HP XC System 2.x Software manual 2Using the System

environment variables, such as PATH and MANPATH, to enable access to various installed software.

One of the key features of using modules is to allow multiple versions of the same software to be used in your environment in a controlled manner. For example, two different versions of the Intel C compiler can be installed on the system at the same time – the version used is based upon which Intel C compiler modulefile is loaded.

The HP XC software provides a number of modulefiles. You can also create your own modulefiles. Modulefiles may be shared by many users on a system, and users may have their own collection of modulefiles to supplement or replace the shared modulefiles.

The following topics are addressed in the corresponding sections:

•Section 2.2.1 provides additional information on modulefiles.

•Section 2.2.2 discusses what modules are supplied.

•Section 2.2.3 discusses what modules are loaded by default.

•Section 2.2.4 discusses how to determine what modules are available.

•Section 2.2.5 discusses how to determine which modules are loaded.

•Section 2.2.6 discusses how to load a module.

•Section 2.2.7 discusses how to unload a module.

•Section 2.2.8 discusses module conflicts.

•Section 2.2.9 discusses creating your own module.

For further information about the Modules software supplied with the HP XC system, see the Modules Web site at the following URL:

http://sourceforge.net/projects/modules/

2.2.1 Notes on Modulefiles

A modulefile does not provide configuration of your environment until it is explicitly loaded. That is, the specific modulefile for a software product or application must be loaded in your environment (with the module load command) before the configuration information in the modulefile is effective.

You or your system administrator can configure your environment so that any desired modulefiles are automatically loaded for you when you log in to the system. You can also load a modulefile yourself, as described in Section 2.2.6.

The Modules software is initialized when you log in to the HP XC system. It provides access to the commands that allow you to display information about modulefiles, load or unload modulefiles, or view a list of available modulefiles.

Modulefiles do not affect packages other than their intended package. For example, a modulefile for a compiler will not adjust MPI_CC (the environment variable used by HP MPI to control which compiler to use). A modulefile for a compiler simply makes it easier to access that particular compiler; it does not try to determine how the compiler will be used.

Similarly, a modulefile for HP MPI will not try to adjust LD_LIBRARY_PATH to correspond to the compiler that the mpicc command uses. The modulefile for MPI simply makes it easier to access the mpi** scripts and libraries. You can specify the compiler it uses through a variety of mechanisms long after the modulefile is loaded.

The previous scenarios were chosen in particular because the HP MPI mpicc command uses heuristics to try to find a suitable compiler when MPI_CC or other default-overriding mechanisms are not in effect. It is possible that mpicc will choose a compiler inconsistent with the most recently loaded compiler module. This could cause inconsistencies in the use

2-2Using the System