Required Services - Red Hat ENTERPRISE LINUX 5 - DEPLOYMENT Deployment Manual

Chapter 19. Network File System (NFS)
Important
In order for NFS to work with a default installation of Red Hat Enterprise Linux with a
firewall enabled, IPTables with the default TCP port 2049 must be configured. Without
proper IPTables configuration, NFS does not function properly.
The NFS initialization script and rpc.nfsd process now allow binding to any specified
port during system start up. However, this can be error prone if the port is unavailable or
conflicts with another daemon.

19.1.1. Required Services

Red Hat Enterprise Linux uses a combination of kernel-level support and daemon processes to
provide NFS file sharing. All NFS versions rely on Remote Procedure Calls (RPC) 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 — (/sbin/service nfs start) starts the NFS server and the appropriate RPC processes
to service requests for shared NFS file systems.
• nfslock — (/sbin/service nfslock start) is a mandatory service that starts the
appropriate RPC processes to allow NFS clients to lock files on the server.
• portmap — accepts port reservations from local RPC services. These ports are then made
available (or advertised) so the corresponding remote RPC services access them. portmap
responds to requests for RPC services and sets up connections to the requested RPC service.
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.
• rpc.nfsd — Allows explicit NFS versions and protocols the server advertises to be defined. 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 — allows NFS clients to lock files on the server. If rpc.lockd is not started, file
locking will fail. rpc.lockd implements the Network Lock Manager (NLM) protocol. 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.
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