What is Linux ?

Linux is a free, open-source operating system (OS) based on Unix. It acts as the interface between computer hardware and the user, managing processes, memory, files, and devices.

Looking Into The Linux Kernel.

The core of the Linux system is the kernel. The kernel controls all of the hardware and software on the computer system, allocating hardware when necessary, and executing software when required.

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The kernel is primarily responsible for four main functions:

■ System memory management

■ Software program management

■ Hardware management

■ Filesystem management

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■ System memory management :

Operating system primary function is to manage memory which is done using space on the hard disk, called the swap space. The kernel swaps the contents of virtual memory locations back and forth from the swap space to the actual physical memory. This allows the system to think there is more memory available than what physically exists. The process of swapping out memory pages for running applications continues for as long as the Linux system is running.

Below is the diagram of Linux system memory map.

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■ Software program management :

The kernel controls how the Linux system manages all the processes running on the system. The kernel creates the first process, called the init process, The Linux operating system uses an init system that utilizes run levels. A run level can be used to direct the init process to run only certain types of processes, as defined in the /etc/inittabs file. -There are five init run levels in the Linux operating system. At run level 1, only the basic system processes are started, along with one console terminal process. This is called single user mode. The standard init run level is 3 . At this run level most application software such as network support software is started. At run level 5, the system starts the graphical X Window Software and allows you to login using a graphical desktop window .

for example ,

The first column in the output shows the process ID (or PID) of the process.The third column shows the current status of the process (S for sleeping, SW for sleeping and waiting, and R for running).The process name is shown in the last column.. Processes that are in brackets are processes that have been swapped out of memory to the disk swap space due to inactivity.

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■ Hardware management :

Another responsibility for kernel is hardware managemnet . Devices that Linux must communicate with must have driver code inserted inside kernel code . two methods used for inserting device driver code in the Linux kernel ,they are:

1. Drivers compiles in the kernel .

2. Driver modules added to the kernel .

Programmers developed the concept of kernel modules to allow you to insert driver code into a running kernel without having to recompile the kernel.

The Linux system identifies hardware devices as special files, called device files. There are three different classifications of device files:

A) Character

Character device files are for devices that can only handle data one character at a time.

B) Block

Block files are for devices that can handle data in large blocks at a time, such as disk drives

C) Network

The network file types are used for devices that use packets to send and receive data. This includes network cards and a special loopback device that allows the Linux system to communi cate with itself using common network programming protocols.

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■ Filesystem management

The Linux kernel interfaces with each file system using the Virtual File System (VFS). This provides a standard interface for the kernel to communicate with any type of file system . VFS caches information in memory as each file system is mounted and used.

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The GNU Utilities :

The GNU project was mainly designed for Unix system administrators to have a Unix-like environment available. The core bundle of utilities supplied for Linux systems is called the coreutils package. The GNU coreutils package consists of three parts: ■ Utilities for handling files . ■ Utilities for manipulating text . ■ Utilities for managing processes . Further, A complete Linux system package is called a distribution. And there are lot of Linux distributions available to meet the required computing needs . The Linux distributions are often divided into three categories. a) Full core Linux distributions. A core Linux distribution contains a kernel, one or more graphical desktop environments, and just about every Linux application that is available, precompiled for the kernel. It provides one-stop shopping for a complete Linux installation. Examples are : Slackware, Red Hat, Fedora, Gentoo etc.

b) Specialized distributions . A Linux distribution which provides specialized software like only ofiice products for business users and customized Linux distributions and also help beginning Linux users by autodetecting and autoconfiguring hardware devices . Examples are: Linspire, Xandros, Ubuntu etc.

c) LiveCD test distributions. Also called as bootable Linux CD distribution.Most modern PCs can boot from a CD instead of the standard hard drive. To take advantage of this, some Linux distributions create a bootable CD that contains a sample Linux system (called a Linux LiveCD). Advances are being made in Linux LiveCD world to solve some of the problems like ,applications running slowly as you access everything from the CD especially when older computers and CD drives are in use . The advances include the ability to : ■ Copy Linux system files from the CD to memory . ■ Copy system files to a file on the hard drive . ■ Store system settings on a USB memory stick . ■ Store user settings on a USB memory stick.

This section explained the origins and structure of the Linux system, highlighting the kernel, GNU utilities, and shell. It covered the evolution of Linux distributions, including full-featured, specialized, and LiveCD versions, which allow users to try Linux without installation.

Here are official links to download and install popular Linux distributions:

🔹 Ubuntu (Beginner-friendly)

https://ubuntu.com/download

🔹 Fedora (Cutting-edge features)

https://getfedora.org/

🔹 Linux Mint (Windows-like experience)

https://linuxmint.com/download.php

🔹 Debian (Stable and widely used)

https://www.debian.org/distrib/