The 4 dates of a file on ext4
For a long time Unix/Linux filesystems maintained 3 dates for each file. Apparently the ext4 filesystem has a 4th. We can use the stat command to show these dates.
Create a file
$ echo hello > file.txt
$ stat file.txt
Access: 2024-07-05 16:03:28.377121409 +0300
Modify: 2024-07-05 16:03:28.377121409 +0300
Change: 2024-07-05 16:03:28.377121409 +0300
Birth: 2024-07-05 16:03:28.377121409 +0300
Changing the meta-data of the file updates the ctime field displayed as "Change" here:
$ chmod a+x file.txt
$ stat file.txt
Access: 2024-07-05 16:03:28.377121409 +0300
Modify: 2024-07-05 16:03:28.377121409 +0300
Change: 2024-07-05 16:04:02.922123687 +0300
Birth: 2024-07-05 16:03:28.377121409 +0300
Changing the content of the file, eg. adding more content will update the mtime field displayed as Modify" and the "ctime" or "Change" field:
$ echo world >> file.txt
$ stat file.txt
Access: 2024-07-05 16:03:28.377121409 +0300
Modify: 2024-07-05 16:04:50.697126837 +0300
Change: 2024-07-05 16:04:50.697126837 +0300
Birth: 2024-07-05 16:03:28.377121409 +0300
Reading the content of the file updates the atime field displayed as "Access".
$ cat file.txt
$ stat file.txt
Access: 2024-07-05 16:06:21.051132794 +0300
Modify: 2024-07-05 16:04:50.697126837 +0300
Change: 2024-07-05 16:04:50.697126837 +0300
Birth: 2024-07-05 16:03:28.377121409 +0300
Finally there is the touch command of Unix/Linux that does not change the content of the file, but updates all 3
timestams.
$ touch file.txt
$ stat file.txt
Access: 2024-07-05 16:09:02.075143411 +0300
Modify: 2024-07-05 16:09:02.075143411 +0300
Change: 2024-07-05 16:09:02.075143411 +0300
Birth: 2024-07-05 16:03:28.377121409 +0300
Update timestamps using Python
>>> file = "file.txt"
>>> os.utime(file)
$ stat file.txt
Access: 2024-07-05 16:11:08.352151736 +0300
Modify: 2024-07-05 16:11:08.352151736 +0300
Change: 2024-07-05 16:11:08.352151736 +0300
Birth: 2024-07-05 16:03:28.377121409 +0300
Get the modify time in Python
import os
print(os.path.getmtime("file.txt"))
1720185068.3521516
Showing the elapsed time since the file was modified
import os
import time
print(time.time() - os.path.getmtime("file.txt"))
137.15206933021545
