command is used to maintain the current table of exported file systems for
NFS. This list is kept in a separate file named
which is read by
when a remote host requests access to mount a file tree, and parts of
the list which are active are kept in the kernel's export table.
file is initialized with the list of all file systems named in
However, administrators can choose to add and delete individual file systems
and it's partner program
work in one of two modes, a legacy mode which applies to 2.4 and
earlier versions of the Linux kernel, and a new mode which applies to
2.6 and later versions providing the
virtual filesystem has been mounted at
If this filesystem is not mounted in 2.6, the legacy mode is used.
In the new mode,
does not give any information to the kernel but only provides it to
will listen to requests from the kernel and will provide information
In the legacy mode,
any export requests which identify a specific host (rather than a
subnet or netgroup etc) are entered directly into the kernel's export
table as well as being written to
Further, any mount points listed in
which match a non host-specific export request will cause an
appropriate export entry for the host given in
to be entered
into the kernel's export table.
Export or unexport all directories.
Specify a list of export options in the same manner as in
file, so that only default options and options given on the command
line are used.
Reexport all directories. It synchronizes /var/lib/nfs/etab
with /etc/exports. It removes entries in /var/lib/nfs/etab
which are deleted from /etc/exports, and remove any entries from the
kernel export table which are no longer valid.
Unexport one or more directories.
In 'new' mode, flush everything out of the kernels export table. Any
clients that are active will get new entries added by
when they make their next request.
Be verbose. When exporting or unexporting, show what's going on. When
displaying the current export list, also display the list of export
The first synopsis shows how to invoke the command when adding new
entries to the export table. When using
all directories in
are added to
and the resulting list is pushed into the kernel.
argument specifies the directory to export along with the host or hosts to
export it to. All formats described in
are supported; to export a directory to the world, simply specify
The export options for a particular host/directory pair derive from
several sources. There is a set of default options which can be overridden by
option is given).
In addition, the administrator may override any options from these sources
argument which takes a comma-separated list of options in the same fashion
as one would specify them in
can also be used to modify the export options of an already exported
Modifications of the kernel export table used by
take place immediately after parsing the command line and updating the
The default export options are
The third synopsis shows how to unexported a currently exported directory.
all entries listed in
are removed from the kernel export tables, and the file is cleared. This
effectively shuts down all NFS activity.
To remove an export to a host, specify a
pair. This deletes the specified entry from
and removes the corresponding kernel entry (if any).
To remove one or more exports to several hosts, use
Dumping the Export Table
without further options shows the current list of exported file systems.
When giving the
option, the list of flags pertaining to each export are shown in addition.
The following adds all directories listed in
and pushes the resulting export entries into the kernel:
# exportfs -a
To export the
directory to host
allowing asynchronous writes, one would do this:
# exportfs -o async django:/usr/tmp
To unexport the
# exportfs -u django:/usr/tmp
To unexport all the directories listed in
# exportfs -au
Exporting to IP networks, DNS and NIS domains does not enable clients
from these groups to access NFS immediately; rather, these sorts of
exports are hints to
to grant any mount requests from these clients.
This is usually not a big problem, because any existing mounts are preserved
When unexporting a network or domain entry, any current exports to members
of this group will be checked against the remaining valid exports and
if they themselves are no longer valid they will be removed.