Unix Systems Programming: Lab 4 - Processes & Signals, Signal Processing

Purpose and Rationale

Recources

All work should be done on a machine in the department's Linux cluster. You can refer to ssh for more information on how to log into a remote machine.

Marks Distribution

LAB 4

Part 1:  Signal Handling.

1. You should accumultate the handling of CTRL-C in the handler.  That is to say, you should have a variable counter accumulate each time the handler is called, and print out the current count in the handler.  For instance, if you've hit CTRL-C 6 times, your handler should print out something to the effect of "You've pressed Ctrl-C 6 times.  Aren't you getting the message that I'm invulnerable?" 
   
   
2. Your program should accept a command line argument that specifies the MAXSTOPS allowed, after which, Ctrl-C is handled in the default way (i.e., the program terminates).  So if the user passes in '10' on the command line, the program prints out it's message above the first 9 times, but the 10th time CTRL-C is pressed, the default action applies (program termination).
   
   
3. You should print out a message that states that your program received the SIGUSR1 signal when it is handled.  You should be able to issue a kill command to send your program the SIGUSR1 signal, and have that signal handled properly (by printing out a receipt notification) and then continue to function and handle subsequent CTRL-C and SIGUSR1 signals.

Please follow these steps to finish this part smoothly:

• Read "signal" sessions in textbooks as per the syllabus.
• Read and understand the example code first.
• Understand that handling SIGUSR1 is one of the most primitive forms of interprocess communication in Unix (i.e., you are communicating with another process).

Part 2 - Shell

• Step 1: Input Processing Part 1
  
  Every good shell project starts with a prompt.  A prompt is just a string printed on each line on which you can enter a command.  Make your shell print the prompt and take input from user in an infinite loop. Once you have recieved a line of input, split it into one array of character pointers by spaces.  If the user enters the special string 'exit', exit the program.  If the user just enters '\n', the shell should do nothing but print the prompt on a new line.  In the example bellow, c1 stands for command 1 and 0, 1, 2, ...i, stand for the ith group of characters arguments). NOTE: we do not need consider the situation about pipe.

  gosh> ls -a -l -d /etc
  c1 0: ls
  c1 1: -a
  c1 2: -l
  c1 3: -d
  c1 4: /etc
  gosh>
  gosh>
  gosh>
  gosh>
  gosh>
  gosh> exit
  hangao@gawaine:~/cspp51081/LAB5$
   

• Step 2: Fork/Exec
  
  Write a simple fork/execvp procedure to execute command c1 in a child process.  If the command inputted does not exist, the child should print an error message and exit. The relevant  examples (C code) from the book are here: create a child process with fork and wait for its termination, replace a process image (details: BLP, chapter 10).

  gosh> ls -l /etc/passwd
  c1 0: ls
  c1 1: -l
  c1 2: /etc/passwd
  Running Command
  ---------------
  lrwxrwxrwx 1 root root 14 Jul 6 1999 /etc/passwd -> ./local/passwd
  ---------------
  Command Returned Exit Code 0
  gosh>
  

Deliverables

Carefully follow the steps below.

1. You are free to organize your source files however you like ("Part1" and "Part2" might make sense). Your directories should contain at least two files:
   
   • One or more source files
   • A makefile. This should produce the executable mysig when we type make on the command line.


2. When you are finished with your directory you will create a compressed archive file using tar (this utility stores your directory as a single file, then compresses its size.)
          tar -czvf   username.lab4.tgz   username.lab4
   


3. You will email your file to our TA as an attachment. He will send an acknowledgement that your assignment has been received.
   
   

To	Nicholas Flees (nickflees@uchicago.edu)
Attachment	username.lab4.tgz
Subject	CSPP51081-lab4

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