145 lines
4.9 KiB
Groff
145 lines
4.9 KiB
Groff
.\" $NetBSD: mount_umap.8,v 1.17 2003/08/07 10:04:31 agc Exp $
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.\"
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.\" 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. 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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.\"
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.Dd March 6, 2001
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.Dt MOUNT_UMAP 8
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.Os
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.Sh NAME
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.Nm mount_umap
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.Nd user and group ID remapping file system layer
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.Sh SYNOPSIS
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.Nm
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.Op Fl o Ar options
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-u
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.Ar uid-mapfile
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-g
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.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,
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a local file system on removable media brought from some foreign
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location that uses a different user/group database, or could be
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a local file system for another operating system which does not
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support Unix-style user/group IDs, or which uses a different
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numbering scheme.
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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 Fl g Ar gid-mapfile
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Use the group ID mapping specified in
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.Ar gid-mapfile .
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This flag is required.
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.It Fl u Ar uid-mapfile
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Use the user ID mapping specified in
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.Ar uid-mapfile .
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This flag is required.
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.El
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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.
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For instance, user smith might have uid 1000 in the original environment,
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while having uid 2000 in the local environment.
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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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.Em 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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.Em 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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.Em uid-mapfile
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and
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.Em gid-mapfile
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describe the mappings to be made between identifiers.
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.Pp
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The format of the user and group ID mapping files is very simple.
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The first line of the file is the total number of mappings present
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in the file.
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The remaining lines each consist of two numbers: the
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ID in the mapped subtree and the ID in the original subtree.
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.Pp
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For example, to map uid 1000 in the original subtree to uid 2000
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in the mapped subtree:
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.Bd -unfilled -offset indent
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1
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2000 1000
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.Ed
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.Pp
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For user IDs in the original subtree for which no mapping exists,
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the user ID will be mapped to the user
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.Dq nobody .
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For group IDs in the original subtree for which no mapping exists,
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the group ID will be mapped to the group
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.Dq nobody .
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.Pp
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There is a limit of 64 user ID mappings and 16 group ID mappings.
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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
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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.
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It will also report an error if the count
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of mappings in the first line of the map files is not correct.
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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 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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.Sh BUGS
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The implementation is not very sophisticated.
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