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Chapter 20 - Shared Address Book (LDAP)

Version: - openldap-servers 2.3.19
- phpLDAPadmin 1.0.1

Initial Concepts
Basic Configuration
Address Book Entries
TLS Link Encryption
phpLDAPadmin Web Administrator
Email Client Settings

Many individuals throughout professional organisations will consider their list of personal and professional contacts as one of their most important assets. Similarly at home keeping our contact details of friends, relatives and professional service providers like physicians is also equally important, however maintaining that contact list across several computers can be very time consuming; even frustrating if it is lost.

Using the Lightweight Directory Access Protocol (LDAP) we can configure a centrally managed address book that can be shared by all the of computer workstations throughout the network (for many large organisations this is a fundamental design concept). A central (or shared) address book allows easy management of all contact details, it can be backed up and restored very easily, and it can also be made available through a secure web interface so it can be accessed remotely from where ever the user may be.

This chapter will detail the procedures necessary to configure the OpenLDAP ( directory service that will provide the basis for our address book and make it available to our network users. We will also look at populating the address book and provide security access controls so that only authenticated users can access the information.

Not all email clients are able to write to the address book (although reading is fine), this is normally due to the functionality of the email client and not a problem with the directory service. Therefore, we will also configure the web server with a web based administration application which will allow full control of the address book; this also allows the remote access if needed.

The following list of man pages can provide further information to assist with configuration or debugging requirements.

Man Pages:
ldap slapd slapcat
ldap.conf slapd.conf slapadd
ldapadd slapd.access slappasswd
ldapsearch slaptest ldif

Initial Concepts

The shared address book is being configured using the LDAP directory services which basically stores different types of information and objects in a database and these entries are accessible using its own directory architecture (X.500 standard).

The naming conventions used to traverse this system can be extremely complex for new users to grasp, so the following table has been provided as an example of what these objects are and the names we are going to use in referencing them.

String Value (DN)
Base Domain
Admin User
Authorised users located here
Authorised user account (example)
Address book entries located here
Also used by client as "Search Base"
Address book entry (example)
cn=Tom Thumb,ou=addressbook,dc=example,dc=com

The following table explains some of the basic acronyms used throughout the directory, there are many more than this that go to make up the naming conventions, however these are the only ones we will be concerned with.

Attribute Type
Distinguished Name
Common Name
Organisational Name
Organisational Unit Name
Domain Component
User Identification

Caution !! Do not confuse the X.500 naming scheme used in LDAP with the email addresses of your contacts, they are totally separate details. This will become clear further on.

Everything inside the directory has a distinguished name (dn) this is what makes each entry unique from the others and also provides a means to easily reference the object. Viewing the top table, the DN for the manager account is "cn=Manager,dc=example,dc=com", while all of the address book entries are contained in the DN of "ou=addressbook,dc=example,dc=com".

The following table displays valid examples of how domains are expressed using the X.500 naming scheme.

Example Domain Names
String Value
dc=home,dc=lan dc=example,dc=com dc=example,dc=org
dc=domain,dc=org,dc=au dc=sub,dc=domain,dc=org,dc=au dc=more,dc=sub,dc=domain,dc=org,dc=au

Note !! If the LDAP server is simply being configured as a shared address book and not for any real networking requirement, then it is acceptable to use a simple domain similar to "home.lan"

Basic Configuration

The OpenLDAP package contains a server and client application. The client application will be used to query the server and insert/update information during the configuration, so it is necessary to configure this as well as the server.

The configuration that we need is very simple, however good house keeping means making backups before adjusting the configuration file.

[bash]# cp /etc/openldap/ldap.conf /etc/openldap/ldap.conf.original
[bash]# vi /etc/openldap/ldap.conf

The following entry is really all that is needed for the client. It identifies where the server is located, and which part of the directory tree to query.

URI ldap://
BASE dc=example,dc=com

The server can be configured with a built-in administrator account that has global root privileges, it is necessary to store the password for the root account inside the server configuration file. The "slappasswd" application allows passwords to be encrypted (or hashed) which stops unauthorised users from viewing the password, or intercepting a plaintext password while it is being transmitted over the network.

Create a suitable password for the root account so it can be placed into the configuration file.

[bash]# slappasswd

The LDAP server is called slapd (Stand-Alone LDAP Daemon), lets backup the configuration file before making adjustments.

