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

 int main(int argc, char* argv[])
 {
   int pid1, ppid1, pid2, ppid2;
   int status;

   pid1 = getpid();
   ppid1 = getppid();

   printf("Start\n");

   /* create a child process  */
   switch (fork())
   {
     case -1:/* error */
             perror("fork - can't create process");
             break;
     case 0 :/* child process */
             pid2 = getpid();
             ppid2 = getppid();
             printf("Process: %d, Parent: %d\n", pid2, ppid2);
             sleep(5);
             break;
     default:/* parent process */
             printf("Process: %d, Parent: %d\n", pid1, ppid1);
             wait(&status);
             printf("End (status = %d)\n", status);
   }
 }

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

 int main(int argc, char* argv[])
 {
   int fd, ppid;

   /* close standard output */
   close(1);

   /* open file */
   fd = open("results.txt", O_CREAT | O_WRONLY | O_APPEND, 0644);
   if (fd == -1)
   {
     perror("Error open file");
     exit(1);
   }

   /* create a child process  */
   if ((ppid = fork()) == 0)
   {
    /* execute ls command */
     execlp("ls", "ls", "-l", "-a", "-i", NULL);
   }

   waitpid(ppid, NULL, NULL);
 }