[Q] What might cause modification dates to shift later by an hour?

Stephen Samuel (gmail) darkonc at gmail.com
Fri Jun 26 05:36:17 UTC 2009

Time zones are the culprit -- Specifically DST shifts.
If you check the absolute time stamp (which is GMT), it hasn't changed...
but the distance between you and GMT changed by one hour when the DST change
kicked in.
Nothing has gone wrong, unless your backup software works internally with TZ
shifted date stamps, in which
case it might get confused twice per yer.

On Thu, Jun 25, 2009 at 11:29 AM, Maurice Volaski <mvolaski at aecom.yu.edu>wrote:

> Recently, our backup software oddly decided to rebackup a good portion of
> our file server instead of just doing an incremental. When I examined
> various sets of presumably identical files, I discovered that the
> modification dates on these files were no longer the same. Many files were
> re-dated to exactly one hour later such that if a file had been modified on
> 3/24/04 at 2:24:53 PM, it's modification date had somehow been changed to
> 3/24/04 at 3:24:53 PM.
> A point to note that is that this server is actually two separate servers
> with independent storage mirrored by drbd. And it's possible that the first
> backup was done on one server and the second on the other. However, drbd
> mirrors the storage bit by bit, so it's hard to see how files on each of
> them could have different modification dates. Also, even if the time on the
> computers were different by an hour (they're current the same to the
> second), it's not clear how the modification dates could somehow get
> re-dated.
> It's also not clear what mechanism could have redated them. I've almost
> certainly run fsck on the affected filesystems. Would there ever be a
> circumstance when fsck might second guess a file's modification time and
> change it? e2fsck is currently 1.41.4, though I don't know if that's the
> version that I ran when I ran it.
> However, there seems to be a field in the backup software called status
> modification date and a lot of these affected files had their status
> modified around the same time, implying something did iterate over the files
> and do something to them.

Stephen Samuel http://www.bcgreen.com  Software, like love,
778-861-7641                              grows when you give it away
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