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SLAPD-META(5) File Formats Manual SLAPD-META(5)
slapd-meta - metadirectory backend to slapd
ETCDIR/slapd.conf
The meta backend to slapd(8) performs basic LDAP proxying with
respect to a set of remote LDAP servers, called "targets". The
information contained in these servers can be presented as
belonging to a single Directory Information Tree (DIT).
A basic knowledge of the functionality of the slapd-ldap(5)
backend is recommended. This backend has been designed as an
enhancement of the ldap backend. The two backends share many
features (actually they also share portions of code). While the
ldap backend is intended to proxy operations directed to a single
server, the meta backend is mainly intended for proxying of
multiple servers and possibly naming context masquerading. These
features, although useful in many scenarios, may result in
excessive overhead for some applications, so its use should be
carefully considered. In the examples section, some typical
scenarios will be discussed.
The proxy instance of slapd(8) must contain schema information for
the attributes and objectClasses used in filters, request DN and
request-related data in general. It should also contain schema
information for the data returned by the proxied server. It is
the responsibility of the proxy administrator to keep the schema
of the proxy lined up with that of the proxied server.
Note: When looping back to the same instance of slapd(8), each
connection requires a new thread; as a consequence, the slapd(8)
threads parameter may need some tuning. In those cases, unless the
multiple target feature is required, one may consider using
slapd-relay(5) instead, which performs the relayed operation
internally and thus reuses the same connection.
There are examples in various places in this document, as well as
in the slapd/back-meta/data/ directory in the OpenLDAP source
tree.
These slapd.conf options apply to the META backend database. That
is, they must follow a "database meta" line and come before any
subsequent "backend" or "database" lines. Other database options
are described in the slapd.conf(5) manual page.
Note: In early versions of back-ldap and back-meta it was
recommended to always set
lastmod off
for ldap and meta databases. This was required because
operational attributes related to entry creation and modification
should not be proxied, as they could be mistakenly written to the
target server(s), generating an error. The current implementation
automatically sets lastmod to off, so its use is redundant and
should be omitted.
Target configuration starts with the "uri" directive. All the
configuration directives that are not specific to targets should
be defined first for clarity, including those that are common to
all backends. They are:
conn-pool-max <int>
This directive defines the maximum size of the privileged
connections pool.
conn-ttl <time>
This directive causes a cached connection to be dropped an
recreated after a given ttl, regardless of being idle or
not.
default-target none
This directive forces the backend to reject all those
operations that must resolve to a single target in case
none or multiple targets are selected. They include: add,
delete, modify, modrdn; compare is not included, as well as
bind since, as they don't alter entries, in case of
multiple matches an attempt is made to perform the
operation on any candidate target, with the constraint that
at most one must succeed. This directive can also be used
when processing targets to mark a specific target as
default.
dncache-ttl {DISABLED|forever|<ttl>}
This directive sets the time-to-live of the DN cache. This
caches the target that holds a given DN to speed up target
selection in case multiple targets would result from an
uncached search; forever means cache never expires;
disabled means no DN caching; otherwise a valid ( > 0 ) ttl
is required, in the format illustrated for the idle-timeout
directive.
onerr {CONTINUE|report|stop}
This directive allows one to select the behavior in case an
error is returned by one target during a search. The
default, continue, consists in continuing the operation,
trying to return as much data as possible. If the value is
set to stop, the search is terminated as soon as an error
is returned by one target, and the error is immediately
propagated to the client. If the value is set to report,
the search is continued to the end but, in case at least
one target returned an error code, the first non-success
error code is returned.
norefs <NO|yes>
If yes, do not return search reference responses. By
default, they are returned unless request is LDAPv2. If
set before any target specification, it affects all
targets, unless overridden by any per-target directive.
noundeffilter <NO|yes>
If yes, return success instead of searching if a filter is
undefined or contains undefined portions. By default, the
search is propagated after replacing undefined portions
with (!(objectClass=*)), which corresponds to the empty
result set. If set before any target specification, it
affects all targets, unless overridden by any per-target
directive.
protocol-version {0,2,3}
This directive indicates what protocol version must be used
to contact the remote server. If set to 0 (the default),
the proxy uses the same protocol version used by the
client, otherwise the requested protocol is used. The
proxy returns unwillingToPerform if an operation that is
incompatible with the requested protocol is attempted. If
set before any target specification, it affects all
targets, unless overridden by any per-target directive.
pseudoroot-bind-defer {YES|no}
This directive, when set to yes, causes the authentication
to the remote servers with the pseudo-root identity (the
identity defined in each idassert-bind directive) to be
deferred until actually needed by subsequent operations.
Otherwise, all binds as the rootdn are propagated to the
targets.
quarantine <interval>,<num>[;<interval>,<num>[...]]
