How to upgrade SSHD without the change of the server key?

Question

So... we need to upgrade the SSHD. How can we do this without having that issue that the people (who are signing in through ssh) would see the message:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
0e:a1:b1:40:85:a2:a7:03:17:1b:52:8f:10:c7:b3:d0.
Please contact your system administrator.
Add correct host key in /home/USERNAME/.ssh/known_hosts to get rid of this message.
Offending key in /home/USERNAME/.ssh/known_hosts:13
RSA host key for [192.168.1.1]:22 has changed and you have requested strict checking.
Host key verification failed.

Answer 1

Just upgrading sshd typically won't replace the host key. So yes just upgrade it and it should be fine.

Note: You won't typically need this but if you want to be on the safe side you can create a backup of the ssh host keys and copy them back after you upgraded your system. Typically you would have to backup /etc/ssh/ssh_host*. If something went wrong you can restore the files later.