My webbserver act as a torrentclient as well.

To start rtorrent in background I using the command screen to do this.

This is how I do:
In terminal type,

bash-4.2$ screen -dmS rtorrent rtorrent

Your have now started rtorrent in a screen named rtorrent, how to access is just type

bash-4.2$ screen -r rtorrent

and there you have it.
And to exit, hold on Ctrl and A release and then press D. Now your are out of rtorrent screen and it still running i background.