Technical data

NFS Client
21.1 Key Concepts
All files below the mount point are available to client users as if they reside
on the local system. The NFS client requests file operations by contacting a
remote NFS server. The server then performs the requested operation. The
NFS client automatically converts all mounted directories and file structures,
contents, and names to the format required by OpenVMS. For example, a
UNIX file named /usr/webster/.login would appear to an OpenVMS client as
DNFS1:[USR.WEBSTER].LOGIN;1
For more information on how NFS converts file names, see Appendix C.
21.1.2 Storing File Attributes
The OpenVMS operating system supports multiple file types and record formats.
In contrast, NFS and UNIX systems support only byte-stream files, seen to the
OpenVMS client as sequential STREAM_LF files.
This means the client must use special record handling to store and access non-
STREAM_LF files. The OpenVMS NFS client accomplishes this with attribute
description files (ADFs). These are special companion files the client uses to
hold the attribute information that would otherwise be lost in the translation to
STREAM_LF format. For example, a SET FILE/NOBACKUP command causes
the client to create an ADF, because NFS has no concept of this OpenVMS
attribute.
21.1.2.1 Using Default ADFs
The client provides default ADFs for files with the following extensions: .EXE,
.HLB, .MLB, .OBJ, .OLB, .STB, and .TLB. (The client does not provide ADFs for
files with the .TXT and .C extensions, because these are STREAM_LF.) The client
maintains these ADFs on the server.
For example, SYS$SYSTEM:TCPIP$EXE.ADF is the default ADF for all .EXE
type files. When you create .EXE files (or if they exist on the server), they are
defined with the record attributes from the single default ADF file. The client
refers only to the record attributes and file characteristics fields in the default
ADF.
21.1.2.2 How the Client Uses ADFs
By default, the client uses ADFs if they exist on the server. The client updates
existing ADFs or creates them as needed for new files. If you create a non-
STREAM_LF OpenVMS file or a file with access control lists (ACLs) associated
with it on the NFS server, the NFS client checks to see whether a default ADF
can be applied. If not, the client creates a companion ADF to hold the attributes.
The client hides these companion files from the user’s view. If a user renames or
deletes the orginal file, the client automatically renames or deletes the companion
file. However, if a user renames or deletes a file on the server side, the user must
also rename the companion file; otherwise, file attributes are lost.
You can modify this behavior with the /NOADF qualifier to the MOUNT
command. The /NOADF qualifier tells the client to handle all files as STREAM_
LF unless a default ADF matches. This mode is only appropriate for read-only
file systems because the client cannot adequately handle application-created files
when /NOADF is operational.
21–2 NFS Client