Phase 1 · Free

1.1 What an Operating System Is, and Why Linux

A computer out of the box is a pile of parts that cannot agree on anything. The processor can do math. The disk can hold data. The screen can light up pixels. Nothing decides who goes first.

20 minPhase 1: Get a Machine RunningFree

Phase 1: Get a Machine Running. Lesson 1 of 5. About 20 minutes.

Plain entry

A computer out of the box is a pile of parts that cannot agree on anything. The processor can do math. The disk can hold data. The screen can light up pixels. Nothing decides who goes first.

The operating systemThe core software that manages a computer's hardware and gives every other program a safe, shared way to use the CPU, memory, storage, and network. Read more → is the part that decides. It hands out memory, schedules which program runs next, talks to the disk and the network card, and keeps one program from trampling another. Every app you have ever used asked the operating system for permission before it did anything.

You are going to install one yourself. Not because installing is hard, but because once you have done it, the machine stops being a black box.

Terms

  • Operating system (OS): the software that manages hardware and runs every other program. Windows, macOS, and Linux are operating systems.
  • KernelThe core of an operating system that runs with full hardware control and decides how every program gets CPU time, memory, and device access. Read more →: the core of the OS. It runs with full control of the hardware and everything else asks it for resources.
  • Linux distributionA complete operating system built around the Linux kernel, bundled with tools, a package manager, an installer, and default settings. Read more → (distro): the Linux kernel bundled with tools, a desktop, and an installer. Ubuntu, Debian, and Fedora are distros.
  • LTSLong Term Support: a software release that receives security and bug-fix updates for an extended period, typically years, without major changes. Read more → (Long Term Support): a release that gets security updates for years. Ubuntu LTS releases get five years of standard support.
  • Virtual machineA software-based emulation of a complete computer that runs its own operating system and applications, isolated from the host hardware. Read more →: a whole computer simulated in software. See the BytesNation Dictionary: virtual machine.

Why Linux, and why Ubuntu

Most of the internet runs on Linux: web servers, cloud instances, routers, phones (Android), and nearly every supercomputer. If you work in IT, you will be handed a Linux box with no desktop and expected to fix it. Learning on Linux means learning on the thing you will actually use.

We use Ubuntu Desktop 26.04 LTS. It is free, widely documented, and the same family as Ubuntu Server, which you will use in the capstone. Ubuntu 24.04 LTS also works for every lesson here if that is what you have.

Depth: what actually happens when you press the power button

  1. FirmwareLow-level software stored on a chip inside a device that controls the hardware directly and runs before any operating system loads. Read more → on the motherboardThe main circuit board that connects every part of a computer, including the CPU, memory, storage, and expansion cards, and holds the system firmware. Read more → (UEFIUnified Extensible Firmware Interface: the modern firmware standard that tests the hardware at power on and starts the bootloader, replacing legacy BIOS. Read more → on anything built in the last decade) wakes up, tests the hardware, and looks for something bootable. Lesson 1.2 covers this.
  2. The firmware loads a bootloader. On Ubuntu that is GRUB.
  3. GRUB loads the Linux kernel and a small starter filesystem into memory.
  4. The kernel takes over the hardware and starts the first process, systemd (process ID 1). See systemd.
  5. systemd starts everything else: networking, logging, the login screen.

You can see the end of that chain on any running Linux machine:

ps -p 1 -o pid,comm

Expected output:

    PID COMMAND
      1 systemd

And the kernel version:

uname -r

Example output (environment-specific, your numbers will differ):

7.0.0-14-generic

That is the kernel the Ubuntu 26.04 desktop ISO ships. After updates, or on a server image, the last number is higher (a 26.04.1 cloud image showed 7.0.0-38-generic). Do not worry if you have no Linux machine yet. You will run both of these at the end of lesson 1.4.

Going further

The kernel runs in “kernel space” with full hardware access. Programs run in “user space” and must make system calls to ask the kernel for anything: open a file, send a packet, allocate memory. Run man 2 syscalls on your new install to see the full list. Phase 4 and the OS Fundamentals track go deep here.

Myth vs fact

Myth: “Linux can’t get malware.” Fact: Linux gets malware, and attackers target it because so many servers run it. Ubuntu publishes security notices every week for flaws it has patched, and MITRE ATT&CK keeps a whole matrix of attack techniques used against Linux. What Linux gives you is good tools to stay safe: a package manager that patches everything at once, accounts that do not run as admin by default, and logs you can read. Those only help if you use them, which is why this course has you update, use sudo sparingly, and read logs.

Self-check

  1. In one sentence, what does an operating system do?
  2. What is the difference between Linux and Ubuntu?
  3. Why does this course use an LTS release?
  4. What is the first process the Linux kernel starts?

Answers: (1) It manages the hardware and runs every other program. (2) Linux is the kernel; Ubuntu is a distribution built around it. (3) It gets security updates for years, so the lessons stay valid. (4) systemd, PID 1.

Sources