rsync minor glitch
 

I always use rsync to sync files on a portable drive and the internal drive.

Usually I create or download files to the portable drive and then
use rsync to help to sync the two drives.

Imagine I connect the portable drive to a linux system for the first time,
work on the data, and
then I sync the data, then disconnect it from the linux system since I need to shutdown the
machine.

Upon reboot, I connect the portable drive to linux again and then do rsync
just to make sure that no files need to synced.

However, I find that from time to time that the time stamp of the identical files on the portable drive and that on the internal drive
changes by just a little bit and this upsets rsync and trigger it to sync
it again.

Luckily, the time stamp will not change upon the second rysync.
Else rsync is going to work very hard as I accumulate more and more data
on the internal drive.

The following shows a typical change:

The GUI diff program "meld" is able to put a little red do tell the diff.

Is there a way to solve this weird feature ?

probably you missed rsync has a feature to copy not only the file but its attributes also (like permissions, ownership and times).
to give more help we need to know how do you invoke rsync

FAT-based file systems can only record time to a resolution of 2 seconds, and such a timestamp can never match one with an odd number of seconds. rsync has a "--modify-window=NUM" option to allow small mtime differences to be ignored. You can use "--modify-window=2" to get around the odd/even problem, but you might need to use "--modify-window=3602" to avoid issues with DST time changes.

rknichols:

Bingo. That's exactly what I was looking for.

For now I am using modify-window=1 because rysnc manuals says:

Of course, --modify-window=2 will work too.

Thanks!