Novell LINUX ENTERPRISE SERVER 10 - INSTALLATION AND ADMINISTRATION 11-05-2007, Руководство по установке

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• Because write accesses can only be executed in a restricted fashion, a directory
service is used to administer mostly unchanging, static information. Data in a con-
ventional database typically changes very often (dynamic data). Phone numbers in
a company directory do not change nearly as often as, for example, the figures ad-
ministered in accounting.
• When static data is administered, updates of the existing data sets are very rare.
When working with dynamic data, especially when data sets like bank accounts or
accounting are concerned, the consistency of the data is of primary importance. If
an amount should be subtracted from one place to be added to another, both opera-
tions must happen concurrently, within a transaction, to ensure balance over the
data stock. Databases support such transactions. Directories do not. Short-term in-
consistencies of the data are quite acceptable in directories.
The design of a directory service like LDAP is not laid out to support complex update
or query mechanisms. All applications accessing this service should gain access
quickly and easily.
36.1 LDAP versus NIS
The Unix system administrator traditionally uses the NIS service for name resolution
and data distribution in a network. The configuration data contained in the files in
/etc
and the directories
group
,
hosts
,
mail
,
netgroup
,
networks
,
passwd
,
printcap
,
protocols
,
rpc
, and
services
are distributed by clients all over the
network. These files can be maintained without major effort because they are simple
text files. The handling of larger amounts of data, however, becomes increasingly dif-
ficult due to nonexistent structuring. NIS is only designed for Unix platforms. This
means it is not suitable as a centralized data administration tool in heterogeneous net-
works.
Unlike NIS, the LDAP service is not restricted to pure Unix networks. Windows servers
(from 2000) support LDAP as a directory service. Application tasks mentioned above
are additionally supported in non-Unix systems.
The LDAP principle can be applied to any data structure that should be centrally admin-
istered. A few application examples are:
• Employment as a replacement for the NIS service
662 Installation and Administration