Turns on quarantine of URIs that returned LDAP_UNAVAILABLE,
so that an attempt to reconnect only occurs at given
intervals instead of any time a client requests an
operation. The pattern is: retry only after at least
interval seconds elapsed since last attempt, for exactly
num times; then use the next pattern. If num for the last
pattern is "+", it retries forever; otherwise, no more
retries occur. This directive must appear before any
target specification; it affects all targets with the same
pattern.
rebind-as-user {NO|yes}
If this option is given, the client's bind credentials are
remembered for rebinds, when trying to re-establish a
broken connection, or when chasing a referral, if
chase-referrals is set to yes.
session-tracking-request {NO|yes}
Adds session tracking control for all requests. The
client's IP and hostname, and the identity associated to
each request, if known, are sent to the remote server for
informational purposes. This directive is incompatible
with setting protocol-version to 2. If set before any
target specification, it affects all targets, unless
overridden by any per-target directive.
single-conn {NO|yes}
Discards current cached connection when the client rebinds.
use-temporary-conn {NO|yes}
when set to yes, create a temporary connection whenever
competing with other threads for a shared one; otherwise,
wait until the shared connection is available.
Target specification starts with a "uri" directive:
uri <protocol>://[<host>]/<naming context> [...]
The <protocol> part can be anything ldap_initialize(3)
accepts ({ldap|ldaps|ldapi} and variants); the <host> may
be omitted, defaulting to whatever is set in ldap.conf(5).
The <naming context> part is mandatory for the first URI,
but it must be omitted for subsequent ones, if any. The
naming context part must be within the naming context
defined for the backend, e.g.:
suffix "dc=foo,dc=com"
uri "ldap://x.foo.com/dc=x,dc=foo,dc=com"
The <naming context> part doesn't need to be unique across
the targets; it may also match one of the values of the
"suffix" directive. Multiple URIs may be defined in a
single URI statement. The additional URIs must be separate
arguments and must not have any <naming context> part.
This causes the underlying library to contact the first
server of the list that responds. For example, if
l1.foo.com and l2.foo.com are shadows of the same server,
the directive
suffix "dc=foo,dc=com"
uri "ldap://l1.foo.com/dc=foo,dc=com" "ldap://l2.foo.com/"
causes l2.foo.com to be contacted whenever l1.foo.com does
not respond. In that case, the URI list is internally
rearranged, by moving unavailable URIs to the end, so that
further connection attempts occur with respect to the last
URI that succeeded.
acl-authcDN <administrative DN for access control purposes>
DN which is used to query the target server for acl
checking, as in the LDAP backend; it is supposed to have
read access on the target server to attributes used on the
proxy for acl checking. There is no risk of giving away
such values; they are only used to check permissions. The
acl-authcDN identity is by no means implicitly used by the
proxy when the client connects anonymously.
acl-passwd <password>
Password used with the acl-authcDN above.
bind-timeout <microseconds>
This directive defines the timeout, in microseconds, used
when polling for response after an asynchronous bind
connection. The initial call to ldap_result(3) is
performed with a trade-off timeout of 100000 us; if that
results in a timeout exceeded, subsequent calls use the
value provided with bind-timeout. The default value is
used also for subsequent calls if bind-timeout is not
specified. If set before any target specification, it
affects all targets, unless overridden by any per-target
directive.
chase-referrals {YES|no}
enable/disable automatic referral chasing, which is
delegated to the underlying libldap, with rebinding
eventually performed if the rebind-as-user directive is
used. The default is to chase referrals. If set before
any target specification, it affects all targets, unless
overridden by any per-target directive.
client-pr {accept-unsolicited|DISABLE|<size>}
This feature allows one to use RFC 2696 Paged Results
control when performing search operations with a specific
target, irrespective of the client's request. When set to
a numeric value, Paged Results control is always used with
size as the page size. When set to accept-unsolicited,
unsolicited Paged Results control responses are accepted
and honored for compatibility with broken remote DSAs. The
client is not exposed to paged results handling between
slapd-meta(5) and the remote servers. By default
(disabled), Paged Results control is not used and responses
are not accepted. If set before any target specification,
it affects all targets, unless overridden by any per-target
directive.
default-target [<target>]
The "default-target" directive can also be used during
target specification. With no arguments it marks the
current target as the default. The optional number marks
target <target> as the default one, starting from 1.
Target <target> must be defined.
filter <pattern>
This directive allows specifying a regex(5) pattern to
indicate what search filter terms are actually served by a
target.
