Software Module System - Lmod

Preface

This guide provides a general overview and introduction to the software system management via Lmod on JUSTUS 2 for new users as well as for experienced users coming, e.g. from sites planted with different Environment modules systems.

Scientific Software available on JUSTUS 2 via Lmod

JUSTUS 2 uses Linux operating system. The standard Linux packages are installed on the front end nodes (login and visualisation nodes). The scientific software is accessible via so called module system. A module system on JUSTUS 2 is Lmod (https://lmod.readthedocs.io/en/latest/). The module system incorporates majority of the computational software available - this includes among others compilers, mpi libraries, numerical libraries, computational chemistry packages, python specific libraries. The programs in the module system are defaultly not utilizable. It has to be "loaded" to become activated. The main functionality of Lmod is load modules by means of

$ module load <module_name>

command. The activation is realized by modifying of the shell environment, including adding new pathes to bin directories with the specific software into the PATH environmental variable. Although, the module system has other useful capabilities. Basic functions of Lmod are:
(i) to list available software
(ii) to load (activate) modules (particular software)
(iii) to search through all packages within the module system
(iv) to provide specific help information for a particular module system

Elementary Lmod Commands

List of available software

$ module available

alternatively also in a short form

$ ml av

Module naming convention: Category/Name/Version

On JUSTUS 2 (similarly as on other HPC sites of bwHPC), the software modules are grouped into several categories as for example chem, compiler, mpi, lib, phys, vis etc. to make it easier for users to get oriented within the module system. For example Gaussian 16 program allowing to calculate electronic structure of molecules is found in the category chem (together with other programs used by theoretical chemists).
The full name of a module always consists of three parts category, name, and version. Consequently, the full name of the module with Gaussian 16 package is chem/gaussian/g16.C.01.

Load a specific software

$ module load <module_name>

or shortly

$ ml <module_name>

For example to load gaussian of version 16 one has to run

$ ml chem/gaussian/g16.C.01

Unload a specific software from the environment

$ module unload <module_name>

or equivalently

$ ml -<module_name>

for example to unload previously loaded vasp module chem/vasp/5.4.4.3.16052018 use

$ ml -chem/vasp/5.4.4.3.16052018

Unload all the loaded modules

$ module purge

or

$ ml purge

Providing a specific help for a particular module

$ module help <module_name>

or

$ ml help <module_name>

List of the loaded modules

$ module list

or simply

$ ml

Simple searching through names of the modules

$ module available <module_name>

or shortly

$ ml av <module_name>

For example, searching for python modules is realized via

$ ml av python

with the following output:

----------------------------------------------------------------------------------- /opt/bwhpc/common/modulefiles/Core ------------------------------------------------------------------------------------
   devel/python/3.8.3    lib/python_matplotlib/3.2.2_numpy-1.19.0_python-3.8.3    numlib/python_numpy/1.19.0_python-3.8.3    numlib/python_scipy/1.5.0_numpy-1.19.0_python-3.8.3

Use "module spider" to find all possible modules and extensions.
Use "module keyword key1 key2 ..." to search for all possible modules matching any of the "keys"

Finding detailed information about a specific module

$ module spider <searching_pattern>

or just

$ ml spider <searching_pattern>

Extended searching through entire module system

$ module keyword <searching_pattern>

For example, to find out which modules contain fftw library:

ml keyword fftw

which gives the following info:

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

The following modules match your search criteria: "fftw"
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

  numlib/mkl: numlib/mkl/2019, numlib/mkl/2020, numlib/mkl/2020.2

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Useful Extras

Conflicts between modules

Some modules cannot be loaded together at the same time. For example two different versions of the same package cannot be activated simultaneously. The modules might already built-in this functionality. In such circumstances, Lmod, during the loading, either prints an error message and no module is loaded, or the module is reloaded - the old module is unloaded and only the new module is become activated.

Module dependencies (why there is no mpi module?)

