Linux Overview

Md. Mahedi Hasan Technology Specialist (Innovation), BdREN, UGC

mahedi@bdren.net.bd

Index

Before Linux

Road to Linux

Linux arrived

Linux development method?

What is GNU?

Language of Linux

Unix and Linux

Unix System Architecture

Unix Philosophy

Linux File system Hierarchy

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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

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Road to Linux

Inspired by the UNIX OS, the Linux kernel was developed as a clone of UNIX

GNU was started in 1984 with a mission to develop a free UNIX-like OS

Linux was the best fit as the kernel for the GNU Project

Linux kernel was passed onto many interested developers throughout the Internet

Linux today is a result of efforts of Linus Torvalds and thousands of individuals, in 1991

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Linux arrived

Linux is basically a kernel, it was combined with the various software and compilers from GNU Project to form an OS, called GNU/Linux

Linux is a full-fledged OS available in the form of various Linux Distributions

RedHat, Fedora, SuSE, Ubuntu, Debian are examples of Linux distros

Linux is supported by big names as IBM, Google, Sun, Novell, Oracle, HP, Dell, and many more

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Linux development method

Linux development method

Person identifies need and begins writing program

Developer announces project on Internet

Others respond and work on different parts of project

Person leading project releases software

People download source code and try program; send back information about problems

Developers fix bugs

Forking

Creating new project based on existing source code

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What is GNU?

Stands for GNUs Not Unix. GNU General Public License. GNU - GPL – Copyleft

Free software, as defined by the FSF (Free Software Foundation), is a "matter of liberty, not price."

Terms for using Linux

You can modify / copy / redistribute the source code at no cost provided you do so under the GPL

If you get source under the GPL, any changes / improvements / spin offs you make to it are also under GPL

You must always distribute source code + GPL of programs that you develop with the help of GPL software online.

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Language of Linux

Linux was written completely in C and ASM.

UNIX (1969) was written in PDP-7 Assembly.

This version of UNIX was not portable to new hardware.

Thomson developed B as a machine independent language to make UNIX portable.

Dennis Ritchie rewrote UNIX in C, a language he developed from B and concepts from other languages.

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Unix System Architecture

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The shell and the window environment are programs

Programs‟ only access to hardware is via the kernel

Fig: Unix System Architecture

Unix and Linux

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Linux is based on Unix Unix philosophy

Unix commands

Unix standards and conventions

Unix Philosophy

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Multi-user

A user needs an account to use a computer

Each user must log in

Complete separation of different users‟ files and configuration

settings

Small components

Each component should perform a single task

Multiple components can be combined and chained together for

more complex tasks

An individual component can be substituted for another, without

affecting other components

What is Linux?

Linux kernel

Developed by Linus Torvalds

Strictly speaking, „Linux‟ is just the kernel

Associated utilities

Standard tools found on (nearly) all Linux systems

Many important parts come from the GNU project

Free Software Foundation‟s project to make a free Unix

Some claim the OS as a whole should be „GNU/Linux‟

Linux distributions

Kernel plus utilities plus other tools, packaged up for end users

Generally with installation program

Distributors include: Red Hat, Debian, SuSE, Ubuntu etc.

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Linux Kernel Diagram

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Hierarchical File System

Files are kept in directories

Directories can hold other directories.

FHS – File system Hierarchy Standard defines the rules for where certain files will always be kept.

The “root” of the Linux FS is always „/‟

Files & directories can be owned by users to enforce security privileges.

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Linux File System Hierarchy

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Fig: The Linux directory structure

Directories defined by the FHS

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Directory Description

/bin Contains binary commands that can be used by system administrators, users, and scripts; this directory shouldn’t contain subdirectories and can be accessed in single user mode

/boot Contains the Linux kernel and static files needed to boot the computer

/dev Contains device files, such as the CD/DVD-ROM drive

/etc Contains static configuration files, which are also unshareable files, meaning they’re local to the machine

/home An optional directory that might not be included in all Linux distributions; in openSUSE, it’s the user’s home directory

/lib Contains shared libraries that are loaded when a program starts

/media Contains the mount point for removable media

Directories defined by the FHS (Cont.)

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Directory Description

/mnt Empty by default, but administrators can use it to mount other resources, such as CD/DVD-ROM drives

/opt Contains static shareable add-on software packages

/root Contains the recommended home directory for the root user; not all Linux distributions use it, but it’s used in CentOS, RHEL, openSUSE,

/sbin Contains system binaries used by the system administrator

/srv Contains data files for services

/tmp Contains temporary files that system administrators should delete whenever the system is booted

/usr Contains shareable, read-only applications and files

/var Contains variable data files, such as log files

BASH – the Linux Shell system

Bourne Again Shell is s command processor

It acts as an interface between the user and the operating system

Commands / applications can be given to this interpreter which can then make the operating system do various tasks

Commands can be stored in shell scripts for ease of access

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Device independent I/O

All physical devices – monitor, mouse, keyboard

printer appear as files in the Linux file system that

are manipulated by the kernel.

