UNIX Operating System: Overview and Introduction

UNIX---Operating System Overview and Introduction Name: Ying LIU ID: #103792

Overview History Variants Architecture Commands Files and Directories Security Application Conclusion Contents

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

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 UNIX History

UNIX SVR4 UNIX SVR3 XENIX 4.2BSD SUN OS SVR4 compatibility Figure 1. Relationship of UNIX System Variants with UNIX SVR4

UNIX Variants

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

Tools Shell Kernel Hardware Applications Figure 2. General UNIX Architecture

Types of Shells

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.

UNIX Operating System: Overview and Introduction