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 automatically
unmounted when they appear to be 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.
The options are as follows:
-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 normalized
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
value alters
the retransmit counter. Useful defaults are supplied if either
or both values are missing.
-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.
-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 separated
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
hostname(1), amq(8), mount(8), umount(8)
Amd - The 4.4 BSD Automounter, available by running ``info
amd''
The amd utility first appeared in 4.4BSD.
Jan-Simon Pendry <jsp@doc.ic.ac.uk>, Department of Computing, Imperial
College, London, UK.
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 symlink(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 features.
OpenBSD 3.6 April 19, 1994
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