5. Configuring slapd

Once the software has been built and installed, you are ready to configure slapd(8) for use at your site. Unlike previous OpenLDAP releases, the slapd(8) runtime configuration in 2.3 (and later) is fully LDAP-enabled and can be managed using the standard LDAP operations with data in LDIF. The LDAP configuration engine allows all of slapd's configuration options to be changed on the fly, generally without requiring a server restart for the changes to take effect. The old style slapd.conf(5) file is still supported, but must be converted to the new slapd-config(5) format to allow runtime changes to be saved. While the old style configuration uses a single file, normally installed as /usr/local/etc/openldap/slapd.conf, the new style uses a slapd backend database to store the configuration. The configuration database normally resides in the /usr/local/etc/openldap/slapd.d directory. When converting from the slapd.conf format to slapd.d format, any include files will also be integrated into the resulting configuration database.

An alternate configuration directory (or file) can be specified via a command-line option to slapd(8). This chapter describes the general format of the configuration system, followed by a detailed description of commonly used config settings.


Note: some of the backends and of the distributed overlays do not support runtime configuration yet. In those cases, the old style slapd.conf(5) file must be used.


5.1. Configuration Layout

The slapd configuration is stored as a special LDAP directory with a predefined schema and DIT. There are specific objectClasses used to carry global configuration options, schema definitions, backend and database definitions, and assorted other items. A sample config tree is shown in Figure 5.1.

Figure 5.1: Sample configuration tree.

Other objects may be part of the configuration but were omitted from the illustration for clarity.

The slapd-config configuration tree has a very specific structure. The root of the tree is named cn=config and contains global configuration settings. Additional settings are contained in separate child entries:

The usual rules for LDIF files apply to the configuration information: Comment lines beginning with a '#' character are ignored. If a line begins with a single space, it is considered a continuation of the previous line (even if the previous line is a comment) and the single leading space is removed. Entries are separated by blank lines.

The general layout of the config LDIF is as follows:

        # global configuration settings
        dn: cn=config
        objectClass: olcGlobal
        cn: config
        <global config settings>

        # schema definitions
        dn: cn=schema,cn=config
        objectClass: olcSchemaConfig
        cn: schema
        <system schema>

        dn: cn={X}core,cn=schema,cn=config
        objectClass: olcSchemaConfig
        cn: {X}core
        <core schema>

        # additional user-specified schema
        ...

        # backend definitions
        dn: olcBackend=<typeA>,cn=config
        objectClass: olcBackendConfig
        olcBackend: <typeA>
        <backend-specific settings>

        # database definitions
        dn: olcDatabase={X}<typeA>,cn=config
        objectClass: olcDatabaseConfig
        olcDatabase: {X}<typeA>
        <database-specific settings>

        # subsequent definitions and settings
        ...

Some of the entries listed above have a numeric index "{X}" in their names. While most configuration settings have an inherent ordering dependency (i.e., one setting must take effect before a subsequent one may be set), LDAP databases are inherently unordered. The numeric index is used to enforce a consistent ordering in the configuration database, so that all ordering dependencies are preserved. In most cases the index does not have to be provided; it will be automatically generated based on the order in which entries are created.

Configuration directives are specified as values of individual attributes. Most of the attributes and objectClasses used in the slapd configuration have a prefix of "olc" (OpenLDAP Configuration) in their names. Generally there is a one-to-one correspondence between the attributes and the old-style slapd.conf configuration keywords, using the keyword as the attribute name, with the "olc" prefix attached.

A configuration directive may take arguments. If so, the arguments are separated by white space. If an argument contains white space, the argument should be enclosed in double quotes "like this". In the descriptions that follow, arguments that should be replaced by actual text are shown in brackets <>.

The distribution contains an example configuration file that will be installed in the /usr/local/etc/openldap directory. A number of files containing schema definitions (attribute types and object classes) are also provided in the /usr/local/etc/openldap/schema directory.


5.2. Configuration Directives

This section details commonly used configuration directives. For a complete list, see the slapd-config(5) manual page. This section will treat the configuration directives in a top-down order, starting with the global directives in the cn=config entry. Each directive will be described along with its default value (if any) and an example of its use.

5.2.1. cn=config

Directives contained in this entry generally apply to the server as a whole. Most of them are system or connection oriented, not database related. This entry must have the olcGlobal objectClass.

5.2.1.1. olcIdleTimeout: <integer>

Specify the number of seconds to wait before forcibly closing an idle client connection. A value of 0, the default, disables this feature.

5.2.1.2. olcLogLevel: <level>

This directive specifies the level at which debugging statements and operation statistics should be syslogged (currently logged to the syslogd(8) LOG_LOCAL4 facility). You must have configured OpenLDAP --enable-debug (the default) for this to work (except for the two statistics levels, which are always enabled). Log levels may be specified as integers or by keyword. Multiple log levels may be used and the levels are additive. To display what levels correspond to what kind of debugging, invoke slapd with -? or consult the table below. The possible values for <level> are:

Table 5.1: Debugging Levels
Level Keyword Description
-1 Any enable all debugging
0   no debugging
1 Trace trace function calls
2 Packets debug packet handling
4 Args heavy trace debugging
8 Conns connection management
16 BER print out packets sent and received
32 Filter search filter processing
64 Config configuration processing
128 ACL access control list processing
256 Stats stats log connections/operations/results
512 Stats2 stats log entries sent
1024 Shell print communication with shell backends
2048 Parse print entry parsing debugging
4096 Cache database cache processing
8192 Index database indexing
16384 Sync syncrepl consumer processing

Example:

 olcLogLevel: -1

This will cause lots and lots of debugging information to be logged.

 olcLogLevel: Conns Filter

Just log the connection and search filter processing.

