How to configure the passwordless  ssh authentication ?

Step 1: .. Firstly we need to create  public and private keys using "ssh-key-gen" command  on server1.



[abhi@server1] $   ssh-keygen

Generating public/private rsa key pair.
Enter file in which to save the key (/home/abhi/.ssh/id_rsa):[Enter key]
Enter passphrase (empty for no passphrase): [Press enter key]
Enter same passphrase again: [Pess enter key]
Your identification has been saved in /home/abhi/.ssh/id_rsa.
Your public key has been saved in /home/abhi/.ssh/id_rsa.pub.

The key fingerprint is:
34:b3:de:af:56:68:18:18:34:d5:de:67:2fdf2:35:g7 abhi@server1

This command will  create two files in ".ssh" directory inside your's home directory (in this case it will  be /home/abhi/.ssh)


 1.   id_rsa
 2.   id_rsa.pub --  this file will contain the public/private   key.


Step 2: You need  to Copy the public key to  the second server(let it's  ip be 192.168.20.1)   using "ssh-copy-id" command.

[abhi@server1] $ ssh-copy-id -i  ~/.ssh/id_rsa.pub  192.168.20.1

abhi@server2's password:
Now try logging into the machine, with "ssh 'remote-host'", and check in:

.ssh/authorized_keys

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

Note: ssh-copy-id appends the keys to the remote-host’s .ssh/authorized_key.

Step 3: Login to remote-host(192.168.20.1) without entering the password

[abhi@server1]  $ ssh  192.168.20.1
Last login: Sun April16 12:18:12 2012 from 192.168.20.1




it dosesn't ask's for password.

* Source Article from : Internet