9.1.1. Required Services
Red Hat Enterprise Linux uses a combination of kernel-level support and daemon processes to provide NFS file sharing. NFSv2 and NFSv3 rely on Remote Procedure Calls (RPC) to encode and decode 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, depending on which version of NFS is implemented:
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. This is not used with NFSv4.
The following RPC processes 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. This is not used with NFSv4.
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. This is not used with NFSv4.
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. This is not used with NFSv4.
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.
rpc.idmapd — This process provides NFSv4 client and server upcalls which map between on-the-wire NFSv4 names (which are strings in the form of user@domain) and local UIDs and GIDs. For idmapd to function with NFSv4, the /etc/idmapd.conf must be configured. This service is required for use with NFSv4.
rpc.svcgssd — This process is used by the NFS server to perform user authentication and is started only when SECURE_NFS=yes is set in the /etc/sysconfig/nfs file.
rpc.gssd — This process is used by the NFS server to perform user authentication and is started only when SECURE_NFS=yes is set in the /etc/sysconfig/nfs file.