I wonder if anyone can help me with this. I just moved an external USB
disk drive to a new computer where amongst other things I want to use it
for scheduled backup - using a script I wrote which calls rsync, and
which has worked successfully so far on the previous machine (I know
there are backup programs available, but I'd rather do it my way).

Anyway I've found that my routine now creates the folder structure, but
doesn't copy any of the files into it. For every file I'm getting
messages like "failed to set times: operation not permitted". The script
does successfully delete the backup-before-last ("/oldbu"), and renames
the last backup to "/oldbu" - which kind of suggests it's not a simple
permissions issue doesn't it?

Nautilus shows that root is the owner of the disk.
gksudo nautilus offers to let me change the owner, but after half a
second reverts it back to root again.
sudo chown at a command line went through and set the owner of every
folder and file to my user name, but when I looked in nautilus it was
back to root again.

Running the rsync command on its own, with sudo preceding it, does work
- so maybe it is permissions after all? However having to enter the
password rather defeats the object of an automated backup.

Any advice please? I'm running 12.04