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@ -4,10 +4,11 @@
H1: Introduction to slapd and slurpd
This document describes how to build, configure, and run the stand-alone
LDAP daemon ({{I:slapd}}) and the stand-alone LDAP update replication
daemon ({{I:slurpd}}). It is intended for newcomers and experienced
administrators alike. This section provides a basic introduction to directory
service, and the directory service provided by {{I:slapd}} in particular.
{{TERM:LDAP}} daemon ({{slapd}}) and the stand-alone LDAP update replication
daemon ({{slurpd}}). It is intended for newcomers and experienced
administrators alike. This section provides a basic introduction to
directory services and, in particular, the directory services provided
by {{slapd}}.
@ -30,31 +31,31 @@ There are many different ways to provide a directory service. Different
methods allow different kinds of information to be stored in the directory,
place different requirements on how that information can be referenced,
queried and updated, how it is protected from unauthorized access, etc.
Some directory services are {{I:local}}, providing service to a restricted
Some directory services are {{local}}, providing service to a restricted
context (e.g., the finger service on a single machine). Other services are
global, providing service to a much broader context (e.g., the entire Internet).
Global services are usually {{I:distributed}}, meaning that the data they
Global services are usually {{distributed}}, meaning that the data they
contain is spread across many machines, all of which cooperate to provide
the directory service. Typically a global service defines a uniform
{{I:namespace}} which gives the same view of the data no matter where
you are in relation to the data itself. The Internet {{Domain Name System}}
{{namespace}} which gives the same view of the data no matter where
you are in relation to the data itself. The Internet {{TERM[expand]DNS}}
is an example of a globally distributed directory service.
H2: What is LDAP?
{{I:Slapd}}'s model for directory service is based on a global directory
{{slapd}}'s model for directory service is based on a global directory
model called {{TERM:LDAP}}. LDAP stands for {{TERM[expand]LDAP}}.
LDAP is a directory access protocol that runs over
{{TCP/IP}}. The nitty-gritty details of LDAP are defined in
{{TERM:TCP}}/{{TERM:IP}}. The nitty-gritty details of LDAP are defined in
{{REF:RFC2251}} "The Lightweight Directory Access Protocol (v3)."
This section gives an overview of LDAP from a user's perspective.
{{I:What kind of information can be stored in the directory?}}
{{What kind of information can be stored in the directory?}}
The LDAP information model is based on {{entries}}. An entry is a
collection of attributes that has a globally-unique {{distinguished
name}} (DN).
collection of attributes that has a globally-unique
{{TERM[expand]DN}} (DN).
The DN is used to refer to the entry unambiguously. Each of the
entry's attributes has a {{type}} and one or more {{values}}.
The types are typically mnemonic strings, like "{{EX:cn}}" for common
@ -64,7 +65,7 @@ be the value {{EX: Babs Jensen}}. A {{EX:mail}} attribute might
contain the value "{{EX:babs@openldap.org}}". A {{EX:jpegPhoto}}
attribute would contain a photograph in the JPEG (binary) format.
{{I:How is the information arranged?}}
{{How is the information arranged?}}
In LDAP, directory entries are arranged in a hierarchical tree-like
structure. Traditionally, this structure reflected the geographic
and/or organizational boundaries. Entries representing countries
@ -87,20 +88,20 @@ FT[align="Center"] Figure 1.2: LDAP directory tree (Internet naming)
In addition, LDAP allows you to control which attributes are required
and allowed in an entry through the use of a special attribute called
{{I:objectClass}}. The values of the {{I:objectClass}} attribute
determine the {{I:schema}} rules the entry must obey.
{{objectClass}}. The values of the {{objectClass}} attribute
determine the {{schema}} rules the entry must obey.
{{I:How is the information referenced?}}
{{How is the information referenced?}}
An entry is referenced by its distinguished name, which is constructed
by taking the name of the entry itself (called the relative distinguished
name, or RDN) and concatenating the names of its ancestor entries. For
by taking the name of the entry itself (called the {{TERM[expand]RDN}}
or RDN) and concatenating the names of its ancestor entries. For
example, the entry for Barbara Jensen in the Internet naming example
above has an RDN of {{EX:uid=babs}} and a DN of
{{EX:uid=babs, ou=People, dc=OpenLDAP, dc=com}}". The full DN format is
described in {{REF:RFC2253}}, "Lightweight Directory Access Protocol (v3):
UTF-8 String Representation of Distinguished Names."
{{I:How is the information accessed?}}
{{How is the information accessed?}}
LDAP defines operations for interrogating and updating the directory.
Operations are provided for adding and deleting
an entry from the directory, changing an existing entry, and changing the
@ -119,7 +120,7 @@ string {{EX:Acme}} in their name, and that have a fax number. LDAP lets
you do this too. The next section describes in more detail what you can
do with LDAP and how it might be useful to you.
