Unix Introduction

Day 1.
Unix Introduction.
Name of
Ananthi Murugesan
presentation
• Company name

Road Map

Unix Biography

Unix System Organization

Evolution of Unix

Kernel/Shell

What is Unix?
Why do I need to know Unix?

File Management

Login in Unix

Architecture of Unix

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Author :- Ananthi Murugesan

Unix Biography

 1964 joint project between AT&T Bell Labs, GE, and MIT to
develop a new OS
 Goal : develop an OS that could provide computational
power, data storage and the ability to share data among
multiple users
 Result: Multiplexed Information & Computer Service MULTICS.

Unix Biography

 1969 Bell Labs withdraws from group, Two Bell Lab
scientists, Ken Thompson and Dennis Ritchie, continue
research.
 At the same time Ken Thompson wrote a game “space
travel” in Fortran to run on GECOS OS
 Thompson ported the game to a little used PDP-7 computer


Unix Biography-PDP-7

 In 1969, Ken Thompson wrote the first UNIX system in
assembly language on a PDP-7, then named Unics as a pun
on Multics

 It’s as the operating system for Space Travel, a game
which required graphics to depict the motion of the
planets


Unix History
Here’s Unix history
1969

1976

1978

1991

Creation by Ken
Thompson and
Denis Ritchie from
Bell Labs

Creation of
Apple


Creation of Linux
by Linus Torvalds
Split between
BSD and type V
Unix


What is Unix
The low-level software which handles the interface to system
hardware (input/output devices, memory, file system, etc),
schedules tasks, and provides common core services such as a
basic user interface.
It’s portable, multi-tasking and multi-user operating system
Portable: runs on many different hardware architectures
(Intel x86, Motorola 680x0etc.).
Pre-emptive multi-tasking: several programs can run at the
same time (time slices, interrupts, and task switching.
Multi-user: many users can share the computer system at
the same time


What is Unix – Other Features

Uses a simple, uniform file model which includes devices
and access to other services in a flexible, hierarchical file
system.
 Written in a high-level language (“C”) making it easy to
read, understand, change and port.
The command prompt is a simple user process, the Unix
shell, which is also a convenient job programming language.
Includes support for regular expressions which are
convenient for complex searching.



What is Unix –Philosophy
Philosophy of Unix system

• Everything is a file
– Hard Drive, CDROM drive, CPU …
• Task segmentation
• A program must be portable
• Write code quickly and to share with the
community
• Correct bugs quickly


Unix Features

Multi- user

Hierarchical file system
Multi tasking
Threads
Virtual memory
Built –in networking

Extensive set of utilities


Unix Merits /Demerits

True multi-tasking

Not that User friendly

Flexible/Portable

Sleep learning curve

“Nice”
Programming Events

Not 100% compatible
with the Microsoft world.


Top ten points
why I need to use
Unix ??



#1 – Flexibility
Unix is more flexible and can be
installed on many different types
of machines, including mainframe
computers, supercomputers and
micro-computers.



#2 – Scalability
• Unix is more stable and
does not go down as often as
Windows does, therefore requires
less administration and
maintenance.



#3 – Security

• Unix has greater built-in security
and permissions features than
Windows.



#4 – Compatibility
Web sites designed and
programmed
to be served under a UNIX-based

web server can easily be hosted on
a Windows server,
whereas the reverse is not always
true.
This makes programming for
UNIX the better choice


#5 – Stability

Servers running on UNIX enjoy
extremely high up-time and high
availability/reliability



#6 – Performance

UNIX servers under high load
(which is what is important)
are superior to Windows



#7 – Command line

• The command line will always
be an invaluable tool for
administration purposes.
Nothing will ever replace
favorite text-based editor



#8 – Software Updates

• Software upgrades from Microsoft
often require the user to purchase
new or more hardware or
prerequisite software.
That is not the case with Unix.



#9 – Price
• The mostly free or inexpensive
open-source operating systems,
such as Linux and BSD.



