- Linux machine doesn't have the same user in system, what Sync should do? If you will add the 3-rd Linux box, what should be uid for the file? It doesn't matter, you should work with uid. And file can have a unknown UID on a Linux server this shouldn't matter - You have the uid but don't have permission to change it. Indeed daemon should run with sufficient rights to change UIDs... Else you set the ones from the user running the daemon as default - You changed uid on one Linux machine, should it be propagated to other? Why not ? This is still a file modification. As for mixed OS cases, there should be a way to detect it and use a safe default scenario... Like you push a file from Linux to Windows, you don't worry about keeping specific rights... Oh and for the use case: I want to use p2p transfer to sync files around the globe between servers. End user have no concerns what is used to synchronize, but the rights files have been pushed with must be kept between servers.