NAME
amd
—
automatically mount file
systems
SYNOPSIS
amd |
[-nprv ]
[-a mount_point]
[-C cluster]
[-c duration]
[-D option]
[-d domain]
[-k kernel-arch]
[-l logfile]
[-t interval.interval]
[-w interval]
[-x log-option]
[-y YP-domain]
[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 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
mount_point- Specify an alternative location for the real mount points. The default is /tmp_mnt.
-C
cluster- Specify an alternative cluster name. The default is the system domain name. This variable is available inside the configuration file as ${cluster}.
-c
duration- Specify a duration, in seconds, that a looked up name remains cached when not in use. The default is 5 minutes.
-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. -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.
-x
log-option- Specify run-time logging options. The options are a comma separated list chosen from: fatal, error, user, warn, info, map, stats, all.
-y
YP-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. This variable is available inside the configuration file as ${domain}.
FILES
- /a
- directory under which filesystems are dynamically mounted
SEE ALSO
hostname(1), amq(8), mount(8), umount(8)
Amd - The 4.4 BSD Automounter, available by running “info amd”
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.
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 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.