How Linux System Works

Introduction to Linux and Its Core Purpose

Linux is an open-source operating system kernel first developed by Linus Torvalds in 1991. Over the decades, it has become the backbone of web servers, supercomputers, embedded systems, mobile devices, and even desktop environments.

At its core, Linux is just a kernel - the part of the operating system that interfaces directly with the hardware. The complete systems you interact with, such as Ubuntu, Fedora, or Arch Linux, are combinations of this kernel with userland tools, libraries, and desktop environments. These bundled systems are referred to as Linux distributions.

How the Linux Boot System Works

What really happens behind the scenes when you press that power button to boot up Linux? Let's break it down.

First, a small program called the BIOS or UEFI kicks in. These are bits of software stored in your motherboard's firmware, and their job is to get your hardware ready. Things like the CPU, memory, screen, keyboard, and hard drives. UEFI is the newer and more advanced version, offering faster boot times and extra security features like Secure Boot. One key difference is that BIOS uses MBR (Master Boot Record), which limits disks to 2TB. UEFI uses GPT (GUID Partition Table), which removes these limits and allows for bigger, more flexible storage setups.

After that, your system performs a quick diagnostic called POST (Power-On Self-Test) to check if everything's working. You might see a beep or error message if something fails here. If everything checks out, BIOS or UEFI looks for a bootloader.

In BIOS systems, this boot loader lives in the first tiny section of the hard drive. With UEFI, there's a separate partition just for booting, and you'll find files like grubx64.efi there.

GRUB and the Kernel

The boot loader's job is simple but critical:

• Locate the operating system's kernel

• Load the kernel into memory

• Start running the kernel

In most Linux systems, this boot loader is GRUB2. It's powerful, lets you choose between multiple OSes, and can be text-based or graphical. Once GRUB finds your Linux kernel, usually named something like /boot/vmlinuz-linux, it loads it and gives control to the kernel.

Now the Linux kernel takes over. It decompresses itself, checks your hardware, loads up device drivers (called kernel modules), and mounts your file systems. This sets up the system's environment.

From Init to Systemd

Once the kernel finishes its part, it launches the first user-space process: Init. These days, most distros use Systemd instead of older systems like SysVinit or Upstart.

Systemd is like the parent of all processes. It mounts the rest of your file systems, loads needed services like networking and sound, starts background daemons, and even handles user logins. It figures out whether you should see a terminal interface or a full desktop, based on configuration targets.

Systemd makes sure all the stuff you don't think about, like network interfaces or power management, is ready when you log in.

That's the behind-the-scenes journey from pressing the power button to using your Linux machine.

Linux Filesystem Hierarchy

At the heart of every Linux system is its filesystem. Everything is treated as a file: hardware devices, directories, and even running processes. Let's explore the most critical directories:

• /bin – Essential command binaries needed during boot and repair.

• /boot – Contains the Linux kernel and GRUB configuration.

• /boot/vmlinuz – The actual Linux kernel binary.

• /dev – Represents devices as files (e.g., /dev/sda1).

• /etc – System configuration files.

• /etc/crontab – Cron job scheduling file.

• /etc/fstab – File system mount configuration.

• /etc/passwd – User account info.

• /home – Home directories for users.

• /lib – Shared libraries essential for binaries in /bin and /sbin.

• /lost+found – Recovered files after disk corruption.

• /media – Mount point for removable media.

• /mnt – Temporary mount points.

• /opt – Optional third-party software.

• /proc – Virtual filesystem for system and process information.

• /root – Home directory of the root user.

• /sbin – System binaries.

• /tmp – Temporary files.

• /usr – User applications and utilities.

• /usr/bin – Most standard user commands.

• /usr/lib – Libraries for /usr/bin.

• /usr/local – Locally compiled software.

• /usr/sbin – System binaries for administrators.

BIOS vs UEFI – What’s the Real Difference?

So when you turn your PC on, the first thing that kicks in isn't Linux—it’s something called BIOS or UEFI. These are both types of firmware, but they work pretty differently behind the scenes.

BIOS – The Old School One

BIOS (Basic Input/Output System) is the old-school way computers start up. It’s been around since the 80s. BIOS runs a little checkup on your system called POST (Power-On Self Test)—checking your memory, CPU, drives, etc.—before passing control over to your operating system.

But here’s the catch:

• It only works with MBR partitioning, so disks can’t be bigger than 2TB.

• You’re stuck with just four partitions max unless you do tricks with extended ones.

• The interface is text-based—no mouse, no pretty menus.

• And it’s kinda slow to boot compared to newer tech.

UEFI – The Modern Way

UEFI (Unified Extensible Firmware Interface) is what most new machines use now. It’s like BIOS 2.0—faster, more secure, and can handle way bigger drives using GPT (GUID Partition Table).

• UEFI can boot from disks over 2TB (no sweat).

• You can have a bunch more partitions—no weird hacks needed.

• It often comes with a GUI interface, sometimes even mouse support.

• Secure Boot helps block malware during startup.

• It stores boot files like grubx64.efi in a separate EFI System Partition (ESP).

In simple terms: BIOS is like a flip phone. UEFI is your modern smartphone, it just does more and does it better.

Linux Kernel vs Linux OS – Not the Same Thing!

People throw around the term “Linux” a lot, but many don’t realize there’s a difference between the Linux kernel and a Linux operating system.

Linux Kernel – The Brains of It All

The kernel is the brain of the Linux system. It's the thing that talks to your hardware—CPU, memory, disk drives—and keeps everything running smoothly. Without the kernel, the rest of the OS wouldn’t know what to do.

It handles:

• Your device drivers (network card, GPU, etc.)

• Managing RAM and CPU tasks

• File systems and permission stuff

• Multitasking and scheduling all your programs

It loads up early in the boot process, usually from a file like /boot/vmlinuz.

Linux OS – What You Actually Use

A Linux operating system or distro (short for distribution) is what you actually interact with. It’s built on top of the kernel and includes all the stuff you see and use:

• Terminal and shell (like Bash)

• Desktop environments (GNOME, KDE, etc.)

• Package managers (APT, Pacman, etc.)

• System tools (systemd, logs, user login)

• Apps, networking, and so on

Some popular Linux OS examples are Ubuntu, Debian, Arch, and Fedora, they all use the same Linux kernel (more or less), but each one has its own look, feel, and set of tools.

In simple terms: the Linux kernel is the engine. The Linux OS is the whole car with the dashboard, wheels, seats, and controls.

Summary

By understanding the Linux boot process and filesystem, you gain deeper insight into the inner workings of a powerful and flexible operating system. Each layer plays a critical role in turning hardware into a usable system, from BIOS/UEFI initialization, through GRUB and the Linux kernel, to Systemd managing services. This deep visibility and modular design make Linux transparent and a favorite among developers, sysadmins, and power users alike.

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