A problem about the code example in OSTEP - memory

Question

In OSTEP(Operating Systems: Three Easy Pieces), the author offers a simple c program code to show how OS Virtualizing it's Memory
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include "common.h"
int
main(int argc, char *argv[])
{
int *p = malloc(sizeof(int));
//assert(p != NULL);
printf("(%d) address pointed to by p: %p\n", getpid(), p);
*p = 0;
while (1) {
sleep(1);
*p = *p + 1;
printf("(%d) p: %d\n", getpid(), *p);
}
return 0;
}
the book says that because of the virtualizing process the outcome shuld be:
prompt> ./mem &; ./mem &
[1]24113
[2]24114
(24113) address pointed to by p: 0x200000 (24114) address pointed to
(24114) address pointed to by p: 0x200000
(24113) p: 1
(24114) p: 1
(24114) p: 2
(24113) p: 2
(24113) p: 3
(24114) p: 3
(24113) p: 4
(24114) p: 4
the author explains why this happens:
Now, we again run multiple instances of this same program to see what
happens (Figure 2.4). We see from the example that each running
program has allocated memory at the same address (0x200000), and yet
each seems to be updating the value at 0x200000 independently! It is
as if each running program has its own private memory, instead of
sharing the same physical memory with other running programs 5 .
...
but in my computer(ubuntu) the outcome is:
it makes me feel really confuse...

Answer 1

In an attempt to frustrate malware, ubuntu is configured to load programs at pseudo-random addresses; so when your program is loaded into memory, the OS choose some base address, then loads the program relative to that. This is widely known as Address Space Layout Randomization (ASLR).
There is a kernel option: /proc/sys/kernel/randomize_va_space which you can set to zero to disable this feature. Note that if this offers any security, by disabling it you are losing that security feature.
as root:
$ oldval = $(cat /proc/sys/kernel/randomize_va_space)
$ echo 0 >> /proc/sys/kernel/randomize_va_space
then, after you have run your examples as somebody other than root, return to this session and:
$ echo "$oldval" >> /proc/sys/kernel/randomize_va_space