How can I get the manpage-like help information of a RPC service?

$ rpcinfo program version netid address service owner 100000 4 tcp6 ::.0.111 portmapper superuser 100000 3 tcp6 ::.0.111 portmapper superuser 100000 4 udp6 ::.0.111 portmapper superuser 100000 3 udp6 ::.0.111 portmapper superuser 100000 4 tcp 0.0.0.0.0.111 portmapper superuser 100000 3 tcp 0.0.0.0.0.111 portmapper superuser 100000 2 tcp 0.0.0.0.0.111 portmapper superuser 100000 4 udp 0.0.0.0.0.111 portmapper superuser 100000 3 udp 0.0.0.0.0.111 portmapper superuser 100000 2 udp 0.0.0.0.0.111 portmapper superuser 100000 4 local /run/rpcbind.sock portmapper superuser 100000 3 local /run/rpcbind.sock portmapper superuser How can I get the manpage-like help information of a service? $ man portmapper No manual entry for portmapper How can I find out the actual program/executable/command name for a RPC service? For example portmapper isn't a command name for portmapper RPC service, otherwise man portmapper would likely works. Thanks.