slapd-meta(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | CONFIGURATION | SPECIAL CONFIGURATION DIRECTIVES | TARGET SPECIFICATION | SCENARIOS | ACLs | REWRITING | Passes | Pattern Matching Flags | Action Flags | Pattern matching: | Substitution Pattern Syntax: | Rewrite context: | Basic configuration syntax | Additional configuration syntax: | Configuration examples: | LDAP Proxy resolution (a possible evolution of slapd-ldap(5)): | ACCESS CONTROL | PROXY CACHE OVERLAY | DEPRECATED STATEMENTS | FILES | SEE ALSO | AUTHOR | COLOPHON

SLAPD-META(5)                File Formats Manual               SLAPD-META(5)

NAME         top

       slapd-meta - metadirectory backend to slapd

SYNOPSIS         top


DESCRIPTION         top

       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.

EXAMPLES         top

       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-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

       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,

              suffix "dc=foo,dc=com"
              uri    "ldap://,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 and are
              shadows of the same server, the directive

              suffix "dc=foo,dc=com"
              uri    "ldap://,dc=com" "ldap://"

              causes to be contacted whenever 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

       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

       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

       filter <pattern>
              This directive allows specifying a regex(5) pattern to
              indicate what search filter terms are actually served by a

              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_cipher_suite=<ciphers>] [tls_ecname=<ciphers>]
              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


              where none is the default, i.e. no identity assertion is

              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



              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


              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

              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


              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.

       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

       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

              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 {[try-]start|[try-]propagate}
              execute the StartTLS extended operation when the connection is
              initialized; only works if the URI directive protocol scheme
              is not ldaps://.  propagate issues the StartTLS operation only
              if the original connection did.  The try- prefix instructs the
              proxy to continue operations if the StartTLS operation failed;
              its use is highly deprecated.  If set before any target
              specification, it affects all targets, unless overridden by
              any per-target directive.

SCENARIOS         top

       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://,dc=foo,dc=com"
              uri      "ldap://,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

       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://,dc=foo,dc=com"
              suffixmassage "dc=a,dc=foo,dc=com" "dc=bar,dc=org"

              uri           "ldap://,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://,dc=com"
              suffixmassage "dc=foo,dc=com" "dc=bar,dc=org"

              uri           "ldap://,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

ACLs         top

       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

       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:
       <>).  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".

REWRITING         top

       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).

Passes         top

       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.

Pattern Matching Flags         top

       `C'    honors case in matching (default is case insensitive)

       `R'    use POSIX ''basic'' regular expressions (default is

       `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.

Action Flags         top

       `:'    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.

Pattern matching:         top

       See regex(7) and/or re_format(7).

Substitution Pattern Syntax:         top

       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

       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'.

Rewrite context:         top

       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

       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)

Basic configuration syntax         top

       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.

Additional configuration syntax:         top

       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.

Configuration examples:         top

       # 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. `'; 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_]+)(\\).*)"
       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 ".*" "" "#"

LDAP Proxy resolution (a possible evolution of slapd-ldap(5)):         top

       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://' ':@'
         rewriteRule '^cn=[m-z].*' 'ldap://' ':@'
         rewriteRule '.*'          'ldap://' ':@'

       (Rule 1 is simply there to illustrate the `G{n}' action; it could
       have been written:

         rewriteRule '^cn=root,.*' 'ldap://' ':@'

       with the advantage of saving one rewrite pass ...)

ACCESS CONTROL         top

       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


       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

       pseudorootdn <substitute DN in case of rootdn bind>
              Use idassert-bind instead.

       pseudorootpw <substitute password in case of rootdn bind>
              Use idassert-bind instead.

FILES         top

              default slapd configuration file

SEE ALSO         top

       slapd.conf(5), slapd-ldap(5), slapo-pcache(5), slapd(8), regex(7),

AUTHOR         top

       Pierangelo Masarati, based on back-ldap by Howard Chu

COLOPHON         top

       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 ⟨⟩.  If you
       have a bug report for this manual page, see
       ⟨⟩.  This page was obtained from the
       project's upstream Git repository
       ⟨⟩ on 2020-09-18.  (At
       that time, the date of the most recent commit that was found in the
       repository was 2020-09-18.)  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

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