#10 – Data security
• Users are required to log in
before they can do anything.
Logging in restricts unauthorised
use, allows all files created by a
user to be identified as
belonging to them and, if
necessary, only visible to that
user



Unix - Quiz

The BSD system is a different Unix system
MacOSX is not based on the Unix system
UNIX system is a multi-task system
UNIX system is a multi-user system



Unix system Organization
Kernel
Hardware

Hardware

Shell

Tools and
Application

Unix
Unix System follows a layered Approach
It has four layers
The innermost layer is the hardware layer
In the second layer, the kernel is placed.
The utilities and the other application programs
form the third layer
Fourth layer is the one with which the user
actually interacts.


Unix – Kernel

Kernel is that part of the OS which directly makes
interface with the hardware system.
Factions:
Provides mechanism for creating and deleting
processes
Provides processor scheduling, memory and IO
management

Does interprocess communication.



Unix – Shell
Shell
Whenever you login to a Unix system you are placed in
a shell program.
The shell's prompt is usually visible at the cursor's
position on your screen. To get your work done, you
enter commands at this prompt.
The shell is a command interpreter;.
It takes each command and passes it to the operating
system kernel to be acted upon.



Types of Shell
Bourne shell (sh)

Shell

C shell (csh)
Korn shell (ksh)

Kron Shell
Bournce Shell
C shell



Unix - Shell
A Utility program that comes with the unix system.
Features of Shell are:

Interactive Processing
Background Processing
I/O Redirection
Pipes
Shell Scripts

Shell Variables
Programming Constructs


Unix
Bourne Shell(sh) – This is the original shell of UNIX which
comes with every UNIX sytem and may be that is the
reason that it is so popular.It was written by Stephen
Bourne at Bell Labs in 1974
• C shell(csh) – It has a syntax that resembles that of the
highly popular C programming language (also developed at
Bell Labs), and thus it is sometimes preferred by
programmers.
Korn shell(ksh) – It is a superset of sh developed by David
Korn at Bell Labs in 1983. It contains many features of the
C shell as well, including a command historys


MS Windows Vs UNIX
C:

/

N:
sue
ollie

cdrom

floppy

users

local

dan

ollie

sue

dan
mail
exec
A:
D:
N:danexec

mail

exec

/users/dan/exec

Unix

[1] Absolute location:
/users/dan/mail/my.doc

[2] Relative to the directory
“sue”
../dan/mail/my.doc

/

cdrom

floppy

users

local

dan

ollie

sue

[3] For Dan, relative to his
homespace:
~/mail/my.doc

[4] For everyone else, relative
to Dan’s homespace:

mail

exec

my.doc


Unix - File Management

Unix uses a hierarchical file system with “/” as its root.
Every non-leaf node of the tree is called as a directory
file.

Every leaf node can either be a file or an empty directory



Unix – CPU Scheduling

Unix uses “Round-Robin” scheduling to support its multiuser and time-sharing feature.
Round-Robin fashion of scheduling is considered to be
oldest,simplest and widely used algorithm.
Here, every process is given a time slice(10-100 millisec.)



What can UNIX do for you ?
Departmental E-mail
 World Wide Web
 Scientific Programming
1.FORTRAN
2.C/C++
3.Matlab
4.Maple
Text Processing

Plotting packages
1.Gnuplot
2.tecplot


Unix
Super User

Group 2

Group 1

Owner

Group
member

Group
member


others

others

others


Unix -Log in

 You will need to have a valid username and a password
 Type your username at the login prompt
UNIX is case sensitive
When the password prompt appears, type in your
password.
Your password is never displayed on the screen as
a security measure



Unix - Login screen



Unix - How to change the passwords

passwd command
Old password: - enter your current password
New password: - enter your new password
Retype new password: - re-enter your new password



Unix -Logging Off The System

– To logout enter the command logout or exit.
– If this does not work, press Ctrl-d.
– If you have a .logout file in your home directory, the system
will execute any commands contained there.



Unix - Stop and Think

Do you have any questions ?

Catch me @ www.ananthim.wordpress.com

Unix Introduction

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