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MOUNT_UMAPFS(8)         FreeBSD System Manager's Manual        MOUNT_UMAPFS(8)

NAME
     mount_umapfs -- sample file system layer

SYNOPSIS
     mount_umapfs [-o options] -u uid-mapfile -g gid-mapfile target
                  mount-point

DESCRIPTION
     The mount_umapfs utility is used to mount a sub-tree of an existing file
     system that uses a different set of uids and gids than the local system.
     Such a file system could be mounted from a remote site via NFS or it
     could be a file system on removable media brought from some foreign loca-
     tion that uses a different password file.

     The mount_umapfs utility uses a set of files provided by the user to make
     correspondences between uids and gids in the sub-tree's original environ-
     ment and some other set of ids in the local environment.  For instance,
     user smith might have uid 1000 in the original environment, while having
     uid 2000 in the local environment.  The mount_umapfs utility allows the
     subtree from smith's original environment to be mapped in such a way that
     all files with owning uid 1000 look like they are actually owned by uid
     2000.

     The options are as follows:

     -o      Options are specified with a -o flag followed by a comma sepa-
             rated string of options.  See the mount(8) man page for possible
             options and their meanings.

     target  Should be the current location of the sub-tree in the local sys-
             tem's name space.

     mount-point
             Should be a directory where the mapped subtree is to be placed.

     -u uid-mapfile

     -g gid-mapfile
             Describe the mappings to be made between identifiers.  Briefly,
             the format of these files is a count of the number of mappings on
             the first line, with each subsequent line containing a single
             mapping.  Each of these mappings consists of an id in the local
             environment and the corresponding id from the original environ-
             ment, separated by white space.  Uid-mapfile should contain all
             uid mappings, and gid-mapfile should contain all gid mappings.
             Any uids not mapped in uid-mapfile will be treated as user
             NOBODY, and any gids not mapped in gid-mapfile will be treated as
             group NULLGROUP.  At most 64 uids can be mapped for a given sub-
             tree, and at most 16 groups can be mapped by a given subtree.

     The mapfiles can be located anywhere in the file hierarchy, but they must
     be owned by root, and they must be writable only by root.  The
     mount_umapfs utility will refuse to map the sub-tree if the ownership or
     permissions on these files are improper.  It will also balk if the count
     of mappings in the first line of the map files is not correct.

     The layer created by the mount_umapfs utility is meant to serve as a sim-
     ple example of file system layering.  It is not meant for production use.
     The implementation is not very sophisticated.

SEE ALSO
     mount(8), mount_nullfs(8)

HISTORY
     The mount_umapfs utility first appeared in 4.4BSD.

BUGS
     THIS FILE SYSTEM TYPE IS NOT YET FULLY SUPPORTED (READ: IT DOESN'T WORK)
     AND USING IT MAY, IN FACT, DESTROY DATA ON YOUR SYSTEM.  USE AT YOUR OWN
     RISK.  BEWARE OF DOG.  SLIPPERY WHEN WET.

     This code also needs an owner in order to be less dangerous - serious
     hackers can apply by sending mail to <hackers@FreeBSD.org> and announcing
     their intent to take it over.

FreeBSD 6.2                       May 1, 1995                      FreeBSD 6.2

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | BUGS

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