Accessing software via Modules
Last updated on 2025-10-08 | Edit this page
Overview
Questions
- How do we load and unload software packages?
Objectives
- Understand how to load and use a software package.
On a HPC system, it is seldom the case that the software we want to use is available when we log in. It may be installed, but we will need to “load” it before it can run.
Before we start using individual software packages, however, we should understand the reasoning behind this approach. The three biggest factors are:
Software incompatibilities
Software incompatibility is a major headache for programmers.
Sometimes the presence (or absence) of a software package will break
others that depend on it. Two of the most famous examples are Python 2
vs 3 and C compiler versions. Python 3 famously provides a
python command that conflicts with that provided by Python
2. And software compiled against a newer version of the C libraries and
then used when they are not present will result in a nasty
'GLIBCXX_3.4.20' not found error.
Versioning
Software versioning is another common issue. A team might depend on a certain package version for their research project - if the software version was to change (for instance, if a package was updated), it might affect their results. Having access to multiple software versions on the same system helps to prevent software versioning issues from affecting their results.
Dependencies
Dependencies are where a particular software package (or even a particular version) depends on having access to another software package (or even a particular version of another software package). For example, the VASP materials science software may depend on having a particular version of the FFTW (Fastest Fourier Transform in the West) software library available for it to work.
Environment Modules
Environment modules are the solution to these problems. A module is a self-contained description of a software package — it contains the settings required to run a software package and, usually, encodes required dependencies on other software packages.
There are a number of different environment module implementations
commonly used on HPC systems: the two most common are TCL
modules and Lmod. Both of these use similar syntax and the
concepts are the same so learning to use one will allow you to use
whichever is installed on the system you are using. In both
implementations the module command is used to interact with
environment modules. An additional subcommand is usually added to the
command to specify what you want to do. For a list of subcommands you
can use module -h or module help. As for all
commands, you can access the full help on the man pages with
man module.
On login you may start out with a default set of modules loaded or you may start out with an empty environment; this depends on the setup of the system you are using.
Listing Available Modules
To see available software modules, use module avail:
OUTPUT
-------------------------------------------------------------- /opt/cray/pe/lmod/modulefiles/core ---------------------------------------------------------------
PrgEnv-amd/8.3.3 (D) aocc/4.0.0 (D) cray-cti/2.16.0 cray-pals/1.2.5 (D) gdb4hpc/4.14.6 (D)
PrgEnv-amd/8.4.0 atp/3.14.16 (D) cray-cti/2.17.1 (D) cray-pals/1.2.12 gdb4hpc/4.15.1
PrgEnv-aocc/8.3.3 (D) atp/3.15.1 cray-cti/2.18.1 cray-pmi/6.1.8 (D) iobuf/2.0.10
