63afba9f66
attempting to export the non-root of a filesystem with -alldirs. This pilot error seems to be very common, and the "could not remount" error message doesn't give much hints about the real reason. See the old PR below for an example. While i was at it, make it possible to entirely omit the often annoying error message in that case by specifying the "quiet" exports flag. This allows to specify something like /cdrom -alldirs,ro,quiet <where to export to> which will silently fail if nothing is mounted under /cdrom, but do the rigth thing as soon as you mount something. While doing this, i've put the embedded example in the exports(5) man page into a subsection of its own as it ought to be. Thanks for Paul Southworth for reminding me about this problem. PR: bin/4448 MFC after: 1 month
368 lines
11 KiB
Groff
368 lines
11 KiB
Groff
.\" Copyright (c) 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)exports.5 8.3 (Berkeley) 3/29/95
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.\" $FreeBSD$
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.\"
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.Dd March 29, 1995
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.Dt EXPORTS 5
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.Os
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.Sh NAME
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.Nm exports
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.Nd define remote mount points for
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.Tn NFS
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mount requests
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.Sh SYNOPSIS
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.Nm
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.Sh DESCRIPTION
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The
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.Nm
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file specifies remote mount points for the
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.Tn NFS
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mount protocol per the
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.Tn NFS
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server specification; see
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.%T "Network File System Protocol Specification" ,
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RFC1094, Appendix A and
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.%T "NFS: Network File System Version 3 Specification" ,
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Appendix I.
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.Pp
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Each line in the file
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(other than comment lines that begin with a #)
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specifies the mount point(s) and export flags within one local server
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filesystem for one or more hosts.
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A long line may be split over several lines by ending all but the
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last line with a backslash
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.Pq Ql \e .
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A host may be specified only once for each local filesystem on the
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server and there may be only one default entry for each server
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filesystem that applies to all other hosts.
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The latter exports the filesystem to the ``world'' and should
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be used only when the filesystem contains public information.
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.Pp
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In a mount entry,
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the first field(s) specify the directory path(s) within a server filesystem
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that can be mounted on by the corresponding client(s).
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There are two forms of this specification.
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The first is to list all mount points as absolute
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directory paths separated by whitespace.
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The second is to specify the pathname of the root of the filesystem
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followed by the
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.Fl alldirs
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flag;
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this form allows the host(s) to mount at any point within the filesystem,
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including regular files if the
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.Fl r
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option is used on
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.Xr mountd 8 .
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The pathnames must not have any symbolic links in them and should not have
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any "." or ".." components.
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Mount points for a filesystem may appear on multiple lines each with
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different sets of hosts and export options.
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.Pp
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The second component of a line specifies how the filesystem is to be
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exported to the host set.
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The option flags specify whether the filesystem
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is exported read-only or read-write and how the client uid is mapped to
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user credentials on the server.
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.Pp
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Export options are specified as follows:
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.Pp
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.Sm off
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.Fl maproot No = Sy user
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.Sm on
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The credential of the specified user is used for remote access by root.
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The credential includes all the groups to which the user is a member
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on the local machine (see
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.Xr id 1 ) .
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The user may be specified by name or number.
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.Pp
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.Sm off
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.Fl maproot No = Sy user:group1:group2:...
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.Sm on
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The colon separated list is used to specify the precise credential
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to be used for remote access by root.
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The elements of the list may be either names or numbers.
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Note that user: should be used to distinguish a credential containing
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no groups from a complete credential for that user.
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.Pp
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.Sm off
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.Fl mapall No = Sy user
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.Sm on
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or
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.Sm off
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.Fl mapall No = Sy user:group1:group2:...
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.Sm on
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specifies a mapping for all client uids (including root)
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using the same semantics as
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.Fl maproot .
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.Pp
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The option
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.Fl r
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is a synonym for
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.Fl maproot
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in an effort to be backward compatible with older export file formats.
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.Pp
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In the absence of
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.Fl maproot
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and
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.Fl mapall
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options, remote accesses by root will result in using a credential of -2:-2.
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All other users will be mapped to their remote credential.
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If a
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.Fl maproot
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option is given,
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remote access by root will be mapped to that credential instead of -2:-2.
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If a
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.Fl mapall
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option is given,
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all users (including root) will be mapped to that credential in
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place of their own.
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.Pp
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The
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.Fl kerb
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option specifies that the Kerberos authentication server should be
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used to authenticate and map client credentials.
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This option requires that the kernel be built with the NFSKERB option.
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The use of this option will prevent the kernel from compiling
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unless calls to the appropriate Kerberos encryption routines
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are provided in the NFS source.
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.Pp
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The
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.Fl ro
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option specifies that the filesystem should be exported read-only
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(default read/write).
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The option
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.Fl o
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is a synonym for
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.Fl ro
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in an effort to be backward compatible with older export file formats.
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.Pp
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.Tn WebNFS
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exports strictly according to the spec (RFC 2054 and RFC 2055) can
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be done with the
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.Fl public
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flag.
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However, this flag in itself allows r/w access to all files in
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the filesystem, not requiring reserved ports and not remapping uids.
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It
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is only provided to conform to the spec, and should normally not be used.
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For a
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.Tn WebNFS
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export,
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use the
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.Fl webnfs
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flag, which implies
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.Fl public ,
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.Sm off
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.Fl mapall No = Sy nobody
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.Sm on
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and
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.Fl ro .
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.Pp
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A
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.Sm off
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.Fl index No = Sy file
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.Sm on
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option can be used to specify a file whose handle will be returned if
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a directory is looked up using the public filehandle
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.Pq Tn WebNFS .
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This is to mimic the behavior of URLs.
