Você está tentando carregar o arquivo errado.
ldapadd requer a sintaxe ldif válida, que o arquivo .schema que você está tentando carregar não possui.
Nota: Eu acho rfc2307bis é geralmente um esquema melhor para usar do que rfc2307 (nis).
É possível converter um arquivo .schema em um arquivo .ldif usando slaptest , mas no momento isso é provavelmente mais um problema do que vale a pena. Não tenho certeza se o Ubuntu, como o CentOS, vem com um arquivo .ldif equivalente, então adicionei um ao final dessa resposta.
$ cat /etc/openldap/schema/nis.ldif
# NIS (RFC2307)
# $OpenLDAP$
## This work is part of OpenLDAP Software <http://www.openldap.org/>.
##
## Copyright 1998-2016 The OpenLDAP Foundation.
## All rights reserved.
##
## Redistribution and use in source and binary forms, with or without
## modification, are permitted only as authorized by the OpenLDAP
## Public License.
##
## A copy of this license is available in the file LICENSE in the
## top-level directory of the distribution or, alternatively, at
## <http://www.OpenLDAP.org/license.html>.
#
# Definitions from RFC2307 (Experimental)
# An Approach for Using LDAP as a Network Information Service
#
# Depends upon core.ldif and cosine.ldif
#
# This file was automatically generated from nis.schema; see that file
# for complete references.
#
dn: cn=nis,cn=schema,cn=config
objectClass: olcSchemaConfig
cn: nis
olcAttributeTypes: ( 1.3.6.1.1.1.1.2 NAME 'gecos' DESC 'The GECOS field; th
e common name' EQUALITY caseIgnoreIA5Match SUBSTR caseIgnoreIA5SubstringsMatc
h SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.3 NAME 'homeDirectory' DESC 'The absolut
e path to the home directory' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1
466.115.121.1.26 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.4 NAME 'loginShell' DESC 'The path to th
e login shell' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.2
6 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.5 NAME 'shadowLastChange' EQUALITY integ
erMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.6 NAME 'shadowMin' EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.7 NAME 'shadowMax' EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.8 NAME 'shadowWarning' EQUALITY integerM
atch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.9 NAME 'shadowInactive' EQUALITY integer
Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.10 NAME 'shadowExpire' EQUALITY integerM
atch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.11 NAME 'shadowFlag' EQUALITY integerMat
ch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.12 NAME 'memberUid' EQUALITY caseExactI
A5Match SUBSTR caseExactIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.
26 )
olcAttributeTypes: ( 1.3.6.1.1.1.1.13 NAME 'memberNisNetgroup' EQUALITY ca
seExactIA5Match SUBSTR caseExactIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.11
5.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.1.1.1.14 NAME 'nisNetgroupTriple' DESC 'Netgr
oup triple' SYNTAX 1.3.6.1.1.1.0.0 )
olcAttributeTypes: ( 1.3.6.1.1.1.1.15 NAME 'ipServicePort' EQUALITY intege
rMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.16 NAME 'ipServiceProtocol' SUP name )
olcAttributeTypes: ( 1.3.6.1.1.1.1.17 NAME 'ipProtocolNumber' EQUALITY int
egerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.18 NAME 'oncRpcNumber' EQUALITY integer
Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.19 NAME 'ipHostNumber' DESC 'IP address
' EQUALITY caseIgnoreIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{128} )
olcAttributeTypes: ( 1.3.6.1.1.1.1.20 NAME 'ipNetworkNumber' DESC 'IP netw
ork' EQUALITY caseIgnoreIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{128} SI
NGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.21 NAME 'ipNetmaskNumber' DESC 'IP netm
ask' EQUALITY caseIgnoreIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{128} SI
NGLE-VALUE )
olcAttributeTypes: ( 1.3.6.1.1.1.1.22 NAME 'macAddress' DESC 'MAC address'
EQUALITY caseIgnoreIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{128} )
olcAttributeTypes: ( 1.3.6.1.1.1.1.23 NAME 'bootParameter' DESC 'rpc.bootp
aramd parameter' SYNTAX 1.3.6.1.1.1.0.1 )
olcAttributeTypes: ( 1.3.6.1.1.1.1.24 NAME 'bootFile' DESC 'Boot image nam
e' EQUALITY caseExactIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
olcAttributeTypes: ( 1.3.6.1.1.1.1.26 NAME 'nisMapName' SUP name )
olcAttributeTypes: ( 1.3.6.1.1.1.1.27 NAME 'nisMapEntry' EQUALITY caseExac
tIA5Match SUBSTR caseExactIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.
