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Environment Modules on VHPC (Lmod)

On the VHPC cluster, we use Lmod (a modern, Lua-based implementation of environment modules) rather than the older TCL-based Environment Modules system. Lmod provides backward compatibility with most module commands, but also includes enhancements such as hierarchical module naming, module collections, and more descriptive error messages.

Basic Commands

The following commands are used to manage your environment on VHPC. They are mostly compatible with TCL module syntax, but Lmod introduces some improvements.

Listing Modules

module avail

Shows all available modules. In Lmod, output is organized by category and path.

module spider <name>

Searches for modules by name, including hidden ones, and shows how to load them.

Loading Modules

module load GCC/12.2.0

Loads the specified module.

Multiple modules can be loaded at once:

module load GCC/12.2.0 OpenMPI/4.1.4-GCC-12.2.0

Unloading Modules

module unload OpenMPI

Removes the specified module from your environment.

Swapping Modules

module swap GCC/11.3.0 GCC/12.2.0

Unloads the first module and loads the second.

Inspecting Modules

module show OpenMPI

Displays the environment changes a module makes.

module help OpenMPI

Displays the help message for the module.

Getting Help

To see help about the module command itself (including subcommands):

module help

You can also use --help or -h to get the same thing:

module --help

The ml Shortcut

Lmod provides the ml command as a shorter alternative to module.

Examples:

ml GCC/12.2.0 OpenMPI/4.1.4-GCC-12.2.0   # load multiple modules
ml -OpenMPI                              # unload a module
ml                                       # list currently loaded modules

ml is especially convenient for quick interactive use.

Managing Your Environment

Saving a Collection

In Lmod, you can save your currently loaded set of modules as a named collection:

module save my_workflow

Later, restore the same environment with:

module restore my_workflow

List your collections:

module savelist

Delete a collection:

module reset my_workflow

Default Collection

You can define a default module collection to be loaded on login:

module save default

To clear all loaded modules and return to the system defaults:

module purge

Differences from TCL Modules

  • Compatibility: Most TCL module commands (load, unload, list, avail, swap) work as expected.
  • Additional Tools: Lmod introduces module spider, module save, and module restore for advanced environment management.
  • Collections vs initfiles: TCL used module initadd and related commands to persist modules; in Lmod you should use collections instead.
  • Hierarchical modules: Some software may only appear in module avail after loading a compiler or MPI library first.

Useful Commands Summary

  • module avail — List available modules.
  • module spider <name> — Search for modules.
  • module load <name> — Load a module.
  • module unload <name> — Unload a module.
  • module swap <old> <new> — Swap modules.
  • module list — Show currently loaded modules.
  • module show <name> — Inspect a module’s environment.
  • module save <name> — Save current module collection.
  • module restore <name> — Restore a saved collection.
  • module purge — Remove all loaded modules.

References