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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 XENIX UNIX SVR3 4.2BSD SUN OS SVR4 compatibility Figure 1. Relationship of UNIX System Variants with UNIX SVR4 UNIX Variants --------------------------------------------------------------------------------- ---------------------------------------------------------- SOLARIS Sun Microsystems UNIXWARE HP-UX Novell Hewlett-Packard 1991-SunOS 1991-Salaris 1.0 ……. 1998-Solaris 7(2.7) 1999-UnixWare 7.1 1986-first version 1997-HP-UX 11.0 1991 LINUX Linus Torvalds SCO UNIX Santa Cruz Operation IRIX Silicon Graphics AIX IBM Tru64 UNIX Compaq ULTRIX 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 Tools Shell Kernel Hardware 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 Korn Shell David Korn Univ. of California, Berkeley AT&T C 2BSD UNIX, late 1970s 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 0-13-0212229. • 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.