OpenLDAP

OpenLDAP is an open-source implementation of the Lightweight Directory Access Protocol (LDAP). It provides a directory service suitable for storing and retrieving information about users, groups, devices, and other resources in a networked environment. The project includes slapd, the directory server, along with libraries implementing the LDAP protocol and a suite of command-line tools such as ldapsearch, ldapadd, and ldapmodify. OpenLDAP adheres to LDAPv3 standards and supports a pluggable authentication framework via SASL and transport layer security with TLS/SSL.

The OpenLDAP Project originated from earlier LDAP implementations and is maintained by a community of volunteers. It is cross-platform and commonly deployed on Unix-like systems, though Windows builds exist from third parties. In production, OpenLDAP organizations typically configure a DIT, the directory information tree, defined by schemas that describe attribute types and object classes. Entries are identified by Distinguished Names and can be indexed to improve search performance.

OpenLDAP offers features such as dynamic configuration (cn=config), access control lists, referrals, and replication. Modern deployments often use the LMDB (formerly BDB/HDB) backend for storage and the syncrepl framework for data replication, including multi-master setups. The software is distributed under the OpenLDAP Public License, a permissive license.

OpenLDAP is widely used to centralize authentication, authorization, address book services, and generic directory services in organizations of varying sizes, providing programmatic access via LDAP clients and APIs.