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

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

License
*******

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.

Source Distribution
*******************

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

If you are in the UK, you can get the latest distribution version of Amd from the UKnet info-server.  Start by sending email to 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 <AMD>amd.tar.Z from host 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

Bug Reports
===========

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

Mailing List
============

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

Introduction
************

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

Amd may be used as a replacement for Sun's automounter.  The choice of which filesystem to mount can be controlled dynamically with selectors.  Selectors allow decisions of the form ``hostname is THIS,'' or ``architecture is not THAT.''  Selectors may be combined arbitrarily.  Amd also supports a variety of filesystem types, including NFS, UFS and the novel 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.

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

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

Overview
********

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

Amd was designed as the basis for experimenting with filesystem layout and management.  Although 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.

Fundamentals
============

The fundamental concept behind 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 /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.

Filesystems and Volumes
=======================

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

In order to access the contents of a volume, 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 sublink is used to refer to the sub-directory within the filesystem where the volume can be found.

Volume Naming
=============

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, /vol/tex might be the name of a TeX distribution which varied for each machine architecture.

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.

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

Volume Binding
==============

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

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, Amd ignores the sublink element and determines whether the required filesystem is already mounted.  This is done by computing the local mount point for the filesystem and checking for an existing filesystem mounted at the same place.  If such a filesystem already exists then it is assumed to be functionally identical to the target filesystem.  By default there is a one-to-one mapping between the pair (host, filesystem) and the local mount point so this assumption is valid.

Operational Principles
======================

Amd operates by introducing new mount points into the namespace. These are called automount points.  The kernel sees these automount points as NFS filesystems being served by Amd.  Having attached itself to the namespace, Amd is now able to control the view the rest of the system has of those mount points.  RPC calls are received from the kernel one at a time.

When a lookup call is received Amd checks whether the name is already known.  If it is not, the required volume is mounted.  A symbolic link pointing to the volume root is then returned.  Once the symbolic link is returned, the kernel will send all other requests direct to the mounted filesystem.

If a volume is not yet mounted, Amd consults a configuration mount-map corresponding to the automount point.  Amd then makes a runtime decision on what and where to mount a filesystem based on the information obtained from the map.

Amd does not implement all the NFS requests; only those relevant to name binding such as lookup, readlink and readdir. Some other calls are also implemented but most simply return an error code; for example mkdir always returns ``read-only filesystem''.

Mounting a Volume
=================

Each automount point has a corresponding mount map.  The mount map contains a list of key--value pairs.  The key is the name of the volume to be mounted.  The value is a list of locations describing where the filesystem is stored in the network.  In the source for the map the value would look like

     location1  location2  ...  locationN

Amd examines each location in turn.  Each location may contain selectors which control whether Amd can use that location. For example, the location may be restricted to use by certain hosts. Those locations which cannot be used are ignored.

Amd attempts to mount the filesystem described by each remaining location until a mount succeeds or Amd can no longer proceed.  The latter can occur in three ways:

  * If none of the locations could be used, or if all of the locations caused an error, then the last error is returned.

  * If a location could be used but was being mounted in the background then Amd marks that mount as being ``in progress'' and continues with the next request; no reply is sent to the kernel.

  * Lastly, one or more of the mounts may have been deferred.  A mount is deferred if extra information is required before the mount can proceed.  When the information becomes available the mount will take place, but in the mean time no reply is sent to the kernel.  If the mount is deferred, Amd continues to try any remaining locations.

Once a volume has been mounted, Amd establishes a volume mapping which is used to satisfy subsequent requests.

Automatic Unmounting
====================

To avoid an ever increasing number of filesystem mounts, Amd removes volume mappings which have not been used recently.  A time-to-live interval is associated with each mapping and when that expires the mapping is removed.  When the last reference to a filesystem is removed, that filesystem is unmounted.  If the unmount fails, for example the filesystem is still busy, the mapping is re-instated and its time-to-live interval is extended.  The global default for this grace period is controlled by the ``-w'' command-line option (see -w).  It is also possible to set this value on a per-mount basis (see opts).

Filesystems can be forcefully timed out using the Amq command. See Run-time Administration.

Keep-alives
===========

Use of some filesystem types requires the presence of a server on another machine.  If a machine crashes then it is of no concern to processes on that machine that the filesystem is unavailable.  However, to processes on a remote host using that machine as a fileserver this event is important.  This situation is most widely recognised when an NFS server crashes and the behaviour observed on client machines is that more and more processes hang.  In order to provide the possibility of recovery, Amd implements a keep-alive interval timer for some filesystem types.  Currently only NFS makes use of this service.

The basis of the NFS keep-alive implementation is the observation that most sites maintain replicated copies of common system data such as manual pages, most or all programs, system source code and so on.  If one of those servers goes down it would be reasonable to mount one of the others as a replacement.

The first part of the process is to keep track of which fileservers are up and which are down.  Amd does this by sending RPC requests to the servers' NFS NullProc and checking whether a reply is returned. While the server state is uncertain the requests are re-transmitted at three second intervals and if no reply is received after four attempts the server is marked down.  If a reply is received the fileserver is marked up and stays in that state for 30 seconds at which time another NFS ping is sent.

Once a fileserver is marked down, requests continue to be sent every 30 seconds in order to determine when the fileserver comes back up.  During this time any reference through Amd to the filesystems on that server fail with the error ``Operation would block''.  If a replacement volume is available then it will be mounted, otherwise the error is returned to the user.

Although this action does not protect user files, which are unique on the network, or processes which do not access files via Amd or already have open files on the hung filesystem, it can prevent most new processes from hanging.

By default, fileserver state is not maintained for NFS/TCP mounts.  The remote fileserver is always assumed to be up.

Non-blocking Operation
======================

Since there is only one instance of Amd for each automount point, and usually only one instance on each machine, it is important that it is always available to service kernel calls.  Amd goes to great lengths to ensure that it does not block in a system call.  As a last resort Amd will fork before it attempts a system call that may block indefinitely, such as mounting an NFS filesystem.  Other tasks such as obtaining filehandle information for an NFS filesystem, are done using a purpose built non-blocking RPC library which is integrated with Amd's task scheduler.  This library is also used to implement NFS keep-alives (see Keep-alives).

Whenever a mount is deferred or backgrounded, Amd must wait for it to complete before replying to the kernel.  However, this would cause Amd to block waiting for a reply to be constructed.  Rather than do this, Amd simply drops the call under the assumption that the kernel RPC mechanism will automatically retry the request.

Supported Platforms
*******************

Amd has been ported to a wide variety of machines and operating systems. The table below lists those platforms supported by the current release.

Supported Operating Systems
===========================

The following operating systems are currently supported by Amd. Amd's conventional name for each system is given.

acis43
     4.3 BSD for IBM RT.  Contributed by Jan-Simon Pendry <jsp@doc.ic.ac.uk>

aix3
     AIX 3.1.  Contributed by Jan-Simon Pendry <jsp@doc.ic.ac.uk>

aux
     System V for Mac-II.  Contributed by Julian Onions <jpo@cs.nott.ac.uk>

bsd44
     4.4 BSD.  Contributed by Jan-Simon Pendry <jsp@doc.ic.ac.uk>

concentrix
     Concentrix 5.0.  Contributed by Sjoerd Mullender <sjoerd@cwi.nl>

convex
     Convex OS 7.1.  Contributed by Eitan Mizrotsky <eitan@shumuji.ac.il>

dgux
     Data General DG/UX.  Contributed by Mark Davies <mark@comp.vuw.ac.nz>

fpx4
     Celerity FPX 4.1/2.  Contributed by Stephen Pope <scp@grizzly.acl.lanl.gov>

hcx
     Harris HCX/UX.  Contributed by Chris Metcalf <metcalf@masala.lcs.mit.edu>

hlh42
     HLH OTS 1.x (4.2 BSD).  Contributed by Jan-Simon Pendry <jsp@doc.ic.ac.uk>

hpux
     HP-UX 6.x or 7.0.  Contributed by Jan-Simon Pendry <jsp@doc.ic.ac.uk>

irix
     SGI Irix.  Contributed by Scott R. Presnell <srp@cgl.ucsf.edu>

next
     Mach for NeXT.  Contributed by Bill Trost <trost%reed@cse.ogi.edu>

pyrOSx
     Pyramid OSx.  Contributed by Stefan Petri <petri@tubsibr.UUCP>

riscix
     Acorn RISC iX.  Contributed by Piete Brooks <pb@cam.cl.ac.uk>

sos3
     SunOS 3.4 & 3.5.  Contributed by Jan-Simon Pendry <jsp@doc.ic.ac.uk>

sos4
     SunOS 4.x.  Contributed by Jan-Simon Pendry <jsp@doc.ic.ac.uk>

u2_2
     Ultrix 2.2.  Contributed by Piete Brooks <pb@cam.cl.ac.uk>

u3_0
     Ultrix 3.  Contributed by Piete Brooks <pb@cam.cl.ac.uk>

u4_0
     Ultrix 4.0.  Contributed by Chris Lindblad <cjl@ai.mit.edu>

umax43
     Umax 4.3 BSD.  Contributed by Sjoerd Mullender <sjoerd@cwi.nl>

utek
     Utek 4.0.  Contributed by Bill Trost <trost%reed@cse.ogi.edu>

xinu43
     mt Xinu MORE/bsd.  Contributed by Jan-Simon Pendry <jsp@doc.ic.ac.uk>

Supported Machine Architectures
===============================

alliant
     Alliant FX/4

arm
     Acorn ARM

aviion
     Data General AViiON

encore
     Encore

fps500
     FPS Model 500

hp9000
     HP 9000/300 family

hp9k8
     HP 9000/800 family

ibm032
     IBM RT

ibm6000
     IBM RISC System/6000

iris4d
     SGI Iris 4D

macII
     Apple Mac II

mips
     MIPS RISC

multimax
     Encore Multimax

orion105
     HLH Orion 1/05

sun3
     Sun-3 family

sun4
     Sun-4 family

tahoe
     Tahoe family

vax
     DEC Vax

Mount Maps
**********

Amd has no built-in knowledge of machines or filesystems. External mount-maps are used to provide the required information. Specifically, Amd needs to know when and under what conditions it should mount filesystems.

