Linux Introduction

Instructor: Mridula SharmaHOL407

Course Evaluations

Assignments ◦3 assignments - 30%

Midterm 30%◦Mid term – 17th October 2014

Final Exam 40%

Overview

What is Unix/Linux?History of LinuxFeatures Supported Under LinuxThe future of Linux

Before Linux

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

Apple MAC was better, but expensiveUNIX 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

GNU project

◦ Established in 1984 by Richard Stallman, who believes that software should be free from restrictions against copying or modification in order to make better and efficient computer programs

GNU is a recursive acronym for “GNU's Not Unix”

Aim at developing a complete Unix-like operating system which is free for copying and modification

Companies make their money by maintaining and distributing the software, e.g. optimally packaging the software with different tools (Redhat, Slackware, Mandrake, SuSE, etc)

Stallman built the first free GNU C Compiler in 1991. But still, an OS was yet to be developed

Beginning of Linux

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

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

◦ In Sept 1991, Linus Torvalds, a second year student of Computer Science at the University of Helsinki, developed the preliminary kernel of Linux, known as Linux version 0.0.1

Message from Professor Andrew Tanenbaum" I still maintain the point that designing a monolithic kernel in 1991 is a fundamental error.  Be thankful you are not my student.  You would not get a high grade for such a design :-)“

(Andrew Tanenbaum to Linus Torvalds)

◦Soon more than a hundred people joined the Linux camp. Then thousands. Then hundreds of thousands◦It was licensed under GNU General Public License, thus ensuring that the source codes will be free for all to copy, study and to change.

Linux Today

◦ Linux has been used for many computing platforms– PC, PDA, Supercomputer,…

◦ Not only character user interface but graphical user interface is available

◦ Commercial vendors moved in Linux itself to provide freely distributed code. They make their money by compiling up various software and gathering them in a distributable format

– Red Hat, Slackware, etc

In order to encourage wide dissemination of his OS, Linus made the source code open to public. At the end of 1992 there were about a hundred Linux developers. Next year there were 1000. And the numbers multiplied every year.

Recent estimates say about 29 million people use Linux worldwide. The effects of the dot-com bust, IT slowdown and global economic recession can be clearly seen.

Source: The Linux Counter

Linux: No of Users

Growing and growing…

138712users registered 155679machines registered

Linux - free software

Free software, as defined by the FSF (Free Software Foundation), is a "matter of liberty, not price." To qualify as free software by FSF standards, you must be able to:

◦Run the program for any purpose you want to, rather than be restricted in what you can use it for.

◦View the program's source code. ◦Study the program's source code and modify it if you need to. ◦Share the program with others. ◦ Improve the program and release those improvements so that

others can use them.

Red Hat Linux : One of the original Linux distribution.The commercial, nonfree version is Red Hat Enterprise Linux, which is aimed at big companies using Linux servers and desktops in a big way. (NJIT)Free version: Fedora Project.

Debian GNU/Linux : A free software distribution. Popular for use on servers. However, Debian is not what many would consider a distribution for beginners, as it's not designed with ease of use in mind.

SuSE Linux : SuSE was recently purchased by Novell. This distribution is primarily available for pay because it contains many commercial programs, although there's a stripped-down free version that you can download.

Mandrake Linux : Mandrake is perhaps strongest on the desktop. Originally based off of Red Hat Linux.

Gentoo Linux : Gentoo is a specialty distribution meant for programmers.

Linux groups

http://www.linux.org/groups/

Linux Distributions

http://www.linux.org/dist/list.htmlhttp://fedora.redhat.com/

Advantages

Linux is a complete operating system:◦stable - the crash of an application is much less

likely to bring down the OS under Linux.◦Reliable - Linux servers are often up for

hundreds of days compared with the regular reboots required with a Windows system.

◦extremely powerfulLinux provides a complete development

environment.

Why Linux?

Excellent networking facilities Ideal environment to run servers such as a web

server, or an ftp server.A wide variety of commercial software is available

if not satisfied by the free softwareEasily upgradeable.Supports multiple processors.True multi-tasking, multi-user OS.An excellent window system called X, the

equivalent of Windows but much more flexible.Full source code is provided and free.

Linux

The Linux system excel in many area, ranging from end user concerns such as stability, speed, ease of use, to serious concerns such as development and networking.◦Linux kernel◦Linux networking ◦Linux file system

Linux Kernel

The kernel is the central nervous system of Linux, include OS code which runs the whole computer. It provides resources to all other programs that you run under Linux, and manages all other programs as they run.◦The kernel includes the code that performs certain

specialized tasks, including TCP/IP networking.◦The kernel design is modular, so that the actual OS

code is very small to be able to load when it needs, and then free the memory afterwards, thus the kernel remains small and fast and highly extensible.

Linux File System

Linux has an hierarchical, unified file system

Supports 256-character filenames.All command line entries are case

sensitive.Use the slash(/) rather than the

backslash(\) you have been using in DOS.

Types of Files

Ordinary files◦ text files◦data files◦command text files◦executable files

directorieslinks

◦ rather than having multiple copies of a file, Linux uses linking to one file to save disk space.

special device files

Linux vs Unix

Linux is free, but Unix is not.Unix is compatible with Linux at the

system call level, meaning most programs written for either Unix or Linux can be recompiled to run on the other system with a minimum of work. But Linux will run faster than Unix on the same hardware.

Linux vs. Microsoft Windows

Both offer some of the graphics capabilities and include some networking capabilities. But Linux networking is excellent.

Linux is multi-user, multi-tasking, but Microsoft Windows doesn’t support it.

Security

Encryption Secure shell(ssh)Principles of security

EncryptionEncryption commonly used to secure

data. It is the ancient technique of hiding information in plain sight. Include:◦strong encryption - is stronger than the 40-

bit encryption maximum that can be exported from the United States under U.S. law.

◦Public-key Encryption - is a type of asymmetric encryption, which is a system that you encrypt your message with one key, and the recipient decrypts it with a mathematically related, but different key.

The Secure Shell(ssh)

The ssh and its tools use strong encryption to allow remotely located systems to exchange data securely.

By using strong encryption, ssh significantly enhances the security of both the authentication process and the session itself.

Principles of security

Two broad categories of attack exist:◦unauthorized access◦denial of service

Defense against the attacks:◦enforce the use of password◦use TCP wrappers to limit which resources are

made available to which categories of users.◦monitor internal users, protect your

organization against unauthorized or inappropriate use of the computer facilities to harass personnel.