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# $OpenLDAP$
# Copyright 2007-2008 The OpenLDAP Foundation, All Rights Reserved.
# COPYING RESTRICTIONS APPLY, see COPYRIGHT.
H1: Overlays
Overlays are software components that provide hooks to functions analogous to
those provided by backends, which can be stacked on top of the backend calls
and as callbacks on top of backend responses to alter their behavior.
Overlays may be compiled statically into {{slapd}}, or when module support
is enabled, they may be dynamically loaded. Most of the overlays
are only allowed to be configured on individual databases, but some
may also be configured globally.
Essentially, they represent a means to:
* customize the behavior of existing backends without changing the backend
code and without requiring one to write a new custom backend with
complete functionality
* write functionality of general usefulness that can be applied to
different backend types
Overlays are usually documented by separate specific man pages in section 5;
the naming convention is
> slapo-<overlay name>
All distributed core overlays have a man page. Feel free to contribute to any,
if you think there is anything missing in describing the behavior of the component
and the implications of all the related configuration directives.
Official overlays are located in
> servers/slapd/overlays/
That directory also contains the file slapover.txt, which describes the
rationale of the overlay implementation, and may serve as guideline for the
development of custom overlays.
Contribware overlays are located in
> contrib/slapd-modules/<overlay name>/
along with other types of run-time loadable components; they are officially
distributed, but not maintained by the project.
They can be stacked on the frontend as well; this means that they can be
executed after a request is parsed and validated, but right before the
appropriate database is selected. The main purpose is to affect operations
regardless of the database they will be handled by, and, in some cases,
to influence the selection of the database by massaging the request DN.
All the current overlays in 2.4 are listed and described in detail in the
following sections.
H2: Access Logging
H3: Overview
This overlay can record accesses to a given backend database on another
database.
This allows all of the activity on a given database to be reviewed using arbitrary
LDAP queries, instead of just logging to local flat text files. Configuration
options are available for selecting a subset of operation types to log, and to
automatically prune older log records from the logging database. Log records
are stored with audit schema to assure their readability whether viewed as LDIF
or in raw form.
It is also used for {{SECT:delta-syncrepl replication}}
H3: Access Logging Configuration
The following is a basic example that implements Access Logging:
> database bdb
> suffix dc=example,dc=com
> ...
> overlay accesslog
> logdb cn=log
> logops writes reads
> logold (objectclass=person)
>
> database bdb
> suffix cn=log
> ...
> index reqStart eq
> access to *
> by dn.base="cn=admin,dc=example,dc=com" read
The following is an example used for {{SECT:delta-syncrepl replication}}:
> database hdb
> suffix cn=accesslog
> directory /usr/local/var/openldap-accesslog
> rootdn cn=accesslog
> index default eq
> index entryCSN,objectClass,reqEnd,reqResult,reqStart
Accesslog overlay definitions for the primary db
> database bdb
> suffix dc=example,dc=com
> ...
