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

Maurice Volaski mvolaski at aecom.yu.edu
Thu Jun 25 18:29:46 UTC 2009

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.

Maurice Volaski, mvolaski at aecom.yu.edu
Computing Support, Rose F. Kennedy Center
Albert Einstein College of Medicine of Yeshiva University

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