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Fundamentals of Linux

LEU-118

Student Guide

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Linux Computing Environment 1

Objectives

Upon completion of this module, you should be able to:

• List the four main components of a computer

• Describe the three main components of the Linux operating system

• Identify the three most common shells in the Linux system

• Distinguish between the multitasking, multiuser, and distributed

processing capabilities of the Linux system

Discussion – Several different components work together to make up a computer system

and a networked environment. What are some of these components?

Introduction to Linux

The UNIX operating system was originally developed at AT&T Bell Labs in

1969. It was created as a tool set by programmers for programmers. The early

source code was made available to universities all over the country. Programmers

at the University of California at Berkeley made significant modifications to the

original source code and called it BSD (Berkeley Software Distribution) UNIX.

They sent this new version of the UNIX environment to other programmers

around the country, who then added tools and code as they saw fit. Possibly the

most important advance made to the software by the programmers at Berkeley

was the addition of networking software which allowed the operating system to

function in a local area network (LAN).

Linux is a UNIX-like operting system, developed by Linus Torvalds, a student at

Helsinki University in Finland, in 1991. It is a modern, flexible, mature and free

operating system. Although it started life on the Intel platform, it has since been

ported to many other platforms such as Amiga, DEC Alpha, Apple Power PC,

Sun workstations, and others. Linux boasts many other features:

• Multitasking. Linux is a true preemptive multitasking operating system. All

processes run independently of each other and leave processor management to

the kernel.

• Symmetrical multiprocessing. Linux currently scales up to 16 processors.

• Networking. Linux supports a multitude of networking protocols.

• Multiuser. Linux handles multiple users at one time logged on to a machine.

• Advanced memory management. Traditional UNIX systems use swapping

to manage memory, where the entire memory structure of a program is written

to disk when the system is running low on memory. Linux uses paging, a

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method that intelligently allocates memory when system memory is running

low by prioritizing memory tasks.

• POSIX support. POSIX defines a minimum interface for UNIX-type

operating systems. Linux currently supports POSIX 1003.1. This ensures that

POSIX-compliant UNIX programs will port easily to Linux.

• Multiple file systems. Linux supports several different file system formats,

including DOS/Windows, OS/2, and Novell formats. This makes

interoperability a reality between operating systems.

Main Components of a Computer

The four main components of a computer are the random access memory (RAM),

the central processing unit (CPU), the input/output (I/O), and the hard disk or

other mass storage device.

Figure 1-1 Main Components of a Computer

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Random Access Memory (RAM)

Random access memory, located on the memory board, is the main

computer memory, often referred to as primary memory. Primary memory

is that part of memory where the activity of the running system takes

place. When you hear, “My system has 16 Mbytes of memory,” the

speaker is talking about primary memory or RAM.

A software program resides on the hard disk. When it is activated, an

image or copy of that program is loaded into RAM.

Images in RAM remain as long as they are needed. Once these images are

no longer required, they are overwritten by other images. If power is lost

or the system is rebooted, images in RAM disappear.

Central Processing Unit (CPU)

The central processing unit is the computer logic chip that executes

instructions (processes) received from the primary computer memory

(RAM). These instructions are stored in binary language.

Input/Output (I/O)

The input/output reads input from a device (such as your keyboard) into

memory, or it writes output from memory to a device. For example, the

keyboard and the mouse are the primary user input devices; the monitor,

printer, and tape drive are the primary output devices.

Hard Disk (or Other Forms of Mass Storage)

The hard disk is a magnetic storage device where information is stored.

All files, including applications (utilities), are stored on a hard disk.

The Linux Distributed Computing Solution

The Linux computing environment is based on the UNIX operating system.

Versions of the UNIX operating system run on many different computer systems

– microcomputers, personal computers (PCs), and mainframes.

The operating system is a set of programs that manages all computer operations. It

also provides a link between the user and system resources, converting requests

which come from the mouse and/or keyboard into computer operations.

There are three main parts of the operating system:

• Kernel

• Shell

• File system

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Kernel

The kernel is the core of the Linux computing environment. It performs the

following functions:

9 The kernel is an executable file that gets loaded into memory when your system

boots. It is called /kernel/genunix .

• Manages devices, memory, and processes

• Controls the functions (transmission of information) between the system

programs (utilities) and the system hardware

• Manages functions such as:

o Swap space – A reserved part of the disk for the kernel to use

during processing

o Daemons – Processes that perform particular system tasks and

monitor disks and execution

o File systems – A hierarchy of directories, subdirectories, and files

Shell

A shell is an interface between the user and the kernel. It acts as an interpreter or

translator. In other words, the shell accepts commands issued by you, interprets

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these commands, and executes the appropriate programs. Three shells are

available in the Linux environment:

• Bourne shell ($) – The default shell for the Linux computing environment.

The Bourne shell was developed for the AT&T System V.2 UNIX

environment. This shell does not have aliasing or history capabilities. It is

typically used by system administrators.

• Korn shell ($) – A superset of the Bourne shell. It has many of the Bourne

shell features plus added features such as aliasing and history. This is the

industry standard for normal system users.

