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Environment Modules


Environment modules is available on the Cori system.

Environment modules provides a mechanism to dynamically modify a user's environment using modulefiles. A modulefile is a recipe required to load a particular application that may include setting environment variables; setting variables such as PATH, LD_LIBRARY_PATH, and MANPATH to include the location where an application is installed; loading dependent modules; and providing a brief description of the software.

Modulefiles are written in Tool Command Language (TCL), and are evaluated by the module function when you load/unload modulefiles via module load or module unload.

About module

module is a shell function that modifies the user shell upon the loading of a modulefile. The module function is defined as follows:

$ type module
module is a function
module ()
    eval `/opt/cray/pe/modules/ bash $*`


module is not a program, so it cannot be invoked directly in a script.

Module Commands


Cray default module is modules/ and documentation is based on this version.

modules/ is also available to support non-Cray modulefiles that require Modules 4.x. While most modulefiles at NERSC should work with Modules 4.x, there are some compatibility issue with PrgEnv- modules, and we don't recommend modules/ for "normal" use.

General usage:

module [switches] [subcommand] [subcommand-args]

Further reading:

  • module --help
  • man module
  • man modulefile
  • Environment Modules Documentation (note: some features may only be available in later versions than what is installed on NERSC systems)

Command Summary

Command Description
module list List active modules in the user environment
module av[ail] [module] List available modules in MODULEPATH
module add|load [module] Load a module file in the user environment
module rm|unload [module] Remove a loaded module from the user environment
module purge Remove all modules from the user environment
module swap|switch [module1] [module2] Replace module1 with module2
module show|display [module] Show content of commands performed by loading module file
module help [module] Show help for a given module
module whatis [module] A brief description of the module, generally single line
module use [-a] [path] Prepend or Append path to MODULEPATH
module unuse [path] Remove path from MODULEPATH
module keyword [text] Search for keyword across all module files

Module Usage

Show availability of all modules containing a substring:

module avail -S <substring>

Display what changes are made when a module is loaded:

module display <module-name>
module show <module-name>

Add a module to your current environment:

module load <module-name>
module add <module-name>


Loading/adding a module is a silent operation unless problems occur with the module.


If you load the name of a module (with no version), you will get the default version.

module load gcc

To load a specific version use the full name:

module load gcc/8.1.0

Remove a module from the current environment:

module unload <module-name>
module rm <module-name>


Unloading/removing will fail silently if the specified module is not loaded.

Switch currently loaded module with a new module:

module swap <old-module> <new-module>
module switch <old-module> <new-module>

To purge all modules:


This will remove all your modules from active environment including startup modules loaded in your shell, which may make your environment unusable at NERSC. To restore your environment with startup modules, we suggest to logout and login again instead.

module purge

To visualize the help of a particular module:

module help <module-name>

The module whatis command displays a brief summary of the module, while module help will provide the full description of modulefile.

$ module whatis PrgEnv-cray
PrgEnv-cray: Programming environment using the Cray CCE compilers.


If a module does not have a help or whatis section in its modulefile, you will see an empty line when you run module help or module whatis

To see a condensed list of modules you can use the -t option with list or avail.

$ module -t list
Currently Loaded Modulefiles:

On Cori there are three Cray-provided Programming Environment modules: PrgEnv-cray, PrgEnv-gnu and PrgEnv-intel (the default). These modules provide respectively the Cray, GNU or Intel compiler via the compiler wrappers cc (C) CC (C++) and ftn (Fortran); see also this page about using compiler wrappers.

Only one PrgEnv module can be loaded at a time: for instance if we try loading PrgEnv-gnu without first unloading PrgEnv-intel we get the following error message.

$ module load PrgEnv-gnu
PrgEnv-gnu/6.0.5(77):ERROR:150: Module 'PrgEnv-gnu/6.0.5' conflicts with the currently loaded module(s) 'PrgEnv-intel/6.0.5'
PrgEnv-gnu/6.0.5(77):ERROR:102: Tcl command execution failed: conflict PrgEnv-intel

To change programming environments, you must swap modules as follows:

module swap PrgEnv-intel PrgEnv-gnu

Or unload the old module and load the new one:

module unload PrgEnv-intel
module load PrgEnv-gnu

Creating a Custom Module Environment

There are ways to modify your environment so that certain modules are automatically loaded when you log in.

The first option is to use shell commands.


In ~/.bash_profile

module swap PrgEnv-${PE_ENV,,} PrgEnv-gnu


In ~/.login

set pe = ` echo $PE_ENV | tr "[:upper:]" "[:lower:]" `
module swap PrgEnv-${pe} PrgEnv-gnu


The second option is to use the "snapshot" feature of modules.

  1. Swap and load modules to your desired configuration.
  2. Save a "snapshot" with module snapshot <snapshot-filename>.

Then at any time later restore the environment with module restore <snapshot-filename>.

Install Your Own Customized Modules

You can create and install your own modules for your convenience or for sharing software among collaborators. See man modulefile or the modulefile documentation for details of the required format and available commands. These custom modulefiles can be made visible to the module command with module use /path/to/the/custom/modulefiles.


Global Common is the recommended location to install software.


Make sure the UNIX file permissions grant access to all users who want to use the software.


Do not give write permissions to your home directory to anyone else.


The module use command prepends new directories before other module search paths (defined as $MODULEPATH), so modules defined in a custom directory will have precedence if there are other modules with the same name in the module search paths. If you prefer to have the new directory added at the end of $MODULEPATH, use module use -a instead of module use.

Known issues with modules

Zero exit code for invalid modules

$ module load X
ModuleCmd_Load.c(244):ERROR:105: Unable to locate a modulefile for 'X'
$ echo $?

This means that module commands often return a "success" code (0) even if the command failed, which can lead to surprising errors in job scripts.

Incompatibilities with modules/

modules/ is available but not recommended. If you do need Modules 4.x, you can access it with module swap modules modules/ (note that module load modules/ will abort with an error). If using Modules 4.x, we recommend carefully checking that your script or usage has the correct outcome.

Please refer to for a summary of differences between module v3.2 and 4.x.

Module FAQ

  • Is there an environment variable that captures loaded modules?

Yes, active modules can be retrieved via the $LOADEDMODULES environment variable, which is automatically updated to reflect active loaded modules (similar to module list). You can access the modulefile path for loaded modules through the $_LMFILES_ environment variable.

  • How can I restore MODULEPATH in my user session?

If you run into an error such as following:

$ module avail
ModuleCmd_Avail.c(217):ERROR:107: 'MODULEPATH' not set

You should try a different login shell and see if it fixes the issue (i.e., bash users try csh; csh users try bash). Then check your startup scripts to see whether the issue is caused by something there. Bash users should examine the files ~/.bashrc and ~/.bash_profile; tcsh/csh users should look at ~/.cshrc.