The map entry corresponding to the requested name contains a list of possible locations from which to resolve the request.  Each location specifies filesystem type, information required by that filesystem (for example the block special device in the case of UFS), and some information describing where to mount the filesystem (see fs Option).  A location may also contain selectors (see Selectors).

Map Types
=========

A mount-map provides the run-time configuration information to Amd. Maps can be implemented in many ways.  Some of the forms supported by Amd are regular files, NIS maps the Hesiod name server and even the password file.

A mount-map name is a sequence of characters.  When an automount point is created a handle on the mount-map is obtained.  For each map type configured Amd attempts to reference the a map of the appropriate type.  If a map is found, Amd notes the type for future use and deletes the reference, for example closing any open file descriptors.  The available maps are configure when Amd is built and can be displayed by running the command amd -v.

By default, Amd caches data in a mode dependent on the type of map. This is the same as specifying cache:=mapdefault and selects a suitable default cache mode depending on the map type.  The individual defaults are described below.  The CACHE option can be specified on automount points to alter the caching behaviour (see Automount Filesystem).

The following map types have been implemented, though some are not available on all machines.  Run the command amd -v to obtain a list of map types configured on your machine.

File maps
---------

When Amd searches a file for a map entry it does a simple scan of the file and supports both comments and continuation lines.

Continuation lines are indicated by a backslash character (\) as the last character of a line in the file.  The backslash, newline character and any leading white space on the following line are discarded.  A maximum line length of 2047 characters is enforced after continuation lines are read but before comments are stripped.  Each line must end with a newline character; that is newlines are terminators, not separators. The following examples illustrate this:

     key     valA   valB;   \
               valC

specifies three locations, and is identical to

     key     valA   valB;   valC

However,

     key     valA   valB;\
               valC

specifies only two locations, and is identical to

     key     valA   valB;valC

After a complete line has been read from the file, including continuations, Amd determines whether there is a comment on the line.  A comment begins with a hash (``#'') character and continues to the end of the line.  There is no way to escape or change the comment lead-in character.

Note that continuation lines and comment support only apply to file maps.

When caching is enabled, file maps have a default cache mode of all (see Automount Filesystem).

NIS maps
--------

When using NIS (formerly YP), an Amd map is implemented directly by the underlying NIS map.  Comments and continuation lines are not supported in the automounter and must be stripped when constructing the NIS server's database.

NIS maps do not support cache mode all and, when caching is enabled, have a default cache mode of inc (see Automount Filesystem).

The following rule illustrates what could be added to your NIS Makefile, in this case causing the amd.home map to be rebuilt:

     $(YPTSDIR)/amd.home.time: $(ETCDIR)/amd.home
             -@sed -e "s/#.*$$//" -e "/^$$/d" $(ETCDIR)/amd.home | \
               awk '{  \
                      for (i = 1; i <= NF; i++) \
                          if (i == NF) { \
                              if (substr($$i, length($$i), 1) == "\\") \
                                  printf("%s", substr($$i, 1, length($$i) - 1)); \
                              else \
                                  printf("%s\n", $$i); \
                          } \
                          else \
                              printf("%s ", $$i); \
                  }' | \
             $(MAKEDBM) - $(YPDBDIR)/amd.home; \
             touch $(YPTSDIR)/amd.home.time; \
             echo "updated amd.home"; \
             if [ ! $(NOPUSH) ]; then \
                     $(YPPUSH) amd.home; \
                     echo "pushed amd.home"; \
             else \
                     : ; \
             fi

Here $(YPTSDIR) contains the time stamp files, and $(YPDBDIR) contains the dbm format NIS files.

Hesiod maps
-----------

When the map name begins with the string hesiod. lookups are made using the Hesiod name server.  The string following the dot is used as a name qualifier and is prepended with the key being located. The entire string is then resolved in the automount context.  For example, if the key is jsp and map name is hesiod.homes then Hesiod is asked to resolve jsp.homes.automount.

Hesiod maps do not support cache mode all and, when caching is enabled, have a default cache mode of inc (see Automount Filesystem).

The following is an example of a Hesiod map entry:

     jsp.homes.automount HS TXT "rfs:=/home/charm;rhost:=charm;sublink:=jsp"
     njw.homes.automount HS TXT "rfs:=/home/dylan/dk2;rhost:=dylan;sublink:=njw"

Password maps
-------------

The password map support is unlike the four previous map types.  When the map name is the string /etc/passwd Amd can lookup a user name in the password file and re-arrange the home directory field to produce a usable map entry.

Amd assumes the home directory has the format `/anydir/dom1/../domN/login'. It breaks this string into a map entry where ${rfs} has the value `/anydir/domN', ${rhost} has the value `domN.....dom1', and ${sublink} has the value login.

Thus if the password file entry was

     /home/achilles/jsp

the map entry used by Amd would be

     rfs:=/home/achilles;rhost:=achilles;sublink:=jsp

Similarly, if the password file entry was

     /home/cc/sugar/mjh

the map entry used by Amd would be

     rfs:=/home/sugar;rhost:=sugar.cc;sublink:=jsp

Union maps
----------

The union map support is provided specifically for use with the union filesystem, see Union Filesystem.

It is identified by the string union: which is followed by a colon separated list of directories.  The directories are read in order, and the names of all entries are recorded in the map cache.  Later directories take precedence over earlier ones.  The union filesystem type then uses the map cache to determine the union of the names in all the directories.

How keys are looked up
======================

The key is located in the map whose type was determined when the automount point was first created.  In general the key is a pathname component.  In some circumstances this may be modified by variable expansion (see Variable Expansion) and prefixing.  If the automount point has a prefix, specified by the PREF option, then that is prepended to the search key before the map is searched.

If the map cache is a regexp cache then the key is treated as an egrep-style regular expression, otherwise a normal string comparison is made.

If the key cannot be found then a wildcard match is attempted. Amd repeatedly strips the basename from the key, appends /* and attempts a lookup.  Finally, Amd attempts to locate the special key *.

For example, the following sequence would be checked if home/dylan/dk2 was being located:

        home/dylan/dk2
        home/dylan/*
        home/*
        *

At any point when a wildcard is found, Amd proceeds as if an exact match had been found and the value field is then used to resolve the mount request, otherwise an error code is propagated back to the kernel. (see Filesystem Types).

Location Format
===============

The value field from the lookup provides the information required to mount a filesystem.  The information is parsed according to the syntax shown below.

     location-list:
                       location-selection
                       location-list white-space || white-space location-selection
     location-selection:
                       location
                       location-selection white-space location
     location:
                       location-info
                       -location-info
                       -
     location-info:
                       sel-or-opt
                       location-info;sel-or-opt
                       ;
     sel-or-opt:
                       selection
                       opt-ass
     selection:
                       selector==value
                       selector!=value
     opt-ass:
                       option:=value
     white-space:
                       space
                       tab

Note that unquoted whitespace is not allowed in a location description. White space is only allowed, and is mandatory, where shown with non-terminal white-space.

A location-selection is a list of possible volumes with which to satisfy the request.  location-selections are separated by the || operator.  The effect of this operator is to prevent use of location-selections to its right if any of the location-selections on its left were selected whether or not any of them were successfully mounted (see Selectors).

The location-selection, and singleton location-list, type:=ufs;dev:=/dev/xd1g would inform Amd to mount a UFS filesystem from the block special device /dev/xd1g.

The sel-or-opt component is either the name of an option required by a specific filesystem, or it is the name of a built-in, predefined selector such as the architecture type.  The value may be quoted with double quotes ", for example type:="ufs";dev:="/dev/xd1g".  These quotes are stripped when the value is parsed and there is no way to get a double quote into a value field.  Double quotes are used to get white space into a value field, which is needed for the program filesystem (see Program Filesystem).

Map Defaults
------------

A location beginning with a dash - is used to specify default values for subsequent locations.  Any previously specified defaults in the location-list are discarded.  The default string can be empty in which case no defaults apply.

The location -fs:=/mnt;opts:=ro would set the local mount point to /mnt and cause mounts to be read-only by default.  Defaults specified this way are appended to, and so override, any global map defaults given with /defaults).

Variable Expansion
------------------

To allow generic location specifications Amd does variable expansion on each location and also on some of the option strings.  Any option or selector appearing in the form $var is replaced by the current value of that option or selector.  For example, if the value of ${key} was bin, ${autodir} was /a and ${fs} was `${autodir}/local/${key}' then after expansion ${fs} would have the value /a/local/bin. Any environment variable can be accessed in a similar way.

