The EESSI client container

Last updated on 2026-10-28 | Edit this page

Estimated time: 30 minutes

Overview

Questions

  • How do you get the EESSI 2025.06 stack when you have no cluster login?
  • What do $EESSI_VERSION and $EESSI_CVMFS_REPO print, and what does the CPU line mean?
  • Which commands are missing inside the client?

Objectives

  • Start the EESSI client with Apptainer and source the 2025.06 init script.
  • Read 2025.06 from $EESSI_VERSION and /cvmfs/software.eessi.io from $EESSI_CVMFS_REPO.
  • Treat x86_64/intel/sapphirerapids as one example CPU line, not as your required path.
  • Show that sbatch is absent and that python3 --version still prints Python 3.13.5.

The same tree, no queue

The cluster episodes use a module command the site provides. When you have no login, the EESSI client container mounts the same CVMFS repository and gives you the same init script.

The client is an Apptainer container. Apptainer 1.0 or newer is required, with --fusemount support. The mount makes /cvmfs/software.eessi.io exist inside the container. That is why the init script path works. The image is docker://ghcr.io/eessi/client:rocky8.

There is no Slurm inside the container. sbatch and squeue are not installed. hostname prints the container’s own name, not a cluster node. Use the container for module and python3. Use Snellius or the course cluster when the work must go through a queue.

The first launch downloads the image and can take a few minutes. Later launches are shorter.

If everyone is already on a cluster, do not spend the time downloading the image. The stack is already mounted. Read the two variable names, show one CPU line, and return to the modules.

Start the client

The directories under $HOME/eessi-work hold the CVMFS state and the home directory you see inside the container. The bind mounts give the container somewhere to write that state. You create them once.

Callout

Type along

Run the tab on a machine where Apptainer works. If you are already on Snellius or the course cluster, read the tab and do not start a second copy of the stack in this shell.

You do not need the client container when you are on the course cluster. module load 2025 loads EESSI 2025.06.

The Snellius and course-cluster tabs say you do not need the container there. The remaining tab is the launch. Inside the container, the next command is the init script:

BASH 

source /cvmfs/software.eessi.io/versions/2025.06/init/lmod/bash

The script loads EESSI/2025.06. It prints that the module loaded, which CPU it selected, and whether it saw a GPU. One host printed:

Module for EESSI/2025.06 loaded successfully
EESSI has selected x86_64/intel/sapphirerapids as the compatible CPU target for EESSI/2025.06
EESSI did not identify an accelerator on the system

x86_64/intel/sapphirerapids is an example. A laptop, a different server, or another container host can print a different CPU. Read your line. Do not paste this example into PATH.

Two variables that stay put

The CPU directory can change. Two variables do not:

BASH 

printf '%s\n' "$EESSI_VERSION"
printf '%s\n' "$EESSI_CVMFS_REPO"

$EESSI_VERSION prints 2025.06. $EESSI_CVMFS_REPO prints /cvmfs/software.eessi.io.

If either line is empty, the init script did not run in this shell. Source it again. Do not also module load 2025 here. The container has no module by that name, and stacking a second init on top of the first is the same mistake as loading two stacks.

Then load the default Python from the previous episode:

BASH 

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

python3 --version prints Python 3.13.5. which python3 starts with /cvmfs/software.eessi.io/versions/2025.06/.

Caution

Login node

This container is not a login node, and it is not a place to avoid the queue by running a long job. python3 --version is the check. A long script waits until you have sbatch on a cluster.

Challenge

Predict the two variables

Source the 2025.06 init script in the client. Before you print them, write down $EESSI_VERSION and $EESSI_CVMFS_REPO. Then run:

BASH 

printf '%s\n' "$EESSI_VERSION"
printf '%s\n' "$EESSI_CVMFS_REPO"
2025.06
/cvmfs/software.eessi.io

The first line is the stack the init script loaded. The second is the CVMFS repository, not a directory under your home. An empty line means the init script has not been sourced in this shell.

Challenge

Your CPU line, not the example

Copy the CPU line the init script printed into your notes. Does it have to be x86_64/intel/sapphirerapids? What would go wrong if a job script hardcoded that directory?

It does not have to be x86_64/intel/sapphirerapids. That string is one host’s example. Your line should contain a CPU target under x86_64/ (or another architecture the script supports) and the words that name the compatible CPU.

A hardcoded sapphirerapids path fails on a machine whose init script selected a different CPU. The builds in that directory match the CPU that was detected, not the CPU written in someone else’s notes. Let the init script select the directory.

Challenge

No batch command, same Python

In the same container shell, after the init script:

BASH 

command -v sbatch || printf 'no-sbatch\n'
module load Python/3.13.5-GCCcore-14.3.0
python3 --version

What do the two output lines mean?

no-sbatch
Python 3.13.5

command -v sbatch prints nothing and returns a failure status, so the shell prints no-sbatch. The client has no Slurm. squeue is missing for the same reason.

Python 3.13.5 is the EESSI 2025.06 default module, the same string as on a cluster that has Python/3.13.5-GCCcore-14.3.0. The stack matches. The queue does not. Submit jobs on Snellius or the course cluster, not in this shell.

Key Points
  • The EESSI client is an Apptainer container that mounts /cvmfs/software.eessi.io.
  • The init script is source /cvmfs/software.eessi.io/versions/2025.06/init/lmod/bash.
  • $EESSI_VERSION prints 2025.06. $EESSI_CVMFS_REPO prints /cvmfs/software.eessi.io.
  • The CPU line x86_64/intel/sapphirerapids is an example and may differ.
  • The container has no sbatch. python3 --version still prints Python 3.13.5.