I think you should read the manual again. That is not a DB_CONFIG. That looks like a slapd config file, in ldif format.

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From: Lepoutre Lionel <leplio@gmail.com>
Sent: Friday, 17 July 2009 10:19 PM
To: openldap-software@openldap.org
Subject: [Openldap 2.4.16] Unable to use DB_CONFIG

Hello,

I am trying to use the DB_CONFIG file as it seems to be the good way to configure my hdb database.
My LDAP start without any DB_CONFIG, but when I put a DB_CONFIG file I have an error:

"unrecognized name-value pair: dn:"

Here is an extract of my files (I have changed my personal information by MY...)
- slapd.conf:
------------------------------------
database        hdb
suffix          "MY_LDAP_SUFFIX"
rootdn          "MY_ROOT_DN"
rootpw          MY_ROOT_PASS
directory       /opt/local/openldap/var/openldap-data

- DB_CONFIG:
-----------------------------------
# global configuration settings
dn: cn=config
objectClass: olcGlobal
cn: config
# schema definitions
dn: cn=schema,cn=config
objectClass: olcSchemaConfig
cn: schema
dn: cn=core,cn=schema,cn=config
objectClass: olcSchemaConfig
cn: core
#backend definitions
dn: olcBackend=hdb,cn=config
objectClass: olcBackendConfig
olcBackend: hdb
# database definitions
dn: olcDatabase=hdb,cn=config
objectClass: olcDatabaseConfig
olcDatabase: hdb
olcSuffix: MY_LDAP_SUFFIX
....

It seems to be because of the first line of my DB_CONFIG file but I have copied it from the documentation (http://www.openldap.org/doc/admin24/slapdconf2.html). Did I miss something? Is it not the good file for such configuration?
Any help is welcome and sorry if it is a stupid question.

Lionel