NAME¶
amd - automatically mount file systems
SYNOPSIS¶
amd -H
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 ] [
directory mapname [
-map-options ] ] ...
DESCRIPTION¶
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 have become quiescent.
Amd 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 filesystem information and some mount options for the given
filesystem.
In the first form depicted above,
amd will print a short help string. In
the second form, if no options are specified, or 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
/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 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 refereed to by ${rhost} is normalized
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 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.
- -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 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.
Amd 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 standard error.
- -w interval
- Specify an interval, in seconds, between attempts to dismount
filesystems that have exceeded their cached times. The default is 2
minutes.
- -x options
- Specify run-time logging options. The options are a comma separated list
chosen from: fatal, error, user, warn, info, map, stats, defaults, and
all. 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 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
strings 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.
- -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 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.
- -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 improves amd's 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 -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¶
- /a
- directory under which filesystems 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 filesystem can be incredibly inefficient. In most
implementations of NFS, their interpolations are not cached by the kernel and
each time a symlink 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.
SEE ALSO¶
amq(8),
domainname(1),
hostname(1),
syslog(3).
amd.conf(5),
mtab(5),
automount(8),
mount(8),
umount(8),
``am-utils''
info(1) entry.
Linux NFS and Automounter Administration by Erez Zadok, ISBN
0-7821-2739-8, (Sybex, 2001).
http://www.am-utils.org
Amd - The 4.4 BSD Automounter
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.