Ubuntu Manpage: exportfs - maintain table of exported NFS file systems

Provided by: nfs-kernel-server_1.2.8-9ubuntu12.3_amd64

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 and
files under /etc/exports.d by invoking exportfs -a. However, a system administrator can
choose to add or delete exports without modifying /etc/exports or files under
/etc/exports.d 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  and  files  under  /etc/exports.d  directory.   Only
              default options and options given on the command line are used.

       -r     Reexport  all  directories,  synchronizing  /var/lib/nfs/etab with /etc/exports and
              files under /etc/exports.d.  This option removes entries in /var/lib/nfs/etab which
              have  been deleted from /etc/exports or files under /etc/exports.d, 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 and files under
/etc/exports.d 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 or files under /etc/exports.d.

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 unexport 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 and files  under  /etc/exports.d
       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 and files under /etc/exports.d:

       # 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

       /etc/exports.d           directory where extra input files are stored.  Note:  only  files
                                that end with .exports are used.

       /var/lib/nfs/etab        master table of exports

       /var/lib/nfs/rmtab       table of clients accessing server's exports

AUTHORS

       Olaf Kirch <okir@monad.swb.de>
       Neil Brown <neilb@cse.unsw.edu.au>

                                         31 December 2009                             exportfs(8)