Directory service

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A directory service or name service maps the names of network resources to their respective network addresses. It is a shared information infrastructure for locating, managing, administering, and organizing everyday items and network resources, which can include volumes, folders, files, printers, users, groups, devices, telephone numbers, and other objects. A directory service is a critical component of a network operating system.

A directory server is a server which provides such a service. Each resource on the network is considered an object by the directory server. Information about a particular resource is stored as a collection of attributes that are associated with that resource or object.

A directory service defines a namespace for the network. The namespace is used to assign a "name," or unique identifier, to each of the objects. Directories typically have a set of rules that determine how network resources are named and identified, which usually includes a requirement that the identifiers be both unique and unambiguous. When using a directory service, a user does not have to remember the physical address of a network resource, because providing a name locates the resource.

Some directory services include access control provisions to limit availability of directory information to authorized users.

Comparison with relational databases[edit]

Several things generally distinguish a directory service from a relational database:

  • directory information is read more often than it is written; this makes features related to transactions and rollback less important.[citation needed]
  • data can be redundant[clarification needed] if it helps performance.


  • Must - attributes that each of its instances must have

Replication and distribution[edit]

Replication and distribution have very distinct meanings in the design and management of a directory service. The term replication is used to indicate that the same directory namespace (the same objects) are copied to another directory server for redundancy and throughput reasons. The replicated namespace is governed by the same authority. The term distribution is used to indicate that multiple directory servers that hold different namespaces are interconnected to form a distributed directory service. Each distinct namespace can be governed by different authorities.

Implementations of directory services[edit]



  • NetInfo: was developed by NeXT in the late 1980s for NEXTSTEP. After being acquired by Apple, it was released as open source and used as the directory service for Mac OS X before being deprecated for the LDAP-based Open Directory. Support for NetInfo was completely removed with the release of 10.5 Leopard.
  • Banyan VINES: was the first scalable directory services offering.
  • NT Domains: was developed by Microsoft to provide directory services for Windows machines before the release of the LDAP-based Active Directory in Windows 2000. Windows Vista continues to support NT Domains, but only after relaxing the minimum authentication protocols it supports.

LDAP implementations[edit]

Among the LDAP/X.500 based implementations are:

There are also plenty of open-source tools to create directory services, including OpenLDAP and the Kerberos protocol, and Samba software, which can act as a Windows Domain Controller with Kerberos and LDAP backends. The administration is done using GOsa or Samba provided SWAT.

Using name services[edit]

Unix OSs[edit]


See also[edit]


  1. ^ [1] Archived October 15, 2007, at the Wayback Machine.
  2. ^ "Oracle and Sun". 2010-09-07. Retrieved 2012-01-09. 
  3. ^ "". Retrieved 2012-01-09.