exportfs - maintain list of NFS exported file systems
SYNOPSIS
/usr/sbin/exportfs [-avi] [-o options,..] [client:/path
..]
/usr/sbin/exportfs -r [-v]
/usr/sbin/exportfs [-av] -u [client:/path ..]
/usr/sbin/exportfs [-v]
DESCRIPTION
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 systems named in /etc/exports by invoking
exportfs -a.
However, administrators can choose to add and delete indi
vidual file systems without modifying /etc/exports using
exportfs.
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
table.
OPTIONS
-a Export or unexport all directories.
-o options,...
Specify a list of export options in the same manner
as in exports(5).
-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nel export table which are no longer valid.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.
what's going on. When displaying the current export
list, also display the list of export options.
DISCUSSION
Exporting Directories
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 kernel.
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 direc
tory to the world, simply specify :/path.
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 entries in /etc/exports
(unless the -i option is given). In addition, the admin
istrator 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 exported directory.
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,no_delay.
Unexporting Directories
The third synopsis shows how to unexported a currently
exported directory. When using exportfs -ua, all entries
listed in xtab are removed from the kernel export tables,
and the file is cleared. This effectively 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 corresponding kernel entry (if any).
Dumping the Export Table
Invoking exportfs without further options shows the cur
rent list of exported file systems. When giving the -v
option, the list of flags pertaining to each export are
shown in addition.
EXAMPLES
The following adds all directories listed in /etc/exports
to /var/lib/nfs/xtab and pushes the resulting export
# exportfs -a
To export the /usr/tmp directory to host djando, allowing
asynchronous writes, one would do this:
# exportfs -o async django:/usr/tmp
DEPENDENCIES
Exporting to IP networks, DNS and NIS domains does not
enable clients from these groups to access NFS immedi
ately; 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 members of this group will be checked against
the remaining valid exports and if they themselves are
nolonger valid they will be removed.
SEE ALSO
exports(5), mountd(8)
AUTHORS
Olaf Kirch, <okir@monad.swb.de>
Neil Brown, <neilb@cse.unsw.edu.au>
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