> overlay accesslog
> logdb cn=accesslog
> logops writes
> logsuccess TRUE
> # scan the accesslog DB every day, and purge entries older than 7 days
> logpurge 07+00:00 01+00:00
An example search result against {{B:cn=accesslog}} might look like:
> [ghenry@suretec ghenry]# ldapsearch -x -b cn=accesslog
> # extended LDIF
> #
> # LDAPv3
> # base <cn=accesslog> with scope subtree
> # filter: (objectclass=*)
> # requesting: ALL
> #
>
> # accesslog
> dn: cn=accesslog
> objectClass: auditContainer
> cn: accesslog
>
> # 20080110163829.000004Z, accesslog
> dn: reqStart=20080110163829.000004Z,cn=accesslog
> objectClass: auditModify
> reqStart: 20080110163829.000004Z
> reqEnd: 20080110163829.000005Z
> reqType: modify
> reqSession: 196696
> reqAuthzID: cn=admin,dc=suretecsystems,dc=com
> reqDN: uid=suretec-46022f8$,ou=Users,dc=suretecsystems,dc=com
> reqResult: 0
> reqMod: sambaPwdCanChange:- ###CENSORED###
> reqMod: sambaPwdCanChange:+ ###CENSORED###
> reqMod: sambaNTPassword:- ###CENSORED###
> reqMod: sambaNTPassword:+ ###CENSORED###
> reqMod: sambaPwdLastSet:- ###CENSORED###
> reqMod: sambaPwdLastSet:+ ###CENSORED###
> reqMod: entryCSN:= 20080110163829.095157Z#000000#000#000000
> reqMod: modifiersName:= cn=admin,dc=suretecsystems,dc=com
> reqMod: modifyTimestamp:= 20080110163829Z
>
> # search result
> search: 2
> result: 0 Success
>
> # numResponses: 3
> # numEntries: 2
For more information, please see {{slapo-accesslog(5)}} and the {{SECT:delta-syncrepl replication}} section.
H2: Audit Logging
The Audit Logging overlay can be used to record all changes on a given backend database to a specified log file.
H3: Overview
If the need arises whereby changes need to be logged as standard LDIF, then the auditlog overlay {{B:slapo-auditlog (5)}}
can be used. Full examples are available in the man page {{B:slapo-auditlog (5)}}
H3: Audit Logging Configuration
If the directory is running vi {{F:slapd.d}}, then the following LDIF could be used to add the overlay to the overlay list
in {{B:cn=config}} and set what file the {{TERM:LDIF}} gets logged to (adjust to suit)
> dn: olcOverlay=auditlog,olcDatabase={1}hdb,cn=config
> changetype: add
> objectClass: olcOverlayConfig
> objectClass: olcAuditLogConfig
> olcOverlay: auditlog
> olcAuditlogFile: /tmp/auditlog.ldif
In this example for testing, we are logging changes to {{F:/tmp/auditlog.ldif}}
A typical {{TERM:LDIF}} file created by {{B:slapo-auditlog (5)}} would look like:
> # add 1196797576 dc=suretecsystems,dc=com cn=admin,dc=suretecsystems,dc=com
> dn: dc=suretecsystems,dc=com
> changetype: add
> objectClass: dcObject
> objectClass: organization
> dc: suretecsystems
> o: Suretec Systems Ltd.
> structuralObjectClass: organization
> entryUUID: 1606f8f8-f06e-1029-8289-f0cc9d81e81a
> creatorsName: cn=admin,dc=suretecsystems,dc=com
> modifiersName: cn=admin,dc=suretecsystems,dc=com
> createTimestamp: 20051123130912Z
> modifyTimestamp: 20051123130912Z
> entryCSN: 20051123130912.000000Z#000001#000#000000
> auditContext: cn=accesslog
> # end add 1196797576
>
> # add 1196797577 dc=suretecsystems,dc=com cn=admin,dc=suretecsystems,dc=com
> dn: ou=Groups,dc=suretecsystems,dc=com
> changetype: add
> objectClass: top
> objectClass: organizationalUnit
> ou: Groups
> structuralObjectClass: organizationalUnit
> entryUUID: 160aaa2a-f06e-1029-828a-f0cc9d81e81a
> creatorsName: cn=admin,dc=suretecsystems,dc=com
> modifiersName: cn=admin,dc=suretecsystems,dc=com
> createTimestamp: 20051123130912Z
> modifyTimestamp: 20051123130912Z
> entryCSN: 20051123130912.000000Z#000002#000#000000
> # end add 1196797577
H2: Chaining
H3: Overview
The chain overlay provides basic chaining capability to the underlying
database.
What is chaining? It indicates the capability of a DSA to follow referrals on
behalf of the client, so that distributed systems are viewed as a single
virtual DSA by clients that are otherwise unable to "chase" (i.e. follow)
referrals by themselves.
