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LDAP Linux HOWTO: Configuring the LDAP Server Next Previous Contents

3. Configuring the LDAP Server

Once the software has been installed and built, you are ready to configure it for use at your site. All slapd runtime configuration is accomplished through the slapd.conf file, installed in the prefix directory you specified in the configuration script or by default in /usr/local/etc/openldap.

This section details the commonly used configuration directives on slapd.conf. For a complete list, see slapd.conf(5) manual page. The configuration file directives are separated into global, backend-specific and data-specific categories. Here you will find descriptions of directives, together with their default values (if any) and with examples of their use.

3.1 Configuration File Format

The slapd.conf file consists of three types of configuration information: global, backend specific, and database specific. Global information is specified first, followed by information associated with a particular backend type, which is then followed by information associated with a particular database instance.

Global directives can be overridden in a backend and/or database directives, backend directives can be overridden by database directives.

Blank lines and comment lines beginning with a '#' character are ignored. If a line begins with white space, it is considered a continuation of the previous line. The general format of slapd.conf is as follows:

# global configuration directives
<global config directives>

# backend definition
backend <typeA>
<backend-specific directives>

# first database definition & config directives
database <typeA>
<database-specific directives>

# second database definition & config directives
database <typeB>
<database-specific directives>

# second database definition & config directives
database <typeA>
<database-specific directives>

# subsequent backend & database definitions & config directives

A configuration directive may take arguments. If so, they are separated by white space. If an argument contains white space, the argument should be enclosed in double quotes "like this". If an argument contains a double quote or a backslash character `\', the character should be preceded by a backslash character `\'.

The distribution contains an example configuration file that will be installed in the /usr/local/etc/openldap directory. A number of files containing schema definitions (attribute types and object classes) are also provided in the /usr/local/etc/openldap/schema directory.

3.2 Global Directives

Directives described in this section apply to all backends and databases unless specifically overridden in a backend or database definition. Arguments that should be replaced by actual text are shown in brackets <>.

access to <what> [ by <who> <accesslevel> <control> ]+

This directive grants access (specified by <accesslevel>) to a set of 
entries and/or attributes (specified by <what>) by one or more requesters
 (specified by <who>). See the Access Control examples for more details.

attributetype <RFC2252 Attribute Type Description>

This directive defines an attribute type.

defaultaccess { none | compare | search | read | write }

This directive specifies the default access to grant requesters when no access
directives have been specified. Any given access level implies all lesser 
access levels (e.g., read access implies search and compare but not write).

defaultaccess read

idletimeout <integer>

Specify the number of seconds to wait before forcibly closing an idle client 
connection. An idletimeout of 0, the default, disables this feature.

include <filename>

This directive specifies that slapd should read additional configuration 
information from the given file before continuing with the next line of the 
current file. The included file should follow the normal slapd config file 
format. The file is commonly used to include files containing schema 

Note: You should be careful when using this directive - there is no small limit on the number of nested include directives, and no loop detection is done.

loglevel <integer>

This directive specifies the level at which debugging statements and operation
statistics should be syslogged (currently logged to the syslogd(8) LOCAL4 
facility). You must have configured OpenLDAP --enable-debug (the default) for 
this to work (except for the two statistics levels, which are always enabled).
Log levels are additive. To display what numbers correspond to what kind of 
debugging, invoke slapd with -? or consult the table below. The possible values
 for <integer> are:

-1 enable all debugging
0 no debugging 
1 trace function calls 
2 debug packet handling 
4 heavy trace debugging 
8 connection management 
16 print out packets sent and received 
32 search filter processing 
64 configuration file processing 
128 access control list processing 
256 stats log connections/operations/results 
512 stats log entries sent 
1024 print communication with shell backends 
2048 print entry parsing debugging 

loglevel 255 or loglevel -1
This will cause lots and lots of debugging information to be syslogged. 
loglevel 256 

objectclass <RFC2252 Object Class Description>

This directive defines an object class.

referral <URI>

This directive specifies the referral to pass back when slapd cannot find a 
local database to handle a request.

referral ldap://root.openldap.org

This will refer non-local queries to the global root LDAP server at the 
OpenLDAP Project. Smart LDAP clients can re-ask their query at that server, but
 note that most of these clients are only going to know how to handle simple 
LDAP URLs that contain a host part and optionally a distinguished name part.

