Hadoop: Remote Host Identification Has Changed error and solution

When you are running Hadoop in pseudo Distributed Mode, you had to run in local server (localhost),


Then, to enable password-less login, generate a new SSH key with an empty passphrase:
         % ssh-keygen -t rsa -P '' -f ~/.ssh/id_rsa
         % cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys

Test this with:
         % ssh localhost

If successful, you should not have to type in a password.
Sometimes you will find below error, to resolve this follow any one of the approach as stated below.



@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ 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
5c:9b:16:56:a6:cd:11:10:3a:cd:1b:a2:91:cd:e5:1c.
Please contact your system administrator.
Add correct host key in /home/user/.ssh/known_hosts to get rid of this message.
Offending key in /home/user/.ssh/known_hosts:1
RSA host key for ras.mydomain.com has changed and you have requested strict checking.
Host key verification failed.

How do I get rid of this message?

If you have reinstalled Linux or UNIX with OpenSSH, you will get the above error. To get rid of this problem:

Solution #1: Remove keys

Use the -R option to removes all keys belonging to hostname from a known_hosts file. This option is useful to delete hashed hosts. If your remote hostname is server.example.com, enter:
$ ssh-keygen -R {server.name.com}
$ ssh-keygen -R {ssh.server.ip.address}
$ ssh-keygen -R server.example.com

$ ssh-keygen -R localhost


Sample output:

/home/vivek/.ssh/known_hosts updated.
Original contents retained as /home/vivek/.ssh/known_hosts.old
Now, you can connect to the host without a problem.

Solution #2: Add correct host key in /home/user/.ssh/known_hosts

It is not necessary to delete the entire known_hosts file, just the offending line in that file. For example if you have 3 server as follows.

myserver1.com,64.2.5.111 ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIEA11FV0EnGahT2EK8qElocjuHTsu1jaCfxkyIgBTlxlrOIRchb2pw8IzJLOs2bcuYYfa8nSXGEcWyaFD1ifUjfHelj94AAAAB3NzaC1yc2EAAAABIwAAAIEA11FV0E
nGahT2EK8qElocjuHTsu1jaCfxkyIgBTlxlrOIRchb2pw8IzJLOs2bcuYYfa8nSXGEcWyaFD1ifUjfHelj94H+uv304/ZDz6xZb9ZWsdm+264qReImZzruAKxnwTo4dcHkgKXKHeefnBKyEvvp/2ExMV9WT5DVe1viVwk=

myserver2.com,125.1.12.5 ssh-rsa
AAAAB3NzaC1yc2EAAAABIwAAAQEAtDiERucsZzJGx/1kUNIOYhJbczbZHN2Z1gCnTjvO/0mO2R6KiQUP4hOdLppIUc9GNvlp1kGc3w7B9tREH6kghXFiBjrIn6VzUO4uwrnsMbnAnscD5EktgI7fG4ZcNUP 5+J7sa3o+rtmOuiFxCA690DXUJ8nX8yDHaJfzMUTKTGxQz4M/H2P8L2R//qLj5s3ofzNmgSM9lSEhZL/IyI4NxHhhpltYZKW/Qz4M/H2P8L2R//qLj5s3ofzNmgSM9lSEhZL/M7L0vKeTObue1SgAsXADtK3162a/Z6MGnAazIviHBldxtGrFwvEnk82+GznkO3IBZt5vOK2heBnqQBfw=

myserver3.com,125.2.1.15 ssh-rsa
5+J7sa3o+rtmOuiFxCA690DXUJ8nX8yDHaJfzMUTKTGx0lVkphVsvYD5hJzm0eKHv+oUXRT9v+QMIL+um/IyI4NxHhhpltYZKW
as3533dka//sd33433////44632Z6MGnAazIviHBldxtGrFwvEnk82/Qz4M/H2P8L2R//qLj5s3ofzNmgSM9lSEhZL/M7L0vKeTObue1SgAsXADtK3162a/Z6MGnAazIviHBldxtGrFwvEnk82+GznkO3IBZt5vOK2heBnqQBfw==

To delete 2nd server (myserver.com), open file:
# vi +2 .ssh/known_hosts

And hit dd command to delete line. Save and close the file. Or use following
$ vi ~/.ssh/known_hosts

Now go to line # 2, type the following command
:2

Now delete line with dd and exit:
dd
:wq

Solution 3:  Just delete the known_hosts file If you have only used one ssh server

$ cd
$ rm .ssh/known_hosts
$ ssh ras.mydomain.com

Now you should be able to connect your server via ssh.