Linux becomes easier when you first understand the job of an operating system.

An operating system sits between applications/users and hardware. It manages CPU time, memory, devices, filesystems, networking, users, permissions, and processes so applications do not have to control hardware directly.

Unix, Linux, Windows, and macOS

The source material starts by comparing Unix, Linux, Windows, and macOS. For a DevOps engineer, the important relationship is:

• Unix established many of the multi-user, multitasking, permissions, process, and command-line ideas that shaped modern operating systems.
• Linux is a free and open-source Unix-like kernel used as the foundation of many distributions and is extremely common on servers and cloud infrastructure.
• macOS is Unix-based and shares many command-line concepts with Unix/Linux, although its userland and system management differ.
• Windows uses a different operating-system lineage, tooling model, and administration stack, although modern infrastructure teams often operate both Windows and Linux systems.

User space vs kernel space

Applications normally run in user space. When they need protected operations—opening a file, sending network traffic, allocating memory, creating a process—they request services from the kernel through system calls.

User / Automation
      ↓
Applications & CLI tools
      ↓
System calls
      ↓
Linux kernel
      ↓
CPU • Memory • Disk • Network • Devices

The Linux mindset

A useful operational mindset is:

1. Everything has state. Processes, services, sockets, mounts, users, and files all have inspectable state.
2. Most state is observable through files or commands. /proc, /sys, /etc, logs, and CLI tools expose what is happening.
3. Troubleshooting is narrowing a layer. Is the problem application, process, service, network, storage, permissions, or host resource pressure?