Default:

 olcLogLevel: Stats

5.2.1.3. olcReferral <URI>

This directive specifies the referral to pass back when slapd cannot find a local database to handle a request.

Example:

        olcReferral: ldap://root.openldap.org

This will refer non-local queries to the global root LDAP server at the OpenLDAP Project. Smart LDAP clients can re-ask their query at that server, but note that most of these clients are only going to know how to handle simple LDAP URLs that contain a host part and optionally a distinguished name part.

5.2.1.4. Sample Entry

dn: cn=config
objectClass: olcGlobal
cn: config
olcIdleTimeout: 30
olcLogLevel: Stats
olcReferral: ldap://root.openldap.org

5.2.2. cn=module

If support for dynamically loaded modules was enabled when configuring slapd, cn=module entries may be used to specify sets of modules to load. Module entries must have the olcModuleList objectClass.

5.2.2.1. olcModuleLoad: <filename>

Specify the name of a dynamically loadable module to load. The filename may be an absolute path name or a simple filename. Non-absolute names are searched for in the directories specified by the olcModulePath directive.

5.2.2.2. olcModulePath: <pathspec>

Specify a list of directories to search for loadable modules. Typically the path is colon-separated but this depends on the operating system.

5.2.2.3. Sample Entries

dn: cn=module{0},cn=config
objectClass: olcModuleList
cn: module{0}
olcModuleLoad: /usr/local/lib/smbk5pwd.la

dn: cn=module{1},cn=config
objectClass: olcModuleList
cn: module{1}
olcModulePath: /usr/local/lib:/usr/local/lib/slapd
olcModuleLoad: accesslog.la
olcModuleLoad: pcache.la

5.2.3. cn=schema

The cn=schema entry holds all of the schema definitions that are hard-coded in slapd. As such, the values in this entry are generated by slapd so no schema values need to be provided in the config file. The entry must still be defined though, to serve as a base for the user-defined schema to add in underneath. Schema entries must have the olcSchemaConfig objectClass.

5.2.3.1. olcAttributeTypes: <RFC4512 Attribute Type Description>

This directive defines an attribute type. Please see the Schema Specification chapter for information regarding how to use this directive.

5.2.3.2. olcObjectClasses: <RFC4512 Object Class Description>

This directive defines an object class. Please see the Schema Specification chapter for information regarding how to use this directive.

5.2.3.3. Sample Entries

dn: cn=schema,cn=config
objectClass: olcSchemaConfig
cn: schema

dn: cn=test,cn=schema,cn=config
objectClass: olcSchemaConfig
cn: test
olcAttributeTypes: ( 1.1.1
  NAME 'testAttr'
  EQUALITY integerMatch
  SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 )
olcAttributeTypes: ( 1.1.2 NAME 'testTwo' EQUALITY caseIgnoreMatch
  SUBSTR caseIgnoreSubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.44 )
olcObjectClasses: ( 1.1.3 NAME 'testObject'
  MAY ( testAttr $ testTwo ) AUXILIARY )

5.2.4. Backend-specific Directives

Backend directives apply to all database instances of the same type and, depending on the directive, may be overridden by database directives. Backend entries must have the olcBackendConfig objectClass.

5.2.4.1. olcBackend: <type>

This directive names a backend-specific configuration entry. <type> should be one of the supported backend types listed in Table 5.2.

Table 5.2: Database Backends
Types Description
bdb Berkeley DB transactional backend
config Slapd configuration backend
dnssrv DNS SRV backend
hdb Hierarchical variant of bdb backend
ldap Lightweight Directory Access Protocol (Proxy) backend
ldif Lightweight Data Interchange Format backend
meta Meta Directory backend
monitor Monitor backend
passwd Provides read-only access to passwd(5)
perl Perl Programmable backend
shell Shell (extern program) backend
sql SQL Programmable backend

Example:

        olcBackend: bdb

There are no other directives defined for this entry. Specific backend types may define additional attributes for their particular use but so far none have ever been defined. As such, these directives usually do not appear in any actual configurations.

5.2.4.2. Sample Entry

 dn: olcBackend=bdb,cn=config
 objectClass: olcBackendConfig
 olcBackend: bdb

5.2.5. Database-specific Directives

Directives in this section are supported by every type of database. Database entries must have the olcDatabaseConfig objectClass.

5.2.5.1. olcDatabase: [{<index>}]<type>

This directive names a specific database instance. The numeric {<index>} may be provided to distinguish multiple databases of the same type. Usually the index can be omitted, and slapd will generate it automatically. <type> should be one of the supported backend types listed in Table 5.2 or the frontend type.

The frontend is a special database that is used to hold database-level options that should be applied to all the other databases. Subsequent database definitions may also override some frontend settings.

The config database is also special; both the config and the frontend databases are always created implicitly even if they are not explicitly configured, and they are created before any other databases.

Example:

        olcDatabase: bdb

This marks the beginning of a new BDB database instance.

5.2.5.2. olcAccess: to <what> [ by <who> [<accesslevel>] [<control>] ]+

This directive grants access (specified by <accesslevel>) to a set of entries and/or attributes (specified by <what>) by one or more requestors (specified by <who>). See the Access Control section of this chapter for a summary of basic usage.


Note: If no olcAccess directives are specified, the default access control policy, to * by * read, allows all users (both authenticated and anonymous) read access.


Note: Access controls defined in the frontend are appended to all other databases' controls.

