Modules Software Environment

NERSC uses the module utility to manage nearly all software. There are two huge advantages of the module approach:

1. NERSC can provide many different versions and/or installations of a single software package on a given machine, including a default version as well as several older and newer versions; and
2. Users can easily switch to different versions or installations without having to explicitly specify different paths.  With modules, the MANPATH and related environment variables are automatically managed. Users simply ``load'' and ``unload'' modules to control their environment.

The module utility consists of two parts: the module command itself and the modulefiles on which it operates. 

Module Command

module help

To get a usage list of module options type the following (the listing has been abbreviated to only those commands discussed on this page) :

% module help  

  Available Commands and Usage:

     +  add|load     modulefile [modulefile ...]
     +  rm|unload    modulefile [modulefile ...] 
     +  switch       modulefile1 modulefile2
     +  display      modulefile [modulefile ...] 
     +  avail        path [path]
     +  list      
     +  help         modulefile [modulefile ...]

To get help on a specific module use:

 % module help [modulefile]

module list

% module list

This lists all the modulefiles that are currently loaded into your environment.

module avail

% module avail

This option lists all the modulefiles that are available to be loaded. Notice that many of them have version numbers associated with them and that where there is more than one version, one is labeled as the default. You can also restrict this command to a single package; for example,

module avail visit

module display

 % module display [modulefile]

Use this command to see exactly what a given modulefile will do to your environment, such as what will be added to the PATH, MANPATH, etc., environment variables.  This is synonymous with

 % module show [modulefile]

module load

% module load [modulefile1] [modulefile2] ...

This command adds one or more modulefiles to your current environment. It does so silently, unless there is a problem with a modulefile. If you load the generic name of a module, you will get the default version. To load a specific version, load the modulefile using its full specification.  For example,

 % module load visit

will do the same thing as

% module load visit//2.1.2

module unload

% module unload [modulefile]

This removes the listed module from the user's current environment. Modulefiles can be removed in any order.  Note that this command will fail silently if the modulefile you specify is not already loaded.

module switch

% module switch [modulefile_old] [modulefile_new]

This command demonstrates the true advantage of using modules. Different versions of entire software packages can be replaced with a single module command.  

This is synonymous with

 % module swap [modulefile_old] [modulefile_new]

Note that the following command would be completely correct and appropriate if, before issuing it, you had issued a "module load" command for a non-default version of the VisIt software and you wish to switch to the default version:

module swap visit visit

Loading Modules into Your Default Environment

You can modify your environment so that certain modules are loaded whenever you log in. Put your changes in one of the following files, depending on your shell.

• .cshrc.ext or .tcshrc.ext
• .bashrc.ext

Here is an example of a .cshrc.ext file with commands to load modules. Notice that, modules specific to a platform are put inside of if-then blocks.

if ($NERSC_HOST == "hopper") then
# Replace the following line with personal settings for Hopper
   module load fftw
endif