ldapmodify raises attributetypes: value #0 invalid per syntax error - ldap

Question

I'm currently implementing a pwdCheckModule library for Openldap version 2.4.14 (Version cannot be changed). During that I'd like to read some attributes from the LDAP database. One of these attributes is called pcpMinNumberLowerUpper and holds minimum number of lower and/or upper characters. The attribute should be part of an already existing objectClass called pwdPolicy located under the cn:schema which already has some other attributes like pwdMaxAge etc.
I'd like to use the ldapmodify terminal command in order to add the attribute to the already existing LDAP database. The command I'v just used looks like the following:
ldapmodify -h localhost -p 389 -D "cn=Administrator,dc=<mydc>,dc=<mydc>..." -w "<mysecret>" -x -f pcp_attribute_upgrade.ldif
The corresponding ldif-file has the following content:
dn: cn=schema
changetype: modify
add: attributetypes
attributetypes: ( 1.3.6.1.4.1.42.2.27.8.1.18 NAME 'pcpMinNumberLowerUpper' DESC 'Minimum of upper or lower characters' SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUED USAGE userApplications )
Now, if I execute the command above it raises the following error message to the terminal output:
ldap_start_tls: Protocol error (2)
additional info: unsupported extended operation
modifying entry "cn=schema"
ldap_modify: Invalid syntax (21)
additional info: attributetypes: value #0 invalid per syntax
I already tried to use olcAttributeTypes instead of attributeTypes but it did not help. Any help would be nice :-)
Thanks in advance,
Flo

Answer 1

With default OpenLdap configuration, for schema modification usually you have to use external authentication from local ldap servers root account:
sudo ldapmodify -Y EXTERNAL -H ldapi:/// -f pcp.ldif
and pcp.ldif should be:
dn: cn=schema,cn=config
changetype: modify
add: olcAttributetypes
olcAttributetypes: ( 1.3.6.1.4.1.42.2.27.8.1.18 NAME 'pcpMinNumberLowerUpper' DESC 'Minimum of upper or lower characters' SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE USAGE userApplications )
(changed dn, "attributeTypes" replaced to "olcAttributetypes" and "SINGLE-VALUED" to "SINGLE-VALUE")

Answer 2

The keyword for single valued attribute is SINGLE-VALUE, as reported when trying to add the schema definition to the OpenDJ LDAP directory server :
The provided value "( 1.3.6.1.4.1.42.2.27.8.1.18 NAME
'pcpMinNumberLowerUpper' DESC 'Minimum of upper or lower characters'
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUED USAGE
userApplications )"could not be parsed as a valid attribute type
description because it contains an illegal token "SINGLE-VALUED"
Change it as below and it'll work.
dn: cn=schema
changetype: modify
add: attributetypes
attributetypes: ( 1.3.6.1.4.1.42.2.27.8.1.18 NAME 'pcpMinNumberLowerUpper' DESC 'Minimum of upper or lower characters' SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE USAGE userApplications )