Two pathname operators are available when expanding a variable.  If the variable name begins with / then only the last component of then pathname is substituted.  For example, if ${path} was /foo/bar then ${/path} would be expanded to bar. Similarly, if the variable name ends with / then all but the last component of the pathname is substituted.  In the previous example, ${path/} would be expanded to /foo.

Two domain name operators are also provided.  If the variable name begins with . then only the domain part of the name is substituted.  For example, if ${rhost} was swan.doc.ic.ac.uk then ${.rhost} would be expanded to doc.ic.ac.uk.  Similarly, if the variable name ends with . then only the host component is substituted.  In the previous example, ${rhost.} would be expanded to swan.

Variable expansion is a two phase process.  Before a location is parsed, all references to selectors, eg ${path}, are expanded.  The location is then parsed, selections are evaluated and option assignments recorded.  If there were no selections or they all succeeded the location is used and the values of the following options are expanded in the order given: SUBLINK, RFS, FS, OPTS, REMOPTS, MOUNT and UNMOUNT.

Note that expansion of option values is done after all assignments have been completed and not in a purely left to right order as is done by the shell.  This generally has the desired effect but care must be taken if one of the options references another, in which case the ordering can become significant.

There are two special cases concerning variable expansion:

 1. before a map is consulted, any selectors in the name received from the kernel are expanded.  For example, if the request from the kernel was for `${arch}.bin' and the machine architecture was vax, the value given to ${key} would be vax.bin.

 2. the value of ${rhost} is expanded and normalized before the other options are expanded.  The normalization process strips any local sub-domain components.  For example, if ${domain} was Berkeley.EDU and ${rhost} was initially snow.Berkeley.EDU, after the normalization it would simply be snow.  Hostname normalization is currently done in a case-dependent manner.

Selectors
---------

Selectors are used to control the use of a location.  It is possible to share a mount map between many machines in such a way that filesystem location, architecture and operating system differences are hidden from the users.  A selector of the form arch==sun3;os==sos4 would only apply on Sun-3s running SunOS 4.x.

Selectors are evaluated left to right.  If a selector fails then that location is ignored.  Thus the selectors form a conjunction and the locations form a disjunction.  If all the locations are ignored or otherwise fail then Amd uses the error filesystem (see Error Filesystem).  This is equivalent to having a location type:=error at the end of each mount-map entry.

The selectors currently implemented are:

arch
     the machine architecture which was automatically determined at compile time.  The architecture type can be displayed by running the command amd -v.  See Supported Machine Architectures.

autodir
     the default directory under which to mount filesystems.  This may be changed by the ``-a'' command line option.  See the FS option.

byte
     the machine's byte ordering.  This is either little, indicating little-endian, or big, indicating big-endian.  One possible use is to share rwho databases (see rwho servers).

cluster
     is provided as a hook for the name of the local cluster.  This can be used to decide which servers to use for copies of replicated filesystems.  ${cluster} defaults to the value of ${domain} unless a different value is set with the ``-C'' command line option.

domain
     the local domain name as specified by the ``-d'' command line option. See host.

host
     the local hostname as determined by gethostname(2).  If no domain name was specified on the command line and the hostname contains a period . then the string before the period is used as the host name, and the string after the period is assigned to ${domain}.  For example, if the hostname is styx.doc.ic.ac.uk then host would be styx and domain would be doc.ic.ac.uk.  hostd would be styx.doc.ic.ac.uk.

hostd
     is ${host} and ${domain} concatenated with a . inserted between them if required.  If ${domain} is an empty string then ${host} and ${hostd} will be identical.

karch
     is provided as a hook for the kernel architecture.  This is used on SunOS 4, for example, to distinguish between different /usr/kvm volumes.  ${karch} defaults to the value of ${arch} unless a different value is set with the ``-k'' command line option.

os
     the operating system.  Like the machine architecture, this is automatically determined at compile time.  The operating system name can be displayed by running the command amd -v.  See Supported Operating Systems.

The following selectors are also provided.  Unlike the other selectors, they vary for each lookup.  Note that when the name from the kernel is expanded prior to a map lookup, these selectors are all defined as empty strings.

key
     the name being resolved.  For example, if /home is an automount point, then accessing /home/foo would set ${key} to the string foo.  The key is prefixed by the PREF option set in the parent mount point.  The default prefix is an empty string.  If the prefix was blah/ then ${key} would be set to blah/foo.

map
     the name of the mount map being used.

path
     the full pathname of the name being resolved.  For example /home/foo in the example above.

wire
     the name of the network to which the primary network interface is attached.  If a symbolic name cannot be found in the networks or hosts database then dotted IP address format is used.  This value is also output by the ``-v'' option.

Selectors can be negated by using != instead of ==.  For example to select a location on all non-Vax machines the selector arch!=vax would be used.

Map Options
-----------

Options are parsed concurrently with selectors.  The difference is that when an option is seen the string following the := is recorded for later use.  As a minimum the TYPE option must be specified.  Each filesystem type has other options which must also be specified.  See Filesystem Types, for details on the filesystem specific options.

Superfluous option specifications are ignored and are not reported as errors.

The following options apply to more than one filesystem type.

delay Option
............

The delay, in seconds, before an attempt will be made to mount from the current location. Auxilliary data, such as network address, file handles and so on are computed regardless of this value.

A delay can be used to implement the notion of primary and secondary file servers. The secondary servers would have a delay of a few seconds, thus giving the primary servers a chance to respond first.

fs Option
.........

The local mount point.  The semantics of this option vary between filesystems.

For NFS and UFS filesystems the value of ${fs} is used as the local mount point.  For other filesystem types it has other meanings which are described in the section describing the respective filesystem type.  It is important that this string uniquely identifies the filesystem being mounted.  To satisfy this requirement, it should contain the name of the host on which the filesystem is resident and the pathname of the filesystem on the local or remote host.

The reason for requiring the hostname is clear if replicated filesystems are considered.  If a fileserver goes down and a replacement filesystem is mounted then the local mount point must be different from that of the filesystem which is hung.  Some encoding of the filesystem name is required if more than one filesystem is to be mounted from any given host.

If the hostname is first in the path then all mounts from a particular host will be gathered below a single directory.  If that server goes down then the hung mount points are less likely to be accidentally referenced, for example when getwd(3) traverses the namespace to find the pathname of the current directory.

The fs option defaults to ${autodir}/${rhost}${rfs}.  In addition, rhost defaults to the local host name (${host}) and rfs defaults to the value of ${path}, which is the full path of the requested file; /home/foo in the example above (see Selectors).  ${autodir} defaults to /a but may be changed with the ``-a'' command line option.  Sun's automounter defaults to /tmp_mnt.  Note that there is no / between the ${rhost} and ${rfs} since ${rfs} begins with a /.

opts Option
...........

The options to pass to the mount system call.  A leading - is silently ignored.  The mount options supported generally correspond to those used by mount(8) and are listed below.  Some additional pseudo-options are interpreted by Amd and are also listed.

Unless specifically overridden, each of the system default mount options applies.  Any options not recognised are ignored.  If no options list is supplied the string rw,defaults is used and all the system default mount options apply.  Options which are not applicable for a particular operating system are silently ignored.  For example, only 4.4 BSD is known to implement the compress and spongy options.

compress
     Use NFS compression protocol.

grpid
     Use BSD directory group-id semantics.

intr
     Allow keyboard interrupts on hard mounts.

noconn
     Don't make a connection on datagram transports.

nocto
     No close-to-open consistency.

nodevs
     Don't allow local special devices on this filesystem.

nolooklease
     When nqnfs is selected, disable the automatic acquiring of leases on lookups.

nosuid
     Don't allow set-uid or set-gid executables on this filesystem.

nqnfs
     Enable leasing extensions to the NFS protocol know as Not Quite NFS. Only supported by the 4.4BSD NFS implementation.

quota
     Enable quota checking on this mount.

resvport
     Use a reserved port number (one less than 1024).  Some NFS servers require this.

retrans=n
     The number of NFS retransmits made before a user error is generated by a soft mounted filesystem, and before a hard mounted filesystem reports NFS server yoyo not responding still trying.

ro
     Mount this filesystem readonly.

rsize=N
     The NFS read packet size.  You may need to set this if you are using NFS/UDP through a gateway.

soft
     Give up after retrans retransmissions.

spongy
     Like soft for status requests, and hard for data transfers.

tcp
     Use TCP/IP instead of UDP/IP, ignored if the NFS implementation does not support TCP/IP mounts.

timeo=N
     The NFS timeout, in tenth-seconds, before a request is retransmitted.

wsize=N
     The NFS write packet size.  You may need to set this if you are using NFS/UDP through a gateway.

The following options are implemented by Amd, rather than being passed to the kernel.

nounmount
     Configures the mount so that its time-to-live will never expire.  This is also the default for some filesystem types.

ping=N
     The interval, in seconds, between keep-alive pings.  When four consecutive pings have failed the mount point is marked as hung.  This interval defaults to 30 seconds.  If the ping interval is less than zero, no pings are sent and the host is assumed to be always up.  By default, pings are not sent for an NFS/TCP mount.

retry=N
     The number of times to retry the mount system call.

utimeout=N
     The interval, in seconds, by which the mount's time-to-live is extended after an unmount attempt has failed.  In fact the interval is extended before the unmount is attempted to avoid thrashing.  The default value is 120 seconds (two minutes) or as set by the ``-w'' command line option.

remopts Option
..............

