exportfs - maintain list of NFS exported file systems
/usr/sbin/exportfs [-avi] [-o options,..] [client:/path ..]
/usr/sbin/exportfs -r [-v]
/usr/sbin/exportfs [-av] -u [client:/path ..]
The exportfs command is used to maintain the current table of exported
file systems for NFS. This list is kept in a separate file named
/var/lib/nfs/xtab which is read by mountd 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.
Normally this xtab file is initialized with the list of all file sys-
tems named in /etc/exports by invoking exportfs -a.
However, administrators can choose to add and delete individual file
systems without modifying /etc/exports using exportfs.
exportfs and it's partner program mountd work in one of two modes, a
legacy mode which applies to 2.4 and earlier versions of the Linux ker-
nel, and a new mode which applies to 2.6 and later versions providing
the nfsd virtual filesystem has been mounted at /proc/fs/nfsd or
/proc/fs/nfs. If this filesystem is not mounted in 2.6, the legacy
mode is used.
In the new mode, exportfs does not give any information to the kernel
but only provides it to mountd through the /var/lib/nfs/xtab file.
mountd will listen to requests from the kernel and will provide infor-
mation as needed.
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 /var/lib/nfs/xtab.
Further, any mount points listed in /var/lib/nfs/rmtab which match a
non host-specific export request will cause an appropriate export entry
for the host given in rmtab to be entered into the kernel's export ta-
-a Export or unexport all directories.
Specify a list of export options in the same manner as in
-i Ignore the /etc/exports file, so that only default options and
options given on the command line are used.
-r Reexport all directories. It synchronizes /var/lib/nfs/xtab with
/etc/exports. It removes entries in /var/lib/nfs/xtab which are
deleted from /etc/exports, and remove any entries from the ker-
nel export table which are no longer valid.
-u Unexport one or more directories.
-f In 'new' mode, flush everything out of the kernels export table.
Any clients that are active will get new entries added by mountd
when they make their next request.
-v Be verbose. When exporting or unexporting, show what's going on.
When displaying the current export list, also display the list
of export options.
The first synopsis shows how to invoke the command when adding new
entries to the export table. When using exportfs -a, all directories
in exports(5) are added to xtab and the resulting list is pushed into
The host:/path argument specifies the directory to export along with
the host or hosts to export it to. All formats described in exports(5)
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 over-
ridden by entries in /etc/exports (unless the -i option is given). In
addition, the administrator may overide any options from these sources
using the -o argument which takes a comma-separated list of options in
the same fashion as one would specify them in exports(5). Thus,
exportfs can also be used to modify the export options of an already
Modifications of the kernel export table used by nfsd(8) take place
immediately after parsing the command line and updating the xtab file.
The default export options are sync,ro,root_squash,wdelay.
The third synopsis shows how to unexported a currently exported direc-
tory. When using exportfs -ua, all entries listed in xtab are removed
from the kernel export tables, and the file is cleared. This effec-
tively shuts down all NFS activity.
To remove individial export entries, one can specify a host:/path pair.
This deletes the specified entry from xtab and removes the correspond-
ing kernel entry (if any).
Dumping the Export Table
Invoking exportfs without further options shows the current list of
exported file systems. When giving the -v option, the list of flags
pertaining to each export are shown in addition.
The following adds all directories listed in /etc/exports to
/var/lib/nfs/xtab and pushes the resulting export entries into the ker-
# exportfs -a
To export the /usr/tmp directory to host django, allowing asynchronous
writes, one would do this:
# exportfs -o async django:/usr/tmp
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 mountd(8) to grant any mount requests from these
clients. This is usually not a big problem, because any existing
mounts are preserved in rmtab across reboots.
When unexporting a network or domain entry, any current exports to mem-
bers of this group will be checked against the remaining valid exports
and if they themselves are nolonger valid they will be removed.
Olaf Kirch, <firstname.lastname@example.org>
Neil Brown, <email@example.com>
18 July 2003 exportfs(8)