove the offending cached key, follow the instructions corresponding to your OS:

Windows (PuTTY)

  1. Open PuTTY
  2. Attempt to connect to the server. You will receive the following dialogue box.
  3. Click “Yes” to update the cache. The connection should be successful.

Mac OS X/Linux

  1. In a terminal window, run the following command to open the SSH key cache file for editing:
    nano ~/.ssh/known_hosts
  2. Locate the line with the key you wish to remove. It will begin with the hostname and/or IP of the server and will look similar to the following:, ssh-rsa AAAAB3Nza...
  3. Delete the entire line (Ctrl-K while on that line), then save and close the file (Ctrl-X).
  4. When you attempt to connect to the server again, you will be prompted to save the new host key to the cache.
ssh_key_removal.txt · Last modified: 2018/04/25 15:25 (external edit)