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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)

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.

HISTORY
     The mount_umapfs utility first appeared in	4.4BSD.

FreeBSD	9.3			  May 1, 1995			   FreeBSD 9.3

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

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