COMP229/4 - System Software - Some Course Materials

This page contains some materials presented by Serguei on Friday labs for the COMP229/4 course, 2002.

Please report any typos, bugs, corrections, and suggestions to mokhov@cs.concordia.ca.

Table of Contents

1. Debugging
   • Buggy Hello World: hw.c
   • Debugged Hello World: hw.c
   
   
2. Shell Scripts
   • Text-Based "Slides" for PA2: HTML | slides.txt
   • Original Sample Shell script: sample.sh
   • Improved Sample Shell script: isample.sh
   
   
3. Introduction to System Calls and Process Management
   • File Management System Calls (for the Assignment #3)
   • Process Management System Calls
   
   
4. Assignment #3 Notes
   • Checkout Advvanced Example in File Management System Calls
   • Marking Scheme
   • Marks (for those who presented their PA3 on Friday, March 15 and March 22)
   • Solution
     Here is the solution in partial fullfillment with the assignment requirements to enable those who haven't finished this assignment, proceed with the next one. Make sure you read NOTES in the ifv.c file. Any problems reports please direct to me. The solution has four files: Makefile (not necessarily needed, but convenient to have), ifv.c - the main module, and the systutil229.h and .c files which the program uses. You will need the latter three files if you want to use the solution (if you do not prefer to have that many files you can copy paste the stuff over, but I wouldn't recommend doing so since you're required to split the ifv.c file anyways :-)). The same set of files is available in /home/courses/comp229/pa3 directory.
   
   
5. Assignment #4 Notes
   • Friday, March 22, Demo files:
     shlnno.c | display_line.h | display_line.c | sysutil229.h | sysutil229.c | Makefile
     Tarball (all-in-one): lib-demo.tar.gz
     
     Don't forget to do:
     $ setenv LD_LIBRARY_PATH your_so_lib_dir
     
     
   • Running program in a new window
     Here (cmdwnd.c, updated) is a first proposed example for the A4 on how to run a program in a new window and quit at user's request. The example illustrates the cal command hardcoded in, but you should allow any command in your assignment solution (which is not hard to do at all :)). Please also review the fork() and exec() notes below (Process System Calls) and man xterm. For the convenience I also provided a Makefile. To run it to see how it works: (a) download all the files, (b) compile (type in make), and (c) run: ./cmdwnd
     Methodology: the cmdwnd program spawns and execs an xterm window with the -e option asking to run cmdwnd again with a desired command. The second incarnation of cmdwnd just forks a copy of itself and execs the desired command. Than the what was an xterm before waits for the command to be completed and prints the prompt as per assignment requirements.
     
     Another approaoh, a simpler than the above, was proposed by Mashrur Mia. You can find it in the same place under the name cmdwnd-m.c. Methodology: instead of runing ourselves twice with different options, we ask the shell (tcsh in our case) to do it for us in the spawned xterm. A bit not conformant with assignment requirements, but much simpler to understand and to use, thus, maybe recommended over the former.
   
   
6. Assignment #5 Notes
   • Brief Makefile Reference
   • Example: See A4 notes on library above
   
   
7. FAQ
   • Why can't I save anything? It says "exceeded quota"...
   
   
8. Links
   • Official Course Web Site
   • Quick Links
     • Assignment 1
     • Assignment 2
     • Assignment 3
     • Assignment 4
     • Assignment 5

File Management System Calls

• Combined COMP229 Utility Functions (Mashrur Mia, Arlin Kipling, Serguei Mokhov)
  • Utility Files (Updated: March 22, 2002): sysutil229.h, sysutil229.c
  • Example of use: sysutildemo.c
  • How to compile with your program:
    1. Put the Utility Files to the same directory as your assignment.
    2. In your ifv.c file along #include lines add this:

       ...
       #include "sysutil229.h"
       ...
       						

    3. Compile and link your program with the sysutil229.c file:
       
       $ gcc -g ifv.c sysutil229.c -o ifv
    
    
  • Advanced Example: shlnno.c
    Shows specified line #, as an option from the user. This code is a sample and in many places is not optimized and may contain bugs. It demonstrates use of File Management System Calls and bunch of other stuff. It uses functions from the sysutil229 lib above. To test type:
    $ gcc -g shlnno.c sysutil229.c -o shlnno
$ ./shlnno shlnno.c
  
  
• Original Files
  • Read a char from STDIN and immediately terminate: readchar.c, by Mashrur Mia.
  • Clear screen example with system(): clr.c
  , by Arlin Kipling.
  
  

Process Management System Calls

• March 1st Slides (more process-oriented, Updated: March 11, 2002): HTML | PPT
• Simplest fork() example: fork_pid.c
• Distinguishing between parent and child with fork(): fork_child.c
• Simplest exec() example: exec_pid.c
• fork() and exec() combined: fork_exec.c

F.A.Q.

Q: Why can't I save anything? It says "exceeded quota"...

A:

Every user on the system is allotted some disk space for their files. Since there are many students out there, quotas aren't so high and people often tend to leave unneeded files, which count against their disk quota. Once you have exceeded your allotted storage, you won't be able to save anything until you free up some space.

In general, typical files students are working with, are not of such a great size; however, there are some system files, sometimes quite large, which you might not be aware of, but they still count against your quota. A typical so troublesome example is the Netscape browser, which leaves after itself a lot of cached pages if not configured properly. After moderate browsing you can easily have your quota used up.

Hints on how to solve the problem. Type the quota command to actually see the quotas for your account. If they exceed allotted space, delete unneeded files and the .netscape directory. In most cases this is more than enough. The .netscape directory is in your home and marked as system, and thus, by a simple ls not shown. Use ls -a or better yet ls -al. Type \rm -r ~/.netscape to remove it. Another torublemaker could be a core dump from a crashed program, which takes up sometimes quite a lot of space. Most of the time you don't need it, so there's no need to keep it too. Check your quota again, and if it's not enough, see what else you can remove. The du -h command will show you disk usage for all the directories starting from your current, and pay special attention to those that take a lot of space as first candidates to removal.

References:

man quota
man du
man ls
man rm

Maintained by Serguei A. Mokhov, mokhov@cs.concordia.ca