{{I:How is the information protected from unauthorized access?}}
{{How is the information protected from unauthorized access?}}
Some directory services provide no protection, allowing anyone to see
the information. LDAP provides a method for a client to authenticate,
or prove its identity to a directory server, paving the way for rich
@ -128,7 +129,7 @@ access control to protect the information the server contains.
H2: How does LDAP work?
LDAP directory service is based on a {{I:client-server}} model. One or more
LDAP directory service is based on a {{client-server}} model. One or more
LDAP servers contain the data making up the LDAP directory tree. An LDAP
client connects to an LDAP server and asks it a question. The server
responds with the answer and/or with a pointer to where the client can
@ -141,51 +142,77 @@ a global directory service, like LDAP.
H2: What is slapd and what can it do?
{{I:Slapd}} is an LDAP directory server that runs on many different
{{slapd}} is an LDAP directory server that runs on many different
platforms. You can use it to provide a directory service of your very own.
Your directory can contain pretty much anything you want to put in it. You
can connect it to the global LDAP directory service, or run a service all by
yourself. Some of slapd's more interesting features and capabilities include:
{{B:Choice of databases}}: {{I:Slapd}} comes with a variety of different
backend databases you can choose from. They include LDBM, a high-performance
disk-based {{embedded}} database; SHELL, a database interface to arbitrary
shell scripts; and PASSWD, a simple password file database.
{{B:LDAPv2}} and {{B:LDAPv3}}: {{slapd}} supports both version 2 and 3
of the {{TERM[expand]LDAP}}. {{slapd}} provides support
for the latest features while maintaining interoperability with existing
clients. {{slapd}} supports both IPv4 and IPv6 protocols.
{{B:Multiple database instances}}: {{I:Slapd}} can be configured to serve
multiple databases at the same time. This means that a single {{I:slapd}}
{{B:{{TERM[expand]SASL}}}}: {{slapd}} supports
strong authentication services through the use of SASL. {{slapd}}'s
SASL implementation utilizes {{PRD:Cyrus}} software which supports
a number of mechanisms including DIGEST-MD5, EXTERNAL, and GSSAPI.
{{B:{{TERM[expand]TLS}}}}: {{slapd}} provides privacy and
integrity protections through the use of TLS (or SSL). {{slapd}}'s
TLS implementation utilizes {{PRD:OpenSSL}} software.
{{B:Access control}}: {{slapd}} provides a rich and powerful access
control facility, allowing you to control access to the information
in your database(s). You can control access to entries based on
LDAP authorization information, {{TERM:IP}} address, domain name
and other criteria.
{{slapd}} supports both {{static}} and {{dynamic}} access control
information.
{{B:Internationalization}}: {{slapd}} supports Unicode and language
tags.
{{B:Choice of databases}}: {{slapd}} comes with a variety of different
backend databases you can choose from. They include
{{TERM:LDBM}}, a high-performance disk-based {{embedded}} database;
SHELL, a database interface to arbitrary shell scripts; and
PASSWD, a simple password file database. LDBM utilizes either
{{PRD:BerkeleyDB}} or {{PRD:GDBM}}.
{{B:Multiple database instances}}: {{slapd}} can be configured to serve
multiple databases at the same time. This means that a single {{slapd}}
server can respond to requests for many logically different portions
of the LDAP tree, using the same or different backend databases.
{{B:Generic database API}}: If you require even more customization,
{{I:slapd}} lets you write your own backend database easily. {{I:Slapd}}
{{B:Generic modules API}}: If you require even more customization,
{{slapd}} lets you write your own modules easily. {{slapd}}
consists of two distinct parts: a front end that handles protocol
communication with LDAP clients; and a backend that handles database
operations. Because these two pieces communicate via a well-defined
C API, you can write your own customized database backend to {{I:slapd}}.
A number of {{programmable}} backends are also provided.
communication with LDAP clients; and modules which handles specific
tasks such as database operations. Because these two pieces communicate
via a well-defined C API, you can write your own customized modules
which extend {{slapd}} in numerous ways. Also, a number of
{{programmable database}} modules are provided. These allowing you
to expose external data sources to {{slapd}} using popular programming
languages ({{PRD:Perl}}, {{Shell}}, {{PRD:SQL}}, and {{PRD:TCL}}.
{{B:Access control}}: {{I:Slapd}} provides a rich and powerful access
control facility, allowing you to control access to the information
in your database(s). You can control access to entries based on
LDAP authentication information, IP address, domain name and other criteria.
{{B:Threads}}: {{slapd}} is threaded for high performance. A
single multi-threaded {{slapd}} process handles all incoming
requests, reducing the amount of system overhead required.
