| Installing and Administering the NFS Client |
In a cross-development environment, the Network File System
(NFS) client support provided by the SAS/C Connectivity
Support Library (CSL) enables the SAS/C Debugger
to communicate with the host workstation. This appendix provides the basic
information necessary to administer this NFS support. Additional information
is contained in Using the NFS Client and SAS Technical Report C-113, SAS/C Connectivity
Support Library, Release 1.00.
As an administrator for the SAS/C CSL
NFS client, you must be concerned with installing the software, establishing
access controls for remote file security, (optionally) developing file-system
mount configurations, and diagnosing problems. This support is provided in
a distributed file systems environment that uses Sun NFS protocol for network
communication between computer systems.
As networking
protocols and applications have become more sophisticated,
file sharing among computers has evolved from simple file transfer to the
construction of distributed file systems. In a distributed file system, programs
and users can access (open, read, write, etc.) file systems from a remote
machine directly, as if they were attached to the local system.
Although numerous designs for distributed file systems
have been implemented experimentally, only a few have achieved commercial
success. Of these, the Sun Microsystems Network File System (NFS) protocol
is by far the most widely used. Although not as full-featured as some other
file systems (most notably the Andrew File System) in areas such as file caching
and integrated security administration, its simple and modest design have
made it easy to implement on a wide variety of systems. NFS software is currently
available for almost every computer and operating system on the market today.
NFS is implemented using
a protocol composed of Sun Remote Procedure Call (RPC) function calls. As
with most RPC applications, the protocol supports a dialog among servers and
clients. The NFS servers are the machines that provide remote access to their
file systems. NFS clients are programs that access the files on another system.
Use of RPC enhances interoperability among diverse machines.
The NFS protocol views all file systems as conforming
to the hierarchical directory organization that has been popularized by the
UNIX operating system and that was subsequently codified by the IEEE POSIX
standard. The NFS protocol not only allows reading and writing of files, it
also supports manipulation of directories.
Each NFS client system builds and maintains
its own file system view. This view results from a hierarchical combination
of its own file systems and the file systems of servers to which it wants
access. At any given directory of this view, the client system may attach
a new sub-tree of directories from an NFS server. This process of attaching
a new sub-tree of directories is called mounting a remote file system. The directory to which the remote file system is mounted is called
the mount point.
An important effect of the mount operation is that the
files in the mount-point directory are no longer visible to the client. The
newly mounted files in the remote file system are visible instead.
Another important principle is that NFS mounts that
are made by a server, when it acts as a client to another system, are not
visible to its clients. The clients see only the files that are physically
located on the server.
For users of MVS and CMS, perhaps the most important
aspect of the NFS design is its orientation toward being a network service
instead of being the file system component of a distributed operating system.
This orientation is critical in enabling the use of NFS on operating systems
that are dissimilar to the UNIX environments in which NFS was originally implemented.
The primary requirements for an operating system to participate in NFS are
the ability to interpret a hierarchical file system structure and to share
UNIX format user identification numbers. Other similarities to UNIX are not
required. The SAS/C CSL NFS implementation
is able to effect support for directories and UNIX user identification on
MVS and CMS.
Copyright © 2001
by SAS Institute Inc., Cary, NC, USA. All rights reserved.
