ssh settings in hadoop...........(passwordless login)

on the host you will connect FROM:
generate the public private keys
> ssh-keygen -t dsa -P '' -f ~/.ssh/id_dsa
copy the public key to every host you will connect TO:

> scp ~/.ssh/id_dsa.pub my_user_id@1.2.3.4:~/.ssh/id_dsa.pub

* this should prompt you for a password
shell into the remote machine

> ssh my_user_id@1.2.3.4

authorize the key by adding it to the list of authorized keys

> cat ~/.ssh/id_dsa.pub >> ~/.ssh/authorized_keys

log out of the current shell

> exit

test that you can log in with no password

if problems persist plz refer:-
http://allthingshadoop.com/?s=Hadoop+Cluster+Setup%2C+SSH+Key+Authentication

http://ambari.apache.org/1.2.0/installing-hadoop-using-ambari/content/ambari-chap1-5-2.html