So far, the examples we have worked with have been run on the same workstation or host. However, as we gain expertise with interprocess communication techniques, it becomes evident that there will be many occasions when we will want to communicate with processes that may reside on different workstations. These workstations might be on our own local area network or part of a larger wide area network. In a UNIX-based, networked computing setting, there are several ways that communications of this nature can be implemented. This chapter examines the techniques involved with remote procedure calls (RPC).  As a programming interface, RPCs are designed to resemble standard, local procedure (function) calls. The client process (the process making the request) invokes a local procedure commonly known as a client stub that contains the network communication details and the actual RPC. The server process (the process performing the request) has a similar server stub , which contains its network communication details. Neither the client nor the server needs to be aware of the underlying network transport protocols. The programming stubs are usually created using a protocol compiler, such as Sun Microsystems rpcgen . This chapter is based on Sun's RPC implementation as ported to Linux. The protocol compiler is passed a protocol definition file written in a C-like language. For rpcgen , the language used is called RPC language. The protocol definition file contains a definition of the remote procedure, its parameters with data types, and its return data type.
 The word remote in RPC is somewhat misleading. RPCs can also be used by processes residing on the same host (indeed, this approach is often used when debugging routines that contain RPCs).
When the client invokes an RPC (generates a request), the client waits for the server to reply. Since the client must wait for a response, several coordination issues are of concern:
Figure 9.1. An RPC clientserver communications overview.
We will find that, while hidden from the casual user , RPC uses socket-based communication. The details of socket-based communication are covered in Chapter 10, "Sockets."
At a system level, the rpcinfo command can be used to direct the system to display all of the currently registered RPC services. When the -p flag is passed to rpcinfo , the services for the current host are displayed. The rpcinfo command is often located in /usr/sbin . If this is the case on your system, /usr/sbin should be part of the search path (so you will not have to fully qualify the path for each invocation). Some versions of rpcinfo require the host name to be specified. If you do not know the host name , the hostname command will display the name of the host upon which you are working.
Programs and Processes
Remote Procedure Calls
Appendix A. Using Linux Manual Pages
Appendix B. UNIX Error Messages
Appendix C. RPC Syntax Diagrams
Appendix D. Profiling Programs