Operating System

fork command

Fork

fork - create a new process

fork

We use C program to create a new process. The program is as follows:

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

int main() {
  pid_t pid, mypid, myppid;
  pid = getpid();
  printf("Before fork: Process id is %d\n", pid);
  pid = fork();

  if (pid < 0) {
    perror("fork() failure\n");
    return 1;
  }

  // Child process
  if (pid == 0) {
    printf("This is child process\n");
    mypid = getpid();
    myppid = getppid();
    printf("Process id is %d and PPID is %d\n", mypid, myppid);
  } else { // Parent process
    sleep(2);
    printf("This is parent process\n");
    mypid = getpid();
    myppid = getppid();
    printf("Process id is %d and PPID is %d\n", mypid, myppid);
    printf("Newly created process id or child pid is %d\n", pid);
  }

  return 0;
}

To compile and run the program, use the following commands(dont copy the $ sign, it represents the terminal prompt):

$ gcc fork.c -o fork
$ ./fork

This will create a new process and print the process id of the parent and child process. The fork system call is used to create a new process.

Questions

What is the use of fork system call?

fork system call is used to create a new process.

What is the output of the program?

The program will print the process id of the parent and child process.

What is the return value of fork system call?

The return value of fork system call is the process ID of the child process.

What is the use of getpid and getppid functions?

getpid function is used to get the process ID of the current process and getppid function is used to get the parent process ID.

What is the use of sleep function?

sleep function is used to make the process sleep for a specified number of seconds.

What is the use of perror function?

perror function is used to print the error message to the standard error stream.

What is the use of pid_t data type?

pid_t data type is used to represent process IDs.