[bash]# cp /etc/openldap/slapd.conf /etc/openldap/slapd.conf.original
[bash]# vi /etc/openldap/slapd.conf

The following slapd.conf file contains the basic configurations required to establish a shared address book on a secure network, however there are no access controls yet defined; security is covered later on. The encrypted root password should be substituted where necessary.

The five lines that are commented below are not needed to configure our simple address book. However they be needed if you wish to advance your LDAP requirements so they have been left as comments only; they may be removed if need be.

include         /etc/openldap/schema/core.schema
include         /etc/openldap/schema/cosine.schema
include         /etc/openldap/schema/inetorgperson.schema
#include         /etc/openldap/schema/nis.schema

pidfile         /var/run/openldap/
argsfile        /var/run/openldap/slapd.args


database        bdb
suffix          "dc=example,dc=com"
rootdn          "cn=Manager,dc=example,dc=com"
rootpw          {SSHA}RZmBkCh3WwEMNhdANh/l3OynzHSifPzF               <-- insert generated root password here

directory       /var/lib/ldap

index objectClass                       eq,pres
#index ou,cn,mail,surname,givenname      eq,pres,sub
#index uidNumber,gidNumber,loginShell    eq,pres
#index uid,memberUid                     eq,pres,sub
#index nisMapName,nisMapEntry            eq,pres,sub

# DB_CONFIG Settings - For SleepyCat Berkeley DB
dbconfig set_cachesize 0 10485760 0
dbconfig set_lg_regionmax 262144
dbconfig set_lg_bsize 2097152

Note !! It is possible to run multiple databases using the one OpenLDAP server, however we are only concerned with one for the time being. Consult the documentation for further details if needed.

After the configuration has been adjusted it can be checked before it is implemented. Any errors should be fixed before restarting the server.

[bash]# /etc/init.d/ldap configtest

The LDAP service should now be set at the appropriate runlevels and checked to ensure they are set correctly.

[bash]# chkconfig --level 345 ldap on
[bash]# chkconfig --list ldap

The service can now be started with the following command.

[bash]# /etc/init.d/ldap restart

Address Book Entries

Information can be imported and exported into an LDAP directory service using the LDAP Data Interchange Format (LDIF) as defined in RFC2849. An LDIF file specifies the contents of a directory entry in a human readable text format, this allows quick manipulation of a file to re-import similar entries into the directory.

Now that the LDAP server has been configured and is running, we can conduct a simple search of the naming context to see our directory information before we start to import our entries. The "namingContexts" should be similar to the example below.

[bash]# ldapsearch -x -b '' -s base '(objectclass=*)' namingContexts
# extended LDIF
# LDAPv3
# base <> with scope base
# filter: (objectclass=*)
# requesting: namingContexts

namingContexts: dc=example,dc=com

# search result
search: 2
result: 0 Success

# numResponses: 2
# numEntries: 1

The following LDIF file will create the hierarchical directory service structure that we will be using for our address book. The first entry is that of the base directory and the second entry is for the Manager's (administrator) account. The last two entries are the two organisational units that we will use to store the authorised users (for adding security later) and the address book entries.

The bolded entries should be changed to suit your configuration requirements.

[bash]# vi /etc/openldap/addressbook.ldif
dn: dc=example,dc=com
objectclass: dcObject
objectclass: organization
o: Home LDAP Server
dc: example

dn: cn=Manager,dc=example,dc=com
objectclass: organizationalRole
cn: Manager

dn: ou=users,dc=example,dc=com
ou: users
objectClass: top
objectClass: organizationalUnit

dn: ou=addressbook,dc=example,dc=com
ou: addressbook
objectClass: top
objectClass: organizationalUnit

Using the "ldapadd" command we can enter the LDIF contents into the server, creating our initial directory scheme.

[bash]# ldapadd -x -D 'cn=Manager,dc=example,dc=com' -W -f /etc/openldap/addressbook.ldif
Enter LDAP Password:
adding new entry "dc=example,dc=com"
adding new entry "cn=Manager,dc=example,dc=com"
adding new entry "ou=users,dc=example,dc=com"
adding new entry "ou=addressbook,dc=example,dc=com"

The following LDAP search is requesting a listing of all entries starting from the base "dc=example,dc=com". This should return all of the entries that where added in the previous step.

