exit

#include "stdlib.h"
#include "stdio.h"
#include "unistd.h"

int main() {
    exit(123);
    printf("hello\n");
    return 123;
}

---
fork

int main() {
    fork();
    fork();
    while(1) {sleep(1);}
}

---
syscall CreateProcess on Windows:

BOOL CreateProcess(
  name,
  commandline,
  security_attr,
  thr_security_attr,
  inheritance?,
  other flags,
  new_env,
  curr_dir_name,
  ...)