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36 .\" @(#)mount_umap.8 8.4 (Berkeley) 5/1/95
37 .\" $FreeBSD: src/sbin/mount_umap/mount_umap.8,v 1.10.2.3 2001/12/20 16:44:17 ru Exp $
44 .Nd sample file system layer
55 command is used to mount a sub-tree of an existing file system
56 that uses a different set of uids and gids than the local system.
57 Such a file system could be mounted from a remote site via NFS or
58 it could be a file system on removable media brought from some
59 foreign location that uses a different password file.
63 command uses a set of files provided by the user to make correspondences
64 between uids and gids in the sub-tree's original environment and
65 some other set of ids in the local environment. For instance, user
66 smith might have uid 1000 in the original environment, while having
67 uid 2000 in the local environment. The
69 command allows the subtree from smith's original environment to be
70 mapped in such a way that all files with owning uid 1000 look like
71 they are actually owned by uid 2000.
73 The options are as follows:
74 .Bl -tag -width indent
76 Options are specified with a
78 flag followed by a comma separated string of options.
81 man page for possible options and their meanings.
83 Should be the current location of the sub-tree in the
84 local system's name space.
87 where the mapped subtree is to be placed.
88 .It Fl u Ar uid-mapfile
89 .It Fl g Ar gid-mapfile
90 Describe the mappings to be made between identifiers.
91 Briefly, the format of these files is a count of the number of
92 mappings on the first line, with each subsequent line containing
93 a single mapping. Each of these mappings consists of an id in
94 the local environment and the corresponding id from the original environment,
95 separated by white space.
97 should contain all uid
100 should contain all gid mappings.
101 Any uids not mapped in
103 will be treated as user NOBODY,
104 and any gids not mapped in
106 will be treated as group
107 NULLGROUP. At most 64 uids can be mapped for a given subtree, and
108 at most 16 groups can be mapped by a given subtree.
111 The mapfiles can be located anywhere in the file hierarchy, but they
112 must be owned by root, and they must be writable only by root.
114 will refuse to map the sub-tree if the ownership or permissions on
115 these files are improper. It will also balk if the count of mappings
116 in the first line of the map files is not correct.
118 The layer created by the
120 command is meant to serve as a simple example of file system layering.
121 It is not meant for production use. The implementation is not very
127 THIS FILESYSTEM TYPE IS NOT YET FULLY SUPPORTED (READ: IT DOESN'T WORK)
128 AND USING IT MAY, IN FACT, DESTROY DATA ON YOUR SYSTEM. USE AT YOUR
129 OWN RISK. BEWARE OF DOG. SLIPPERY WHEN WET.
131 This code also needs an owner in order to be less dangerous - serious
132 hackers can apply by sending mail to
133 .Aq hackers@FreeBSD.org
135 their intent to take it over.
139 utility first appeared in