sizelimit <integer>

This directive specifies the maximum number of entries to return from a search

sizelimit 500

timelimit <integer>

This directive specifies the maximum number of seconds (in real time) slapd 
will spend answering a search request. If a request is not finished in this 
time, a result indicating an exceeded timelimit will be returned.

timelimit 3600

3.3 General Backend Options

Directives in this section apply only to the backend in which they are defined. They are supported by every type of backend. Backend directives apply to all databases instances of the same type and, depending on the directive, may be overridden by database directives.

backend <type>

This directive marks the beginning of a backend definition. <type> should
 be one of ldbm, shell, passwd, or other supported backend type.

3.4 General Database Directives

Directives in this section apply only to the database in which they are defined. They are supported by every type of database.

database <type>

This directive marks the beginning of a new database instance definition. 
<type> should be one of ldbm, shell, passwd, or other supported database

database ldbm

This marks the beginning of a new LDBM backend database instance definition.

readonly { on | off }

This directive puts the database into "read-only" mode. Any attempts to modify
the database will return an "unwilling to perform" error.

readonly off


replica host=<hostname>[:<port>] [bindmethod={ simple | kerberos | sasl }] ["binddn=<DN>"] [mech=<mech>] [authcid=<identity>] [authzid=<identity>] [credentials=<password>] [srvtab=<filename>]

This directive specifies a replication site for this database. The 
host= parameter specifies a host and optionally a port where the slave slapd 
instance can be found. Either a domain name or IP address may be used for 
<hostname>. If <port> is not given, the standard LDAP port number 
(389) is used.

The binddn= parameter gives the DN to bind as for updates to the slave slapd. 
It should be a DN which has read/write access to the slave slapd's database, 
typically given as a rootdn in the slave's config file. It must also match the
updatedn directive in the slave slapd's config file. Since DNs are likely to 
contain embedded spaces, the entire "binddn=<DN>" string should be 
enclosed in double quotes.

The bindmethod is simple or kerberos or sasl, depending on whether simple 
password-based authentication or Kerberos authentication or SASL authentication
 is to be used when connecting to the slave slapd.

Simple authentication should not be used unless adequate integrity and privacy
protections are in place (e.g. TLS or IPSEC). Simple authentication requires 
specification of binddn and credentials parameters.

Kerberos authentication is deprecated in favor of SASL authentication 
mechanisms, in particular the KERBEROS_V4 and GSSAPI mechanisms. Kerberos 
authentication requires binddn and srvtab parameters.

SASL authentication is generally recommended. SASL authentication requires 
specification of a mechanism using the mech parameter. Depending on the 
mechanism, an authentication identity and/or credentials can be specified using
 authcid and credentials respectively. The authzid parameter may be used to 
specify an authorization identity.

replogfile <filename>

This directive specifies the name of the replication log file to which slapd 
will log changes. 
The replication log is typically written by slapd and read by slurpd. Normally,
 this directive is only used if slurpd is being used to replicate the database.
 However, you can also use it to generate a transaction log, if slurpd is not 
running. In this case, you will need to periodically truncate the file, since 
it will grow indefinitely otherwise.

rootdn <dn>

This directive specifies the DN that is not subject to access control or 
administrative limit restrictions for operations on this database. The DN 
need not refer to an entry in the directory. The DN may refer to a SASL 

Entry-based Example:
rootdn "cn=Manager, dc=example, dc=com"

SASL-based Example:
rootdn "uid=root@EXAMPLE.COM"

rootpw <password>

This directive specifies a password for the DN given above that will always 
work, regardless of whether an entry with the given DN exists or has a 
password. This directive is deprecated in favor of SASL based authentication.

rootpw secret

suffix <dn suffix>

This directive specifies the DN suffix of queries that will be passed to this 
backend database. Multiple suffix lines can be given, and at least one is 
required for each database definition.

suffix "dc=example, dc=com"

Queries with a DN ending in "dc=example, dc=com" will be passed to this 

Note: When the backend to pass a query to is selected, slapd looks at the 
suffix line(s) in each database definition in the order they appear in the 
file. Thus, if one database suffix is a prefix of another, it must appear after
 it in the config file. 

updatedn <dn>

This directive is only applicable in a slave slapd. It specifies the DN allowed
 to make changes to the replica. This may be the DN slurpd(8) binds as when 
making changes to the replica or the DN associated with a SASL identity.

