1. An experimental addition to UNIX allows a user to connect a watchdog program to a file. The watchdog is invoked whenever a program requests access to the file. The watchdog then either grants or denies access to the file. Discuss two pros and two cons of using watchdogs for security.

2. What benefits does the FUSE filesystem offer?

3. Servers can be designed to limit the number of open connections. For example, a server may wish to have only N socket connections at any point in time. As soon as N connections are made, the server will not accept another incoming connection until an existing connection is released. Explain how semaphores can be used by a server to limit the number of concurrent connections.

4. The UNIX program COPS scans a given system for possible security holes and alerts the user to possible problems. What are two potential hazards of using such a system for security? How can these problems be limited or eliminated?

5. What is the cause of thrashing? How does the system detect thrashing? Once it detects thrashing, what can the system do to eliminate this problem?

6. Calculate the total head movements for the following queues using C-LOOK (head starts at 53)

46, 73, 11, 20, 151, 115, 130, 49

7. In what ways is using a nameserver better than using static host tables? What problems or complications are associated with name servers? What methods could you use to decrease the amount of traffic nameservers generate to satisfy translation requests?

8. What is the purpose of system calls?