In a search request, if the search filter matches the
pattern the target is considered while fulfilling the
request; otherwise the target is ignored. There may be
multiple occurrences of the filter directive for each
target.
idassert-authzFrom <authz-regexp>
if defined, selects what local identities are authorized to
exploit the identity assertion feature. The string
<authz-regexp> follows the rules defined for the authzFrom
attribute. See slapd.conf(5), section related to
authz-policy, for details on the syntax of this field.
idassert-bind bindmethod=none|simple|sasl [binddn=<simple DN>]
[credentials=<simple password>] [saslmech=<SASL mech>]
[secprops=<properties>] [realm=<realm>]
[authcId=<authentication ID>] [authzId=<authorization ID>]
[authz={native|proxyauthz}] [mode=<mode>] [flags=<flags>]
[starttls=no|yes|critical] [tls_cert=<file>]
[tls_key=<file>] [tls_cacert=<file>] [tls_cacertdir=<path>]
[tls_reqcert=never|allow|try|demand]
[tls_reqsan=never|allow|try|demand]
[tls_cipher_suite=<ciphers>] [tls_ecname=<ciphers>]
[tls_protocol_min=<major>[.<minor>]]
[tls_crlcheck=none|peer|all]
Allows one to define the parameters of the authentication
method that is internally used by the proxy to authorize
connections that are authenticated by other databases. The
identity defined by this directive, according to the
properties associated to the authentication method, is
supposed to have auth access on the target server to
attributes used on the proxy for authentication and
authorization, and to be allowed to authorize the users.
This requires to have proxyAuthz privileges on a wide set
of DNs, e.g. authzTo=dn.subtree:"", and the remote server
to have authz-policy set to to or both. See slapd.conf(5)
for details on these statements and for remarks and
drawbacks about their usage. The supported bindmethods are
none|simple|sasl
where none is the default, i.e. no identity assertion is
performed.
The authz parameter is used to instruct the SASL bind to
exploit native SASL authorization, if available; since
connections are cached, this should only be used when
authorizing with a fixed identity (e.g. by means of the
authzDN or authzID parameters). Otherwise, the default
proxyauthz is used, i.e. the proxyAuthz control (Proxied
Authorization, RFC 4370) is added to all operations.
The supported modes are:
<mode> := {legacy|anonymous|none|self}
If <mode> is not present, and authzId is given, the proxy
always authorizes that identity. <authorization ID> can be
u:<user>
[dn:]<DN>
The former is supposed to be expanded by the remote server
according to the authz rules; see slapd.conf(5) for
details. In the latter case, whether or not the dn: prefix
is present, the string must pass DN validation and
normalization.
The default mode is legacy, which implies that the proxy
will either perform a simple bind as the authcDN or a SASL
bind as the authcID and assert the client's identity when
it is not anonymous. Direct binds are always proxied. The
other modes imply that the proxy will always either perform
a simple bind as the authcDN or a SASL bind as the authcID,
unless restricted by idassert-authzFrom rules (see below),
in which case the operation will fail; eventually, it will
assert some other identity according to <mode>. Other
identity assertion modes are anonymous and self, which
respectively mean that the empty or the client's identity
will be asserted; none, which means that no proxyAuthz
control will be used, so the authcDN or the authcID
identity will be asserted. For all modes that require the
use of the proxyAuthz control, on the remote server the
proxy identity must have appropriate authzTo permissions,
or the asserted identities must have appropriate authzFrom
permissions. Note, however, that the ID assertion feature
is mostly useful when the asserted identities do not exist
on the remote server. When bindmethod is SASL, the authcDN
must be specified in addition to the authcID, although it
is not used within the authentication process.
Flags can be
override,[non-]prescriptive,proxy-authz-[non-]critical
When the override flag is used, identity assertion takes
place even when the database is authorizing for the
identity of the client, i.e. after binding with the
provided identity, and thus authenticating it, the proxy
performs the identity assertion using the configured
identity and authentication method.
When the prescriptive flag is used (the default),
operations fail with inappropriateAuthentication for those
identities whose assertion is not allowed by the
idassert-authzFrom patterns. If the non-prescriptive flag
is used, operations are performed anonymously for those
identities whose assertion is not allowed by the
idassert-authzFrom patterns.
When the proxy-authz-non-critical flag is used (the
default), the proxyAuthz control is not marked as critical,
in violation of RFC 4370. Use of proxy-authz-critical is
recommended.
The TLS settings default to the same as the main slapd TLS
settings, except for tls_reqcert which defaults to
"demand", and tls_reqsan which defaults to "allow"..
The identity associated to this directive is also used for
privileged operations whenever idassert-bind is defined and
acl-bind is not. See acl-bind for details.
idle-timeout <time>
This directive causes a cached connection to be dropped an
recreated after it has been idle for the specified time.