5.2.5.3. olcReadonly { TRUE | FALSE }

This directive puts the database into "read-only" mode. Any attempts to modify the database will return an "unwilling to perform" error.

Default:

        olcReadonly: FALSE

5.2.5.4. olcRootDN: <DN>

This directive specifies the DN that is not subject to access control or administrative limit restrictions for operations on this database. The DN need not refer to an entry in this database or even in the directory. The DN may refer to a SASL identity.

Entry-based Example:

        olcRootDN: "cn=Manager,dc=example,dc=com"

SASL-based Example:

        olcRootDN: "uid=root,cn=example.com,cn=digest-md5,cn=auth"

See the SASL Authentication section for information on SASL authentication identities.

5.2.5.5. olcRootPW: <password>

This directive can be used to specify a password for the DN for the rootdn (when the rootdn is set to a DN within the database).

Example:

        olcRootPW: secret

It is also permissible to provide a hash of the password in RFC2307 form. slappasswd(8) may be used to generate the password hash.

Example:

        olcRootPW: {SSHA}ZKKuqbEKJfKSXhUbHG3fG8MDn9j1v4QN

The hash was generated using the command slappasswd -s secret.

5.2.5.6. olcSizeLimit: <integer>

This directive specifies the maximum number of entries to return from a search operation.

Default:

        olcSizeLimit: 500

5.2.5.7. olcSuffix: <dn suffix>

This directive specifies the DN suffix of queries that will be passed to this backend database. Multiple suffix lines can be given, and usually at least one is required for each database definition. (Some backend types, such as frontend and monitor use a hard-coded suffix which may not be overridden in the configuration.)

Example:

        olcSuffix: "dc=example,dc=com"

Queries with a DN ending in "dc=example,dc=com" will be passed to this backend.


Note: When the backend to pass a query to is selected, slapd looks at the suffix value(s) in each database definition in the order in which they were configured. Thus, if one database suffix is a prefix of another, it must appear after it in the configuration.

5.2.5.8. olcSyncrepl

        olcSyncrepl: rid=<replica ID>
                provider=ldap[s]://<hostname>[:port]
                [type=refreshOnly|refreshAndPersist]
                [interval=dd:hh:mm:ss]
                [retry=[<retry interval> <# of retries>]+]
                searchbase=<base DN>
                [filter=<filter str>]
                [scope=sub|one|base]
                [attrs=<attr list>]
                [attrsonly]
                [sizelimit=<limit>]
                [timelimit=<limit>]
                [schemachecking=on|off]
                [bindmethod=simple|sasl]
                [binddn=<DN>]
                [saslmech=<mech>]
                [authcid=<identity>]
                [authzid=<identity>]
                [credentials=<passwd>]
                [realm=<realm>]
                [secprops=<properties>]
                [starttls=yes|critical]
                [tls_cert=<file>]
                [tls_key=<file>]
                [tls_cacert=<file>]
                [tls_cacertdir=<path>]
                [tls_reqcert=never|allow|try|demand]
                [tls_ciphersuite=<ciphers>]
                [tls_crlcheck=none|peer|all]
                [logbase=<base DN>]
                [logfilter=<filter str>]
                [syncdata=default|accesslog|changelog]

This directive specifies the current database as a replica of the master content by establishing the current slapd(8) as a replication consumer site running a syncrepl replication engine. The master database is located at the replication provider site specified by the provider parameter. The replica database is kept up-to-date with the master content using the LDAP Content Synchronization protocol. See RFC4533 for more information on the protocol.

The rid parameter is used for identification of the current syncrepl directive within the replication consumer server, where <replica ID> uniquely identifies the syncrepl specification described by the current syncrepl directive. <replica ID> is non-negative and is no more than three decimal digits in length.

The provider parameter specifies the replication provider site containing the master content as an LDAP URI. The provider parameter specifies a scheme, a host and optionally a port where the provider slapd instance can be found. Either a domain name or IP address may be used for <hostname>. Examples are ldap://provider.example.com:389 or ldaps://192.168.1.1:636. If <port> is not given, the standard LDAP port number (389 or 636) is used. Note that the syncrepl uses a consumer-initiated protocol, and hence its specification is located at the consumer site, whereas the replica specification is located at the provider site. syncrepl and replica directives define two independent replication mechanisms. They do not represent the replication peers of each other.

The content of the syncrepl replica is defined using a search specification as its result set. The consumer slapd will send search requests to the provider slapd according to the search specification. The search specification includes searchbase, scope, filter, attrs, attrsonly, sizelimit, and timelimit parameters as in the normal search specification. The searchbase parameter has no default value and must always be specified. The scope defaults to sub, the filter defaults to (objectclass=*), attrs defaults to "*,+" to replicate all user and operational attributes, and attrsonly is unset by default. Both sizelimit and timelimit default to "unlimited", and only positive integers or "unlimited" may be specified.

The LDAP Content Sychronization protocol has two operation types: refreshOnly and refreshAndPersist. The operation type is specified by the type parameter. In the refreshOnly operation, the next synchronization search operation is periodically rescheduled at an interval time after each synchronization operation finishes. The interval is specified by the interval parameter. It is set to one day by default. In the refreshAndPersist operation, a synchronization search remains persistent in the provider slapd instance. Further updates to the master replica will generate searchResultEntry to the consumer slapd as the search responses to the persistent synchronization search.

If an error occurs during replication, the consumer will attempt to reconnect according to the retry parameter which is a list of the <retry interval> and <# of retries> pairs. For example, retry="60 10 300 3" lets the consumer retry every 60 seconds for the first 10 times and then retry every 300 seconds for the next three times before stop retrying. + in <# of retries> means indefinite number of retries until success.

