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These steps ensure the right version of Java is installed and available from the command line without having to use lengthy pathnames to refer to the install location.

Remember that the preceding commands only affect the currently running shell and the settings will be lost after you log out, close the shell, or reboot. To ensure the same setup is always available, you can add these to the startup files for your shell of choice, within the .bash_profile file for the BASH shell or the .cshrc file for TCSH, for example.

An alternative favored by me is to put all required configuration settings into a standalone file and then explicitly call this from the command line; for example:

$ source Hadoop_config.sh

This technique allows you to keep multiple setup files in the same account without making the shell startup overly complex; not to mention, the required configurations for several applications may actually be incompatible. Just remember to begin by loading the file at the start of each session!

Setting up Hadoop

One of the most confusing aspects of Hadoop to a newcomer is its various components, projects, sub-projects, and their interrelationships. The fact that these have evolved over time hasn't made the task of understanding it all any easier. For now, though, go to http://hadoop.apache.org and you'll see that there are three prominent projects mentioned:

The last two of these should be familiar from the explanation in Chapter 1, What It's All About, and common projects comprise a set of libraries and tools that help the Hadoop product work in the real world. For now, the important thing is that the standard Hadoop distribution bundles the latest versions all of three of these projects and the combination is what you need to get going.