[bash]# ldapsearch -x -b 'dc=example,dc=com' '(objectclass=*)'
dn: dc=example,dc=com
objectClass: top
objectClass: dcObject
objectClass: organization
o: Home LDAP Network
dc: example

# Manager,
dn: cn=Manager,dc=example,dc=com
objectClass: organizationalRole
cn: Manager

# users,
dn: ou=users,dc=example,dc=com
ou: users
objectClass: top
objectClass: organizationalUnit

# addressbook,
dn: ou=addressbook,dc=example,dc=com
ou: addressbook
objectClass: top
objectClass: organizationalUnit

Now that we have defined and imported our directory scheme, we are able to create user entries to populate the addressbook. The following is a simple example LDIF entry for a contact.

The first line (dn:) designates where about in the directory the entry will belong when its imported, this should be changed to suit your needs.

[bash]# vi newcontact.ldif
dn:cn=Tom Thumb,ou=addressbook,dc=example,dc=com
cn: Tom Thumb
gn: Tom
sn: Thumb
o: Home
l: Brisbane
street: 12 Banana Ave
st: QLD
postalCode: 4100
pager: 5555 1111
homePhone: 5555 1234
telephoneNumber: 5555 1235
facsimileTelephoneNumber: 5555 1236
mobile: 0400 123 123
mail: [email protected]
objectClass: top
objectClass: inetOrgPerson

The contents of the LDIF file can be added into the directory service using the "ldapadd" command below.

The standard access controls for the server defines that everyone can read the directory entries, but only the manager (administrator) can write to the directories. To add the LDIF file the manager is authenicating on the command line with the "-D 'cn=Manager,dc=example,dc=com' -W" string.

[bash]# ldapadd -x -D 'cn=Manager,dc=example,dc=com' -W -f newcontact.ldif
Enter LDAP Password:
adding new entry "cn=Tom Thumb,ou=addressbook,dc=example,dc=com"

Now that the first entry has been successfully added to the directory server, the file can be copied so more entries can be added. Alternatively, extra entries can be added to the same file ensuring that a blank line is used to separate each different entry.

TLS Link Encryption

The standard security settings for the LDAP server allows everyone to connect (bind) to the server and read the entire directory contents, while only the administrative account can make changes or add new entries. For your small home network you may find this entirely suitable in its current format, however the following details will provide some extra security configurations to make it less accessible, this is also important if you wish to access your home server from beyond your home network.

The access controls are defined within the servers main configuration file.

[bash]# vi /etc/openldap/slapd.conf

The following details are typical of the security settings that you may consider implementing. The first section details any link encryption using TLS/SSL and it also enforces which actions can be done on the server depending on the level of link security that has been implemented.

The second section details the access controls based on the users authentication and basic anonymous access. The default access controls (below) have been defined to deny everyone access, however people are allowed to bind to the server to authenticate. All authenticated users are allowed to change their own details, and all of the entries in the "ou=addressbook,dc=example,dc=com" directory; anonymous access it disallowed.

TLSCACertificateFile /etc/pki/tls/certs/ca-bundle.crt
TLSCertificateFile /etc/pki/tls/certs/slapd.pem
TLSCertificateKeyFile /etc/pki/tls/certs/slapd.pem
security ssf=1 update_ssf=112 simple_bind=64

disallow bind_anon
access to *
       by self write
       by anonymous auth
       by users read
access to dn.subtree="ou=addressbook,dc=example,dc=com"
       by users write

Note !! The term "users" defines those people that have successfully authenticated with the server.

You will need to create an SSL certificate for use with your server, the following code will create a self-signed certificate which is good enough for our requirements.

[bash]# cd /etc/pki/tls/certs
[bash]# make slapd.pem
Country Name (2 letter code) [GB]:AU
State or Province Name (full name) [Berkshire]:QLD
Locality Name (eg, city) [Newbury]:Brisbane
Organization Name (eg, company) [My Company Ltd]:Miles Brennan
Organizational Unit Name (eg, section) []:Home Linux Server
Common Name (eg, your name or your server's hostname) []
Email Address []:[email protected]

The ownership and permissions for the self-signed certificate need to be adjusted slighty so the basic "LDAP" user account can read the certificate details.

[bash]# chown root.ldap /etc/pki/tls/certs/slapd.pem
[bash]# chmod 640 /etc/pki/tls/certs/slapd.pem

Now that the server has been configured for TLS/SSL, the LDAP client also needs to be configured for TLS/SSL otherwise they will not be able to communicate.