The schema checking can be enforced at the LDAP Sync consumer site by turning on the schemachecking parameter. If it is turned on, every replicated entry will be checked for its schema as the entry is stored into the replica content. Every entry in the replica should contain those attributes required by the schema definition. If it is turned off, entries will be stored without checking schema conformance. The default is off.

The binddn parameter gives the DN to bind as for the syncrepl searches to the provider slapd. It should be a DN which has read access to the replication content in the master database.

The bindmethod is simple or sasl, depending on whether simple password-based authentication or SASL authentication is to be used when connecting to the provider slapd instance.

Simple authentication should not be used unless adequate data integrity and confidentiality protections are in place (e.g. TLS or IPsec). Simple authentication requires specification of binddn and credentials parameters.

SASL authentication is generally recommended. SASL authentication requires specification of a mechanism using the saslmech parameter. Depending on the mechanism, an authentication identity and/or credentials can be specified using authcid and credentials, respectively. The authzid parameter may be used to specify an authorization identity.

The realm parameter specifies a realm which a certain mechanisms authenticate the identity within. The secprops parameter specifies Cyrus SASL security properties.

The starttls parameter specifies use of the StartTLS extended operation to establish a TLS session before authenticating to the provider. If the critical argument is supplied, the session will be aborted if the StartTLS request fails. Otherwise the syncrepl session continues without TLS. Note that the main slapd TLS settings are not used by the syncrepl engine; by default the TLS parameters from a ldap.conf(5) configuration file will be used. TLS settings may be specified here, in which case any ldap.conf(5) settings will be completely ignored.

Rather than replicating whole entries, the consumer can query logs of data modifications. This mode of operation is referred to as delta syncrepl. In addition to the above parameters, the logbase and logfilter parameters must be set appropriately for the log that will be used. The syncdata parameter must be set to either "accesslog" if the log conforms to the slapo-accesslog(5) log format, or "changelog" if the log conforms to the obsolete changelog format. If the syncdata parameter is omitted or set to "default" then the log parameters are ignored.

The syncrepl replication mechanism is supported by the bdb and hdb backends.

See the LDAP Sync Replication chapter of this guide for more information on how to use this directive.

5.2.5.9. olcTimeLimit: <integer>

This directive specifies the maximum number of seconds (in real time) slapd will spend answering a search request. If a request is not finished in this time, a result indicating an exceeded timelimit will be returned.

Default:

        olcTimeLimit: 3600

5.2.5.10. olcUpdateref: <URL>

This directive is only applicable in a slave slapd. It specifies the URL to return to clients which submit update requests upon the replica. If specified multiple times, each URL is provided.

Example:

        olcUpdateref:   ldap://master.example.net

5.2.5.11. Sample Entries

dn: olcDatabase=frontend,cn=config
objectClass: olcDatabaseConfig
objectClass: olcFrontendConfig
olcDatabase: frontend
olcReadOnly: FALSE

dn: olcDatabase=config,cn=config
objectClass: olcDatabaseConfig
olcDatabase: config
olcRootDN: cn=Manager,dc=example,dc=com

5.2.6. BDB and HDB Database Directives

Directives in this category apply to both the BDB and the HDB database. They are used in an olcDatabase entry in addition to the generic database directives defined above. For a complete reference of BDB/HDB configuration directives, see slapd-bdb(5). In addition to the olcDatabaseConfig objectClass, BDB and HDB database entries must have the olcBdbConfig and olcHdbConfig objectClass, respectively.

5.2.6.1. olcDbDirectory: <directory>

This directive specifies the directory where the BDB files containing the database and associated indices live.

Default:

        olcDbDirectory: /usr/local/var/openldap-data

5.2.6.2. olcDbCachesize: <integer>

This directive specifies the size in entries of the in-memory cache maintained by the BDB backend database instance.

Default:

        olcDbCachesize: 1000

5.2.6.3. olcDbCheckpoint: <kbyte> <min>

This directive specifies how often to checkpoint the BDB transaction log. A checkpoint operation flushes the database buffers to disk and writes a checkpoint record in the log. The checkpoint will occur if either <kbyte> data has been written or <min> minutes have passed since the last checkpoint. Both arguments default to zero, in which case they are ignored. When the <min> argument is non-zero, an internal task will run every <min> minutes to perform the checkpoint. See the Berkeley DB reference guide for more details.

Example:

        olcDbCheckpoint: 1024 10

5.2.6.4. olcDbConfig: <DB_CONFIG setting>

This attribute specifies a configuration directive to be placed in the DB_CONFIG file of the database directory. At server startup time, if no such file exists yet, the DB_CONFIG file will be created and the settings in this attribute will be written to it. If the file exists, its contents will be read and displayed in this attribute. The attribute is multi-valued, to accommodate multiple configuration directives. No default is provided, but it is essential to use proper settings here to get the best server performance.

Any changes made to this attribute will be written to the DB_CONFIG file and will cause the database environment to be reset so the changes can take immediate effect. If the environment cache is large and has not been recently checkpointed, this reset operation may take a long time. It may be advisable to manually perform a single checkpoint using the Berkeley DB db_checkpoint utility before using LDAP Modify to change this attribute.

Example:

        olcDbConfig: set_cachesize 0 10485760 0
        olcDbConfig: set_lg_bsize 2097512
        olcDbConfig: set_lg_dir /var/tmp/bdb-log
        olcDbConfig: set_flags DB_LOG_AUTOREMOVE

In this example, the BDB cache is set to 10MB, the BDB transaction log buffer size is set to 2MB, and the transaction log files are to be stored in the /var/tmp/bdb-log directory. Also a flag is set to tell BDB to delete transaction log files as soon as their contents have been checkpointed and they are no longer needed. Without this setting the transaction log files will continue to accumulate until some other cleanup procedure removes them. See the Berkeley DB documentation for the db_archive command for details.

