amd.8

早期freebsd实现

.\"
.\" Copyright (c) 1989 Jan-Simon Pendry
.\" Copyright (c) 1989 Imperial College of Science, Technology & Medicine
.\" Copyright (c) 1989, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Jan-Simon Pendry at Imperial College, London.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
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.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. 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.
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.\"     @(#)amd.8	5.10 (Berkeley) 4/19/94
.\"
.\" $Id: amd.8,v 5.2.2.1 1992/02/09 15:11:39 jsp beta $
.\"
.Dd "April 19, 1994"
.Dt AMD 8
.Os
.Sh NAME
.Nm amd
.Nd automatically mount file systems
.Sh SYNOPSIS
.Nm amd
.Op Fl nprv
.Op Fl a Ar mount_point
.Op Fl c Ar duration
.Op Fl d Ar domain
.Bk -words
.Op Fl k Ar kernel-arch
.Ek
.Op Fl l Ar logfile
.Op Fl t Ar interval.interval
.Bk -words
.Op Fl w Ar interval
.Ek
.Op Fl x Ar log-option
.Op Fl y Ar YP-domain
.Bk -words
.Op Fl C Ar cluster-name
.Ek
.Op Fl D Ar option
.Oo
.Ar directory mapname
.Op Fl map-options
.Oc
.Ar ...
.Sh DESCRIPTION
.Nm Amd
is a daemon that automatically mounts filesystems
whenever a file or directory
within that filesystem is accessed.
Filesystems are automatically unmounted when they
appear to be quiescent.
.Pp
.Nm Amd
operates by attaching itself as an
.Tn NFS
server to each of the specified
.Ar directories .
Lookups within the specified directories
are handled by
.Nm amd ,
which uses the map defined by
.Ar mapname
to determine how to resolve the lookup.
Generally, this will be a host name, some filesystem information
and some mount options for the given filesystem.
.Sh OPTIONS
.Bl -tag -width Ds
.It Fl a Ar temporary-directory
Specify an alternative location for the real mount points.
The default is
.Pa /a .
.It Fl c Ar duration
Specify a
.Ar duration ,
in seconds, that a looked up name remains
cached when not in use.  The default is 5 minutes.
.It Fl d Ar domain
Specify the local domain name.  If this option is not
given the domain name is determined from the hostname.
.It Fl k Ar kernel-arch
Specifies the kernel architecture.  This is used solely
to set the ${karch} selector.
.It Fl l Ar logfile
Specify a logfile in which to record mount and unmount events.
If
.Ar logfile
is the string
.Em syslog ,
the log messages will be sent to the system log daemon by
.Xr syslog 3 .
.It Fl n
Normalize hostnames.
The name referred to by ${rhost} is normalized relative to the
host database before being used.  The effect is to translate
aliases into ``official'' names.
.It Fl p
Print
.Em PID .
Outputs the process-id of
.Nm amd
to standard output where it can be saved into a file.
.It Fl r
Restart existing mounts.
.Nm Amd
will scan the mount file table to determine which filesystems
are currently mounted.  Whenever one of these would have
been auto-mounted,
.Nm amd
.Em inherits
it.
.It Fl t Ar interval.interval
Specify the
.Ar interval ,
in tenths of a second, between
.Tn NFS/RPC/UDP
retries.
The default is 0.8 seconds.
The second values alters the retransmit counter.
Useful defaults are supplied if either or both
values are missing.
.It Fl v
Version.  Displays version and configuration information on standard error.
.It Fl w Ar interval
Specify an
.Ar interval ,
in seconds, between attempts to dismount
filesystems that have exceeded their cached times.
The default is 2 minutes.
.It Fl y Ar domain
Specify an alternative
.Tn NIS
domain from which to fetch the
.Tn NIS
maps.
The default is the system domain name.
This option is ignored if
.Tn NIS
support is not available.
.It Fl x Ar options
Specify run-time logging options.  The options are a comma separated
list chosen from: fatal, error, user, warn, info, map, stats, all.
.It Fl D Ar option
Select from a variety of debug options.  Prefixing an
option with the string
.Em no
reverses the effect of that option.  Options are cumulative.
The most useful option is
.Ar all .
.El
.Pp
Since
.Fl D
is only used for debugging other options are not documented here:
the current supported set of options is listed by the
.Fl v
option
and a fuller description is available in the program source.
.Sh FILES
.Bl -tag -width /axx
.It Pa /a
directory under which filesystems are dynamically mounted
.El
.Sh CAVEATS
Some care may be required when creating a mount map.
.Pp
Symbolic links on an
.Tn NFS
filesystem can be incredibly inefficient.
In most implementations of
.Tn NFS ,
their interpolations are not cached by
the kernel and each time a symbolic link is
encountered during a
.Em lookuppn
translation it costs an
.Tn RPC
call to the
.Tn NFS
server.
A large improvement in real-time
performance could be gained by adding a cache somewhere.
Replacing
.Xr symlinks 2
with a suitable incarnation of the auto-mounter
results in a large real-time speedup, but also causes a large
number of process context switches.
.Pp
A weird imagination is most useful to gain full advantage of all
the features.
.Sh SEE ALSO
.Xr amq 8 ,
.Xr hostname 1 ,
.Xr mount 8 ,
.Xr umount 8 ,
.Rs
.%T Amd \- The 4.4 BSD Automounter
.Re
.Sh AUTHOR
.An Jan-Simon Pendry
<[e-mail]>, Department of Computing, Imperial College, London, UK.
.Sh HISTORY
The
.Nm amd
utility first appeared in 4.4BSD.