This is probably very basic, but I am totally new to Linux.

I am tryng to sync a usb data stick to Documents directory using:
rsync -auvhi /media/2C24-DC8F/ ~/Documents/

I then sync the other way [rsync -auvhin ~/Documents/ /media/2C24-DC8F/] expecting little or nothing, but end up with a massive list. A typical item being: .f.....g... boats/Siskiwit-Bay-SOF.pdf

My very limited undertanding makes me think that the group has changed during the first operation despite using -a, which I thought preserved the group.

Basically I am trying to keep /Documents and my data stick identical as I move between computers. Any suggestions?

Thanks

What does "ls -l" show for the two files?

It's a bit more complex than just "basic." The USB flash drive is probably formatted FAT32, which cannot preserve all of the Linux permissions. On Linux you cannot give a file a GID for a group you are not a member of, so the GIDs may not match even on files you just copied. When rsync-ing to/from a USB flash drive, I always include the options "--no-g" and "--modify-window=3602". The "--no-g" will ignore GIDs, and the "--modify-window" avoids issues with time resolution (2 seconds on FAT32) and changes in Daylight Savings Time status (FAT32 uses local time in its time stamps).

Documents: -rwxr-xr-x 1 robert robert 2860731 Sep 19 18:22 Siskiwit-Bay-SOF.pdf
Flash drive: -rwxr-xr-x 1 root root 2860731 Sep 19 18:22 Siskiwit-Bay-SOF.pdf

It is FAT, but I also use an ex-FAT disc so that I can have a file >4Gb; I haven't tried rsync on it yet.

Your suggestions seem to work a treat. Thanks for the help.