PrgEnv-aocc/8.4.0 cce/15.0.0 (L,D) cray-dsmml/0.2.2 (L) cray-pmi/6.1.12 papi/6.0.0.17 (D)
PrgEnv-cray-amd/8.3.3 cce/16.0.1 cray-dyninst/12.1.1 (D) cray-python/3.9.13.1 (D) papi/7.0.1.1
PrgEnv-cray-amd/8.4.0 (D) cpe-cuda/22.12 (D) cray-dyninst/12.3.0 cray-python/3.10.10 perftools-base/22.12.0 (L,D)
PrgEnv-cray/8.3.3 (L,D) cpe-cuda/23.09 cray-libpals/1.2.5 (D) cray-stat/4.11.13 (D) perftools-base/23.09.0
PrgEnv-cray/8.4.0 cpe/22.12 (D) cray-libpals/1.2.12 cray-stat/4.12.1 rocm/5.2.3
PrgEnv-gnu-amd/8.3.3 cpe/23.09 cray-libsci/22.12.1.1 (L,D) craype/2.7.19 (L,D) sanitizers4hpc/1.0.4 (D)
PrgEnv-gnu-amd/8.4.0 (D) cray-R/4.2.1.1 (D) cray-libsci/23.09.1.1 craype/2.7.23 sanitizers4hpc/1.1.1
PrgEnv-gnu/8.3.3 (D) cray-R/4.2.1.2 cray-libsci_acc/22.12.1.1 (D) craypkg-gen/1.3.28 (D) valgrind4hpc/2.12.10 (D)
PrgEnv-gnu/8.4.0 cray-ccdb/4.12.13 (D) cray-libsci_acc/23.09.1.1 craypkg-gen/1.3.30 valgrind4hpc/2.13.1
amd/5.2.3 cray-ccdb/5.0.1 cray-mrnet/5.0.4 (D) gcc/10.3.0
aocc/3.2.0 cray-cti/2.15.14 cray-mrnet/5.1.1 gcc/11.2.0 (D)
----------------------------------------------------- /opt/cray/pe/lmod/modulefiles/craype-targets/default ------------------------------------------------------
craype-accel-amd-gfx908 craype-arm-grace craype-hugepages2G craype-hugepages64M craype-x86-genoa craype-x86-spr
craype-accel-amd-gfx90a craype-hugepages128M craype-hugepages2M craype-hugepages8M craype-x86-milan-x craype-x86-trento
craype-accel-host craype-hugepages16M craype-hugepages32M craype-network-none craype-x86-milan
craype-accel-nvidia70 craype-hugepages1G craype-hugepages4M craype-network-ofi (L) craype-x86-rome (L)
craype-accel-nvidia80 craype-hugepages256M craype-hugepages512M craype-network-ucx craype-x86-spr-hbm
...
Many more
...
Listing Currently Loaded Modules
You can use the module list command to see which modules
you currently have loaded in your environment. If you have no modules
loaded, you will see a message telling you so
OUTPUT
Currently Loaded Modules:
1) craype-x86-rome 6) cce/15.0.0 11) PrgEnv-cray/8.3.3
2) libfabric/1.12.1.2.2.0.0 7) craype/2.7.19 12) bolt/0.8
3) craype-network-ofi 8) cray-dsmml/0.2.2 13) epcc-setup-env
4) perftools-base/22.12.0 9) cray-mpich/8.1.23 14) load-epcc-module
5) xpmem/2.5.2-2.4_3.30__gd0f7936.shasta 10) cray-libsci/22.12.1.1Loading and Unloading Software
To load a software module, use module load. Let’s say we
would like to use the HDF5 utility h5dump.
On login, h5dump is not available. We can test this by
using the which command. which looks for
programs the same way that Bash does, so we can use it to tell us where
a particular piece of software is stored.
OUTPUT
which: no h5dump in (/work/y07/shared/utils/core/bolt/0.8/bin:/mnt/lustre/a2fs-work4/work/y07/shared/utils/core/bin:/opt/cray/pe/mpich/8.1.23/ofi/crayclang/10.0/bin:/opt/cray/pe/mpich/8.1.23/bin:/opt/cray/pe/craype/2.7.19/bin:/opt/cray/pe/cce/15.0.0/binutils/x86_64/x86_64-pc-linux-gnu/bin:/opt/cray/pe/cce/15.0.0/binutils/cross/x86_64-aarch64/aarch64-linux-gnu/../bin:/opt/cray/pe/cce/15.0.0/utils/x86_64/bin:/opt/cray/pe/cce/15.0.0/bin:/opt/cray/pe/cce/15.0.0/cce-clang/x86_64/bin:/opt/cray/pe/perftools/22.12.0/bin:/opt/cray/pe/papi/6.0.0.17/bin:/opt/cray/libfabric/1.12.1.2.2.0.0/bin:/usr/local/bin:/usr/bin:/bin:/usr/lib/mit/bin:/opt/cray/pe/bin)We can find the h5dump command by using
module load:
OUTPUT
/opt/cray/pe/hdf5/1.12.2.1/bin/h5dumpSo, what just happened?
To understand the output, first we need to understand the nature of
the $PATH environment variable. $PATH is a
special environment variable that controls where a UNIX system looks for
software. Specifically, $PATH is a list of directories
(separated by :) that the OS searches through for a command
before giving up and telling us it can’t find it. As with all
environment variables we can print it out using echo.
OUTPUT
/opt/cray/pe/hdf5/1.12.2.1/bin:/work/y07/shared/utils/core/bolt/0.8/bin:/mnt/lustre/a2fs-work4/work/y07/shared/utils/core/bin:/opt/cray/pe/mpich/8.1.23/ofi/crayclang/10.0/bin:/opt/cray/pe/mpich/8.1.23/bin:/opt/cray/pe/craype/2.7.19/bin:/opt/cray/pe/cce/15.0.0/binutils/x86_64/x86_64-pc-linux-gnu/bin:/opt/cray/pe/cce/15.0.0/binutils/cross/x86_64-aarch64/aarch64-linux-gnu/../bin:/opt/cray/pe/cce/15.0.0/utils/x86_64/bin:/opt/cray/pe/cce/15.0.0/bin:/opt/cray/pe/cce/15.0.0/cce-clang/x86_64/bin:/opt/cray/pe/perftools/22.12.0/bin:/opt/cray/pe/papi/6.0.0.17/bin:/opt/cray/libfabric/1.12.1.2.2.0.0/bin:/usr/local/bin:/usr/bin:/bin:/usr/lib/mit/bin:/opt/cray/pe/binYou’ll notice a similarity to the output of the which
command. In this case, there’s only one difference: the different
directory at the beginning. When we ran the module load
command, it added a directory to the beginning of our
$PATH. Let’s examine what’s there:
OUTPUT
gif2h5 h5c++ h5clear h5debug h5dump h5format_convert h5jam h5mkgrp h5redeploy h5repart h5unjam
h52gif h5cc h5copy h5diff h5fc h5import h5ls h5perf_serial h5repack h5stat h5watchIn summary, module load will add software to your
$PATH. module load may also load additional
modules with software dependencies.
To unload a module, use module unload with the relevant
module name.
Unload!
Confirm you can unload the cray-hdf5 module and check
what happens to the PATH environment variable.
Software versioning
So far, we’ve learned how to load and unload software packages. This is very useful, however we have not yet addressed the issue of software versioning. At some point or other, you will run into issues where only one particular version of some software will be suitable. Perhaps a key bugfix only happened in a certain version, or version X broke compatibility with a file format you use. In either of these example cases, it helps to be very specific about what software is loaded.
Let’s examine the output of module avail more
closely.
OUTPUT
------------------------------------------------------- /opt/cray/pe/lmod/modulefiles/mpi/crayclang/14.0/ofi/1.0/cray-mpich/8.0 --------------------------------------------------------
cray-hdf5-parallel/1.12.2.1 (D) cray-hdf5-parallel/1.12.2.7
---------------------------------------------------------------- /opt/cray/pe/lmod/modulefiles/compiler/crayclang/14.0 -----------------------------------------------------------------
cray-hdf5/1.12.2.1 (L,D) cray-hdf5/1.12.2.7
Where:
L: Module is loaded
D: Default Module
Note that we have two different versions of
cray-hdf5.
Using module swap
Load module cray-hdf5 as before. Note that if we do not
specifify a particular version, we load a default version. If we wish to
change versions, we can use
module swap <old-module> <new-module>. Try this
to obtain cray-hdf5/1.12.2.7. Check what has happened to
the location of the h5dump utility.
Using Software Modules in Scripts
Create a job that is able to run h5dump --version.
Remember, submitting a job is just like logging in to a new remote
system. What modules would you expect to be there?
- HPC systems use modules to help deal with software incompatibilities, versioning and dependencies
- We can see what modules we currently have loaded with
module list - We can see what modules are available with
module avail - We can load a module with
module load softwareName. - We can unload a module with
module unload softwareName. - We can swap modules for different versions with
module swap old-softwareName new-softwareName.