UNIX---Operating System Overview and Introduction

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UNIX---Operating System
Overview and
Introduction

• Name Ying LIU
• ID 103792

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Contents

• Overview
• History
• Variants
• Architecture
• Commands

• Files and Directories
• Security
• Application
• Conclusion

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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

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• 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

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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

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Figure 1. Relationship of UNIX System Variants
with UNIX SVR4
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UNIX Variants
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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

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Tools
Shell
Kernel
Hardware
Applications
Figure 2. General UNIX Architecture
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Types of Shells
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• Function of Shells
• Interpret commands entered at the command line
  prompt when running interactively.
• Customize the users environment, normally done
  in shell initialization files
• Be used as an interpreted programming language

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• Tools and Applications
• hundreds of tools available
• certain functions
• such as word processing, business applications,
  or programming

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UNIX Commands

• Types of Commands
• Aliases--define within the shells memory
• Built-in commands-- are internal routines in the
  shell
• Functions-- define within the shells memory
• Executables programs --reside on disk

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• 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.

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UNIX Files and Directory

• Hierarchical file system
• files are organized in a top-down, or inverted
  tree, structure
• Tree-structured directory

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• 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.

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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

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• 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.

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

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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.

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Conclusion

• Many of UNIXs approaches and notations have
  influenced the entire span of subsequent
  operating systems.
• Thirty years after its creation, UNIX still
  remains a phenomenon!.

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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/

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Acknowledgment

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