This option has the same use as ${opts} but applies only when the remote host is on a non-local network.  For example, when using NFS across a gateway it is often necessary to use smaller values for the data read and write sizes.  This can simply be done by specifying the small values in REMOPTS.  When a non-local host is accessed, the smaller sizes will automatically be used.

Amd determines whether a host is local by examining the network interface configuration at startup.  Any interface changes made after Amd has been started will not be noticed.  The likely effect will be that a host may incorrectly be declared non-local.

Unless otherwise set, the value of ${rem} is the same as the value of ${opts}.

sublink Option
..............

The subdirectory within the mounted filesystem to which the reference should point.  This can be used to prevent duplicate mounts in cases where multiple directories in the same mounted filesystem are used.

type Option
...........

The filesystem type to be used.  See Filesystem Types, for a full description of each type.

Amd Command Line Options
************************

Many of Amd's parameters can be set from the command line.  The command line is also used to specify automount points and maps.

The general format of a command line is

     amd [options] { directory map-name [-map-options] } ...

For each directory and map-name given, Amd establishes an automount point.  The map-options may be any sequence of options or selectors---see Location Format.  The map-options apply only to Amd's mount point.

type:=toplvl;cache:=mapdefault;fs:=${map} is the default value for the map options.  Default options for a map are read from a special entry in the map whose key is the string /defaults.  When default options are given they are prepended to any options specified in the mount-map locations as explained in.  See Map Defaults, for more details.

The options are any combination of those listed below.

Once the command line has been parsed, the automount points are mounted. The mount points are created if they do not already exist, in which case they will be removed when Amd exits. Finally, Amd disassociates itself from its controlling terminal and forks into the background.

Note: Even if Amd has been built with -DDEBUG it will still background itself and disassociate itself from the controlling terminal. To use a debugger it is necessary to specify -D nodaemon on the command line.

-a DIRECTORY
============

Specifies the default mount directory.  This option changes the variable ${autodir} which otherwise defaults to /a.  For example, some sites prefer /amd.

     amd -a /amd ...

-c CACHE-INTERVAL
=================

Selects the period, in seconds, for which a name is cached by Amd. If no reference is made to the volume in this period, Amd discards the volume name to filesystem mapping.

Once the last reference to a filesystem has been removed, Amd attempts to unmount the filesystem.  If the unmount fails the interval is extended by a further period as specified by the -w command line option or by the utimeout mount option.

The default cache-interval is 300 seconds (five minutes).

-d DOMAIN
=========

Specifies the host's domain.  This sets the internal variable ${domain} and affects the ${hostd} variable.

If this option is not specified and the hostname already contains the local domain then that is used, otherwise the default value of ${domain} is unknown.domain.

For example, if the local domain was doc.ic.ac.uk, Amd could be started as follows:

     amd -d doc.ic.ac.uk ...

-k KERNEL-ARCHITECTURE
======================

Specifies the kernel architecture of the system.  This is usually the output of arch -k and its only effect is to set the variable ${karch}.  If this option is not given, ${karch} has the same value as ${arch}.

This would be used as follows:

     amd -k `arch -k` ...

-l LOG-OPTION
=============

Selects the form of logging to be made.  Two special log-options are recognised.

 1. If log-option is the string syslog, Amd will use the syslog(3) mechanism.

 2. If log-option is the string /dev/stderr, Amd will use standard error, which is also the default target for log messages.  To implement this, Amd simulates the effect of the /dev/fd driver.

Any other string is taken as a filename to use for logging.  Log messages are appended to the file if it already exists, otherwise a new file is created.  The file is opened once and then held open, rather than being re-opened for each message.

If the syslog option is specified but the system does not support syslog or if the named file cannot be opened or created, Amd will use standard error.  Error messages generated before Amd has finished parsing the command line are printed on standard error.

Using syslog is usually best, in which case Amd would be started as follows:

     amd -l syslog ...

-n
==

Normalises the remote hostname before using it.  Normalisation is done by replacing the value of ${rhost} with the primary name returned by a hostname lookup.

This option should be used if several names are used to refer to a single host in a mount map.

-p
==

Causes Amd's process id to be printed on standard output. This can be redirected to a suitable file for use with kill:

     amd -p > /var/run/amd.pid ...

This option only has an affect if Amd is running in daemon mode. If Amd is started with the -D nodaemon debug flag, this option is ignored.

-r
==

Tells Amd to restart existing mounts (see Inheritance Filesystem).

-t TIMEOUT.RETRANSMIT
=====================

Specifies the RPC timeout and retransmit intervals used by the kernel to communicate to Amd.  These are used to set the timeo and retrans mount options.

Amd relies on the kernel RPC retransmit mechanism to trigger mount retries.  The value of this parameter changes the retry interval.  Too long an interval gives poor interactive response, too short an interval causes excessive retries.

-v
==

Print version information on standard error and then exit.  The output is of the form:

     amd 5.2.1.11 of 91/03/17 18:04:05 5.3Alpha11 #0: Sun Mar 17 18:07:28 GMT 1991
     Built by pendry@vangogh.Berkeley.EDU for a hp300 running bsd44 (big-endian).
     Map support for: root, passwd, union, file, error.
     FS: ufs, nfs, nfsx, host, link, program, union, auto, direct, toplvl, error.
     Primary network is 128.32.130.0.

The information includes the version number, release date and name of the release.  The architecture (see Supported Machine Architectures), operating system (see Supported Operating Systems) and byte ordering are also printed as they appear in the ${os}, ${arch} and ${byte} variables.

-w WAIT-TIMEOUT
===============

Selects the interval in seconds between unmount attempts after the initial time-to-live has expired.

This defaults to 120 seconds (two minutes).

-x OPTS
=======

Specifies the type and verbosity of log messages.  opts is a comma separated list selected from the following options:

fatal
     Fatal errors

error
     Non-fatal errors

user
     Non-fatal user errors

warn
     Recoverable errors

warning
     Alias for warn

info
     Information messages

map
     Mount map usage

stats
     Additional statistics

all
     All of the above

Initially a set of default logging flags is enabled.  This is as if -x all,nomap,nostats had been selected.  The command line is parsed and logging is controlled by the ``-x'' option.  The very first set of logging flags is saved and can not be subsequently disabled using Amq.  This default set of options is useful for general production use.

The info messages include details of what is mounted and unmounted and when filesystems have timed out.  If you want to have the default set of messages without the info messages then you simply need -x noinfo.  The messages given by user relate to errors in the mount maps, so these are useful when new maps are installed.  The following table lists the syslog priorites used for each of the message types.

fatal
     LOG_CRIT

error
     LOG_ERR

user
     LOG_WARNING

warning
     LOG_WARNING

info
     LOG_INFO

debug
     LOG_DEBUG

map
     LOG_DEBUG

stats
     LOG_INFO

The options can be prefixed by the string no to indicate that this option should be turned off.  For example, to obtain all but info messages the option -x all,noinfo would be used.

If Amd was built with debugging enabled the debug option is automatically enabled regardless of the command line options.

-y NIS-DOMAIN
=============

Selects an alternate NIS domain.  This is useful for debugging and cross-domain shared mounting.  If this flag is specified, Amd immediately attempts to bind to a server for this domain.

-C CLUSTER-NAME
===============

Specifies the name of the cluster of which the local machine is a member. The only effect is to set the variable ${cluster}. The cluster-name is will usually obtained by running another command which uses a database to map the local hostname into a cluster name. ${cluster} can then be used as a selector to restrict mounting of replicated data. If this option is not given, ${cluster} has the same value as ${domain}. This would be used as follows:

     amd -C `clustername` ...

-D OPTS
=======

Controls the verbosity and coverage of the debugging trace; opts is a comma separated list of debugging options.  The ``-D'' option is only available if Amd was compiled with -DDEBUG.  The memory debugging facilities are only available if Amd was compiled with -DDEBUG_MEM (in addition to -DDEBUG).

The most common options to use are -D trace and -D test (which turns on all the useful debug options).  See the program source for a more detailed explanation of the available options.

Filesystem Types
****************

To mount a volume, Amd must be told the type of filesystem to be used.  Each filesystem type typically requires additional information such as the fileserver name for NFS.

From the point of view of Amd, a filesystem is anything that can resolve an incoming name lookup.  An important feature is support for multiple filesystem types.  Some of these filesystems are implemented in the local kernel and some on remote fileservers, whilst the others are implemented internally by Amd.

The two common filesystem types are UFS and NFS.  Four other user accessible filesystems (link, program, auto and direct) are also implemented internally by Amd and these are described below.  There are two additional filesystem types internal to Amd which are not directly accessible to the user (inherit and error).  Their use is described since they may still have an effect visible to the user.

Network Filesystem (type:=nfs)
==============================

The nfs filesystem type provides access to Sun's NFS.

The following options must be specified:

rhost
     the remote fileserver.  This must be an entry in the hosts database.  IP addresses are not accepted.  The default value is taken from the local host name (${host}) if no other value is specified.

rfs
     the remote filesystem. If no value is specified for this option, an internal default of ${path} is used.

