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Amd has no built-in knowledge of machines or filesystems. External mount-maps are used to provide the required information. Specifically, Amd needs to know when and under what conditions it should mount filesystems.
The map entry corresponding to the requested name contains a list of possible locations from which to resolve the request. Each location specifies filesystem type, information required by that filesystem (for example the block special device in the case of UFS), and some information describing where to mount the filesystem (see section 3.3.4.3 fs Option). A location may also contain selectors (see section 3.3.3 Selectors).
3.1 Map Types | ||
3.2 How keys are looked up | ||
3.3 Location Format |
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A mount-map provides the run-time configuration information to Amd. Maps can be implemented in many ways. Some of the forms supported by Amd are regular files, ndbm databases, NIS maps, the Hesiod name server, and even the password file.
A mount-map name is a sequence of characters. When an automount point is created a handle on the mount-map is obtained. For each map type configured, Amd attempts to reference the map of the appropriate type. If a map is found, Amd notes the type for future use and deletes the reference, for example closing any open file descriptors. The available maps are configured when Amd is built and can be displayed by running the command `amd -v'.
When using an Amd configuration file (see section 6. Amd Configuration File) and the keyword `map_type' (see section 6.4.3 map_type Parameter), you may force the map used to any type.
By default, Amd caches data in a mode dependent on the type of map. This is the same as specifying `cache:=mapdefault' and selects a suitable default cache mode depending on the map type. The individual defaults are described below. The cache option can be specified on automount points to alter the caching behavior (see section 5.18 Automount Filesystem (`auto')).
The following map types have been implemented, though some are not available on all machines. Run the command `amd -v' to obtain a list of map types configured on your machine.
3.1.1 File maps | ||
3.1.2 ndbm maps | ||
3.1.3 NIS maps | ||
3.1.4 NIS+ maps | ||
3.1.5 Hesiod maps | ||
3.1.6 Password maps | ||
3.1.7 Union maps | ||
3.1.8 LDAP maps |
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When Amd searches a file for a map entry it does a simple scan of the file and supports both comments and continuation lines.
Continuation lines are indicated by a backslash character (`\') as the last character of a line in the file. The backslash, newline character and any leading white space on the following line are discarded. A maximum line length of 2047 characters is enforced after continuation lines are read but before comments are stripped. Each line must end with a newline character; that is newlines are terminators, not separators. The following examples illustrate this:
key valA valB; \ valC |
specifies three locations, and is identical to
key valA valB; valC |
However,
key valA valB;\ valC |
specifies only two locations, and is identical to
key valA valB;valC |
After a complete line has been read from the file, including continuations, Amd determines whether there is a comment on the line. A comment begins with a hash ("`#'") character and continues to the end of the line. There is no way to escape or change the comment lead-in character.
Note that continuation lines and comment support only apply to
file maps, or ndbm maps built with the mk-amd-map
program.
When caching is enabled, file maps have a default cache mode of
all
(see section 5.18 Automount Filesystem (`auto')).
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An ndbm map may be used as a fast access form of a file map. The program,
mk-amd-map
, converts a normal map file into an ndbm database.
This program supports the same continuation and comment conventions that
are provided for file maps. Note that ndbm format files may not
be sharable across machine architectures. The notion of speed generally
only applies to large maps; a small map, less than a single disk block,
is almost certainly better implemented as a file map.
ndbm maps have a default cache mode of `all' (see section 5.18 Automount Filesystem (`auto')).
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When using NIS (formerly YP), an Amd map is implemented directly by the underlying NIS map. Comments and continuation lines are not supported in the automounter and must be stripped when constructing the NIS server's database.
NIS maps have a default cache mode of all
(see section 5.18 Automount Filesystem (`auto')).
The following rule illustrates what could be added to your NIS `Makefile', in this case causing the `amd.home' map to be rebuilt:
$(YPTSDIR)/amd.home.time: $(ETCDIR)/amd.home -@sed -e "s/#.*$$//" -e "/^$$/d" $(ETCDIR)/amd.home | \ awk '{ \ for (i = 1; i <= NF; i++) \ if (i == NF) { \ if (substr($$i, length($$i), 1) == "\\") \ printf("%s", substr($$i, 1, length($$i) - 1)); \ else \ printf("%s\n", $$i); \ } \ else \ printf("%s ", $$i); \ }' | \ $(MAKEDBM) - $(YPDBDIR)/amd.home; \ touch $(YPTSDIR)/amd.home.time; \ echo "updated amd.home"; \ if [ ! $(NOPUSH) ]; then \ $(YPPUSH) amd.home; \ echo "pushed amd.home"; \ else \ : ; \ fi |
Here $(YPTSDIR)
contains the time stamp files, and $(YPDBDIR)
contains
the dbm format NIS files.
