2 # Copyright 2007 The OpenLDAP Foundation, All Rights Reserved.
3 # COPYING RESTRICTIONS APPLY, see COPYRIGHT.
7 Overlays are software components that provide hooks to functions analogous to
8 those provided by backends, which can be stacked on top of the backend calls
9 and as callbacks on top of backend responses to alter their behavior.
11 Overlays may be compiled statically into slapd, or when module support
12 is enabled, they may be dynamically loaded. Most of the overlays
13 are only allowed to be configured on individual databases, but some
14 may also be configured globally.
16 Essentially they represent a means to:
18 * customize the behavior of existing backends without changing the backend
19 code and without requiring one to write a new custom backend with
20 complete functionality
21 * write functionality of general usefulness that can be applied to
22 different backend types
24 Overlays are usually documented by separate specific man pages in section 5;
25 the naming convention is
27 > slapo-<overlay name>
29 Not all distributed overlays have a man page yet. Feel free to contribute one,
30 if you think you well understood the behavior of the component and the
31 implications of all the related configuration directives.
33 Official overlays are located in
35 > servers/slapd/overlays/
37 That directory also contains the file slapover.txt, which describes the
38 rationale of the overlay implementation, and may serve as guideline for the
39 development of custom overlays.
41 Contribware overlays are located in
43 > contrib/slapd-modules/<overlay name>/
45 along with other types of run-time loadable components; they are officially
46 distributed, but not maintained by the project.
48 They can be stacked on the frontend as well; this means that they can be
49 executed after a request is parsed and validated, but right before the
50 appropriate database is selected. The main purpose is to affect operations
51 regardless of the database they will be handled by, and, in some cases,
52 to influence the selection of the database by massaging the request DN.
54 All the current overlays in 2.4 are listed and described in detail in the
63 This overlay can record accesses to a given backend database on another
67 H3: Access Logging Configuration
72 This overlay records changes on a given backend database to an LDIF log
79 H3: Audit Logging Configuration
87 The chain overlay provides basic chaining capability to the underlying
90 What is chaining? It indicates the capability of a DSA to follow referrals on
91 behalf of the client, so that distributed systems are viewed as a single
92 virtual DSA by clients that are otherwise unable to "chase" (i.e. follow)
93 referrals by themselves.
95 The chain overlay is built on top of the ldap backend; it is compiled by
96 default when --enable-ldap.
99 H3: Chaining Configuration
101 In order to demonstrate how this overlay works, we shall discuss a typical
102 scenario which might be one master server and three Syncrepl slaves.
104 On each replica, add this near the top of the file (global), before any database
108 > chain-uri "ldap://ldapmaster.example.com"
109 > chain-idassert-bind bindmethod="simple"
110 > binddn="cn=Manager,dc=example,dc=com"
111 > credentials="<secret>"
114 > chain-return-error TRUE
116 Add this below your {{syncrepl}} statement:
118 > updateref "ldap://ldapmaster.example.com/"
120 The {{B:chain-tls}} statement enables TLS from the slave to the ldap master.
121 The DITs are exactly the same between these machines, therefore whatever user
122 bound to the slave will also exist on the master. If that DN does not have
123 update privileges on the master, nothing will happen.
125 You will need to restart the slave after these changes. Then, if you are using
126 {{loglevel 256}}, you can monitor an {{ldapmodify}} on the slave and the master.
128 Now start an {{ldapmodify}} on the slave and watch the logs. You should expect
131 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 fd=31 ACCEPT from IP=143.199.102.216:45181 (IP=143.199.102.216:389)
132 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 op=0 STARTTLS
133 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 op=0 RESULT oid= err=0 text=
134 > Sep 6 09:27:25 slave1 slapd[29274]: conn=11 fd=31 TLS established tls_ssf=256 ssf=256
135 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=1 BIND dn="uid=user1,ou=people,dc=example,dc=com" method=128
136 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=1 BIND dn="uid=user1,ou=People,dc=example,dc=com" mech=SIMPLE ssf=0
137 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=1 RESULT tag=97 err=0 text=
138 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 MOD dn="uid=user1,ou=People,dc=example,dc=com"
139 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 MOD attr=mail
140 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 RESULT tag=103 err=0 text=
141 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=3 UNBIND
142 > Sep 6 09:27:28 slave1 slapd[29274]: conn=11 fd=31 closed
143 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: LDAP_RES_SEARCH_ENTRY(LDAP_SYNC_MODIFY)
144 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: be_search (0)
145 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: uid=user1,ou=People,dc=example,dc=com
146 > Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: be_modify (0)
148 And on the master you will see this:
150 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 PROXYAUTHZ dn="uid=user1,ou=people,dc=example,dc=com"
151 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 MOD dn="uid=user1,ou=People,dc=example,dc=com"
152 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 MOD attr=mail
153 > Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 RESULT tag=103 err=0 text=
155 Note: You can clearly see the PROXYAUTHZ line on the master, indicating the
156 proper identity assertion for the update on the master. Also note the slave
157 immediately receiving the Syncrepl update from the master.
