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

If you know the files are identical, then why must you go out of your way to not copy over them to get the date/time stamp you require? — Tim, Dec 28 '11 at 16:54
@Tim Today I just spent an entire day migrating over 300 GB of data over a slow network. When sftp finished, it was already midnight. It was only during my final check using `ls` and `stat` that I realized I lost all the timestamps (forgot to use `sftp -p`!) They are important for me to identify the history of the files. I was saved by the answer, `rsync -vrt --size-only` only took 60 seconds to run! — 比尔盖子, Dec 20 '20 at 19:30

score 95 · Answer 1 · edited Nov 21 '12 at 14:06

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Using -t (preserve timestamps) and --size-only will only compare files on size. If the size matches, rsync will not copy the file but since -t is specified, it will update the timestamp on the destination file without recopying it.

Make sure to not use -u (update) as this will skip files that already exist and completely skip updating the timestamp.

I had the problem of originally not using rsync to copy a bunch of files to a new drive, and therefore the timestamps were updated to current time. I used the command below to sync everything correctly in a decent amount of time:

rsync -vrt --size-only /src /dest

edited Nov 21 '12 at 14:06

Scott Pack

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answered Nov 21 '12 at 13:43

Grant Pannell

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I also suggest adding `--existing` to prevent accidental copies of new files. – leden Mar 26 '16 at 23:15
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The flag `--archive` (or `-a`) includes `-r`, `-t` and more :) – Dor Mar 19 '17 at 14:15
prefer this answer since rsync works over remotes also – troseman Aug 19 '20 at 21:11

score 8 · Answer 2 · answered Mar 30 '12 at 13:58

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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.

answered Mar 30 '12 at 13:58

user115916

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Adding --checksum on top of that should take care of files with the same size but different contents. – user1602 Sep 21 '21 at 08:04

score 3 · Answer 3 · answered Dec 28 '11 at 17:05

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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!:)

answered Dec 28 '11 at 17:05

Stone

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Thanks. I think I will probably stick with Rsync for the moment, but I will definitely go out to the web and learn the different components of your script, as it may be useful in the future. – artella Dec 28 '11 at 18:38
That seemed to be exactly my solution! I want to preserve the times while adding some meta data to my music library. However, apparently it can't handle spaces in file names ): – Burcardo Jul 15 '16 at 11:52

knorke · Answer 4 · 2017-09-29T14:41:50.513

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Use the source (e.g. /path/to/source) directory as reference for the touch command. Just cd to your target directory and do

find -type f -exec touch -r /path/to/source/{} {} \;

You cannot copy sub-second timestamps with rsync (yet).

This also works for directories and pseudo files (just remove or change the -type f)

edited Sep 29 '17 at 14:41

answered Sep 29 '17 at 14:36

knorke

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This was useful for me as I needed atime to be copied. I noticed it does not copy ctime, which was ok in my case. – snapfractalpop Mar 24 '18 at 07:44
Just read the manpage of 'touch'. You can set atime and mtime both with this command. – knorke Mar 27 '18 at 12:25
Yes, I know you can use ```touch -ar``` but that still does not change the ctime. I suppose that's rarely desired. – snapfractalpop Mar 27 '18 at 17:02
Ah, I see the problem now. Thanks. Yes, ctime is hard to change and I don't know why. – knorke Mar 28 '18 at 08:10

score 1 · Answer 5 · answered Dec 28 '11 at 16:53

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.

Thanks, I was unaware of this feature of rsync (it is discussed in wikipedia too). — artella, Dec 28 '11 at 18:36

score 0 · Answer 6 · answered Jul 22 '16 at 08:19

For people like me who intend to modify the files and want to retain the original timestamp (e.g. you update the meta tags of your music library).

It's based on the solution provided by Stone. However, here about the modification time and a working script to restore the timestamps. FIRST do step one, then start working with your files.

Preserve old timestamps. It operates from the current directory, excludes all hidden files, and saves it to the temporary file in /tmp/files. You can always change parameters, but better stay with -printf '"%t" "%p"\n' since the later touch command utilizes that.

find . ! -iname ".*" -printf '"%t" "%p"\n' -type f > /tmp/files
Modify your files as much as you like
now create a file that helps you restoring the timestamps:

while read line; do echo touch -a -d $line >> job.sh; done < /tmp/times
And finally apply the old dates to the modified files

sh job.sh

Caveat: works for files with name spacing, special characters, but for instance no files with a $ sign in it.

To avoid (some) problems with backslashes in your file names, use `read -r line`. Well, _always_ use `read` with `-r`. Besides, you can avoid opening `job.sh` for each file. Just put the redirection at the end of the command: `while read -r path; do echo touch -a -d $path ; done < /tmp/times > job.sh` — hagello, Feb 19 '18 at 12:21
2nd Caveat: This script does not transfer the timestamps the directories. (Well, the OP did not ask for it.) — hagello, Feb 19 '18 at 12:22

score 0 · Answer 7 · edited Jun 11 '20 at 10:02

Best way to copy only timestamp on Windows :

for files : use "touch" command, as described here https://superuser.com/questions/491980/copying-the-timestamp-from-one-file-to-another-using-powershell-2-0-on-windows :

To copy any file's last created/modified/accessed time stamp to another, you can use:

touch /c /m /a /r SourceFile DestFile

(This version of Touch is part of the Win32 Console ToolBox http://www.stevemiller.net/apps/ )

for directories : use the "robocopy" command, with the GUI shell http://www.turnssoft.com/robocop-robocopy.html

Robocopy "SOURCE_DIRECTORY" "DESTINATION_DIRECTORY" /E /COPYALL /DCOPY:DAT /XF . /R:10 /W:5 /V /ETA

score -1 · Answer 8 · answered Dec 28 '11 at 16:57

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

answered Dec 28 '11 at 16:57

Tim

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I couldn't see`-N`. Why do you recommend these anyway? – Tom Hale Oct 05 '19 at 15:05
@TomHale `-N` (`--crtimes`) indeed exists, but only in newer versions of rsync. But yeah, it's almost useless for this scenario - it means "preserve create times (newness)" - as far as I know, "file create time" is never implemented by most Unix file systems, ext4 was the only major file system that included it in the specification, but still, is never actually implemented in the Linux kernel. – 比尔盖子 Dec 23 '20 at 15:34

Rsync : copying over timestamps only

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