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The UNIX Operating System

The UNIX Operating System. UNIX Operating System. Objectives : Learn about the Unix Operating System and develop the skills required to build software applications in the Unix Environment. Contents :. 1. Introduction & History of UNIX 2. File System 3. Basic Utilities

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The UNIX Operating System

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  1. The UNIX Operating System

  2. UNIX Operating System Objectives : Learn about the Unix Operating System and develop the skills required to build software applications in the Unix Environment.

  3. Contents : 1. Introduction & History of UNIX 2. File System 3. Basic Utilities 4. Shell Features 5. Advanced Utilities 6. Communication Features 7. System Calls

  4. Chapter 1 Introduction and History of UNIX

  5. Introduction and History of UNIX • 1. Evolution • 2. Development • 3. Standard release- AT&T versions • 4. BSD UNIX • 5. Other implementations of UNIX • 6. Features of UNIX • 7. UNIX Philosophy • 8. UNIX operating system • 9. UNIX Kernel • 10. Programming Environment • 11. Design Principles • 12. Limitations

  6. Evolution • Primarily influenced by MULTICS • MULTICS • - Developed for GENERAL ELECTRIC 645 • mainframe computer • - Interactive operating system • - Batch - mode characteristics • UNIX Operating System - First Version developed in 1969 by • Ken Thompson on DEC PDP Series ( PDP - 7 ) • - Business, Scientific and Industrial Users

  7. Development • * Originally written in assembly language for PDP-7 • * Transportability facilitated by Thompson who developed the B language • * B language modified by Ritchie and renamed as C language • * Thompson (1980) and others wrote UNIX in C which could be ported to any computer

  8. Standard release - AT&T Versions • Version 3 • Written in C • • Moved to PDP - 11/45 and • PDP - 11/70 • Version 6 • Released in 1975 • • For use by universities only • Version 7 • Released in 1978 • • First commercial version but primarly used in universities • • 32V - VAX version • Version 8 • UNIX Support Group(USG) takes responsibility • • Research Group still busy

  9. Standard release - AT&T Versions …Contd... • System III • Released in 1981 • • Commercial orientation • • Over 100 manufacturers of UNIX-based • micro , mini and mainframes • • UNIX users > 100,000 • System V • Release 1 • Released in 1983 • • Enhancement of System III • System V • Release 2 • Released in 1984 • • Enhancements of System V , Release 1 • System V • Release 3 • Released in 1988 • System V • Release 4.0 •

  10. BSD UNIX (from Berkeley Software Distributions) * UNIX's entry into University of California, Berkeley Campus during 1976-77 * Inputs of UCB Faculty/researchers incorporated in System V of AT&T UNIX UNIX 3BSD • Released in 1978 • Developed by Bill Joy and Ozalp Baboglu • Added Virtual memory, Demand paging to the VAX version 32V UNIX 4BSD • DARPA - funded Development • Provided support for DARPA TCP/IP • C-Shell , ex/vi , new compilers for PASCAL and LISP were added UNIX 4.1 BSD • Released in 1981 UNIX 4.2 BSD • Released in 1983 UNIX 4.3 BSD • Latest Release

  11. Other Implementations of UNIX (based on Version 7, System III, System V of AT&T UNIX or UNIX 4.2 BSD) Xenix Microsoft’s UNIX operating system to run on microcomputers IBM PC/IX IBM PC Zeus Zilog Computers DEC Ultrix DEC HP-UX HP UNIX SUN Elxsi UNIX ELXSI Pyramid UNIX Pyramid Data General UNIX Data General Perkin Elmer UNIX Perkin Elmer MassComp UNIX Mass Computers NBI UNIX NBI Amdahl UNIX Amdahl

  12. UNIX Features • Multitasking Performing tasks simultaneously rather than sequentially • e.g., While printing a document , start editing another document • Each task is considered to be a process • Multi-user Several users can use the same computer simultaneously • i.e , more than one keyboard and terminal • can be connected to one computer • Highly cost-effective • Portability Easier to modify the UNIX system code for installation on a new computer rather • than write from scratch a new operating system