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NIS+ maps do not support cache mode `all' and, when caching is enabled, have a default cache mode of `inc'.
XXX: FILL IN WITH AN EXAMPLE.
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When the map name begins with the string `hesiod.' lookups are made
using the Hesiod name server. The string following the dot is
used as a name qualifier and is prepended with the key being located.
The entire string is then resolved in the automount
context, or
the amd.conf parameter `hesiod_base' (see section 6.5.9 hesiod_base Parameter). For example, if the key is `jsp' and map name is
`hesiod.homes' then Hesiod is asked to resolve
`jsp.homes.automount'.
Hesiod maps do not support cache mode `all' and, when caching is enabled, have a default cache mode of `inc' (see section 5.18 Automount Filesystem (`auto')).
The following is an example of a Hesiod map entry:
jsp.homes.automount HS TXT "rfs:=/home/charm;rhost:=charm;sublink:=jsp" njw.homes.automount HS TXT "rfs:=/home/dylan/dk2;rhost:=dylan;sublink:=njw" |
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The password map support is unlike the four previous map types. When the map name is the string `/etc/passwd' Amd can lookup a user name in the password file and re-arrange the home directory field to produce a usable map entry.
Amd assumes the home directory has the format
`/anydir/dom1/../domN/login'.
It breaks this string into a map entry where ${rfs}
has the
value `/anydir/domN', ${rhost}
has the value
`domN.....dom1', and ${sublink}
has the
value login.
Thus if the password file entry was
/home/achilles/jsp |
the map entry used by Amd would be
rfs:=/home/achilles;rhost:=achilles;sublink:=jsp |
Similarly, if the password file entry was
/home/cc/sugar/mjh |
the map entry used by Amd would be
rfs:=/home/sugar;rhost:=sugar.cc;sublink:=jsp |
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The union map support is provided specifically for use with the union filesystem, see section 5.20 Union Filesystem (`union').
It is identified by the string `union:' which is followed by a colon separated list of directories. The directories are read in order, and the names of all entries are recorded in the map cache. Later directories take precedence over earlier ones. The union filesystem type then uses the map cache to determine the union of the names in all the directories.
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LDAP (Lightweight Directory Access Protocol) maps do not support cache mode `all' and, when caching is enabled, have a default cache mode of `inc'.
For example, an Amd map `amd.home' that looks as follows:
/defaults opts:=rw,intr;type:=link zing -rhost:=shekel \ host==shekel \ host!=shekel;type:=nfs |
$ amd2ldif amd.home CUCS < amd.home dn: cn=amdmap timestamp, CUCS cn : amdmap timestamp objectClass : amdmapTimestamp amdmapTimestamp: 873071363 dn: cn=amdmap amd.home[/defaults], CUCS cn : amdmap amd.home[/defaults] objectClass : amdmap amdmapName : amd.home amdmapKey : /defaults amdmapValue : opts:=rw,intr;type:=link dn: cn=amdmap amd.home[], CUCS cn : amdmap amd.home[] objectClass : amdmap amdmapName : amd.home amdmapKey : amdmapValue : dn: cn=amdmap amd.home[zing], CUCS cn : amdmap amd.home[zing] objectClass : amdmap amdmapName : amd.home amdmapKey : zing amdmapValue : -rhost:=shekel host==shekel host!=shekel;type:=nfs |
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The key is located in the map whose type was determined when the automount point was first created. In general the key is a pathname component. In some circumstances this may be modified by variable expansion (see section 3.3.2 Variable Expansion) and prefixing. If the automount point has a prefix, specified by the pref option, then that is prepended to the search key before the map is searched.
If the map cache is a `regexp' cache then the key is treated as an egrep-style regular expression, otherwise a normal string comparison is made.
If the key cannot be found then a wildcard match is attempted. Amd repeatedly strips the basename from the key, appends `/*' and attempts a lookup. Finally, Amd attempts to locate the special key `*'.