• C shell (%) – A shell based on the C programming language. Like

the Korn shell, it has additional features such as aliasing and

history. C shell was developed by Sun’s Bill Joy for programmers,

but is used with increasing frequency by normal system users.

The File System

The Linux computing environment file structure is a hierarchy of directories,

subdirectories, and files that are grouped together for a specific purpose.

• Directory – A location for other files and directories. The Linux file

system, or directory structure, enables you to create files and directories

accessed through a hierarchy of directories.

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• Subdirectory – Any directory below another directory. For example, some

of the subdirectories under the root (/) directory are/usr, /etc, and

/kernel.

root ( / )

usr opt dev etc home var

bin sbin lib user1 user2 user3

Figure 1-4 Common Linux Subdirectories

The file system is integrated with the kernel to provide an organizational structure

to store your data.

The topmost directory is called the root directory. It is the starting point of the

file-system hierarchy. The root directory (/) is required for the operating

system to function and contains critical systems files (such as the kernel, called

/kernel/genunix).

The /usr directory contains executable commands, system administration

utilities, and library routines.

The /opt directory contains Linux’s unbundled software applications.

The /etc directory contains system administration files.

The /home directory contains the user’s home directory. Depending on how the

system has been set up by the administrator, the home directories may instead be

found in /export/home.

The /dev directory contains files which are pointers to device names.

The file system organizes data in a hierarchical structure of directories,

similar to the way a filing cabinet stores information.

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Directories are like file drawers. Subdirectories are similar to folders. Files are

like the individual pages of information contained in the folder.

The Linux operating system contains many different kinds of files:

• Directories

• Plain ASCII (American Standard Code for Information Interchange)

documents

• Applications (databases, word processing programs, and spreadsheets)

• Executable programs

Main Capabilities of the Operating System

The Linux computing environment was designed for:

• Multitasking – Enables the kernel to keep track of several processes

simultaneously, which allows more than one tool or application to be used

at a time

9 A user can run a program (like a spreadsheet) and edit a document using a word

processor at the same time.

• Multiuser capability – Enables more than one user to access the same

system resources

• Distributed processing – Enables the use of resources across the network

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Main Capabilities of the Common Desktop Environment

(CDE)

CDE is Motif-based and users of other UNIX and personal computer (PC)

desktops should be comfortable using CDE; many of the features are common to

other desktop environments.

The Common Desktop Environment (CDE)

• Is a graphical user interface (GUI) between the user and the operating

system

• Provides built-in menus for users to select and run utilities and programs

without using Linux environment commands

• Enables users to control multiple documents or applications on the screen

at the same time

• Controls activities in windows using both the mouse and the Keyboard

9 The icons pictured above represent some of the major programs and tools

available with CDE. CDE is discussed in greater detail in subsequent modules.

Exercise: Using the Linux Computing Environment

Exercise objective – This exercise helps you review the basics of the computing

environment.

Tasks

Answer the following questions:

1. Identify the four main components of a computer.

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

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2. Describe the three main functions of the kernel.

__________________________________________________

__________________________________________________

__________________________________________________

3. In the blank spaces, write one of these three terms: kernel, shell, or file system.

¾ The _________ represents the user interface, which translates requests into

actions.

¾ The _________ manages and allocates resources among users.

¾ The _________ provides command interpretation.

¾ The _________ organizes and stores data in a hierarchical structure.

¾ The _________ performs memory management.

¾ The _________ components are files and directories.

¾ The _________ controls disks, tapes, printers, terminals, communication lines,

and other devices.

4. In the blank spaces, write one of these three capabilities: multitasking, multiuser, or

distributed processing.

¾ The _________ capability enables users to share system resources.

¾ The _________ capability is the ability to perform several processes

simultaneously.

¾ The _________ capability is the ability to use resources across a network.

Workshop Labs

Use what you have learned so far in this course to work through the following:

1. A new UNIX environment user calls the system administrator with a problem.

Yesterday, the user was working on a project when there was a power outage. When the

system recovered, the work the user had done was no longer available. What happened?

2. A user is working at a Linux workstation that has no hard disk. What options might

this user have for saving work that is done during the day?

Exercise Summary

Discussion – Take a few minutes to discuss what experiences, issues, or discoveries you

had during the lab exercises.

9 Manage the discussion here based on the time allowed for this module, which was

given in the “About This Course” module. If you find you do not have time to

spend on discussion, then just highlight the key concepts students should have

learned from the lab exercise.

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• Experiences

9 Ask students what their overall experiences with this exercise have been. You

might want to go over any trouble spots or especially confusing areas at this time.

• Interpretations

9 Ask students to interpret what they observed during any aspects of this exercise.

• Conclusions

9 Have students articulate any conclusions they reached as a result of this exercise

experience.

• Applications

9 Explore with students how they might apply what they learned in this exercise to

situations at their workplace.

