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RSS FeedDecember 8th, 2012
Project 2 Presentations
Just wrapping up project 2 presentations in the CS 6212 – Algorithms class. Here is a survey that is open to students.
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July 13th, 2012
A graph that requires 5 colors but does not contain K5 (complete graph on 5 vertices)
This was a question in the Design and Analysis of Algorithms (CS 6212) final last night. I don’t know how the students did, but essentially, one way to create such a graph is take a C5 (a cycle on 5 vertices), that we know requires 3 colors. Then, to this, we attach a K2 (a simple 2 node connected graph), and connect the two vertices of K2 to each vertex in C5. 
This graph requires 5 colors (3 for C5 + 2 other ones that cannot overlap with colors used in C5), and this graph does not have a K5, since the original graph (C5) does not have a triangle.
So far so good. Interesting question – What is the graph with fewest number of vertices, such that it is K5 free, and it’s chromatic number is at least 5? I suspect this is the same graph, but I do not have any proof.
May 2nd, 2012
UNIX System Administration – Study Guide (Another Semester Draws to a Close)
So as another semester draws to a close, the questions about a “study guide” “mock finals” and such arise again. This guide is a brief outline in that regard for CSCI 4418 (UNIX System Administration) – the undergraduate + graduate computer class that I taught at GWU during Spring 2012. This is not an exhaustive guide, and there are almost always some questions in the final which are not touched upon here – the lectures and the class discussions are a superset of this document. Students should feel free to discuss these topics and questions amongst yourselves, but I do not provide answers to these. And the answers change every year anyway.
Topics
Scripting and Shell, Access Control, Process management, File system, User management, Software management, Setting up Cron, Backup – Dump and Restore, Drivers, Devices and Kernel, Networking, Routing and DNS, Web Applications, Performance Monitoring
Broad Questions
There is really only one basic question that I want to ask at the end of my class, and that question is the same, at the end of every class, and the end of every semester (or a weekend, if I happen to be teaching a weekend seminar class). That question is: How has this class changed your outlook on the subject matter covered, and what are some of the things that you may do differently now, with the benefit of this class.
Since that question has the abstractness of Eliot’s poetry in it, sometimes I use other questions in it’s stead. These are some examples of questions that are intentionally vague. Focus is on checking how broad you think. Real life problems are usually this vague. In each of these, the setting is that you are the system administrator for the IT system (the set of servers, etc,) for that organization.
- A user complains that another user has been able to read his private files. What measures would you take to prevent this from happening again.
- Your applications team wants to build and deploy a web application that will allow the employees to see how much vacation time they have left. What are some of the security considerations you will check/ensure/discuss with them.
- Some of the servers seem to slow down suddenly at different times. What debugging would you perform to check the server performance, see who & what is causing the slowness, and then to possibly improve it?
- You have many users who are business analysts, and they have secretly confided in you that their definition of computer usage involves Facebook more than it involves UNIX/Linux. When they log into a UNIX server that you manage, they go through a list of items: set system color settings so they can read the system outputs, connect to an Oracle database, run some reports, download those reports, etc. They would like to not have to do all these repetitive work. The reports that they run can change from day to day, but the rest of it is pretty much the same. How can you help them get through the repetitive work?
- Your users occasionally delete some files and ask you to “restore” them. How can you create a scheme or a framework for preparing for these kinds of requests? You may not be able to prevent data loss completely, but your goal is to create a framework for “reasonable” backups. For example, if the total size for files for all users is 20 TB, approximately how much space are you allocating for backups?
- Your users would like to share some files. What options will you consider?
- Your application team is using a database which has many reads and writes. They have heard that RAIDing is a “good idea”. What are some of the RAID choices that you may consider, and what are their advantages and disadvantages?
- When might you need to write a device driver?
Scripting Questions (1 Example)
Write a script that counts all unique words that appear in any of *.txt files that exist anywhere inside the folder /home/courses/cs4418. For example, suppose these are the two files:
/home/courses/cs4418/a/b/c/d/e/f/abc.txt: {Justin Bieber is a great singer.}
/home/courses/cs4418/de/f/xyz.txt: {Lady Gaga is a superb singer.}
Then, your script should print the answer that there are a total of 9 unique words in 2 files.
Objective Questions
Objective questions for this question typically test the student’s knowledge of specific commands, and specific concepts. For example:
- How many times would a given cron job run between two given dates.
- ______ command does x.
- Command y does ____.
- What is kernel space?
- What are two broad kernel architectures?
January 28th, 2012
Teaching Unix System Administration at GWU
During the spring 2012, I am teaching Unix system administration at GWU, which is a mix undergraduate and graduate class. Most of the students are graduate students, and they bring a lot of interesting perspectives to this class. When we finish this class in May, there is a small likelihood that the following scenario plays out somewhere:
