Modules

Environment variables are finicky, prone to typos, and a lot of work to edit manually. Modules make dynamically changing environment variables a lot easier and safer. Modules contain all the necessary environment variables for running a particular application or providing access to a particular library. In addition:

• They are a convenient way to dynamically change the user’s environment
• They help avoid conflicts between program versions, compilers, libraries, etc.

Different clusters have different implementations of modules. More info on the TACC implementation of modules can be found here

To list all of your currently loaded modules:

$ module list

To list modules that are available for you to load, do:

$ module avail

There are quite a few! Modules are organized both by version, and by compiler dependencies (more on this later). To filter, search for modules either by the name of the application, or a keyword. For example:

$ module avail paraview/5.2.0
$ module spider paraview/5.2.0

Each module, when loaded, will modify your environment variables so that you can run the desired application. To see what the effect of loading a module is, do:

$ module show paraview/5.2.0

Once you have identified the module you are interested in, you can load it to put it in your PATH, and unload it to remove it from your PATH:

$ module list
$ module load qt/4.8.4 paraview/5.2.0
$ module list
$ module unload paraview/5.2.0 qt/4.8.4
$ module list
$ ml paraview/5.2.0              # ml is a shortcut for module load

Paraview is a graphic visualization tool that runs in X11, we will see later how to launch a VNC session. However Paraview requires a Graphical User Interface (GUI) framework called QT. If you try just “module load paraview” this message will appear:

Lmod has detected the following error:  Cannot load module "paraview/5.2.0". At least
one of these module(s) must be loaded:
   qt/4.8.4

While processing the following module(s):
    Module fullname  Module Filename
    ---------------  ---------------
    paraview/5.2.0   /opt/apps/intel15/mvapich2_2_1/modulefiles/paraview/5.2.0

Finally, find more help on using module commands by doing:

$ module help

Exercise

1. Search the module system for any application(s) that you need for your research.
2. Figure out if any dependencies are required to load the module.
3. Load the module and determine what effect it has on your environment.
4. Make sure the desired executables (and correct version) are in your PATH.

Click here for solution

Review of Topics Covered

Command	Effect
module list	list currently loaded modules
module avail	see what modules are available
module avail name	search for module “name”
module spider name	search for module “name”
module key keyword	search for modules with a keyword
module show name	show the contents of module “name”
module load name	load module “name”
ml name	ml is a shortcut for module load
module unload name	unload module “name”
module help	show module command help

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