The value can be specified as
[<d>d][<h>h][<m>m][<s>[s]]
where <d>, <h>, <m> and <s> are respectively treated as
days, hours, minutes and seconds. If set before any target
specification, it affects all targets, unless overridden by
any per-target directive.
keepalive <idle>:<probes>:<interval>
The keepalive parameter sets the values of idle, probes,
and interval used to check whether a socket is alive; idle
is the number of seconds a connection needs to remain idle
before TCP starts sending keepalive probes; probes is the
maximum number of keepalive probes TCP should send before
dropping the connection; interval is interval in seconds
between individual keepalive probes. Only some systems
support the customization of these values; the keepalive
parameter is ignored otherwise, and system-wide settings
are used.
tcp-user-timeout <milliseconds>
If non-zero, corresponds to the TCP_USER_TIMEOUT set on the
target connections, overriding the operating system
setting. Only some systems support the customization of
this parameter, it is ignored otherwise and system-wide
settings are used.
map {attribute|objectclass} [<local name>|*] {<foreign name>|*}
This maps object classes and attributes as in the LDAP
backend. See slapd-ldap(5).
network-timeout <time>
Sets the network timeout value after which
poll(2)/select(2) following a connect(2) returns in case of
no activity. The value is in seconds, and it can be
specified as for idle-timeout. If set before any target
specification, it affects all targets, unless overridden by
any per-target directive.
nretries {forever|never|<nretries>}
This directive defines how many times a bind should be
retried in case of temporary failure in contacting a
target. If defined before any target specification, it
applies to all targets (by default, 3 times); the global
value can be overridden by redefinitions inside each target
specification.
rewrite* ...
The rewrite options are described in the "REWRITING"
section.
subtree-{exclude|include} <rule>
This directive allows one to indicate what subtrees are
actually served by a target. The syntax of the supported
rules is
<rule>: [dn[.<style>]:]<pattern>
<style>: subtree|children|regex
When <style> is either subtree or children the <pattern> is
a DN that must be within the naming context served by the
target. When <style> is regex the <pattern> is a regex(5)
pattern. If the dn.<style>: prefix is omitted, dn.subtree:
is implicitly assumed for backward compatibility.
In the subtree-exclude form if the request DN matches at
least one rule, the target is not considered while
fulfilling the request; otherwise, the target is considered
based on the value of the request DN. When the request is
a search, also the scope is considered.
In the subtree-include form if the request DN matches at
least one rule, the target is considered while fulfilling
the request; otherwise the target is ignored.
| match | exclude |
+---------+---------+-------------------+
| T | T | not candidate |
| F | T | continue checking |
+---------+---------+-------------------+
| T | F | candidate |
| F | F | not candidate |
+---------+---------+-------------------+
There may be multiple occurrences of the subtree-exclude or
subtree-include directive for each of the targets, but they
are mutually exclusive.
suffixmassage <virtual naming context> <real naming context>
All the directives starting with "rewrite" refer to the
rewrite engine that has been added to slapd. The
"suffixmassage" directive was introduced in the LDAP
backend to allow suffix massaging while proxying. It has
been obsoleted by the rewriting tools. However, both for
backward compatibility and for ease of configuration when
simple suffix massage is required, it has been preserved.
It wraps the basic rewriting instructions that perform
suffix massaging. See the "REWRITING" section for a
detailed list of the rewrite rules it implies.
t-f-support {NO|yes|discover}
enable if the remote server supports absolute filters (see
RFC 4526 for details). If set to discover, support is
detected by reading the remote server's root DSE. If set
before any target specification, it affects all targets,
unless overridden by any per-target directive.
timeout [<op>=]<val> [...]
This directive allows one to set per-operation timeouts.
Operations can be
<op> ::= bind, add, delete, modrdn, modify, compare, search
The overall duration of the search operation is controlled
either by the timelimit parameter or by server-side
enforced time limits (see timelimit and limits in
slapd.conf(5) for details). This timeout parameter
controls how long the target can be irresponsive before the
operation is aborted. Timeout is meaningless for the
remaining operations, unbind and abandon, which do not
imply any response, while it is not yet implemented in
currently supported extended operations. If no operation
is specified, the timeout val affects all supported
operations. If specified before any target definition, it
affects all targets unless overridden by per-target
directives.
Note: if the timeout is exceeded, the operation is
cancelled (according to the cancel directive); the protocol
does not provide any means to rollback operations, so the
client will not be notified about the result of the
operation, which may eventually succeeded or not. In case
the timeout is exceeded during a bind operation, the
connection is destroyed, according to RFC4511.
tls {none|[try-]start|[try-]propagate|ldaps}
[starttls=no] [tls_cert=<file>] [tls_key=<file>]
[tls_cacert=<file>] [tls_cacertdir=<path>]
[tls_reqcert=never|allow|try|demand]
[tls_reqsan=never|allow|try|demand]
[tls_cipher_suite=<ciphers>] [tls_ecname=<names>]
[tls_crlcheck=none|peer|all]
Specify TLS settings regular connections.
If the first parameter is not "none" then this configures
the TLS settings to be used for regular connections. The
StartTLS extended operation will be used when establishing
the connection unless the URI directive protocol scheme is
ldaps://. In that case this keyword may only be set to
"ldaps" and the StartTLS operation will not be used.
