Installation and configuration of openldap in Ubuntu

This entry is part 2 of 8 in the series Openldap Tutorial


This article deals with the installation and configuration of openldap in ubuntu 16.04

Install Openldap

Open your terminal and execute the below command

 apt install slapd ldap-utils


In the next screen provide your LDAP admin password and select OK.

openldap installation - 1


You’ll be asked to confirm your admin password again

openldap installation - 2


We have now installed openldap but we will customize the configuration again. You can verify the installation by checking if the slapd service is running.

 systemctl status slapd


The above steps would have installed openldap and configured it with the default values for suffix. In order to have a more specific installation, we will relaunch the configuration through the debian tool.

dpkg-reconfigure slapd


You’ll be prompted with a window as below. Select ‘No‘ in order to write a new configuration

openldap configuration - 1


In the next step enter the domain name that will be our DIT suffix. ( devopsideas.com in this example )

openldap configuration - 2


Next you need to enter the name of your organization,

openldap configuration - 3


Next you’ll be asked to enter administrator password ( This is the credentials for the rootDN of your database instance )

openldap configuration - 4


Confirm the password again,


Next you can choose the backend database. We’ll be using the default MDB in this example,

openldap configuration - 6


In the next step, it’ll ask whether the database should be removed when removing openldap. If you have a good backup in place, you can select ‘Yes‘ for this option.

openldap configuration - 7


Purge old (dirty) directory. The debian installer will detect the old installation, it suggests you to move the old directory. If you have given Yes in the previous step, select ‘Yes‘ in this step as well.

openldap configuration - 8


In the next step, LDAP protocol version to be used. If this is a fresh install, you can disallow LDAPv2. If you have existing application that uses LDAP and that needs LDAPv2, then you need to select ‘Yes‘. For this example we will select ‘No’.

openldap configuraiton - 9


We are done with the installation and re-configuration steps. The installation process set up 2 DITs. One for slapd-config (cn=config) and one for our own data (dc=devopsideas,dc=com). Let’s take a look.


Olc / slapd.d / cn=config Method

The configuration we will see here is OLC ( Online Configuration ) or otherwise called as slapd.d  or cn=config configuration. The OLC configuration allows us to make changes dynamically. There is no need for the restart of the slapd process after any configuration changes which was not the case in the earlier slapd.conf configuration.

For this purpose, slapd is designed to be configured within slapd itself by dedicating a separate DIT for that purpose. This allows one to dynamically configure slapd without the need to restart the service.



cn=config Tree

(Other objects may be part of the configuration but were omitted from the illustration for clarity)

 This is what the slapd-config database/DIT looks like and it lives under /etc/ldap/slapd.d



As you can see, some classical schemas (cosine, nis, inetorgperson) come pre-loaded with slapd. There is also an included “core” schema, a pre-requisite for any schema to work. olcDatabase={1}mdb.ldif is the database instance that contains dc=devopsideas,dc=com DIT

To understand it easier, you can think of cn=config as the global config option that gets applied to all DIT’s that we create. From the diagram we can see that the configuration is common to  olcDatabase={1}mdb.ldif  database. If we create another DIT, for example dc=example,dc=com the cn=config configuration will be global to that as well.


LDAP search command

ldapsearch command is part of the ldap utils package and which we will use predominantly in openldap. Let us run our first ldapsearch command to see what we have in our DIT dc=devopsideas,dc=com

$ ldapsearch -W -LLL -D cn=admin,dc=devopsideas,dc=com -b dc=devopsideas,dc=com 'dn'

Enter LDAP Password:

dn: dc=devopsideas,dc=com

dn: cn=admin,dc=devopsideas,dc=com

ldapsearch command explanation,

-W – Prompt for simple authentication.  This is used instead of specifying the password on the command line.