159 H3: Handling Chaining Errors
161 By default, if chaining fails, the original referral is returned to the client
162 under the assumption that the client might want to try and follow the referral.
164 With the following directive however, if the chaining fails at the provider
165 side, the actual error is returned to the client.
167 > chain-return-error TRUE
175 This overlay enforces a regular expression constraint on all values
176 of specified attributes. It is used to enforce a more rigorous
177 syntax when the underlying attribute syntax is too general.
180 H3: Constraint Configuration
183 H2: Dynamic Directory Services
188 This overlay supports dynamic objects, which have a limited life after
189 which they expire and are automatically deleted.
192 H3: Dynamic Directory Service Configuration
200 This overlay extends the Compare operation to detect
201 members of a dynamic group. This overlay is now deprecated
202 as all of its functions are available using the
203 {{SECT:Dynamic Lists}} overlay.
206 H3: Dynamic Group Configuration
214 This overlay allows expansion of dynamic groups and lists. Instead of having the
215 group members or list attributes hard coded, this overlay allows us to define
216 an LDAP search whose results will make up the group or list.
218 H3: Dynamic List Configuration
220 This module can behave both as a dynamic list and dynamic group, depending on
221 the configuration. The syntax is as follows:
224 > dynlist-attrset <group-oc> <URL-ad> [member-ad]
226 The parameters to the {{F:dynlist-attrset}} directive have the following meaning:
227 * {{F:<group-oc>}}: specifies which object class triggers the subsequent LDAP search.
228 Whenever an entry with this object class is retrieved, the search is performed.
229 * {{F:<URL-ad>}}: is the name of the attribute which holds the search URI. It
230 has to be a subtype of {{F:labeledURI}}. The attributes and values present in
231 the search result are added to the entry unless {{F:member-ad}} is used (see
233 * {{F:member-ad}}: if present, changes the overlay behaviour into a dynamic group.
234 Instead of inserting the results of the search in the entry, the distinguished name
235 of the results are added as values of this attribute.
237 Here is an example which will allow us to have an email alias which automatically
238 expands to all user's emails according to our LDAP filter:
240 In {{slapd.conf}}(5):
242 > dynlist-attrset nisMailAlias labeledURI
244 This means that whenever an entry which has the {{F:nisMailAlias}} object class is
245 retrieved, the search specified in the {{F:labeledURI}} attribute is performed.
247 Let's say we have this entry in our directory:
248 > cn=all,ou=aliases,dc=example,dc=com
250 > objectClass: nisMailAlias
251 > labeledURI: ldap:///ou=People,dc=example,dc=com?mail?one?(objectClass=inetOrgPerson)
253 If this entry is retrieved, the search specified in {{F:labeledURI}} will be
254 performed and the results will be added to the entry just as if they have always
255 been there. In this case, the search filter selects all entries directly
256 under {{F:ou=People}} that have the {{F:inetOrgPerson}} object class and retrieves
257 the {{F:mail}} attribute, if it exists.
259 This is what gets added to the entry when we have two users under {{F:ou=People}}
260 that match the filter:
261 !import "allmail-en.png"; align="center"; title="Dynamic list for email aliases"
262 FT[align="Center"] Figure X.Y: Dynamic List for all emails
264 The configuration for a dynamic group is similar. Let's see an example which would
265 automatically populate an {{F:allusers}} group with all the user accounts in the
268 In {{F:slapd.conf}}(5):
270 > dynlist-attrset groupOfNames labeledURI member
272 Let's apply it to the following entry:
273 > cn=allusers,ou=group,dc=example,dc=com
275 > objectClass: groupOfNames
276 > labeledURI: ldap:///ou=people,dc=example,dc=com??one?(objectClass=inetOrgPerson)
278 The behaviour is similar to the dynamic list configuration we had before:
279 whenever an entry with the {{F:groupOfNames}} object class is retrieved, the
280 search specified in the {{F:labeledURI}} attribute is performed. But this time,
281 only the distinguished names of the results are added, and as values of the
282 {{F:member}} attribute.
