11. Backends
Backends do the actual work of storing or retrieving data in response to LDAP requests. Backends may be compiled statically into slapd, or when module support is enabled, they may be dynamically loaded.
If your installation uses dynamic modules, you may need to add the relevant moduleload directives to the examples that follow. The name of the module for a backend is usually of the form:
back_<backend name>.la
So for example, if you need to load the mdb backend, you would configure
moduleload back_mdb.la
11.1. LDAP
11.1.1. Overview
The LDAP backend to slapd(8) is not an actual database; instead it acts as a proxy to forward incoming requests to another LDAP server. While processing requests it will also chase referrals, so that referrals are fully processed instead of being returned to the slapd client.
Sessions that explicitly Bind to the back-ldap database always create their own private connection to the remote LDAP server. Anonymous sessions will share a single anonymous connection to the remote server. For sessions bound through other mechanisms, all sessions with the same DN will share the same connection. This connection pooling strategy can enhance the proxy's efficiency by reducing the overhead of repeatedly making/breaking multiple connections.
The ldap database can also act as an information service, i.e. the identity of locally authenticated clients is asserted to the remote server, possibly in some modified form. For this purpose, the proxy binds to the remote server with some administrative identity, and, if required, authorizes the asserted identity.
It is heavily used by a lot of other Backends and Overlays.
11.1.2. back-ldap Configuration
As previously mentioned, slapd-ldap(5) is used behind the scenes by many other Backends and Overlays. Some of them merely provide a few configuration directive themselves, but have available to the administrator the whole of the slapd-ldap(5) options.
For example, the Translucent Proxy, which retrieves entries from a remote LDAP server that can be partially overridden by the defined database, has only four specific translucent- directives, but can be configured using any of the normal slapd-ldap(5) options. See slapo-translucent(5) for details.
Other Overlays allow you to tag directives in front of a normal slapd-ldap(5) directive. For example, the slapo-chain(5) overlay does this:
"There are very few chain overlay specific directives; however, directives related to the instances of the ldap backend that may be implicitly instantiated by the overlay may assume a special meaning when used in conjunction with this overlay. They are described in slapd-ldap(5), and they also need to be prefixed by chain-."
You may have also seen the slapd-ldap(5) backend used and described in the
It should therefore be obvious that the slapd-ldap(5) backend is extremely flexible and heavily used throughout the OpenLDAP Suite.
The following is a very simple example, but already the power of the slapd-ldap(5) backend is seen by use of a uri list:
database ldap
suffix "dc=suretecsystems,dc=com"
rootdn "cn=slapd-ldap"
uri ldap://localhost/ ldap://remotehost ldap://remotehost2
The URI list is space or comma-separated. Whenever the server that responds is not the first one in the list, the list is rearranged and the responsive server is moved to the head, so that it will be first contacted the next time a connection needs be created.
This feature can be used to provide a form of load balancing when using Mirror mode replication.
11.1.3. Further Information
slapd-ldap(5)
11.2. LDIF
11.2.1. Overview
The LDIF backend to slapd(8) is a basic storage backend that stores entries in text files in LDIF format, and exploits the filesystem to create the tree structure of the database. It is intended as a cheap, low performance easy to use backend.
When using the cn=config dynamic configuration database with persistent storage, the configuration data is stored using this backend. See slapd-config(5) for more information
11.2.2. back-ldif Configuration
Like many other backends, the LDIF backend can be instantiated with very few configuration lines:
include ./schema/core.schema
database ldif
directory ./ldif
suffix "dc=suretecsystems,dc=com"
rootdn "cn=LDIF,dc=suretecsystems,dc=com"
rootpw LDIF
If we add the dcObject for dc=suretecsystems,dc=com, you can see how this is added behind the scenes on the file system:
dn: dc=suretecsystems,dc=com objectClass: dcObject objectClass: organization dc: suretecsystems o: Suretec Systems Ltd
Now we add it to the directory:
ldapadd -x -H ldap://localhost:9011 -f suretec.ldif -D "cn=LDIF,dc=suretecsystems,dc=com" -w LDIF adding new entry "dc=suretecsystems,dc=com"
And inside ./ldif we have:
ls ./ldif dc=suretecsystems,dc=com.ldif
which again contains:
cat ldif/dc\=suretecsystems\,dc\=com.ldif dn: dc=suretecsystems objectClass: dcObject objectClass: organization dc: suretecsystems o: Suretec Systems Ltd. structuralObjectClass: organization entryUUID: 2134b714-e3a1-102c-9a15-f96ee263886d creatorsName: cn=LDIF,dc=suretecsystems,dc=com createTimestamp: 20080711142643Z entryCSN: 20080711142643.661124Z#000000#000#000000 modifiersName: cn=LDIF,dc=suretecsystems,dc=com modifyTimestamp: 20080711142643Z
This is the complete format you would get when exporting your directory using slapcat etc.
11.2.3. Further Information
slapd-ldif(5)
11.3. LMDB
11.3.1. Overview
The mdb backend to slapd(8) is the recommended primary backend for a normal slapd database. It uses OpenLDAP's own Lightning Memory-Mapped Database (
It supports indexing, it uses no caching, and requires no tuning to deliver maximum search performance. It is fully hierarchical and supports subtree renames in constant time.
