Preface
Twenty years ago, most computer centers had a few large computers
shared by several hundred users. The "computing
environment" was usually a room containing dozens of terminals.
All users worked in the same place, with one set of disks, one user
account information file, and one view of all resources. Today, local
area networks have made terminal rooms much less common. Now, a
"computing environment"
almost always refers to distributed
computing, where users have personal desktop machines, and shared
resources are provided by special-purpose systems such as file,
computer, and print servers. Each desktop requires redundant
configuration files, including user information, network host
addresses, and local and shared remote filesystem information.
A mechanism to provide consistent access to all files and
configuration information ensures that all users have access to the
"right" machines, and that once they have logged in they
will see a set of files that is both familiar and complete. This
consistency must be provided in a way that is transparent to the
users; that is, a user should not know that a filesystem is located
on a remote fileserver. The transparent view of resources must be
consistent across all machines and also consistent with the way
things work in a non-networked environment. In a networked computing
environment, it's usually up to the system administrator to
manage the machines on the network (including centralized servers) as
well as the network itself. Managing the network means
ensuring
that the network is transparent to users rather than an impediment to
their work.
The
Network File
System (NFS)
and the
Network Information
Service (NIS)
[1] provide mechanisms for solving
"consistent and transparent" access problems. The NFS and
NIS protocols were developed by Sun Microsystems
and
are now
licensed to hundreds of vendors and universities, not to mention
dozens of implementations from the published NFS and NFS
specifications. NIS centralizes commonly replicated configuration
files, such as the password file, on a single host. It
eliminates
duplicate copies of user and system information and allows the system
administrator to make changes from one place. NFS makes remote
filesystems appear to be local, as if they were
on
disks attached to the local host. With NFS, all machines can share a
single set of files, eliminating duplicate copies of files on
different machines in the network. Using NFS and NIS together greatly
simplifies the management of various combinations of machines, users,
and filesystems.
NFS provides network and filesystem transparency
because it
hides the actual, physical location of the filesystem. A user's
files could be on a local disk, on a shared disk on a fileserver, or
even on a machine located across a wide-area network. As a user,
you're most content when you see the same files on all
machines. Just having the files available, though, doesn't mean
that you can access them if your user information isn't
correct. Missing or inconsistent user and group information will
break Unix file
permission checking. This is where NIS complements NFS, by adding
consistency to the information used to build and describe the shared
filesystems. A user can sit down in front of any workstation in his
or her group that is running NIS and be reasonably assured that he or
she can log in, find his or her home directory, and access tools such
as compilers, window systems, and publishing packages. In addition to
making life easier for the users, NFS and NIS simplify the tasks of
system administrators, by centralizing the management of both
configuration information and disk resources.
NFS can be used to create very complex filesystems, taking components
from many different servers on the network. It is possible to
overwhelm users by providing "everything everywhere," so
simplicity should rule network design. Just as a database programmer
constructs views of a database to present only the relevant fields to
an application, the user community should see a logical collection of
files, user account information, and system services from each
viewpoint in the computing environment. Simplicity often satisfies
the largest number of users, and it makes the system
administrator's job easier.
0.1. Who this book is for
This book is of interest to system administrators and network
managers who are installing or planning new NFS and NIS networks, or
debugging and tuning existing networks and servers. It is also aimed
at the network user who is interested in the mechanics that hold the
network together.
We'll assume that you are familiar with
the basics of Unix
system administration and TCP/IP networking. Terms that are commonly
misused or particular to a discussion will be defined as needed.
Where appropriate, an explanation of a low-level phenomenon, such as
Ethernet congestion will be provided if it is important to a more
general discussion such as NFS performance on a congested network.
Models for these phenomena will be drawn from everyday examples
rather than their more rigorous mathematical and statistical roots.
This book focuses on the way NFS and NIS work, and how to use them to
solve common problems in a distributed computing environment. Because
Sun Microsystems developed and continues to innovate NFS and NIS,
this book uses Sun's Solaris operating system as the frame of
reference. Thus if you are administering NFS on non-Solaris systems,
you should use this book in conjunction with your vendor's
documentation, since utilities and their options will vary by
implementation and release. This book explains what the configuration
files and utilities do, and how their options affect performance and
system administration issues. By walking through the steps comprising
a complex operation or by detailing each step in the debugging
process, we hope to shed light on techniques for effective management
of distributed computing environments. There are very few absolute
constraints or thresholds that are universally applicable, so we
refrain from stating them. This book should help you to determine the
fair utilization and performance constraints for your network.
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