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+.TH SLAPD.BACKENDS 5 "RELEASEDATE" "OpenLDAP LDVERSION"
+.\" Copyright 2006-2021 The OpenLDAP Foundation All Rights Reserved.
+.\" Copying restrictions apply.  See COPYRIGHT/LICENSE.
+.\" $OpenLDAP$
+.SH NAME
+slapd.backends \- backends for slapd, the stand-alone LDAP daemon
+.SH DESCRIPTION
+The
+.BR slapd (8)
+daemon can use a variety of different backends for serving LDAP requests.
+Backends may be compiled statically into slapd, or when module support
+is enabled, they may be dynamically loaded. Multiple instances of a
+backend can be configured, to serve separate databases from the same
+slapd server.
+
+
+Configuration options for each backend are documented separately in the
+corresponding
+.BR slapd\-<backend> (5)
+manual pages.
+.TP
+.B bdb
+This was the recommended primary backend through OpenLDAP 2.3, but it has
+since been superseded by the
+.BR mdb
+backend.  It takes care to configure it properly.
+It uses the transactional database interface of the Oracle Berkeley
+DB (BDB) package to store data.
+.TP
+.B config
+This backend is used to manage the configuration of slapd at run-time.
+Unlike other backends, only a single instance of the
+.B config
+backend may be defined. It also instantiates itself automatically,
+so it is always present even if not explicitly defined in the
+.BR slapd.conf (5)
+file.
+.TP
+.B dnssrv
+This backend is experimental.
+It serves up referrals based upon SRV resource records held in the
+Domain Name System.
+.TP
+.B hdb
+This was the recommended primary backend through OpenLDAP 2.4.40 but it has
+since been superseded by the
+.BR mdb
+backend.  It takes care to configure it properly.
+.B hdb
+is a variant of the
+.B bdb
+backend that uses a hierarchical database
+layout.
+This layout stores entry DNs more efficiently than the
+.B bdb
+backend,
+using less space and requiring less work to create, delete, and rename
+entries. It is also one of the few backends to support subtree renames.
+.TP
+.B ldap
+This backend acts as a proxy to forward incoming requests to another
+LDAP server.
+.TP
+.B ldif
+This database uses the filesystem to build the tree structure
+of the database, using plain ascii files to store data.
+Its usage should be limited to very simple databases, where performance
+is not a requirement. This backend also supports subtree renames.
+.TP
+.B mdb
+This is the recommended primary backend, superseding
+.BR hdb .
+This backend uses OpenLDAP's own MDB transactional database
+library. It is extremely compact and extremely efficient, delivering
+much higher performance than the Berkeley DB backends while using
+significantly less memory.  Also, unlike Berkeley DB, MDB is crash proof,
+and requires no special tuning or maintenance.
+This backend also supports subtree renames.
+.TP
+.B meta
+This backend performs basic LDAP proxying with respect to a set of
+remote LDAP servers. It is an enhancement of the
+.B ldap
+backend.
+.TP
+.B monitor
+This backend provides information about the running status of the slapd
+daemon. Only a single instance of the
+.B monitor
+backend may be defined.
+.TP
+.B ndb
+This backend is experimental.
+It uses the transactional database interface of the MySQL Cluster Engine
+(NDB) to store data. Note that Oracle, which now owns MySQL, has withdrawn
+support for NDB and this backend is unlikely to be developed any further.
+.TP
+.B null
+Operations in this backend succeed but do nothing.
+.TP
+.B passwd
+This backend is provided for demonstration purposes only.
+It serves up user account information from the system
+.BR passwd (5)
+file.
+.TP
+.B perl
+This backend embeds a
+.BR perl (1)
+interpreter into slapd.
+It runs Perl subroutines to implement LDAP operations.
+.TP
+.B relay
+This backend is experimental.
+It redirects LDAP operations to another database
+in the same server, based on the naming context of the request.
+Its use requires the 
+.B rwm
+overlay (see
+.BR slapo\-rwm (5)
+for details) to rewrite the naming context of the request.
+It is primarily intended to implement virtual views on databases
+that actually store data.
+.TP
+.B shell
+This backend executes external programs to implement LDAP operations.
+It is primarily intended to be used in prototypes.
+.TP
+.B sql
+This backend is experimental.
+It services LDAP requests from an SQL database.
+.SH FILES
+.TP
+ETCDIR/slapd.conf
+default slapd configuration file
+.TP
+ETCDIR/slapd.d
+default slapd configuration directory
+.SH SEE ALSO
+.BR ldap (3),
+.BR slapd\-bdb (5),
+.BR slapd\-config (5),
+.BR slapd\-dnssrv (5),
+.BR slapd\-hdb (5),
+.BR slapd\-ldap (5),
+.BR slapd\-ldif (5),
+.BR slapd\-mdb (5),
+.BR slapd\-meta (5),
+.BR slapd\-monitor (5),
+.BR slapd\-ndb (5),
+.BR slapd\-null (5),
+.BR slapd\-passwd (5),
+.BR slapd\-perl (5),
+.BR slapd\-relay (5),
+.BR slapd\-shell (5),
+.BR slapd\-sql (5),
+.BR slapd.conf (5),
+.BR slapd.overlays (5),
+.BR slapd (8).
+"OpenLDAP Administrator's Guide" (http://www.OpenLDAP.org/doc/admin/)
+.SH ACKNOWLEDGEMENTS
+.so ../Project