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Section 17.1:Methodology
17 Network File System (NFS)
NFS (Network File System) exists to allow remote hosts to mount partitions on a particular system
and use them as though they were local filesystems. This allows files to be organized in a central
location, while providing the functionality of allowing authorized users continuous access to them.
Two versions of NFS are currently in use. NFS version 2, which has been around for several years, is
widely supported by various operating systems. NFS version 3 has several more features, including a
variable file handle size and better error reporting. Red Hat Linux supports both NFSv2 and NFSv3,
and uses NFSv3 by default when connecting with a server which supports it.
This chapter will focus on NFS version 2, though many of the concepts discussed also apply to version
3. Additionally, only fundamental NFS concepts and supplemental information will be provided. For
specific instructions regarding the configuration and operation of NFS on client or server machines,
see the Official Red Hat Linux Customization Guide.
17.1 Methodology
Linux uses a combination of kernel-level support and continuously running daemon processes to pro-
vide NFS file sharing, and NFS support must be enabled in the Linux kernel to function. NFS uses
Remote Procedure Calls (RPC) to route requests between clients and servers, meaning that the
portmap service must be enabled and active at the proper runlevels for NFS communication to occur.
Working with portmap, various other processes ensure that a particular NFS connection is allowed
and may proceed without error:
•
rpc.mountd — The running process that receives the mount request from an NFS client and
checks to see if it matches with a currently exported filesystem.
•
rpc.nfsd — The process that implements the user-level part of the NFS service. It works with
the Linux kernel to meet the dynamic demands of NFS clients, such as providing additional server
threads for NFS clients to utilize.
•
rpc.lockd — A daemon that is not necessary with modern kernels. NFS file locking is now
done by the kernel. It is included with the nfs-utils package for users utilizing older kernels
that do not include this functionality by default.
•
rpc.statd — Implements the Network Status Monitor (NSM) RPC protocol. This provides
reboot notification when an NFS server is restarted without being gracefully brought down.
•
rpc.rquotad — An RPC server that provides user quota information for remote users.
Not all of these programs are required for NFS service. The only services that must be enabled are
rpc.mountd, rpc.nfsd, and portmap. The other daemons provide additional functionality,
based on the particular requirements of your server environment.
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