For example, the following sequence would be checked if `home/dylan/dk2' was being located:
home/dylan/dk2 home/dylan/* home/* * |
At any point when a wildcard is found, Amd proceeds as if an exact match had been found and the value field is then used to resolve the mount request, otherwise an error code is propagated back to the kernel. (see section 5. Filesystem Types).
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The value field from the lookup provides the information required to mount a filesystem. The information is parsed according to the syntax shown below.
location-list: location-selection location-list white-space || white-space location-selection location-selection: location location-selection white-space location location: location-info -location-info - location-info: sel-or-opt location-info;sel-or-opt ; sel-or-opt: selection opt-ass selection: selector==value selector!=value opt-ass: option:=value white-space: space tab |
Note that unquoted whitespace is not allowed in a location description. White space is only allowed, and is mandatory, where shown with non-terminal white-space.
A location-selection is a list of possible volumes with which to satisfy the request. location-selections are separated by the `||' operator. The effect of this operator is to prevent use of location-selections to its right if any of the location-selections on its left were selected whether or not any of them were successfully mounted (see section 3.3.3 Selectors).
The location-selection, and singleton location-list, `type:=ufs;dev:=/dev/xd1g' would inform Amd to mount a UFS filesystem from the block special device `/dev/xd1g'.
The sel-or-opt component is either the name of an option required by a specific filesystem, or it is the name of a built-in, predefined selector such as the architecture type. The value may be quoted with double quotes `"', for example `type:="ufs";dev:="/dev/xd1g"'. These quotes are stripped when the value is parsed and there is no way to get a double quote into a value field. Double quotes are used to get white space into a value field, which is needed for the program filesystem (see section 5.14 Program Filesystem (`program')).
3.3.1 Map Defaults | ||
3.3.2 Variable Expansion | ||
3.3.3 Selectors | ||
3.3.4 Map Options |
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A location beginning with a dash `-' is used to specify default values for subsequent locations. Any previously specified defaults in the location-list are discarded. The default string can be empty in which case no defaults apply.
The location `-fs:=/mnt;opts:=ro' would set the local mount point to `/mnt' and cause mounts to be read-only by default. Defaults specified this way are appended to, and so override, any global map defaults given with `/defaults').
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To allow generic location specifications Amd does variable expansion
on each location and also on some of the option strings. Any option or
selector appearing in the form $var
is replaced by the
current value of that option or selector. For example, if the value of
${key}
was `bin', ${autodir}
was `/a' and
${fs}
was `${autodir}/local/${key}' then
after expansion ${fs}
would have the value `/a/local/bin'.
Any environment variable can be accessed in a similar way.
Two pathname operators are available when expanding a variable. If the
variable name begins with `/' then only the last component of the
pathname is substituted. For example, if ${path}
was
`/foo/bar' then ${/path}
would be expanded to `bar'.
Similarly, if the variable name ends with `/' then all but the last
component of the pathname is substituted. In the previous example,
${path/}
would be expanded to `/foo'.
Two domain name operators are also provided. If the variable name
begins with `.' then only the domain part of the name is
substituted. For example, if ${rhost}
was
`swan.doc.ic.ac.uk' then ${.rhost}
would be expanded to
`doc.ic.ac.uk'. Similarly, if the variable name ends with `.'
then only the host component is substituted. In the previous example,
${rhost.}
would be expanded to `swan'.
Variable expansion is a two phase process. Before a location is parsed,
all references to selectors, eg ${path}
, are expanded. The
location is then parsed, selections are evaluated and option assignments
recorded. If there were no selections or they all succeeded the
location is used and the values of the following options are expanded in
the order given: sublink, rfs, fs, opts,
remopts, mount and unmount.
Note that expansion of option values is done after all assignments have been completed and not in a purely left to right order as is done by the shell. This generally has the desired effect but care must be taken if one of the options references another, in which case the ordering can become significant.
There are two special cases concerning variable expansion:
${key}
would be
`vax.bin'.
${rhost}
is expanded and normalized before the
other options are expanded. The normalization process strips any local
sub-domain components. For example, if ${domain}
was
`Berkeley.EDU' and ${rhost}
was initially
`snow.Berkeley.EDU', after the normalization it would simply be
`snow'. Hostname normalization is currently done in a
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Selectors are used to control the use of a location. It is possible to share a mount map between many machines in such a way that filesystem location, architecture and operating system differences are hidden from the users. A selector of the form `arch==sun3;os==sunos4' would only apply on Sun-3s running SunOS 4.x.
