Using EESSI#

The European Environment for Scientific Software Installations (EESSI, pronounced as “easy”) provides an additional stack of scientific software, next to installations which are provided locally and located in the /apps/${VSC_INSTITUTE} directory. Compared to the local installations, the advantages of EESSI for VSC users are:

  • Since EESSI is a collaboration between many partners of the HPC community, a wide range of scientific software is readily available and can be streamed on-demand. This means users no longer need to wait for a support team to do the local installation, provided the required modules are available in EESSI.

  • EESSI distributes software using CernVM-FS, which provides good performance when accessing software.

  • Because EESSI works on a large range of systems, including laptops, HPC clusters and cloud infrastructure, workflows making use of EESSI software are portable.

If you want to know more details, you can have a look at the introductory EESSI documentation. The remainder of this section will focus on the practical aspects of using EESSI on the VSC clusters.

Note

You can check if EESSI is supported by executing ls /cvmfs/software.eessi.io and verify it prints some files and directories. If on the other hand the command results in ls: cannot access '/cvmfs/software.eessi.io': No such file or directory, this means EESSI is not supported.

EESSI is currently not (yet) available on the UAntwerpen clusters.

Althought EESSI is typically installed on all nodes of participating VSC clusters, the modules for the software provided by EESSI are not available by default, and some commands need to be run to set up EESSI in your session. Also note that modules from EESSI are not compatible with locally installed modules, so the recommended commands to set up EESSI first make the locally installed modules unavailable:

# Force unload any cluster module
module --force purge
# Make EESSI available as a module
unset MODULEPATH
module use /cvmfs/software.eessi.io/init/modules/
# Load an EESSI module
module load EESSI/2025.06

These setup commands need to be executed in each session where you want to use EESSI. Note that you can search for other EESSI versions by running module avail EESSI. After loading the EESSI module, you can use the module commands as described in the section on module system basics, but now those commands will interact with the EESSI software stack instead of locally installed modules. For example:

$ module av GROMACS
-- /cvmfs/software.eessi.io/versions/2025.06/software/linux/x86_64/intel/skylake_avx512/modules/all --
   GROMACS/2025.2-foss-2025a

As you can see, the path above the listed module indicates this module indeed comes from EESSI. Also note how EESSI automatically figured out the most appropriate module based on the architecture of the node where these commands are executed.

If for any reason you want to switch back to locally installed modules, you can execute the following commands:

# Unload EESSI
module purge
# Restore your original modulepath
unset MODULEPATH
module use /apps/leuven/etc/modules:/apps/leuven/common/modules/all:/usr/share/lmod/lmod/modulefiles/Core
# Restore the cluster module, the version depends on the node you are working on
module load cluster/wice/batch

or simply start a new session on the cluster.

If for any reason you want to switch back to locally installed modules, you can execute the following commands:

# Unload EESSI
module purge
# Restore your original modulepath
unset MODULEPATH
module use /etc/modulefiles/vsc
# Restore the cluster module, the version depends on the node you are working on
module load cluster/doduo

or simply start a new session on the cluster.

If for any reason you want to switch back to locally installed modules, simply start a new session on the cluster.

Additional links: