2_intro to linux

7/31/2019 2_Intro to Linux

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UNIX OS implemented by Ken Thompson andDennis Ritchie in 1969 and first released in

1970.

UNIX is one of the most popular operating

systems worldwide because of its largesupport base and distribution.

It was originally developed as a multitasking

system for minicomputers and mainframes.

Most versions of UNIX for personal computersare quite expensive and cumbersome.

Ken Thompson& Dennis RitchiCreator of Unix


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In 1983, Richard Stallman started the GNU project

with the goal of creating a free UNIX-like operating

system.

In October 1985 he founded the Free Software

Foundation (FSF).

As part of this work, he wrote the GNU General

Public License (GPL).

By the early 1990s there was almost enough

available software to create a full operating system.

However, the GNU kernel, called Hurd, failed to

attract enough attention from developers leaving

GNU incomplete.

Richard Stallman

Founder of FSF


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MINIX, a Unix-like system was released byAndrew S. Tanenbaum in 1987 intended to teach

his students the inner workings of a real

operating system.

While source code for the system was available,modification and redistribution were restricted.

MINIX's 16-bit design was not well adapted to

the 32-bit features of the increasingly cheap and

popular Intel 386 architecture for personalcomputers.

Andrew S. TanenbaumUS-born Dutch professor


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The History of Linux began in 1991 with thecommencement of a personal project by a Finnish

student, Linus Torvalds, to create a new operating

system kernel.

Lack of a widely adopted, free kernel provided theimpetus for Torvalds's starting his project.

Torvalds announced in 1996 that there would be a

mascot for Linux, a penguin. This was due the fact

when they were about to select the mascot,

Torvalds was bitten by a littlepenguin on a visit to

the National Zoo & Aquarium, Canberra, Australia.

Linus Torvalds

Founder of Linux Kernel


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Linux is an operating system that is freely distributed under the terms ofthe GNU Public License.

It behaves like Unix, but does not come from the same source code

base. Linux is available in both source code and binary form.

Linux offers standard Unix features, such as multiuser support,

multitasking, networking and many more.

The complete Linux operating system consists of the Linux core, or

kernel, combined with the utilities and applications required for a fully

functional operating system.


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Linux Architecture

Linux consists oflayers of software that are required to provide the nice

graphical user interface to interact with. The main components of a

standard Linux distribution are:

The Linux kernel

Runs all the time.

Manage what programs are allowed to run and how they are run.

Users never interact with the kernel directly.

The CLI (command line interpreter) or Shell

Provides a means for communicating and controlling the machine.

The command shell running on top of the kernel provides the

minimum working system that users can interact with.

Often when Linux is used as a server, the Shell will suffice, and the

higher layers of the system need not be loaded.


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The X Window System The software that provides the basic graphical interface capabilities.

Often referred to as X11.

The Window Manager Makes the windows look and behave the way we see them.

Manage the buttons frames and basic window behaviors.

The Desktop Provides a rich user experience on top of the facilities provided by

the window manager.

Two main Desktop options available KDE and Gnome.

Linux Architecture


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Linux Architecture


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The Linux kernel can be further divided into three gross levels:

System Call Interface

Resides at the top of the kernel.

Implements the basic functions such as read and write.

Kernel Code The architecture-independent kernel code.

Common to all of the processor architectures supported by Linux.

Architecture-dependent Code

Forms a BSP (Board Support Package).

This code serves as the processor and platform-specific code for the

given architecture.

Linux Architecture


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Linux Architecture


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Why such layers and how it differs from Windows?

Each of these layers of software communicate with each other in well

defined standard ways.

So as long as the software used in each of the layers sticks to the rules,

different programs can be used in any layer.

This is one of the key strengths of Linux; through careful choice of

software in each layer, its possible to create a Linux system that will runon a pocket sized mobile phones.

Windows has a kernel which is similar in function to the Linux kernel,

but the layers above that are not so well defined.

You can't choose a different window manager that better suits yourpurposes.

You can't even write an improvement you need, since its all proprietary

there's no way to know how all the programs inside Windows talk to

each other.


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Another noticeable differences between Linux and Windows is the

directory structure.

Linux File Structure

/

/bin /sbin /etc /proc /var/dev

/tmp /usr /home /lib /opt/boot

/media /srv/mnt


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/ Root

Every single file and directory starts from the root directory.

Only root user has write privilege under this directory.

Please note that /root is root users home directory, which is not

same as /.

/bin User Binaries

Contains binary executables.

Common linux commands that need to be used in single-user

modes are located under this directory.

Commands used by all the users of the system are located here.

For example: ps, ls, ping, grep, cp.


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/sbin System Binaries

Just like /bin, /sbin also contains binary executables.

But, the linux commands located under this directory are used

typically by system aministrator, for system maintenance purpose.

For example: iptables, reboot, fdisk, ifconfig, swapon.

/etc Configuration Files

Contains configuration files required by all programs.

This also contains startup and shutdown shell scripts used to

start/stop individual programs.

For example: /etc/resolv.conf, /etc/logrotate.conf


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/dev Device Files

Contains device files.

These include terminal devices, usb, or any device attached to the

system.

For example: /dev/tty1, /dev/usbmon0

/proc Process Information

Contains information about running system processes.

For example: /proc/{pid} directory contains information about the

process with that particular pid.

This is a virtual filesystem with text information about system

resources. For example: /proc/uptime


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/var Variable Files

Content of the files that are expected to grow can be found under

this directory.

This includes system log files (/var/log); packages and database

files (/var/lib); emails (/var/mail); print queues (/var/spool); lock

files (/var/lock); temp files needed across reboots (/var/tmp), etc.

/tmp Temporary Files

Directory that contains temporary files created by system andusers.

Files under this directory are deleted when system is rebooted.


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/usr User Programs

Contains binaries, libraries, documentation, and source-code for

second level programs.

/usr/bin contains binary files for user programs. If you cant find a

user binary under /bin, look under /usr/bin.

/usr/sbin contains binary files for system administrators. If you

cant find a system binary under /sbin, look under /usr/sbin.

/usr/lib contains libraries for /usr/bin and /usr/sbin

/usr/local contains users programs that you install from source. Forexample, when you install apache from source, it goes under

/usr/local/apache2


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/home Home Directories

Home directories for all users to store their personal files.

For example: /home/john, /home/rasel.

/boot

Boot Loader Files

Contains boot loader related files.

Kernel initrd, vmlinux, grub files are located under /boot.

For example: initrd.img-2.6.32-24-generic, vmlinuz-2.6.32-24-

generic.


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/lib System Libraries

Contains library files that supports the binaries located under /bin

and /sbin.

Library filenames are either ld* or lib*.so.*

For example: ld-2.11.1.so, libncurses.so.5.7.

/opt Optional add-on Applications

Contains add-on applications from individual vendors.

Add-on applications should be installed under either /opt/ or /opt/

sub-directory./mnt Mount Directory

Temporary mount directory where sysadmins can mount

filesystems.


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/media Removable Media Devices

Temporary mount directory for removable devices.

For examples, /media/cdrom for CD-ROM; /media/floppy for floppy

drives; /media/cdrecorder for CD writer.

/srv Service Data

srv stands for service.

Contains server specific services related data.

For example, /srv/cvs contains CVS related data.


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A complete multitasking, multiuser operating system. This means that

many users can log into and run programs on the same machine

simultaneously.

Developed with source code portability in mind, and its easy to find

commonly used features that are shared by more than one platform.

All of the source code including the kernel, device drivers, libraries, user

programs, and development tools, is freely distributable.

Supports various file systems for storing data, like the ext2, ext3, vfat,etc. file system, which was developed specifically for Linux.

Software Features


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A shell is a program which reads and executes commands from the user.

In addition, many shells provide features like job control, managing

several processes at once, input and output redirection, and a

command language for writing shell scripts. Many types of shells are

available for Linux like :

C SHell (csh).

Bourne SHell (sh).

GNU Bourne Again Shell (bash).

Korn Shell (ksh).

The standard compiler for Linux is GNU gcc, which is an advanced,

modern compiler that supports C++.

Software Features


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Provides a complete implementation of TCP/IP networking software.This includes:

Device drivers for many popular Ethernet cards.

SLIP (Serial Line Internet Protocol).

PPP (Point-to-Point Protocol).

PLIP (Parallel Line Internet Protocol).

NFS (Network File System).

The complete range of TCP/IP clients and services is also supported,

which includes FTP, telnet, NNTP, and SMTP.

Software Features


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The X Window System allows users to have multiple terminal windows

on the screen at once, each having a different login session.

The X Window System was originally developed at the Massachusetts

Institute of Technology and is freely distributable.

Linux includes web server software as well as web browsers. The most

common server is Apache. Thousands of Linux systems run Apache on

the Internet today, including the Linux Resources site,

www.linuxresources.com.

Several relational databases are available for Linux, including Postgres,

Ingres, MySQL, etc.

