amdref.texinfo

早期freebsd实现

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

For NFS and UFS filesystems the value of @code{$@{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 @dfn{local} mount point @dfn{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 @b{getwd}(3) traverses the namespace to
find the pathname of the current directory.

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

@node     opts Option, remopts Option, fs Option, Map Options
@comment  node-name,  next,  previous,  up
@subsubsection opts Option
@cindex Setting system mount options
@cindex Passing parameters to the mount system call
@cindex mount system call
@cindex mount system call flags
@cindex The mount system call
@cindex opts, mount option
@cindex Mount option; opts

The options to pass to the mount system call.  A leading @samp{-} is
silently ignored.  The mount options supported generally correspond to
those used by @b{mount}(8) and are listed below.  Some additional
pseudo-options are interpreted by @i{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 @samp{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 @code{compress} and @code{spongy} options.

@table @code
@item compress
Use NFS compression protocol.
@item grpid
Use BSD directory group-id semantics.
@item intr
Allow keyboard interrupts on hard mounts.
@item noconn
Don't make a connection on datagram transports.
@item nocto
No close-to-open consistency.
@item nodevs
Don't allow local special devices on this filesystem.
@item nosuid
Don't allow set-uid or set-gid executables on this filesystem.
@item quota
Enable quota checking on this mount.
@item retrans=@i{n}
The number of NFS retransmits made before a user error is generated by a
@samp{soft} mounted filesystem, and before a @samp{hard} mounted
filesystem reports @samp{NFS server @dfn{yoyo} not responding still
trying}.
@item ro
Mount this filesystem readonly.
@item rsize=@var{n}
The NFS read packet size.  You may need to set this if you are using
NFS/UDP through a gateway.
@item soft
Give up after @dfn{retrans} retransmissions.
@item spongy
Like @samp{soft} for status requests, and @samp{hard} for data transfers.
@item tcp
Use TCP/IP instead of UDP/IP, ignored if the NFS implementation does not
support TCP/IP mounts.
@item timeo=@var{n}
The NFS timeout, in tenth-seconds, before a request is retransmitted.
@item wsize=@var{n}
The NFS write packet size.  You may need to set this if you are using
NFS/UDP through a gateway.
@end table

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

@table @code
@item nounmount
Configures the mount so that its time-to-live will
never expire.  This is also the default for some filesystem types.
@c
@c Implementation broken:
@item ping=@var{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.
@item retry=@var{n}
The number of times to retry the mount system call.
@item utimeout=@var{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.
@end table

@node     remopts Option, sublink Option, opts Option, Map Options
@comment  node-name,  next,  previous,  up
@subsubsection remopts Option
@cindex Setting system mount options for non-local networks
@cindex remopts, mount option
@cindex Mount option; remopts

This option has the same use as @code{$@{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 @var{remopts}.  When a non-local host is accessed, the
smaller sizes will automatically be used.

@i{Amd} determines whether a host is local by examining the network
interface configuration at startup.  Any interface changes made after
@i{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 @code{$@{rem@}} is the same as the
value of @code{$@{opts@}}.

@node     sublink Option, type Option, remopts Option, Map Options
@comment  node-name,  next,  previous,  up
@subsubsection sublink Option
@cindex Setting the sublink option
@cindex sublink, mount option
@cindex Mount option; sublink

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.

@node     type Option, , sublink Option, Map Options
@comment  node-name,  next,  previous,  up
@subsubsection type Option
@cindex Setting the filesystem type option
@cindex type, mount option
@cindex Mount option; type

The filesystem type to be used.  @xref{Filesystem Types}, for a full
description of each type.@refill

@node     Amd Command Line Options, Filesystem Types, Mount Maps, Top
@comment  node-name,  next,  previous,  up
@chapter @i{Amd} Command Line Options
@cindex Command line options, Amd
@cindex Amd command line options
@cindex Overriding defaults on the command line

Many of @i{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

@example
amd [@i{options}] @{ @i{directory} @i{map-name} [-@i{map-options}] @} ...
@end example

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

@samp{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 @samp{/defaults}.  When default options
are given they are prepended to any options specified in the mount-map
locations as explained in.  @xref{Map Defaults}, for more details.

The @dfn{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 @i{Amd} exits.
Finally, @i{Amd} disassociates itself from its controlling terminal and
forks into the background.

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

@menu
* -a Option::	Automount directory.
* -c Option::	Cache timeout interval.
* -d Option::	Domain name.
* -k Option::	Kernel architecture.
* -l Option::	Log file.
* -n Option::	Hostname normalisation.
* -p Option::	Output process id.
* -r Option::	Restart existing mounts.
* -t Option::	Kernel RPC timeout.
* -v Option::	Version information.
* -w Option::	Wait interval after failed unmount.
* -x Option::	Log options.
* -y Option::	NIS domain.
* -C-Option::	Cluster name.
* -D-Option::	Debug flags.
@end menu

@node     -a Option, -c Option, Amd Command Line Options, Amd Command Line Options
@comment  node-name,  next,  previous,  up
@section @code{-a} @var{directory}
@cindex Automount directory
@cindex Setting the default mount directory

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

@example
amd -a /amd ...
@end example

@node     -c Option, -d Option, -a Option, Amd Command Line Options
@comment  node-name,  next,  previous,  up
@section @code{-c} @var{cache-interval}
@cindex Cache interval
@cindex Interval before a filesystem times out
@cindex Setting the interval before a filesystem times out
@cindex Changing the interval before a filesystem times out

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

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

The default @dfn{cache-interval} is 300 seconds (five minutes).

@node     -d Option, -k Option, -c Option, Amd Command Line Options
@comment  node-name,  next,  previous,  up
@section @code{-d} @var{domain}
@cindex Domain name
@cindex Setting the local domain name
@cindex Overriding the local domain name

Specifies the host's domain.  This sets the internal variable
@code{$@{domain@}} and affects the @code{$@{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
@code{$@{domain@}} is @samp{unknown.domain}.

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

@example
amd -d doc.ic.ac.uk ...
@end example

@node     -k Option, -l Option, -d Option, Amd Command Line Options
@comment  node-name,  next,  previous,  up
@section @code{-k} @var{kernel-architecture}
@cindex Setting the Kernel architecture

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

This would be used as follows:

@example
amd -k `arch -k` ...
@end example

@node     -l Option, -n Option, -k Option, Amd Command Line Options
@comment  node-name,  next,  previous,  up
@section @code{-l} @var{log-option}
@cindex Log filename
@cindex Setting the log file
@cindex Using syslog to log errors
@cindex syslog

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

@enumerate
@item
If @dfn{log-option} is the string @samp{syslog}, @i{Amd} will use the
@b{syslog}(3) mechanism.@refill

@item
If @dfn{log-option} is the string @samp{/dev/stderr}, @i{Amd} will use
standard error, which is also the default target for log messages.  To
implement this, @i{Amd} simulates the effect of the @samp{/dev/fd}
driver.
@end enumerate

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 @samp{syslog} option is specified but the system does not support
syslog or if the named file cannot be opened or created, @i{Amd} will
use standard error.  Error messages generated before @i{Amd} has
finished parsin