amdref.texinfo

早期freebsd实现

\input texinfo		@c -*-texinfo-*-
@c
@c Copyright (c) 1989 Jan-Simon Pendry
@c Copyright (c) 1989 Imperial College of Science, Technology & Medicine
@c Copyright (c) 1989 The Regents of the University of California.
@c All rights reserved.
@c
@c This code is derived from software contributed to Berkeley by
@c Jan-Simon Pendry at Imperial College, London.
@c
@c Redistribution and use in source and binary forms, with or without
@c modification, are permitted provided that the following conditions
@c are met:
@c 1. Redistributions of source code must retain the above copyright
@c    notice, this list of conditions and the following disclaimer.
@c 2. Redistributions in binary form must reproduce the above copyright
@c    notice, this list of conditions and the following disclaimer in the
@c    documentation and/or other materials provided with the distribution.
@c 3. All advertising materials mentioning features or use of this software
@c    must display the following acknowledgement:
@c      This product includes software developed by the University of
@c      California, Berkeley and its contributors.
@c 4. Neither the name of the University nor the names of its contributors
@c    may be used to endorse or promote products derived from this software
@c    without specific prior written permission.
@c
@c THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
@c ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
@c IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
@c ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
@c FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
@c DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
@c OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
@c HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
@c LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
@c OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
@c
@c	@(#)amdref.texinfo	8.1 (Berkeley) 6/6/93
@c
@c $Id: amdref.texinfo,v 5.2.2.1 1992/02/09 15:11:50 jsp beta $
@c
@setfilename amdref.info
@c @setfilename /usr/local/emacs/info/amd
@tex
\overfullrule=0pt
@end tex

@settitle 4.4 BSD Automounter Reference Manual
@titlepage
@sp 6
@center @titlefont{Amd}
@sp 2
@center @titlefont{The 4.4 BSD Automounter}
@sp 2
@center @titlefont{Reference Manual}
@sp 2
@center @authorfont{Jan-Simon Pendry}
@sp
@center @i{and}
@sp
@center @authorfont{Nick Williams}
@sp 4
@center Last updated March 1991
@center Documentation for software revision 5.3 Alpha
@page
Copyright @copyright{} 1989 Jan-Simon Pendry
@sp -1
Copyright @copyright{} 1989 Imperial College of Science, Technology & Medicine
@sp -1
Copyright @copyright{} 1989 The Regents of the University of California.
@sp 0
All Rights Reserved.
@vskip 1ex
Permission to copy this document, or any portion of it, as
necessary for use of this software is granted provided this
copyright notice and statement of permission are included.
@end titlepage
@page
@ifinfo
@node Top, License, , (DIR)

Amd - The 4.4 BSD Automounter
*****************************

Amd is the 4.4 BSD Automounter.  This Info file describes how
to use and understand Amd.
@end ifinfo

@menu
* License::                  Explains the terms and conditions for using
                             and distributing Amd.
* Distrib::                  How to get the latest Amd distribution.
* Intro::                    An introduction to Automounting concepts.
* Overview::                 An overview of Amd.
* Supported Platforms::      Machines and Systems supported by Amd.
* Mount Maps::               Details of mount maps
* Amd Command Line Options:: All the Amd command line options explained. 
* Filesystem Types::         The different mount types supported by Amd.
* Run-time Administration::  How to start, stop and control Amd.
* FSinfo::                   The FSinfo filesystem management tool.
* Internals::                Internals.
* Acknowledgements & Trademarks:: Legal notes.
* Examples::                 Some examples showing how Amd might be used.
* Internals::                Implementation details.
* Acknowledgements & Trademarks::

Indexes
* Index::                    An item for each concept.
@end menu

@iftex
@unnumbered Preface

This manual documents the use of the 4.4 BSD automounter---@i{Amd}.
This is primarily a reference manual.  Unfortunately, no tutorial
exists.

