You've previously mentioned that the client uploads the file via ftp, which means you must be running an ftp server on the Mac that's running the LabVIEW application. While there is a TCP Listen VI I do not believe that it will allow you to act on a connection if some other process is also listening and accepting connections on that port, such as your ftp server. Even if it did, you wouldn't know when the file transfer is completed. Keep in mind that, as mentioned previously in your related thread, these functions are meant to operate at a network layer that doesn't handle "sniffing". For that you need to use something like Ethereal, or its Pcap library.
You previously mentioned in the other thread (see how having all the information in one place helps) you could set up the Linux side to ping the Mac. Instead of pinging you could simply perform a "regular" TCP connection. This will allow you to use the TCP Listen VI so the Mac knows there's a file available.
