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== How to use execute a shell command on the nodes ==

This feature is only available in NodeHandler v4 and above.

Before going through this tutorial, you should know [wiki:Tutorial/HowToImage how to install a disk image]. 

You should also have installed a disk image with Node Agent v4 on the nodes of the testbed you are using (e.g. "baseline-7.11.ndz").

=== Goal ===

In this tutorial, you will learn a simple way to run a shell commands on the nodes of a testbed.
  
=== The tutorial experiment ===

This experiment is given in the attached script [attachment:tut_cmd_1.rb tut_cmd_1.rb]. 

This file contains extensive comments that should help you understand the different steps involved in executing a shell command on the nodes of a testbed. It also shows how you could process the command outputs, e.g. redirect them to a text file.

For more information on the basics of writing and using an experiment script, please refer to the previous tutorials, [wiki:Tutorial/HowtoWriteScripts here] and [wiki:Tutorial/HelloWorld here].

To run this example script, use the following command:

 {{{
  nodehandler4 tut_cmd_1
 }}}

(This assumes that you previously logged in to a testbed, and imaged its nodes with a disk image such as "baseline-7.11.ndz".)

=== The Results ===

The experiment screen output should then look like [attachment:sb1_2007_11_19_18_45_06-Output.txt this]. And the experiment log file should look like  [attachment:sb1_2007_11_19_18_45_06.log this]. 

=== More... ===

This method of executing a shell command on nodes is well suited for one-off or temporary experiments. If you plan on re-using or sharing the same commands among multiple experiment scripts, then you should consider [wiki:Tutorial/HowtoApplication this other method] which uses application definition.