NFS Server Configuration Files

Configuring a system to share files and directories using NFS is straightforward. Every filesystem being exported to remote users via NFS, as well as the access rights relating to those filesystems, is located in the /etc/exports file. This file is read by the exportfs command to give rpc.mountd and rpc.nfsd the information necessary to allow the remote mounting of a filesystem by an authorized host.

The exportfs command allows you to selectively export or unexport directories without restarting the various NFS services. When exportfs is passed the proper options, the filesystems to be exported are written to /var/lib/nfs/xtab. Since rpc.mountd refers to the xtab file when deciding access privileges to a filesystem, changes to the list of exported filesystems take effect immediately.

Various options are available when using exportfs:

If no options are passed to the exportfs command, it displays a list of currently exported filesystems.

Changes to /etc/exports can also be read by reloading the NFS service with the service nfs reload command. This keeps the NFS daemons running while re-exporting the /etc/exports file.


The /etc/exports file is the standard for controlling which filesystems are exported to which hosts, as well as specifying particular options that control everything. Blank lines are ignored, comments can be made using #, and long lines can be wrapped with a backslash (\). Each exported filesystem should be on its own line. Lists of authorized hosts placed after an exported filesystem must be separated by space characters. Options for each of the hosts must be placed in parentheses directly after the host identifier, without any spaces separating the host and the first parenthesis.

In its simplest form, /etc/exports only needs to know the directory to be exported and the hosts permitted to utilize it:


After re-exporting /etc/exports with the /sbin/service nfs reload command, the host will be able to mount /some/directory and can mount /another/exported/directory. Because no options are specified in this example, several default NFS preferences take effect:

In order to override these defaults, you must specify an option that takes its place. For example, if you do not specify rw, then that export will only be shared read-only. Each default for every exported filesystem must be explicitly overridden. Additionally, other options are available where no default value is in place. These include the ability to disable sub-tree checking, allow access from insecure ports, and allow insecure file locks (necessary for certain early NFS client implementations). See the exports man page for details on these lesser used options.

When specifying hosts to be allowed to use a particular exported filesystem, a variety of methods can be used, including:


The way in which the /etc/exports file is formatted is very important, particularly concerning the use of space characters. Remember to always separate exported filesystems from hosts and hosts from one another with a space character. However, there should be no other space characters in the file unless they are used in comment lines.

For example, the following two lines do not mean the same thing:

/home (rw)

The first line allows only users from read-write access to the /home directory. The second line allows users from to mount the directory read-only (the default), but the rest of the world can mount it read-write. Be careful where space characters are used in /etc/exports.