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Introduction to UNIX Harish Kumar .H .C
Assistant Professor
Department of CSE
What is UNIX?
• UNIX is an operating system is a set of Programs that acts as a interface between the computer and the user.
• The development of UNIX started around 1969 at AT&T Bell Labs by
Ken Thompson and Dennis Ritchie.
• UNIX is written in C Programming Language.
• UNIX was originally meant to be convenient platform forprogrammers developing software to be run on it and other system.
Features of UNIX
• Portable
Unix is developed by using C language.
• Multiuser
The UNIX design allows multiple users to concurrently share hardware and software.
• Multitasking
Allows the users to run more than one job at a time
Features of UNIX(continue…)
• Networking
Networking allows user at one location to log into system at other
sites.
• Organized file system
Unix has a very well organized file and directory system that allows
users to organize and maintain files.
• Device Independence
Unix treats every thing(input/output device) like a file.
Features of UNIX(continue…)
• Utilities
Productivity is directly proportional to the software facilities available
on a system.
• Services
In a large user environment. Specially designated administrators(system administrator) monitor the system and help user when necessary.
Unix includes the support utilities for system administration and control.
Computer system
• Computer system = Hardware + Software
• Hardware is the physical equipments.
• Software is a set of programs(instructions)that allows the hardware to do its job.
Computer System
ComputerSystem
Hardware Software
Hardware
• The Hardware in a computer system is the combination of devices that can be seen and touched.
• Computer is made up of four basic types of devices1. input devices
2. output devices
3. Central Processing Unit(CPU)
4. Auxiliary(secondary) devices
Hardware(continue …)
Software
• The software of a computer system is the combination of programs written to make the computer a multipurpose machine.
Software
System software
Application software
Software(continue…)
• System Software consists of the set of programs that serves the of computer itself
Ex: Operating system and set of support programs
• Application Software consists of set of programs that are written to solve user’s Problem
The operating system
• The OS is a special category of system software that manages all the operating facets of the computer.
• OS gives the computer its heart and character.
• Primary tasks performed by the OS are1. Resource allocation and scheduling.
2. Data management include file input and output.
3. System security.
The UNIX Environment
• UNIX is multiuser,multiprogramming,portable operating systemdesigned to facilitate programming, text processing, communicationand many other tasks.
• OS contains hundreds of simple, single-purpose functions that can be combined to do virtually every processing task imaginable.
There are three different computing environments:• Personal Environment.
a) UNIX is a multiuser environment, many users are installing UNIX
on their personal computers.
b) Personal UNIX systems accelerated in the mid-1990’s with the
availability of Linux
• Time Sharing Environment.
• Client/Server Environment.
Time-Sharing Environment
• All of the computing must be done by the central computer.
• Central computer control the shared resources and manage the shared data.
• Slow response and less productive.
Client/Server Environment
• Splits the computing environment between a central computer anduser’s computers.
• The user’s microcomputers or workstations are called client.
• The central computer, which may be a powerful microcomputer, aminicomputer, or a central main frame system, is know as the server.
• Fast response and more productive.
UNIX structure
• UNIX consists of four major components:a. The kernel
b. The shell
c. A standard set of utilities.
d. Application programs.
The kernel
• The kernel is the heart of the UNIX system.
• The kernel contains the two most basic parts of the operating systemProcess control.
Resource management.
The Shell
• Visible to the user.
• Receives and interprets the commands entered by the user.
• To do anything in the system, we must give the shell acommand.
• If the command requires a utility, the shell requests that thekernel execute the utility. If the command requires anapplication program, the shell requests that it be run.
Some standard UNIX shells
StandardShells
Bourne C Korn
Bash tcsh
Shell script and Shell Program
• A shell script is a file that contains shell commands that perform a useful function. It is also known as shell Program.
• There are three standard shells used in UNIX today.
Bourne shell developed by Steve Bourne at AT&T labs.
C shell developed by Bill joy in Berkeley.
Korn shell developed by David Korn at AT&T labs.
Utilities
• A utility is a standard UNIX program that provide a support process for users.
• Common utilities are text editors, search programs and sort program.
• Utilities are sophisticated applications.
• Standard Utilities started there out as applications years ago and proved so useful that they are now part of the system.
Applications
• Applications are the programs that are not a standard part of UNIX.
• Applications are written by System administrators, ProfessionalProgrammers, or users.
• Applications provides an extended capability to the system.
Accessing UNIX
• log in: Enter in to UNIX system.
• Log out: come out of UNIX system.
• Session: The time spent working with the system.
• User id: you (user) and your (his/her) account are identified by a
special code.
Created by system administrator(sys admin).
• Password: is a secret code that you (user) supply to the server so that
no one can figure out what they are.
Interactive session= login +Interaction+logout
Commands
• The basis of all UNIX interaction is the command.
• A UNIX command is an action request given to the UNIX shell forexecution.
• The simplest commands are a single line entered at the line prompt
that cause a program or shell to be executed.
• They can also be included in executable files to form scripts.
• All UNIX commands apply an action or series of actions to some input data and create some output data.
Source and Destination of Data
Command Syntax
• $ verb [options][arguments]
• verb is the command name. The command indicates what action is to be taken.
• Options modifies how the action is applied.
• Options are usually one character preceded by + or – sign.
• argument provides additional information to the command.