2. Introduction

2.1. What is NFS?

The Network File System (NFS) was developed to allow machines to mount a disk partition on a remote machine as if it were on a local hard drive. This allows for fast, seamless sharing of files across a network.

It also gives the potential for unwanted people to access your hard drive over the network (and thereby possibly read your email and delete all your files as well as break into your system) if you set it up incorrectly. So please read the Security section of this document carefully if you intend to implement an NFS setup.

There are other systems that provide similar functionality to NFS. Samba provides file services to Windows clients. The Andrew File System from IBM (http://www.transarc.com/Product/EFS/AFS/index.html), recently open-sourced, provides a file sharing mechanism with some additional security and performance features. The Coda File System (http://www.coda.cs.cmu.edu/) is still in development as of this writing but is designed to work well with disconnected clients. Many of the features of the Andrew and Coda file systems are slated for inclusion in the next version of NFS (Version 4) (http://www.nfsv4.org). The advantage of NFS today is that it is mature, standard, well understood, and supported robustly across a variety of platforms.

2.2. What is this HOWTO and what is it not?

This HOWTO is intended as a complete, step-by-step guide to setting up NFS correctly and effectively. Setting up NFS involves two steps, namely configuring the server and then configuring the client. Each of these steps is dealt with in order. The document then offers some tips for people with particular needs and hardware setups, as well as security and troubleshooting advice.

This HOWTO is not a description of the guts and underlying structure of NFS. For that you may wish to read Managing NFS and NIS by Hal Stern, published by O'Reilly & Associates, Inc. While that book is severely out of date, much of the structure of NFS has not changed, and the book describes it very articulately. A much more advanced and up-to-date technical description of NFS is available in NFS Illustrated by Brent Callaghan.

This document is also not intended as a complete reference manual, and does not contain an exhaustive list of the features of Linux NFS. For that, you can look at the man pages for nfs(5), exports(5), mount(8), fstab(5), nfsd(8), lockd(8), statd(8), rquotad(8), and mountd(8).

It will also not cover PC-NFS, which is considered obsolete (users are encouraged to use Samba to share files with PC's) or NFS Version 4, which is still in development.

2.3. Knowledge Pre-Requisites

You should know some basic things about TCP/IP networking before reading this HOWTO; if you are in doubt, read the Networking- Overview-HOWTO.

2.4. Software Pre-Requisites: Kernel Version and nfs-utils

The difference between Version 2 NFS and version 3 NFS will be explained later on; for now, you might simply take the suggestion that you will need NFS Version 3 if you are installing a dedicated or high-volume file server. NFS Version 2 should be fine for casual use.

NFS Version 2 has been around for quite some time now (at least since the 1.2 kernel series) however you will need a kernel version of at least 2.2.18 if you wish to do any of the following:

• Mix Linux NFS with other operating systems' NFS

• Use file locking reliably over NFS

• Use NFS Version 3.

There are also patches available for kernel versions above 2.2.14 that provide the above functionality. Some of them can be downloaded from the Linux NFS homepage. If your kernel version is 2.2.14- 2.2.17 and you have the source code on hand, you can tell if these patches have been added because NFS Version 3 server support will be a configuration option. However, unless you have some particular reason to use an older kernel, you should upgrade because many bugs have been fixed along the way.

Version 3 functionality will also require the nfs-utils package of at least version 0.1.6, and mount version 2.10m or newer. However because nfs-utils and mount are fully backwards compatible, and because newer versions have lots of security and bug fixes, there is no good reason not to install the newest nfs-utils and mount packages if you are beginning an NFS setup.

All 2.4 and higher kernels have full NFS Version 3 functionality.

All kernels after 2.2.18 support NFS over TCP on the client side. As of this writing, server-side NFS over TCP only exists in the later 2.2 series (but not yet in the 2.4 kernels), is considered experimental, and is somewhat buggy.

Because so many of the above functionalities were introduced in kernel version 2.2.18, this document was written to be consistent with kernels above this version (including 2.4.x). If you have an older kernel, this document may not describe your NFS system correctly.

As we write this document, NFS version 4 is still in development as a protocol, and it will not be dealt with here.

2.5. Where to get help and further information

As of November 2000, the Linux NFS homepage is at http://nfs.sourceforge.net. Please check there for NFS related mailing lists as well as the latest version of nfs-utils, NFS kernel patches, and other NFS related packages.

You may also wish to look at the man pages for nfs(5), exports(5), mount(8), fstab(5), nfsd(8), lockd(8), statd(8), rquotad(8), and mountd(8).