Selectors can be negated by using `!=' instead of `=='. For example to select a location on all non-Vax machines the selector `arch!=vax' would be used.
Selectors are evaluated left to right. If a selector fails then that location is ignored. Thus the selectors form a conjunction and the locations form a disjunction. If all the locations are ignored or otherwise fail then Amd uses the error filesystem (see section 5.21 Error Filesystem (`error')). This is equivalent to having a location `type:=error' at the end of each mount-map entry.
The default value of many of the selectors listed here can be overridden by an Amd command line switch or in an Amd configuration file. See section 6. Amd Configuration File.
The following selectors are currently implemented.
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The machine architecture which was automatically determined at compile time. The architecture type can be displayed by running the command `amd -v'. See section 2. Supported Platforms.
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The default directory under which to mount filesystems. This may be
changed by the -a
command line option. See section 3.3.4.3 fs Option.
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The machine's byte ordering. This is either `little', indicating little-endian, or `big', indicating big-endian. One possible use is to share `rwho' databases (see section 11.5 `rwho' servers). Another is to share ndbm databases, however this use can be considered a courageous juggling act.
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This is provided as a hook for the name of the local cluster. This can
be used to decide which servers to use for copies of replicated
filesystems. ${cluster}
defaults to the value of
${domain}
unless a different value is set with the -C
command line option.
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The local domain name as specified by the -d
command line option.
See section 3.3.3.7 host Selector Variable.
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This is a special variable, whose sole purpose is to produce a literal dollar sign in the value of another variable. For example, if you have a remote file system whose name is `/disk$s', you can mount it by setting the remote file system variable as follows:
rfs:=/disk${dollar}s |
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The local hostname as determined by gethostname(2). If no domain
name was specified on the command line and the hostname contains a
period `.' then the string before the period is used as the host
name, and the string after the period is assigned to ${domain}
.
For example, if the hostname is `styx.doc.ic.ac.uk' then
host
would be `styx' and domain
would be
`doc.ic.ac.uk'. hostd
would be
`styx.doc.ic.ac.uk'.
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This resolves to the ${host}
and ${domain}
concatenated with a `.' inserted between them if required. If
${domain}
is an empty string then ${host}
and
${hostd}
will be identical.
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This is provided as a hook for the kernel architecture. This is used on
SunOS 4 and SunOS 5, for example, to distinguish between different
`/usr/kvm' volumes. ${karch}
defaults to the "machine"
value gotten from uname(2). If the uname(2) system call is not
available, the value of ${karch}
defaults to that of
${arch}
. Finally, a different value can be set with the -k
command line option.
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The operating system. Like the machine architecture, this is automatically determined at compile time. The operating system name can be displayed by running the command `amd -v'. See section 2. Supported Platforms.
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The operating system version. Like the machine architecture, this is automatically determined at compile time. The operating system name can be displayed by running the command `amd -v'. See section 2. Supported Platforms.
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The full name of the operating system, including its version. This value is automatically determined at compile time. The full operating system name and version can be displayed by running the command `amd -v'. See section 2. Supported Platforms.
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The name of the vendor of the operating system. This value is automatically determined at compile time. The name of the vendor can be displayed by running the command `amd -v'. See section 2. Supported Platforms.
<HR> The following selectors are also provided. Unlike the other selectors, they vary for each lookup. Note that when the name from the kernel is expanded prior to a map lookup, these selectors are all defined as empty strings.
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The name being resolved. For example, if `/home' is an automount
point, then accessing `/home/foo' would set ${key}
to the
string `foo'. The key is prefixed by the pref option set in
the parent mount point. The default prefix is an empty string. If the
prefix was `blah/' then ${key}
would be set to
`blah/foo'.
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The name of the mount map being used.
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This selector is identical to the `in_network' selector function, see 3.3.3.26 in_network Selector Function. It will match either the name or number of any network interface on which this host is connected to. The names and numbers of all attached interfaces are available from the output of `amd -v'.
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This selector is identical to the `in_network' selector function, see 3.3.3.26 in_network Selector Function. It will match either the name or number of any network interface on which this host is connected to. The names and numbers of all attached interfaces are available from the output of `amd -v'.
