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The amd utility is a daemon that automatically mounts file systems whenever a file or directory within that file system is accessed. File systems are automatically unmounted when they appear to be quiescent.
The amd utility operates by attaching itself as an NFS server to each of the specified 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 file system information and some mount options for the given file system.
In the first form depicted above,
amd
will print a short help string.
In the second form, if no options are
specified, or if the
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Specify an alternative location for the real mount points. The default is /.amd_mnt. | |
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Specify a duration, in seconds, that a looked up name remains cached when not in use. The default is 5 minutes. | |
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Specify the local domain name. If this option is not given the domain name is determined from the hostname. | |
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Specifies the kernel architecture. This is used solely to set the ${karch} selector. | |
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Specify a logfile in which to record mount and unmount events. If logfile is the string "syslog", then the log messages will be sent to the system log daemon by syslog(3). The default syslog facility used is LOG_DAEMON. If you wish to change it, append its name to the log file name, delimited by a single colon. For example, if logfile is the string "syslog:local7" then amd will log messages via syslog(3) using the LOG_LOCAL7 facility (if it exists on the system). | |
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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. | |
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Override the compiled-in version number of the operating system. Useful when 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. | |
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Print PID. Outputs the process ID of amd to standard output where it can be saved into a file. | |
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Restart existing mounts. The amd utility will scan the mount file table to determine which file systems are currently mounted. Whenever one of these would have been auto-mounted, amd inherits it. | |
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Specify the NFS
timeout
interval,
in tenths of a second, between
NFS/RPC
retries (for UDP only).
The default
is 0.8 seconds.
The second value alters the retransmit counter, which
defaults to 11 retransmissions.
Both of these values are used by the kernel
to communicate with amd.
Useful defaults are supplied if either or both
values are missing.
The amd(8) utility relies on the kernel RPC retransmit mechanism to trigger mount retries. The values of these parameters change the overall retry interval. Too long an interval gives poor interactive response; too short an interval causes excessive retries. | |
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Version. Displays version and configuration information on standard error. | |
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Specify an interval, in seconds, between attempts to dismount file systems that have exceeded their cached times. The default is 2 minutes. | |
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Specify run-time logging options. The options are a comma separated list chosen from: fatal, error, user, warn, info, map, stats, defaults, all. Note that "fatal" and "error" are mandatory and cannot be turned off. | |
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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. | |
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Specifies the OS architecture. This is used solely to set the ${arch} selector. | |
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Specify an alternative HP-UX cluster name to use. | |
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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
| |
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Specify an amd configuration file to use. See amd.conf(5) for description of this file's format. This configuration file is used to specify any options in lieu of typing many of them on the command line. The amd.conf(5) file includes directives for every command line option amd has, and many more that are only available via the configuration file facility. The configuration file specified by this option is processed after all other options had been processed, regardless of the actual location of this option on the command line. | |
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Print help and usage string. | |
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Override the compiled-in name of the operating system. Useful when the built in name is not desired for backward compatibility reasons. For example, 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. | |
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Do not lock the running executable pages of
amd
into memory.
To improve
Ns
performance, systems that support the
plock(3)
call, could lock the
amd
process into memory.
This way there is less chance
the operating system will schedule, page out, and swap the
amd
process as
needed.
This tends to improve
Ns
performance, at the cost of reserving the
memory used by the
amd
process (making it unavailable for other processes).
If this behavior is not desired, use the
| |
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Specify a tag to use with amd.conf(5). All map entries tagged with tag will be processed. Map entries that are not tagged are always processed. Map entries that are tagged with a tag other than tag will not be processed. | |
/.amd_mnt | directory under which file systems are dynamically mounted |
/etc/amd.conf | |
default configuration file | |
Symbolic links on an NFS file system 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. It would appear that a large improvement in real-time performance could be gained by adding a cache somewhere. Replacing symlinks 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 features.
"am-utils" info(1) entry.
Linux NFS and Automounter Administration, ISBN 0-7821-2739-8, Sybex, 2001.
,Amd \- The 4.4 BSD Automounter,
Erez Zadok <ezk@cs.sunysb.edu>, Computer Science Department, Stony Brook University, Stony Brook, New York, USA.
Other authors and contributors to am-utils are listed in the AUTHORS file distributed with am-utils.
AMD (8) | November 22, 2019 |
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