This means that if a program is written to manipulate

this file, then the kernel will take it to mean an action

on the physical I/O device.

This allows for a standard API for I/O in all Linux

systems.

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Linux User Interface

Can be controlled through command Line

Interface(CLI) or Graphical User Interface (GUI)

GUI run through Desktop Environments (DE)

KDE, GNOME, Xfce, E17 are popular Desktop

Environments (DE)

The GUI interface is easy-to-use and much like that

of Windows and Mac OSX

The CLI is similar to that of UNIX/BSD

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Programming in Linux

Modern languages are cross-platform, like Python,

Ruby, Perl, Java

Most Linux distros support these languages and

have their runtimes pre-installed

GTK+ and Qt are widely used to design applications

for Linux

IDEs like NetBeans, Anjuta, KDevelop,

MonoDevelop, Eclipse are available for Linux too

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Linux on the Desktop

Linux is desktop computer ready

Large number of distros targeted at Desktop users

are available

Linux desktop distros come with many commonly

used pre-installed software's

The modern Linux interface is user-friendly and

makes the interaction with computer easy

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Linux on Servers and Supercomputers

Linux is the most used OS on servers

6 out of 10 reliable web hosting companies use Linux

Linux is the cornerstone of the LAMP server software

combination (Linux, Apache, MySQL, Perl, PHP,

Python) which has achieved popularity among

developers

Out of top 500 supercomputers, Linux is deployed

on 427 of them

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Why should you use Linux?

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Linux systems are extremely stable

Linux is Free

No/Very few threat of viruses

Linux comes with most of the required software pre-installed

Update all your software with minimum fuss

Linux never gets slow

Linux does not need defragmentation

Linux can even run on oldest hardware

Adding more software is a matter of a few clicks

Most Windows-only apps have their either their native version or alternatives for Linux

With Linux, you get the highest degree of possible customizability

Linux Desktop

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Linux Terminal

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Basic commands

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Basic Linux Commands

– File Handling

– Text Processing

– System Administration

– Managing Users and Groups

– Archival

– Network

– File Systems

– Advanced Commands

File Handling

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mkdir – make directories

Usage: mkdir [OPTION] DIRECTORY...

Example: mkdir mahedi

ls – list directory contents

Usage: ls [OPTION] [FILE]

Example: ls, ls -l, ls –l mahedi

cd – changes directories

Usage: cd [DIRECTORY PATH]

Example: cd mahedi

File Handling (cont.)

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pwd -print name of current working directory

Usage: pwd

vim – Vi Improved, a programmers text editor

Usage: vim [OPTION] [file]...

Example: vim file1.txt

cp – copy files and directories

Usage: cp [OPTION]... [SOURCE] [DEST]

Example: cp sample.txt sample_copy.txt

cp sample_copy.txt target_dir

File Handling (cont.)

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rm -remove files or directories

Usage: rm [OPTION]... FILE...

Example: rm file1.txt

rm –rf file1.txt

find – search for files in a directory hierarchy

Usage: find [OPTION] [path] [pattern]

Example: find / -name mahedi

history – prints recently used commands

Usage: history

Text Processing

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cat- concatenate files and print on the standard output

Usage: cat [OPTION] [FILE]...

Example: cat file1.txt file2.txt

cat -n file1.txt

echo – display a line of text Usage: echo [OPTION] [string] ...

Example: echo I love Debian

echo $

Text Processing (Cont.)

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grep- print lines matching a pattern

Usage: grep [OPTION] PATTERN [FILE]...

Example: grep mahedi file1.txt

wc – print the number of newlines, words, and bytes

in files Usage: wc [OPTION]... [FILE]...

Example: wc file1.txt

wc L file1.txt

Managing Users and Groups

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Account information is stored in: /etc/passwd and /etc/shadow

Accounts have the following attributes: username

UID

GID (default group)

Comment

home directory

shell

Managing Users and Groups (Cont.)

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Create accounts with useradd.

Delete accounts with userdel.

Modify accounts with usermod.

Managing Users and Groups (Cont.)

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Group information is stored in /etc/group.

Create groups with groupadd.

Delete groups with groupdel.

Modify groups with groupmod.

To view group memberships use groups. groups [ACCOUNT]

groups

groups mahedi

System Administration

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chmod - change file access permissions

Usage: chmod [OPTION] [MODE] [FILE]

Example: chmod 744 file1.txt

chown – change file owner and group

Usage: chown [OPTION]... OWNER:GROUP FILE

Example: chown mahedi file1.txt

ls -la

System Administration (Cont.)

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su - change user ID or become super user

Usage: su [OPTION] [LOGIN]

Example: su - mahedi

passwd – update a user’s authentication tokens(s) Usage: passwd [OPTION]

Example: passwd mahedi

who – show who is logged on

Usage: who [OPTION]

Example: who

Advanced Commands

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reboot - reboot the system

Usage: reboot [OPTION]]

Example: reboot

poweroff – power off the system Usage: poweroff [OPTION]

Example: poweroff

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Thank You

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