The chain overlay is built on top of the ldap backend; it is compiled by
default when {{B:--enable-ldap}}.
H3: Chaining Configuration
In order to demonstrate how this overlay works, we shall discuss a typical
scenario which might be one master server and three Syncrepl slaves.
On each replica, add this near the top of the file (global), before any database
definitions:
> overlay chain
> chain-uri "ldap://ldapmaster.example.com"
> chain-idassert-bind bindmethod="simple"
> binddn="cn=Manager,dc=example,dc=com"
> credentials="<secret>"
> mode="self"
> chain-tls start
> chain-return-error TRUE
Add this below your {{syncrepl}} statement:
> updateref "ldap://ldapmaster.example.com/"
The {{B:chain-tls}} statement enables TLS from the slave to the ldap master.
The DITs are exactly the same between these machines, therefore whatever user
bound to the slave will also exist on the master. If that DN does not have
update privileges on the master, nothing will happen.
You will need to restart the slave after these changes. Then, if you are using
{{loglevel stats}} (256), you can monitor an {{ldapmodify}} on the slave and the master.
Now start an {{ldapmodify}} on the slave and watch the logs. You should expect
something like:
> 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)
> Sep 6 09:27:25 slave1 slapd[29274]: conn=11 op=0 STARTTLS
> Sep 6 09:27:25 slave1 slapd[29274]: conn=11 op=0 RESULT oid= err=0 text=
> Sep 6 09:27:25 slave1 slapd[29274]: conn=11 fd=31 TLS established tls_ssf=256 ssf=256
> Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=1 BIND dn="uid=user1,ou=people,dc=example,dc=com" method=128
> 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
> Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=1 RESULT tag=97 err=0 text=
> Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 MOD dn="uid=user1,ou=People,dc=example,dc=com"
> Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 MOD attr=mail
> Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=2 RESULT tag=103 err=0 text=
> Sep 6 09:27:28 slave1 slapd[29274]: conn=11 op=3 UNBIND
> Sep 6 09:27:28 slave1 slapd[29274]: conn=11 fd=31 closed
> Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: LDAP_RES_SEARCH_ENTRY(LDAP_SYNC_MODIFY)
> Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: be_search (0)
> Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: uid=user1,ou=People,dc=example,dc=com
> Sep 6 09:27:28 slave1 slapd[29274]: syncrepl_entry: be_modify (0)
And on the master you will see this:
> Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 PROXYAUTHZ dn="uid=user1,ou=people,dc=example,dc=com"
> Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 MOD dn="uid=user1,ou=People,dc=example,dc=com"
> Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 MOD attr=mail
> Sep 6 09:23:57 ldapmaster slapd[2961]: conn=55902 op=3 RESULT tag=103 err=0 text=
Note: You can clearly see the PROXYAUTHZ line on the master, indicating the
proper identity assertion for the update on the master. Also note the slave
immediately receiving the Syncrepl update from the master.
H3: Handling Chaining Errors
By default, if chaining fails, the original referral is returned to the client
under the assumption that the client might want to try and follow the referral.
With the following directive however, if the chaining fails at the provider
side, the actual error is returned to the client.
> chain-return-error TRUE
H2: Constraints
H3: Overview
This overlay enforces a regular expression constraint on all values
of specified attributes during an LDAP modify request that contains add or modify
commands. It is used to enforce a more rigorous syntax when the underlying attribute
syntax is too general.
H3: Constraint Configuration
Configuration via {{slapd.conf}}(5) would look like:
> overlay constraint
> constraint_attribute mail regex ^[:alnum:]+@mydomain.com$
> constraint_attribute title uri
> ldap:///dc=catalog,dc=example,dc=com?title?sub?(objectClass=titleCatalog)
A specification like the above would reject any {{mail}} attribute which did not
look like {{<alpha-numeric string>@mydomain.com}}.
It would also reject any title attribute whose values were not listed in the
title attribute of any {{titleCatalog}} entries in the given scope.
