ldap — OpenLDAP Lightweight Directory Access Protocol API


OpenLDAP LDAP (libldap, -lldap)


#include <ldap.h>


The Lightweight Directory Access Protocol (LDAP) (RFC 4510) provides access to X.500 directory services.  These services may be stand-alone or part of a distributed directory service.  This client API supports LDAP over TCP (RFC 4511), LDAP over TLS/SSL, and LDAP over IPC (UNIX domain sockets).  This API supports SASL (RFC 4513) and Start TLS (RFC 4513) as well as a number of protocol extensions.  This API is loosely based upon IETF/LDAPEXT C LDAP API draft specification, a (orphaned) work in progress.

The OpenLDAP Software package includes a stand-alone server in slapd(8), various LDAP clients, and an LDAP client library used to provide programmatic access to the LDAP protocol. This man page gives an overview of the LDAP library routines.

Both synchronous and asynchronous APIs are provided.  Also included are various routines to parse the results returned from these routines. These routines are found in the -lldap library.

The basic interaction is as follows.  A session handle is created using ldap_initialize(3) and set the protocol version to 3 by calling ldap_set_option(3). The underlying session is established first operation is issued.  This would generally be a Start TLS or Bind operation, or a Search operation to read attributes of the Root DSE. A Start TLS operation is performed by calling ldap_start_tls_s(3). A LDAP bind operation is performed by calling ldap_sasl_bind(3) or one of its friends. A Search operation is performed by calling ldap_search_ext_s(3) or one of its friends.

Subsequently, additional operations are performed by calling one of the synchronous or asynchronous routines (e.g., ldap_compare_ext_s(3) or ldap_compare_ext(3) followed by ldap_result(3)). Results returned from these routines are interpreted by calling the LDAP parsing routines such as ldap_parse_result(3). The LDAP association and underlying connection is terminated by calling ldap_unbind_ext(3). Errors can be interpreted by calling ldap_err2string(3).

LDAP versions

This library supports version 3 of the Lightweight Directory Access Protocol (LDAPv3) as defined in RFC 4510.  It also supports a variant of version 2 of LDAP as defined by U-Mich LDAP and, to some degree, RFC 1777.  Version 2 (all variants) are considered obsolete. Version 3 should be used instead.

For backwards compatibility reasons, the library defaults to version 2. Hence, all new applications (and all actively maintained applications) should use ldap_set_option(3) to select version 3.  The library manual pages assume version 3 has been selected.


All character string input/output is expected to be/is UTF-8 encoded Unicode (version 3.2).

Distinguished names (DN) (and relative distinguished names (RDN) to be passed to the LDAP routines should conform to RFC 4514 UTF-8 string representation.

Search filters to be passed to the search routines are to be constructed by hand and should conform to RFC 4515 UTF-8 string representation.

LDAP URLs to be passed to routines are expected to conform to RFC 4516 format.  The ldap_url(3) routines can be used to work with LDAP URLs.

LDAP controls to be passed to routines can be manipulated using the ldap_controls(3) routines.

Displaying Results

Results obtained from the search routines can be output by hand, by calling ldap_first_entry(3) and ldap_next_entry(3) to step through the entries returned, ldap_first_attribute(3) and ldap_next_attribute(3) to step through an entry's attributes, and ldap_get_values(3) to retrieve a given attribute's values.  Attribute values may or may not be displayable.

Utility Routines

Also provided are various utility routines.  The ldap_sort(3) routines are used to sort the entries and values returned via the ldap search routines.

Deprecated Interfaces

A number of interfaces are now considered deprecated.  For instance, ldap_add(3) is deprecated in favor of ldap_add_ext(3). Deprecated interfaces generally remain in the library.  The macro LDAP_DEPRECATED can be defined to a non-zero value (e.g., -DLDAP_DEPRECATED=1) when compiling program designed to use deprecated interfaces.  It is recommended that developers writing new programs, or updating old programs, avoid use of deprecated interfaces. Over time, it is expected that documentation (and, eventually, support) for deprecated interfaces to be eliminated.

