When a program first becomes available on a machine, it registers itself with the local port map program. The program passes its program number prog, version number vers, transport protocol number prot, and the port port on which it receives service requests. The procedure refuses to establish a mapping if one already exists for the specified port and it is bound. If the mapping exists and the port is not bound, portmap unregisters the port and performs the requested mapping. The PMAPPROC_SET procedure returns TRUE if the procedure successfully established the mapping and FALSE otherwise. See also the pmap_set() function in the rpc_soc(3NSL) man page.