NFS relies on Remote Procedure Calls (RPC) to route requests between clients and servers. RPC services under Linux are controlled by the portmap service. To share or mount NFS file systems, the following services work together:
NFS service port number 2049,
Portmapper service port number -111
nfs — Starts the appropriate RPC processes to service requests for shared NFS file systems.
nfslock — An optional service that starts the appropriate RPC processes to allow NFS clients to lock files on the server.
portmap — The RPC service for Linux; it responds to requests for RPC services and sets up connections to the requested RPC service.
The following RPC processes work together behind the scenes to facilitate NFS services:
rpc.mountd — This process receives mount requests from NFS clients and verifies the requested file system is currently exported. This process is started automatically by the nfs service and does not require user configuration.
rpc.nfsd — This process is the NFS server. It works with the Linux kernel to meet the dynamic demands of NFS clients, such as providing server threads each time an NFS client connects. This process corresponds to the nfs service.
rpc.lockd — An optional process that allows NFS clients to lock files on the server. This process corresponds to the nfslock service.
rpc.statd — This process implements the Network Status Monitor (NSM) RPC protocol which notifies NFS clients when an NFS server is restarted without being gracefully brought down. This process is started automatically by the nfslock service and does not require user configuration.
rpc.rquotad — This process provides user quota information for remote users. This process is started automatically by the nfs service and does not require user configuration.