NFS mounts require a two stage process.  First, the file handle of the remote file system must be obtained from the server.  Then a mount system call must be done on the local system.  Amd keeps a cache of file handles for remote file systems.  The cache entries have a lifetime of a few minutes.

If a required file handle is not in the cache, Amd sends a request to the remote server to obtain it.  Amd does not wait for a response; it notes that one of the locations needs retrying, but continues with any remaining locations.  When the file handle becomes available, and assuming none of the other locations was successfully mounted, Amd will retry the mount.  This mechanism allows several NFS filesystems to be mounted in parallel. The first one which responds with a valid file handle will be used.

An NFS entry might be:

     jsp  host!=charm;type:=nfs;rhost:=charm;rfs:=/home/charm;sublink:=jsp

The mount system call and any unmount attempts are always done in a new task to avoid the possibilty of blocking Amd.

Network Host Filesystem (type:=host)
====================================

The host filesystem allows access to the entire export tree of an NFS server.  The implementation is layered above the nfs implementation so keep-alives work in the same way.  The only option which needs to specified is rhost which is the name of the fileserver to mount.

The host filesystem type works by querying the mount daemon on the given fileserver to obtain its export list.  Amd then obtains filehandles for each of the exported filesystems.  Any errors at this stage cause that particular filesystem to be ignored.  Finally each filesystem is mounted.  Again, errors are logged but ignored.  One common reason for mounts to fail is that the mount point does not exist. Although Amd attempts to automatically create the mount point, it may be on a remote filesystem to which Amd does not have write permission.

When an attempt to unmount a host filesystem mount fails, Amd remounts any filesystems which had successfully been unmounted.  To do this Amd queries the mount daemon again and obtains a fresh copy of the export list.  Amd then tries to mount any exported filesystems which are not currently mounted.

Sun's automounter provides a special -hosts map.  To achieve the same effect with Amd requires two steps.  First a mount map must be created as follows:

     /defaults  type:=host;fs:=${autodir}/${rhost}/root;rhost:=${key}
     *          opts:=rw,nosuid,grpid

and then start Amd with the following command

     amd /n net.map

where net.map is the name of map described above.  Note that the value of ${fs} is overridden in the map.  This is done to avoid a clash between the mount tree and any other filesystem already mounted from the same fileserver.

If different mount options are needed for different hosts then additional entries can be added to the map, for example

     host2       opts:=ro,nosuid,soft

would soft mount host2 read-only.

Network Filesystem Group (type:=nfsx)
=====================================

The nfsx filesystem allows a group of filesystems to be mounted from a single NFS server.  The implementation is layered above the nfs implementation so keep-alives work in the same way.

The options are the same as for the nfs filesystem with one difference.

The following options must be specified:

rhost
     the remote fileserver.  This must be an entry in the hosts database.  IP addresses are not accepted.  The default value is taken from the local host name (${host}) if no other value is specified.

rfs
     as a list of filesystems to mount.  The list is in the form of a comma separated strings.

For example:

     pub      type:=nfsx;rhost:=gould;\
     		rfs:=/public,/,graphics,usenet;fs:=${autodir}/${rhost}/root

The first string defines the root of the tree, and is applied as a prefix to the remaining members of the list which define the individual filesystems.  The first string is not used as a filesystem name. A parallel operation is used to determine the local mount points to ensure a consistent layout of a tree of mounts.

Here, the three filesystems, /public, /public/graphics and /public/usenet, would be mounted.

A local mount point, ${fs}, must be specified.  The default local mount point will not work correctly in the general case. A suggestion is to use fs:=${autodir}/${rhost}/root.

Unix Filesystem (type:=ufs)
===========================

The ufs filesystem type provides access to the system's standard disk filesystem---usually a derivative of the Berkeley Fast Filesystem.

The following option must be specified:

dev
     the block special device to be mounted.

A UFS entry might be:

     jsp   host==charm;type:=ufs;dev:=/dev/xd0g;sublink:=jsp

Program Filesystem (type:=program)
==================================

The program filesystem type allows a program to be run whenever a mount or unmount is required.  This allows easy addition of support for other filesystem types, such as MIT's Remote Virtual Disk (RVD) which has a programmatic interface via the commands rvdmount and rvdunmount.

The following options must be specified:

mount
     the program which will perform the mount.

unmount
     the program which will perform the unmount.

The exit code from these two programs is interpreted as a Unix error code.  As usual, exit code zero indicates success.  To execute the program Amd splits the string on whitespace to create an array of substrings.  Single quotes ' can be used to quote whitespace if that is required in an argument.  There is no way to escape or change the quote character.

To run the program rvdmount with a host name and filesystem as arguments would be specified by mount:="/etc/rvdmount rvdmount fserver ${path}".

The first element in the array is taken as the pathname of the program to execute.  The other members of the array form the argument vector to be passed to the program, including argument zero.  This means that the split string must have at least two elements.  The program is directly executed by Amd, not via a shell.  This means that scripts must begin with a #! interpreter specification.

If a filesystem type is to be heavily used, it may be worthwhile adding a new filesystem type into Amd, but for most uses the program filesystem should suffice.

When the program is run, standard input and standard error are inherited from the current values used by Amd.  Standard output is a duplicate of standard error.  The value specified with the ``-l'' command line option has no effect on standard error.

Symbolic Link Filesystem (type:=link)
=====================================

Each filesystem type creates a symbolic link to point from the volume name to the physical mount point.  The link filesystem does the same without any other side effects.  This allows any part of the machines name space to be accessed via Amd.

One common use for the symlink filesystem is /homes which can be made to contain an entry for each user which points to their (auto-mounted) home directory.  Although this may seem rather expensive, it provides a great deal of administrative flexibility.

The following option must be defined:

fs
     The value of FS option specifies the destination of the link, as modified by the SUBLINK option.  If SUBLINK is non-null, it is appended to ${fs}/ and the resulting string is used as the target.

The link filesystem can be though of as identical to the ufs filesystem but without actually mounting anything.

An example entry might be:

     jsp   host==charm;type:=link;fs:=/home/charm;sublink:=jsp

which would return a symbolic link pointing to /home/charm/jsp.

Symbolic Link Filesystem II (type:=linkx)
=========================================

The linkx filesystem type is identical to link with the exception that the target of the link must exist.  Existence is checked with the lstat system call.

The linkx filesystem type is particularly useful for wildcard map entries.  In this case, a list of possible targets can be give and Amd will choose the first one which exists on the local machine.

Automount Filesystem (type:=auto)
=================================

The auto filesystem type creates a new automount point below an existing automount point.  Top-level automount points appear as system mount points.  An automount mount point can also appear as a sub-directory of an existing automount point.  This allows some additional structure to be added, for example to mimic the mount tree of another machine.

The following options may be specified:

cache
     specifies whether the data in this mount-map should be cached.  The default value is none, in which case no caching is done in order to conserve memory. However, better performance and reliability can be obtained by caching some or all of a mount-map.

     If the cache option specifies all, the entire map is enumerated when the mount point is created.

     If the cache option specifies inc, caching is done incrementally as and when data is required. Some map types do not support cache mode all, in which case inc is used whenever all is requested.

     Caching can be entirely disabled by using cache mode none.

     If the cache option specifies regexp then the entire map will be enumerated and each key will be treated as an egrep-style regular expression.  The order in which a cached map is searched does not correspond to the ordering in the source map so the regular expressions should be mutually exclusive to avoid confusion.

     Each mount map type has a default cache type, usually inc, which can be selected by specifying mapdefault.

     The cache mode for a mount map can only be selected on the command line. Starting Amd with the command:

          amd /homes hesiod.homes -cache:=inc

     will cause /homes to be automounted using the Hesiod name server with local incremental caching of all successfully resolved names.

     All cached data is forgotten whenever Amd receives a SIGHUP signal and, if cache all mode was selected, the cache will be reloaded.  This can be used to inform Amd that a map has been updated.  In addition, whenever a cache lookup fails and Amd needs to examine a map, the map's modify time is examined.  If the cache is out of date with respect to the map then it is flushed as if a SIGHUP had been received.

     An additional option (sync) may be specified to force Amd to check the map's modify time whenever a cached entry is being used.  For example, an incremental, synchronised cache would be created by the following command:

          amd /homes hesiod.homes -cache:=inc,sync

fs
     specifies the name of the mount map to use for the new mount point.

     Arguably this should have been specified with the ${rfs} option but we are now stuck with it due to historical accident.

pref
     alters the name that is looked up in the mount map.  If ${pref}, the prefix, is non-null then it is prepended to the name requested by the kernel before the map is searched.

The server dylan.doc.ic.ac.uk has two user disks: /dev/dsk/2s0 and /dev/dsk/5s0.  These are accessed as /home/dylan/dk2 and /home/dylan/dk5 respectively.  Since /home is already an automount point, this naming is achieved with the following map entries:

     dylan        type:=auto;fs:=${map};pref:=${key}/
     dylan/dk2    type:=ufs;dev:=/dev/dsk/2s0
     dylan/dk5    type:=ufs;dev:=/dev/dsk/5s0

Direct Automount Filesystem (type:=direct)
==========================================

The direct filesystem is almost identical to the automount filesystem.  Instead of appearing to be a directory of mount points, it appears as a symbolic link to a mounted filesystem.  The mount is done at the time the link is accessed.  See Automount Filesystem, for a list of required options.

