vfork() gives "Segmentation fault (core dumped)" after code is executed

Question

Hi,

I have tried to execute a simple example of vfork() to understand its working.

Issue:
The code completed execution as expected but terminates with a "Segmentation fault (core dumped)" error.
I have read that behavior of vfork() is quite unpredictable.

Can someone explain me where did I go wrong?

Code:

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
int main()
{
int pid = vfork(); //creating the child process
if (pid == 0) //if this is a child process
{
printf("\nParent process is paused...");
printf("\nChild process started...\n");
}
else//parent process execution
{
printf("\nParent process resumed...\n");
}
return 0;
}

Output:

shweta@ubuntu:~$ ./a.out

Parent process is paused...
Child process started...

Parent process resumed...
Segmentation fault (core dumped)

shweta@ubuntu:~$

Answer 1

It is because returning from the function where vfork() is called or calling any other function before successfully calling *_exit()* or one of the *exec()* family of functions leads to undefined behaviour.

You can see this in the manpage of vfork() 👇
https://man7.org/linux/man-pages/man2/vfork.2.html

Answer 2

Part of your problem is that the parent process is NOT paused. You need to wait on the child process to complete before exiting.