This manual comes in two forms: the published form and the Info form.
The Info form is for on-line perusal with the INFO program which is
distributed along with GNU Emacs.  Both forms contain substantially the
same text and are generated from a common source file, which is
distributed with the @i{Amd} source.
@end iftex

@node License, Distrib, Top, Top
@unnumbered License
@cindex License Information

@i{Amd} is not in the public domain; it is copyrighted and there are
restrictions on its distribution.

Redistribution and use in source and binary forms are permitted provided
that: (1) source distributions  retain this entire  copyright notice and
comment, and (2) distributions including  binaries display the following
acknowledgement: ``This product  includes  software  developed  by   The
University  of California,   Berkeley  and its  Contributors''  in   the
documentation  or other materials provided with  the distribution and in
all advertising materials mentioning  features  or use of this software.
neither the name of the University nor the names of its Contributors may
be  used   to endorse or promote   products  derived from  this software
without specific prior written permission.

THIS SOFTWARE IS  PROVIDED ``AS IS''  AND WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING,  WITHOUT  LIMITATION,  THE IMPLIED  WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

@node Distrib, Intro, License, Top
@unnumbered Source Distribution
@cindex Source code distribution
@cindex Obtaining the source code

If you have access to the Internet, you can get the latest distribution
version of @i{Amd} from host @file{usc.edu} using anonymous FTP.  Move to
the directory @file{/pub/amd} on that host and fetch the file @file{amd.tar.Z}.

If you are in the UK, you can get the latest distribution version of
@i{Amd} from the UKnet info-server.  Start by sending email to
@file{info-server@@doc.ic.ac.uk}.

Sites on the UK JANET network can get the latest distribution by using
anonymous NIFTP to fetch the file @samp{<AMD>amd.tar.Z} from host
@samp{uk.ac.imperial.doc.src}.

Revision 5.2 was part of the 4.3 BSD Reno distribution.

Revision 5.3bsdnet, a late alpha version of 5.3, was part
of the BSD network version 2 distribution

@unnumberedsec Bug Reports
@cindex Bug reports

Send all bug reports to @file{jsp@@doc.ic.ac.uk} quoting the details of
the release and your configuration.  These can be obtained by running
the command @samp{amd -v}.

@unnumberedsec Mailing List
@cindex Mailing list

There is a mailing list for people interested in keeping uptodate with
developments.  To subscribe, send a note to @file{amd-workers-request@@acl.lanl.gov}.

@node Intro, Overview, Distrib, Top
@unnumbered Introduction
@cindex Introduction

An @dfn{automounter} maintains a cache of mounted filesystems.
Filesystems are mounted on demand when they are first referenced,
and unmounted after a period of inactivity.

@i{Amd} may be used as a replacement for Sun's automounter.  The choice
of which filesystem to mount can be controlled dynamically with
@dfn{selectors}.  Selectors allow decisions of the form ``hostname is
@var{this},'' or ``architecture is not @var{that}.''  Selectors may be
combined arbitrarily.  @i{Amd} also supports a variety of filesystem
types, including NFS, UFS and the novel @dfn{program} filesystem.  The
combination of selectors and multiple filesystem types allows identical
configuration files to be used on all machines so reducing the
administrative overhead.

@i{Amd} ensures that it will not hang if a remote server goes down.
Moreover, @i{Amd} can determine when a remote server has become
inaccessible and then mount replacement filesystems as and when they
become available.

@i{Amd} contains no proprietary source code and has been ported to
numerous flavours of Unix.

@node Overview, Supported Platforms, Intro, Top
@chapter Overview

@i{Amd} maintains a cache of mounted filesystems.  Filesystems are
@dfn{demand-mounted} when they are first referenced, and unmounted after
a period of inactivity.  @i{Amd} may be used as a replacement for Sun's
@b{automount}(8) program.  It contains no proprietary source code and
has been ported to numerous flavours of Unix.  @xref{Supported Operating
Systems}.@refill

@i{Amd} was designed as the basis for experimenting with filesystem
layout and management.  Although @i{Amd} has many direct applications it
is loaded with additional features which have little practical use.  At
some point the infrequently used components may be removed to streamline
the production system.

