Consider a System That Supports 5,000 Users

This week we were asked to consider a system that supports 5,000 users and suppose we want to allow 4,990 of those users to be able to access one file. Suggest another protection scheme that can be used more effectively for this purpose than the scheme provided by UNIX? Before we answer we need to cover a few things about UNIX file management, traditional UNIX file access control and some of the issues encountered when fulfilling requirements among users.

In today’s technologically driven world it is almost a requirement for sharing files among users in a multiuser system. As a result, a couple of issues arise: management of simultaneous access and access rights. With management of simultaneous access, discipline must be enforced by the OS or file management system when there is a requirement to grant users access to append or update files. For file access rights, the system should provide options on how a particular file that is access can be controlled. There are many options for example: NONE, KNOWLEDGE, EXECUTION, READING, APPENDING, UPDATING, CHANGING PROTECTION and DELETION. These rights make up a hierarchy were if a user is granted READING they would also inherit EXECUTION and KNOWLEDGE.

The UNIX file system has six types of files, REGULA, DIRECTORY, SPECIAL, NAMED PIPES, LINKS AND SYMBOLIC LINKS which are supported by modern UNIX operating systems. They are managed via inodes (index node); an inode is a structure that contains the information needed for by the OS for a particular file. There can be multiple files for one inode, but only one file for an active inode. The files permissions and control information are stored in the inode; note the structure of the inode varies from one UNIX implementation to another. The file allocation portion is done on a block basis and the allocation is dynamic. Finally, the directories are in a hierarchial tree structure and contains files and other directories. The directory entries come with an integer called an...