File Modified Time Fractional Seconds? (Manjaro-Plasma, EXT4 on SSD)

[robbie-hatley]

I noticed in the docs for Perl’s “Time::HiRes” module that it includes a nanosecond-resolution version of “lstat”, so I could include that in my Perl scripts; however, it would do nothing if that information is not actually present in the directories being read. So my question is, on an up-to-date Manjaro-Plasma system, using an EXT4 file system on an SSD, how does the OS store the “seconds” part of “file modified time”? Is it floating-point, integer-plus-fraction, integer-only, or what?

[fasto]

The ext4 file system does support nanosecond resolution on stored times if the inodes are big enough to support the extended time information (256 bytes or larger).

• https://stackoverflow.com/a/14393315

You can check the inode size of your system with the following command:

sudo tune2fs -l /dev/yourpartitionname | grep "Inode size"

[Nachlese]

… just on very first impression upon reading:

a nanosecond is a very tiny amount of time
I’d think that a “normal” system timer could not provide that resolution.

If that is so - the information would not be present (down to that resolution).

That would not be Plasma specific - but due to what the underlying OS (or the hardware) is capable of doing.

ps:
@fasto seems to have actual information - instead of my conjecture and doubt

[robbie-hatley]

Ok, let me see if that information is present in an “ls --full-time” printout of a collection of scenic photos:

2020-08-26 06:33:06.000000000 -0700
2020-11-26 19:48:23.000000000 -0800
2021-12-08 17:17:59.000000000 -0800
2022-10-27 12:57:39.409183409 -0700
2022-10-27 12:57:39.425850077 -0700
2022-10-27 12:57:39.445850077 -0700
2020-06-13 19:18:44.000000000 -0700
2022-10-27 12:57:39.469183412 -0700
2022-10-27 12:57:39.512516747 -0700

Interesting! It seems that yes, this system is storing file-mod times to the nearest nanosecond, but roughly half of these files do not have that information. I suspect it’s because these files are from all different sources, and some of those sources did not include fractional seconds on mod times.

%echo “Hello!” > Fred.txt
%ls --full-time Fred.txt
-rw-rw-r-- 1 aragorn aragorn 6 2023-03-09 13:06:10.584676566 -0800 Fred.txt

So, it appears that yes, Manjaro stores that info; but no, not all files are going to have that info, depending on their provenance.