Direct automount points are created by specifying the direct filesystem type on the command line:

     amd ... /usr/man auto.direct -type:=direct

where auto.direct would contain an entry such as:

     usr/man    -type:=nfs;rfs:=/usr/man \
                rhost:=man-server1  rhost:=man-server2

In this example, man-server1 and man-server2 are file servers which export copies of the manual pages.  Note that the key which is looked up is the name of the automount point without the leading /.

Union Filesystem (type:=union)
==============================

The union filesystem type allows the contents of several directories to be merged and made visible in a single directory.  This can be used to overcome one of the major limitations of the Unix mount mechanism which only allows complete directories to be mounted.

For example, supposing /tmp and /var/tmp were to be merged into a new directory called /mtmp, with files in /var/tmp taking precedence.  The following command could be used to achieve this effect:

     amd ... /mtmp union:/tmp:/var/tmp -type:=union

Currently, the unioned directories must not be automounted.  That would cause a deadlock.  This seriously limits the current usefulness of this filesystem type and the problem will be addressed in a future release of Amd.

Files created in the union directory are actually created in the last named directory.  This is done by creating a wildcard entry which points to the correct directory.  The wildcard entry is visible if the union directory is listed, so allowing you to see which directory has priority.

The files visible in the union directory are computed at the time Amd is started, and are not kept uptodate with respect to the underlying directories.  Similarly, if a link is removed, for example with the rm command, it will be lost forever.

Error Filesystem (type:=error)
==============================

The error filesystem type is used internally as a catch-all in the case where none of the other filesystems was selected, or some other error occurred. Lookups and mounts always fail with ``No such file or directory''. All other operations trivially succeed.

The error filesystem is not directly accessible.

Top-level Filesystem (type:=toplvl)
===================================

The toplvl filesystems is derived from the auto filesystem and is used to mount the top-level automount nodes.  Requests of this type are automatically generated from the command line arguments and can also be passed in by using the ``-M'' option of the Amq command.

Root Filesystem
===============

The root (type:=root) filesystem type acts as an internal placeholder onto which Amd can pin toplvl mounts.  Only one node of this type need ever exist and one is created automatically during startup.  The effect of creating a second root node is undefined.

Inheritance Filesystem
======================

The inheritance (type:=inherit) filesystem is not directly accessible.  Instead, internal mount nodes of this type are automatically generated when Amd is started with the ``-r'' option. At this time the system mount table is scanned to locate any filesystems which are already mounted.  If any reference to these filesystems is made through Amd then instead of attempting to mount it, Amd simulates the mount and inherits the filesystem.  This allows a new version of Amd to be installed on a live system simply by killing the old daemon with SIGTERM and starting the new one.

This filesystem type is not generally visible externally, but it is possible that the output from amq -m may list inherit as the filesystem type.  This happens when an inherit operation cannot be completed for some reason, usually because a fileserver is down.

Run-time Administration
***********************

Starting Amd
============

Amd is best started from /etc/rc.local:

     if [ -f /etc/amd.start ]; then
             sh /etc/amd.start; (echo -n ' amd')      >/dev/console
     fi

The shell script, amd.start, contains:

     #!/bin/sh -
     PATH=/etc:/bin:/usr/bin:/usr/ucb:$PATH export PATH

     #
     # Either name of logfile or "syslog"
     #
     LOGFILE=syslog
     #LOGFILE=/var/log/amd

     #
     # Figure out whether domain name is in host name
     # If the hostname is just the machine name then
     # pass in the name of the local domain so that the
     # hostnames in the map are domain stripped correctly.
     #
     case `hostname` in
     *.*) dmn= ;;
     *) dmn='-d doc.ic.ac.uk'
     esac

     #
     # Zap earlier log file
     #
     case "$LOGFILE" in
     */*)
             mv "$LOGFILE" "$LOGFILE"-
             > "$LOGFILE"
             ;;
     syslog)
             : nothing
             ;;
     esac

     cd /usr/sbin
     #
     # -r            restart
     # -d dmn        local domain
     # -w wait       wait between unmount attempts
     # -l log        logfile or "syslog"
     #
     eval ./amd -r $dmn -w 240 -l "$LOGFILE" \
             /homes amd.homes -cache:=inc \
             /home amd.home -cache:=inc \
             /vol amd.vol -cache:=inc \
             /n amd.net -cache:=inc

If the list of automount points and maps is contained in a file or NIS map it is easily incorporated onto the command line:

     ...
     eval ./amd -r $dmn -w 240 -l "$LOGFILE" `ypcat -k auto.master`

Stopping Amd
============

Amd stops in response to two signals.

SIGTERM
     causes the top-level automount points to be unmounted and then Amd to exit.  Any automounted filesystems are left mounted.  They can be recovered by restarting Amd with the ``-r'' command line option.

SIGINT
     causes Amd to attempt to unmount any filesystems which it has automounted, in addition to the actions of SIGTERM.  This signal is primarly used for debugging.

Actions taken for other signals are undefined.

Controlling Amd
===============

It is sometimes desirable or necessary to exercise external control over some of Amd's internal state.  To support this requirement, Amd implements an RPC interface which is used by the Amq program. A variety of information is available.

Amq generally applies an operation, specified by a single letter option, to a list of mount points.  The default operation is to obtain statistics about each mount point.  This is similar to the output shown above but includes information about the number and type of accesses to each mount point.

Amq default information
-----------------------

With no arguments, Amq obtains a brief list of all existing mounts created by Amd.  This is different from the list displayed by df(1) since the latter only includes system mount points.

The output from this option includes the following information:

  * the automount point,

  * the filesystem type,

  * the mount map or mount information,

  * the internal, or system mount point.

For example:

     /            root   "root"                    sky:(pid75)
     /homes       toplvl /usr/local/etc/amd.homes  /homes
     /home        toplvl /usr/local/etc/amd.home   /home
     /homes/jsp   nfs    charm:/home/charm         /a/charm/home/charm/jsp
     /homes/phjk  nfs    toytown:/home/toytown     /a/toytown/home/toytown/ai/phjk

If an argument is given then statistics for that volume name will be output.  For example:

     What            Uid   Getattr Lookup RdDir   RdLnk   Statfs Mounted@
     /homes          0     1196    512    22      0       30     90/09/14 12:32:55
     /homes/jsp      0     0       0      0       1180    0      90/10/13 12:56:58

What
     the volume name.

Uid
     ignored.

Getattr
     the count of NFS getattr requests on this node.  This should only be non-zero for directory nodes.

Lookup
     the count of NFS lookup requests on this node.  This should only be non-zero for directory nodes.

RdDir
     the count of NFS readdir requests on this node.  This should only be non-zero for directory nodes.

RdLnk
     the count of NFS readlink requests on this node.  This should be zero for directory nodes.

Statfs
     the could of NFS statfs requests on this node.  This should only be non-zero for top-level automount points.

Mounted@
     the date and time the volume name was first referenced.

Amq -f option
-------------

The ``-f'' option causes Amd to flush the internal mount map cache. This is useful for Hesiod maps since Amd will not automatically notice when they have been updated.  The map cache can also be synchronised with the map source by using the sync option (see Automount Filesystem).

Amq -h option
-------------

By default the local host is used.  In an HP-UX cluster the root server is used since that is the only place in the cluster where Amd will be running.  To query Amd on another host the ``-h'' option should be used.

Amq -m option
-------------

The ``-m'' option displays similar information about mounted filesystems, rather than automount points.  The output includes the following information:

  * the mount information,

  * the mount point,

  * the filesystem type,

  * the number of references to this filesystem,

  * the server hostname,

  * the state of the file server,

  * any error which has occured.

For example:

     "root"           truth:(pid602)     root   1 localhost is up
     hesiod.home      /home              toplvl 1 localhost is up
     hesiod.vol       /vol               toplvl 1 localhost is up
     hesiod.homes     /homes             toplvl 1 localhost is up
     amy:/home/amy    /a/amy/home/amy    nfs    5 amy is up
     swan:/home/swan  /a/swan/home/swan  nfs    0 swan is up (Permission denied)
     ex:/home/ex      /a/ex/home/ex      nfs    0 ex is down

When the reference count is zero the filesystem is not mounted but the mount point and server information is still being maintained by Amd.

Amq -M option
-------------

The ``-M'' option passes a new map entry to Amd and waits for it to be evaluated, possibly causing a mount.  For example, the following command would cause /home/toytown on host toytown to be mounted locally on /mnt/toytown.

     amq -M '/mnt/toytown type:=nfs;rfs:=/home/toytown;rhost:=toytown;fs:=${key}'

Amd applies some simple security checks before allowing this operation.  The check tests whether the incoming request is from a privileged UDP port on the local machine.  ``Permission denied'' is returned if the check fails.

A future release of Amd will include code to allow the mount(8) command to mount automount points:

     mount -t amd /vol hesiod.vol

This will then allow Amd to be controlled from the standard system filesystem mount list.

Amq -s option
-------------

The ``-s'' option displays global statistics.  If any other options are specified or any filesystems named then this option is ignored.  For example:

     requests  stale     mount     mount     unmount
     deferred  fhandles  ok        failed    failed
     1054      1         487       290       7017

Deferred requests
     are those for which an immediate reply could not be constructed.  For example, this would happen if a background mount was required.

