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SLAPD-META(5)

     NAME
          slapd-meta - metadirectory backend

     SYNOPSIS
          /etc/openldap/slapd.conf

     DESCRIPTION
          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.

     EXAMPLES
          There are examples in various places in this document, as
          well as in the slapd/back-meta/data/ directory in the
          OpenLDAP source tree.

     CONFIGURATION
          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: as with the ldap backend, operational attributes
          related to entry creation/modification should not be used,
          as they would be passed to the target servers, generating an
          error.  Moreover, it makes little sense to use such
          attributes in proxying, as the proxy server doesn't actually
          store data, so it should have no knowledge of such
          attributes.  While code to strip the modification attributes
          has been put in place (and #ifdef'd), it implies unmotivated
          overhead.  So it is strongly recommended to set
               lastmod  off
          for every ldap and meta backend.

     SPECIAL CONFIGURATION DIRECTIVES
          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:

          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 {forever|disabled|<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 in seconds is required.

     TARGET SPECIFICATION
          Target specification starts with a "uri" directive:

          uri <protocol>://[<host>[:<port>]]/<naming context>
               The "server" directive that was allowed in the LDAP
               backend (although deprecated) has been discarded in the
               Meta backend.  The <protocol> part can be anything
               ldap_initialize(3) accepts ({ldap|ldaps|ldapi} and
               variants); <host> and <port> may be omitted, defaulting
               to whatever is set in /etc/ldap.conf.  The <naming
               context> part is mandatory.  It must end with one of
               the naming contexts 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 argument.  The URIs must be separated by TABs (e.g.
          '\t'), and the additional URIs must have no <naming context>
          part.  This causes the underlying library to contact the
          first server of the list that responds.

          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.

          binddn <administrative DN for access control purposes>
               This directive, as in the LDAP backend, allows to
               define the DN that is used to query the target server
               for acl checking; it should 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.

          bindpw <password for access control purposes>
               This directive sets the password for acl checking in
               conjunction with the above mentioned "binddn"
               directive.

          rebind-as-user
               If this option is given, the client's bind credentials
               are remembered for rebinds when chasing referrals.

          pseudorootdn <substitute DN in case of rootdn bind>
               This directive, if present, sets the DN that will be
               substituted to the bind DN if a bind with the backend's
               "rootdn" succeeds.  The true "rootdn" of the target
               server ought not be used; an arbitrary administrative
               DN should used instead.

          pseudorootpw <substitute password in case of rootdn bind>
               This directive sets the credential that will be used in
               case a bind with the backend's "rootdn" succeeds, and
               the bind is propagated to the target using the
               "pseudorootdn" DN.

          Note: cleartext credentials must be supplied here; as a
          consequence, using the pseudorootdn/pseudorootpw directives
          is inherently unsafe.

          rewrite* ...
               The rewrite options are described in the "REWRITING"
               section.

          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.

          Note: this also fixes a flaw in suffix massaging, which
          operated on (case insensitive) DNs instead of normalized
          DNs, so "dc=foo, dc=com" would not match "dc=foo,dc=com".

          See the "REWRITING" section.

          map {attribute|objectclass} [<local name>|*] {<foreign name>|*}
               This maps object classes and attributes as in the LDAP
               backend.  See slapd-ldap(5).

     SCENARIOS
          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.

     ACLs
          Note on ACLs: at present you may add whatever ACL rule you
          desire to 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 drop me a note if you can find
          other exceptions: <ando@openldap.org>).  The rule

               access to dn="<dn>" attr=<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
          A string is rewritten according to a set of rules, called a
          `rewrite context'.  The rules are based on Regular
          Expressions (POSIX 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
          An incoming string is matched agains 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 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 behaviorm while the
          latter alter the action that is taken after substitution.

     Pattern Matching Flags
          `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.

     Action Flags
          `:'  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:
          See regex(7).

     Substitution Pattern Syntax:
          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, as
          discussed in regex(7);

          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
               derefenced 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(7) escaping requires two
          `\' symbols, e.g. `.*\.foo\.bar' must be written as
          `.*\\.foo\\.bar'.

     Rewrite context:
          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         passwd exop 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
          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 aliase
               another one.  In this case the alias context contains
               no rule, and any reference to it will result in
               accessing the aliased one.

     <flags> ]
          rewriteRule <regex match pattern> <substitution pattern> [
               Determines how a string can be rewritten if a pattern
               is matched.  Examples are reported below.

     Additional configuration syntax:
          rewriteMap <map type> <map name> [ <map attrs> ]
               Allows 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
               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:
          # 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 ".*" "" "#"

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

     PROXY CACHE OVERLAY
          The proxy cache overlay allows caching of LDAP search
          requests (queries) in a local database.  For an incoming
          query, the proxy cache determines its corresponding
          template. If the template was specified as cacheable using
          the proxytemplate directive and the request is contained in
          a cached request, it is answered from the proxy cache.
          Otherwise, the search is performed as usual and cacheable
          search results are saved in the cache for use in future
          queries.

          A template is defined by a filter string and an index
          identifying a set of attributes. The template string for a
          query can be obtained by removing assertion values from the
          RFC 2254 representation of its search filter. A query
          belongs to a template if its template string and set of
          projected attributes correspond to a cacheable template.
          Examples of template strings are (mail=), (|(sn=)(cn=)),
          (&(sn=)(givenName=)).

          The following cache specific directives can be used to
          configure the proxy cache:

          overlay proxycache
               This directive adds the proxycache overlay to the
               current backend. The proxycache overlay may be used
               with any backend but is intended for use with the ldap
               and meta backends.

     <cc_period>
          proxycache <database> <max_entries> <numattrsets> <entry_limit>
               The directive enables proxy caching in the current
               backend and sets general cache parameters. A <database>
               backend will be used internally to maintain the cached
               entries. The chosen database will need to be configured
               as well, as shown below. Cache replacement is invoked
               when the cache size grows to <max_entries> entries and
               continues till the cache size drops below this size.
               <numattrsets> should be equal to the number of
               following proxyattrset directives. Queries are cached
               only if they correspond to a cacheable template
               (specified by the proxytemplate directive) and the
               number of entries returned is less than <entry_limit>.
               Consistency check is performed every <cc_period>
               duration (specified in secs). In each cycle queries
               with expired "time to live(TTL)" are removed. A sample
               cache configuration is:

               proxycache bdb 10000 1 50 100

          proxyattrset <index> <attrs...>
               Used to associate a set of attributes <attrs..> with an
               <index>. Each attribute set is associated with an
               integer from 0 to <numattrsets>-1. These indices are
               used by the proxytemplate directive to define cacheable
               templates.

          proxytemplate <template_string> <attrset_index> <ttl>
               Specifies a cacheable template and "time to live" (in
               sec) <ttl> of queries belonging to the template.

          The following adds a template with filter string
          (&sn=)(givenName=)) and attributes mail, postaladdress,
          telephonenumber and a TTL of 1 hour.

               proxyattrset 0 mail postaladdress telephonenumber
               proxytemplate (&(sn=)(givenName=)) 0 3600

          Directives for configuring the underlying database must also
          be given, as shown here:

               directory /var/tmp/cache
               cachesize 100

          Any valid directives for the chosen database type may be
          used.

     FILES
          /etc/openldap/slapd.conf

               default slapd configuration file

     SEE ALSO
          slapd.conf(5), slapd-ldap(5), slapd(8), regex(7).

     AUTHOR
          Pierangelo Masarati, based on back-ldap by Howard Chu




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