| MOUNT_UMAP(8) | System Manager's Manual | MOUNT_UMAP(8) | 
mount_umap —
| mount_umap | [ -ooptions]-ggid-mapfile-uuid-mapfile
      target mount-point | 
mount_umap command 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, a
  local file system on removable media brought from some foreign location that
  uses a different user/group database, or could be a local file system for
  another operating system which does not support Unix-style user/group IDs, or
  which uses a different numbering scheme.
Both target and mount-point are converted to absolute paths before use.
The options are as follows:
-g
    gid-mapfile-o-o flag followed by a
      comma separated string of options. See the
      mount(8) man page for
      possible options and their meanings.-u
    uid-mapfileThe mount_umap command uses a set of files
    provided by the user to make correspondences between uids and gids in the
    sub-tree'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 owning
    uid 1000 look like they are actually owned by uid 2000.
target should be the current location of the sub-tree 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 the user and group ID mapping files is very simple. The first line of the file is the total number of mappings present in the file. The remaining lines each consist of two numbers: the ID in the mapped subtree and the ID in the original subtree.
For example, to map uid 1000 in the original subtree to uid 2000 in the mapped subtree:
1 2000 1000
For user IDs in the original subtree for which no mapping exists, the user ID will be mapped to the user “nobody”. For group IDs in the original subtree for which no mapping exists, the group ID will be mapped to the group “nobody”.
There is a limit of 64 user ID mappings and 16 group ID mappings.
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 sub-tree if the
    ownership or permissions on these files are improper. It will also report an
    error if the count of mappings in the first line of the map files is not
    correct.
mount_umap utility first appeared in
  4.4BSD.
| March 6, 2001 | NetBSD 9.4 |