NAME
exportfs - maintain table of exported NFS 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]
/usr/sbin/exportfs -f
DESCRIPTION
An NFS server maintains a table of local physical file systems that are
accessible to NFS clients. Each file system in this table is referred
to as an exported file system, or export, for short.
The exportfs command maintains the current table of exports for the NFS
server. The master export table is kept in a file named
/var/lib/nfs/etab. This file is read by rpc.mountd when a client sends
an NFS MOUNT request.
Normally the master export table is initialized with the contents of
/etc/exports by invoking exportfs -a. However, a system administrator
can choose to add or delete exports without modifying /etc/exports by
using the exportfs command.
exportfs and its partner program rpc.mountd 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 nfsd virtual filesystem has been mounted at /proc/fs/nfsd
or /proc/fs/nfs. On 2.6 kernels, if this filesystem is not mounted,
the legacy mode is used.
In the new mode, exportfs does not give any information to the kernel,
but provides it only to rpc.mountd through the /var/lib/nfs/etab file.
rpc.mountd then manages kernel requests for information about exports,
as needed.
In the legacy mode, exports which identify a specific host, rather than
a subnet or netgroup, are entered directly into the kernel's export
table, as well as being written to /var/lib/nfs/etab. Further, exports
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 added to 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. Only default options and options
given on the command line are used.
-r Reexport all directories, synchronizing /var/lib/nfs/etab with
/etc/exports. This option removes entries in /var/lib/nfs/etab
which have been deleted from /etc/exports, and removes any
entries from the kernel export table which are no longer valid.
-u Unexport one or more directories.
-f If /proc/fs/nfsd or /proc/fs/nfs is mounted, flush everything
out of the kernel's export table. Fresh entries for active
clients are added to the kernel's export table by rpc.mountd
when they make their next NFS mount 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.
DISCUSSION
Exporting Directories
The first synopsis shows how to invoke exportfs when adding new entries
to the export table. When using exportfs -a, all exports listed in
/etc/exports are added to /var/lib/nfs/etab. The kernel's export table
is also updated as needed.
The host:/path argument specifies a local directory to export, along
with the client or clients who are permitted to access it. See
exports(5) for a description of supported options and access list
formats. To export a directory to the world, simply specify :/path.
The export options for a particular host/directory pair derive from
several sources. The default export options are
sync,ro,root_squash,wdelay. These can be overridden by entries in
/etc/exports.
A system administrator may override options from these sources using
the -o command-line option on exportfs. This option takes a comma-
separated list of options in the same fashion as one would specify them
in /etc/exports. In this way exportfs can be used to modify the export
options of an already exported directory.
Unexporting Directories
The third synopsis shows how to unexported a currently exported
directory. When using exportfs -ua, all entries listed in
/var/lib/nfs/etab are removed from the kernel export tables, and the
file is cleared. This effectively shuts down all NFS activity.
To remove an export, specify a host:/path pair. This deletes the
specified entry from /var/lib/nfs/etab and removes the corresponding
kernel entry (if any).
Dumping the Export Table
Invoking exportfs without options shows the current list of exported
file systems. Adding the -v option causes exportfs to display the
export options for each export.
EXAMPLES
The following adds all directories listed in /etc/exports to
/var/lib/nfs/etab and pushes the resulting export entries into the
kernel:
# exportfs -a
To export the /usr/tmp directory to host django, allowing insecure file
locking requests from clients:
# exportfs -o insecure_locks django:/usr/tmp
To unexport the /usr/tmp directory:
# exportfs -u django:/usr/tmp
To unexport all exports listed in /etc/exports:
# exportfs -au
USAGE NOTES
Exporting to IP networks or DNS and NIS domains does not enable clients
from these groups to access NFS immediately. Rather, these sorts of
exports are hints to rpc.mountd(8) to grant any mount requests from
these clients. This is usually not a 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 no longer valid they will be
removed.
FILES
/etc/exports input file listing exports, export options,
and access control lists
/var/lib/nfs/etab master table of exports
/var/lib/nfs/rmtab table of clients accessing server's exports
SEE ALSO
exports(5), rpc.mountd(8), netgroup(5)
AUTHORS
Olaf Kirch <okir@monad.swb.de>
Neil Brown <neilb@cse.unsw.edu.au>
31 December 2009 exportfs(8)