The OS of the Cloud
Linux is a family of open-source Unix-like operating systems based on the Linux kernel. If you are learning DevOps, Linux is non-negotiable.
Over 90% of cloud infrastructure, containers, and web servers run on Linux. It is lightweight, secure, highly customizable, and strictly permission-driven.
Open Source and the Kernel
Because it is open source, anyone can view, modify, and distribute the source code. The Linux Kernel manages the hardware resources, memory, and CPU processes. However, a kernel alone is not an operating system. It requires GNU utilities, package managers, and init systems to become a fully usable system.
In a modern DevOps environment, you will mostly deploy applications onto "headless" Linux servers, meaning they have no GUI (Graphical User Interface) and are entirely managed via the command line.