Entry-based Example:
updatedn "cn=Update Daemon, dc=example, dc=com"

SASL-based Example:
updatedn "uid=slurpd@EXAMPLE.COM"

updateref <URL>

This directive is only applicable in a slave slapd. It specifies the URL to 
return to clients which submit update requests upon the replica. If specified 
multiple times, each URL is provided.

update  ldap://master.example.net

3.5 LDBM Backend-Specific Directives

Directives in this category only apply to the LDBM backend database. That is, they must follow a "database ldbm" line and come before any other "database" line.

cachesize <integer>

This directive specifies the size in entries of the in-memory cache maintained
by the LDBM backend database instance.

cachesize 1000

dbcachesize <integer>

This directive specifies the size in bytes of the in-memory cache associated 
with each open index file. If not supported by the underlying database method,
this directive is ignored without comment. Increasing this number uses more 
memory but can cause a dramatic performance increase, especially during 
modifies or when building indexes.

dbcachesize 100000


This option, if present, disables database locking. Enabling this option may 
improve performance at the expense of data security.


This option causes on-disk database contents not be immediately synchronized 
with in memory changes upon change. Enabling this option may improve 
performance at the expense of data security.

directory <directory>

This directive specifies the directory where the LDBM files containing the 
database and associated indexes live.

directory /usr/local/var/openldap-ldbm

index {<attrlist> | default} [pres,eq,approx,sub,none]

This directive specifies the indexes to maintain for the given attribute. If 
only an <attrlist> is given, the default indexes are maintained.

index default pres,eq
index objectClass,uid
index cn,sn eq,sub,approx

The first line sets the default set of indices to maintain to present and 
equality. The second line causes the default (pres,eq) set of indices to be 
maintained for objectClass and uid attribute types. The third line causes 
equality, substring, and approximate indices to be maintained for cn and sn 
attribute types.

mode <integer>

This directive specifies the file protection mode that newly created database 
index files should have.

mode 0600

3.6 Other Backend Databases

slapd supports a number of backend database types besides the default LDBM:

  • ldbm: Berkeley or GNU DBM compatible backend
  • passwd: Provides read-only access to /etc/passwd
  • shell: Shell (extern program) backend
  • sql: SQL Programmable backend

Take a look on the slapd.conf(5) manpage for details.

3.7 Access Control Examples

The access control facility presented on section 3.2 is quite powerful. This section shows some examples of its use. First, some simple examples:

access to * by * read 

This access directive grants read access to everyone. If it appears alone it is the same as the following defaultaccess line.

defaultaccess read 

The following example shows the use of a regular expression to select the entries by DN in two access directives where ordering is significant.

access to dn=".*, o=U of M, c=US" 
by * search 
access to dn=".*, c=US" 
by * read 

Read access is granted to entries under the c=US subtree, except for those entries under the "o=University of Michigan, c=US" subtree, to which search access is granted. If the order of these access directives was reversed, the U-M-specific directive would never be matched, since all U-M entries are also c=US entries.

The next example again shows the importance of ordering, both of the access directives and the "by" clauses. It also shows the use of an attribute selector to grant access to a specific attribute and various <who> selectors.

access to dn=".*, o=U of M, c=US" attr=homePhone 
by self write 
by dn=".*, o=U of M, c=US" search 
by domain=.*\.umich\.edu read 
by * compare 
access to dn=".*, o=U of M, c=US" 
by self write 
by dn=".*, o=U of M, c=US" search 
by * none 

This example applies to entries in the "o=U of M, c=US" subtree. To all attributes except homePhone, the entry itself can write them, other U-M entries can search by them, anybody else has no access. The homePhone attribute is writable by the entry, searchable by other U-M entries, readable by clients connecting from somewhere in the umich.edu domain, and comparable by everybody else.