An example for use with {{cn=config}}:
> dn: olcOverlay=constraint,olcDatabase={1}hdb,cn=config
> changetype: add
> objectClass: olcOverlayConfig
> objectClass: olcConstraintConfig
> olcOverlay: constraint
> olcConstraintAttribute: mail regex ^[:alnum:]+@mydomain.com$
> olcConstraintAttribute: title uri ldap:///dc=catalog,dc=example,dc=com?title?sub?(objectClass=titleCatalog)
H2: Dynamic Directory Services
H3: Overview
The {{dds}} overlay to {{slapd}}(8) implements dynamic objects as per RFC 2589.
The name {{dds}} stands for Dynamic Directory Services. It allows to define
dynamic objects, characterized by the {{dynamicObject}} objectClass.
Dynamic objects have a limited lifetime, determined by a time-to-live (TTL)
that can be refreshed by means of a specific refresh extended operation. This
operation allows to set the Client Refresh Period (CRP), namely the period
between refreshes that is required to preserve the dynamic object from expiration.
The expiration time is computed by adding the requested TTL to the current time.
When dynamic objects reach the end of their lifetime without being further
refreshed, they are automatically {{deleted}}. There is no guarantee of immediate
deletion, so clients should not count on it.
H3: Dynamic Directory Service Configuration
A usage of dynamic objects might beto implement dynamic meetings; in this case,
all the participants to the meeting are allowed to refresh the meeting object,
but only the creator can delete it (otherwise it will be deleted when the TTL expires).
If we add the overlay to an example database, specifying a Max TTL of 1 day, a
min of 10 seconds, with a default TTL of 1 hour. We'll also specify an interval
of 5 seconds between expiration checks and a tolerance of 1 second (lifetime of
a dynamic object will be {{B:entryTtl + tolerance}}.
> overlay dds
> dds-max-ttl 1d
> dds-min-ttl 10s
> dds-default-ttl 1h
> dds-interval 5s
> dds-tolerance 1s
So let's create an entry using:
> dn: cn=Dynamic,dc=example,dc=com
> objectClass: inetOrgPerson
> objectClass: dynamicObject
> cn: Dynamic Object
> sn: Object
MORE coming.
H4: Dynamic Directory Service ACLs
Allow users to start a meeting and to join it; restrict refresh to the {{B:member}}s;
restrict delete to the creator:
> access to attrs=userPassword
> by self write
> by * read
>
> access to dn.base="cn=Meetings,dc=example,dc=com"
> attrs=children
> by users write
>
> access to dn.onelevel="cn=Meetings,dc=example,dc=com"
> attrs=entry
> by dnattr=creatorsName write
> by * read
>
> access to dn.onelevel="cn=Meetings,dc=example,dc=com"
> attrs=participant
> by dnattr=creatorsName write
> by users selfwrite
> by * read
>
> access to dn.onelevel="cn=Meetings,dc=example,dc=com"
> attrs=entryTtl
> by dnattr=member manage
> by * read
H2: Dynamic Groups
H3: Overview
This overlay extends the Compare operation to detect
members of a dynamic group. This overlay is now deprecated
as all of its functions are available using the
{{SECT:Dynamic Lists}} overlay.
H3: Dynamic Group Configuration
H2: Dynamic Lists
H3: Overview
This overlay allows expansion of dynamic groups and lists. Instead of having the
group members or list attributes hard coded, this overlay allows us to define
an LDAP search whose results will make up the group or list.
H3: Dynamic List Configuration
This module can behave both as a dynamic list and dynamic group, depending on
the configuration. The syntax is as follows:
> overlay dynlist
> dynlist-attrset <group-oc> <URL-ad> [member-ad]
The parameters to the {{F:dynlist-attrset}} directive have the following meaning:
* {{F:<group-oc>}}: specifies which object class triggers the subsequent LDAP search.
