MAN page from Fedora 28 am-utils-6.2.0-33.fc28.i686.rpm


Section: Maintenance Commands (8)
Updated: 3 November 1989


amd - automatically mount file systems 


amd[-F conf_file]
amd[-nprvHS] [-a mount_point] [-c duration] [-d domain] [-k kernel-arch] [-l logfile] [-o op_sys_ver] [-t interval.interval] [-w interval] [-x log-option] [-y YP-domain] [-A arch] [-C cluster-name] [-D option] [-F conf_file] [-O op_sys_name] [-T tag][directorymapname[ -map-options ]] ... 


Amdis a daemon that automatically mounts filesystemswhenever a file or directorywithin that filesystem is accessed.Filesystems are automatically unmounted when theyappear to have become quiescent.

Amdoperates by attaching itself as anNFSserver to each of the specifieddirectories.Lookups within the specified directoriesare handled byamd,which uses the map defined bymapnameto determine how to resolve the lookup.Generally, this will be a host name, some filesystem informationand some mount options for the given filesystem.

In the first form depicted above,amdwill print a short help string. In the second form, if no options arespecified, or the-Fis used,amdwill read configuration parameters from the fileconf_filewhich defaults to/etc/amd.conf.The last form is described below. 


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

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

-d domain
Specify the local domain name. If this option is notgiven the domain name is determined from the hostname.

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

-l logfile
Specify a logfile in which to record mount and unmount events.Iflogfileis the stringsyslogthen the log messages will be sent to the system log daemon bysyslog(3).The default syslog facility used is LOG_DAEMON. If youwish to change it, append its name to the log file name, delimited by asingle colon. For example, iflogfileis the stringsyslog:local7thenAmdwill log messages viasyslog(3)using the LOG_LOCAL7 facility (if it exists on the system).

Normalize hostnames.The name refereed to by ${rhost} is normalized relative to thehost database before being used. The effect is to translatealiases into ``official'' names.

-o op_sys_ver
Override the compiled-in version number of the operating system. Usefulwhen the built in version is not desired for backward compatibility reasons.For example, if the build in version is ``2.5.1'', you can override it to``5.5.1'', and use older maps that were written with the latter in mind.

Print PID.Outputs the process-id ofamdto standard output where it can be saved into a file.

Restart existing mounts.Amdwill scan the mount file table to determine which filesystemsare currently mounted. Whenever one of these would havebeen auto-mounted,amdinheritsit.

-t timeout.retransmit
Specify the NFS timeoutinterval,in tenths of a second, between NFS/RPC retries (for UDP only). The defaultis 0.8 seconds. The second value alters the retransmit counter, whichdefaults to 11 retransmissions. Both of these values are used by the kernelto communicate with amd. Useful defaults are supplied if either or bothvalues are missing.

Amd relies on the kernel RPC retransmit mechanism to trigger mount retries.The values of these parameters change the overall retry interval. Too longan interval gives poor interactive response; too short an interval causesexcessive retries.

Version. Displays version and configuration information on standard error.

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

-x options
Specify run-time logging options. The options are a comma separatedlist chosen from: fatal, error, user, warn, info, map, stats, defaults, andall. Note that "fatal" and "error" are mandatory and cannot be turned off.

-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 NISsupport is not available.

-A arch
Specifies the OS architecture. This is used solely to set the ${arch}selector.

-C cluster-name
Specify an alternative HP-UX cluster name to use.

-D option
Select from a variety of debug options. Prefixing anoption with the stringsnoreverses the effect of that option. Options are cumulative.The most useful option isall.Since-Dis only used for debugging other options are not documented here:the current supported set of options is listed by the -v optionand a fuller description is available in the program source.

-F conf_file
Specify an amd configuration file to use. Seeamd.conf(5)for description of this file's format. This configuration file is used tospecify any options in lieu of typing many of them on the command line. Theamd.conffile includes directives for every command line option amd has, and manymore that are only available via the configuration file facility. Theconfiguration file specified by this option is processed after all otheroptions had been processed, regardless of the actual location of this optionon the command line.

Print help and usage string.

-O op_sys_name
Override the compiled-in name of the operating system. Useful when thebuilt in name is not desired for backward compatibility reasons. Forexample, if the build in name is ``sunos5'', you can override it to``sos5'', and use older maps which were written with the latter in mind.

Do not lock the running executable pages of amd into memory. To improveamd's performance, systems that support theplock(3)call, could lock the amd process into memory. This way there is less chancethe operating system will schedule, page out, and swap the amd process asneeded. This tends improves amd's performance, at the cost of reserving thememory used by the amd process (making it unavailable for other processes).If this behavior is not desired, use the-Soption.

-T tag
Specify a tag to use withamd.conf(5).All map entries tagged withtagwill be processed. Map entries that are not tagged are always processed.Map entries that are tagged with a tag other thantagwill not be processed.



directory under which filesystems are dynamically mounted
default configuration file


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 cachedby the kernel and each time a symlink is encountered during alookuppntranslation it costs an RPC call to the NFS server.It would appear that a large improvement in real-timeperformance could be gained by adding a cache somewhere.Replacing symlinks with a suitable incarnation of the auto-mounterresults in a large real-time speedup, but also causes a largenumber of process context switches.

A weird imagination is most useful to gain full advantage of allthe features. 




Linux NFS and Automounter Administrationby Erez Zadok, ISBN 0-7821-2739-8, (Sybex, 2001).

Amd - The 4.4 BSD Automounter 


Jan-Simon Pendry <>, Department of Computing, Imperial College, London, UK.Erez Zadok <>, Computer Science Department, Stony BrookUniversity, Stony Brook, New York, USA.Other authors and contributors to am-utils are listed in theAUTHORSfile distributed with am-utils.




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