558408f95d
that nullfs really doesn't work, he askes why this isn't noted for the "dangerous" filesystems, I go "hmmm."
141 lines
5.2 KiB
Groff
141 lines
5.2 KiB
Groff
.\" Copyright (c) 1992, 1993, 1994
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.\" The Regents of the University of California. All rights reserved.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software donated to Berkeley by
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.\" Jan-Simon Pendry and from John Heidemann of the UCLA Ficus project.
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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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.\" @(#)mount_umap.8 8.4 (Berkeley) 5/1/95
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.\" $Id: mount_umap.8,v 1.8 1998/07/15 06:12:31 charnier Exp $
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.\"
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.Dd May 1, 1995
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.Dt MOUNT_UMAP 8
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.Os BSD 4.4
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.Sh NAME
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.Nm mount_umap
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.Nd sample file system layer
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.Sh SYNOPSIS
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.Nm mount_umap
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.Op Fl o Ar options
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.Fl u Ar uid-mapfile
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.Fl g Ar gid-mapfile
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.Ar target
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.Ar mount-point
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.Sh DESCRIPTION
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The
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.Nm
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command is used to mount a sub-tree of an existing file system
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that uses a different set of uids and gids than the local system.
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Such a file system could be mounted from a remote site via NFS or
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it could be a file system on removable media brought from some
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foreign location that uses a different password file.
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.Pp
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The
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.Nm
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command uses a set of files provided by the user to make correspondences
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between uids and gids in the sub-tree's original environment and
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some other set of ids in the local environment. For instance, user
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smith might have uid 1000 in the original environment, while having
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uid 2000 in the local environment. The
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.Nm
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command allows the subtree from smith's original environment to be
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mapped in such a way that all files with owning uid 1000 look like
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they are actually owned by uid 2000.
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.Pp
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The options are as follows:
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.Bl -tag -width indent
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.It Fl o
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Options are specified with a
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.Fl o
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flag followed by a comma separated string of options.
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See the
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.Xr mount 8
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man page for possible options and their meanings.
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.It Ar target
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Should be the current location of the sub-tree in the
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local system's name space.
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.It Ar mount-point
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Should be a directory
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where the mapped subtree is to be placed.
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.It Fl u Ar uid-mapfile
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.It Fl g Ar gid-mapfile
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Describe the mappings to be made between identifiers.
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Briefly, the format of these files is a count of the number of
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mappings on the first line, with each subsequent line containing
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a single mapping. Each of these mappings consists of an id in
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the local environment and the corresponding id from the original environment,
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separated by white space.
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.Ar Uid-mapfile
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should contain all uid
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mappings, and
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.Ar gid-mapfile
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should contain all gid mappings.
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Any uids not mapped in
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.Ar uid-mapfile
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will be treated as user NOBODY,
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and any gids not mapped in
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.Ar gid-mapfile
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will be treated as group
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NULLGROUP. At most 64 uids can be mapped for a given subtree, and
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at most 16 groups can be mapped by a given subtree.
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.El
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.Pp
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The mapfiles can be located anywhere in the file hierarchy, but they
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must be owned by root, and they must be writable only by root.
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.Nm Mount_umap
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will refuse to map the sub-tree if the ownership or permissions on
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these files are improper. It will also balk if the count of mappings
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in the first line of the map files is not correct.
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.Pp
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The layer created by the
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.Nm
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command is meant to serve as a simple example of file system layering.
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It is not meant for production use. The implementation is not very
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sophisticated.
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.Sh SEE ALSO
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.Xr mount 8 ,
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.Xr mount_null 8
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.Sh BUGS
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THIS FILESYSTEM TYPE IS NOT YET FULLY SUPPORTED (READ: IT DOESN'T WORK)
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AND USING IT MAY, IN FACT, DESTROY DATA ON YOUR SYSTEM. USE AT YOUR
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OWN RISK. BEWARE OF DOG. SLIPPERY WHEN WET.
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This code also needs an owner in order to be less dangerous - serious
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hackers can apply by sending mail to hackers@freebsd.org and announcing
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their intent to take it over.
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.Sh HISTORY
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The
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.Nm
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utility first appeared in
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.Bx 4.4 .
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