-D – Distinguished name to bind to the LDAP directory. In this case we are binding with our admin credential

-LLL – A single -L restricts the output to LDIFv1. A second -L disables comments.  A third -L disables printing of the LDIF version

-b – searchbase – This defines the starting point for the search instead of the default

dn –  This will filter the output to display only the values of dn


  • Explanation of entries:

    • dc=devopsideas,dc=com: base of the DIT

    • cn=admin,dc=devopsideas,dc=com: administrator (rootDN) for this DIT (set up during package install)


Configuring credentials for cn=config

By default there is no administrative account created for the slapd-config database. Hence we need to create a new DN (cn=admin,cn=config)  and provide access to cn=config DIT. We will be using ldapmodify command and LDIF ( LDAP Data Interchange Format ) to achieve this. LDIF is a standard plain text data interchange format for representing LDAP (Lightweight Directory Access Protocol) directory content and update requests. 

First, we will create the ssha encrypted password that we will us in the LDIF file. Run the below command to create ssha encrypted password.

slappasswd -h {ssha}
New password:
Re-enter new password:

You’ll be prompted to enter the password. Once you confirm the password, you’ll get the hashed content of the password you entered.


Create the LDIF file to make necessary configuration changes in cn=config. Create a file called config.ldif and copy the below content to it.

dn: cn=config
changetype: modify

dn: olcDatabase={0}config,cn=config
changetype: modify
add: olcRootDN
olcRootDN: cn=admin,cn=config

dn: olcDatabase={0}config,cn=config
changetype: modify
add: olcRootPW
olcRootPW: {SSHA}cvSVqzUKS/RG1aPIDIKGLJtL4tl1tX9/


Description of the above content,

1)  The first line indicates that the change we are going to make is in cn=config. The space between content indicates that it is a different change

2)  The second para (dn: olcDatabase={0}config,cn=config) indicates that we are going to make the change in slapd configuration database (cn=config). The changetype is modify (since we are modifying existing entry ) and the type of change is add. Here we are adding olcRootDN and assigning it a value ‘cn=admin,cn=config’. ( Basically we are setting a rootDN to access cn=config )

3) Similar to the previous change, we are adding another attribute ‘olcRootPW’ and assigning it the value that we got through slappasswd.


Next, implement the changes using ldapadd command and by passing the content of above file as input

$ ldapadd -Y EXTERNAL -H ldapi:/// -f config.ldif

SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
modifying entry "cn=config"

modifying entry "olcDatabase={0}config,cn=config"

modifying entry "olcDatabase={0}config,cn=config"


The content highlighted in blue indicates that changes are implemented without any errors. The ldapadd command is used to add new entries. There is also an ldapmodify command which is used to modify existing entries.

Let’s verify the change by accessing cn=config DIT,

# ldapsearch -W -LLL -D cn=admin,cn=config -b cn=config dn
Enter LDAP Password:
dn: cn=config

dn: cn=module{0},cn=config

dn: cn=schema,cn=config

dn: cn={0}core,cn=schema,cn=config

dn: cn={1}cosine,cn=schema,cn=config

dn: cn={2}nis,cn=schema,cn=config

dn: cn={3}inetorgperson,cn=schema,cn=config

dn: olcBackend={0}mdb,cn=config

dn: olcDatabase={-1}frontend,cn=config

dn: olcDatabase={0}config,cn=config

dn: olcDatabase={1}mdb,cn=config

After entering the password which we gave in slappasswd, we will get the above output. Let us see what each entry means.

Explanation of entries:

  • cn=config: global settings

  • cn=module{0},cn=config: a dynamically loaded module

  • cn=schema,cn=config: contains hard-coded system-level schema

  • cn={0}core,cn=schema,cn=config: the hard-coded core schema

  • cn={1}cosine,cn=schema,cn=config: the cosine schema

  • cn={2}nis,cn=schema,cn=config: the nis schema

  • cn={3}inetorgperson,cn=schema,cn=config: the inetorgperson schema

  • olcBackend={0}mdb,cn=config: the ‘mdb’ backend storage type

  • olcDatabase={-1}frontend,cn=config: frontend database, default settings for other databases

  • olcDatabase={0}config,cn=config: slapd configuration database (cn=config)

  • olcDatabase={1}mdb,cn=config: your database instance (dc=devopsideas,dc=com)


Enabling and Enforcing TLS

When authenticating to an OpenLDAP server it is best to do so using an encrypted session. This can be accomplished using Transport Layer Security (TLS).

