NFS Howto Intro

From Linux NFS

Revision as of 17:05, 5 April 2006

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 (http://www.samba.org) 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.

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 Linux NFS and Automounter Administration by Erez Zadok (Sybex, 2001). The classic NFS book, updated and still quite useful, is Managing NFS and NIS by Hal Stern, published by O'Reilly & Associates, Inc. A much more advanced 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 Windows machines) or NFS Version 4, which is still in development.

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.

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. Kernel 2.2.19 contains some additional locking improvements over 2.2.18.

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.

In all cases, if you are building your own kernel, you will need to select NFS and NFS Version 3 support at compile time. Most (but not all) standard distributions come with kernels that support NFS version 3.

Handling files larger than 2 GB will require a 2.4x kernel and a 2.2.x version of glibc.

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 a buggy form as an experimental option in the post-2.2.18 series; patches for 2.4 and 2.5 kernels have been introduced starting with 2.4.17 and 2.5.6. The patches are believed to be stable, though as of this writing they are relatively new and have not seen widespread use or integration into the mainstream 2.4 kernel.

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 has only recently been finalized as a protocol, and no implementations are considered production-ready. It will not be dealt with here.

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.

When you encounter a problem or have a question not covered in this manual, the faq or the man pages, you should send a message to the nfs mailing list nfs@lists.sourceforge.net. To best help the developers and other users help you assess your problem you should include:

• the version of nfs-utils you are using
• the version of the kernel and any non-stock applied kernels.
• the distribution of linux you are using
• the version(s) of other operating systems involved.

It is also useful to know the networking configuration connecting the hosts.

If your problem involves the inability mount or export shares please also include:

• a copy of your /etc/exports file
• the output of rpcinfo -p localhost run on the server
• the output of rpcinfo -p servername run on the client

Sending all of this information with a specific question, after reading all the documentation, is the best way to ensure a helpful response from the list.

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).