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The full pathname of the name being resolved. For example `/home/foo' in the example above.
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This selector is identical to the `in_network' selector function, see 3.3.3.26 in_network Selector Function. It will match either the name or number of any network interface on which this host is connected to. The names and numbers of all attached interfaces are available from the output of `amd -v'.
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This selector provides the numeric effective user ID (UID) of the user which last accessed an automounted path name. This simple example shows how floppy mounting can be assigned only to machine owners:
floppy -type:=pcfs \ uid==2301;host==shekel;dev:=/dev/floppy \ uid==6712;host==titan;dev=/dev/fd0 \ uid==0;dev:=/dev/fd0c \ type:=error |
The example allows two machine owners to mount floppies on their designated workstations, allows the root user to mount on any host, and otherwise forces an error.
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This selector provides the numeric effective group ID (GID) of the user which last accessed an automounted path name.
<HR> The following boolean functions are selectors which take an argument ARG. They return a value of true or false, and thus do not need to be compared with a value. Each of these may be negated by prepending `!' to their name.
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If the file listed by ARG exists (via lstat(2)), this function evaluates to true. Otherwise it evaluates to false.
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Always evaluates to false. ARG is ignored.
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If the current host as determined by the value of ${host}
(e.g., short host name) is a member of the netgroup ARG, this
selector evaluates to true. Otherwise it evaluates to false.
For example, suppose you have a netgroup `ppp-hosts', and for reasons of performance, these have a local `/home' partition, while all other clients on the faster network can access a shared home directory. A common map to use for both might look like the following:
home/* netgrp(ppp-hosts);type:=link;fs:=/local/${key} \ !netgrp(ppp-hosts);type:=nfs;rhost:=serv1;rfs:=/remote/${key} |
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If the current host as determined by the value of ${hostd}
is a
member of the netgroup ARG, this selector evaluates to true.
Otherwise it evaluates to false.
The `netgrpd' function uses fully-qualified host names
(${hostd}
) to match netgroup names, while the `netgrp'
function (see section 3.3.3.24 netgrp Selector Function) uses short host names
(${host}
).
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This selector matches against any network name or number with an optional netmask. First, if the current host has any network interface that is locally attached to the network specified in ARG (either via name or number), this selector evaluates to true.
Second, `in_network' supports a network/netmask syntax such as `128.59.16.0/255.255.255.0', `128.59.16.0/24', `128.59.16.0/0xffffff00', or `128.59.16.0/'. Using the last form, Amd will match the specified network number against the default netmasks of each of the locally attached interfaces.
If the selector does not match, it evaluates to false.
For example, suppose you have two servers that have an exportable `/opt' that smaller clients can NFS mount. The two servers are say, `serv1' on network `foo-net.site.com' and `serv2' on network `123.4.5.0'. You can write a map to be used by all clients that will attempt to mount the closest one as follows:
opt in_network(foo-net.site.com);rhost:=serv1;rfs:=/opt \ in_network(123.4.5.0);rhost:=serv2;rfs:=/opt \ rhost:=fallback-server |
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Always evaluates to true. ARG is ignored.
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Options are parsed concurrently with selectors. The difference is that when an option is seen the string following the `:=' is recorded for later use. As a minimum the type option must be specified. Each filesystem type has other options which must also be specified. See section 5. Filesystem Types, for details on the filesystem specific options.
Superfluous option specifications are ignored and are not reported as errors.
The following options apply to more than one filesystem type.
3.3.4.1 addopts Option | ||
3.3.4.2 delay Option | ||
3.3.4.3 fs Option | ||
3.3.4.4 opts Option | ||
3.3.4.5 remopts Option | ||
3.3.4.6 sublink Option | ||
3.3.4.7 type Option |
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This option adds additional options to default options normally specified in the `/defaults' entry or the defaults of the key entry being processed (see section 3.3.4.4 opts Option). Normally when you specify `opts' in both the `/defaults' and the map entry, the latter overrides the former completely. But with `addopts' it will append the options and override any conflicting ones.
`addopts' also overrides the value of the `remopts' option (see section 3.3.4.5 remopts Option), which unless specified defaults to the value of `opts'.
