PDNS is normally launched by the init.d script but is actually a binary called pdns_server. This file is started by the start and monitor commands to the init.d script. Other commands are implemented using the controlsocket.
The controlsocket is the means to contact a running PDNS daemon, or as we now know, a running pdns_server. Over this sockets, instructions can be sent using the pdns_control program. Like the pdns_server, this program is normally accessed via the init.d script.
To communicate with PDNS over the controlsocket, the pdns_control command is used. The init.d script also calls pdns_control. The syntax is simple: pdns_control command arguments. Currently this is most useful for telling backends to rediscover domains or to force the transmission of notifications. See Section 12.3.