Provided by: slapd_2.4.7-6ubuntu3_i386 bug


       slapd-meta - metadirectory backend to slapd




       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.

       Note:  When  looping  back  to  the  same  instance  of  slapd(8), each
       connection requires a new thread; as a consequence,  slapd(8)  must  be
       compiled  with  thread support, and the 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-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 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 continuated to the end  but,  in
              case  at least one target returned an error code, the first non-
              success error code is returned.

       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 {NO|yes}
              This  directive,  when  set to yes, causes the authentication to
              the remote servers with the pseudo-root identity to be  deferred
              until actually needed by subsequent operations.

       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://,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

       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

       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.

       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.

       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.

       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.

       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.

       subtree-exclude <DN>
              This  directive instructs back-meta to ignore the current target
              for operations whose requestDN is subordinate to DN.  There  may
              be  multiple  occurrences  of  the subtree-exclude directive for
              each of the targets.

       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
              draft-zeilenga-ldap-t-f  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 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 {[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.


       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 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://,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 scenarios.


       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

       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:
       <>).  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 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

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

:’    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) and/or re_format(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;

       a ‘%’ followed by a ‘{’ invokes an advanced substitution.  The  pattern

              ‘%’ ‘{’ [ <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’.

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

       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

       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:

       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 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:

       # 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)):

       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 ...)


       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.


              default slapd configuration file


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


       Pierangelo Masarati, based on back-ldap by Howard Chu