Books
Learn the basics of Linux through official Red Hat Developer E-books.
Red Hat Universal Base Images (UBI) Book

As a developer, you need a source of container base images that have many of the qualities of Red Hat Enterprise Linux, but that can be consumed by your users/customers without acquiring a Red Hat subscription. Red Hat provides this with Universal Base Images (UBI), a subset of Red Hat Enterprise Linux for building applications in containers - what’s different is they have their own unique EULA which means they are freely redistributable. Access the book here.
SELinux Coloring Book

Learn the basics of SELinux, including type enforcement, Multi-Category Security (MCS) Enforcement, and Multi-Level Security (MLS) Enforcement, with the help of some friendly cats and dogs! Access the book here.