Sometimes it is usefull to permit a particular DN to add or remove itself from an attribute. For example, if you would like to create a group and allow people too add and remove only their own DN from the member attribute, you could accomplish it with an access directive like this:

access to attr=member,entry 
by dnattr=member selfwrite 

The dnattr <who> selector says that the access applies to entries listed in the member attribute. The selfwrite access selector says that such members can only add or delete their own DN from the attribute, not other values. The addition of the entry attribute is required because access to the entry is required to access any of the entry's attributes.

Note that the attr=member construct in the <what> clause is a shorthand for the clause "dn=* attr=member" (i.e., it matches the member attribute in all entries).

Note: Take a look on OpenLDAP Administrator's Guide at http://www.openldap.org to learn more about Access Control on Ldap.

3.8 Configuration File Example

The following is an example configuration file, interspersed with explanatory text. It defines two databases to handle different parts of the X.500 tree; both are LDBM database instances. The line numbers shown are provided for reference only and are not included in the actual file. First, the global configuration section:

  1.    # example config file - global configuration section
  2.    include /usr/local/etc/schema/core.schema
  3.    referral ldap://root.openldap.org
  4.    access to * by * read

Line 1 is a comment. Line 2 includes another config file which containing core schema definitions. The referral directive on line 3 means that queries not local to one of the databases defined below will be referred to the LDAP server running on the standard port (389) at the host root.openldap.org.

Line 4 is a global access control. It is used only if no database access controls match or when the target objects are not under the control of any database (such as the Root DSE).

The next section of the configuration file defines an LDBM backend that will handle queries for things in the "dc=example,dc=com" portion of the tree. The database is to be replicated to two slave slapds, one on truelies, the other on judgmentday. Indexes are to be maintained for several attributes, and the userPassword attribute is to be protected from unauthorized access.

  5.    # ldbm definition for the example.com
  6.    database ldbm
  7.    suffix "dc=example, dc=com"
  8.    directory /usr/local/var/openldap
  9.    rootdn "cn=Manager, dc=example, dc=com"
 10.    rootpw secret
 11.    # replication directives
 12.    replogfile /usr/local/var/openldap/slapd.replog
 13.    replica host=slave1.example.com:389
 14.            binddn="cn=Replicator, dc=example, dc=com"
 15.            bindmethod=simple credentials=secret
 16.    replica host=slave2.example.com
 17.            binddn="cn=Replicator, dc=example, dc=com"
 18.            bindmethod=simple credentials=secret
 19.    # indexed attribute definitions
 20.    index uid pres,eq
 21.    index cn,sn,uid pres,eq,approx,sub
 22.    index objectClass eq
 23.    # ldbm access control definitions
 24.    access to attr=userPassword
 25.            by self write
 26.            by anonymous auth
 27.            by dn="cn=Admin,dc=example,dc=com" write
 28.            by * none
 29.    access to *
 30.            by dn="cn=Admin,dc=example,dc=com" write
 31.            by * read

Line 5 is a comment. The start of the database definition is marked by the database keyword on line 6. Line 7 specifies the DN suffix for queries to pass to this database. Line 8 specifies the directory in which the database files will live.

Lines 9 and 10 identify the database "super user" entry and associated password. This entry is not subject to access control or size or time limit restrictions.

Lines 11 through 18 are for replication. Line 11 specifies the replication log file (where changes to the database are logged - this file is written by slapd and read by slurpd). Lines 12 through 14 specify the hostname and port for a replicated host, the DN to bind as when performing updates, the bind method (simple) and the credentials (password) for the binddn. Lines 15 through 18 specify a second replication site.

Lines 20 through 22 indicate the indexes to maintain for various attributes.

Lines 24 through 31 specify access control for entries in the database. For all entries, the userPassword attribute is writable by the entry itself and by the "admin" entry. It may be used for authentication/authorization purposes, but is otherwise not readable. All other attributes are writable by the "admin" entry and may be read by authenticated users.

The next section of the example configuration file defines another LDBM database. This one handles queries involving the dc=example,dc=net subtree. Note that without line 37, the read access would be allowed due to the global access rule at line 4.

 32.    # ldbm definition for example.net
 33.    database ldbm
 34.    suffix "dc=example, dc=net"
 35.    directory /usr/local/var/ldbm-example-net
 36.    rootdn "cn=Manager, dc=example, dc=com"
 37.    access to * by users read

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