Tutorial 6

Objectives and Outcomes | Lab Class Issues | Review Lecture Material | Sample Exam Questions

1. Objectives and Outcomes

1.1 Objectives

1. to discuss issues arising from Labs 4 and 5;
2. to review material relating to disk scheduling
3. to review material relating to security and protection

1.2 Outcomes

1. you should understand the basic models of secondary storage (disks) and generic I/O handling;
2. you should understand the basic approaches to both the theory and practice of protection and security in inter-networked computer systems; and

2. Lab Class Issues

1. Are there any issues arising from Lab class 4 or 5 (memory management and process scheduling)?
2. Students are invited to raise other issues of concern.

3. Review Lecture Material

1. What were difficult topics in Deadlocks, Mass Storage, Protection and Security materials covered in the last few weeks?
2. Students are invited to raise other issues of concern.

4. Sample Exam Questions

1. You need to arrange a meeting between yourself and two friends as soon as possible. Describe a protocol for using the telephone (with no conference call facility) to arrange such a meeting. What relevance does this problem have to I/O systems?
2. List the advantages of writing I/O device drivers to have generic functionality. What features would you include in a generic disk driver?
3. Is disk scheduling, other than FCFS, useful in a single-user environment? Explain your answer.
4. Explain why SSTF tends to favour middle cylinders over the innermost and outermost cylinders.
5. Why is it difficult to protect a system in which users are allowed to do their own I/O?
6. In a given protection domain, the following access rights exist.
   < O₂, {read, write}>
   < O₃, {execute, write}>
   Can O₃ be executed? Can O₂ call (execute) O₃? Why (not)?
7. Information Technology Services of the university has a number of policies in place to increase the security of its systems. Here is a quote from the policy (taken from http://www.policy.monash.edu/policy-bank/management/its/acceptable-use-student-policy.html)
   Each user is responsible for

   • The unique computer accounts which the University has authorised for the user's benefit;
   • Selecting and keeping a secure password for each of these accounts, including not sharing passwords and logging off after using a computer. Users must not compromise or attempt to compromise the security of any IT facility belonging to Monash or other organisations or individuals, nor exploit or attempt to exploit any security deficiency
   Explain the security implications and motivation for this policy.
8. The finger program allows remote users to ascertain certain key pieces of information about users on a system. Here's the entry from (an old) computer system for me:

   ajh@hawthorn /home/ajh/os/tutorials 1007 $ finger ajhLogin: ajh                              Name: John HurstDirectory: /home/ajh                    Shell: /bin/bashOn since Mon Oct  9 07:49 (EST) on tty3    5 hours 48 minutes idleLast login Mon Oct  9 13:10 (EST) on 7 from fangornMail forwarded to ajh@hawthorn.csse.monash.edu.auNo mail.No Plan. ajh@hawthorn /home/ajh/os/tutorials 1008 $ 

   Why is this a potential security risk?

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