Ideally the BDB cache must be at least as large as the working set of the database, the log buffer size should be large enough to accommodate most transactions without overflowing, and the log directory must be on a separate physical disk from the main database files. And both the database directory and the log directory should be separate from disks used for regular system activities such as the root, boot, or swap filesystems. See the FAQ-o-Matic and the Berkeley DB documentation for more details.

5.2.6.5. olcDbNosync: { TRUE | FALSE }

This option causes on-disk database contents to not be immediately synchronized with in memory changes upon change. Setting this option to TRUE may improve performance at the expense of data integrity. This directive has the same effect as using

        olcDbConfig: set_flags DB_TXN_NOSYNC

5.2.6.6. olcDbIDLcacheSize: <integer>

Specify the size of the in-memory index cache, in index slots. The default is zero. A larger value will speed up frequent searches of indexed entries. The optimal size will depend on the data and search characteristics of the database, but using a number three times the entry cache size is a good starting point.

Example:

        olcDbIDLcacheSize: 3000

5.2.6.7. olcDbIndex: {<attrlist> | default} [pres,eq,approx,sub,none]

This directive specifies the indices to maintain for the given attribute. If only an <attrlist> is given, the default indices are maintained. The index keywords correspond to the common types of matches that may be used in an LDAP search filter.

Example:

        olcDbIndex: default pres,eq
        olcDbIndex: uid
        olcDbIndex: cn,sn pres,eq,sub
        olcDbIndex: objectClass eq

The first line sets the default set of indices to maintain to present and equality. The second line causes the default (pres,eq) set of indices to be maintained for the uid attribute type. The third line causes present, equality, and substring indices to be maintained for cn and sn attribute types. The fourth line causes an equality index for the objectClass attribute type.

There is no index keyword for inequality matches. Generally these matches do not use an index. However, some attributes do support indexing for inequality matches, based on the equality index.

A substring index can be more explicitly specified as subinitial, subany, or subfinal, corresponding to the three possible components of a substring match filter. A subinitial index only indexes substrings that appear at the beginning of an attribute value. A subfinal index only indexes substrings that appear at the end of an attribute value, while subany indexes substrings that occur anywhere in a value.

Note that by default, setting an index for an attribute also affects every subtype of that attribute. E.g., setting an equality index on the name attribute causes cn, sn, and every other attribute that inherits from name to be indexed.

By default, no indices are maintained. It is generally advised that minimally an equality index upon objectClass be maintained.

        olcDbindex: objectClass eq

Additional indices should be configured corresponding to the most common searches that are used on the database. Presence indexing should not be configured for an attribute unless the attribute occurs very rarely in the database, and presence searches on the attribute occur very frequently during normal use of the directory. Most applications don't use presence searches, so usually presence indexing is not very useful.

If this setting is changed while slapd is running, an internal task will be run to generate the changed index data. All server operations can continue as normal while the indexer does its work. If slapd is stopped before the index task completes, indexing will have to be manually completed using the slapindex tool.

5.2.6.8. olcDbLinearIndex: { TRUE | FALSE }

If this setting is TRUE slapindex will index one attribute at a time. The default settings is FALSE in which case all indexed attributes of an entry are processed at the same time. When enabled, each indexed attribute is processed individually, using multiple passes through the entire database. This option improves slapindex performance when the database size exceeds the BDB cache size. When the BDB cache is large enough, this option is not needed and will decrease performance. Also by default, slapadd performs full indexing and so a separate slapindex run is not needed. With this option, slapadd does no indexing and slapindex must be used.

5.2.6.9. olcDbMode: <integer>

This directive specifies the file protection mode that newly created database index files should have.

Default:

        olcDbMode: 0600

5.2.6.10. olcDbSearchStack: <integer>

Specify the depth of the stack used for search filter evaluation. Search filters are evaluated on a stack to accommodate nested AND / OR clauses. An individual stack is allocated for each server thread. The depth of the stack determines how complex a filter can be evaluated without requiring any additional memory allocation. Filters that are nested deeper than the search stack depth will cause a separate stack to be allocated for that particular search operation. These separate allocations can have a major negative impact on server performance, but specifying too much stack will also consume a great deal of memory. Each search uses 512K bytes per level on a 32-bit machine, or 1024K bytes per level on a 64-bit machine. The default stack depth is 16, thus 8MB or 16MB per thread is used on 32 and 64 bit machines, respectively. Also the 512KB size of a single stack slot is set by a compile-time constant which may be changed if needed; the code must be recompiled for the change to take effect.

Default:

        olcDbSearchStack: 16

5.2.6.11. olcDbShmKey: <integer>

Specify a key for a shared memory BDB environment. By default the BDB environment uses memory mapped files. If a non-zero value is specified, it will be used as the key to identify a shared memory region that will house the environment.

