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@ljrk @mcc

Haven't tested, but I believe that's been fixed since 2015. From the release notes for 8.30 (2018):

``` 'mv -n A B' no longer suffers from a race condition that can
overwrite a simultaneously-created B. This bug fix requires
platform support for the renameat2 or renameatx_np syscalls, found
in recent Linux and macOS kernels. As a side effect, 'mv -n A A'
now silently does nothing if A exists.
[bug introduced with coreutils-7.1]
```