Ber Library

Also included in the distribution is a set of lightweight Basic Encoding Rules routines.  These routines are used by the LDAP library routines to encode and decode LDAP protocol elements using the (slightly simplified) Basic Encoding Rules defined by LDAP.  They are not normally used directly by an LDAP application program except in the handling of controls and extended operations.  The routines provide a printf and scanf-like interface, as well as lower-level access.  These routines are discussed in lber-decode(3), lber-encode(3), lber-memory(3), and lber-types(3).



initialize the LDAP library without opening a connection to a server


wait for the result from an asynchronous operation


abandon (abort) an asynchronous operation


asynchronously add an entry


synchronously add an entry


asynchronously bind to the directory


synchronously bind to the directory


synchronously unbind from the LDAP server and close the connection

ldap_unbind(3) and ldap_unbind_s(3) are

equivalent to ldap_unbind_ext(3)


dispose of memory allocated by LDAP routines.


asynchronously compare to a directory entry


synchronously compare to a directory entry


asynchronously delete an entry


synchronously delete an entry


LDAP error indication


list of LDAP errors and their meanings


convert LDAP error indication to a string


asynchronously perform an arbitrary extended operation


synchronously perform an arbitrary extended operation


return first attribute name in an entry


return next attribute name in an entry


return first entry in a chain of search results


return next entry in a chain of search results


return number of entries in a search result


extract the DN from an entry


return an attribute's values with lengths


free memory allocated by ldap_get_values_len(3)


return number of values


asynchronously modify an entry


synchronously modify an entry


free array of pointers to mod structures used by ldap_modify_ext(3)


asynchronously rename an entry


synchronously rename an entry


free results allocated by ldap_result(3)


return the message type of a message from ldap_result(3)


return the message id of a message from ldap_result(3)


asynchronously search the directory


synchronously search the directory


check a URL string to see if it is an LDAP URL


break up an LDAP URL string into its components


sort a list of search results


sort a list of attribute values


case insensitive string comparison

See Also

ldap.conf(5), slapd(8), draft-ietf-ldapext-ldap-c-api-xx.txt <http://www.ietf.org>


OpenLDAP Software is developed and maintained by The OpenLDAP Project <http://www.openldap.org/>. OpenLDAP Software is derived from the University of Michigan LDAP 3.3 Release.  

These API manual pages are loosely based upon descriptions provided in the IETF/LDAPEXT C LDAP API Internet Draft, a (orphaned) work in progress.

Referenced By

ldap2zone(1), ldap_abandon(3), ldap_add(3), ldap_bind(3), ldap_compare(3), ldapcompare(1), ldap.conf(5), ldap_control_create(3), ldap_count_entries(3), ldap_delete(3), ldapdelete(1), ldap_first_attribute(3), ldap_first_message(3), ldap_first_reference(3), ldap_get_dn(3), ldap_get_option(3), ldap_get_values(3), ldap_init(3), ldap_memfree(3), ldap_modify(3), ldapmodify(1), ldap_modrdn(3), ldapmodrdn(1), ldap_parse_reference(3), ldap_parse_result(3), ldap_perror(3), ldap_rename(3), ldap_result(3), ldap_search(3), ldapsearch(1), ldap_sort(3), ldap_str2syntax(3), ldap_sync(3), ldap_tls(3), ldap_url(3), ldapurl(1), ldapwhoami(1), ldif(5), slapacl(8), slapadd(8), slapauth(8), slapcat(8), slapd(8), slapd.backends(5), slapd.conf(5), slapd-config(5), slapd-ldap(5), slapd-monitor(5), slapdn(8), slapd.overlays(5), slapindex(8), slapo-ppolicy(5), slapschema(8), slaptest(8), zone2ldap(1).

2018/12/19 OpenLDAP 2.4.47