Here, we will be our own Certificate Authority and then create and sign our LDAP server certificate as that CA. Since slapd is compiled using the gnutls library, we will use the certtool utility to complete these tasks.

1)  Install the gnutls-bin and ssl-cert packages:

apt install gnutls-bin ssl-cert


2) Create a private key for the Certificate Authority:

sh -c "certtool --generate-privkey > /etc/ssl/private/cakey.pem"


3) Create the template/file /etc/ssl/ca.info to define the CA:

cn = <Company Name>

Replace <Company Name> with the name of your company


4) Create the self-signed CA certificate:

certtool --generate-self-signed \
--load-privkey /etc/ssl/private/cakey.pem \ 
--template /etc/ssl/ca.info \
--outfile /etc/ssl/certs/cacert.pem


5) Make a private key for the server:

certtool --generate-privkey \
--bits 2048 \
--outfile /etc/ssl/private/ldap_slapd_key.pem


6) Create the /etc/ssl/ldap.info file containing:

organization = <Company name>
cn = <Host name>
expiration_days = 3650

Replace <Company name> with your company name and <Host name> with the host name of your server. The above certificate is good for 10 years. Adjust accordingly.


7) Create the server’s certificate:

certtool --generate-certificate \
--load-privkey /etc/ssl/private/ldap_slapd_key.pem \
--load-ca-certificate /etc/ssl/certs/cacert.pem \
--load-ca-privkey /etc/ssl/private/cakey.pem \
--template /etc/ssl/ldap.info \
--outfile /etc/ssl/certs/ldap_slapd_cert.pem


8) Adjust permissions and ownership:

chgrp openldap /etc/ssl/private/ldap_slapd_key.pem
chmod 0640 /etc/ssl/private/ldap_slapd_key.pem
gpasswd -a openldap ssl-cert


9) Now restart slapd, since we added the ‘openldap’ user to the ‘ssl-cert’ group:

systemctl restart slapd.service

Your server is now ready to accept the new TLS configuration.


Now lets make changes in LDAP config ( cn=config ) to make use of the certificate we created for secure connection. Create the file certinfo.ldif with the following contents

dn: cn=config
add: olcTLSCACertificateFile
olcTLSCACertificateFile: /etc/ssl/certs/cacert.pem
add: olcTLSCertificateFile
olcTLSCertificateFile: /etc/ssl/certs/ldap_slapd_cert.pem
add: olcTLSCertificateKeyFile
olcTLSCertificateKeyFile: /etc/ssl/private/ldap_slapd_key.pem


Use the ldapmodify command to tell slapd about our TLS work via the slapd-config database:

ldapmodify -D cn=admin,cn=config -f certinfo.ldif


We have made changes in LDAP to accept TLS/SSL connection. However, the configuration is such that it still accepts insecure connection. Let’s enforce LDAP connection to use only TLS connection ( We are not preferring LDAP over SSL since it is deprecated in favour of StartTLS ).  Create the file forcetls.ldif with the below content

dn: olcDatabase={1}mdb,cn=config
changetype: modify
add: olcSecurity
olcSecurity: tls=1


Use the ldapmodify command to enforce TLS for dc=devopsideas,dc=com DIT using the forcetls.ldif file

ldapmodify -D cn=admin,cn=config -f forcetls.ldif


We need to one other small change. Edit /etc/ldap/ldap.conf file and replace TLS_CACERT with the following content. Basically you need to point it to the CA cert that we created above

 TLS_CACERT /etc/ssl/certs/cacert.pem


Restart the slapd service after the above change,

systemctl restart slapd.service


That’s it! We have enforced TLS connections to the DIT dc=devopsideas,dc=com in our openldap configuration. This makes us to use one more mandatory flag in order to specify that we need to establish TLS connection in our ldap commands.

ldapsearch -W -Z -D cn=admin,dc=devopsideas,dc=com -b dc=devopsideas,dc=com

Here -Z  will issue StartTLS operation.


In the next article we will  some GUI utilities that we can make use of for easier administration of openldap.

Series Navigation<< Openldap Tutorial – Practical Realtime Implementation and IntegrationInstalling phpLDAPadmin – Web based LDAP Client >>

Chris Sam

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