  13. UNIX Features UNIX System supplied tools Integral utilities Basic Operation of Operating system like Command interpreter or Shell Tools Text print formatting like nroff and typesetting troff

  14. * Available on micros, minis and mainframes • * UNIX Communication and electronic mail • • Communication between different terminals hooked to same computer • • Communication between computers of different • sizes and types in different locations as far away • as other countries • * Incorporation of third party application programs • * Hierarchical File System • * On-Line Help facility • Example : man <Command> • * Library of application software

  15. The UNIX Philosophy • Make each program do one thing well • Expect the output of one program to become the input to another • Suited for prototype development i.e., design and build easily • Modular approach i.e., be prepared to throw and rebuild • Usage of tools • Building essential tools

  16. The UNIX Operating System Kernel Schedules tasks and manages data storage Shell A program that • interprets the user commands/requests • calls programs from memory and • executes them one at a time or in a series (called a pipe) Tools & Specific capabilities added on to the OS Applications Kernel( Heart of Unix Operating System) Shell Interpreter Tools and Applications

  17. The Users • Shells and Commands • Compilers and Interpreters • System Libraries • System Call Interface to Kernel • Signal File System CPU Scheduling • Terminal Swapping Page • Handling Replacement • Character Block Demand Paging • I/O System I/O System • Terminal Disk & Tape Virtual • Drivers Drivers Memory • Kernel Interface to the Hardware • Terminal Device Memory • Controller Controller Controller • Terminals Disks & Tapes Physical • Memory

  18. File Management And Security Networking Services Input / Output Services Date and Time Services Process Scheduling Signal Handling System Administration and Accounting Memory Management The UNIX Kernel UNIX SYSTEM KERNEL

  19. The Programming Environment * A GOOD operating system !! • Simple yet powerful • Allows building of tools, writing of small programs and putting them together • A rich & productive environment * A PORTABLE operating system !! • Written in C • Runs on a range of computers • Source code is available

  20. The Design Principles • * Designed for Programmers • * Interactive • * Multiple Processes can be initiated • Foreground Process • Background Process • * Methods to Co-ordinate Process • * Signal to communicate with processes • * Files, Directories, Devices treated as files • * Tree structured directories to hold files • * Emphasis on program development facilities • * Sources available on-line • * Simplicity before efficiency

  21. Drawbacks of UNIX • * Designed for computer professionals • * Not a real-time operating system • * File Security depends on owner • * Defective programs may keep running

  22. Chapter 2 File System

  23. The UNIX File System • 1. File System Layout • 2. Concepts of file • 3. Features of File system • 4. Starting and Ending a session • 5. File Management utilities • 6. Directory Management • 7. File operation • 8. Mountable File System • 9. File security

  24. File Systems in UNIX • Disks are partitioned into File Systems. • - Logical blocks of 512 bytes or multiples • - Arranged to form a hierarchical structure • - Convenient to manage data • File System Layout • Boot Super Inode Data • block block list block • Boot block • - generally occupies the first sector • - may contain bootstrap code • Super block • - Information about the file system • How large, where free and other details • Inode list • - Contains a list of inodes • - One inode is the root inode • Data block • - Contains file and administrative data • - Allocated data can belong to that block • only

  25. Classification of files in UNIX • - Ordinary Files • - Directory Files • - Special Files • - Standard Files

  26. Concept of Ordinary Files * A File in UNIX is a Stream of bytes ( 8-bits) Kernel does not impose a structure on files * File may contain text, data and even machine language code Examples Text Files : Lines of ASCII characters separated by a new-line Commands : Sequence of commands interpreted by UNIX text Data : File containing data as stream of bytes Executable : File containing machine language instructions * The files format remains unchanged but only the way the program interprets it is different

  27. Concept of Directory Files • * Gathering together related files in a common place • * Every file is assigned to a Directory • * Directories have names (maximum of 14 characters) • * A file within a Directory can itself be another Directory (A Sub-directory) • * Internally a Directory is just a file that contains • - a list of file names • - their Inode Numbers and • - a pointer to the actual file on the disk • * An upper limit of around 35 sub -directories • Examples • / ( Forward slash ) Prime or Root Directory • Note - in DOS it is \ ( Backward slash ) • /usr Directory for the user • /usr/trg1 Sub-Directory for trg1 under Directory usr

