SSH Login without Password in Nix

You want to use Linux/AIX/Unix and OpenSSH to atomize your tasks. Therefore you need an automatic login from hostA as user a to hostB as the same user. You don’t want to enter any passwords, because (for example) you want to call ssh from a within a shell script.

First log in on hostA as user a and generate a pair of authentication keys. Do not enter a passphrase:

# ssh-keygen -t rsa

Generating public/private rsa key pair.

Enter file in which to save the key (/home/a/.ssh/id_rsa):

Created directory '/home/a/.ssh'.

Enter passphrase (empty for no passphrase):

Enter same passphrase again:

Your identification has been saved in /home/a/.ssh/id_rsa.

Your public key has been saved in /home/a/.ssh/id_rsa.pub.

The key fingerprint is:

3e:4f:05:79:3a:9f:96:7c:3b:ad:e9:58:37:bc:37:e4 ....

Now use ssh to create a directory ~/.ssh as on hostB (the directory may already exist, which is fine):

# ssh user@hostB mkdir -p .ssh

user@hostB's password:

Finally append a’s new public key to user@B:.ssh/authorized_keys and enter b’s password one last time:

# cat .ssh/id_rsa.pub | ssh user@hostB 'cat >> .ssh/authorized_keys'

user@hostB's password:

From now on you can log into hostB as “user” from hostA as a without password:

# ssh user@hostB hostname

Depending on your version of SSH you might also have to do the following changes:

Put the public key in .ssh/authorized_keys2

Change the permissions of .ssh to 700

Change the permissions of .ssh/authorized_keys2 to 640

njoy the simplicity.......
Atul Singh