Whenever an entry with this object class is retrieved, the search is performed.
* {{F:<URL-ad>}}: is the name of the attribute which holds the search URI. It
has to be a subtype of {{F:labeledURI}}. The attributes and values present in
the search result are added to the entry unless {{F:member-ad}} is used (see
below).
* {{F:member-ad}}: if present, changes the overlay behavior into a dynamic group.
Instead of inserting the results of the search in the entry, the distinguished name
of the results are added as values of this attribute.
Here is an example which will allow us to have an email alias which automatically
expands to all user's emails according to our LDAP filter:
In {{slapd.conf}}(5):
> overlay dynlist
> dynlist-attrset nisMailAlias labeledURI
This means that whenever an entry which has the {{F:nisMailAlias}} object class is
retrieved, the search specified in the {{F:labeledURI}} attribute is performed.
Let's say we have this entry in our directory:
> cn=all,ou=aliases,dc=example,dc=com
> cn: all
> objectClass: nisMailAlias
> labeledURI: ldap:///ou=People,dc=example,dc=com?mail?one?(objectClass=inetOrgPerson)
If this entry is retrieved, the search specified in {{F:labeledURI}} will be
performed and the results will be added to the entry just as if they have always
been there. In this case, the search filter selects all entries directly
under {{F:ou=People}} that have the {{F:inetOrgPerson}} object class and retrieves
the {{F:mail}} attribute, if it exists.
This is what gets added to the entry when we have two users under {{F:ou=People}}
that match the filter:
!import "allmail-en.png"; align="center"; title="Dynamic list for email aliases"
FT[align="Center"] Figure X.Y: Dynamic List for all emails
The configuration for a dynamic group is similar. Let's see an example which would
automatically populate an {{F:allusers}} group with all the user accounts in the
directory.
In {{F:slapd.conf}}(5):
> overlay dynlist
> dynlist-attrset groupOfNames labeledURI member
Let's apply it to the following entry:
> cn=allusers,ou=group,dc=example,dc=com
> cn: all
> objectClass: groupOfNames
> labeledURI: ldap:///ou=people,dc=example,dc=com??one?(objectClass=inetOrgPerson)
The behavior is similar to the dynamic list configuration we had before:
whenever an entry with the {{F:groupOfNames}} object class is retrieved, the
search specified in the {{F:labeledURI}} attribute is performed. But this time,
only the distinguished names of the results are added, and as values of the
{{F:member}} attribute.
This is what we get:
!import "allusersgroup-en.png"; align="center"; title="Dynamic group for all users"
FT[align="Center"] Figure X.Y: Dynamic Group for all users
Note that a side effect of this scheme of dynamic groups is that the members
need to be specified as full DNs. So, if you are planning in using this for
{{F:posixGroup}}s, be sure to use RFC2307bis and some attribute which can hold
distinguished names. The {{F:memberUid}} attribute used in the {{F:posixGroup}}
object class can hold only names, not DNs, and is therefore not suitable for
dynamic groups.
H2: Reverse Group Membership Maintenance
H3: Overview
In some scenarios, it may be desirable for a client to be able to determine
which groups an entry is a member of, without performing an additional search.
Examples of this are applications using the {{TERM:DIT}} for access control
based on group authorization.
The {{B:memberof}} overlay updates an attribute (by default {{B:memberOf}}) whenever
changes occur to the membership attribute (by default {{B:member}}) of entries of the
objectclass (by default {{B:groupOfNames}}) configured to trigger updates.
Thus, it provides maintenance of the list of groups an entry is a member of,
when usual maintenance of groups is done by modifying the members on the group
entry.
