Ubuntu/Applications/PDSH

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Overview

PDSH is currently (2015) one of the most popular solutions for Parallel Distributed Shell. It allows you to execute remote commands on a group or cluster of servers at the same time.

Step 1: Password-less SSH

PDSH is not coded to handle authentication prompts, so it requires that you setup pair of authentication keys rather than using /passwd.
Create the ssh public/private keys on the host (computer you will be connecting FROM).

~$ ssh-keygen
 Generating public/private rsa key pair.
 Enter file in which to save the key (/home/a/.ssh/id_rsa): [Enter key]
 Created directory '/home/a/.ssh'.
 Enter passphrase (empty for no passphrase): [Press enter key]
 Enter same passphrase again: [Press enter key]
 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

Copy the public key to the remote-host (computer you will be connecting TO).

~$ ssh-copy-id -i ~/.ssh/id_rsa.pub remote-host
 a@remote-host'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.

You should now be able to ssh into the remote-host without a password:

~$ ssh remote-host
 Last login: Sun Nov 16 17:22:33 2008 from 192.168.1.2
 [Note: SSH did not ask for password.]
 
 a@remote-host$ [Note: You are on remote-host here]

Step 2: Install PDSH on Host

Simple.

 ~$ sudo apt-get update && sudo apt-get install pdsh -y

Step 3: send a test command from the host to a few servers

PDSH allows you to create a HOSTLIST which you can use to easily call groups of computers. I'm not going to cover that, but you can find more information about it by visiting their wiki here.