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The software pool is ready to be used under a version control system called environment modules. It is made for a user friendly activation and deactivation of software and allows to have several versions of the same software package installed in parallel at non-default places. "loading a module" can be thought as synonymous for "making software accessable". The most important commands to know are:

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A complete list of all module commands is available with module help.Below, a few examples are introduced.

Available modules overview

       module avail

This command shows all modules available to be loaded.  Notice the version numbers and that some are marked as default. Modules makes it easy to switch between different software versions. At HLRN the modules are sorted into CATEGORIES (all capital letters).

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This command seeks  through  the  so-called whatis  informations  of  all  available modulefiles for the specified string.  All module whatis informations matching the string search for *String* (case sensitive) will be displayed. Use the parameter *-i* to ignore case sensitivity. 

Load and unload modules

       module load <package>/<version>
       module unload <package>/<version>
       module switch <package>/<version1> <package>/<version2>

If you load the generic name of a module, you will get the default version. Loading a module manipulates the shell environment to make software visible for shell commands. Note, these changes of environmental variables are fully reversible and are taken back, if a module is unloaded. For example the path to a specific software can be prepended to PATH. To see all currently loaded modules, use

       module list

The modules command can also be used to manipulate environment variables directly. This is reversible and more save than manipulating the environment "by hand".

       prepend-path VAR val 
       append-var VAR val       
       remove-path VAR val

change the environment variable VAR without loading any module file. 

Getting module details

To investigate details of a module the commands

       module whatis <package>/<version> 
       module help <package>/<version>       
       module show <package>/<version>
       

Especially module show delivers information on the modified environment variables.

The modified environmental variables can be used by compilers, linkers, make, cmake or private software installation tools, to recognise details of installed libraries and link them accordingly. Typical examples are PATH, LD_RUNPATH, LD_LIBRARY_PATH or PKG_CONFIG_PATH.

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