H3: Member Of Configuration
The typical use of this overlay requires just enabling the overlay for a
specific database. For example, with the following minimal slapd.conf:
> include /usr/share/openldap/schema/core.schema
> include /usr/share/openldap/schema/cosine.schema
> modulepath /usr/lib/openldap
> moduleload memberof.la
> authz-regexp "gidNumber=0\\\+uidNumber=0,cn=peercred,cn=external,cn=auth"
> "cn=Manager,dc=example,dc=com"
> database bdb
> suffix "dc=example,dc=com"
> rootdn "cn=Manager,dc=example,dc=com"
> rootpw secret
> directory /var/lib/ldap2.4
> checkpoint 256 5
> index objectClass eq
> index uid eq,sub
>
> overlay memberof
adding the following ldif:
> cat memberof.ldif
> dn: dc=example,dc=com
> objectclass: domain
> dc: example
>
> dn: ou=Group,dc=example,dc=com
> objectclass: organizationalUnit
> ou: Group
>
> dn: ou=People,dc=example,dc=com
> objectclass: organizationalUnit
> ou: People
>
> dn: uid=test1,ou=People,dc=example,dc=com
> objectclass: account
> uid: test1
>
> dn: cn=testgroup,ou=Group,dc=example,dc=com
> objectclass: groupOfNames
> cn: testgroup
> member: uid=test1,ou=People,dc=example,dc=com
Results in the following output from a search on the test1 user:
> # ldapsearch -LL -Y EXTERNAL -H ldapi:/// "(uid=test1)" -b dc=example,dc=com memberOf
> SASL/EXTERNAL authentication started
> SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
> SASL SSF: 0
> version: 1
>
> dn: uid=test1,ou=People,dc=example,dc=com
> memberOf: cn=testgroup,ou=Group,dc=example,dc=com
Note that the {{B:memberOf}} attribute is an operational attribute, so it must be
requested explicitly.
H2: The Proxy Cache Engine
{{TERM:LDAP}} servers typically hold one or more subtrees of a
{{TERM:DIT}}. Replica (or shadow) servers hold shadow copies of
entries held by one or more master servers. Changes are propagated
from the master server to replica (slave) servers using LDAP Sync
replication. An LDAP cache is a special type of replica which holds
entries corresponding to search filters instead of subtrees.
H3: Overview
The proxy cache extension of slapd is designed to improve the
responsiveness of the ldap and meta backends. It handles a search
request (query)
by first determining whether it is contained in any cached search
filter. Contained requests are answered from the proxy cache's local
database. Other requests are passed on to the underlying ldap or
meta backend and processed as usual.
E.g. {{EX:(shoesize>=9)}} is contained in {{EX:(shoesize>=8)}} and
{{EX:(sn=Richardson)}} is contained in {{EX:(sn=Richards*)}}
Correct matching rules and syntaxes are used while comparing
assertions for query containment. To simplify the query containment
problem, a list of cacheable "templates" (defined below) is specified
at configuration time. A query is cached or answered only if it
belongs to one of these templates. The entries corresponding to
cached queries are stored in the proxy cache local database while
its associated meta information (filter, scope, base, attributes)
is stored in main memory.
A template is a prototype for generating LDAP search requests.
Templates are described by a prototype search filter and a list of
attributes which are required in queries generated from the template.
The representation for prototype filter is similar to {{REF:RFC4515}},
except that the assertion values are missing. Examples of prototype
filters are: (sn=),(&(sn=)(givenname=)) which are instantiated by
search filters (sn=Doe) and (&(sn=Doe)(givenname=John)) respectively.
The cache replacement policy removes the least recently used (LRU)
query and entries belonging to only that query. Queries are allowed
a maximum time to live (TTL) in the cache thus providing weak
consistency. A background task periodically checks the cache for
expired queries and removes them.
The Proxy Cache paper
({{URL:http://www.openldap.org/pub/kapurva/proxycaching.pdf}}) provides
design and implementation details.
H3: Proxy Cache Configuration
The cache configuration specific directives described below must
appear after a {{EX:overlay proxycache}} directive within a
{{EX:"database meta"}} or {{EX:database ldap}} section of
the server's {{slapd.conf}}(5) file.