Exercise Solutions

1. Identify the four main components of a computer.

Memory, CPU, I/O, and hard disk

2. Describe the three main functions of the kernel.

It manages all computer operations, controls the hardware, and converts

requests coming from the mouse and keyboard into computer operations.

3. In the blank spaces, write one of these three terms: kernel, shell, or

file system.

¾ The shell represents the user interface, which translates requests into actions.

¾ The kernel manages and allocates resources among users.

¾ The shell provides command interpretation.

¾ The file system organizes and stores data in a hierarchical structure.

¾ The kernel performs memory management.

¾ The file system components are files and directories.

¾ The kernel controls disks, tapes, printers, terminals, communication lines, and

other devices.

4. In the blank spaces, write one of these three capabilities: multitasking, multiuser, or

distributed processing.

¾ The multiuser capability enables users to share system resources.

¾ The multitasking capability is the ability to perform several processes

simultaneously.

¾ The distributed processing capability is the ability to use resources across a

network.

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Check Your Progress

Before continuing on to the next module, check that you are able to accomplish or answer

the following:

™ List the four main components of a computer

™ Describe the three main components of the Linux operating system

™ Identify the three most common shells in the Linux system

™ Distinguish between the multitasking, multiuser, and distributed processing

capabilities of the Linux system

Think Beyond

What features of the Linux UNIX environment set it apart from a typical standalone PC

environment? What would some of the benefits of these features be to a company?

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Accessing Your System 2

Objectives

Upon completion of this module, you should be able to :

• List the characteristics of an effective password

• Change your password

• Describe the function of a mouse button

• Log in and log out of a system from the command line

• Log in and out of a CDE session

• Manipulate windows within the CDE

• Invoke and use menus and menu bars

Discussion – Passwords are a major key to a secure system. What characteristics would a

good password have?

User Accounts

You must have a user account on the system to log in. The user account is defined

in the /etc/passwd file and contains the elements which identify each unique

user to the system.

System administrators are responsible for creating and maintaining user accounts.

The Root Account

The root account is the system administration account and is set up by the

installation process. The root login account owns all system files and has access to

all files.

The /etc/passwd Entry

Each entry in the /etc/passwd file is made up of seven fields separated by a

colon.

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• Login ID – Is the identification required by the operating system for a successful

login. It is the user’s “public name.” Depending on the system administrator,

login IDs are usually some combination of a user’s first and last names. For

example, user Bob Wood’s login ID might be bobw, bwood, woodb, or bw2.

The login ID must:

¾ Be limited to 32 characters

¾ Do not accept special characters: !, @, #, $, %,^, &

¾ Be unique

• Placeholder – Maintains the field for the password, which is kept in the

/etc/shadow file. The /etc/shadow file contains encrypted passwords

and password aging information (for example, how long before a user must

change a password and how long a password must be in use before it can be

changed). This file can only be read by the system administrator.

• UID – Identifies the user to the operating system.

• GID – Identifies the primary group to which the user belongs.

• Comment – Is usually the full name of the user.

• Login directory – Is commonly referred to as the “home” directory, where users

store their files.

• Default shell – Defines which shell the user will have upon login.

Password Requirements

Your password protects your account from unauthorized access. In the Linux computing

environment, a password

• Should contain at least two alphabetic characters and one numeric or special

character

• Should differ from the login ID

• Should differ from the previous password by at least three characters

• May contain spaces

• These password requirements do not apply to the system administrator

(superuser).

The Mouse Buttons

The mouse settings can be modified to suit a user’s preferences. Once a setting has been

modified, that setting can be stored into a userspecific file. This means that any

personalized settings will be the default whenever a CDE session is initiated.

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The Left Mouse Button

Most actions use the left mouse button, alternatively known as button 1 or the

SELECT button. This button is used to make selections in any of the following

ways:

• Make a window active by clicking the left mouse button while the mouse

pointer is in that window area

• Invoke a window menu by clicking on the left mouse button while the

mouse pointer is on the window’s menu box area

• Select an option from the Front Panel

• Select a File or Folder icon while working with the File Manager

• Open an icon by double-clicking the left mouse button while the pointer is

over the icon

• Highlight text to be selected by dragging over the text area, while the left

mouse button is being pressed

The Middle Mouse Button

Button 2, also known as the ADJUST button, is used to paste selected text. The

text must have been selected using the left mouse button as described previously.

The Right Mouse Button

When the right mouse button, or MENU button, is clicked or held down, a menu

of choices will appear. The options available on the menu will be determined by

the position of the mouse pointer when button 3 was pressed.

Note – For the purposes of this course, you will be instructed to left or

right click to perform a specific action. This assumes the standard

right-hand configuration of the buttons. These notes will instruct you

when a double-click is required.

Logging In

Logging in identifies you to the system. You can log in using the login screen shown in

CDE (graphic mode) , or at the command line (text mode).

Logging in text mode

To log in at the command line, follow these steps:

1. Type your user name (login ID) at the prompt and press Return.

2. Type your password at the password prompt and press Return.

Note – Your password does not appear as you type it. By default, if you do not

have a password, you are automatically prompted for one during the initial login.

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