11.3.2. back-mdb Configuration
The mdb backend can be instantiated with very few configuration lines:
include ./schema/core.schema
database mdb
directory ./mdb
suffix "dc=suretecsystems,dc=com"
rootdn "cn=mdb,dc=suretecsystems,dc=com"
rootpw mdb
maxsize 1073741824
In addition to the usual parameters that a minimal configuration requires, the mdb backend requires a maximum size to be set. This should be the largest that the database is ever anticipated to grow (in bytes). The filesystem must also provide enough free space to accommodate this size.
11.3.3. Further Information
slapd-mdb(5)
11.4. Metadirectory
11.4.1. Overview
The meta backend to slapd(8) performs basic LDAP proxying with respect to a set of remote LDAP servers, called "targets". The information contained in these servers can be presented as belonging to a single Directory Information Tree (
A basic knowledge of the functionality of the slapd-ldap(5) backend is recommended. This backend has been designed as an enhancement of the ldap backend. The two backends share many features (actually they also share portions of code). While the ldap backend is intended to proxy operations directed to a single server, the meta backend is mainly intended for proxying of multiple servers and possibly naming context masquerading.
These features, although useful in many scenarios, may result in excessive overhead for some applications, so its use should be carefully considered.
11.4.2. back-meta Configuration
LATER
11.4.3. Further Information
slapd-meta(5)
11.5. Monitor
11.5.1. Overview
The monitor backend to slapd(8) is not an actual database; if enabled, it is automatically generated and dynamically maintained by slapd with information about the running status of the daemon.
To inspect all monitor information, issue a subtree search with base cn=Monitor, requesting that attributes "+" and "*" are returned. The monitor backend produces mostly operational attributes, and LDAP only returns operational attributes that are explicitly requested. Requesting attribute "+" is an extension which requests all operational attributes.
See the Monitoring section.
11.5.2. back-monitor Configuration
The monitor database can be instantiated only once, i.e. only one occurrence of "database monitor" can occur in the slapd.conf(5) file. Also the suffix is automatically set to "cn=Monitor".
You can however set a rootdn and rootpw. The following is all that is needed to instantiate a monitor backend:
include ./schema/core.schema
database monitor
rootdn "cn=monitoring,cn=Monitor"
rootpw monitoring
You can also apply Access Control to this database like any other database, for example:
access to dn.subtree="cn=Monitor"
by dn.exact="uid=Admin,dc=my,dc=org" write
by users read
by * none
Note: The core.schema must be loaded for the monitor database to work.
A small example of the data returned via ldapsearch would be:
ldapsearch -x -H ldap://localhost:9011 -b 'cn=Monitor'
# extended LDIF
#
# LDAPv3
# base <cn=Monitor> with scope subtree
# filter: (objectclass=*)
# requesting: ALL
#
# Monitor
dn: cn=Monitor
objectClass: monitorServer
cn: Monitor
description: This subtree contains monitoring/managing objects.
description: This object contains information about this server.
description: Most of the information is held in operational attributes, which
must be explicitly requested.
# Backends, Monitor
dn: cn=Backends,cn=Monitor
objectClass: monitorContainer
cn: Backends
description: This subsystem contains information about available backends.
Please see the Monitoring section for complete examples of information available via this backend.
11.5.3. Further Information
slapd-monitor(5)
11.6. Null
11.6.1. Overview
The Null backend to slapd(8) is surely the most useful part of slapd:
- Searches return success but no entries.
- Compares return compareFalse.
- Updates return success (unless readonly is on) but do nothing.
- Binds other than as the rootdn fail unless the database option "bind on" is given.
- The slapadd(8) and slapcat(8) tools are equally exciting.
Inspired by the /dev/null device.
11.6.2. back-null Configuration
This has to be one of the shortest configurations you'll ever do. In order to test this, your slapd.conf file would look like:
database null
suffix "cn=Nothing"
bind on
bind on means:
"Allow binds as any DN in this backend's suffix, with any password. The default is "off"."
To test this backend with ldapsearch:
ldapsearch -x -H ldap://localhost:9011 -D "uid=none,cn=Nothing" -w testing -b 'cn=Nothing'
# extended LDIF
#
# LDAPv3
# base <cn=Nothing> with scope subtree
# filter: (objectclass=*)
# requesting: ALL
#
# search result
search: 2
result: 0 Success
# numResponses: 1
11.6.3. Further Information
slapd-null(5)
11.7. Passwd
11.7.1. Overview
The PASSWD backend to slapd(8) serves up the user account information listed in the system passwd(5) file (defaulting to /etc/passwd).
This backend is provided for demonstration purposes only. The DN of each entry is "uid=<username>,<suffix>".
