Tip of the Day : SSHD - How to connect a server using SSH and without entering login credentials

From time to time you will need to connect your servers remotely and execute commands there using scheduled jobs. As the nature of these scheduled jobs/scripts, they have no capability of user interaction like entering user/pass information. (I'm talking about simple shell scripts, you can also use Perl's use Net::SSH::Perl for entering user/pass info) For these scenarios we have the below trick of generating RSA/DSA key pairs and putting it into the authorized_keys file:

[root@server-a ~]# ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):   --- leave empty
Enter same passphrase again:   --- leave empty

Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.

The key fingerprint is:
35:ee:f1:53:f6:d7:85:4b:65:c3:68:f0:b6:59:f5:50 root@server-a

[root@server-a ~]# scp .ssh/id_dsa.pub server-b:/root/.ssh/id_dsa_lr.pub

[root@server-b ~]# cd /root/.ssh/
[root@server-b ~]# cat id_dsa_lr.pub >> authorized_keys
[root@servera ~]# ssh server-b

Last login: Mon Sep  3 12:29:09 2007 from X.X.X.X

[root@server-b ~]#

This example gives server-a the ability of connecting server-b via SSH and without entering any user/pass information.

NOTE : You can also use this trick to connect your Windows boxes using Cygwin SSHD. I will give details on Cygwin on a future article.