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AMD(8)			  BSD System Manager's Manual			AMD(8)

     amd — automatically mount file systems

     amd [-nprv] [-a mount_point] [-c duration] [-d domain] [-k kernel-arch]
	 [-l logfile] [-t interval.interval] [-w interval] [-x log-option]
	 [-y YP-domain] [-C cluster-name] [-D option] [directory mapname
	 [-map-options]] ...

     Amd is a daemon that automatically mounts filesystems whenever a file or
     directory within that filesystem is accessed.  Filesystems are automati‐
     cally unmounted when they appear to be quiescent.

     Amd operates by attaching itself as an NFS server to each of the speci‐
     fied directories.	Lookups within the specified directories are handled
     by amd, which uses the map defined by mapname to determine how to resolve
     the lookup.  Generally, this will be a host name, some filesystem infor‐
     mation and some mount options for the given filesystem.

     -a temporary-directory
	     Specify an alternative location for the real mount points.	 The
	     default is /a.

     -c duration
	     Specify a duration, in seconds, that a looked up name remains
	     cached when not in use.  The default is 5 minutes.

     -d domain
	     Specify the local domain name.  If this option is not given the
	     domain name is determined from the hostname.

     -k kernel-arch
	     Specifies the kernel architecture.	 This is used solely to set
	     the ${karch} selector.

     -l logfile
	     Specify a logfile in which to record mount and unmount events.
	     If logfile is the string syslog, the log messages will be sent to
	     the system log daemon by syslog(3).

     -n	     Normalize hostnames.  The name referred to by ${rhost} is normal‐
	     ized relative to the host database before being used.  The effect
	     is to translate aliases into ``official'' names.

     -p	     Print PID.	 Outputs the process-id of amd to standard output
	     where it can be saved into a file.

     -r	     Restart existing mounts.  Amd will scan the mount file table to
	     determine which filesystems are currently mounted.	 Whenever one
	     of these would have been auto-mounted, amd inherits it.

     -t interval.interval
	     Specify the interval, in tenths of a second, between 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.

     -v	     Version.  Displays version and configuration information on stan‐

	     dard error.

     -w interval
	     Specify an interval, in seconds, between attempts to dismount
	     filesystems that have exceeded their cached times.	 The default
	     is 2 minutes.

     -y domain
	     Specify an alternative NIS domain from which to fetch the NIS
	     maps.  The default is the system domain name.  This option is
	     ignored if NIS support is not available.

     -x options
	     Specify run-time logging options.	The options are a comma sepa‐
	     rated list chosen from: fatal, error, user, warn, info, map,
	     stats, all.

     -D option
	     Select from a variety of debug options.  Prefixing an option with
	     the string no reverses the effect of that option.	Options are
	     cumulative.  The most useful option is all.

     Since -D is only used for debugging other options are not documented
     here: the current supported set of options is listed by the -v option and
     a fuller description is available in the program source.

     /a	   directory under which filesystems are dynamically mounted

     Some care may be required when creating a mount map.

     Symbolic links on an NFS filesystem can be incredibly inefficient.	 In
     most implementations of NFS, their interpolations are not cached by the
     kernel and each time a symbolic link is encountered during a lookuppn
     translation it costs an RPC call to the NFS server.  A large improvement
     in real-time performance could be gained by adding a cache somewhere.
     Replacing 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.

     A weird imagination is most useful to gain full advantage of all the fea‐

     amq(8), hostname(1), mount(8), umount(8),

     Amd - The 4.4 BSD Automounter.

     Jan-Simon Pendry <>, Department of Computing, Imperial
     College, London, UK.

     The amd utility first appeared in 4.4BSD.

BSD			      September 24, 2021			   BSD

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