SSH Auto-Login - No password!

There comes a time in every Linux Admin's career when we need to set up an automated SSH login to a remote server. Whether it be backups, replication or just plain convenience, this is something that can save lots of time throughout the life of a server. Keep in mind that you should have a seperate user for each process and try not to use the 'root' account. Of course, if you haven't changed the default sshd config file then root can't log in directly anyways...

Steps that we'll cover:

1. Set up .ssh under the /home/user/ folder.
2. Create a DSA keypair (private/public).
3. Copy the public key from one server to the other.
4. Append the public key info to the authorized_keys file.
5. Update twitter account with link to this article.

[TO BE DONE ON BOTH SERVERS]

First, make sure your user has the correct home directory structure set up:

mkdir -p /home/user/.ssh
cd /home/user/.ssh

Next, we'll generate a dsa (as opposed to rsa) keypair:

ssh-keygen -t dsa

You should now see these files in your .ssh directory:

id_dsa - Private key (DO NOT DISTRIBUTE THIS FILE!)
id_dsa.pub - Public Key (This is the one to distribute)

Now we'll ssh from SERVER1 to SERVER2:

ssh user@SERVER2
cd /home/user/.ssh

Now use scp to get the public key from SERVER1:

scp user@SERVER1:/home/user/.ssh/id_dsa.pub ./SERVER1.pub
(this will grab the id_dsa.pub from SERVER1 and rename it in the current directory)


Append the public key to the authorized_keys file:
cat SERVER1.pub >> authorized_keys

Perform the same steps on the other server. If you only need a one-way connection, then you should only set up one server with the public key. A basic rule of security in any operating system is: If you don't need it, don't enable it!

I should also mention that OpenSSH was created by uber-genius Theo DeRaadt (as part of the OpenBSD O/S project) who lives in Alberta, Canada. He was born in South America, but we won't hold that against him...

OpenSSH is THE secure remote access standard on (AFAIK) all Linux/BSD/Unix operating systems. I believe it to be the most important utility ever developed...yeah, it's that important!