I don't know how it works on non-Unix systems, but on Unix,
the owner will be the EUID of the process. That is, if the
process at the moment of the mkdir has root priviledges, the
new directory will be owned by root. Otherwise, it will be
owned by whichever user the process was running as.
This is indeed something that has nothing to do with Perl,
but all with the OS. It's unclear to me what you mean by
"server". (Disk server? FTP server? Mail server? NFS server?
NIS server? Application server? Database server? Jumpstart
server? Media server? Quake server?) Not that that is relevant. Some, insecure, OSses allow you to "give away" files, but more secure OSses will not allow you to determine
who owns files or directories.