WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED

If you have reinstalled Linux  with Open SSH, you will get the below error.


 [root@sujeet ~]# ssh 192.168.1.100
@@@@@@@@@@@@@@@@@@@@@@@
@    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
b7:b8:a3:8d:8f:27:c0:5c:4b:72:04:91:02:75:3c:8a.
Please contact your system administrator.
Add correct host key in /root/.ssh/known_hosts to get rid of this message.
Offending key in /root/.ssh/known_hosts:12
RSA host key for 192.168.1.100 has changed and you have requested strict checking.
Host key verification failed.


Solution:- 
The message does explain itself:

• The remote host identified itself with a key
• Your previous copy of the key for that host is different
• So there is a chance that the remote host is not who they say they are

If you trust the remote host, you can delete line 12 from your /root/.ssh/known_hosts and ssh will ask you if it can add the new key next time you try to connect
If you don't trust the remote host, you have to contact the host administrators to find out if and why they changed ssh keys. If they haven't it means your traffic is being intercepted

Manually You can edit it :-

Edit /root/.ssh/known_hosts file.

 In this file what about your last IP address just delete it all line save this file after that try again.

[root@sujeet~]# vi /root/.ssh/known_hosts

Add below line & edit IP Address.
192.168.1.109 ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAsvJjyPp1VzzqkrvwgG6IddVjHE85glBzqWEi5w1mCZGEatFP8VEJiK6gv68qCOPbMyX6UuYp1yFB3DFuXLgM7AbyER5nbW5jLGHXoHvN1C1Lb77mHTGqEFMF3LFoqgUtWhbTAi+byYNqDWHu2/BsamC0X70OnB4kqNZ42RpQEvAt+cwRat9yDHj35cmnftYTN4y9/NLslSw6YmyD9amFyXkuB4hlIOzMiaxyX/ubYDRgiRuMyC8xosanS9FuNCMRjcrZ84y7SvTjSSgocJkEYzZGqDZVTFP2VIvGXJx0w8hXujiLzHQIN884kMbBvYVduYAepC4vUIganz6mjxxDrw==
192.168.1.100 ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA0u2Xf8aNwFzRD2rFIH71WNOgMn5IQmaHrPjTs00kxgzyeELkR6U4fW1YS4QArN/X53VC2UVuDpfQREatj1nNn4w+t7dyc4Vd62aHHuo0KNL5o4qeaR9gNXwdK0ethu8sUypt4DGuWhLe3HYXZvSqpa6OXgR4jGlvYZ+xDLwejLzAkfp0+D2hehY/Z12QdWq27bj8/PvnkHZ/5ffH+yvnwJiZGniMP4m5te7Zi+CqDmAZ7e6n9B5gUaOn2wn7IqNBZiOXlBX8fq91L64ZkjTb5H2brNST0s9NmyLkjbPjOBTMfmAJaK+6+6qDjAQ0UQT/3jW3mRYaQ2wmbPPPwOzMcQ==

save it
After that try again hope its work.


[root@sujeet ~]# ssh 192.168.1.100

The authenticity of host '192.168.1.100 (192.168.1.100)' can't be established.
RSA key fingerprint is b7:b8:a3:8d:8f:27:c0:5c:4b:72:04:91:02:75:3c:8a.
Are you sure you want to continue connecting (yes/no)? yes

Warning: Permanently added '192.168.1.100' (RSA) to the list of known hosts.
root@192.168.1.100's password:
Last login: Tue Dec 23 16:11:48 2014

[root@sujeet ~]# cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1       localhost.localdomain localhost
::1             localhost6.localdomain6 localhost6
192.168.1.100   sujeet.oracle.com   sujeet

[root@sujeet ~]#

What does that mean?

It is “only” a warning but hinders you in logging in to the host. This means that the host identification (fingerprint) you accepted when you logged in for the first time does not match the fingerprint on this connection attempt. As the message states, that can be a man in the middle attack, but – as in my case – this also happens when you have re-installed your server. The IP/DNS name is the same, but the fingerprint has changed. If you know this is the reason, you will need to remove the old host-key/fingerprint and then on the next login attempt accept the new fingerprint.

Possibility one

On OS X, edit the file ‘/Users/username/.ssh/known_hosts’, go to the line the message told you and delete the line (make sure it is really the right line that you delete).

Possibility two

The easier way is to just run a command which will do the editing for you. It will create a backup of the old known_hosts file as /Users/username/.ssh/known_hosts.old. Of course if you edit it twice, it will override the first backup. To do this run the following:

ssh-keygen -R 192.168.1.100