In Docker, we run processes in isolated environments, such as Rails applications or Node.js applications. Why, then, do Docker "image" files start with lines like FROM ubuntu? Are containers running full Ubuntu operating systems? If not, why do we specify an entire operating system? For that matter, what does it even mean to "run an operating system? These instructions are tailed for MacOS users, but work for Linux users as well. Just replace Homebrew with your package manager. Let's install…