285 !import "allusersgroup-en.png"; align="center"; title="Dynamic group for all users"
286 FT[align="Center"] Figure X.Y: Dynamic Group for all users
288 Note that a side effect of this scheme of dymamic groups is that the members
289 need to be specified as full DNs. So, if you are planning in using this for
290 {{F:posixGroup}}s, be sure to use RFC2307bis and some attribute which can hold
291 distinguished names. The {{F:memberUid}} attribute used in the {{F:posixGroup}}
292 object class can hold only names, not DNs, and is therefore not suitable for
295 H2: Reverse Group Membership Maintenance
299 In some scenarios, it may be desirable for a client to be able to determine
300 which groups an entry is a member of, without performing an additional search.
301 Examples of this are applications using the {{TERM:DIT}} for access control
302 based on group authorization.
304 The {{B:memberof}} overlay updates an attribute (by default {{B:memberOf}}) whenever
305 changes occur to the membership attribute (by default {{B:member}}) of entries of the
306 objectclass (by default {{B:groupOfNames}}) configured to trigger updates.
308 Thus, it provides maintenance of the list of groups an entry is a member of,
309 when usual maintenance of groups is done by modifying the members on the group
312 H3: Member Of Configuration
314 The typical use of this overlay requires just enabling the overlay for a
315 specific database. For example, with the following minimal slapd.conf:
317 > include /usr/share/openldap/schema/core.schema
318 > include /usr/share/openldap/schema/cosine.schema
319 > modulepath /usr/lib/openldap
320 > moduleload memberof.la
321 > authz-regexp "gidNumber=0\\\+uidNumber=0,cn=peercred,cn=external,cn=auth"
322 > "cn=Manager,dc=example,dc=com"
324 > suffix "dc=example,dc=com"
325 > rootdn "cn=Manager,dc=example,dc=com"
327 > directory /var/lib/ldap2.4
329 > index objectClass eq
334 adding the following ldif:
337 > dn: dc=example,dc=com
338 > objectclass: domain
341 > dn: ou=Group,dc=example,dc=com
342 > objectclass: organizationalUnit
345 > dn: ou=People,dc=example,dc=com
346 > objectclass: organizationalUnit
349 > dn: uid=test1,ou=People,dc=example,dc=com
350 > objectclass: account
353 > dn: cn=testgroup,ou=Group,dc=example,dc=com
354 > objectclass: groupOfNames
356 > member: uid=test1,ou=People,dc=example,dc=com
358 Results in the following output from a search on the test1 user:
360 > # ldapsearch -LL -Y EXTERNAL -H ldapi:/// "(uid=test1)" -b dc=example,dc=com memberOf
361 > SASL/EXTERNAL authentication started
362 > SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
366 > dn: uid=test1,ou=People,dc=example,dc=com
367 > memberOf: cn=testgroup,ou=Group,dc=example,dc=com
369 Note that the {{B:memberOf}} attribute is an operational attribute, so it must be
370 requested explicitly.
373 H2: The Proxy Cache Engine
375 {{TERM:LDAP}} servers typically hold one or more subtrees of a
376 {{TERM:DIT}}. Replica (or shadow) servers hold shadow copies of
377 entries held by one or more master servers. Changes are propagated
378 from the master server to replica (slave) servers using LDAP Sync
379 replication. An LDAP cache is a special type of replica which holds
380 entries corresponding to search filters instead of subtrees.
384 The proxy cache extension of slapd is designed to improve the
385 responsiveness of the ldap and meta backends. It handles a search
387 by first determining whether it is contained in any cached search
388 filter. Contained requests are answered from the proxy cache's local
389 database. Other requests are passed on to the underlying ldap or
390 meta backend and processed as usual.
392 E.g. {{EX:(shoesize>=9)}} is contained in {{EX:(shoesize>=8)}} and
393 {{EX:(sn=Richardson)}} is contained in {{EX:(sn=Richards*)}}
395 Correct matching rules and syntaxes are used while comparing
396 assertions for query containment. To simplify the query containment
397 problem, a list of cacheable "templates" (defined below) is specified
398 at configuration time. A query is cached or answered only if it
399 belongs to one of these templates. The entries corresponding to
400 cached queries are stored in the proxy cache local database while
401 its associated meta information (filter, scope, base, attributes)
402 is stored in main memory.