11.7.2. back-passwd Configuration
The configuration using slapd.conf a slightly longer, but not much. For example:
include ./schema/core.schema
database passwd
suffix "cn=passwd"
Again, testing this with ldapsearch would result in something like:
ldapsearch -x -H ldap://localhost:9011 -b 'cn=passwd'
# extended LDIF
#
# LDAPv3
# base <cn=passwd> with scope subtree
# filter: (objectclass=*)
# requesting: ALL
#
# passwd
dn: cn=passwd
cn: passwd
objectClass: organizationalUnit
# root, passwd
dn: uid=root,cn=passwd
objectClass: person
objectClass: uidObject
uid: root
cn: root
sn: root
description: root
11.7.3. Further Information
slapd-passwd(5)
11.8. Perl
11.8.1. Overview
The Perl backend to slapd(8) works by embedding a perl(1) interpreter into slapd(8). Any perl database section of the configuration file slapd.conf(5) must then specify what Perl module to use. Slapd then creates a new Perl object that handles all the requests for that particular instance of the backend.
11.8.2. back-perl Configuration
LATER
11.8.3. Further Information
slapd-perl(5)
11.9. Relay
11.9.1. Overview
The primary purpose of this slapd(8) backend is to map a naming context defined in a database running in the same slapd(8) instance into a virtual naming context, with attributeType and objectClass manipulation, if required. It requires the rwm overlay.
This backend and the above mentioned overlay are experimental.
11.9.2. back-relay Configuration
LATER
11.9.3. Further Information
slapd-relay(5)
11.10. SQL
11.10.1. Overview
The primary purpose of this slapd(8) backend is to PRESENT information stored in some RDBMS as an LDAP subtree without any programming (some SQL and maybe stored procedures can't be considered programming, anyway ;).
That is, for example, when you (some ISP) have account information you use in an RDBMS, and want to use modern solutions that expect such information in LDAP (to authenticate users, make email lookups etc.). Or you want to synchronize or distribute information between different sites/applications that use RDBMSes and/or LDAP. Or whatever else...
It is NOT designed as a general-purpose backend that uses RDBMS instead of LMDB (as the standard back-mdb backend does), though it can be used as such with several limitations. Please see LDAP vs RDBMS for discussion.
The idea is to use some meta-information to translate LDAP queries to SQL queries, leaving relational schema untouched, so that old applications can continue using it without any modifications. This allows SQL and LDAP applications to interoperate without replication, and exchange data as needed.
The SQL backend is designed to be tunable to virtually any relational schema without having to change source (through that meta-information mentioned). Also, it uses ODBC to connect to RDBMSes, and is highly configurable for SQL dialects RDBMSes may use, so it may be used for integration and distribution of data on different RDBMSes, OSes, hosts etc., in other words, in highly heterogeneous environments.
This backend is experimental and deprecated.
11.10.2. back-sql Configuration
This backend has to be one of the most abused and complex backends there is. Therefore, we will go through a simple, small example that comes with the OpenLDAP source and can be found in servers/slapd/back-sql/rdbms_depend/README
For this example we will be using PostgreSQL.
First, we add to /etc/odbc.ini a block of the form:
[example] <===
Description = Example for OpenLDAP's back-sql
Driver = PostgreSQL
Trace = No
Database = example <===
Servername = localhost
UserName = manager <===
Password = secret <===
Port = 5432
;Protocol = 6.4
ReadOnly = No
RowVersioning = No
ShowSystemTables = No
ShowOidColumn = No
FakeOidIndex = No
ConnSettings =
The relevant information for our test setup is highlighted with '<===' on the right above.
Next, we add to /etc/odbcinst.ini a block of the form:
[PostgreSQL]
Description = ODBC for PostgreSQL
Driver = /usr/lib/libodbcpsql.so
Setup = /usr/lib/libodbcpsqlS.so
FileUsage = 1
We will presume you know how to create a database and user in PostgreSQL and how to set a password. Also, we'll presume you can populate the 'example' database you've just created with the following files, as found in servers/slapd/back-sql/rdbms_depend/pgsql
backsql_create.sql, testdb_create.sql, testdb_data.sql, testdb_metadata.sql
Lastly, run the test:
[root@localhost]# cd $SOURCES/tests
[root@localhost]# SLAPD_USE_SQL=pgsql ./run sql-test000
Briefly, you should see something like (cut short for space):
Cleaning up test run directory leftover from previous run.
Running ./scripts/sql-test000-read...
running defines.sh
Starting slapd on TCP/IP port 9011...
Testing SQL backend read operations...
Waiting 5 seconds for slapd to start...
Testing correct bind... dn:cn=Mitya Kovalev,dc=example,dc=com
Testing incorrect bind (should fail)... ldap_bind: Invalid credentials (49)
......
Filtering original ldif...
Comparing filter output...
>>>>> Test succeeded
The test is basically readonly; this can be performed by all RDBMSes (listed above).
There is another test, sql-test900-write, which is currently enabled only for PostgreSQL and IBM db2.
Using sql-test000, files in servers/slapd/back-sql/rdbms_depend/pgsql/ and the man page, you should be set.
Note: This backend is experimental and deprecated.
11.10.3. Further Information
slapd-sql(5) and servers/slapd/back-sql/rdbms_depend/README