With propagate, the proxy issues the StartTLS operation
only if the original connection has a TLS layer set up.
The try- prefix instructs the proxy to continue operations
if the StartTLS operation failed; its use is not
recommended.
The TLS settings default to the same as the main slapd TLS
settings, except for tls_reqcert which defaults to
"demand", tls_reqsan which defaults to "allow", and
starttls which is overshadowed by the first keyword and
thus ignored.
If set before any target specification, it affects all
targets, unless overridden by any per-target directive.
A powerful (and in some sense dangerous) rewrite engine has been
added to both the LDAP and Meta backends. While the former can
gain limited beneficial effects from rewriting stuff, the latter
can become an amazingly powerful tool.
Consider a couple of scenarios first.
1) Two directory servers share two levels of naming context; say
"dc=a,dc=foo,dc=com" and "dc=b,dc=foo,dc=com". Then, an
unambiguous Meta database can be configured as:
database meta
suffix "dc=foo,dc=com"
uri "ldap://a.foo.com/dc=a,dc=foo,dc=com"
uri "ldap://b.foo.com/dc=b,dc=foo,dc=com"
Operations directed to a specific target can be easily resolved
because there are no ambiguities. The only operation that may
resolve to multiple targets is a search with base "dc=foo,dc=com"
and scope at least "one", which results in spawning two searches
to the targets.
2a) Two directory servers don't share any portion of naming
context, but they'd present as a single DIT [Caveat: uniqueness of
(massaged) entries among the two servers is assumed; integrity
checks risk to incur in excessive overhead and have not been
implemented]. Say we have "dc=bar,dc=org" and "o=Foo,c=US", and
we'd like them to appear as branches of "dc=foo,dc=com", say
"dc=a,dc=foo,dc=com" and "dc=b,dc=foo,dc=com". Then we need to
configure our Meta backend as:
database meta
suffix "dc=foo,dc=com"
uri "ldap://a.bar.com/dc=a,dc=foo,dc=com"
suffixmassage "dc=a,dc=foo,dc=com" "dc=bar,dc=org"
uri "ldap://b.foo.com/dc=b,dc=foo,dc=com"
suffixmassage "dc=b,dc=foo,dc=com" "o=Foo,c=US"
Again, operations can be resolved without ambiguity, although some
rewriting is required. Notice that the virtual naming context of
each target is a branch of the database's naming context; it is
rewritten back and forth when operations are performed towards the
target servers. What "back and forth" means will be clarified
later.
When a search with base "dc=foo,dc=com" is attempted, if the scope
is "base" it fails with "no such object"; in fact, the common root
of the two targets (prior to massaging) does not exist. If the
scope is "one", both targets are contacted with the base replaced
by each target's base; the scope is derated to "base". In
general, a scope "one" search is honored, and the scope is
derated, only when the incoming base is at most one level lower of
a target's naming context (prior to massaging).
Finally, if the scope is "sub" the incoming base is replaced by
each target's unmassaged naming context, and the scope is not
altered.
2b) Consider the above reported scenario with the two servers
sharing the same naming context:
database meta
suffix "dc=foo,dc=com"
uri "ldap://a.bar.com/dc=foo,dc=com"
suffixmassage "dc=foo,dc=com" "dc=bar,dc=org"
uri "ldap://b.foo.com/dc=foo,dc=com"
suffixmassage "dc=foo,dc=com" "o=Foo,c=US"
All the previous considerations hold, except that now there is no
way to unambiguously resolve a DN. In this case, all the
operations that require an unambiguous target selection will fail
unless the DN is already cached or a default target has been set.
Practical configurations may result as a combination of all the
above scenarios.
Note on ACLs: at present you may add whatever ACL rule you desire
to the Meta (and LDAP) backends. However, the meaning of an ACL
on a proxy may require some considerations. Two philosophies may
be considered:
a) the remote server dictates the permissions; the proxy simply
passes back what it gets from the remote server.
b) the remote server unveils "everything"; the proxy is
responsible for protecting data from unauthorized access.
Of course the latter sounds unreasonable, but it is not. It is
possible to imagine scenarios in which a remote host discloses
data that can be considered "public" inside an intranet, and a
proxy that connects it to the internet may impose additional
constraints. To this purpose, the proxy should be able to comply
with all the ACL matching criteria that the server supports. This
has been achieved with regard to all the criteria supported by
slapd except a special subtle case (please file an ITS if you can
find other exceptions: <http://www.openldap.org/its/>). The rule
access to dn="<dn>" attrs=<attr>
by dnattr=<dnattr> read
by * none
cannot be matched iff the attribute that is being requested,
<attr>, is NOT <dnattr>, and the attribute that determines
membership, <dnattr>, has not been requested (e.g. in a search)
In fact this ACL is resolved by slapd using the portion of entry
it retrieved from the remote server without requiring any further
intervention of the backend, so, if the <dnattr> attribute has not
been fetched, the match cannot be assessed because the attribute
is not present, not because no value matches the requirement!
