Unix - An Introduction

UNIX Operating System
An Introduction
http://www.deepanshugahlaut.com/blog/introduction-to-unix-operating-system/
By:
Deepanshu Gahlaut
Web and Social Media Enthusiastic
www.deepanshugahlaut.com

What is Operating System?
The Operating System is the System
S/W which acts as an interface
between user and computer’s H/W.
It acts as the brain of computer system
which controls all other component of
computer system.

Unix is a multiuser, multitasking OS from
AT & T that runs on a wide variety of
computer system from micro to super
computers. UNIX was developed in 1969
by Ken Thompson & Dennis Ritchie. Unix
was written in C language.
What is UNIX?

We use the term "Unix" in a collective
sense to refer to Unix, Unix-derived,
and Unix-like systems.

UNIX Categories
There are three kinds of Unix System -
Genetic UNIX
Trademark or Branded UNIX
Functional UNIX

Those systems with a historical connection
to the AT&T codebase. For example -
BSD systems.
#1. Genetic UNIX

Systems such as Linux or Minix that
behave similarly to a UNIX system but
have no genetic or trademark
connection to the AT&T code base.
#2. Functional UNIX

These systems—largely commercial in
nature—have been determined by the
Open Group and are allowed to carry
the UNIX name.
For ex- System V , Apple Mac OS X 10.5
#3. Trademark or Branded UNIX

There are more than fifty flavors of UNIX in use
today. Brands and versions of UNIX that are in
common use are:
AIX from IBM
Solaris from SUN Microsystems
HP-UX and Tru64 from Hewlett Packard
UnixWare from Caldera
Linux and FreeBSD, which are open source
UNIX Historical Implementation

UNIX Features
Portability
Multi-user Capability
Multitasking Capability
Security
Built-in Networking
Programming Facility
The UNIX Toolkit

The architecture of UNIX can be divided into three
levels of functionality-
The lowest level is the kernel is the core of OS &
communicates directly to H/w.
 The next level is the shell, which acts as the interface
b/w user & kernel.
Kernel is represented by file /stand/unix or /unix
The highest level is utilities, or application programs
which provides utility functions.
The shell is represented by sh(Bourne Shell), csh(C shell),
ksh(Korn Shell), bash(Bash shell).
To know running shell use echo $shell

UNIX has a large family of powerful commands.
Some major commands are:
date, mkdir, cd, pwd, rmdir, ls, cp, mv, rm, cat, cal, who,
tput clear, man, passwd, path, ps, chmod, chown, more
etc.
UNIX Commands

date: displays the date and time.
ex: $ date [enter]
wed march 31 16: 22:40 IST 2005
cal: displays the calendar of any specific month or year.
ex: $ cal 2004 [enter]
who: displays the list of users that are currently logged into
system.
ex: $ who [enter]
Deepanshu console may 9 09:31
John pts/4 may 9 09:31
cat: creates a file.
ex: $ cat>filename [enter]

ls: displays the list of files and directories.
ex: $ date [enter]
wed march 31 16: 22:40 IST 2005
mkdir: creates directories.
ex: $ mkdir abc [enter]
rmdir: removes directories.
ex: $ rmdir abc [enter]
mv: perform two functions.
1. Renames a file or directory.
2. Moves a group of files to different directory.
ex: $ mv c1 b1 [enter]
renames c1 to b1
$ mv c1 c2 abc[enter]
moves c1, c2 to directory abc

cp: for copying one or more files.
ex: $ cp sourcefilename destinationfilename [enter]
rm: deletes one or more files.
ex: $ rm c1 c2 c3 [enter]
cat: display contents of file on screen.
ex: $ cat filename [enter]
tput clear: clears the screen.
ex: $ tput clear [enter]
pwd: display path of your present working directory.
ex: $ pwd [enter]
/home/sharma
cd: change the current working directory to another.
ex: $ cd ram [enter]
$pwd
/home/sharma/ram

Unix provides various general purpose
utilities having diverse functionality . Some
of them are:
cal, date, echo, bc, printf, passwd, man,
whatis, mailx etc.
General Purpose Utilities

bc: is the text based calculator.
ex: $ bc [enter]
12+5 [enter]
17 [ctrl+d]
echo: is used to print messages.
ex: $ echo Deepanshu [enter]
printf: is an alternative to echo.
ex: $ printf “Deepanshu” [enter]
mailx: is the universal mailer to send or receive mails.
Ex. $mailx Deepanshu [enter]
subject: Attention
call me now [ctrl-d]
Will send the mail to Deepanshu.

passwd: for changing password.
ex: $ passwd [enter]
(Current) UNIX password: ***** (12345)
New password: ***** (56789)
Re-enter: ***** (56789)
passwd(SYSTEM): password successfully changed.
man: is the help facility.
ex: $ man bc [enter]
Will give a page having complete documentation about
bc command including options, descriptions, usage etc.

The UNIX file system contains following directories
within the different system files resides.
/bin: contains all commonly UNIX commands.
/etc: contains configuration files of system.
/dev: contains all device files.
/lib: contains all library files in binary form.
/home: different users are housed here.
/tmp: contains all temporary files.
/var: is the variable part of the system. Contains all your print job,
incoming & outgoing mails.
/stand: holds the commands usable only by System Administrator.

Administrator is the person who grants you the authority to
use the system. It is the super user that has vast powers
having access to everything.
The job of System Administration includes:
Maintaining Security by: passwd & set user id(SUID)
User Management by: groupadd, useradd & Userdel
Startup & Shutdown
Managing Disk Space by: df & du
Backup & Restore by: cpio & cpio-i
System Administration

Linux is a full UNIX clone created by Linus Torvalds when
he was a student at the university of Helsinki in 1991.It is
the free operating system based on UNIX. It is written in C
language.
Primary Advantages of Linux:
1. Its initial price is free.
2. Help is always available on internet.
3. It is portable to any Hardware platform.
4. It is scalable and secure.
Popular Linux Distribution :
Red Hat Enterprise Edition, Fedora Core, Debian, SuSE Linux
Linux’s Root in UNIX

The best thing about UNIX are:
 UNIX has greater built-in security and permissions
features than Windows.
 Mostly free or inexpensive open-source operating
systems, such as Linux and BSD.
 Multitasking & Multi-user Features.
 The Community & online support.
 Unix is more flexible and portable and can be
installed on many different types of machines.
Why UNIX?

 Today UNIX has joined the desktop market.
 On the server side, provides database and
trading services for companies.
 In creation of movies such as "Titanic",
"Shrek" and others.
 In real time environments such as flight
management, weapon control etc.
Applications of UNIX

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References
Introduction To UNIX Operating System
Roundup – Top 50 UNIX Commands Every User Must Know
What is Unix Shell and What Does It Do?

Unix - An Introduction

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