Question

What does it mean if(!fork())? I’m a little bit confused about it, I dont know when Im in parent and child process:

if(!fork())
{
  // is it child or parent process?
}else{
  // is it child or parent process?
}

Answer 1

From the fork(2) manpage:

Return Value

On success, the PID of the child process is returned in the parent,
and 0 is returned in the child. On failure, -1 is returned in the
parent, no child process is created, and errno is set appropriately.

Since fork() returns 0 to the child, the if clause tests if it’s a child:

if (!fork()) // same as: if (fork() == 0)
{
  // child
}else{
  // parent
}