Note on ACLs and attribute mapping: ACLs are applied to the mapped
attributes; for instance, if the attribute locally known as "foo"
is mapped to "bar" on a remote server, then local ACLs apply to
attribute "foo" and are totally unaware of its remote name. The
remote server will check permissions for "bar", and the local
server will possibly enforce additional restrictions to "foo".
A string is rewritten according to a set of rules, called a
`rewrite context'. The rules are based on POSIX (''extended'')
regular expressions (regex) with substring matching; basic
variable substitution and map resolution of substrings is allowed
by specific mechanisms detailed in the following. The behavior of
pattern matching/substitution can be altered by a set of flags.
The underlying concept is to build a lightweight rewrite module
for the slapd server (initially dedicated to the LDAP backend).
An incoming string is matched against a set of rules. Rules are
made of a regex match pattern, a substitution pattern and a set of
actions, described by a set of flags. In case of match a string
rewriting is performed according to the substitution pattern that
allows one to refer to substrings matched in the incoming string.
The actions, if any, are finally performed. The substitution
pattern allows map resolution of substrings. A map is a generic
object that maps a substitution pattern to a value. The flags are
divided in "Pattern matching Flags" and "Action Flags"; the former
alter the regex match pattern behavior while the latter alter the
action that is taken after substitution.
`C' honors case in matching (default is case insensitive)
`R' use POSIX ''basic'' regular expressions (default is
''extended'')
`M{n}' allow no more than n recursive passes for a specific rule;
does not alter the max total count of passes, so it can
only enforce a stricter limit for a specific rule.
`:' apply the rule once only (default is recursive)
`@' stop applying rules in case of match; the current rule is
still applied recursively; combine with `:' to apply the
current rule only once and then stop.
`#' stop current operation if the rule matches, and issue an
`unwilling to perform' error.
`G{n}' jump n rules back and forth (watch for loops!). Note that
`G{1}' is implicit in every rule.
`I' ignores errors in rule; this means, in case of error, e.g.
issued by a map, the error is treated as a missed match.
The `unwilling to perform' is not overridden.
`U{n}' uses n as return code if the rule matches; the flag does
not alter the recursive behavior of the rule, so, to have
it performed only once, it must be used in combination with
`:', e.g. `:U{16}' returns the value `16' after exactly
one execution of the rule, if the pattern matches. As a
consequence, its behavior is equivalent to `@', with the
return code set to n; or, in other words, `@' is equivalent
to `U{0}'. By convention, the freely available codes are
above 16 included; the others are reserved.
The ordering of the flags can be significant. For instance:
`IG{2}' means ignore errors and jump two lines ahead both in case
of match and in case of error, while `G{2}I' means ignore errors,
but jump two lines ahead only in case of match.
More flags (mainly Action Flags) will be added as needed.
See regex(7) and/or re_format(7).
Everything starting with `%' requires substitution;
the only obvious exception is `%%', which is left as is;
the basic substitution is `%d', where `d' is a digit; 0 means the
whole string, while 1-9 is a submatch;
a `%' followed by a `{' invokes an advanced substitution. The
pattern is:
`%' `{' [ <op> ] <name> `(' <substitution> `)' `}'
where <name> must be a legal name for the map, i.e.
<name> ::= [a-z][a-z0-9]* (case insensitive)
<op> ::= `>' `|' `&' `&&' `*' `**' `$'
and <substitution> must be a legal substitution pattern, with no
limits on the nesting level.
The operators are:
> sub context invocation; <name> must be a legal, already
defined rewrite context name
| external command invocation; <name> must refer to a legal,
already defined command name (NOT IMPL.)
& variable assignment; <name> defines a variable in the
running operation structure which can be dereferenced
later; operator & assigns a variable in the rewrite context
scope; operator && assigns a variable that scopes the
entire session, e.g. its value can be dereferenced later by
other rewrite contexts
* variable dereferencing; <name> must refer to a variable
that is defined and assigned for the running operation;
operator * dereferences a variable scoping the rewrite
context; operator ** dereferences a variable scoping the
whole session, e.g. the value is passed across rewrite
contexts
$ parameter dereferencing; <name> must refer to an existing
parameter; the idea is to make some run-time parameters set
by the system available to the rewrite engine, as the
client host name, the bind DN if any, constant parameters
initialized at config time, and so on; no parameter is
currently set by either back-ldap or back-meta, but
constant parameters can be defined in the configuration
file by using the rewriteParam directive.
Substitution escaping has been delegated to the `%' symbol, which
is used instead of `\' in string substitution patterns because `\'
is already escaped by slapd's low level parsing routines; as a
consequence, regex escaping requires two `\' symbols, e.g.