{{B:Threads}}: {{I:Slapd}} is threaded for high performance. A
single multi-threaded {{I:slapd}} process handles all incoming
requests, reducing the amount of system overhead required. {{I:Slapd}}
will automatically select the best thread support for your platform.
{{B:Replication}}: {{slapd}} can be configured to maintain replica
copies of its database. This {{single-master/multiple-slave}}
replication scheme is vital in high-volume environments where a
single {{slapd}} just doesn't provide the necessary availability
or reliability. {{slapd}}
also includes experimental support for {{multi-master}} replication.
{{B:Replication}}: {{I:Slapd}} can be configured to maintain replica
copies of its database. This master/slave replication scheme is
vital in high-volume environments where a single {{I:slapd}} just
doesn't provide the necessary availability or reliability.
{{B:Configuration}}: {{I:Slapd}} is highly configurable through a
{{B:Configuration}}: {{slapd}} is highly configurable through a
single configuration file which allows you to change just about
everything you'd ever want to change. Configuration options have
reasonable defaults, making your job much easier.
{{I:Slapd}} also has its limitations, of course. The main LDBM
{{slapd}} also has its limitations, of course. The main LDBM
database backend does not handle range queries or negation queries
very well. These features and more will be coming in a future release.
@ -193,33 +220,34 @@ very well. These features and more will be coming in a future release.
H2: What about X.500?
Technically, LDAP is a directory access protocol to an X.500 directory
service, the OSI directory service. Initial LDAP servers were
were gateway between LDAP and the X.500 Directory Access Protocol (DAP).
DAP is a heavyweight protocol that runs over a full OSI stack and
requires a significant amount of computing resources to run. LDAP
runs directly over TCP and provides most of the functionality of DAP
at a much lower cost.
Technically, LDAP is a directory access protocol to an {{TERM:X.500}}
directory service, the {{TERM:OSI}} directory service. Initial
LDAP servers were were gateway between LDAP and the X.500
{{TERM[expand]DAP}} (DAP).
DAP is a heavyweight protocol that runs over a full OSI protocol stack
and requires a significant amount of computing resources to run.
LDAP is designed to operate over {{TERM:TCP}}/{{TERM:IP}} and provides
most of the functionality of DAP at a much lower cost.
This use of LDAP makes it easy to access the X.500 directory, but still
requires a full X.500 service to make data available to the many LDAP
clients being developed. As with full X.500 DAP clients, a full X.500
DAP server is no small piece of software to run.
The stand-alone LDAP daemon, or {{I:slapd}}(8), is meant to remove much
The stand-alone LDAP daemon, or {{slapd}}(8), is meant to remove much
of the burden from the server side just as LDAP itself removed much of
the burden from clients. If you are already running an X.500 DAP service
and you want to continue to do so, you can probably stop reading this
guide, which is all about running LDAP via {{I:slapd}}, without running
guide, which is all about running LDAP via {{slapd}}, without running
X.500 DAP. If you are not running X.500 DAP, want to stop running
X.500 DAP, or have no immediate plans to run X.500 DAP, read on.
It is possible to replicate data from a {{I:slapd}} directory
server to a X.500 DSA, which allows your organization to make your
data available as part of the global X.500 DAP directory service
on a "read-only" basis. This is discussed in section 11.6.
It is possible to replicate data from a {{slapd}} directory
server to a X.500 {{TERM:DSA}}, which allows your organization to
make your data available as part of the global X.500 DAP directory
service on a "read-only" basis. This is discussed in section 11.6.
Another way to make data in a {{I:slapd}} server available to the
Another way to make data in a {{slapd}} server available to the
X.500 community would be by using a X.500 DAP to LDAP gateway. At
this time, no such software has been written (to the best of our
knowledge), but hopefully some group will see fit to write such a
@ -228,11 +256,11 @@ gateway.
H2: What is slurpd and what can it do?
{{I:Slurpd}}(8) is a daemon that helps {{I:slapd}} provide
{{slurpd}}(8) is a daemon that helps {{slapd}} provide
replicated service. It is responsible for distributing changes made
to the master {{I:slapd}} database out to the various {{I:slapd}}
replicas. It frees {{I:slapd}} from having to worry that some
to the master {{slapd}} database out to the various {{slapd}}
replicas. It frees {{slapd}} from having to worry that some
replicas might be down or unreachable when a change comes through;
{{I:slurpd}} handles retrying failed requests automatically.
{{I:Slapd}} and {{I:slurpd}} communicate through a simple text
{{slurpd}} handles retrying failed requests automatically.
{{slapd}} and {{slurpd}} communicate through a simple text
file that is used to log changes.