Example:

        olcDbShmKey: 42

5.2.6.12. Sample Entry

dn: olcDatabase=hdb,cn=config
objectClass: olcDatabaseConfig
objectClass: olcHdbConfig
olcDatabase: hdb
olcSuffix: "dc=example,dc=com"
olcDbDirectory: /usr/local/var/openldap-data
olcDbCacheSize: 1000
olcDbCheckpoint: 1024 10
olcDbConfig: set_cachesize 0 10485760 0
olcDbConfig: set_lg_bsize 2097152
olcDbConfig: set_lg_dir /var/tmp/bdb-log
olcDbConfig: set_flags DB_LOG_AUTOREMOVE
olcDbIDLcacheSize: 3000
olcDbIndex: objectClass eq

5.3. Access Control

Access to slapd entries and attributes is controlled by the olcAccess attribute, whose values are a sequence of access directives. The general form of the olcAccess configuration is:

        olcAccess: <access directive>
        <access directive> ::= to <what>
                [by <who> [<access>] [<control>] ]+
        <what> ::= * |
                [dn[.<basic-style>]=<regex> | dn.<scope-style>=<DN>]
                [filter=<ldapfilter>] [attrs=<attrlist>]
        <basic-style> ::= regex | exact
        <scope-style> ::= base | one | subtree | children
        <attrlist> ::= <attr> [val[.<basic-style>]=<regex>] | <attr> , <attrlist>
        <attr> ::= <attrname> | entry | children
        <who> ::= * | [anonymous | users | self
                        | dn[.<basic-style>]=<regex> | dn.<scope-style>=<DN>]
                [dnattr=<attrname>]
                [group[/<objectclass>[/<attrname>][.<basic-style>]]=<regex>]
                [peername[.<basic-style>]=<regex>]
                [sockname[.<basic-style>]=<regex>]
                [domain[.<basic-style>]=<regex>]
                [sockurl[.<basic-style>]=<regex>]
                [set=<setspec>]
                [aci=<attrname>]
        <access> ::= [self]{<level>|<priv>}
        <level> ::= none | disclose | auth | compare | search | read | write | manage
        <priv> ::= {=|+|-}{m|w|r|s|c|x|d|0}+
        <control> ::= [stop | continue | break]

where the <what> part selects the entries and/or attributes to which the access applies, the <who> part specifies which entities are granted access, and the <access> part specifies the access granted. Multiple <who> <access> <control> triplets are supported, allowing many entities to be granted different access to the same set of entries and attributes. Not all of these access control options are described here; for more details see the slapd.access(5) man page.

5.3.1. What to control access to

The <what> part of an access specification determines the entries and attributes to which the access control applies. Entries are commonly selected in two ways: by DN and by filter. The following qualifiers select entries by DN:

        to *
        to dn[.<basic-style>]=<regex>
        to dn.<scope-style>=<DN>

The first form is used to select all entries. The second form may be used to select entries by matching a regular expression against the target entry's normalized DN. (The second form is not discussed further in this document.) The third form is used to select entries which are within the requested scope of DN. The <DN> is a string representation of the Distinguished Name, as described in RFC4514.

The scope can be either base, one, subtree, or children. Where base matches only the entry with provided DN, one matches the entries whose parent is the provided DN, subtree matches all entries in the subtree whose root is the provided DN, and children matches all entries under the DN (but not the entry named by the DN).

For example, if the directory contained entries named:

        0: o=suffix
        1: cn=Manager,o=suffix
        2: ou=people,o=suffix
        3: uid=kdz,ou=people,o=suffix
        4: cn=addresses,uid=kdz,ou=people,o=suffix
        5: uid=hyc,ou=people,o=suffix

Then:

Entries may also be selected using a filter:

        to filter=<ldap filter>

where <ldap filter> is a string representation of an LDAP search filter, as described in RFC4515. For example:

        to filter=(objectClass=person)

Note that entries may be selected by both DN and filter by including both qualifiers in the <what> clause.

        to dn.one="ou=people,o=suffix" filter=(objectClass=person)

Attributes within an entry are selected by including a comma-separated list of attribute names in the <what> selector:

        attrs=<attribute list>

A specific value of an attribute is selected by using a single attribute name and also using a value selector:

        attrs=<attribute> val[.<style>]=<regex>

There are two special pseudo attributes entry and children. To read (and hence return) a target entry, the subject must have read access to the target's entry attribute. To add or delete an entry, the subject must have write access to the entry's entry attribute AND must have write access to the entry's parent's children attribute. To rename an entry, the subject must have write access to entry's entry attribute AND have write access to both the old parent's and new parent's children attributes. The complete examples at the end of this section should help clear things up.

Lastly, there is a special entry selector "*" that is used to select any entry. It is used when no other <what> selector has been provided. It's equivalent to "dn=.*"

5.3.2. Who to grant access to

The <who> part identifies the entity or entities being granted access. Note that access is granted to "entities" not "entries." The following table summarizes entity specifiers:

Table 5.3: Access Entity Specifiers
Specifier Entities
* All, including anonymous and authenticated users
anonymous Anonymous (non-authenticated) users
users Authenticated users
self User associated with target entry
dn[.<basic-style>]=<regex> Users matching a regular expression
dn.<scope-style>=<DN> Users within scope of a DN

The DN specifier behaves much like <what> clause DN specifiers.

Other control factors are also supported. For example, a <who> can be restricted by an entry listed in a DN-valued attribute in the entry to which the access applies:

        dnattr=<dn-valued attribute name>

The dnattr specification is used to give access to an entry whose DN is listed in an attribute of the entry (e.g., give access to a group entry to whoever is listed as the owner of the group entry).

Some factors may not be appropriate in all environments (or any). For example, the domain factor relies on IP to domain name lookups. As these can easily spoofed, the domain factor should not be avoided.

5.3.3. The access to grant

The kind of <access> granted can be one of the following:

Table 5.4: Access Levels
Level Privileges Description
none =0 no access
disclose =d needed for information disclosure on error
auth =dx needed to authenticate (bind)
compare =cdx needed to compare
search =scdx needed to apply search filters
read =rscdx needed to read search results
write =wrscdx needed to modify/rename
manage =mwrscdx needed to manage

Each level implies all lower levels of access. So, for example, granting someone write access to an entry also grants them read, search, compare, auth and disclose access. However, one may use the privileges specifier to grant specific permissions.