`.*\.foo\.bar' must be written as `.*\\.foo\\.bar'.
A rewrite context is a set of rules which are applied in sequence.
The basic idea is to have an application initialize a rewrite
engine (think of Apache's mod_rewrite ...) with a set of rewrite
contexts; when string rewriting is required, one invokes the
appropriate rewrite context with the input string and obtains the
newly rewritten one if no errors occur.
Each basic server operation is associated to a rewrite context;
they are divided in two main groups: client -> server and server
-> client rewriting.
client -> server:
(default) if defined and no specific context
is available
bindDN bind
searchBase search
searchFilter search
searchFilterAttrDN search
compareDN compare
compareAttrDN compare AVA
addDN add
addAttrDN add AVA
modifyDN modify
modifyAttrDN modify AVA
modrDN modrdn
newSuperiorDN modrdn
deleteDN delete
exopPasswdDN password modify extended operation DN if proxy
server -> client:
searchResult search (only if defined; no default;
acts on DN and DN-syntax attributes
of search results)
searchAttrDN search AVA
matchedDN all ops (only if applicable)
rewriteEngine { on | off }
If `on', the requested rewriting is performed; if `off', no
rewriting takes place (an easy way to stop rewriting
without altering too much the configuration file).
rewriteContext <context name> [ alias <aliased context name> ]
<Context name> is the name that identifies the context,
i.e. the name used by the application to refer to the set
of rules it contains. It is used also to reference sub
contexts in string rewriting. A context may alias another
one. In this case the alias context contains no rule, and
any reference to it will result in accessing the aliased
one.
rewriteRule <regex match pattern> <substitution pattern> [ <flags>
]
Determines how a string can be rewritten if a pattern is
matched. Examples are reported below.
rewriteMap <map type> <map name> [ <map attrs> ]
Allows one to define a map that transforms substring
rewriting into something else. The map is referenced
inside the substitution pattern of a rule.
rewriteParam <param name> <param value>
Sets a value with global scope, that can be dereferenced by
the command `%{$paramName}'.
rewriteMaxPasses <number of passes> [<number of passes per rule>]
Sets the maximum number of total rewriting passes that can
be performed in a single rewrite operation (to avoid
loops). A safe default is set to 100; note that reaching
this limit is still treated as a success; recursive
invocation of rules is simply interrupted. The count
applies to the rewriting operation as a whole, not to any
single rule; an optional per-rule limit can be set. This
limit is overridden by setting specific per-rule limits
with the `M{n}' flag.
# set to `off' to disable rewriting
rewriteEngine on
# the rules the "suffixmassage" directive implies
rewriteEngine on
# all dataflow from client to server referring to DNs
rewriteContext default
rewriteRule "(.*)<virtualnamingcontext>$" "%1<realnamingcontext>" ":"
# empty filter rule
rewriteContext searchFilter
# all dataflow from server to client
rewriteContext searchResult
rewriteRule "(.*)<realnamingcontext>$" "%1<virtualnamingcontext>" ":"
rewriteContext searchAttrDN alias searchResult
rewriteContext matchedDN alias searchResult
# Everything defined here goes into the `default' context.
# This rule changes the naming context of anything sent
# to `dc=home,dc=net' to `dc=OpenLDAP, dc=org'
rewriteRule "(.*)dc=home,[ ]?dc=net"
"%1dc=OpenLDAP, dc=org" ":"
# since a pretty/normalized DN does not include spaces
# after rdn separators, e.g. `,', this rule suffices:
rewriteRule "(.*)dc=home,dc=net"
"%1dc=OpenLDAP,dc=org" ":"
# Start a new context (ends input of the previous one).
# This rule adds blanks between DN parts if not present.
rewriteContext addBlanks
rewriteRule "(.*),([^ ].*)" "%1, %2"
# This one eats blanks
rewriteContext eatBlanks
rewriteRule "(.*),[ ](.*)" "%1,%2"
# Here control goes back to the default rewrite
# context; rules are appended to the existing ones.
# anything that gets here is piped into rule `addBlanks'
rewriteContext default
rewriteRule ".*" "%{>addBlanks(%0)}" ":"
# Rewrite the search base according to `default' rules.
rewriteContext searchBase alias default
# Search results with OpenLDAP DN are rewritten back with
# `dc=home,dc=net' naming context, with spaces eaten.
rewriteContext searchResult
rewriteRule "(.*[^ ]?)[ ]?dc=OpenLDAP,[ ]?dc=org"
"%{>eatBlanks(%1)}dc=home,dc=net" ":"
# Bind with email instead of full DN: we first need
# an ldap map that turns attributes into a DN (the
# argument used when invoking the map is appended to
# the URI and acts as the filter portion)
rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"
