Tiến trình, PID, và /proc

  Tien trinh (mot khong gian dia chi rieng)
  +-------------------------------------------+
  |  ma lenh   (.text)     chi doc            |
  |  du lieu   (.data .bss) bien toan cuc     |
  |  heap                  malloc lon len ->  |
  |     ...                                   |
  |  <- ngan xep lon xuong  bien cuc bo       |
  +-------------------------------------------+
  |  bang mo ta tep: 0 stdin, 1 stdout, ...   |
  +-------------------------------------------+

/* Moi tien trinh co bang mo ta tep RIENG va khong gian dia chi
   RIENG. Hai tien trinh cung chay mot chuong trinh van la hai
   khong gian dia chi tach biet: sua bien trong cai nay khong
   anh huong cai kia. Do la khac biet co ban voi luong (Chuong 45),
   noi cac luong CHIA SE khong gian dia chi. */

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

int main(void) {
    pid_t pid  = getpid();      /* PID cua CHINH tien trinh nay */
    pid_t ppid = getppid();     /* PID cua tien trinh CHA */
    uid_t uid  = getuid();      /* ID nguoi dung so huu */

    printf("PID  = %d\n", pid);
    printf("PPID = %d\n", ppid);
    printf("UID  = %d\n", uid);
    return 0;
}