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sr #110388: tar --diff complains about mtime, but mtime's match

Submitter:  None
Submitted:  Wed 02 Dec 2020 05:52:25 PM UTC
Category:  None Priority:  5 - Normal
Severity:  5 - Blocker Status:  None
Privacy:  Public Assigned to:  None
Originator Email:  -email is unavailable- Open/Closed:  Open
Operating System:  GNU/Linux
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Tue 08 Dec 2020 03:52:37 PM UTC, comment #2: 

I'm pretty convinced now: GNU tar --diff likes GNU format tar input, but does not like pax format tar input.

I did a tar --diff of a multi-terabyte filesystem and got only expected errors with gnu format.  Practically the same command with pax format quickly descends into a mess of spurious mtime detections.

Dan Stromberg <strombrg>
Wed 02 Dec 2020 11:37:46 PM UTC, comment #1: 

original submission:

> Hi folks.


> $ tar --diff < /tmp/replication.tar
> digital-assets/movie/Schindlers List/Side A/handbrake/Disc ls.txt: Mod time differs

This used to work better I think.

The python code is open()'ing the tar archive with:, mode="w|", bufsize=1048576, encoding='UTF-8')

...which I believe will use the default tar format.  The default format was GNU tar format until CPython 3.8, and became PAX format in 3.8 and up.

This suggests that perhaps GNU tar --diff does not like PAX format.

> Thanks for GNU tar.  It's great!

Wed 02 Dec 2020 05:52:25 PM UTC, original submission:  

Hi folks.

I'm attempting to verify a large tar backup of an entire filesystem.

I'm getting many mtime differences that do not make a lot of sense.

The tar archive was created using python's tarfile module, and I'm attempting to verify the tarball+filesystem using GNU tar --diff.

I've tried GNU tar 1.32 as well as a build of the 'master' branch cloned yesterday, 2020-12-01.

The error looks like:

$ tar --verbose --list --file=/tmp/replication.tar
-rw-rw-r-- dstromberg/dstromberg 874 2020-09-14 23:00 digital-assets/movie/Schindlers List/Side A/handbrake/Disc ls.txt

$ ls -l /digital-assets/movie/Schindlers\ List/Side\ A/handbrake/Disc\ ls.txt
-rw-rw-r-- 1 dstromberg dstromberg 874 Sep 14 23:00 '/digital-assets/movie/Schindlers List/Side A/handbrake/Disc ls.txt'

$ tar --diff < /tmp/replication.tar
digital-assets/movie/Schindlers List/Side A/handbrake/Disc ls.txt: Mod time differs

I'm attaching an example tar archive (replication.tar) that exhibits the problem. It contains a single small text file.

Thanks for GNU tar.  It's great!



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file #50377:  replication.tar added by None (10KiB - application/x-tar)


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    Date Changed by Updated Field Previous Value => Replaced by
    2020-12-02 None Attached File- Added replication.tar, #50377

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