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.


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.


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.


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.


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).


ldap_initialize(3) initialize the LDAP library without opening a connection to a server
ldap_result(3) wait for the result from an asynchronous operation
abandon (abort) an asynchronous operation
asynchronously add an entry
ldap_add_ext_s(3) synchronously add an entry
ldap_sasl_bind(3) asynchronously bind to the directory
ldap_sasl_bind_s(3) synchronously bind to the directory
ldap_unbind_ext(3) 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)
ldap_memfree(3) dispose of memory allocated by LDAP routines.
ldap_compare_ext(3) asynchronously compare to a directory entry
ldap_compare_ext_s(3) synchronously compare to a directory entry
ldap_delete_ext(3) asynchronously delete an entry
ldap_delete_ext_s(3) synchronously delete an entry
ld_errno(3) LDAP error indication
ldap_errlist(3) list of LDAP errors and their meanings
ldap_err2string(3) 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
ldap_first_entry(3) return first entry in a chain of search results
ldap_next_entry(3) return next entry in a chain of search results
ldap_count_entries(3) return number of entries in a search result
ldap_get_dn(3) 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
ldap_modify_ext(3) asynchronously modify an entry
ldap_modify_ext_s(3) synchronously modify an entry
ldap_mods_free(3) free array of pointers to mod structures used by ldap_modify_ext(3)
ldap_rename(3) asynchronously rename an entry
ldap_rename_s(3) synchronously rename an entry
ldap_msgfree(3) free results allocated by ldap_result(3)
ldap_msgtype(3) return the message type of a message from ldap_result(3)
ldap_msgid(3) return the message id of a message from ldap_result(3)
ldap_search_ext(3) asynchronously search the directory
ldap_search_ext_s(3) synchronously search the directory
ldap_is_ldap_url(3) check a URL string to see if it is an LDAP URL
ldap_url_parse(3) break up an LDAP URL string into its components
ldap_sort_entries(3) sort a list of search results
ldap_sort_values(3) sort a list of attribute values
 case insensitive string comparison


ldap.conf(5), slapd(8), draft-ietf-ldapext-ldap-c-api-xx.txt <>


OpenLDAP Software is developed and maintained by The OpenLDAP Project <>. OpenLDAP Software is derived from 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.

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