@c @i{Amd} supports the notion of @dfn{replicated} filesystems by evaluating
@c each member of a list of possible filesystem locations in parallel.
@c @i{Amd} checks that each cached mapping remains valid.  Should a mapping be
@c lost -- such as happens when a fileserver goes down -- @i{Amd} automatically
@c selects a replacement should one be available.
@c
@menu
* Fundamentals::
* Filesystems and Volumes::
* Volume Naming::
* Volume Binding::
* Operational Principles::
* Mounting a Volume::
* Automatic Unmounting::
* Keep-alives::
* Non-blocking Operation::
@end menu

@node     Fundamentals, Filesystems and Volumes, Overview, Overview
@comment  node-name,  next,  previous,  up
@section Fundamentals
@cindex Automounter fundamentals

The fundamental concept behind @i{Amd} is the ability to separate the
name used to refer to a file from the name used to refer to its physical
storage location.  This allows the same files to be accessed with the
same name regardless of where in the network the name is used.  This is
very different from placing @file{/n/hostname} in front of the pathname
since that includes location dependent information which may change if
files are moved to another machine.

By placing the required mappings in a centrally administered database,
filesystems can be re-organised without requiring changes to
configuration files, shell scripts and so on.

@node     Filesystems and Volumes, Volume Naming, Fundamentals, Overview
@comment  node-name,  next,  previous,  up
@section Filesystems and Volumes
@cindex Filesystem
@cindex Volume
@cindex Fileserver
@cindex sublink

@i{Amd} views the world as a set of fileservers, each containg one or
more filesystems where each filesystem contains one or more
@dfn{volumes}.  Here the term @dfn{volume} is used to refer to a
coherent set of files such as a user's home directory or a @TeX{}
distribution.@refill

In order to access the contents of a volume, @i{Amd} must be told in
which filesystem the volume resides and which host owns the filesystem.
By default the host is assumed to be local and the volume is assumed to
be the entire filesystem.  If a filesystem contains more than one
volume, then a @dfn{sublink} is used to refer to the sub-directory
within the filesystem where the volume can be found.

@node     Volume Naming, Volume Binding, Filesystems and Volumes, Overview
@comment  node-name,  next,  previous,  up
@section Volume Naming
@cindex Volume names
@cindex Network-wide naming
@cindex Replicated volumes
@cindex Duplicated volumes
@cindex Replacement volumes

Volume names are defined to be unique across the entire network.  A
volume name is the pathname to the volume's root as known by the users
of that volume.  Since this name uniquely identifies the volume
contents, all volumes can be named and accessed from each host, subject
to administrative controls.

Volumes may be replicated or duplicated.  Replicated volumes contain
identical copies of the same data and reside at two or more locations in
the network.  Each of the replicated volumes can be used
interchangeably.  Duplicated volumes each have the same name but contain
different, though functionally identical, data.  For example,
@samp{/vol/tex} might be the name of a @TeX{} distribution which varied
for each machine architecture.@refill

@i{Amd} provides facilities to take advantage of both replicated and
duplicated volumes.  Configuration options allow a single set of
configuration data to be shared across an entire network by taking
advantage of replicated and duplicated volumes.

@i{Amd} can take advantage of replacement volumes by mounting them as
required should an active fileserver become unavailable.

@node     Volume Binding, Operational Principles, Volume Naming, Overview
@comment  node-name,  next,  previous,  up
@section Volume Binding
@cindex Volume binding
@cindex Unix namespace
@cindex Namespace
@cindex Binding names to filesystems

Unix implements a namespace of hierarchically mounted filesystems.  Two
forms of binding between names and files are provided.  A @dfn{hard
link} completes the binding when the name is added to the filesystem.  A
@dfn{soft link} delays the binding until the name is accessed.  An
@dfn{automounter} adds a further form in which the binding of name to
filesystem is delayed until the name is accessed.@refill

The target volume, in its general form, is a tuple (host, filesystem,
sublink) which can be used to name the physical location of any volume
in the network.

When a target is referenced, @i{Amd} ignores the sublink element and