Stale filehandles
     counts the number of times the kernel passes a stale filehandle to Amd. Large numbers indicate problems.

Mount ok
     counts the number of automounts which were successful.

Mount failed
     counts the number of automounts which failed.

Unmount failed
     counts the number of times a filesystem could not be unmounted.  Very large numbers here indicate that the time between unmount attempts should be increased.

Amq -u option
-------------

The ``-u'' option causes the time-to-live interval of the named mount points to be expired, thus causing an unmount attempt.  This is the only safe way to unmount an automounted filesystem.  It is not possible to unmount a filesystem which has been mounted with the nounmount flag.

Amq -v option
-------------

The ``-v'' option displays the version of Amd in a similar way to Amd's ``-v'' option.

Other Amq options
-----------------

Three other operations are implemented.  These modify the state of Amd as a whole, rather than any particular filesystem.  The ``-l'', ``-x'' and ``-D'' options have exactly the same effect as Amd's corresponding command line options.  The ``-l'' option is rejected by Amd in the current version for obvious security reasons.  When Amd receives a ``-x''flag it limits the log options being modified to those which were not enabled at startup.  This prevents a user turning off any logging option which was specified at startup, though any which have been turned off since then can still be turned off.  The ``-D'' option has a similar behaviour.

Examples
********

User Filesystems
================

With more than one fileserver, the directories most frequently cross-mounted are those containing user home directories.  A common convention used at Imperial College is to mount the user disks under /home/machine.

Typically, the /etc/fstab file contained a long list of entries such as:

     machine:/home/machine /home/machine nfs ...

for each fileserver on the network.

There are numerous problems with this system.  The mount list can become quite large and some of the machines may be down when a system is booted.  When a new fileserver is installed, /etc/fstab must be updated on every machine, the mount directory created and the filesystem mounted.

In many environments most people use the same few workstations, but it is convenient to go to a colleague's machine and access your own files.  When a server goes down, it can cause a process on a client machine to hang.  By minimising the mounted filesystems to only include those actively being used, there is less chance that a filesystem will be mounted when a server goes down.

The following is a short extract from a map taken from a research fileserver at Imperial College.

Note the entry for localhost which is used for users such as the operator (opr) who have a home directory on most machine as /home/localhost/opr.

     /defaults       opts:=rw,intr,grpid,nosuid
     charm           host!=${key};type:=nfs;rhost:=${key};rfs:=/home/${key} \
                     host==${key};type:=ufs;dev:=/dev/xd0g
     #
     ...

     #
     localhost       type:=link;fs:=${host}
     ...
     #
     # dylan has two user disks so have a
     # top directory in which to mount them.
     #
     dylan           type:=auto;fs:=${map};pref:=${key}/
     #
     dylan/dk2       host!=dylan;type:=nfs;rhost:=dylan;rfs:=/home/${key} \
                     host==dylan;type:=ufs;dev:=/dev/dsk/2s0
     #
     dylan/dk5       host!=dylan;type:=nfs;rhost:=dylan;rfs:=/home/${key} \
                     host==dylan;type:=ufs;dev:=/dev/dsk/5s0
     ...
     #
     toytown         host!=${key};type:=nfs;rhost:=${key};rfs:=/home/${key} \
                     host==${key};type:=ufs;dev:=/dev/xy1g
     ...
     #
     zebedee         host!=${key};type:=nfs;rhost:=${key};rfs:=/home/${key} \
                     host==${key};type:=ufs;dev:=/dev/dsk/1s0
     #
     # Just for access...
     #
     gould           type:=auto;fs:=${map};pref:=${key}/
     gould/staff     host!=gould;type:=nfs;rhost:=gould;rfs:=/home/${key}
     #
     gummo           host!=${key};type:=nfs;rhost:=${key};rfs:=/home/${key}
     ...

This map is shared by most of the machines listed so on those systems any of the user disks is accessible via a consistent name. Amd is started with the following command

     amd /home amd.home

Note that when mounting a remote filesystem, the automounted mount point is referenced, so that the filesystem will be mounted if it is not yet (at the time the remote mountd obtains the file handle).

Home Directories
================

One convention for home directories is to locate them in /homes so user jsp's home directory is /homes/jsp.  With more than a single fileserver it is convenient to spread user files across several machines.  All that is required is a mount-map which converts login names to an automounted directory.

Such a map might be started by the command:

     amd /homes amd.homes

where the map amd.homes contained the entries:

     /defaults   type:=link   # All the entries are of type:=link
     jsp         fs:=/home/charm/jsp
     njw         fs:=/home/dylan/dk5/njw
     ...
     phjk        fs:=/home/toytown/ai/phjk
     sjv         fs:=/home/ganymede/sjv

Whenever a login name is accessed in /homes a symbolic link appears pointing to the real location of that user's home directory.  In this example, /homes/jsp would appear to be a symbolic link pointing to /home/charm/jsp.  Of course, /home would also be an automount point.

This system causes an extra level of symbolic links to be used. Although that turns out to be relatively inexpensive, an alternative is to directly mount the required filesystems in the /homes map.  The required map is simple, but long, and its creation is best automated. The entry for jsp could be:

     jsp   -sublink:=${key};rfs:=/home/charm \
                    host==charm;type:=ufs;dev:=/dev/xd0g \
                    host!=charm;type:=nfs;rhost:=charm

This map can become quite big if it contains a large number of entries. By combining two other features of Amd it can be greatly simplified.

First the UFS partitions should be mounted under the control of /etc/fstab, taking care that they are mounted in the same place that Amd would have automounted them.  In most cases this would be something like /a/host/home/host and /etc/fstab on host charm would have a line:

     /dev/xy0g /a/charm/home/charm 4.2 rw,nosuid,grpid 1 5

The map can then be changed to:

     /defaults    type:=nfs;sublink:=${key};opts:=rw,intr,nosuid,grpid
     jsp          rhost:=charm;rfs:=/home/charm
     njw          rhost:=dylan;rfs:=/home/dylan/dk5
     ...
     phjk         rhost:=toytown;rfs:=/home/toytown;sublink:=ai/${key}
     sjv          rhost:=ganymede;rfs:=/home/ganymede

This map operates as usual on a remote machine (ie ${host} not equal to ${rhost}).  On the machine where the filesystem is stored (ie ${host} equal to ${rhost}), Amd will construct a local filesystem mount point which corresponds to the name of the locally mounted UFS partition.  If Amd is started with the ``-r'' option then instead of attempting an NFS mount, Amd will simply inherit the UFS mount (see Inheritance Filesystem).  If ``-r'' is not used then a loopback NFS mount will be made.  This type of mount is known to cause a deadlock on many systems.

Architecture Sharing
====================

Often a filesystem will be shared by machines of different architectures. Separate trees can be maintained for the executable images for each architecture, but it may be more convenient to have a shared tree, with distinct subdirectories.

A shared tree might have the following structure on the fileserver (called fserver in the example):

     local/tex
     local/tex/fonts
     local/tex/lib
     local/tex/bin
     local/tex/bin/sun3
     local/tex/bin/sun4
     local/tex/bin/hp9000
     ...

In this example, the subdirectories of local/tex/bin should be hidden when accessed via the automount point (conventionally /vol). A mount-map for /vol to achieve this would look like:

     /defaults   sublink:=${/key};rhost:=fserver;type:=link
     tex         type:=auto;fs:=${map};pref:=${key}/
     tex/fonts   host!=fserver;type:=nfs;rfs:=/vol/tex \
                 host==fserver;fs:=/usr/local/tex
     tex/lib     host!=fserver;type:=nfs;rfs:=/vol/tex \
                 host==fserver;fs:=/usr/local/tex
     tex/bin     -sublink:=${/key}/${arch} host!=fserver;type:=nfs;rfs:=/vol/tex \
                 host:=fserver;fs:=/usr/local/tex

When /vol/tex/bin is referenced, the current machine architecture is automatically appended to the path by the ${sublink} variable.  This means that users can have /vol/tex/bin in their PATH without concern for architecture dependencies.

Wildcard names & Replicated Servers
===================================

By using the wildcard facility, Amd can overlay an existing directory with additional entries. The system files are usually mounted under /usr.  If instead Amd is mounted on /usr, additional names can be overlayed to augment or replace names in the ``master'' /usr. A map to do this would have the form:

     local  type:=auto;fs:=local-map
     share  type:=auto;fs:=share-map
     *      -type:=nfs;rfs:=/export/exec/${arch};sublink:="${key}" \
             rhost:=fserv1  rhost:=fserv2  rhost:=fserv3

Note that the assignment to ${sublink} is surrounded by double quotes to prevent the incoming key from causing the map to be misinterpreted.  This map has the effect of directing any access to /usr/local or /usr/share to another automount point.

