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