Description

Total 1 point
Objective
At the end of this mini-lab, you will be able to:
• Gain hands-on experience in process-related system calls, e.g. fork(), wait(), and exec().
• Understand the parental relationship between processes.
Instructions
In this mini-lab, you will implement a simple multiprocessing program and fork() and exec() to understand how the operating system manages multiple processes.
1. Open two terminals marked as Terminal 1 and Terminal 2.
2. In Terminal 1, find out and record process id of the current shell using echo $$ > t1-pid.txt.
3. Complete all TODO sections in lab3-process.c using fork(), exec(), and wait() following the inline instructions.
4. In Terminal 1, compile and execute lab3-process.c. If your implementation is correct, the child process will sleep 20 seconds.
5. Before the process returns in Terminal 1, in Terminal 2, execute pstree -sp $(cat t1-pid.txt) to monitor the tree of running processes. We can see a chain of processes like SSH > Bash (Terminal 1) > parent process (lab3-process) > child process (sleep 20).
Explanation of their relations: Upon connecting remotely, the SSH process forks to create a new Bash shell for the user’s session. When lab3-process is executed within this Bash shell, Bash forks again to run the program, which lab3-process forks once more to create a child process for the sleep 20 command. This sequence of fork operations establishes the chain: SSH forks Bash > Bash forks Parent (lab3-process) > Parent forks Child (sleep
20).
1
Submission
(1 pt) Complete all TODO sections and submit your code as lab3-process_<your_student_id>.c.
COMP3230 Mini-lab 3 Page 2
Appendix
// file: lab3-process.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
int main(int argc, char *argv[]) { pid_t pid = -1;
printf(“Before fork(). variable pid = %d, getpid()=%d, getppid()=%d “, pid, getpid(), getppid());
fflush(stdout);
// TODO: Create a child process using fork() and store the return value in pid (~1 line)
if (pid < 0) {
fprintf(stderr, “fork() Failed”); exit(-1);
} else if (pid == 0) { // Child Process
printf(“Child Process. variable pid = %d, getpid()=%d, getppid()=%d
“, pid, getpid(), getppid());
// TODO: Use exec() family to replace the current process image with “sleep”, “20” (~1 line)
} else {
// TODO: Make the parent process wait for the child to complete (~1
line)
printf(“Parent Process. variable pid = %d, getpid()=%d, getppid()=% d “, pid, getpid(), getppid());
}
return 0;
} // main
COMP3230 Mini-lab 3 Page 3