Some modules can depends on other modules. Typically, many modules depends on mpi library, Mpi library depends on a compiler, etc.. The user does not need to care about these fundamental dependencies. Majority of modules automatically take care about loading of all necessary packages it is depending on. However, there is an eminent exception - mpi library. While the most of the installed parallel applications exist for only one compiler-mpi combination, there are variety of mpi libraries of the same versions built with different compilers. For example there are two sets of OpenMPI 4.0 modules for intel and gnu compilers. Thus, an user who wants to load a specific mpi must chose (load) a particular compiler prior the mpi module load. Note, that the mpi modules also remains "invisible" for "module av <mpi_name>" command until a certain compiler is not loaded. This due to the module hierarchy of Lmod. More details about the hierarchy is below in https://wiki.bwhpc.de/e/Software_Modules_Lmod#Semi_hierarchical_layout_of_modules_on_JUSTUS_2.

For users migrating from 'Environment Modules' to Lmod

There exist several software implementations for a dynamical management of environmental variables throughout the HPC world. Some systems host Environment Modules package based on Tcl, while there is a Lua based module system Lmod (https://lmod.readthedocs.io/en/latest/#) installed on JUSTUS 2. Despite of the various software solutions, the difference in handling of the modules from users' perspective of view stays tiny. The biggest change lies in the introducing of the partial software hierarchy implemented in modules system on JUSTUS 2. Besides that, Lmod extends the basic environment modules by adding predefined shortcuts and a more powerful search capability.

Lmod commands

The much of module commands and its functionality has remained same on JUSTUS 2, although Lmod offers new functions as for example module spider as an extension of "old" module avail functionality.
Thus, e.g. the default Gaussian module is initialized by

$ module load chem/gaussian

which is pretty much the same as on JUSTUS 1 or with using of the Lmod shorthand version

$ ml chem/gaussian

Full list of the Lmod module commands is available online on https://lmod.readthedocs.io/en/latest/010_user.html

Rather than the divergence of module commands, JUSTUS 1 users has to get a grasp of the modulefile system hierarchy built-in JUSTUS 2 software layout. The layout is no more flat as on JUSTUS 1, however JUSTUS 2 adopts a partial module hierarchy for mpi modules.

Consequences of the partial module hierarchy for mpi modules

Due the flat layout of software modules on JUSTUS 1 module avail command showed all pre-installed software packages including those directly depended on another modules. This is no more true on JUSTUS 2, in particular for mpi modules. mpi modules remains invisible for a user (prompted module avail) until some compiler module has been loaded. Once the compiler module has been activated corresponding mpi modules, i.e. built with the particular compiler, become visible.

E.g., with the originally empty list of the loaded modules, the module command

$ module avail

or its shorthand analogue

 
$ ml av

displays no mpi module available. After running

ml compiler/intel/19.1
ml av

mpi packages compatible with the intel 19.1 compiler becomes visible

------------ /opt/bwhpc/common/modulefiles/Compiler/intel/19.1 --------------------
   mpi/impi/2019.7    mpi/openmpi/4.0

in the list of the available software.

Lmod Module System on JUSTUS 2

JUSTUS 2 system uses Lmod (the Lua Based Module System) environment management package to support dynamical modification of the user environment via modulefiles. Each modulefile contains information needed to configure the shell, i.e. its environmental variables, required to run a particular software application. To make major changes in the users' environment, such as modifications of PATH, LD_LIBRARY_PATH, CC or FC variables for, e.g. a switching to a different compiler, use the appropriate single or sequence of modules commands instead of a reconfiguration of the shell by hand.

E.g. in order to activate the default vasp module run a single command:

$ module load chem/vasp

or its shorthand variant

$ml chem/vasp

For an activation of the module of intel mpi built with the corresponding intel compiler a sequence of two module commands

$ module load compiler/intel
$ module load mpi/impi

has to be run.

Online user guide of Lmod

The complete user guide can be found on Lmod websites https://lmod.readthedocs.io/en/latest/010_user.html

Which shells supports module commands?

