Rsync temporary file extension

Question

I am having difficulties finding how Rsync "chooses" the extension for the temporary file created while copying the file if I don't use the --inplace option.

Example : I want to copy sourceDirectory/myFile.txt into targetDirectory/ with Rsync.

While copying myFile.txt into targetDirectory/ Rsync will create a file named .myFile.txt.W4zvLi in targetDirectory/.

Then Rsync will rename .myFile.txt.W4zvLi into myFile.txt.

The question is how why Rsync uses the W4zvLi extension and why it seems to change each time I execute the Rsync program?

score 5 · Accepted Answer · answered Nov 07 '16 at 15:01

5

rsync uses the mktemp(3) POSIX function to generate a unique temporary file name. You pass a template string to the mktemp function, and it will return a file name with any X characters in the template replaced by a random character.

In particular, rsync passes .XXXXXX to mktemp. If you want to try it out from the command line you can use the mktemp(1) binary like so:

mktemp -u "/tmp/foo.XXXXXX"

answered Nov 07 '16 at 15:01

remmy

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Exactly what I was searching for – Jean-Paul Goodwin Nov 07 '16 at 15:12

score 0 · Answer 2 · answered Nov 07 '16 at 14:03

0

man rsync:

Beginning with rsync 3.1.1, the  temp-file  names  inside
              the specified DIR will not be prefixed with an extra dot (though
              they will still have a random suffix added).

answered Nov 07 '16 at 14:03

Ipor Sircer

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Explaining that the extension is chosen randomly might be a good idea. – terdon Nov 07 '16 at 14:07
Any clue about how the "random" suffix is calculated? – Jean-Paul Goodwin Nov 07 '16 at 14:08
The clue is in the source of rsync and kernel. – Ipor Sircer Nov 07 '16 at 14:12
The man quote refers to the specific case when temp files are created in a temp-dir specifed by the -T --temp-dir option. The default behavior seems to be unchanged in 3.1.1: temporary files starts with a dot in the same directory as the target file. – Hontvári Levente May 06 '20 at 08:48

Rsync temporary file extension

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