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How to use execute a shell command on the nodes

Prerequisite

This feature is only available in NodeHandler v4 and above.

Before going through this tutorial, you should know the basics of writing and running an experiment script (see here and here).

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"). See How to install a disk image.

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 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.

To run this example script, use the following command:

 nodehandler4 tut_cmd_1

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

The Results

The experiment screen output should then look like this​. And the experiment log file should look like 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 this other method which uses application definition.