So far Bash is only supported shell on JUSTUS 2 to interpret module commands.

Basic Module System tasks

Lmod offers more than 25 sub-commands plus various options to manage the modulefile system installed on JUSTUS 2. See, e.g. output of "module --help" command. Large majority of users will use only couple of them. A complete list of module sub-commands can be displayed by entering "module --help" command or in Lmod online documentation. The following text lists only a couple of them.

Lmod shortcuts

Lmod extends the basic environment modules by adding simple shortcuts. The ml shortcut can be used in place of module, av in instead of avail, ml instead of module list, or - can alternate unload.
For instance, following combinations are interchangeble:

module list      <==>   ml

module avail      <==>   ml av

module load compiler/intel      <==>   ml compiler/intel

module unload compiler/intel      <==>   ml -compiler/intel

Loading and unloading modulefiles

To load and unload a module of a specific package use "module load category/package" and "module unload category/package", respectively. Thus, e.g, to load default version of VASP which belongs into category chem, enter

$ module load chem/VASP

and for unloading of the package use

$ module unload chem/VASP

Complete unloading of all modulefiles

To clean the environment from all entries set by lmod use "module purge" command.

$ module purge

Beware that the "module purge" does not always restore the environmental variables that existed prior entering first "module load" command. I.e., some of the entries in PATH, or environmental variables, etc. originally existed in the environment might be cleaned by "module purge" if those would be duplicates of the variables set by any modulefiles that was loaded.

What is Loaded Now?

To see which modules are currently loaded in your environment, enter the command "module list".

$ module list

Which modulefiles/software is available?

To see what modulefiles are available on JUSTUS 2, you can enter the following command:

$ module avail

or alternatively

$ ml av

which comes with lmod to save typewriting.

Module specific help

To access the module specific help, use the "module help" command. For example, to see the module help associated with the default VASP module, enter this command:

$ module help chem/vasp

It is always a good practice to read through all the info provided by a specific module help since this serves as an important communication channel between a user and the person who install the piece of a software.

Semi hierarchical layout of modules on JUSTUS 2

Module hierarchy in Lmod

The structure of software modules on JUSTUS 2 exploits a "semi" hierarchical structure. This is slightly different from what can be seen on another HPC systems with "full" hierarchical structure. The typical systems with full hierarchy put compiler modules (i.e., intel, gcc) in the uppermost (Core) level, depending libraries (e.g., MPI) on the second level, and more depending libraries on a third level. As a consequence, not all the modules contained in the module system are initially visible, namely the modules putted in the second and third layer. Only after a loading a compiler module, the modules of the second layer directly depending on the particular compiler will become available. And similarly, loading an MPI module will make the modules of the third layer depending on the loaded MPI library visible.

Semi hierarchy of software stack on JUSTUS 2

JUSTUS 2 adopted the hierarchical structure of the modules layout only partially. In particular, there is only "Core" and the "second" level presented and there are only mpi modules contained in the second level. All other modules, i.e. for example those from the "chem" sub-cathegory such as vasp, turbomole, or gaussian, or those located in the "numlib" sub-cathegory such as mkl or python_numpy, are embodied in the "Core" level.

Module dependency

The adopted hierarchy models is not the only tool handling the module dependency. As a matter of fact, most of the modules on JUSTUS 2 require a provision of functionalities from another modules, albeit located in the "Core" level. Such provisioning is implemented in a modulefile either automatically without a need of any action from the user (the depending modulefile, while loading, loads all additional modules automatically) or the depending modulefile, while loading, informs the user about necessity to pre-load additional modules if those has not been activated yet (in this case the user must repeat the loading operation). Which of the solution is applied rests with the decision of the person who built the particular module.

An example of module with the implemented automated pre-loading is orca module. With the pre-emptied list of the loading modules, i.e.

$ ml

shows

No modules loaded

, the command sequence

$ ml chem/orca
$ ml