1.\" $NetBSD: mount_umap.8,v 1.14 2001/11/16 11:21:38 wiz Exp $ 2.\" 3.\" Copyright (c) 1992, 1993, 1994 4.\" The Regents of the University of California. All rights reserved. 5.\" All rights reserved. 6.\" 7.\" This code is derived from software donated to Berkeley by 8.\" Jan-Simon Pendry and from John Heidemann of the UCLA Ficus project. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. All advertising materials mentioning features or use of this software 19.\" must display the following acknowledgement: 20.\" This product includes software developed by the University of 21.\" California, Berkeley and its contributors. 22.\" 4. Neither the name of the University nor the names of its contributors 23.\" may be used to endorse or promote products derived from this software 24.\" without specific prior written permission. 25.\" 26.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36.\" SUCH DAMAGE. 37.\" 38.\" @(#)mount_umap.8 8.4 (Berkeley) 5/1/95 39.\" 40.Dd March 6, 2001 41.Dt MOUNT_UMAP 8 42.Os 43.Sh NAME 44.Nm mount_umap 45.Nd user and group ID remapping file system layer 46.Sh SYNOPSIS 47.Nm "" 48.Op Fl o Ar options 49-u 50.Ar uid-mapfile 51-g 52.Ar gid-mapfile 53.Ar target 54.Ar mount-point 55.Sh DESCRIPTION 56The 57.Nm 58command is used to mount a sub-tree of an existing file system 59that uses a different set of uids and gids than the local system. 60Such a file system could be mounted from a remote site via NFS, 61a local file system on removable media brought from some foreign 62location that uses a different user/group database, or could be 63a local file system for another operating system which does not 64support Unix-style user/group IDs, or which uses a different 65numbering scheme. 66.Pp 67The options are as follows: 68.Bl -tag -width indent 69.It Fl o 70Options are specified with a 71.Fl o 72flag followed by a comma separated string of options. 73See the 74.Xr mount 8 75man page for possible options and their meanings. 76.It Fl g Ar gid-mapfile 77Use the group ID mapping specified in 78.Ar gid-mapfile . 79This flag is required. 80.It Fl u Ar uid-mapfile 81Use the user ID mapping specified in 82.Ar uid-mapfile . 83This flag is required. 84.El 85.Pp 86The 87.Nm 88command uses a set of files provided by the user to make correspondences 89between uids and gids in the sub-tree's original environment and 90some other set of ids in the local environment. For instance, user 91smith might have uid 1000 in the original environment, while having 92uid 2000 in the local environment. The 93.Nm 94command allows the subtree from smith's original environment to be 95mapped in such a way that all files with owning uid 1000 look like 96they are actually owned by uid 2000. 97.Pp 98.Em target 99should be the current location of the sub-tree in the 100local system's name space. 101.Em mount-point 102should be a directory 103where the mapped subtree is to be placed. 104.Em uid-mapfile 105and 106.Em gid-mapfile 107describe the mappings to be made between identifiers. 108.Pp 109The format of the user and group ID mapping files is very simple. 110The first line of the file is the total number of mappings present 111in the file. The remaining lines each consist of two numbers: the 112ID in the mapped subtree and the ID in the original subtree. 113.Pp 114For example, to map uid 1000 in the original subtree to uid 2000 115in the mapped subtree: 116.Bd -unfilled -offset indent 1171 1182000 1000 119.Ed 120.Pp 121For user IDs in the original subtree for which no mapping exists, 122the user ID will be mapped to the user 123.Dq nobody . 124For group IDs in the original subtree for which no mapping exists, 125the group ID will be mapped to the group 126.Dq nobody . 127.Pp 128There is a limit of 64 user ID mappings and 16 group ID mappings. 129.Pp 130The mapfiles can be located anywhere in the file hierarchy, but they 131must be owned by root, and they must be writable only by root. 132.Nm 133will refuse to map the sub-tree if the ownership or permissions on 134these files are improper. It will also report an error if the count 135of mappings in the first line of the map files is not correct. 136.Sh SEE ALSO 137.Xr mount 8 , 138.Xr mount_null 8 139.Sh HISTORY 140The 141.Nm 142utility first appeared in 143.Bx 4.4 . 144.Sh BUGS 145The implementation is not very sophisticated. 146