AMD(8) BSD System Manager's Manual AMD(8)NAMEamd — automatically mount file systems
SYNOPSISamd-H
amd [-F conf_file]
amd [-nprvHS] [-a mount_point] [-c duration] [-d domain] [-k kernel-arch]
[-l logfile] [-o op_sys_ver] [-t timeout.retransmit] [-w interval]
[-x log-option] [-y YP-domain] [-A arch] [-C cluster-name]
[-D option] [-F conf_file] [-O op_sys_name] [-T tag] [directory
mapname [-map-options]] ...
DESCRIPTION
The amd utility is a daemon that automatically mounts file systems when‐
ever a file or directory within that file system is accessed. File sys‐
tems 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 sys‐
tem 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 -F is used, amd
will read configuration parameters from the file conf_file which defaults
to /etc/amd.conf. The last form is described below.
OPTIONS-a temporary-directory
Specify an alternative location for the real mount points. The
default is /.amd_mnt.
-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”, 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).
-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.
-o op_sys_ver
Override the compiled-in version number of the operating system.
Useful when the built in version is not desired for backward com‐
patibility 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.
-p Print PID. Outputs the process ID of amd to standard output
where it can be saved into a file.
-r 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.
-t timeout.retransmit
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.
-v Version. Displays version and configuration information on stan‐
dard error.
-w interval
Specify an interval, in seconds, between attempts to dismount
file systems that have exceeded their cached times. The default
is 2 minutes.
-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.
-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.
-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 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 docu‐
mented here: the current supported set of options is listed by
the -v option and a fuller description is available in the pro‐
gram source.
-F conf_file
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 avail‐
able 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.
-H Print help and usage string.
-O op_sys_name
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.
-S Do not lock the running executable pages of amd into memory. To
improve amd's 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 amd's per‐
formance, 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 -S option.
-T tag 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.
FILES
/.amd_mnt directory under which file systems are dynamically mounted
/etc/amd.conf default configuration file
CAVEATS
Some care may be required when creating a mount map.
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 fea‐
tures.
SEE ALSOdomainname(1), hostname(1), syslog(3), amd.conf(5), mtab(5), amq(8),
mount(8), umount(8)
“am-utils” info(1) entry.
Erez Zadok, Linux NFS and Automounter Administration, Sybex, 2001, ISBN
0-7821-2739-8.
http://www.am-utils.org/
Amd - The 4.4 BSD Automounter.
HISTORY
The amd utility first appeared in 4.4BSD.
AUTHORS
Jan-Simon Pendry ⟨jsp@doc.ic.ac.uk⟩, Department of Computing, Imperial
College, London, UK.
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.
BSD January 2, 2006 BSD