The EESSI software stack is available in Hábrók as a separate software stack and can be quickly initialized with:

module load EESSI/2023.06
or
module load EESSI/2025.06

EESSI has different releases, and each release comes with its own set of software. The Available Software page of the EESSI documentation has an overview of the different applications included in every EESSI release.

After this setup, the usual module commands will be aware of the EESSI stack, for example:

module avail OpenFOAM/12-foss-2023a
 
--------------------- /cvmfs/software.eessi.io/versions/2023.06/software/linux/x86_64/amd/zen3/modules/all --------------------- 
   OpenFOAM/12-foss-2023a (D)
 
  Where:
   D:  Default Module

The module above (OpenFOAM/12-foss-2023a) is not available in Hábrók's internal software stack but upon loading EESSI, it becomes available. To use it, we can load it with module load OpenFOAM/12-foss-2023a just like any other module.

Because the EESSI software stack is continually updated with new optimized software installations, there are good chances that your software of choice is already available there, even if it hasn't been locally installed in Hábrók yet.

Note that EESSI's software stack cannot be used simultaneously with Hábrók's locally installed software stack (that is, the one you can access directly upon login, without loading EESSI/2023.06). When you load EESSI, the Hábrók software stack will be automatically disabled. You can restore it by loading the Hábrók stack again, with module load 2023.01. This is to ensure that potentially incompatible software is not loaded at the same time.

Before compiling your own binaries with compilers from the EESSI stack, you would first need to decide which toolchain you want to use. A toolchain is EasyBuild terminology and basically consists of the compilers and important (mathematical and communication) libraries that many applications often need. The main toolchain in EESSI is the foss toolchain, but different versions of this toolchain are available (see https://www.eessi.io/docs/available_software/detail/foss/) and each version comes with its own versions of these compilers and libraries. Depending on other modules that you would want to use or specific requirement of your code, you may want to pick a specific toolchain version, but otherwise you could simply try the latest one.

Once you have determined which toolchain you want to use, load the corresponding buildenv module for this toolchain. This is a helper module that ensures that self-compiled binaries will be able to find all their dependencies at runtime. For instance, for foss/2025b you would load buildenv/default-foss-2025b. You can then compile your application. Compiling without this buildenv module would lead to runtime errors like:

error while loading shared libraries: libsomelibrary.so: cannot open shared object file: No such file or directory

You can also use the EESSI software stack locally on your laptop, desktop computer or lab workstation. The installation process is very simple, for more details see the relevant documentation page.

Additionally, EESSI is also deployed in the University's Linux Work Place, meaning the entire EESSI software stack is also available in this environment!