Finding and loading a module

Last updated on 2026-10-27 | Edit this page

Overview

Questions

  • Which command lists only the modules you can load right now, and which command searches the rest?
  • Which Python module is the EESSI 2025.06 default, and what does python3 --version print?
  • Where do you load QCG-PilotJob if module spider cannot find it in EESSI?

Objectives

  • Use module avail, module spider, module load, module list, module unload, and module purge.
  • Load Python/3.13.5-GCCcore-14.3.0 and read Python 3.13.5.
  • Switch to EESSI 2023.06 only after a purge, and read Python 3.11.5.
  • State that QCG-PilotJob is a site module and is not in the EESSI tree.

Two lists

module avail prints modules you can load in this shell, right now. EESSI is hierarchical. A Python build sits behind the stack module, and often behind a compiler module. Until those are loaded, module avail Python can be empty or short. That does not mean Python is missing.

module spider searches the whole tree. It finds names that module avail hides. module spider Python is the search you want when you know the program and not the compiler.

module help prints the command options. module whatis Python/3.13.5-GCCcore-14.3.0 prints the short description stored in that module file. module list prints what this shell has loaded. ml is the short form of module once the init script has run. ml Python is the same action as module load Python.

Command What it does
module avail Modules you can load right now
module spider Every matching module, including hidden ones
module load Puts a module in this shell
module unload Removes one module
module list Shows what is loaded
module purge Removes all modules
module whatis Prints the module’s short description

One Python from the 2025.06 stack

Load the stack the way your tab shows, then search.

In EESSI 2025.06 the Python modules include:

  • Python/3.12.3-GCCcore-13.3.0
  • Python/3.13.1-GCCcore-14.2.0
  • Python/3.13.5-GCCcore-14.3.0 (the default)

The name has the version and the GCCcore it was built with. Load the default:

BASH 

module load Python/3.13.5-GCCcore-14.3.0
python3 --version

python3 --version prints Python 3.13.5. which python3 prints a path under /cvmfs/software.eessi.io/versions/2025.06/. The CPU directory in the middle of that path is the one the init script chose. It is not /usr/bin/python3.

On Snellius, module load 2025 selects the site 2025 stack. If module spider Python does not list Python/3.13.5-GCCcore-14.3.0, load the newest 3.13 it does list and write that full name in your notes. Do not invent a version.

A faded load, for the stack this course uses:

BASH 

module load Python/________
python3 --version

The module is Python/3.13.5-GCCcore-14.3.0. The version line is Python 3.13.5.

Unload one, or clear the shell

module unload Python/3.13.5-GCCcore-14.3.0 removes that Python. The stack module can stay loaded. module list no longer includes the Python name.

module purge removes every module. module list then reports that no modules are loaded. Purge is the step between stacks.

EESSI 2023.06 has Python/3.11.5-GCCcore-13.2.0. After a purge:

BASH 

module load EESSI/2023.06
module load Python/3.11.5-GCCcore-13.2.0
python3 --version

python3 --version prints Python 3.11.5. Do not load EESSI/2025.06 and EESSI/2023.06 in one shell. Do not source the 2025.06 init script and then module load 2025 on top of it. Two stacks in one shell is how two Pythons end up on PATH.

Callout

Conda stays separate

A Conda environment and a loaded module often conflict. The site stack is the supported copy. Do not mix a Conda activate with these modules in the same shell.

QCG-PilotJob is not in EESSI

module spider QCG-PilotJob in an EESSI-only shell does not find it. The tool is not part of the 2025.06 release. Do not spend the episode walking the CVMFS tree looking for it.

On the clusters it is a site module. The load line is the tab, not a path you guess.

Course scripts name QCG-PilotJob/0.14.1-gfbf-2024a after the stack load. If spider prints that name, load it. If spider prints a different full name, load the name it prints. The container will still not have it. Later episodes that need the pilot use the cluster.

Caution

Login node

python3 --version and module list are fine on the login node. A long Python script is not. The login node is shared. Send the long run to the queue.

Challenge

Predict the version lines

Write down the two version lines before you run the block. Use a shell you are allowed to purge.

In the container, or on any machine where /cvmfs/software.eessi.io is mounted:

BASH 

module purge
source /cvmfs/software.eessi.io/versions/2025.06/init/lmod/bash
module load Python/3.13.5-GCCcore-14.3.0
python3 --version
module purge
module load EESSI/2023.06
module load Python/3.11.5-GCCcore-13.2.0
python3 --version

On a cluster, do not source the init script in a shell where you also ran module load 2025. Use the tab’s load command for the 2025 stack, check python3 --version, purge, and only then try EESSI/2023.06. If that module name does not exist on Snellius, stop. Do not load a second stack on top of the first.

In the EESSI client the two python3 --version lines are:

Python 3.13.5
Python 3.11.5

The first comes from Python/3.13.5-GCCcore-14.3.0 on EESSI 2025.06. The second comes from Python/3.11.5-GCCcore-13.2.0 on EESSI 2023.06. module purge between them is required. which python3 for the first load starts with /cvmfs/software.eessi.io/versions/2025.06/.

On Snellius, if the 3.13.5 module name is absent, the version line is the one for the module you actually loaded. Record that name. A missing EESSI/2023.06 is a stop, not a reason to skip the purge.

If the init script stops because a variable is unset, run set +u before source and set -u afterwards. The two version lines do not change.

Challenge

List, unload, purge

Load the 2025.06 default Python. Run module list. Unload that Python module and run module list again. Purge and run module list a third time. What happens to the Python name?

After the load, module list includes Python/3.13.5-GCCcore-14.3.0. Other modules may be there too, because loading Python also loads the libraries it needs. That is expected.

After module unload Python/3.13.5-GCCcore-14.3.0, that name is gone. The stack module can still be listed.

After module purge, module list reports that no modules are loaded. The next python3 is no longer the stack copy unless something else on PATH provides one.

Challenge

Search for a module that is not in the stack

Run module spider QCG-PilotJob in a shell that has only EESSI loaded. Then look at the tab above and say where the tool actually comes from.

Spider reports that it cannot find QCG-PilotJob in the EESSI tree. That result is correct. The tool is not in the 2025.06 release.

On a cluster, load it the way the tab shows: the stack name first (module load 2025 on Snellius, module load 2024 on the course cluster), then module load QCG-PilotJob. module list then includes QCG-PilotJob. The full name in the course scripts is QCG-PilotJob/0.14.1-gfbf-2024a when spider lists that name.

The container has no site module to add. A failed spider search there does not mean you should install a private copy during this lesson.

Key Points
  • module avail is the current level. module spider searches the rest.
  • module load selects. module unload removes one. module purge clears the shell.
  • EESSI 2025.06 default Python is Python/3.13.5-GCCcore-14.3.0, and python3 --version prints Python 3.13.5.
  • EESSI 2023.06 has Python/3.11.5-GCCcore-13.2.0. Purge before you load it.
  • QCG-PilotJob is a site module. Spider does not find it in EESSI.