FOSS toolchain

The foss toolchain consists entirely of free and open source software components. When building third-party software, or developing your own, load the module for the toolchain:

$ module load foss/<version>

where <version> should be replaced by the one to be used, e.g., 2014a. See the documentation on the software module system for more details.

Compilers: GNU

Three GCC compilers are available:

  • C: gcc
  • C++: g++
  • Fortran: gfortran

For example, to compile/link a Fortran program fluid.f90 to an executable fluid with architecture specific optimization for processors that support AVX2 instructions, use:

$ gfortran -O2  -march=haswell  -o fluid  fluid.f90

Documentation on GCC other compiler flags and options is available on the project’s website for the GCC documentation.


Do not forget to load the toolchain module first!

Optimizing for a CPU architecture

To optimize your application or library for specific CPU architectures, use the appropriate option listed in the table below.

CPU architecture compiler option
Ivy Bridge -march=ivybridge
Sandy Bridge -march=sandybridge
Haswell -march=haswell
Broadwell -march=broadwell
Skylake -march=skylake-avx512
Cascade Lake -march=cascadelake
Napels/Rome (AMD) -march=znver2
detect host CPU -march=native


GCC doesn’t support applications with multiple code paths, so you have to build multiple versions optimized for specific architectures. Dispatching can be done at runtime by checking the value of the $VSC_ARCH_LOCAL environment variable.


The compiler switch to use to compile/link OpenMP C/C++ or Fortran code is -fopenmp. For example, to compile/link a OpenMP C program scattter.c to an executable scatter, use:

$ gcc -fopenmp  -O2  -o scatter  scatter.c


The OpenMP runtime library used by GCC is of inferior quality when compared to Intel’s, so developers are strongly encouraged to use the Intel toolchain when developing/building OpenMP software.

Running an OpenMP job

When submitting a job, remember to specify as many processes per node as the number of threads the executable is supposed to run. This can be done using the ppn resource specification, e.g., -l nodes=1:ppn=10 for an executable that should be run with 10 OpenMP threads.


The number of threads should not exceed the number of cores on a compute node.

Communication library: Open MPI

For the foss toolchain, Open MPI is used as the communications library. To compile/link MPI programs, wrappers are supplied, so that the correct headers and libraries are used automatically. These wrappers are:

  • C: mpicc
  • C++: mpic++
  • Fortran: mpif77, mpif90

The compiler wrappers take the same options as the corresponding compilers.

Using the MPI compilers from Open MPI

For example, to compile/link a C program thermo.c to an executable thermodynamics:

$ mpicc -O2  -o thermodynamics  thermo.c

Extensive documentation is provided on the Open MPI documentation site.


Do not forget to load the toolchain module first.

Running an Open MPI program

Note that an MPI program must be run with the exact same version of the toolchain as it was originally build with. The listing below shows a PBS job script thermodynamics.pbs that runs the thermodynamics executable.

#!/bin/bash -l

module load foss/<version>
mpirun ./thermodynamics

The hosts and number of processes is retrieved from the queue system, that gets this information from the resource specification for that job.

FOSS mathematical libraries

The FOSS toolchain contains the basic HPC mathematical libraries, it offers:

Version numbers

  2021a 2020b 2020a 2019a 2018b 2018a 2017b 2017a 2016b 2016a
GCC 10.3.0 10.2.0 9.3.0 8.2.0 7.3.0 6.4.0 6.4.0 6.3 5.4 4.9.3
Open MPI 4.1.1 4.0.5 4.0.3 3.1.3 3.1.1 2.1.2 2.1.1 2.0.2 1.10.3 1.10.2
UCX 1.10.0 1.9.0                
OpenBLAS 0.3.15 0.3.12 0.3.9 0.3.5 0.3.1 0.2.20 0.2.20 0.2.19 0.2.18 0.2.15
ScaLAPACK 2.1.0 2.1.0 2.1.0 2.0.2 2.0.2 2.0.2 2.0.2 2.0.2 2.0.2 2.0.2
FFTW 3.3.9 3.3.8 3.3.8 3.3.8 3.3.8 3.3.7 3.3.6 3.3.6 3.3.4 3.3.4
binutils 2.36.1 2.35 2.34 2.32 2.30 2.28 2.28 2.27 2.26 2.25