COMP 3000 Lab 3 2011

Please answer using text files. Do not use doc, docx, pdf etc. Submit your solutions via WebCT by October 21st at 8 PM.

Part A (in Tutorial)

Notes:

• execve example
• fork, execve example
• generate, receive user signal
• change scheduling priorities program

1. Compile run-program.c with the command gcc -g run-program.c -o run-program and use it to answer the following questions.
   1. Is the line "Is this line printed?" when you execute ./run-program /bin/ls -a /tmp? Why?
   2. Change the program to use execve instead of execvp . What is the new line?
2. Linux signals is a simple form of IPC that is used for a variety of purposes.
   1. What signal is generated when a program attempts to dereference an illegal pointer? Give a simple program that generates such a signal.
   2. How would you send a signal to a process to have it pause execution? Resume?

Part B (on your own)

• catch segfault signal, sigchild?
• make very simple shell based on skeleton?
• run fork bomb, play with priorities to reduce impact, set quota

1. Create run-program-reverse.c that is the same as run-program.c except that it interprets its arguments in reverse order. Hence, ./run-program-reverse /tmp -a /bin/ls will do the same as ./run-program /bin/ls -a /tmp.
2. Create a simple program receive-usr1.c that uses sigaction in order to print "Ouch!" when you send the program the USR1 signal. Note that your program should not consume much CPU time while waiting (i.e., do not poll for the signal).

Program Listings

/* run-program.c */

#include <unistd.h>
#include <stdio.h>

int main( int argc, char *argv[], char *envp[] ) {

   if( argc < 2 ) {
       printf( "Insufficient arguments.\n" );
       return -1;
   }
   execvp( argv[1], argv + 1 );
   printf( "Is this line printed?\n" );
   return 0;
}