1.26{1024} SINGLE-VALUE )
olcObjectClasses: ( 1.3.6.1.1.1.2.0 NAME 'posixAccount' DESC 'Abstraction o
f an account with POSIX attributes' SUP top AUXILIARY MUST ( cn $ uid $ uidNu
mber $ gidNumber $ homeDirectory ) MAY ( userPassword $ loginShell $ gecos $
description ) )
olcObjectClasses: ( 1.3.6.1.1.1.2.1 NAME 'shadowAccount' DESC 'Additional a
ttributes for shadow passwords' SUP top AUXILIARY MUST uid MAY ( userPassword
$ shadowLastChange $ shadowMin $ shadowMax $ shadowWarning $ shadowInactive
$ shadowExpire $ shadowFlag $ description ) )
olcObjectClasses: ( 1.3.6.1.1.1.2.2 NAME 'posixGroup' DESC 'Abstraction of
a group of accounts' SUP top STRUCTURAL MUST ( cn $ gidNumber ) MAY ( userPas
sword $ memberUid $ description ) )
olcObjectClasses: ( 1.3.6.1.1.1.2.3 NAME 'ipService' DESC 'Abstraction an I
nternet Protocol service' SUP top STRUCTURAL MUST ( cn $ ipServicePort $ ipSe
rviceProtocol ) MAY description )
olcObjectClasses: ( 1.3.6.1.1.1.2.4 NAME 'ipProtocol' DESC 'Abstraction of
an IP protocol' SUP top STRUCTURAL MUST ( cn $ ipProtocolNumber $ description
) MAY description )
olcObjectClasses: ( 1.3.6.1.1.1.2.5 NAME 'oncRpc' DESC 'Abstraction of an O
NC/RPC binding' SUP top STRUCTURAL MUST ( cn $ oncRpcNumber $ description ) M
AY description )
olcObjectClasses: ( 1.3.6.1.1.1.2.6 NAME 'ipHost' DESC 'Abstraction of a ho
st, an IP device' SUP top AUXILIARY MUST ( cn $ ipHostNumber ) MAY ( l $ desc
ription $ manager ) )
olcObjectClasses: ( 1.3.6.1.1.1.2.7 NAME 'ipNetwork' DESC 'Abstraction of a
n IP network' SUP top STRUCTURAL MUST ( cn $ ipNetworkNumber ) MAY ( ipNetmas
kNumber $ l $ description $ manager ) )
olcObjectClasses: ( 1.3.6.1.1.1.2.8 NAME 'nisNetgroup' DESC 'Abstraction of
a netgroup' SUP top STRUCTURAL MUST cn MAY ( nisNetgroupTriple $ memberNisNe
tgroup $ description ) )
olcObjectClasses: ( 1.3.6.1.1.1.2.9 NAME 'nisMap' DESC 'A generic abstracti
on of a NIS map' SUP top STRUCTURAL MUST nisMapName MAY description )
olcObjectClasses: ( 1.3.6.1.1.1.2.10 NAME 'nisObject' DESC 'An entry in a
NIS map' SUP top STRUCTURAL MUST ( cn $ nisMapEntry $ nisMapName ) MAY descri
ption )
olcObjectClasses: ( 1.3.6.1.1.1.2.11 NAME 'ieee802Device' DESC 'A device w
ith a MAC address' SUP top AUXILIARY MAY macAddress )
olcObjectClasses: ( 1.3.6.1.1.1.2.12 NAME 'bootableDevice' DESC 'A device
with boot parameters' SUP top AUXILIARY MAY ( bootFile $ bootParameter ) )