H4: Setting cache parameters
> proxyCache <DB> <maxentries> <nattrsets> <entrylimit> <period>
This directive enables proxy caching and sets general cache
parameters. The <DB> parameter specifies which underlying database
is to be used to hold cached entries. It should be set to
{{EX:bdb}} or {{EX:hdb}}. The <maxentries> parameter specifies the
total number of entries which may be held in the cache. The
<nattrsets> parameter specifies the total number of attribute sets
(as specified by the {{EX:proxyAttrSet}} directive) that may be
defined. The <entrylimit> parameter specifies the maximum number of
entries in a cacheable query. The <period> specifies the consistency
check period (in seconds). In each period, queries with expired
TTLs are removed.
H4: Defining attribute sets
> proxyAttrset <index> <attrs...>
Used to associate a set of attributes to an index. Each attribute
set is associated with an index number from 0 to <numattrsets>-1.
These indices are used by the proxyTemplate directive to define
cacheable templates.
H4: Specifying cacheable templates
> proxyTemplate <prototype_string> <attrset_index> <TTL>
Specifies a cacheable template and the "time to live" (in sec) <TTL>
for queries belonging to the template. A template is described by
its prototype filter string and set of required attributes identified
by <attrset_index>.
H4: Example
An example {{slapd.conf}}(5) database section for a caching server
which proxies for the {{EX:"dc=example,dc=com"}} subtree held
at server {{EX:ldap.example.com}}.
> database ldap
> suffix "dc=example,dc=com"
> rootdn "dc=example,dc=com"
> uri ldap://ldap.example.com/
> overlay proxycache
> proxycache bdb 100000 1 1000 100
> proxyAttrset 0 mail postaladdress telephonenumber
> proxyTemplate (sn=) 0 3600
> proxyTemplate (&(sn=)(givenName=)) 0 3600
> proxyTemplate (&(departmentNumber=)(secretary=*)) 0 3600
>
> cachesize 20
> directory ./testrun/db.2.a
> index objectClass eq
> index cn,sn,uid,mail pres,eq,sub
H5: Cacheable Queries
A LDAP search query is cacheable when its filter matches one of the
templates as defined in the "proxyTemplate" statements and when it references
only the attributes specified in the corresponding attribute set.
In the example above the attribute set number 0 defines that only the
attributes: {{EX:mail postaladdress telephonenumber}} are cached for the following
proxyTemplates.
H5: Examples:
> Filter: (&(sn=Richard*)(givenName=jack))
> Attrs: mail telephoneNumber
is cacheable, because it matches the template {{EX:(&(sn=)(givenName=))}} and its
attributes are contained in proxyAttrset 0.
> Filter: (&(sn=Richard*)(telephoneNumber))
> Attrs: givenName
is not cacheable, because the filter does not match the template,
nor is the attribute givenName stored in the cache
> Filter: (|(sn=Richard*)(givenName=jack))
> Attrs: mail telephoneNumber
is not cacheable, because the filter does not match the template ( logical
OR "|" condition instead of logical AND "&" )
H2: Password Policies
H3: Overview
This overlay provides a variety of password control mechanisms,
e.g. password aging, password reuse and duplication control, mandatory
password resets, etc.
H3: Password Policy Configuration
H2: Referential Integrity
H3: Overview
This overlay can be used with a backend database such as slapd-bdb(5)
to maintain the cohesiveness of a schema which utilizes reference
attributes.
Whenever a {{modrdn}} or {{delete}} is performed, that is, when an entry's DN
is renamed or an entry is removed, the server will search the directory for
references to this DN (in selected attributes: see below) and update them
accordingly. If it was a {{delete}} operation, the reference is deleted. If it
was a {{modrdn}} operation, then the reference is updated with the new DN.
