How to enable "password-less" login for ssh between 2 Linux machines ?

1. Generate a dsa or rsa public & private keys:

#ssh-keygent -t dsa
or
#ssh-keygen -t rsa

2. Copy the public key and complete the required formalities on the remote machine:

#ssh-copy-id -i ~/.ssh/id_dsa.pub user@IP-address

3. If all goes well you have successfully enabled password-less communication with the remote machine. Test it using "ssh"
#ssh IP-address