Question

This question is a continuation of my question in another thread.Since the point of this question is slightly different,I thought I’d post it as a new question.

I experimented getting accessed time for some files in my linux machine(ubuntu lucid),using python .The idea is to have a function which goes through files in a particular directory,see if they have been accessed in the last 2 minutes,and print only those files which have not been accessed.

For accessing a file ,I defined a readfile() method

def readfile(fname):
    with open(fname) as f:
        ct = f.read()
        print 'read file at:',time.time()
        print 'length of file:',len(ct)

For convenience ,I defined some filenames

f1='/home/me/dev/misc/usedfiles/one.txt'
f2='/home/me/dev/misc/usedfiles/two.txt'
f3='/home/me/dev/misc/usedfiles/three.txt'
f4='/home/me/dev/misc/usedfiles/four.txt'

sothat calling readfile(f1) would access the file one.txt

I defined another function to go through the directory and print those files not accessed in last 2 minutes

def files_not_accessed():
    dirname = '/home/me/dev/misc/usedfiles'
    filenames = os.listdir(dirname)
    filenames = [os.path.join(dirname,filename) for filename in filenames]
    for filename in filenames:
        try:
            last_access = os.stat(filename).st_atime #secs since epoch
        except IOError:
            print 'could not get info about %s' % filename
        else:
            timediff =  time.time()-last_access
            print filename,'  last_access=',last_access
            print filename,'  timediff=',timediff
            if timediff > 2*60:
                print filename,'---older than 2 mts'
        print ''

Initially I ran the function files_not_accessed() and it gave the following output

/home/me/dev/misc/usedfiles/two.txt   last_access= 1341459500.0
/home/me/dev/misc/usedfiles/two.txt   timediff= 11668.9905779
/home/me/dev/misc/usedfiles/two.txt ---older than 2 mts

/home/me/dev/misc/usedfiles/one.txt   last_access= 1341460126.0
/home/me/dev/misc/usedfiles/one.txt   timediff= 11042.990674
/home/me/dev/misc/usedfiles/one.txt ---older than 2 mts

/home/me/dev/misc/usedfiles/three.txt   last_access= 1341459504.0
/home/me/dev/misc/usedfiles/three.txt   timediff= 11664.99072
/home/me/dev/misc/usedfiles/three.txt ---older than 2 mts

/home/me/dev/misc/usedfiles/four.txt   last_access= 1341459510.0
/home/me/dev/misc/usedfiles/four.txt   timediff= 11658.990757
/home/me/dev/misc/usedfiles/four.txt ---older than 2 mts

Now,I ran the readfile(f1) function to read the file one.txt

read file at: 1341471195.88
length of file: 47293

As you can see from output of files_not_accessed() function,the file one.txt was last accessed at 1341460126.0 ,and now it is again read at 1341471195.88 by readfile(f1)

And (immediately)ran the files_not_accessed() function and expected that ,it would not output the file one.txt since it was recently accessed.I expected its last_access time to be 1341471195.88

Strangely,I am again getting the previous output

/home/me/dev/misc/usedfiles/two.txt   last_access= 1341459500.0
/home/me/dev/misc/usedfiles/two.txt   timediff= 11715.1272521
/home/me/dev/misc/usedfiles/two.txt ---older than 2 mts

/home/me/dev/misc/usedfiles/one.txt   last_access= 1341460126.0
/home/me/dev/misc/usedfiles/one.txt   timediff= 11089.1273479
/home/me/dev/misc/usedfiles/one.txt ---older than 2 mts

/home/me/dev/misc/usedfiles/three.txt   last_access= 1341459504.0
/home/me/dev/misc/usedfiles/three.txt   timediff= 11711.1273921
/home/me/dev/misc/usedfiles/three.txt ---older than 2 mts

/home/me/dev/misc/usedfiles/four.txt   last_access= 1341459510.0
/home/me/dev/misc/usedfiles/four.txt   timediff= 11705.1274359
/home/me/dev/misc/usedfiles/four.txt ---older than 2 mts

I cannot understand why the file one.txt has last_access= 1341460126.0 instead of the expected 1341471195.88

Any idea why this happens?

Answer 1

Ubuntu lucid by default mounts filesystems with “relatime”. If you need strict atimes, you need to mount with “strictatime” (at a performance cost).