UNIX---Operating System

Overview and Introduction

Name: Ying LIU

ID: #103792

Contents

• Overview• History• Variants• Architecture• Commands

• Files and Directories• Security• Application• Conclusion

UNIX Overview

• What is UNIX?– narrow sense: is a computer operation system– wider sense: encompasses a broad set of

commands, or “utilities”

• What does it do?– operates a computer – lets a number of programmers access the

computer

• The Uniqueness of UNIX– Multitasking capability

• Running more than one tasks at same time

– Multiuser capability • multitasking permits multiple users to use the computer

– Portability • move from one brand of computer to another with a

minimum of code changes

– UNIX programs • Integral utilities• Tools

– Library of application software

UNIX History

• Bell Lab• Ken Thompson

Dennis Ritchie Doug McIlroy Brian Kernighan

• 1960s--dependable timesharing OS

• 1970--PDP-7, CTSS, Multics

• 1974--rewritten in C• 1975--Version 6

Table 1 Early versions of the UNIX system-----------------------------------------------------------------------------------------------------------------------------

Version Year released Applications

------------------------------------------------------------------------------------------------------------------------------

Version 6 1975 Universities

Version 7 1978 Universities and commercial. The basis for System V.

System III 1981 Commercial

System V, Release 1 1983 Commercial

System V, Release 2 1984 Commercial, enhancements and performance improvements

Version 8 1985 Universities

Version 9 1986 Universities

Version 10 1989 Universities

--------------------------------------------------------------------------------------------------------------------------------

* In addition, there are several university versions, the most important being the UNIX-Berkeley BSD

distributions.

UNIX SVR4

SUN OS

4.2BSD

UNIX SVR3

XENIX

SVR4 compatibility

Figure 1. Relationship of UNIX System Variants with UNIX SVR4

UNIX Variants--------------------------------------------------------------------------------- ----------------------------------------------------------

SOLARIS Sun Microsystems 1991-SunOS 1991-Salaris 1.0 ……. 1998-Solaris 7(2.7)UNIXWARE Novell 1999-UnixWare 7.1HP-UX Hewlett-Packard 1986-first version 1997-HP-UX 11.0LINUX Linus Torvalds 1991SCO UNIX Santa Cruz OperationIRIX Silicon GraphicsAIX IBMTru64 UNIX CompaqULTRIX Digital Equipment Corporation------------------------------------------------------------------------------------------

UNIX Architecture

• Kerenel– schedules tasks and manages storage

• Shell– connects and interprets users' commands– calls programs from memory and executes them

• Tools and Applications– offer additional functionality to the operating

system

Kernel

Hardware

Shell

Tools

Applications

Figure 2. General UNIX Architecture

Types of Shells

Types Programmer Company Language First Release---------------------------------------------------------------------------------------------------------------------------------Bourne Shell Stephen Bourne AT&T Algol V7UNIX, late1979

C Shell Bill Joy Univ. of California, Berkeley C 2BSD UNIX, late 1970s

Korn Shell David Korn AT&T Algol SVR4 UNIX, mid 1980s

______________________________________________________________________________________

• Function of Shells– Interpret commands entered at the command

line prompt when running interactively.– Customize the user’s environment, normally

done in shell initialization files– Be used as an interpreted programming

language

• Tools and Applications– hundreds of tools available – certain functions

• such as word processing, business applications, or programming

UNIX Commands

• Types of Commands– Aliases--define within the shell’s memory– Built-in commands-- are internal routines in the

shell– Functions-- define within the shell’s memory– Executables programs --reside on disk

• Generic Syntax– Command [flags] argument1 argument2…

• Basic Commands– logging on (rlogin)– changing password (passwd)– getting out (exit), listing files (ls)– copying files (cp)– removing files (rm)– navigating the directory tree (cd)– so on.

UNIX Files and Directory

• Hierarchical file system– files are organized in a top-down, or inverted

tree, structure

• Tree-structured directory

• Four types of file system:– Regular file system: Files that contain information

entered in them by a user, an application program, or a system utility program.

– Directory file system: contains a list of file names plus pointers to associated inodes (index nodes)..

– Device file system: used to access peripheral devices, such as terminals and printers. Each I/O device is associated with a special file.

– Named file system: named pipes. A pipe is a circular buffer allowing two processes to communicate on the producer-consumer model.

UNIX Security

• Risk and Treat– Risk: the possibility of an intruder attempting to

access– Treat: the motivation to attempt to gain

unauthorized access

• Protection– Password system– Intrusion detection

• There are four general categories of attack: – Interruption: an asset of the system is destroyed

or becomes unavailable or unusable. This is an attack on availability.

– Interception: an unauthorized party gains access to an asset. This is an attack on confidentiality.

– Modification: an unauthorized party not only gains access to but tampers with an asset. This is an attack on integrity.

– Fabrication: an unauthorized party inserts counterfeit objects into the system. This is an attack on authenticity.

• Table 2 Network Security Architecture• -----------------------------------------------------------------------------------------------

• Layer Name Functional Description

• -----------------------------------------------------------------------------------------------

• Layer 7 Policy Policy Definition And Directives

• Layer 6 Personnel People Who Use Equipment And Data

• Layer 5 LAN Computer Equipment And Data Assets

• Layer 4 Internal-Demark Concentrator - Internal Connect

• Layer 3 Gateway Functions For OSI 7, 6, 5, 4

• Layer 2 Packet-Filter Functions For OSI 3, 2, 1

• Layer 1 External-Demark Public Access - External Connect

• ---------------------------------------------------------------------------------------------

UNIX Applications

• Horizontal applications– not specific to any particular industry. Are used

throughout academia, government, and the commercial world

• Vertical applications– are used for applications designed to solve

problems in specific industries such as retailing, hotel management, or finance.

Conclusion

• Many of UNIX’s approaches and notations have influenced the entire span of subsequent operating systems.

• “Thirty years after its creation, UNIX still remains a phenomenon!”.

References

• Ellie Quigley: UNIX Shells by Example, second edition.. 1999 by Prentice Hall PTR. ISBN 0-13-02-12229.

• Stephen Prata, Donald Martin, The Waite Group: UNIX System V Bible--Commands and Utilites.. 1987 by The Waite Group, Inc. first edition. ISBN: 0-672-22562.

• Ralph M. Stair and George W. Reynolds: Principles of Information System, Fourth Edition. 1000 by Course Technology. ISBN 0-7600-1079-X.

• William Stallings: Operating Systems: Internals and Design Principles. Third Edition. 1998 by Prentice hall Engineering, Science & Math. ISBN 0-13-887407-7.

• Kenneth H Rosen, Douglas A Host, James M. Farber, Richard R Rosinski. UNIX: The complete Reference. 1999 by The McGraw-Hill Companies. ISBN 0-07-211892-X.

• http://www.bell-labs.com/history/UNIX

• http://www.msoe.edu/~taylor/4ltrwrd/

Acknowledgment

• I gratefully thank Professor M. Anvari for the suggestion on the paper organization.