FreeBSD supports the Network File System (NFS), which allows a server to share directories and files with clients over a network. With NFS, users and programs can access files on remote systems as if they were stored locally.
NFS has many practical uses. Some of the more common uses include:
Data that would otherwise be duplicated on each client can be kept in a single location and accessed by clients on the network.
Several clients may need access to the
/usr/ports/distfiles
directory.
Sharing that directory allows for quick access to the
source files without having to download them to each
client.
On large networks, it is often more convenient to configure a central NFS server on which all user home directories are stored. Users can log into a client anywhere on the network and have access to their home directories.
Administration of NFS exports is simplified. For example, there is only one file system where security or backup policies must be set.
Removable media storage devices can be used by other machines on the network. This reduces the number of devices throughout the network and provides a centralized location to manage their security. It is often more convenient to install software on multiple machines from a centralized installation media.
NFS consists of a server and one or more clients. The client remotely accesses the data that is stored on the server machine. In order for this to function properly, a few processes have to be configured and running.
These daemons must be running on the server:
Daemon | Description |
---|---|
nfsd | The NFS daemon which services requests from NFS clients. |
mountd | The NFS mount daemon which carries out requests received from nfsd. |
rpcbind | This daemon allows NFS clients to discover which port the NFS server is using. |
Running nfsiod(8) on the client can improve performance, but is not required.
The file systems which the NFS server
will share are specified in /etc/exports
.
Each line in this file specifies a file system to be exported,
which clients have access to that file system, and any access
options. When adding entries to this file, each exported file
system, its properties, and allowed hosts must occur on a
single line. If no clients are listed in the entry, then any
client on the network can mount that file system.
The following /etc/exports
entries
demonstrate how to export file systems. The examples can be
modified to match the file systems and client names on the
reader's network. There are many options that can be used in
this file, but only a few will be mentioned here. See
exports(5) for the full list of options.
This example shows how to export
/cdrom
to three hosts named
alpha
,
bravo
, and
charlie
:
/cdrom -roalpha
bravo
charlie
The -ro
flag makes the file system
read-only, preventing clients from making any changes to the
exported file system. This example assumes that the host
names are either in DNS or in
/etc/hosts
. Refer to hosts(5) if
the network does not have a DNS
server.
The next example exports /home
to
three clients by IP address. This can be
useful for networks without DNS or
/etc/hosts
entries. The
-alldirs
flag allows subdirectories to be
mount points. In other words, it will not automatically mount
the subdirectories, but will permit the client to mount the
directories that are required as needed.
/usr/home -alldirs 10.0.0.2 10.0.0.3 10.0.0.4
This next example exports /a
so that
two clients from different domains may access that file
system. The -maproot=root
allows root
on the remote system to
write data on the exported file system as root
. If
-maproot=root
is not specified, the
client's root
user
will be mapped to the server's nobody
account and will be
subject to the access limitations defined for nobody
.
/a -maproot=root host.example.com box.example.org
A client can only be specified once per file system. For
example, if /usr
is a single file system,
these entries would be invalid as both entries specify the
same host:
# Invalid when /usr is one file system /usr/src client /usr/ports client
The correct format for this situation is to use one entry:
/usr/src /usr/ports client
The following is an example of a valid export list, where
/usr
and /exports
are local file systems:
# Export src and ports to client01 and client02, but only # client01 has root privileges on it /usr/src /usr/ports -maproot=root client01 /usr/src /usr/ports client02 # The client machines have root and can mount anywhere # on /exports. Anyone in the world can mount /exports/obj read-only /exports -alldirs -maproot=root client01 client02 /exports/obj -ro
To enable the processes required by the
NFS server at boot time, add these options
to /etc/rc.conf
:
rpcbind_enable="YES" nfs_server_enable="YES" mountd_enable="YES"
The server can be started now by running this command:
#
service nfsd start
Whenever the NFS server is started,
mountd also starts automatically.
