Automount Filesystem (`auto')
=============================
The "auto" (`type:=auto') filesystem type creates a new automount
point below an existing automount point. Top-level automount points
appear as system mount points. An automount mount point can also
appear as a sub-directory of an existing automount point. This allows
some additional structure to be added, for example to mimic the mount
tree of another machine.
The following options may be specified:
`cache'
specifies whether the data in this mount-map should be cached.
The default value is `none', in which case no caching is done in
order to conserve memory.
However, better performance and reliability can be obtained by
caching some or all of a mount-map.
If the cache option specifies `all', the entire map is enumerated
when the mount point is created.
If the cache option specifies `inc', caching is done incrementally
as and when data is required. Some map types do not support cache
mode `all', in which case `inc' is used whenever `all' is
requested.
Caching can be entirely disabled by using cache mode `none'.
If the cache option specifies `regexp' then the entire map will be
enumerated and each key will be treated as an egrep-style regular
expression. The order in which a cached map is searched does not
correspond to the ordering in the source map so the regular
expressions should be mutually exclusive to avoid confusion.
Each mount map type has a default cache type, usually `inc', which
can be selected by specifying `mapdefault'.
The cache mode for a mount map can only be selected on the command
line. Starting Amd with the command:
amd /homes hesiod.homes -cache:=inc
will cause `/homes' to be automounted using the "Hesiod" name
server with local incremental caching of all successfully resolved
names.
All cached data is forgotten whenever Amd receives a `SIGHUP'
signal and, if cache `all' mode was selected, the cache will be
reloaded. This can be used to inform Amd that a map has been
updated. In addition, whenever a cache lookup fails and Amd needs
to examine a map, the map's modify time is examined. If the cache
is out of date with respect to the map then it is flushed as if a
`SIGHUP' had been received.
An additional option (`sync') may be specified to force Amd to
check the map's modify time whenever a cached entry is being used.
For example, an incremental, synchronized cache would be created
by the following command:
amd /homes hesiod.homes -cache:=inc,sync
`fs'
specifies the name of the mount map to use for the new mount point.
Arguably this should have been specified with the `${rfs}' option
but we are now stuck with it due to historical accident.
`pref'
alters the name that is looked up in the mount map. If `${pref}',
the "prefix", is non-null then it is prepended to the name
requested by the kernel "before" the map is searched.
`opts'
Normally, `auto' style maps are not browsable even if you turn on
directory browsability (Note:browsable_dirs Parameter). To
enable browsing entries in `auto' maps, specify `opts:=browsable'
in the description of this map.
The server `dylan.doc.ic.ac.uk' has two user disks: `/dev/dsk/2s0'
and `/dev/dsk/5s0'. These are accessed as `/home/dylan/dk2' and
`/home/dylan/dk5' respectively. Since `/home' is already an automount
point, this naming is achieved with the following map entries:
dylan type:=auto;fs:=${map};pref:=${key}/
dylan/dk2 type:=ufs;dev:=/dev/dsk/2s0
dylan/dk5 type:=ufs;dev:=/dev/dsk/5s0