NAME    [Toc]    [Back]

     mount_umap - sample file system layer

SYNOPSIS    [Toc]    [Back]

     mount_umap [-o options] -u uid-mapfile -g gid-mapfile target
mount_point

DESCRIPTION    [Toc]    [Back]

     The  mount_umap command is used to mount a subtree 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 location
 that uses a different password file.

     The options are as follows:

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

     -g gid-mapfile
             Use  the  group ID mapping specified in gid-mapfile.
This flag is
             required.

     -u uid-mapfile
             Use the user ID mapping  specified  in  uid-mapfile.
This flag is
             required.

     The  mount_umap  command uses a set of files provided by the
user to make
     correspondences between UIDs and GIDs in the subtree's original environment
  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_umap command
allows the
     subtree from smith's original environment to  be  mapped  in
such a way that
     all  files  with  owner UID 1000 look like they are actually
owned by UID
     2000.

     target should be the current location of the subtree in  the
local system's
  name  space.  mount_point should be a directory where
the mapped
     subtree is to be placed.  uid-mapfile  and  gid-mapfile  describe the mappings
 to be made between identifiers.

     The format of these files is very simple.  The first line is
a count of
     the number of mappings.  Each subsequent line  contains  two
numbers.  The
     first is the ID in the mapped subtree, and the second is the
ID in the
     original subtree.  IDs in the original subtree for which  no
mapping exists
  will  be mapped to ``nobody''.  At most 64 UIDs can be
mapped for a
     given subtree, 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.
mount_umap
     will  refuse  to map the subtree 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.

SEE ALSO    [Toc]    [Back]

     mount(2), mount(8), mount_null(8)

HISTORY    [Toc]    [Back]

     The mount_umap utility first appeared in 4.4BSD.

BUGS    [Toc]    [Back]

     It  is  not meant for production use.  The implementation is
not very sophisticated.


OpenBSD     3.6                          March      27,      1994