===== SSH login without password =====

==== The goal =====

You want to use Linux and OpenSSH to automate your tasks. Therefore you need an automatic login **from ''user__a__@host__A__'' to user__b__@Host__B__**. You don't want to enter any passwords, because you want to call ssh from a within a shell script.

==== How to do it ====

First log in on ''A'' as user ''a'' and generate a pair of authentication keys. Do not enter a passphrase:
<code bash>
a@A:~> 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 a@A
</code>

Now use ssh to create a directory ''~/.ssh'' as user ''b'' on ''B''. (The directory may already exist, which is fine):
<code bash>
a@A:~> ssh b@B mkdir -p .ssh
b@B's password: 
</code>

Finally append ''a'''s new public key to ''b@B'' in file ''.ssh/authorized_keys'' and enter ''b'''s password one last time:
<code bash>
a@A:~> cat .ssh/id_rsa.pub | ssh b@B 'cat >> .ssh/authorized_keys'
b@B's password: 
</code>

From now on you can log into B as b from A as a without password:
<code bash>
a@A:~> ssh b@B
</code>

A note from one of our readers: 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

Source : [[http://linuxproblem.org/art_9.html]]