Host key for server does not match

UCS - Univention Corporate Server
#1

I had an issue on my backup1 DC host, so I deleted from the maser DC, and installed again on a new virtual machine. But now after the join, I can’t login and when I do a system diagostic on master DC I have an issue about the key. It’s seem they still old information from the old backup1 machine on the Master DC, so impossible to do a clean join.

Copy from the System Diagnostic result:

SSH connection to UCS server failed!
The ssh connection to at least one other UCS server failed. The following list shows the affected remote servers and the reason for the failed ssh connection:

backup1 - Host key for server does not match!

Host key for server does not match - The ssh host key of the remote server has changed (maybe the host was reinstalled). Please repair the host key of the remote server in /root/.ssh/known_hosts on master.corp.medair.org.

Thank you very much !

#2

When an SSH connection is made from one machine to another the target machine’s public SSH key is stored on the source machine’s known_hosts file. This is done in order to prevent malicious third parties from eavesdropping on the connection.

In situations such as yours the previous machine’s key is now actively preventing new connection attempts. The fix is easy, though, and the error message hints at it already: simply remove the old host’s key from the known_hosts file; in this case: the one for the root user.

So what you’ve got to do is

[ul][li]log in to master.corp.medair.org via ssh as root[/li]
[li]try to connect to the new backup1 DC host via ssh – this will fail but it should also contain the information which line in the known_hosts file contains the key[/li]
[li]now edito /root/.ssh/known_hosts and remove the line[/li]
[li]try to join the machine again[/li][/ul]

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