UNIX & file system cosc513 Deyong Xu ID:103816 Nov.9 2000

What is Unix A computer operating system that works with users to run programs, manages resources,and communicates with other computer system.

Unix Characters Multitasking Multiuser Multichoice Portability

Multitasking Users can run several programs at the same time , such as editing a file while their another program is running on the backstage . Users don’t have to wait for one application to end before starting another one.

Multiusers Multiple users can log on unix system at the same time. Unix can take the commands of a number of users to run program, access file, and print documents at the same time which means a number of users can share computer resources simultaneously with each user running a different program .

Multichoice Unix has three different types of shell. Shell is to act as an interpreter between the user and the computer. Bourne Shell. C Shell . Korn Sell.

Portability Unix can be moved from one brand of computer to another with a minimum of code change Unix can be upgraded without having all the customer’s data inputted again Decrease the user’s learning time when moving from one system to an other . Provide more choices among the hardware vendors

UNIX File System 3 types of unix files Regular files Programs and data files eg: Source code of a program Email received from friend Executable programs and applications

Continue … Directory files Basic management tools in UNIX file system Files that contain other files Save information of files (like size,location etc.)

Continue … Device files Each hardware is treated like a file Eg1 : Terminals,Printers, Keyboards, etc Eg2:Read from a keyboard device file(input). Eg3:Copy the file to the printer device file(print).

File System Architecture A bottom-up tree with root on the top Root (/), a special directory file

A Example Root (/) bin/ dev/ etc/ usr/ Xdy/ wjj/ lgx/ ...

3 Classes of Users Owner: used by user Group : shared by group members Other : shared by any user

File Three Permissions Read permission: read 1/0 Write permission: modify, delete 1/0 Execute permission: run 1/0

Example: permission of the file is (111 101 000)