The RealPort daemon controls communication between the RealPort driver module and your PortServers across the network. One daemon must remain in the background for each PortServer, maintaining the communication link. You should not need to start the daemon by hand. The dgrp_cfg_node program does this automatically. See Managing PortServers with Digi RealPort Manager or Managing PortServers with dgrp_cfg_node.
To determine whether any RealPort daemons are currently running on your system, as well as to determine which PortServer 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 which is installed with the driver package.