.\"@(#)exportfs.8"
.\"
.\" Copyright (C) 1995 Olaf Kirch <okir@monad.swb.de>
.\" Modifications 1999-2003 Neil Brown <neilb@cse.unsw.edu.au>
.\"
.TH exportfs 8 "31 December 2009"
.SH NAME
exportfs \- maintain table of exported NFS file systems
.SH SYNOPSIS
.BI "/usr/sbin/exportfs [-avi] [-o " "options,.." "] [" "client:/path" " ..]
.br
.BI "/usr/sbin/exportfs -r [-v]"
.br
.BI "/usr/sbin/exportfs [-av] -u [" "client:/path" " ..]
.br
.BI "/usr/sbin/exportfs [-v]
.br
.BI "/usr/sbin/exportfs -f"
.br
.SH 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
.IR "exported file system" ,
or
.IR export ,
for short.
.PP
The
.B exportfs
command maintains the current table of exports for the NFS server.
The master export table is kept in a file named
.IR /var/lib/nfs/etab .
This file is read by
.B rpc.mountd
when a client sends an NFS MOUNT request.
.PP
Normally the master export table is initialized with the contents of
.I /etc/exports
and files under
.I /etc/exports.d
by invoking
.BR "exportfs -a" .
However, a system administrator can choose to add or delete
exports without modifying
.I /etc/exports
or files under
.I /etc/exports.d
by using the
.B exportfs
command.
.PP
.B exportfs
and its partner program
.B 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
.B nfsd
virtual filesystem has been mounted at
.I /proc/fs/nfsd
or
.IR /proc/fs/nfs .
On 2.6 kernels, if this filesystem is not mounted, the legacy mode is used.
.PP
In the new mode,
.B exportfs
does not give any information to the kernel, but provides it only to
.B rpc.mountd
through the
.I /var/lib/nfs/etab
file.
.B rpc.mountd
then manages kernel requests for information about exports, as needed.
.PP
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
.IR /var/lib/nfs/etab .
Further, exports listed in
.I /var/lib/nfs/rmtab
which match a non host-specific export request will cause an
appropriate export entry for the host given in
.I rmtab
to be added to the kernel's export table.
.SH OPTIONS
.TP
.B -a
Export or unexport all directories.
.TP
.BI "-o " options,...
Specify a list of export options in the same manner as in
.BR exports (5).
.TP
.B -i
Ignore the
.I /etc/exports
file and files under
.I /etc/exports.d
directory.  Only default options and options given on the command line are used.
.TP
.B -r
Reexport all directories, synchronizing
.I /var/lib/nfs/etab
with
.IR /etc/exports 
and files under 
.IR /etc/exports.d .
This option removes entries in
.I /var/lib/nfs/etab
which have been deleted from
.I /etc/exports
or files under
.IR /etc/exports.d , 
and removes any entries from the
kernel export table which are no longer valid.
.TP
.B -u
Unexport one or more directories.
.TP
.B -f
If
.I /proc/fs/nfsd
or
.I /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
.B rpc.mountd
when they make their next NFS mount request.
.TP
.B -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.
.SH DISCUSSION
.SS Exporting Directories
The first synopsis shows how to invoke
.B exportfs
when adding new entries to the export table.  When using
.BR "exportfs -a" ,
all exports listed in
.I /etc/exports
and files under
.I /etc/exports.d
are added to
.IR /var/lib/nfs/etab .
The kernel's export table is also updated as needed.
.PP
The
.I host:/path
argument specifies a local directory to export,
along with the client or clients who are permitted to access it.
See
.B exports(5)
for a description of supported options and access list formats.
To export a directory to the world, simply specify
.IR :/path .
.PP
The export options for a particular host/directory pair derive from
several sources.
The default export options are
.BR sync,ro,root_squash,wdelay .
These can be overridden by entries in
.IR /etc/exports 
or files under
.IR /etc/exports.d .
.PP
A system administrator may override options from these sources using the
.B -o
command-line option on
.BR exportfs .
This option takes a comma-separated list of options in the same fashion
as one would specify them in
.IR /etc/exports .
In this way
.B exportfs
can be used to modify the export options of an already exported directory.
.SS Unexporting Directories
The third synopsis shows how to unexport a currently exported directory.
When using
.BR "exportfs -ua" ,
all entries listed in
.I /var/lib/nfs/etab
are removed from the kernel export tables, and the file is cleared. This
effectively shuts down all NFS activity.
.PP
To remove an export, specify a
.I host:/path
pair. This deletes the specified entry from
.I /var/lib/nfs/etab
and removes the corresponding kernel entry (if any).
.PP
.SS Dumping the Export Table
Invoking
.B exportfs
without options shows the current list of exported file systems.
Adding the
.B -v
option causes
.B exportfs
to display the export options for each export.
.SH EXAMPLES
The following adds all directories listed in
.I /etc/exports
and files under
.I /etc/exports.d
to
.I /var/lib/nfs/etab
and pushes the resulting export entries into the kernel:
.PP
.nf
.B "# exportfs -a
.fi
.PP
To export the
.I /usr/tmp
directory to host
.BR django ,
allowing insecure file locking requests from clients:
.PP
.nf
.B "# exportfs -o insecure_locks django:/usr/tmp
.fi
.PP
To unexport the
.I /usr/tmp
directory:
.PP
.nf
.B "# exportfs -u django:/usr/tmp
.fi
.PP
To unexport all exports listed in
.IR /etc/exports 
and files under
.IR /etc/exports.d :
.PP
.nf
.B "# exportfs -au
.fi
.SH 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
.BR rpc.mountd (8)
to grant any mount requests from these clients.
This is usually not a problem, because any existing mounts are preserved in
.I rmtab
across reboots.
.PP
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.
.SH FILES
.TP 2.5i
.I /etc/exports
input file listing exports, export options, and access control lists
.TP 2.5i
.I /etc/exports.d
directory where extra input files are stored.
.B Note:
only files that end with 
.I .exports
are used.
.TP 2.5i
.I /var/lib/nfs/etab
master table of exports
.TP 2.5i
.I /var/lib/nfs/rmtab
table of clients accessing server's exports
.SH SEE ALSO
.BR exports (5),
.BR rpc.mountd (8),
.BR netgroup (5)
.SH AUTHORS
Olaf Kirch <okir@monad.swb.de>
.br
Neil Brown <neilb@cse.unsw.edu.au>