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Network File Sharing. Module - Network File Sharing. Overview This module focuses on configuring Network File System (NFS) for servers and clients. This enables clients to share files across Linux and UNIX networks. Lessons covered in this module Introduction to NFS

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module network file sharing
Module - Network File Sharing


This module focuses on configuring Network File System (NFS) for servers and clients. This enables clients to share files across Linux and UNIX networks.

Lessons covered in this module

Introduction to NFS

Configuring NFS Server

Configuring NFS Client

lesson 1 introduction to nfs
Lesson 1 - Introduction to NFS


The NFS is a method of sharing files. It provides local access to remote disks and file systems. Its proper understanding will help in sharing files and directories on other systems in a different city or country.

Topics covered in this lesson

Understanding NFS

NFS Installation

Merits and Demerits

topic 1 understanding nfs
Topic 1 – Understanding NFS

NFS has client/server architecture. The NFS server has consists of physical disks that contain the shared file systems. NFS daemons show and provide them to users on the network.

The NFS daemons provide remote access to the exported file systems, enable file locking and help enforce quotas on the NFS exports.

An NFS client has only to mount the exported files locally into a file system called an NFS mount.

NFS is also used to store users' home directories on a central server and to mount them when users log in or boot their systems.

topic 2 nfs installation
Topic 2 – NFS Installation

The considerations for a good NFS installation

Take into account site-specific need

Decide which file systems to export

Determine the amount of data to be shared

Understand the underlying network you will use

Other network services to be provided

The number and type of servers and clients

Installation involves configuring the exports and starting the daemons, testing to ensure that the naming convention and mounting scheme work properly and monitoring.

topic 3 merits and demerits
Topic 3 - Merits and Demerits


NFS provides centralized control, maintenance, and administration.

It is easier to back up file systems stored on a single server.

NFS conserves disk space and prevent duplication of resources.

Log in and access the home directories from any system.

Protect important data by storing it on an NFS mounted file system.


Sensitive to network congestion, heavy network traffic slows it down.

Heavy disk activity on server reduces performance speed.

If the disk or server crashes that resource becomes inaccessible.

Potential security problems and unsafe across the Internet.

lesson 2 configuring nfs server
Lesson 2 – Configuring NFS Server


Configuring NFS server involves understanding the contents, format and options of configuration files. These determine the characteristics of the exported file systems and affect the performance of NFS.

Topics covered in this lesson

Configuration Files

Server Daemons

Server Scripts and Commands

topic 1 configuration files
Topic 1 - Configuration files

The NFS server configuration file is /etc/exports. It has a list of file systems to export, the clients permitted to mount them, and the export options. Each line in /etc/exports has the following format:

dir [host] (options) [ .……]

dir indicates a directory to export, host denotes the hosts permitted to mount dir, and options denotes mount options. If there is space between hostname and options it will make the directory world accessible. The options determine the characteristics of the exported file system

topic 2 server daemons
Topic 2 - Server Daemons

NFS Server Daemons

lockd starts NFS lock manager in the kernel

mountd is used to process mount requests from NFS clients

nfsd is responsible for all NFS services other than file locking and quota management

portmap informs about the NFS services available on any particular NFS server

rquotad informs about file system quota of NFS exports to clients

statd is used for lock recovery if an NFS server crashes

topic 3 server scripts and commands
Topic 3 - Server Scripts and Commands

Server Scripts

portmap maps calls from other devices to the correct RPC service

nfsd translates NFS requests into requests on the local file system

rpc.mountd is for mounting and unmounting file systems


exportfs -r updates the server's shared files list in /etc/exports.

exportfs -v displays list of shares and options on a server.

exportfs -a exports shared files listed in /etc/exports.

exportfs -u unexports all files without arguments.

showmount –e localhost shows the shared files on the host.

lesson 3 configuring nfs client
Lesson 3 - Configuring NFS Client


In order to be able to use NFS services the client system should be configured. This helps in determining the various options for sharing files across the network and security issues.

Topics covered in this lesson

Configuration Procedure

Automount Services

Security Issues

NFS Troubleshooting

topic 1 configuration procedure
Topic 1 - Configuration Procedure

NFS is implemented in client machines as a kernel module. Network mounts are specified /etc/fstab file. NFS shared files are mounted at boot time by /etc/rc.d/init.d/nfs . autofs can be used to mount and unmount NFS shared files.

NFS options in /etc/fstab :

rsize=8192 and wsize=8192 speed up NFS throughput

soft returns with an error on a failed I/O attempt

hard will block if you try to access an unshared file

intr interrupts or kills NFS requests if server is unreachable

nolock disables file locking (lockd) and allows interoperation with other NFS servers

topic 2 automount services
Topic 2 - Automount Services

The easiest way to mount NFS exports is to use autofs. This automatically mounts file systems. autofs uses the automount daemon to mount and unmount file systems configured to control. autofs uses a master map file, /etc/auto.master to associate mount points with secondary map files.

The secondary map file defines the mount options for file systems mounted under the corresponding directory. Each line in a secondary map file has the general form:

root@ server1~]# localdir [-[options]] remotefs

localdir is the directory beneath the NFS mount point. remotefs specifies the host and pathname of the NFS mount.

topic 3 security issues
Topic 3 - Security Issues

The /etc/exports file is a weak point in NFS.

Use host access control to limit access to services

Use of IP packet firewalls and netfilter or TCP Wrappers increase NFS server security

Always use the root_squash option in /etc/exports

All critical files should be owned by root

Export file systems using the all_squash option

Disable SUID root programs on NFS mounts with the nosuid option.

topic 4 nfs troubleshooting
Topic 4 – NFS Troubleshooting

Export Failures

Entering a user name as the anonymous user when the option requires a UID number (such as 505).

The name of the computer being allowed to share the directory failing to have its address resolved.

Unmount Failures

If there is a process holding the directory open it should be killed to unmount.


topic 4 nfs troubleshooting1
Topic 4 – NFS Troubleshooting

Mount Failures - reasons

Wrong share Information

Firewalls blocking NFS ports

Directory is not being accessed.

You don't have proper permission

lab exercises
Lab Exercises

Configuring NFS to share users home directory with the server has read-write.



NFS monitoring is necessary to export file systems, network security and satisfactory performance. NFS has potential security problems and is unsafe across the Internet.

NFS services daemons portmap, mountd, nfsd, statd, lockd, and rquotad. NFS commands configure the server with access permissions and export characteristics.

nosuid option, file locking, TCP wrappers, and packet filters can ensure security for NFS clients. Mount, unmount and export failures can occur in NFS due to wrong share information or firefalls.

Question and Answer Session