| 1 | .\" Copyright (c) 1992, 1993 |
| 2 | .\" The Regents of the University of California. All rights reserved. |
| 3 | .\" All rights reserved. |
| 4 | .\" |
| 5 | .\" This code is derived from software donated to Berkeley by |
| 6 | .\" Jan-Simon Pendry and from John Heidemann of the UCLA Ficus project. |
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| 36 | .\" @(#)mount_umap.8 8.1 (Berkeley) 6/9/93 |
| 37 | .\" |
| 38 | .Dd "June 9, 1993" |
| 39 | .Dt MOUNT_UMAP 8 |
| 40 | .Os BSD 4.4 |
| 41 | .Sh NAME |
| 42 | .Nm mount_umap |
| 43 | .Nd sample file system layer |
| 44 | .Sh SYNOPSIS |
| 45 | .Nm mount_umap |
| 46 | .Op Fl F Ar fsoptions |
| 47 | .Ar target mount-point uid-mapfile gid-mapfile |
| 48 | .Sh DESCRIPTION |
| 49 | The |
| 50 | .Nm mount_umap |
| 51 | command is used to mount a sub-tree of an existing file system |
| 52 | that uses a different set of uids and gids than the local system. |
| 53 | Such a file system could be mounted from a remote site via NFS or |
| 54 | it could be a file system on removable media brought from some |
| 55 | foreign location that uses a different password file. |
| 56 | The |
| 57 | .Nm mount_umap |
| 58 | command uses a set of files provided by the user to make correspondences |
| 59 | between uids and gids in the sub-tree's original environment and |
| 60 | some other set of ids in the local environment. For instance, user |
| 61 | smith might have uid 1000 in the original environment, while having |
| 62 | uid 2000 in the local environment. The |
| 63 | .Nm mount_umap |
| 64 | command allows the subtree from smith's original environment to be |
| 65 | mapped in such a way that all files with owning uid 1000 look like |
| 66 | they are actually owned by uid 2000. |
| 67 | .Pp |
| 68 | .Em target |
| 69 | should be the current location of the sub-tree in the |
| 70 | local system's name space. |
| 71 | .Em mount-point |
| 72 | should be a directory |
| 73 | where the mapped subtree is to be placed. |
| 74 | .Em uid-mapfile |
| 75 | and |
| 76 | .Em gid-mapfile |
| 77 | describe the mappings to be made between identifiers. |
| 78 | Briefly, the format of these files is a count of the number of |
| 79 | mappings on the first line, with each subsequent line containing |
| 80 | a single mapping. Each of these mappings consists of an id from |
| 81 | the original environment and the corresponding id in the local environment, |
| 82 | separated by white space. |
| 83 | .Em uid-mapfile |
| 84 | should contain all uid |
| 85 | mappings, and |
| 86 | .Em gid-mapfile |
| 87 | should contain all gid mappings. |
| 88 | Any uids not mapped in |
| 89 | .Em uid-mapfile |
| 90 | will be treated as user NOBODY, |
| 91 | and any gids not mapped in |
| 92 | .Em gid-mapfile |
| 93 | will be treated as group |
| 94 | NULLGROUP. At most 64 uids can be mapped for a given subtree, and |
| 95 | at most 16 groups can be mapped by a given subtree. |
| 96 | .Pp |
| 97 | The mapfiles can be located anywhere in the file hierarchy, but they |
| 98 | must be owned by root, and they must be writable only by root. |
| 99 | .Nm mount_umap |
| 100 | will refuse to map the sub-tree if the ownership or permissions on |
| 101 | these files are improper. It will also balk if the count of mappings |
| 102 | in the first line of the map files is not correct. |
| 103 | .Pp |
| 104 | The layer created by the |
| 105 | .Nm mount_umap |
| 106 | command is meant to serve as a simple example of file system layering. |
| 107 | It is not meant for production use. The implementation is not very |
| 108 | sophisticated. |
| 109 | .Sh SEE ALSO |
| 110 | .Xr mount_null 8 , |
| 111 | .Xr mount_lofs 8 |
| 112 | .Sh HISTORY |
| 113 | The |
| 114 | .Nm mount_umap |
| 115 | utility first appeared in 4.4BSD. |