  28. Concept of Special Files • * Used to reference Physical devices such as terminals, disks, floppy drives and tape drives • * Read and written like ordinary files • * Requests cause activation of the associated Physical Device • * Device Drivers associated with each file • * Types : • Character file Terminal (tty0, tty1 ) Transmits data Character by • Character • Block file Disk Drives (hd0,fd0) Transmits data in 512 or 1024 • byte chunks • * Major and Minor numbers identify the hardware link • Major No.s : Indicates type of device • Minor No.s : Different instances of the device

  29. Concept of Standard Files • * Helps display information on the screen • * Special Names for Communication channels • * Keyboard input channel is called Standard input • (stdin) - file id is 0 • * Terminal Screen output is called Standard output • (stdout) - file id is 1 • Diagnostic error messages (generated by a program) are sent to Standard error • (stderr) - file id is 2 ( shown on terminal screen ) • * All three files are open by default at the time of login

  30. File Names * A means for the system to identify a file Note : Unix is case sensitive * User accesses a file by a user-assigned file name * Can be a sequence of characters (a maximum of 14 ) * May be identified by two or more names (Multiple links to a file) * Internally assigned a unique inode number (for a File System) * Different files can be grouped under a directory

  31. Path Names Absolute Path name * A file is identified by the path name from the root e.g., /usr/trg/c/test.c where • test.c is an ordinary file • usr, trg, c are directories • trg is a sub-directory under usr Relative path name * UNIX keeps track of the user's current directory * If a "/" does not precede a file name then the name interpretation begins with the current directory e.g., If current directory is /usr/trg then the file could be just referenced as c/test.c

  32. Features • * Hierarchical • * Security on each file • - Owner • - Group • - All others • * Separate security for • - read • - write and • - execute • * Removable • * File Independence - • * Time stamp on each file • - Modification time • - Access time

  33. spell Unix bin troff console --- dev lp0 src tty0 man sh uch bin --- csh bin --- local lib Libc.a lib --- --- / usr include *.h spool tmac lib troff passwd etc group --- init tmp --- tmp ---

  34. Standard File Hierarchy • /bin Basic Unix utilities cp, mv, ln • /dev Special I/O device files fd0, lp0 • /etc Administrative Programs passwd, shutdown • /lib Libraries used by Unix libc.a • /usr/bin Unix utilities cal, bc,spell • /usr/adm Administrative commands • and files adduser • /tmp Temporary files created • on error conditions

  35. /usr/games - Game Programs • /usr/include - Include files for language procedure • Examples : C-header files • stdio.h, math.h • /usr/lib - Archive libraries • Example : troff • /usr/mail - Mail files • Example : mailbox • /usr/news - News files • /usr/spool - Spool files • /usr/tmp - Temporary files • /usr/src -Program Source Files

  36. Security and Access Methods • * Three levels of access • User/Owner, group, others • * Three types of access on Files and Directories • Read, Write, Execute • Access Mode Ordinary Directory • Read Examination of Listing of • File Contents files within Directory • Write Allows changing Creating new • of file contents files within Directory • Execute Executing file as Searching the • a command Directory allowed allowed

  37. Starting and Ending a Session • login : User can type his name and password to identify himself • login command can be used as • $ exec login • to log-on onto another user account after identifying yourself in response to prompts for user name and password • su setuser • This is used to become another user or super-user provided the password is known. • e.g., $su • Prompt the user for the superuser password $su - trg2 • Prompt the user for the password of user trg2 $su - trg2 -c "ls -l" • Temporarily changes to trg2 and executes the command ls -l and • comes back to the original user

  38. Starting And Ending A Session …Contd…. • passwdChange the password for the user • e.g., $ passwd • Prompt you for old password and new password • logout This command exits or logs-out from the current user • and executes the file .logout before coming out • e.g., $ logout • or • $ exit • or • $ <ctrl-d> • exits from the current login