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If no
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.Fl index
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option is specified, a directory filehandle will be returned as usual.
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The
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.Fl index
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option only makes sense in combination with the
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.Fl public
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or
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.Fl webnfs
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flags.
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.Pp
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Specifying the
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.Fl quiet
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option will inhibit some of the syslog diagnostics for bad lines in
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.Pa /etc/exports .
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This can be useful to avoid annoying error messages for known possible
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problems (see
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.Sx EXAMPLES
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below).
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.Pp
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The third component of a line specifies the host set to which the line applies.
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The set may be specified in three ways.
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The first way is to list the host name(s) separated by white space.
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(Standard Internet ``dot'' addresses may be used in place of names.)
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The second way is to specify a ``netgroup'' as defined in the netgroup file (see
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.Xr netgroup 5 ) .
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The third way is to specify an Internet subnetwork using a network and
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network mask that is defined as the set of all hosts with addresses within
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the subnetwork.
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This latter approach requires less overhead within the
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kernel and is recommended for cases where the export line refers to a
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large number of clients within an administrative subnet.
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.Pp
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The first two cases are specified by simply listing the name(s) separated
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by whitespace.
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All names are checked to see if they are ``netgroup'' names
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first and are assumed to be hostnames otherwise.
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Using the full domain specification for a hostname can normally
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circumvent the problem of a host that has the same name as a netgroup.
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The third case is specified by the flag
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.Sm off
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.Fl network No = Sy netname
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.Sm on
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and optionally
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.Sm off
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.Fl mask No = Sy netmask .
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.Sm on
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If the mask is not specified, it will default to the mask for that network
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class (A, B or C; see
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.Xr inet 4 ) .
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See the
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.Sx EXAMPLES
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section below.
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.Pp
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The
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.Xr mountd 8
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utility can be made to re-read the
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.Nm
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file by sending it a hangup signal as follows:
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.Bd -literal -offset indent
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kill -s HUP `cat /var/run/mountd.pid`
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.Ed
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.Pp
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After sending the
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.Dv SIGHUP ,
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check the
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.Xr syslogd 8
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output to see whether
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.Xr mountd 8
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logged any parsing errors in the
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.Nm
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file.
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.Sh FILES
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.Bl -tag -width /etc/exports -compact
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.It Pa /etc/exports
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the default remote mount-point file
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.El
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.Sh EXAMPLES
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.Bd -literal -offset indent
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/usr /usr/local -maproot=0:10 friends
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/usr -maproot=daemon grumpy.cis.uoguelph.ca 131.104.48.16
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/usr -ro -mapall=nobody
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/u -maproot=bin: -network 131.104.48 -mask 255.255.255.0
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/u2 -maproot=root friends
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/u2 -alldirs -kerb -network cis-net -mask cis-mask
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/cdrom -alldirs,quiet,ro -network 192.168.33.0 -mask 255.255.255.0
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.Ed
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.Pp
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Given that
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.Sy /usr ,
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.Sy /u
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and
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.Sy /u2
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are
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local filesystem mount points, the above example specifies the following:
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.Sy /usr
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is exported to hosts
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.Em friends
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where friends is specified in the netgroup file
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with users mapped to their remote credentials and
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root mapped to uid 0 and group 10.
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It is exported read-write and the hosts in ``friends'' can mount either /usr
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or /usr/local.
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It is exported to
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.Em 131.104.48.16
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and
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.Em grumpy.cis.uoguelph.ca
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with users mapped to their remote credentials and
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root mapped to the user and groups associated with ``daemon'';
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it is exported to the rest of the world as read-only with
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all users mapped to the user and groups associated with ``nobody''.
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.Pp
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.Sy /u
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is exported to all hosts on the subnetwork
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.Em 131.104.48
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with root mapped to the uid for ``bin'' and with no group access.
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.Pp
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.Sy /u2
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is exported to the hosts in ``friends'' with root mapped to uid and groups
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associated with ``root'';
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it is exported to all hosts on network ``cis-net'' allowing mounts at any
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directory within /u2 and mapping all uids to credentials for the principal
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that is authenticated by a Kerberos ticket.
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.Pp
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The filesystem rooted at
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.Sy /cdrom
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will exported read-only to the entire network 192.168.33.0/24, including
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all its subdirectories.
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Since
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.Sy /cdrom
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is the conventional mountpoint for a CD-ROM device, this export will
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fail if no CD-ROM medium is currently mounted there since that line
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would then attempt to export a subdirectory of the root filesystem
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with the
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.Fl alldirs
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option which is not allowed.
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The
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.Fl quiet
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option will then suppress the error message for this condition that
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would normally be syslogged.
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As soon as an actual CD-ROM is going to be mounted,
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.Xr mount 8
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will notify
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.Xr mountd 8
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about this situation, and the
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.Sy /cdrom
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filesystem will be exported as intented.
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Note that without using the
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.Fl alldirs
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option, the export would always succeed.
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While there is no CD-ROM medium mounted under
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.Sy /cdrom ,
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it would export the (normally empty) directory
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.Sy /cdrom
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of the root filesystem instead.
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.Sh SEE ALSO
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.Xr netgroup 5 ,
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.Xr mountd 8 ,
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.Xr nfsd 8 ,
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.Xr showmount 8
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.Sh BUGS
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The export options are tied to the local mount points in the kernel and
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must be non-contradictory for any exported subdirectory of the local
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server mount point.
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It is recommended that all exported directories within the same server
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filesystem be specified on adjacent lines going down the tree.
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You cannot specify a hostname that is also the name of a netgroup.
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Specifying the full domain specification for a hostname can normally
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circumvent the problem.
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