What is an Operating System? What is Unix/Linux ?




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Chapter1

What is an Operating System?
What is Unix/Linux ?
What is Red Hat Linux ?
Overview of Files and Disks
File Names, File Types. And Directories
Interfaces
Linux and Users

What is an Operating System?

An Operating System is the Software program that acts as a set of instructions between the hardware (disk, memory,…) and the software ( applications programs such as world processors or web browsers)







Read from disk/write to disk


Control Unit Arithmetic

(CU) Logic Unit

(ALU)

Operating System


Utilities and

Application

Programs





Central Processing Control

Unit (CPU)








Monitor


(Screen)

Keyboard


Program Memory Data Memory
Random Access Memory

RAM


GNU/Linux:

The Product of the Internet

- UNIX was developed in 1975 by AT&T


- University of California at Berkeley made major additions and changes – and

created BSD ( Berkely Software Distribution )


- 1991 Linus Torvalds (Finland ) released Linux version 0.01 ( Kernel )
- programmers throughout the world extended the system and created an AT&T

UNIX and BSD work-alike system.


- Source code was free ( developed by the Free Software Foundation (FSF) for the

GNU – Gnu’s not UNIX project)


- In 1983 – Richard Stallman – GNU project – created an OS ( kernel and system

programs) – and the concept of free use of the software ( the code is free )

- The present - GNU/Linux
- GNU/Linux can be obtained at no cost over the Internet or via mail

under the GPL (General Public License) – with the right to copy modify and

distribute the code along with the GPL agreement
- Today, A rich selection of applications is available of GNU/Linux – both free

and commercial


- Supports and amazing breadth of peripherals
- supports prebuilt binaries that are easy to install, Ex: Netscape
- Runs on Intel, Power Pc, Apple, Compaq … and provides emulators that can run

DOS, MS Windows, and MacIntosh programs




GNU/LINUX Operating System Characteristics

- Portable ( adaptable - can run on many different machines )


- Generic - Popular with Manufacturers – it is not a proprietary OS but

- can be extended and become proprietary – serves both needs

- takes advantage of available hardware power
- Standards - POSIX – Portable Operating System Interface - allows software developers to develop applications that run on all conforming versions of Unix, GNU/Linux and other operating systems.
- C Programming Language – More than 95% is written in C makes UNIX portable
- Multi-User – concurrent use by many individuals on a single computer or network
- Multi Tasking - concurrent execution of several processes
- Secure Hierarchical File system
- Filename Generation ( use patterns of special characters)
- Device-Independent input and Output (I/O redirection)
- Shell interface ( Command Interpreter and Programming Language)

and shell functions

- job control features
- Large Collection of Useful Utilities

- Interprocess communication

-system Administration

A layered View of the GNU/Linux Operating system




GNU Shell/Utilities Other Shell Utilities X window System


Linux Kernel

Hardware



Other features



Command Line interface has always dominated UNIX – today most systems use a

Graphical User Interface – GUI



The X Window System, also called (mistakenly) X Windows ( developed at MIT-1984) (originally without a particular OS in mind – later became a standard for UNIX )

Application Programs ( X Clients)

Desktop Environment (optional)

(most common: KDE ( Kommon Desktop Environment – default for Red Hat

and

GNOME (GNU Object Model Environment)
(Desktop Environments include a full set of GUI tools, file mangers, drawing programs, development toolkits,.. ….)


