17.02.2015 NDGLinuxEssentialsChapter1IntroductiontoLinux

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1.3.1 Role of the KernelThe kernel of the operating system is like an air traffic controller at an airport. The kerneldictates which program gets which pieces of memory, it starts and kills programs, and ithandles displaying text on a monitor. When an application needs to write to disk, it must askthe operating system to do it. If two applications ask for the same resource, the kernel decideswho gets it, and in some cases, kills off one of the applications in order to save the rest of thesystem.

The kernel also handles switching of applications. A computer will have a small number ofCPUs and a finite amount of memory. The kernel takes care of unloading one task and loadinga new task if there are more tasks than CPUs. When the current task has run a sufficientamount of time, the CPU pauses the task so that another may run. This is called pre-emptivemultitasking. Multitasking means that the computer is doing several tasks at once, and pre-emptive means that the kernel is deciding when to switch focus between tasks. With the tasksrapidly switching, it appears that the computer is doing many things at once.

Each application may think it has a large block of memory on the system, but it is the kernelthat maintains this illusion, remapping smaller blocks of memory, sharing blocks of memorywith other applications, or even swapping out blocks that havent been touched to disk.

When the computer starts up it loads a small piece of code called a boot loader. The bootloaders job is to load the kernel and get it started. If you are more familiar with operatingsystems such as Microsoft Windows or Apples OS X, you probably never see the boot loader,but in the UNIX world its usually visible so that you can tweak the way your computer boots.

The boot loader loads the Linux kernel, and then transfers control. Linux then continues withrunning the programs necessary to make the computer useful, such as connecting to thenetwork or starting a web server.

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*Startingdomainnameservice...bind9[OK]WelcometoUbuntu12.04.5LTS(GNU/Linux3.17.7+x86_64)*Documentation:https://help.ubuntu.com/

CHAPTER 1 - INTRODUCTION TO LINUX

Introduction (1.1)

Linux Essentials Exam Objectives (1.2)

Linux Evolution and Popular OperatingSystems (1.3)

Role of the Kernel (1.3.1)

Applications (1.3.2)

Role of Open Source (1.3.3)

Linux Distributions (1.3.4)

What is a Command? (1.3.4.4)

Hardware Platforms (1.3.5)

Choosing an Operating System (1.4)

Decision Points (1.4.1)

Microsoft Windows (1.4.2)

Apple OS X (1.4.3)

BSD (1.4.4)

Other Commercial UNIXes (1.4.5)

Linux (1.4.6)