Process Creation Using fork() in CentOS 7

Program 1: Print “Hello World”

To write a C program that prints Hello World on the terminal.

#include <stdio.h>

int main() {
    printf("Hello World\n");
    return 0;
}

Output

Hello World

Program 2: Print “Hello World” with fork()

To write a C program that prints Hello World using fork() so that both the parent and the child process print the line.

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

int main() {
    fork();
    printf("Hello World\n");
    return 0;
}

Output

Hello World
Hello World

Program 3: Display PID and PPID of Parent and Child

To write a C program using fork() and <sys/types.h> that creates a child process and displays the PID and PPID of both the parent and the child processes.

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>

int main() {
    pid_t pid;

    pid = fork();

    if (pid < 0) {
        printf("Fork failed\n");
        return 1;
    } else if (pid == 0) {
        printf("Child process : PID = %d, PPID = %d\n", getpid(), getppid());
    } else {
        printf("Parent process: PID = %d, PPID = %d\n", getpid(), getppid());
    }

    return 0;
}

Output

Parent process: PID = 3421, PPID = 2890
Child process : PID = 3422, PPID = 3421

Program 4: Parent and Child Behavior with sleep()

To write a C program using fork() and <sys/types.h> that adds sleep() in the child process and observe the parent and child process behavior during execution.

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>

int main() {
    pid_t pid;

    pid = fork();

    if (pid < 0) {
        printf("Fork failed\n");
        return 1;
    } else if (pid == 0) {
        sleep(2);
        printf("Child process : PID = %d, PPID = %d\n", getpid(), getppid());
    } else {
        printf("Parent process: PID = %d, PPID = %d\n", getpid(), getppid());
    }

    return 0;
}

Output

Parent process: PID = 3510, PPID = 2890
Child process : PID = 3511, PPID = 1

Result

C programs using fork() were written and executed successfully. The PID and PPID of parent and child processes were displayed, and the effect of sleep() on parent–child behavior was observed.