Rsync : copying over timestamps only

Question

Currently I have two directories A/ and B/ which are identical in every respect, with the exception of the timestamps. Therefore if I run the command :

rsync --dry-run -crvv A/ B/

then all files are marked "uptodate", whereas the command :

rsync --dry-run -rvv A/ B/

shows that all files are to be copied over from A/ to B/.

My question is this : given that I know the files are identical (in respect to contents), then is there any way (via rsync or otherwise) to set the timestamps for files in B/ to be identical to the timestamps of the files in A/, without copying over all the files from A/ to B/ ?

Thanks

Answer 1

Well, you could certainly write a script that reads the timestamp from one side and then uses touch to set it on same file on the other side.

But that would likely take you much longer than simply letting rsync try to copy all the files. Very little data will actually be transferred (only block hashes if the files are truly identical). But the full contents of every file will have to be read on each side at the least. So of you are limited by disk bandwidth or IOPS it could take a while. But still probably less time than writing and testing a script to do it.

Answer 2

I think rsync is the right tool to make this but if you want some script to do this than someting this can give a good start.

You can get a file list with timestamps (acces times) like this:

find . -printf '"%p" %a\n' -type f > /tmp/times

And get the appropriate time update commands from it:

 while read line; do echo touch -a -d \"${line#* }\" ${line%% *}; done < /tmp/times

It isn't a complete script but a good start place!:)

Answer 3

The rsync manual: man rsync lists a -t and -N switch, they might be worth fiddling with.

Answer 4

Using --size-only will cause rsync to skip comparing file timestamps (and therefore file contents) if the sizes match. Combining this with --times will clone the timestamps across to the target tree.