5.3.4. Access Control Evaluation

When evaluating whether some requester should be given access to an entry and/or attribute, slapd compares the entry and/or attribute to the <what> selectors given in the configuration. For each entry, access controls provided in the database which holds the entry (or the first database if not held in any database) apply first, followed by the global access directives (which are held in the frontend database definition). Within this priority, access directives are examined in the order in which they appear in the configuration attribute. Slapd stops with the first <what> selector that matches the entry and/or attribute. The corresponding access directive is the one slapd will use to evaluate access.

Next, slapd compares the entity requesting access to the <who> selectors within the access directive selected above in the order in which they appear. It stops with the first <who> selector that matches the requester. This determines the access the entity requesting access has to the entry and/or attribute.

Finally, slapd compares the access granted in the selected <access> clause to the access requested by the client. If it allows greater or equal access, access is granted. Otherwise, access is denied.

The order of evaluation of access directives makes their placement in the configuration file important. If one access directive is more specific than another in terms of the entries it selects, it should appear first in the configuration. Similarly, if one <who> selector is more specific than another it should come first in the access directive. The access control examples given below should help make this clear.

5.3.5. Access Control Examples

The access control facility described above is quite powerful. This section shows some examples of its use for descriptive purposes.

A simple example:

        olcAccess: to * by * read

This access directive grants read access to everyone.

        olcAccess: to *
                by self write
                by anonymous auth
                by * read

This directive allows the user to modify their entry, allows anonymous to authenticate against these entries, and allows all others to read these entries. Note that only the first by <who> clause which matches applies. Hence, the anonymous users are granted auth, not read. The last clause could just as well have been "by users read".

It is often desirable to restrict operations based upon the level of protection in place. The following shows how security strength factors (SSF) can be used.

        olcAccess: to *
                by ssf=128 self write
                by ssf=64 anonymous auth
                by ssf=64 users read

This directive allows users to modify their own entries if security protections of strength 128 or better have been established, allows authentication access to anonymous users, and read access when strength 64 or better security protections have been established. If the client has not establish sufficient security protections, the implicit by * none clause would be applied.

The following example shows the use of style specifiers to select the entries by DN in two access directives where ordering is significant.

        olcAccess: to dn.children="dc=example,dc=com"
                by * search
        olcAccess: to dn.children="dc=com"
                by * read

Read access is granted to entries under the dc=com subtree, except for those entries under the dc=example,dc=com subtree, to which search access is granted. No access is granted to dc=com as neither access directive matches this DN. If the order of these access directives was reversed, the trailing directive would never be reached, since all entries under dc=example,dc=com are also under dc=com entries.

Also note that if no olcAccess: to directive matches or no by <who> clause, access is denied. That is, every olcAccess: to directive ends with an implicit by * none clause and every access list ends with an implicit olcAccess: to * by * none directive.

The next example again shows the importance of ordering, both of the access directives and the by <who> clauses. It also shows the use of an attribute selector to grant access to a specific attribute and various <who> selectors.

        olcAccess: to dn.subtree="dc=example,dc=com" attrs=homePhone
                by self write
                by dn.children=dc=example,dc=com" search
                by peername.regex=IP:10\..+ read
        olcAccess: to dn.subtree="dc=example,dc=com"
                by self write
                by dn.children="dc=example,dc=com" search
                by anonymous auth

This example applies to entries in the "dc=example,dc=com" subtree. To all attributes except homePhone, an entry can write to itself, entries under example.com entries can search by them, anybody else has no access (implicit by * none) excepting for authentication/authorization (which is always done anonymously). The homePhone attribute is writable by the entry, searchable by entries under example.com, readable by clients connecting from network 10, and otherwise not readable (implicit by * none). All other access is denied by the implicit access to * by * none.

Sometimes it is useful to permit a particular DN to add or remove itself from an attribute. For example, if you would like to create a group and allow people to add and remove only their own DN from the member attribute, you could accomplish it with an access directive like this:

        olcAccess: to attrs=member,entry
                by dnattr=member selfwrite

The dnattr <who> selector says that the access applies to entries listed in the member attribute. The selfwrite access selector says that such members can only add or delete their own DN from the attribute, not other values. The addition of the entry attribute is required because access to the entry is required to access any of the entry's attributes.

5.3.6. Access Control Ordering

Since the ordering of olcAccess directives is essential to their proper evaluation, but LDAP attributes normally do not preserve the ordering of their values, OpenLDAP uses a custom schema extension to maintain a fixed ordering of these values. This ordering is maintained by prepending a "{X}" numeric index to each value, similarly to the approach used for ordering the configuration entries. These index tags are maintained automatically by slapd and do not need to be specified when originally defining the values. For example, when you create the settings

        olcAccess: to attrs=member,entry
                by dnattr=member selfwrite
        olcAccess: to dn.children="dc=example,dc=com"
                by * search
        olcAccess: to dn.children="dc=com"
                by * read

when you read them back using slapcat or ldapsearch they will contain

        olcAccess: {0}to attrs=member,entry
                by dnattr=member selfwrite
        olcAccess: {1}to dn.children="dc=example,dc=com"
                by * search
        olcAccess: {2}to dn.children="dc=com"
                by * read

The numeric index may be used to specify a particular value to change when using ldapmodify to edit the access rules. This index can be used instead of (or in addition to) the actual access value. Using this numeric index is very helpful when multiple access rules are being managed.

