Linux Introduction

                   Linux Introduction

History of Unix:

           

History of Unix

Unix is also an OS.

    Unix is a Command line OS written in the C Programming language.

    Started in 1965 by AT & Bell labs.

    Created by Dennis Ritchie & Ken Thompson in 1969.

    Written in 100% C language and released in 1973.

    Support only CLI mode.

UNIX Flavors:

Before Linux

    In 80’s, Microsoft’s DOS was the dominated OS for PC

    Apple MAC was better, but expensive

    UNIX was much better, but much, much more expensive. Only for minicomputer for commercial applications.

    People was looking for a UNIX based system, which is cheaper and can run on PC.

    Both DOS, MAC and UNIX were proprietary, i.e., the source code of their kernel is protected

    No modification is possible without paying high license fees

   Beginning of Linux:

   A famous professor Andrew developed Minix, a simplified version of UNIX that runs on PC

   Minix is for class teaching only. No intention for commercial use.

  History of Linux

   Linux is an open source operating system.

   Linux kernel is developed by Linus Torvalds in 1991.

   Linux is an update version of Unix OS.

   Linus Torvalds creates open source, UNIX-like kernel, released under the GPL (General Public License). 

   At that time Linus Torvalds was a graduate student from Helsinki university.

   Written in C & C++ Languages.

   Support CLI & GUI modes.

   Linux version 0.0.1

Developer of Unix,Minix & Linux

Feature of Linux:

                                                                    Multi-user

Allow multiple users to login and use the resources at the same time.

Multi-processing

Allow to performs multiple process at the same time.

Multitasking

Capable of running multiple applications and process at the same time.

Portability

Can be installed on all hardware architecture.

Reliability

Large servers have been successfully being running without a single second of down time.

Security

Inbuilt firewall (iptables) and SELinux.

Open Source

Free Software along with the source code and documentation.

Linux Architecture:

KERNEL:

Kernel is a computer program that manages I/O (input/output) requests from software, and translates them into data processing instructions for the central processing unit and other electronic components of a computer. The kernel is a fundamental part of a modern computer's operating system.

Work of Kernel: -                                                                 

   Schedules programs

   Manages data/file access and storage

   Enforces security mechanisms

   Performs all hardware access

   Provides access to Shell

Kernel Diagram

  

 SHELL:

A shell is a program that provides the traditional, text-only user interface for Linux and other Unix-like operating systems.

Work of Shell: -

   Presents each user with a prompt

   Interprets commands types by a user

   Executes user commands

   Supports a custom environment for each user

Shell Diagram

APPLICATION & Utility: 

   Open Office: word processing, spreadsheets, drawing

   Adobe Acrobat Reader

   Mozilla: GNOME web Browser

   Kmail: The KDE Mail Application

   Evolution: An Email and Calendar Program

   X-CD-ROAST: CD/DVD Burning Application

   Sound Applications 

Type of Login User:

When a shell is used interactively, it displays a string when it is waiting for a command from the user. This is called the shell prompt. When a regular user starts a shell, the default prompt ends with a $ character.

The $ is replaced by a # if the shell is running as the super user, root.

Virtual Console:

Users access the bash shell through a terminal. A terminal provides a keyboard for user input and a display for output. On text-based installations, this can be the Linux machine's physical console, the hardware keyboard and display. Terminal access can also be configured through serial ports.

Another way to access a shell is from a virtual console. A Linux machine's physical console supports multiple virtual consoles which act like separate terminals. Each virtual console supports an independent login session.

If the graphical environment is available, it will run on the first virtual console in Linux 7. Five additional text login prompts are available on consoles two through six (or one through five if the graphical environment is turned off). With a graphical environment running, access a text login prompt on a virtual console by holding Ctrl +Alt and pressing a function key (F2 through F6). Press Ctrl+Alt+Fl to return to the first virtual console and the graphical desktop.