How to setup an SSH configuration

# How to setup an SSH configuration :

$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/oracle/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/oracle/.ssh/id_rsa.
Your public key has been saved in /home/oracle/.ssh/id_rsa.pub.
The key fingerprint is:
77:7d:c0:10:98:9f:71:55:95:ff:5a:36:2a:69:05:1d oracle@slc03mzv

# Generate the remote hostname keys

$ ssh-keygen -R host.example.com

# Copy the generate key over to the remote hosts.

$ ssh-copy-id oracle@host.example.com

The authenticity of host 'host.example.com (10.244.15.16)' can't be established.
RSA key fingerprint is 4f:43:cb:f2:c7:da:eb:a1:61:0c:9b:cb:42:0c:cb:ac.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'host.example.com' (RSA) to the list of known hosts.
Warning: the RSA host key for 'host.example.com' differs from the key for the IP address '10.244.15.16'
Offending key for IP in /home/oracle/.ssh/known_hosts:1
Are you sure you want to continue connecting (yes/no)? yes
oracle@host.example.com's password:
Warning: untrusted X11 forwarding setup failed: xauth key data not generated
Warning: No xauth data; using fake authentication data for X11 forwarding.
Now try logging into the machine, with "ssh 'oracle@host.example.com'", and check in:

  .ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

# If you get following errors while login, you can update the known_hosts with ip address as well.

$ ssh host.example.com
Warning: the RSA host key for 'host.example.com' differs from the key for the IP address '10.244.15.16'
Offending key for IP in /home/oracle/.ssh/known_hosts:1
Matching host key in /home/oracle/.ssh/known_hosts:13
Are you sure you want to continue connecting (yes/no)? yes
Warning: untrusted X11 forwarding setup failed: xauth key data not generated
Warning: No xauth data; using fake authentication data for X11 forwarding.
Last login: Mon May 23 06:23:16 2016 from dhcp.in.example.com

# If you get any ip address related error, update the ip address in the known_hosts file

$ vi /home/oracle/.ssh/known_hosts

host.example.com, ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEArjg18OaP/3kBgcOQ87DsEwbrEJA4n/e/2E4LBikgptHKfEdlXKh1DQGeLVBjS+cxWGmQ3Q+j2BPci540QwxDaP2zOY/syjJRWQSM1YMAsL+7BJtGCoSgBmdcSBxyZftnUGdl6/81EiuEzfox4yM4pIFbi6yD4ykxk4qPEzDCvEOxqFeHqtCkfxsqRI5quf38QbRHSCYrkgugRGDRSRQMEybksde0GV208JhbjVZUKjnc1xrQP2YcrWY12kfnk+GsGDkAbHPAQZdtH2T4/nywdqJp9vSwXirB2sbVXHiAH0Xf2DSlrplOtb5Hb/Z3NnGnt5q5BMNrSXMfWB+PALjZuQ==

# After setting up the ssh, it will not ask any password when you login to remote host. ( The option Y here enables trusted X11 forwarding )
$ ssh -Y hostname

Ref Links :

https://www.digitalocean.com/community/tutorials/how-to-set-up-ssh-keys–2
http://stackoverflow.com/questions/20840012/ssh-remote-host-identification-has-changed
http://serverfault.com/questions/538045/offending-key-warning-when-i-do-ssh-to-vps