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

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

3. 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

4. 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

5. 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

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

8. UNIX Variants

9. 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

10. Kernel Hardware Shell Tools Applications Figure 2. General UNIX Architecture

12. Types of Shells

13. 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

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

15. 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

16. 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.

17. UNIX Files and Directory Hierarchical file system –files are organized in a top-down, or inverted tree, structure Tree-structured directory

19. 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.

20. 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

21. 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.

22. 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 ---------------------------------------------------------------------------------------------

23. 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.

24. 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!”.

25. 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/

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