mv is relying on operation "similar" to rename() defined by POSIX which specifies that it should be atomic.
So, the assumption "On Unix, mv is atomic operation" is not true. If your underlying FS is fully POSIX-compliant, mv will be an atomic operation.
I think it's important to stress it because there are some distributed FS that might even try to be POSIX-compliant but which are not guaranteeing atomic rename's and therefore this trick would not work well.
Comments
mv is relying on operation "similar" to rename() defined by POSIX which specifies that it should be atomic.
So, the assumption "On Unix, mv is atomic operation" is not true. If your underlying FS is fully POSIX-compliant, mv will be an atomic operation.
I think it's important to stress it because there are some distributed FS that might even try to be POSIX-compliant but which are not guaranteeing atomic rename's and therefore this trick would not work well.