UNIX system administrators need to be aware of one other important class of network services, based on Sun Microsystem's (RPC) Remote Procedure Call protocol.
The RPC protocol allows processes to make subroutine calls on one machine that are executed by processes on remote machines.
RPC is used by many important network services, especially the Network File System (NFS)
and NIS/NIS+ (the Network Information Systems)
NFS: Network File System (NFS) is a Unix-based file system that allows remote access to shared disk resources.
Network Information Service (NIS): NIS is Sun Microsystems's Yellow Pages (yp) client-server protocol for distributing system
configuration data such as user and host names between computers on a network.
The most important aspect of the RPC protocol that a UNIX system administrator needs to understand is the role of the portmapper process (also
Services available using RPC do not use well-defined port numbers. Instead, a server process using RPC registers itself with a special
process that functions as a directory. This process used to be called the portmapper (it mapped RPC requests to port numbers) but now tends to
have the less informative name of rpcbind. When a client needs to contact a particular RPC service, it first asks the portmapper process which
port it should contact to find the desired service. The portmapper is the only RPC process with a well-known port number (111).
One important consequence of this arrangement is that if for some reason the portmapper process is not running, many important system
functions will crash. Error messages that mention program not registered usually refer to some problem with the portmapper
process, or another RPC-related problem.
In these simulations, you will check the status of the portmapper process rpcbind, and use the
rpcinfo command to learn what RPC
services are available on your machine. Choose which UNIX version you would like to simulate by clicking either the Linux or the Solaris button.