404 A template is a prototype for generating LDAP search requests.
405 Templates are described by a prototype search filter and a list of
406 attributes which are required in queries generated from the template.
407 The representation for prototype filter is similar to {{REF:RFC4515}},
408 except that the assertion values are missing. Examples of prototype
409 filters are: (sn=),(&(sn=)(givenname=)) which are instantiated by
410 search filters (sn=Doe) and (&(sn=Doe)(givenname=John)) respectively.
412 The cache replacement policy removes the least recently used (LRU)
413 query and entries belonging to only that query. Queries are allowed
414 a maximum time to live (TTL) in the cache thus providing weak
415 consistency. A background task periodically checks the cache for
416 expired queries and removes them.
418 The Proxy Cache paper
419 ({{URL:http://www.openldap.org/pub/kapurva/proxycaching.pdf}}) provides
420 design and implementation details.
423 H3: Proxy Cache Configuration
425 The cache configuration specific directives described below must
426 appear after a {{EX:overlay proxycache}} directive within a
427 {{EX:"database meta"}} or {{EX:database ldap}} section of
428 the server's {{slapd.conf}}(5) file.
430 H4: Setting cache parameters
432 > proxyCache <DB> <maxentries> <nattrsets> <entrylimit> <period>
434 This directive enables proxy caching and sets general cache
435 parameters. The <DB> parameter specifies which underlying database
436 is to be used to hold cached entries. It should be set to
437 {{EX:bdb}} or {{EX:hdb}}. The <maxentries> parameter specifies the
438 total number of entries which may be held in the cache. The
439 <nattrsets> parameter specifies the total number of attribute sets
440 (as specified by the {{EX:proxyAttrSet}} directive) that may be
441 defined. The <entrylimit> parameter specifies the maximum number of
442 entries in a cacheable query. The <period> specifies the consistency
443 check period (in seconds). In each period, queries with expired
446 H4: Defining attribute sets
448 > proxyAttrset <index> <attrs...>
450 Used to associate a set of attributes to an index. Each attribute
451 set is associated with an index number from 0 to <numattrsets>-1.
452 These indices are used by the proxyTemplate directive to define
455 H4: Specifying cacheable templates
457 > proxyTemplate <prototype_string> <attrset_index> <TTL>
459 Specifies a cacheable template and the "time to live" (in sec) <TTL>
460 for queries belonging to the template. A template is described by
461 its prototype filter string and set of required attributes identified
467 An example {{slapd.conf}}(5) database section for a caching server
468 which proxies for the {{EX:"dc=example,dc=com"}} subtree held
469 at server {{EX:ldap.example.com}}.
472 > suffix "dc=example,dc=com"
473 > rootdn "dc=example,dc=com"
474 > uri ldap://ldap.example.com/
476 > proxycache bdb 100000 1 1000 100
477 > proxyAttrset 0 mail postaladdress telephonenumber
478 > proxyTemplate (sn=) 0 3600
479 > proxyTemplate (&(sn=)(givenName=)) 0 3600
480 > proxyTemplate (&(departmentNumber=)(secretary=*)) 0 3600
483 > directory ./testrun/db.2.a
484 > index objectClass eq
485 > index cn,sn,uid,mail pres,eq,sub
488 H5: Cacheable Queries
490 A LDAP search query is cacheable when its filter matches one of the
491 templates as defined in the "proxyTemplate" statements and when it references
492 only the attributes specified in the corresponding attribute set.
493 In the example above the attribute set number 0 defines that only the
494 attributes: {{EX:mail postaladdress telephonenumber}} are cached for the following
499 > Filter: (&(sn=Richard*)(givenName=jack))
500 > Attrs: mail telephoneNumber
502 is cacheable, because it matches the template {{EX:(&(sn=)(givenName=))}} and its
503 attributes are contained in proxyAttrset 0.
