Get last access time of the file?

Question

I want to get when the file accessed last time, I tried following code:

import os, time

os.system("python test.py")
print os.stat('test.py').st_atime

time.sleep(60)

os.system("python test.py")
print os.stat('test.py').st_atime

But each time the output is same as follows :

1358489344.72
1358489344.72

I was expecting a difference in output before delay and after delay. also output is same wen I run the code every time.

what could be wrong?

Answer 1

The field st_atime is changed by file accesses, for example, by execve(2), mknod(2), pipe(2), utime(2) and read(2) (of more than zero bytes). Other routines, like mmap(2), may or may not update st_atime.

While you run "python test.py", it won't call read(2), instead it would call mmap(2). That's why the access time didn't be udpated.

Here is output of "strace python test.py"

open("test.py", O_RDONLY)               = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=36, ...}) = 0
mmap(NULL, 65536, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x2ad626cdd000

Answer 2

Maybe the filesystem is mounted with noatime option

noatime
     Do not update inode access times on this filesystem 
     (e.g, for faster access on the news spool to speed up news servers).

check your /etc/fstab

More about access time https://superuser.com/questions/464290/why-is-cat-not-changing-the-access-time