For example, if we needed to change the second rule above to grant write access instead of search, we could try this LDIF:

        changetype: modify
        delete: olcAccess
        olcAccess: to dn.children="dc=example,dc=com" by * search
        -
        add: olcAccess
        olcAccess: to dn.children="dc=example,dc=com" by * write
        -

But this example will not guarantee that the existing values remain in their original order, so it will most likely yield a broken security configuration. Instead, the numeric index should be used:

        changetype: modify
        delete: olcAccess
        olcAccess: {1}
        -
        add: olcAccess
        olcAccess: {1}to dn.children="dc=example,dc=com" by * write
        -

This example deletes whatever rule is in value #1 of the olcAccess attribute (regardless of its value) and adds a new value that is explicitly inserted as value #1. The result will be

        olcAccess: {0}to attrs=member,entry
                by dnattr=member selfwrite
        olcAccess: {1}to dn.children="dc=example,dc=com"
                by * write
        olcAccess: {2}to dn.children="dc=com"
                by * read

which is exactly what was intended.


5.4. Configuration Example

The following is an example configuration, interspersed with explanatory text. It defines two databases to handle different parts of the X.500 tree; both are BDB database instances. The line numbers shown are provided for reference only and are not included in the actual file. First, the global configuration section:

  1.    # example config file - global configuration entry
  2.    dn: cn=config
  3.    objectClass: olcGlobal
  4.    cn: config
  5.    olcReferral: ldap://root.openldap.org
  6.

Line 1 is a comment. Lines 2-4 identify this as the global configuration entry. The olcReferral: directive on line 5 means that queries not local to one of the databases defined below will be referred to the LDAP server running on the standard port (389) at the host root.openldap.org. Line 6 is a blank line, indicating the end of this entry.

  7.    # internal schema
  8.    dn: cn=schema,cn=config
  9.    objectClass: olcSchemaConfig
 10.    cn: schema
 11.

Line 7 is a comment. Lines 8-10 identify this as the root of the schema subtree. The actual schema definitions in this entry are hardcoded into slapd so no additional attributes are specified here. Line 11 is a blank line, indicating the end of this entry.

 12.    # include the core schema
 13.    include: file:///usr/local/etc/openldap/schema/core.ldif
 14.

Line 12 is a comment. Line 13 is an LDIF include directive which accesses the core schema definitions in LDIF format. Line 14 is a blank line.

Next comes the database definitions. The first database is the special frontend database whose settings are applied globally to all the other databases.

 15.    # global database parameters
 16.    dn: olcDatabase=frontend,cn=config
 17.    objectClass: olcDatabaseConfig
 18.    olcDatabase: frontend
 19.    olcAccess: to * by * read
 20.

Line 15 is a comment. Lines 16-18 identify this entry as the global database entry. Line 19 is a global access control. It applies to all entries (after any applicable database-specific access controls).

The next entry defines a BDB backend that will handle queries for things in the "dc=example,dc=com" portion of the tree. Indices are to be maintained for several attributes, and the userPassword attribute is to be protected from unauthorized access.

 21.    # BDB definition for example.com
 22.    dn: olcDatabase=bdb,cn=config
 23.    objectClass: olcDatabaseConfig
 24.    objectClass: olcBdbConfig
 25.    olcDatabase: bdb
 26.    olcSuffix: "dc=example,dc=com"
 27.    olcDbDirectory: /usr/local/var/openldap-data
 28.    olcRootDN: "cn=Manager,dc=example,dc=com"
 29.    olcRootPW: secret
 30.    olcDbIndex: uid pres,eq
 31.    olcDbIndex: cn,sn,uid pres,eq,approx,sub
 32.    olcDbIndex: objectClass eq
 33.    olcAccess: to attrs=userPassword
 34.      by self write
 35.      by anonymous auth
 36.      by dn.base="cn=Admin,dc=example,dc=com" write
 37.      by * none
 38.    olcAccess: to *
 39.      by self write
 40.      by dn.base="cn=Admin,dc=example,dc=com" write
 41.      by * read
 42.

Line 21 is a comment. Lines 22-25 identify this entry as a BDB database configuration entry. Line 26 specifies the DN suffix for queries to pass to this database. Line 27 specifies the directory in which the database files will live.

Lines 28 and 29 identify the database super-user entry and associated password. This entry is not subject to access control or size or time limit restrictions.

Lines 30 through 32 indicate the indices to maintain for various attributes.

Lines 33 through 41 specify access control for entries in this database. As this is the first database, the controls also apply to entries not held in any database (such as the Root DSE). For all applicable entries, the userPassword attribute is writable by the entry itself and by the "admin" entry. It may be used for authentication/authorization purposes, but is otherwise not readable. All other attributes are writable by the entry and the "admin" entry, but may be read by all users (authenticated or not).

Line 42 is a blank line, indicating the end of this entry.

The next section of the example configuration file defines another BDB database. This one handles queries involving the dc=example,dc=net subtree but is managed by the same entity as the first database. Note that without line 52, the read access would be allowed due to the global access rule at line 19.

 43.    # BDB definition for example.net
 44.    dn: olcDatabase=bdb,cn=config
 45.    objectClass: olcDatabaseConfig
 46.    objectClass: olcBdbConfig
 47.    olcDatabase: bdb
 48.    olcSuffix: "dc=example,dc=net"
 49.    olcDbDirectory: /usr/local/var/openldap-data-net
 50.    olcRootDN: "cn=Manager,dc=example,dc=com"
 51.    olcDbIndex: objectClass eq
 52.    olcAccess: to * by users read