  39. File Management Utilities • Directory Operation File Comp. Security • Management • cd cmp passwd • pwd comm crypt • mkdir chown • rmdir chgrp • mvdir umask • chmod • File File Mountable Copy, Move • contents compression file Remove & Time • cat pack mount cp • ls unpack umount ln • wc mv • file rm • touch

  40. mkdir creates a new directory • rm removes a file • rmdir removes a directory • du displays disk usage • df displays number of free block • touch updates the time of last modification • find locates files that match certain area • file displays the type of file • pwd displays full pathname of current directory

  41. Command Structure General Structure: Command Name [Options] [Arguments] E.g., Command Name Tells the shell what to do (in this case list files) Options Control how the command will work (in this case ask for a long listing) Arguments on which the command works (in this case the directory usr/trg ) -l ls /usr/trg

  42. Directory Management cd Change working Directory cd.. Parent Directory cd. Current Directory e.g., $ cd /usr/trg/c ( current Directory is c ) $ cd .. ( current Directory is trg ) $ cd ./c ( current Directory is again c ) or $ cd c $ cd ( home directory - in this case /usr/trg) mkdirMake a Directory $ mkdir pathname Makes Directory in 777 mode Write permission should at least be permitted for owner in parent Directory e.g., $ mkdir /usr/trg2 ( makes directory trg2 )

  43. rmdir Remove a Directory • $ rmdir pathname • * Directory should be empty, or else • rm -r (recursively remove) • e.g., • $ rmdir /usr/trg2 (removes directory trg2) • pwd Print Working Directory

  44. File Contents • cat Concatenate & Print on screen or printer • $cat [Options] [Arguments] • Options - take input from stdin -n no. of output lines • -s squeeze adj. blank lines • -v enable display of non-printing characters • -b used with -n to avoid numbering blank lines • e.g., • $ cat try.c Display the contents of try.c on the screen • $ cat Takes input from stdin i.e. keyboard and displays on screen

  45. $ cat f1 > f2 Takes input from file f1 & puts it • on file f2 • $ cat f2 > f3f3 contains the contents of f1 • $ cat f4 >> f3 Appends the contents of f4 to • file f3 • $ cat try[0-3] > final The file final contains contents of try0, try1, try2 try3 • $ cat test* > report The file report contains all files beginning with test

  46. Is[Options]List the Directory Contents • Options -1 number one single column output • -l long format (II also used) • -a all entries including dot files • -s gives no. of disk blocks • -i inode no. • -t ordered by modification time recent • first recursively display all directories, • starting specified or current directory

  47. $ Is -I List the files along with the protection bits and the user • $ Is -a List the files starting with .and..also • $ Is -1 symtab.c • symtab.o • treegen • test • $ Is -I -rw-r—r— 1 smj proj1 30766 Mar 3 15:08 symtab.c • -rw-r—r— 1 smj proj1 8759 Mar 3 15:12 symtab.o • -rwxr-xr-x 4 smj proj1 40743 Mar 3 15:23 treegen • drwxrwxr-x 1 smj proj1 53 Mar 1 09:15 test • $ Is -a . • .. • .profile • .cshrc • symtab.c • ... • $ Is -iI 10936-rw-r—r—I smj proj1 3076 Mar 3 15:08 test.c • 10936 - inode number of file test.c

  48. wc Word Count • $wc [Options] filename • Options - Display no. of lines, words, characters • -I Display no. of lines • -w Display no. of words • -c Display no. of characters • e.g., $ wc test.c • 20 200 5678 • 20 - lines • 200 - words • 5678- characters • nl no. of lines in the file and temp’ly lists out the file • Similar to wc -l < filename >

  49. file Determine file types • $file [Options] [Arguments] • Options -f filelist • Normal File Types • - C program text • - assembler program text • - commands text • - ASCII text • - English text • e.g., $ file test.c • C Program test

  50. cp copy a file • -i - user interactive mode • e.g., • $ cp test.c test.c.bak • test.c and test.c.bak contain the same contents • Extra disk storage • In Create link • e.g., • $ ln first.c second.c • The file is referenced by two different names • No Extra disk storage

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