505 > Filter: (&(sn=Richard*)(telephoneNumber))
508 is not cacheable, because the filter does not match the template,
509 nor is the attribute givenName stored in the cache
511 > Filter: (|(sn=Richard*)(givenName=jack))
512 > Attrs: mail telephoneNumber
514 is not cacheable, because the filter does not match the template ( logical
515 OR "|" condition instead of logical AND "&" )
518 H2: Password Policies
523 This overlay provides a variety of password control mechanisms,
524 e.g. password aging, password reuse and duplication control, mandatory
525 password resets, etc.
528 H3: Password Policy Configuration
531 H2: Referential Integrity
536 This overlay can be used with a backend database such as slapd-bdb(5)
537 to maintain the cohesiveness of a schema which utilizes reference
540 Whenever a {{modrdn}} or {{delete}} is performed, that is, when an entry's DN
541 is renamed or an entry is removed, the server will search the directory for
542 references to this DN (in selected attributes: see below) and update them
543 accordingly. If it was a {{delete}} operation, the reference is deleted. If it
544 was a {{modrdn}} operation, then the reference is updated with the new DN.
546 For example, a very common administration task is to maintain group membership
547 lists, specially when users are removed from the directory. When an
548 user account is deleted or renamed, all groups this user is a member of have to be
549 updated. LDAP administrators usually have scripts for that. But we can use the
550 {{F:refint}} overlay to automate this task. In this example, if the user is
551 removed from the directory, the overlay will take care to remove the user from
552 all the groups he/she was a member of. No more scripting for this.
554 H3: Referential Integrity Configuration
556 The configuration for this overlay is as follows:
558 > refint_attributes <attribute [attribute ...]>
559 > refint_nothing <string>
561 * {{F:refint_attributes}}: this parameter specifies a space separated list of
562 attributes which will have the referential integrity maintained. When an entry is
563 removed or has its DN renamed, the server will do an internal search for any of the
564 {{F:refint_attributes}} that point to the affected DN and update them accordingly. IMPORTANT:
565 the attributes listed here must have the {{F:distinguishedName}} syntax, that is,
567 * {{F:refint_nothing}}: some times, while trying to maintain the referential
568 integrity, the server has to remove the last attribute of its kind from an
569 entry. This may be prohibited by the schema: for example, the
570 {{F:groupOfNames}} object class requires at least one member. In these cases,
571 the server will add the attribute value specified in {{F:refint_nothing}}
574 To illustrate this overlay, we will use the group membership scenario.
578 > refint_attributes member
579 > refint_nothing "cn=admin,dc=example,dc=com"
581 This configuration tells the overlay to maintain the referential integrity of the {{F:member}}
582 attribute. This attribute is used in the {{F:groupOfNames}} object class which always needs
583 a member, so we add the {{F:refint_nothing}} directive to fill in the group with a standard
584 member should all the members vanish.
586 If we have the following group membership, the refint overlay will
587 automatically remove {{F:john}} from the group if his entry is removed from the
590 !import "refint.png"; align="center"; title="Group membership"
591 FT[align="Center"] Figure X.Y: Maintaining referential integrity in groups
593 Notice that if we rename ({{F:modrdn}}) the {{F:john}} entry to, say, {{F:jsmith}}, the refint
594 overlay will also rename the reference in the {{F:member}} attribute, so the group membership
597 If we removed all users from the directory who are a member of this group, then the end result
598 would be a single member in the group: {{F:cn=admin,dc=example,dc=com}}. This is the
599 {{F:refint_nothing}} parameter kicking into action so that the schema is not violated.
606 This overlay is useful to test the behavior of clients when
607 server-generated erroneous and/or unusual responses occur.
610 H3: Return Code Configuration
618 It performs basic DN/data rewrite and
619 objectClass/attributeType mapping.
622 H3: Rewrite/Remap Configuration
630 This overlay implements the provider-side support for syncrepl
631 replication, including persistent search functionality
634 H3: Sync Provider Configuration
637 H2: Translucent Proxy
642 This overlay can be used with a backend database such as slapd-bdb (5)
643 to create a "translucent proxy".
645 Content of entries retrieved from a remote LDAP server can be partially
646 overridden by the database.
649 H3: Translucent Proxy Configuration
652 H2: Attribute Uniqueness
657 This overlay can be used with a backend database such as slapd-bdb (5)
658 to enforce the uniqueness of some or all attributes within a subtree.
661 H3: Attribute Uniqueness Configuration
669 This overlay can be used to enforce a specific order for the values
670 of an attribute when it is returned in a search.
673 H3: Value Sorting Configuration
682 H3: Example Scenarios