However, mountd only reads
/etc/exports
when it is started. To make
subsequent /etc/exports
edits take effect
immediately, force mountd to reread
it:
#
service mountd reload
To enable NFS clients, set this option
in each client's /etc/rc.conf
:
nfs_client_enable="YES"
Then, run this command on each NFS client:
#
service nfsclient start
The client now has everything it needs to mount a remote
file system. In these examples, the server's name is
server
and the client's name is
client
. To mount
/home
on
server
to the
/mnt
mount point on
client
:
#
mount server:/home /mnt
The files and directories in
/home
will now be available on
client
, in the
/mnt
directory.
To mount a remote file system each time the client boots,
add it to /etc/fstab
:
server:/home /mnt nfs rw 0 0
Refer to fstab(5) for a description of all available options.
Some applications require file locking to operate
correctly. To enable locking, add these lines to
/etc/rc.conf
on both the client and
server:
rpc_lockd_enable="YES" rpc_statd_enable="YES"
Then start the applications:
#
service lockd start
#
service statd start
If locking is not required on the server, the
NFS client can be configured to lock
locally by including -L
when running
mount. Refer to mount_nfs(8)
for further details.
The autofs(5) automount facility is supported starting with FreeBSD 10.1-RELEASE. To use the automounter functionality in older versions of FreeBSD, use amd(8) instead. This chapter only describes the autofs(5) automounter.
The autofs(5) facility is a common name for several components that, together, allow for automatic mounting of remote and local filesystems whenever a file or directory within that file system is accessed. It consists of the kernel component, autofs(5), and several userspace applications: automount(8), automountd(8) and autounmountd(8). It serves as an alternative for amd(8) from previous FreeBSD releases. Amd is still provided for backward compatibility purposes, as the two use different map format; the one used by autofs is the same as with other SVR4 automounters, such as the ones in Solaris, MacOS X, and Linux.
The autofs(5) virtual filesystem is mounted on specified mountpoints by automount(8), usually invoked during boot.
Whenever a process attempts to access file within the autofs(5) mountpoint, the kernel will notify automountd(8) daemon and pause the triggering process. The automountd(8) daemon will handle kernel requests by finding the proper map and mounting the filesystem according to it, then signal the kernel to release blocked process. The autounmountd(8) daemon automatically unmounts automounted filesystems after some time, unless they are still being used.
The primary autofs configuration file is
/etc/auto_master
. It assigns individual
maps to top-level mounts. For an explanation of
auto_master
and the map syntax, refer to
auto_master(5).
There is a special automounter map mounted on
/net
. When a file is accessed within
this directory, autofs(5) looks up the corresponding
remote mount and automatically mounts it. For instance, an
attempt to access a file within
/net/foobar/usr
would tell
automountd(8) to mount the /usr
export from the host
foobar
.
In this example, showmount -e
shows
the exported file systems that can be mounted from the
NFS server,
foobar
:
%
showmount -e foobar
Exports list on foobar: /usr 10.10.10.0 /a 10.10.10.0%
cd /net/foobar/usr
The output from showmount
shows
/usr
as an export.
When changing directories to /host/foobar/usr
,
automountd(8) intercepts the request and attempts to
resolve the hostname foobar
. If successful,
automountd(8) automatically mounts the source
export.
To enable autofs(5) at boot time, add this line to
/etc/rc.conf
:
autofs_enable="YES"
Then autofs(5) can be started by running:
#
service automount start
#
service automountd start
#
service autounmountd start
The autofs(5) map format is the same as in other operating systems. Information about this format from other sources can be useful, like the Mac OS X document.
Consult the automount(8), automountd(8), autounmountd(8), and auto_master(5) manual pages for more information.
All FreeBSD documents are available for download at https://download.freebsd.org/ftp/doc/
Questions that are not answered by the
documentation may be
sent to <freebsd-questions@FreeBSD.org>.
Send questions about this document to <freebsd-doc@FreeBSD.org>.