Software Features


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Linux is covered by the GNU General Public License, or GNUGPL.

Software covered by the GPL may be distributed and used free of

charge. Free, in this sense, refers to distribution, not cost.

Originally, Linus Torvalds released Linux under a license more restrictive

than the GPL, which allowed the software to be freely distributed andmodified, but without any profit making.

On the other hand, the GPL allows people to sell and profit from free

software, but does not allow them to restrict anothers right to

distribute the software in any way.

GPL-licensed software is also not shareware. Generally, shareware is

owned and copyrighted by an author who requires users to send in

money for its use.

Copyright Issues


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The Linux model of software development discards the entire concept of

organized development, source code control systems, structured bugreporting, and statistical quality control.

Linux is, and likely always will be, a hackers operating system.

The thrust behind Linux development is not to release perfect, bug-freecode: it is to develop a free UNIX implementation.

There is no single organization responsible for developing Linux. Anyone

with enough know-how has the opportunity to help develop and debug

the kernel, port new software, write documentation, and help new

users.

The system itself is designed using an open-ended, feature-minded

approach.

Philosophy of Linux


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Anyone who has a new feature or software application generally makes it

available in an alpha versionthat is, a test version, for those brave userswho want to hash out problems in the initial code.

Linux software is generally released as a distribution, a set of

prepackaged software which comprises an entire system.

many software distributions are available which include everything

necessary to install and run a complete system.

There is no single, standard distributionthere are many, and each has

its own advantages and disadvantages.

Philosophy of Linux


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Debian-based

Knoppix-based

Ubuntu-based

Official distributions

Contributed distributions

Third-party distributions Gentoo-based

Pacman-based

RPM-based

Fedora-based

Red Hat Enterprise Linux-based

Mandriva Linux-based

Slackware-based

Slax-based

Linux Distributions


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aLinux Alpine Linux ALT Linux Annvix

Arch Linux Ark Linux Asianux BLAG Linux and GNUBodhi Linux Caixa Mgica CentOS CRUX

Damn Small Linux Debian deepOfix Mail Server DeLi Linux

Devil-Linux dyne:bolic EasyPeasy Edubuntu

Elive EnGarde Secure Linux Fedora Finnix

Foresight Linux Freespire Frugalware GentoogNewSense gnuLinEx GoboLinux Gobuntu

Impi Linux Kanotix Knoppix KnoppMyth

Kubuntu Kurumin Linux Mint Lunar Linux

Mageia MintPPC Musix GNU/Linux Slax

NimbleX NUbuntu openSUSE Pardus

Parsix PCLinuxOS Platypux Puppy Linux

Sabayon Linux Scientific Linux sidux Slackware

Network Security

Toolkit

SliTaz GNU/Linux Source Mage

GNU/Linux

Symphony OS

Linux Distributions


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Red Hat (Enterprise) Linux is probably the largest commercial Linux

vendor. Focus on stability and long term support. Red Hat sponsors acommunity version (Fedora) which undergoes a more rapid development

cycle.

KNOPPIX The first Live CD version. The OS can be booted from, and run

completely off the CD. KNOPPIX is based on Debian Linux. Many vendors

now offer Live versions. No installation necessary.

Ubuntu based on Debian Linux. Ubuntu claims to be most popular

desktop version. Many applications and excellent updatemechanism

contribute to its success. Revenue is created by selling technical support.

Puppy This distribution is small enough to be loaded entirely in RAM.

This frees up the CD/DVD drive for other uses. Configuration can be saved

to a file between reboots.

Recovery Is Possible (RIP) good for data recovery of corrupted media or

backup. Tools such as ddrescue allows copying media sector by sector.

Can repair NTFS or FAT partitions.31

Linux Distributions


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Red Hat Enterprise Linux (RHEL) is a Linux-based operating system developed by Red

Hat and targeted toward the commercial market.

Red Hat Enterprise Linux is released in server versions for x86, x86-64, Itanium, PowerPC

and IBM System z, and desktop versions for x86 and x86-64.

Red Hat Enterprise Linux is often abbreviated to RHEL, although this is not an official

designation.

While Red Hat uses strict trademark rules to restrict free re-distribution of their officially

supported versions of Red Hat Enterprise Linux, Red Hat freely provides the source code

for the distribution's software, both for free software whose license requires such

publishing and open source software where this is not mandatory.

As a result, several distributors have created re-branded and/or community-supported

re-builds of Red Hat Enterprise Linux that can legally be made available, without official

support from Red Hat.

CentOS aims to provide 100% binary compatibility to Redhat Linux.

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