10.7 Consider a system that supports 5,000 users. Suppose that you want to allow 4,990 of these users to be able to access one fifile. a. How would you specify this protection scheme in UNIX? b. Can you suggest another protection scheme that can be used more effectively for this purpose than the scheme provided by UNIX?

a. To specify this protection scheme in UNIX, you can set the file permissions using the chmod command. Specifically, you can set the permission bits such that the owner and group have full access to the file, while the other users have no access to the file. This can be achieved by setting the permission bits to 770, where the first digit represents owner permissions, the second digit represents group permissions, and the third digit represents other permissions. The value 7 represents full access, 6 represents read and write access, 5 represents read and execute access, and so on. Therefore, the command to set the permissions for the file would be:

chmod 770 file

This command would allow the owner and group to read, write, and execute the file, while all other users would have no access to the file.

b. Another protection scheme that can be used more effectively for this purpose than the scheme provided by UNIX is Access Control Lists (ACLs). ACLs allow for more fine-grained control over file permissions by allowing specific users or groups to be granted or denied access to a file. In this case, you could create an ACL that grants access to the 4,990 users who need access to the file, while denying access to all other users. This would provide a more flexible and scalable solution than the standard UNIX file permissions, especially if the number of users who need access to the file changes frequently.