In this example, it is assumed that the /usr files are replicated on three fileservers: fserv1, fserv2 and fserv3. For any references other than to local and share one of the servers is used and a symbolic link to ${autodir}/${rhost}/export/exec/${arch}/whatever is returned once an appropriate filesystem has been mounted.

rwho servers
============

The /usr/spool/rwho directory is a good candidate for automounting. For efficiency reasons it is best to capture the rwho data on a small number of machines and then mount that information onto a large number of clients.  The data written into the rwho files is byte order dependent so only servers with the correct byte ordering can be used by a client:

     /defaults         type:=nfs
     usr/spool/rwho    -byte==little;rfs:=/usr/spool/rwho \
                           rhost:=vaxA  rhost:=vaxB \
                       || -rfs:=/usr/spool/rwho \
                           rhost:=sun4  rhost:=hp300

/vol
====

/vol is used as a catch-all for volumes which do not have other conventional names.

Below is part of the /vol map for the domain doc.ic.ac.uk. The r+d tree is used for new or experimental software that needs to be available everywhere without installing it on all the fileservers. Users wishing to try out the new software then simply include /vol/r+d/{bin,ucb} in their path.

The main tree resides on one host gould.doc.ic.ac.uk, which has different bin, etc, lib and ucb sub-directories for each machine architecture.  For example, /vol/r+d/bin for a Sun-4 would be stored in the sub-directory bin/sun4 of the filesystem /usr/r+d.  When it was accessed a symbolic link pointing to /a/gould/usr/r+d/bin/sun4 would be returned.

     /defaults    type:=nfs;opts:=rw,grpid,nosuid,intr,soft
     wp           -opts:=rw,grpid,nosuid;rhost:=charm \
                  host==charm;type:=link;fs:=/usr/local/wp \
                  host!=charm;type:=nfs;rfs:=/vol/wp
     ...
     #
     src          -opts:=rw,grpid,nosuid;rhost:=charm \
                  host==charm;type:=link;fs:=/usr/src \
                  host!=charm;type:=nfs;rfs:=/vol/src
     #
     r+d          type:=auto;fs:=${map};pref:=r+d/
     # per architecture bin,etc,lib&ucb...
     r+d/bin      rhost:=gould.doc.ic.ac.uk;rfs:=/usr/r+d;sublink:=${/key}/${arch}
     r+d/etc      rhost:=gould.doc.ic.ac.uk;rfs:=/usr/r+d;sublink:=${/key}/${arch}
     r+d/include  rhost:=gould.doc.ic.ac.uk;rfs:=/usr/r+d;sublink:=${/key}
     r+d/lib      rhost:=gould.doc.ic.ac.uk;rfs:=/usr/r+d;sublink:=${/key}/${arch}
     r+d/man      rhost:=gould.doc.ic.ac.uk;rfs:=/usr/r+d;sublink:=${/key}
     r+d/src      rhost:=gould.doc.ic.ac.uk;rfs:=/usr/r+d;sublink:=${/key}
     r+d/ucb      rhost:=gould.doc.ic.ac.uk;rfs:=/usr/r+d;sublink:=${/key}/${arch}
     # hades pictures
     pictures     -opts:=rw,grpid,nosuid;rhost:=thpfs \
                  host==thpfs;type:=link;fs:=/nbsd/pictures \
                  host!=thpfs;type:=nfs;rfs:=/nbsd;sublink:=pictures
     # hades tools
     hades        -opts:=rw,grpid,nosuid;rhost:=thpfs \
                  host==thpfs;type:=link;fs:=/nbsd/hades \
                  host!=thpfs;type:=nfs;rfs:=/nbsd;sublink:=hades
     # bsd tools for hp.
     bsd          -opts:=rw,grpid,nosuid;arch==hp9000;rhost:=thpfs \
                  host==thpfs;type:=link;fs:=/nbsd/bsd \
                  host!=thpfs;type:=nfs;rfs:=/nbsd;sublink:=bsd

Internals
*********

Log Messages
============

In the following sections a brief explanation is given of some of the log messages made by Amd.  Where the message is in typewriter font, it corresponds exactly to the message produced by Amd.  Words in italic are replaced by an appropriate string.  Variables, ${var}, indicate that the value of the appropriate variable is output.

Log messages are either sent direct to a file, or logged via the syslog(3) mechanism. Messages are logged with facility LOG_DAEMON when using syslog(3). In either case, entries in the file are of the form:

     date-string  hostname amd[pid]  message

Fatal errors
------------

Amd attempts to deal with unusual events.  Whenever it is not possible to deal with such an error, Amd will log an appropriate message and, if it cannot possibly continue, will either exit or abort. These messages are selected by -x fatal on the command line. When syslog(3) is being used, they are logged with level LOG_FATAL.  Even if Amd continues to operate it is likely to remain in a precarious state and should be restarted at the earliest opportunity.

Attempting to inherit not-a-filesystem
     The prototype mount point created during a filesystem restart did not contain a reference to the restarted filesystem.  This erorr ``should never happen''.

Can't bind to domain "NIS-domain"
     A specific NIS domain was requested on the command line, but no server for that domain is available on the local net.

Can't determine IP address of this host (hostname)
     When Amd starts it determines its own IP address.  If this lookup fails then Amd cannot continue.  The hostname it looks up is that obtained returned by gethostname(2) system call.

Can't find root file handle for automount point
     Amd creates its own file handles for the automount points.  When it mounts itself as a server, it must pass these file handles to the local kernel.  If the filehandle is not obtainable the mount point is ignored. This error ``should never happen''.

Must be root to mount filesystems (euid = euid)
     To prevent embarrassment, Amd makes sure it has appropriate system privileges.  This amounts to having an euid of 0.  The check is made after argument processing complete to give non-root users a chance to access the ``-v'' option.

No work to do - quitting
     No automount points were given on the command line and so there is no work to do.

Out of memory in realloc
     While attempting to realloc some memory, the memory space available to Amd was exhausted.  This is an unrecoverable error.

Out of memory
     While attempting to malloc some memory, the memory space available to Amd was exhausted.  This is an unrecoverable error.

cannot create rpc/udp service
     Either the NFS or AMQ endpoint could not be created.

gethostname: description
     The gethostname(2) system call failed during startup.

host name is not set
     The gethostname(2) system call returned a zero length host name. This can happen if Amd is started in single user mode just after booting the system.

ifs_match called!
     An internal error occurred while restarting a pre-mounted filesystem. This error ``should never happen''.

mount_afs: description
     An error occured while Amd was mounting itself.

run_rpc failed
     Somehow the main NFS server loop failed.  This error ``should never happen''.

unable to free rpc arguments in amqprog_1
     The incoming arguments to the AMQ server could not be free'ed.

unable to free rpc arguments in nfs_program_1
     The incoming arguments to the NFS server could not be free'ed.

unable to register (AMQ_PROGRAM, AMQ_VERSION, udp)
     The AMQ server could not be registered with the local portmapper or the internal RPC dispatcher.

unable to register (NFS_PROGRAM, NFS_VERSION, 0)
     The NFS server could not be registered with the internal RPC dispatcher.

Info messages
-------------

Amd generates information messages to record state changes.  These messages are selected by -x info on the command line.  When syslog(3) is being used, they are logged with level LOG_INFO.

The messages listed below can be generated and are in a format suitable for simple statistical analysis.  mount-info is the string that is displayed by Amq in its mount information column and placed in the system mount table.

mount of "${path}" on ${fs} timed out
     Attempts to mount a filesystem for the given automount point have failed to complete within 30 seconds.

"${path}" forcibly timed out
     An automount point has been timed out by the Amq command.

restarting mount-info on ${fs}
     A pre-mounted file system has been noted.

"${path}" has timed out
     No access to the automount point has been made within the timeout period.

file server ${rhost} is down - timeout of "${path}" ignored
     An automount point has timed out, but the corresponding file server is known to be down.  This message is only produced once for each mount point for which the server is down.

Re-synchronizing cache for map ${map}
     The named map has been modified and the internal cache is being re-synchronized.

Filehandle denied for "${rhost}:${rfs}"
     The mount daemon refused to return a file handle for the requested filesystem.

Filehandle error for "${rhost}:${rfs}": description
     The mount daemon gave some other error for the requested filesystem.

file server ${rhost} type nfs starts up
     A new NFS file server has been referenced and is known to be up.

file server ${rhost} type nfs starts down
     A new NFS file server has been referenced and is known to be down.

file server ${rhost} type nfs is up
     An NFS file server that was previously down is now up.

file server ${rhost} type nfs is down
     An NFS file server that was previously up is now down.

Finishing with status exit-status
     Amd is about to exit with the given exit status.

mount-info mounted fstype ${type} on ${fs}
     A new file system has been mounted.

mount-info restarted fstype ${type} on ${fs}
     Amd is using a pre-mounted filesystem to satisfy a mount request.

mount-info unmounted fstype ${type} from ${fs}
     A file system has been unmounted.

mount-info unmounted fstype ${type} from ${fs} link ${fs}/${sublink}
     A file system of which only a sub-directory was in use has been unmounted.

Acknowledgements & Trademarks
*****************************

Thanks to the Formal Methods Group at Imperial College for suffering patiently while Amd was being developed on their machines.

Thanks to the many people who have helped with the development of Amd, especially Piete Brooks at the Cambridge University Computing Lab for many hours of testing, experimentation and discussion.

  * DEC, VAX and Ultrix are registered trademarks of Digital Equipment Corporation.

  * AIX and IBM are registered trademarks of International Business Machines Corporation.

  * Sun, NFS and SunOS are registered trademarks of Sun Microsystems, Inc.

  * Unix is a registered trademark of AT&T Unix Systems Laboratories in the USA and other countries.