Let's say I want to see if my ftp server is online, how could I do this in a program. Also, what do you think would be the easiest least intrusive way.
Connect to the port of your FTP server to see if it is accepting connections.
If you want to go one step further you could send an ls command and check that you get a sensible response.
If you want to do it in Python you can use ftplib.