For example, a very common administration task is to maintain group membership
lists, specially when users are removed from the directory. When an
user account is deleted or renamed, all groups this user is a member of have to be
updated. LDAP administrators usually have scripts for that. But we can use the
{{F:refint}} overlay to automate this task. In this example, if the user is
removed from the directory, the overlay will take care to remove the user from
all the groups he/she was a member of. No more scripting for this.
H3: Referential Integrity Configuration
The configuration for this overlay is as follows:
> overlay refint
> refint_attributes <attribute [attribute ...]>
> refint_nothing <string>
* {{F:refint_attributes}}: this parameter specifies a space separated list of
attributes which will have the referential integrity maintained. When an entry is
removed or has its DN renamed, the server will do an internal search for any of the
{{F:refint_attributes}} that point to the affected DN and update them accordingly. IMPORTANT:
the attributes listed here must have the {{F:distinguishedName}} syntax, that is,
hold DNs as values.
* {{F:refint_nothing}}: some times, while trying to maintain the referential
integrity, the server has to remove the last attribute of its kind from an
entry. This may be prohibited by the schema: for example, the
{{F:groupOfNames}} object class requires at least one member. In these cases,
the server will add the attribute value specified in {{F:refint_nothing}}
to the entry.
To illustrate this overlay, we will use the group membership scenario.
In {{F:slapd.conf}}:
> overlay refint
> refint_attributes member
> refint_nothing "cn=admin,dc=example,dc=com"
This configuration tells the overlay to maintain the referential integrity of the {{F:member}}
attribute. This attribute is used in the {{F:groupOfNames}} object class which always needs
a member, so we add the {{F:refint_nothing}} directive to fill in the group with a standard
member should all the members vanish.
If we have the following group membership, the refint overlay will
automatically remove {{F:john}} from the group if his entry is removed from the
directory:
!import "refint.png"; align="center"; title="Group membership"
FT[align="Center"] Figure X.Y: Maintaining referential integrity in groups
Notice that if we rename ({{F:modrdn}}) the {{F:john}} entry to, say, {{F:jsmith}}, the refint
overlay will also rename the reference in the {{F:member}} attribute, so the group membership
stays correct.
If we removed all users from the directory who are a member of this group, then the end result
would be a single member in the group: {{F:cn=admin,dc=example,dc=com}}. This is the
{{F:refint_nothing}} parameter kicking into action so that the schema is not violated.
H2: Return Code
H3: Overview
This overlay is useful to test the behavior of clients when
server-generated erroneous and/or unusual responses occur.
H3: Return Code Configuration
H2: Rewrite/Remap
H3: Overview
It performs basic DN/data rewrite and
objectClass/attributeType mapping.
H3: Rewrite/Remap Configuration
H2: Sync Provider
H3: Overview
This overlay implements the provider-side support for syncrepl
replication, including persistent search functionality
H3: Sync Provider Configuration
H2: Translucent Proxy
H3: Overview
This overlay can be used with a backend database such as slapd-bdb (5)
to create a "translucent proxy".
Content of entries retrieved from a remote LDAP server can be partially
overridden by the database.
H3: Translucent Proxy Configuration
H2: Attribute Uniqueness
H3: Overview
This overlay can be used with a backend database such as slapd-bdb (5)
to enforce the uniqueness of some or all attributes within a subtree.
H3: Attribute Uniqueness Configuration
H2: Value Sorting
H3: Overview
This overlay can be used to enforce a specific order for the values
of an attribute when it is returned in a search.
H3: Value Sorting Configuration
H2: Overlay Stacking
H3: Overview
Overlays can be stacked, which means that more than one overlay
can be instantiated for each database, or for the frontend.
As a consequence, each overlay's function is called, if defined,
when overlay execution is invoked.
Multiple overlays are executed in reverse order (it's a stack, all in all)
with respect to their definition in slapd.conf (5), or with respect
to their ordering in the config database, as documented in slapd-config (5).
H3: Example Scenarios
H4: Samba
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