# Then we need to detect DN made up of a single email,
# e.g. `mail=someone@example.com'; note that the rule
# in case of match stops rewriting; in case of error,
# it is ignored. In case we are mapping virtual
# to real naming contexts, we also need to rewrite
# regular DNs, because the definition of a bindDn
# rewrite context overrides the default definition.
rewriteContext bindDN
rewriteRule "^mail=[^,]+@[^,]+$" "%{attr2dn(%0)}" ":@I"
# This is a rather sophisticated example. It massages a
# search filter in case who performs the search has
# administrative privileges. First we need to keep
# track of the bind DN of the incoming request, which is
# stored in a variable called `binddn' with session scope,
# and left in place to allow regular binding:
rewriteContext bindDN
rewriteRule ".+" "%{&&binddn(%0)}%0" ":"
# A search filter containing `uid=' is rewritten only
# if an appropriate DN is bound.
# To do this, in the first rule the bound DN is
# dereferenced, while the filter is decomposed in a
# prefix, in the value of the `uid=<arg>' AVA, and
# in a suffix. A tag `<>' is appended to the DN.
# If the DN refers to an entry in the `ou=admin' subtree,
# the filter is rewritten OR-ing the `uid=<arg>' with
# `cn=<arg>'; otherwise it is left as is. This could be
# useful, for instance, to allow apache's auth_ldap-1.4
# module to authenticate users with both `uid' and
# `cn', but only if the request comes from a possible
# `cn=Web auth,ou=admin,dc=home,dc=net' user.
rewriteContext searchFilter
rewriteRule "(.*\\()uid=([a-z0-9_]+)(\\).*)"
"%{**binddn}<>%{&prefix(%1)}%{&arg(%2)}%{&suffix(%3)}"
":I"
rewriteRule "[^,]+,ou=admin,dc=home,dc=net"
"%{*prefix}|(uid=%{*arg})(cn=%{*arg})%{*suffix}" ":@I"
rewriteRule ".*<>" "%{*prefix}uid=%{*arg}%{*suffix}" ":"
# This example shows how to strip unwanted DN-valued
# attribute values from a search result; the first rule
# matches DN values below "ou=People,dc=example,dc=com";
# in case of match the rewriting exits successfully.
# The second rule matches everything else and causes
# the value to be rejected.
rewriteContext searchResult
rewriteRule ".*,ou=People,dc=example,dc=com" "%0" ":@"
rewriteRule ".*" "" "#"
In case the rewritten DN is an LDAP URI, the operation is
initiated towards the host[:port] indicated in the uri, if it does
not refer to the local server. E.g.:
rewriteRule '^cn=root,.*' '%0' 'G{3}'
rewriteRule '^cn=[a-l].*' 'ldap://ldap1.my.org/%0' ':@'
rewriteRule '^cn=[m-z].*' 'ldap://ldap2.my.org/%0' ':@'
rewriteRule '.*' 'ldap://ldap3.my.org/%0' ':@'
(Rule 1 is simply there to illustrate the `G{n}' action; it could
have been written:
rewriteRule '^cn=root,.*' 'ldap://ldap3.my.org/%0' ':@'
with the advantage of saving one rewrite pass ...)
The meta backend does not honor all ACL semantics as described in
slapd.access(5). In general, access checking is delegated to the
remote server(s). Only read (=r) access to the entry pseudo-
attribute and to the other attribute values of the entries
returned by the search operation is honored, which is performed by
the frontend.
The proxy cache overlay allows caching of LDAP search requests
(queries) in a local database. See slapo-pcache(5) for details.
The following statements have been deprecated and should no longer
be used.
pseudorootdn <substitute DN in case of rootdn bind>
Use idassert-bind instead.
pseudorootpw <substitute password in case of rootdn bind>
Use idassert-bind instead.
ETCDIR/slapd.conf
default slapd configuration file
slapd.conf(5), slapd-asyncmeta(5), slapd-ldap(5), slapo-pcache(5),
slapd(8), regex(7), re_format(7).
Pierangelo Masarati, based on back-ldap by Howard Chu
This page is part of the OpenLDAP (an open source implementation
of the Lightweight Directory Access Protocol) project.
Information about the project can be found at
⟨http://www.openldap.org/⟩. If you have a bug report for this
manual page, see ⟨http://www.openldap.org/its/⟩. This page was
obtained from the project's upstream Git repository
⟨https://git.openldap.org/openldap/openldap.git⟩ on 2025-08-11.
(At that time, the date of the most recent commit that was found
in the repository was 2025-08-05.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
OpenLDAP LDVERSION RELEASEDATE SLAPD-META(5)
Pages that refer to this page: slapd-asyncmeta(5), slapd.backends(5), slapd-ldap(5), slapd-meta(5), slapd.overlays(5), slapo-pcache(5), slapo-rwm(5), slapo-translucent(5)
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