1. CST334 Unix & X Window System
Overview of UNIX
Purpose of an Operating System (OS)
History Unix OS
Characteristics of Unix OS
History of Linux OS
The Drive for compatability (POSIX standards) 2

2. Attention For additional reading, consult
Appendix B and Chapter 1 of Forouzan and Gilberg, Unix and Shell Programming
your textbook 6

3. Definition of an Operating System (OS)
An operating system is a control program for a computer that performs the following operations:
allocates computer resources
schedules routine tasks
provides a platform to run application software for users to accomplish tasks
provides an interface between the user & the computer 7

4. History of Unix OS
Prior to Unix, many operating systems ran collections or “batches” of operations one at a time.
This single-user “batch-processing” approach did not take advantage of the potential processing power and speed of computers
Enter data in
files to be later
processed
Process
Collection or
“Batch” of files
Receive
information of
processed data
Note: batch processing lacks the advantage of immediate feedback as opposed to online processing 8

5. History of Unix OS
The Unix OS was developed (based on Multics & CTSS operating systems) by Ken Thompson at the AT&T Bell Laboratories in He wanted to create an multi-user operating system to run “space travel” game.
Ken’s philosophy was to create an operating system with commands or “utilities” that would do one thing well (i.e. UNIX). Pipes could be used combine commands... 9

6. History of Unix OS
The first versions of UNIX were written in “machine-dependent” program (such as PDP-7).
Ken Thompson approach Dennis Ritchie developer of C program), and in 1973 they compiled UNIX in C programming language to make operating system “portable” to other computers systems. 10

7. History of Unix
Ken Thompson (recently retired from Bell Labs) is on left, and Dennis Ritchie is in the middle. What`s his name is on the right… 11

8. UNIX Features
The Unix OS is a multi-user OS allowing more that more person to directly communicate with the computer.
Although the OS can only work on one task at a time, a small piece of time (time slice) is dedicated to each task or user - this is referred to as “time-sharing”.
Time sharing gives the illusion that the CPU is giving all the users its full attention 12

9. Illustration of Time-Sharing
User 8
User 1
User 2
User 7
User 6
User 3
TIME
User 4
User 5 13

10. Development of Unix OS
Unix became a popular OS among institutions such as colleges & universities through a 4-year “try before you buy” deal.
Efficient and inexpensive way of networking
promotes Internet use and file-sharing
Open system allows for source code to be shared among many programmers - allows for better coordination among programmers 14

11. Development of Unix OS
Students at University of California (in Berkley) further developed the UNIX operating system and introduced the BDS version of Unix
Unix
Bell Labs UNIX System V (5) Proprietary
Berkley Software Distribution (BSD) Free 15

12. Development of Unix OS
There were versions of UNIX for the Personal Computer (PC), such as XENIX, etc., but they didn’t catch on in popularity until Linux was developed in the early 90’s. 16

13. History of Linux
Linux operating system developed by programming student Linus Torvalds
Linus wanted to develop Unix-like OS just to experiment with new 386 computer at the time... 17

14. Why Has Linux Become so Popular?
Linus decided to make Linux OS source-code for Linux Kernal open to all:
Unlike traditional Operating Systems, anyone can modify and distribute Linux OS (as long as they distribute source code of Linux Kernel)
“Competition among Hackers” allow code to be improved and distributed often
Many users can spot bugs in the operating system or application if source code is “open” 18

15. Why Has Linux Become so Popular?
Other Factors:
PC’s have increased processing power and a there has been a noted shift from mainframes and minicomputers to PCs.
Since Linux is a “Unix Work-alike”, this OS has a reputation to be a very stable platform for networking (creating at-home servers) and running / maintaining applications.
Agencies such as Free Software Foundation created GNU project to provide free software. 19

16. Concerns
Some people claim that “there are as many version of Linux as there are users…”
POSIX (Portable Operating System Interface for Computer Environments) is a government standard to ensure consistency among different UNIX and Linux versions.
Many versions of Linux are approaching POSIX standard. 20

17. Concerns
Freedom of allowing Linux users to create “servers” connected up to Internet can lead to attacks from experienced hackers.
Linux commands may be considered “user-unfriendly” although GUIs are now used.
Prior reputation for difficult install process including the loss of data on other hard disk partitions. 21

18. Attention
The following material is taken from chapter one of your textbook ,
Unix and Shell Programming

19. Advantages of Unix Portable Multi user Multitasking
Networking – log into the any site
Organized file system
Device independence – i/o vs files
Utilities – > 100 utilities, productivity
Services – administrative tools built in

20. Figure 1-1
Computer System

21. A computer system Hardware Software
Input , output, CPU, auxiliary/secondary storage
Software
Systems software
Primary purpose to support computer
Applications software
Programs written to solve users problems

22. Components of Computer Hardware
Figure 1-2
Components of Computer Hardware

23. Operating system
A special category of systems software that manages all operating facets of the computer
Heart and character of a computer:
DOS, Windows , Mac, UNIX
Performs resource allocation, scheduling, data management (file I/O), system security

24. Unix environments Personal environment Timesharing environment
Linux, Apple’s System X (Unix kernel)
Timesharing environment
Many users connected to one computer
Client/server environment
Computing split between a central computer (server) and users’ computers (clients)

25. The Time-Sharing Environment
Figure 1-4
The Time-Sharing Environment

26. The Client/Server Environment
Figure 1-5
The Client/Server Environment

27. Figure 1-6
Components of UNIX

28. Components of the Unix OS, cont
The kernel: contains most basic parts
including process control and resource management
The shell: receives & interprets the commands entered by the user
Interpreter and script programming language
Three standard shells: Bourne (sh/bash) , C (csh/tcsh), Korn (used in text)

29. Components of the Unix OS, cont
Utilities: hundreds ! Primarily
Text editors, search programs, sort programs
ls, cp, mv, vi, emacs, grep, chmod, sort, cal, date, plus countless options
the real heart of the class
Applications: written by systems administrators, professional programmers, or users
Extended capability , sometimes made into future utilities

30. Accessing Unix
User ID
Passwords
Interactive session

31. Figure 1-8
Interactive Session

32. Common commands
date
date -u
cal
cal
cal 2005
who
passwd
man

33. Command Source and Destination
Figure 1-9
Command Source and Destination

34. General Command Format
Figure 1-10
General Command Format

35. Figure 1-11
The date Command

36. Figure 1-12
The calendar Command

37. Figure 1-13
The who Command

38. Figure 1-14
The passwd Command

39. Passwords a) must be >=6 characters long,
b) must contain 2 out of 3 of
upper-case letters,
lower-case letters,
non-letters (digits, punct)
c) may not be a dictionary word or too similar to your name

40. Exit—to Log Out Type exit
if it says "there are stopped jobs" type exit again

41. Figure 1-15
The echo Command

42. Figure 1-16
The man Command

43. Figure 1-17
The lpr Command

44. Figure 1-18
The tty Command

45. Figure 1-19
The clear Command

46. Figure 1-20
The stty Command

47. Figure 1-21
The script Command

48. Figure 1-22
The uname Command