Window Manager (modifies look of windows, open window, close window,…)


KDE uses K Window Manager (kwm) and Qt toolkit for C++ programmers

GNOME desktop uses Sawfish Window Manager and the GTK+ toolkit

Others: fvwm, twm, Enlightenment, Window Maker…)






X Window System ( device independent –runs over network )


Video Adapter Card hardware


LINUX


GUI Application (Client)






Window

is the client

(xterm)

Workstation


Supports

X Windows

( Server )


Two layers run under X. The Desktop Manager and the Window Manager


The Desktop Manager ( Desktop Environment) allows you to work with icons… etc

The Window Manager ( which runs under the Desktop Manager) manages the windows and allows the user to open or close windows and customize the window environment

Therefore, the look of the windows can be different on different stations
- designed to run on workstations

- built with a network in mind

- user can communicate with a remote computer - run X-applications and output is

sent to the local display screen

- user can interact with the Computer through multiple windows on the screen

- X is an across-the-network protocol that allows a user to open a window on a

workstation that is remote from the CPU


Internetworking Utilities



Software Development Support
Text-based Editors
GUI Editors
Electronic Mail

What is Red Hat Linux?
Red Hat is one of the best maintained Linux distributions available
- Red Hat Linux Personal
- Red Hat Linux Professional
Both support GUI and command-line interface
GNOME and KDE are the two most popular GUIS for Red Hat
GNOME is the default

The GNU/Linux File System

The Hierarchical File System

(upside down tree structure ( set of connected files) – root is on top of tree with branches extending down.)
Purpose: to organize files so that you can easily find a particular one.
Each user starts with one directory inside the file structure
User can make as many subdirectories as he/she likes according to his/her needs
User typically organizes his/her files in a logical order based on departments, projects, …etc









Ordinary

File


Ordinary

File








Ordinary File



Ordinary File

Ordinary File

Directories and ordinary files


Key: Directories




Ordinary files



Ordinary Files ( or files ) are the ends of paths and cannot support other paths

Directory files, usually referred to a directories or folders – are points to other paths

( subdirectories closer to the root are called parents, if they are farther from root they are referred to as children.)


Filenames
The length of the file names varies according to the file system

Typically- maximum length is 255 characters long


To avoid confusion ( i.e. the interpretation by the shell of special characters) the user should use only the following characters:
Note: LINUX is case sensitive – upper and lower case characters are not the same
- Upper case letters (A-Z)
- Lower case letters (a-z)
- Numbers (0 – 9)
- Underscores ( _ )
- Period ( . )
- Comma ( , )
The root directory /
At the top of the hierarchy is the root directory.

The name of the root directory is / ( forward slash)

No other file can have that name

However, the forward slash is a special character that is used

to separate the path ( subdirectories ) to a file
A file or directory is identified uniquely to the Operating system by its path and the file or directory name.

There are three major types of computer files:
- user data files
- program ( executable ) files
- system files
files that begin with a . ( period) are considered hidden files

Interfaces


Linux provides 2 major interfaces GUI and Command Line Interface


When the user uses the Command Line Interface, commands are entered at the keyboard and interpreted by the Shell utility program. i.e. the user interfaces with the shell
When the user use the GUI interface the shell is by-passed
X-Window system is independent of the desk top interface – it is responsible to pen a window, draw points, and display graphics on the screen.

The X- Server provides the fundamental services that create and mange the graphical interface


It response to key strokes and requests by the clients ( Window Manager and applications such as Word processors, spreadsheets …)
The Window Manager X- client is responsible how that window is displayed on the screen, the placement, the border, the decorations … It allows for the manipulation of the window. Red Hat uses window manger called Sawfish.
The Desk top Environment is another component of the GUI

The Desktop Environments include a full set of GUI tools, file mangers, menus, icons (that allow users to communicate with the file manager ( Nautalis), use drag and drop, ..), drawing programs, development toolkits, editors, calculator .. ….)

GNOME is the default des top manager – it can be used with any window manager


Users can customize the desktop using the GNOME control center
Linux and Users
There are two types of users:

- super user or root user and


- ordinary user

The root ( or super or privileged ) user has unrestricted access to the system – he/she controls the system.


The ordinary user’s access is restricted and he/she has fewer privileges
Both, root user and ordinary users need a login and password
The super users login is always root He should be the only one to know his password.
Ordinary users have a login assigned by the system administrator adding the accounts for the user. They have a default password initially assigned by the system administrator.


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