Options which start with `no' will override those with the same name that do not start with `no' and vice verse. Special handling is given to inverted options such as `soft' and `hard', `bg' and `fg', `ro' and `rw', etc.
For example, if the default options specified were
opts:=rw,nosuid,intr,rsize=1024,wsize=1024,quota,posix |
and the ones specified in a map entry were
addopts:=grpid,suid,ro,rsize=2048,quota,nointr |
then the actual options used would be
wsize=1024,posix,grpid,suid,ro,rsize=2048,quota,nointr |
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The delay, in seconds, before an attempt will be made to mount from the current location. Auxiliary data, such as network address, file handles and so on are computed regardless of this value.
A delay can be used to implement the notion of primary and secondary file servers. The secondary servers would have a delay of a few seconds, thus giving the primary servers a chance to respond first.
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The local mount point. The semantics of this option vary between filesystems.
For NFS and UFS filesystems the value of ${fs}
is used as the
local mount point. For other filesystem types it has other meanings
which are described in the section describing the respective filesystem
type. It is important that this string uniquely identifies the
filesystem being mounted. To satisfy this requirement, it should
contain the name of the host on which the filesystem is resident and the
pathname of the filesystem on the local or remote host.
The reason for requiring the hostname is clear if replicated filesystems are considered. If a fileserver goes down and a replacement filesystem is mounted then the local mount point must be different from that of the filesystem which is hung. Some encoding of the filesystem name is required if more than one filesystem is to be mounted from any given host.
If the hostname is first in the path then all mounts from a particular host will be gathered below a single directory. If that server goes down then the hung mount points are less likely to be accidentally referenced, for example when getcwd(3) traverses the namespace to find the pathname of the current directory.
The `fs' option defaults to
${autodir}/${rhost}${rfs}
. In addition,
`rhost' defaults to the local host name (${host}
) and
`rfs' defaults to the value of ${path}
, which is the full
path of the requested file; `/home/foo' in the example above
(see section 3.3.3 Selectors). ${autodir}
defaults to `/a' but may
be changed with the -a
command line option. Sun's automounter
defaults to `/tmp_mnt'. Note that there is no `/' between
the ${rhost}
and ${rfs}
since ${rfs}
begins
with a `/'.
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The options to pass to the mount system call. A leading `-' is silently ignored. The mount options supported generally correspond to those used by mount(8) and are listed below. Some additional pseudo-options are interpreted by Amd and are also listed.
Unless specifically overridden, each of the system default mount options
applies. Any options not recognized are ignored. If no options list is
supplied the string `rw,defaults' is used and all the system
default mount options apply. Options which are not applicable for a
particular operating system are silently ignored. For example, only 4.4BSD
is known to implement the compress
and spongy
options.
acdirmax=n
acdirmin=n
acregmax=n
acregmin=n
actimeo=n
auto
ignore
cache
compress
defperm
dev
dumbtimr
extatt
fsid
gens
grpid
int
intr
lock
multi
maxgroups
nfsv3
noac
noauto
nocache
noconn
nocto
nodefperm
nodev
nodevs
noexec
noint
nolock
nomnttab
norrip
nosub
nosuid
noversion
optionstr
overlay
pgthresh=n
port=n
posix
proplist
proto=s
"tcp"
or "udp"
).
quota
rdonly
ro
resvport
retrans=n
retry
rrip
rsize=n
rw
soft
spongy
suid
symttl
sync
tcp
timeo=n
vers=n
wsize=n
The following options are implemented by Amd, rather than being passed to the kernel.
nounmount
ping=n
retry=n
utimeout=n
-w
command line option.
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This option has the same use as ${opts}
but applies only when
the remote host is on a non-local network. For example, when using NFS
across a gateway it is often necessary to use smaller values for the
data read and write sizes. This can simply be done by specifying the
small values in remopts. When a non-local host is accessed, the
smaller sizes will automatically be used.
Amd determines whether a host is local by examining the network interface configuration at startup. Any interface changes made after Amd has been started will not be noticed. The likely effect will be that a host may incorrectly be declared non-local.
Unless otherwise set, the value of ${remopts}
is the same as
the value of ${opts}
.
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The subdirectory within the mounted filesystem to which the reference should point. This can be used to prevent duplicate mounts in cases where multiple directories in the same mounted filesystem are used.
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The filesystem type to be used. See section 5. Filesystem Types, for a full description of each type.
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