Question

Good daytime to all

I am confused with fork(). Does fork() forks child process or only parent?

please help on some examples

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

int main() {
  if (fork()) {
    fork();
    printf(" X\n");
  }
  return 0;
}

is this how i suppose to build the processes:

    parent
      |
   /    \
Parent  Child

so the output would be

  X X X

another example is

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

int main() {
  fork();
  fork();
  fork();

  printf(" X \n");

  return 0;
}

the graph would be like this?

                 Fork start
                    /     \
                Parent    Child        1st fork done output 2 of X
                /  \      /   \
              P     C    P    C        2nd fork done output 4 of X
            / \    / \  /\    /\
           P  C   P  C P  C  P  C      3rd fork done output 8 of X

another question how can I draw

if (fork() || fork() || fork())
  fork();

or

if (fork() && fork())
  fork();

I would be glad if someone correct me.

Answer 1

fork doesn’t “create parent and child process”, no. It creates a copy of the current process (the copy being the child and the current process being the parent). The distinction is done based on the fork return value.