What Is Linux?

Why Linux matters to an administrator

Linux runs most of the servers on the internet, almost all public cloud workloads, containers, supercomputers and a huge number of embedded devices. As a RHEL administrator you will mostly work on servers without a graphical desktop, through a text shell, often remotely over SSH. That is exactly the environment of the RHCSA exam.

Open source in practice

Open source software gives you the source code together with a licence that grants four freedoms: use the program for any purpose, study how it works, change it, and share copies, modified or not. "Free" here means freedom, not price: Red Hat sells subscriptions (support, updates, certifications), not the code itself.

Licences fall into two families:

The Linux kernel itself is GPLv2.

Kernel versus distribution

Strictly speaking, Linux is only the kernel: the program that manages memory, processes, devices and file systems. A distribution packages the kernel together with everything you need to actually use it: the shell and core utilities, libraries, an installer, a package manager, configuration defaults, documentation and security updates. RHEL, Fedora, Debian and Ubuntu are all distributions built on the same kernel family.

How code flows in the Red Hat ecosystem

Red Hat develops upstream first: changes go into the community projects, and products are built from them.

1. Fedora — community distribution, new releases about every six months; new technology appears here first.
2. CentOS Stream — continuously delivered, it shows what the next minor release of RHEL will contain.
3. RHEL — the stabilised, certified, supported product, with a long life cycle (about ten years per major version) and minor releases roughly every six months (9.0, 9.1…).

Rebuilds such as Rocky Linux and AlmaLinux are binary-compatible with RHEL 9 and free, which makes them perfect for your practice VM. Commands, file locations and behaviour match what you will meet in the exam.

Getting RHEL for study

A no-cost Red Hat Developer Subscription for Individuals gives access to real RHEL for up to 16 systems, plus documentation and downloads. The Red Hat Customer Portal hosts the official product documentation, which is excellent background reading for each exam objective.

Try it on the practice VM

cat /etc/redhat-release      # which release is installed
cat /etc/os-release          # more detail, used by scripts
uname -r                     # running kernel version
hostnamectl                  # OS, kernel, architecture, virtualisation