The RealPort daemon (process) controls communication between the RealPort driver module and your Digi Devices across the network. One daemon must remain in the background for each Digi Device, maintaining the communication link. You should not need to start the daemon by hand. The dgrp_cfg_node program does this automatically.
However, to determine whether any RealPort daemons are currently running on your system, as well as to determine which Digi Device each daemon is communicating with, you can execute the following command:
ps ax | grep drpd
For more information about the RealPort daemon, see the drpd man page that is installed with the driver package.