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For example, the file system /home/sweet/home has been exported, and
/home/sweet is a parent directory of /home/sweet/home. You cannot now export
/home/sweet unless it exists on a different local file system.
4. You can only export local file systems. Any file systems or proper subsets of file
systems that exist on remote systems cannot be exported except by those
remote systems.
For example, /help exists on a different server than the one you are currently
accessing. You must be able to access that remote server in order to export
/help.
A more complicated example involves trying to export a file system which a
local client mounts from a remote server. For example, the file system
/home/troupe resides on a local client, and the file system /remote1 exists on a
remote server. If the client mounts /remote1 over /home/troupe, then the client
cannot export /home/troupe. This is because it actually exists on a remote
server and not the local client.
The first rule allows you to export only selected portions of a large file system. You
can export and mount a single file, a feature which is used extensively by clients
without local disks. The second and third rules say that you can export a local file
system in one way, and one way only. Once you export a sub-directory of a file
system, you cannot go
upstream
and export the whole file system. Also, once you
have made the entire file system public, you cannot restrict the
downstream
flow of
the export to include only a few files.
Exporting sub-directories is similar to creating views on a relational database. You
choose the portions of the database that a user needs to see, hiding information
that is either extraneous or confidential. In this way, system administrators can limit
access to sensitive material.
CHGNFSEXP (Change Network File System Export) Command
Purpose
The Change Network File System Export (CHGNFSEXP) command adds directory
names to (
exports
) the list of directory trees that are currently exported to NFS
clients (the export table). This command also removes (
unexports
) the list of
directory trees that are currently exported to NFS clients. The flags in the OPTIONS
list indicate what actions you want the CHGNFSEXP command to perform. For a
complete description of CHGNFSEXP options, see
CL Reference,
SC41-4722.
A list of directories and options for exporting a file system and its contents is stored
in the /etc/exports file. The CHGNFSEXP command allows you to export all of the
directory trees specified in the file using the ’-A’ flag. CHGNFSEXP also allows you
to export a single directory tree by specifying the directory name. When the
directory tree being exported exists in the /etc/exports file, you can export it with
the options specified there, or you can use the ’-I’ flag to override the options,
specifying the new options on the CHGNFSEXP command.
You can also export a directory tree not previously defined in the /etc/exports file
by providing the ’-I’ and the options for it on the CHGNFSEXP command. You can
unexport directory trees by using the ’-U’ flag on the CHGNFSEXP command. You
can unexport any file systems that you have previously exported, even if remote
clients have mounted them. The result is that the NFS server will send the remote
clients the ESTALE error number on their next attempt to operate on an object in
that file system.
30 OS/400 Network File System Support V4R4