It's worth pointing out that this is what most people think of as the traditional "Linux Operating System" but sans the Linux kernel.

Also, there are a few components on these supercomputers that you won't find on a typical workstation or cluster machine.

First, the kernel itself is frequently very small, lightweight, and much closer to what you would find on an embedded system than on a traditional desktop computer. That's because once the program on a supercomputer is loaded, the kernel's job has been mostly to get out of the way. This isn't to say that you don't find the Linux kernel on these supercomputers, it just isn't as common as you would think from reading this piece.

Fear not, many pieces of these operating systems are still open source. Here's IBM's fusedOS prototype:https://github.com/ibm-research/fusedos.

Second, many of these computers primarily only run code in C, C++, Fortran, and Python. These tend to be the only major languages in play on the HPC machines, with acceleration frameworks such as OpenMP, OpenCL, and CUDA playing major roles.

Finally, everything is glued together with MPI, a high-level (at least it was in the 90s) abstraction for scientific programming that maps down to very high-performance networks designed to help scientific codes "scale", that is, run effectively when millions of cores are simultaneously engaged.

These are beautiful machines producing important science, and the GNU/Linux operating system plays an incredibly important role in both their implementation and culture.