[bash]# vi /etc/openldap/ldap.conf
URI ldaps://
BASE dc=example,dc=com
TLS_REQCERT demand                         <-- see warning below, may need to be "allow"
TLS_CACERT /etc/pki/tls/certs/ca-bundle.crt

Warning !! Refer to "man ldap.conf" and "man slapd.conf" for the exact meanings of the TLS options. Incorrect settings when working with a "self signed" PEM certificate may prevent your LDAP client from successfully connecting to your SLAPD server.

An access control list may be prone to user syntax errors and will not be accepted by the LDAP server, so the configuration should be tested before it is loaded.

[bash]# /etc/init.d/ldap configtest

If the configuration passes integrity testing, the server can be restarted.

[bash]# /etc/init.d/ldap restart

The new security access controls now prevent unauthorised access to the directory service, so simple user objects must be prepared that will allow people to authenticate with the server.

The user objects will be imported into the LDAP server using an LDIF file. Remember that everything in an LDIF file is human readable so plain text passwords are a VERY BAD idea, especially if you are following this guide for an organisation; no plain text passwords please.

The slappasswd application can be used to create a hashed value of a users password, these are saved to store in a text file. This does not mean they are completely safe, it just means they can not be easily read. An attacker can still subject the password value to a brute force attack, but it would take them an awfully long time. Physical security is still important.

[bash]# slappasswd

The default algorithm for the hashed password is SSHA, this can be changed at the command line to other formats; the default type (SSHA) is recommended.

[bash]# slappasswd -h {MD5}

The basic user object can now be created and imported into the LDAP server. This file uses the "UID" (User ID) string to distinguish the object and the contents are all that we need to create a basic authentication mechanism.

It should also be noted that this object is stored in the "users" organisational unit, which is located outside of the address book directory.

[bash]# vi useraccount.ldif
uid: alice
userPassword: {MD5}poocSzW4TMBN3fOtmVOQHg==
objectClass: top
objectClass: account
objectClass: simpleSecurityObject

The user account can now be entered into the LDAP server.

[bash]# ldapadd -x -D 'cn=Manager,dc=example,dc=com' -W -f useraccount.ldif
Enter LDAP Password:
adding new entry "uid=alice,ou=users,dc=example,dc=com"

Hint !! For Alice to authenticate to the server, she needs to pass "uid=alice,ou=users,dc=example,dc=com" as her username along with the the plain text value of her password, the hashed value is only for storage purposes.

Backing Up The Database

The OpenLDAP server allows for easy importing and exporting of directory entries using the LDIF format, this makes it extremely easy to extract the complete contents of the database for backup purposes.

The service should be stopped before extracting or importing the directory service listing.

[bash]# /etc/init.d/ldap stop

Caution !! The LDAP server should be stopped before executing the "slapcat" or "slapadd" commands. This prevents the possibility of data corruption and ensures database integrity is maintained.

The following "slapcat" command will extract the entire database contents into the "backup_slapd.ldif" file. This file should be stored in a save place, particularly if password information is contained in the file.

[bash]# slapcat -vl /etc/openldap/backup_slapd.ldif

The contents of the stored "backup_slapd.ldif" file can be imported back into the LDAP server using the following command. This is a quick and easy method to rebuild your entire address book after a system rebuild.

[bash]# slapadd -vl /etc/openldap/backup_slapd.ldif

If an LDIF restore is being done on a new LDAP server, there is a possibility that the database directory has not been configured correctly for the ldap user account. If this is the case then the server may not start correctly because the file permissions are incorrect.

To restore the file permissions on a newly restored LDAP database, use the following command to grant user and group ownership to the "ldap" user account. This may be different for each Linux distribution, please refer to your configuration details first.

[bash]# chown ldap.ldap /var/lib/ldap/*

The service can now be started to access the directory services.

[bash]# /etc/init.d/ldap restart

phpLDAPadmin Web Administrator

There are many different email clients available today that are capable of using an LDAP server as a central address book, however even less of these clients are able to write new contacts details to the server or even make changes to an existing entry (this is not a server problem). One of the easiest mays to interface and administer the shared address book is by using a web based application installed on the web server; this provides easy management and remote access to the address book.

phpLDAPadmin ( is a PHP based web application designed specifically to allow remote management of an LDAP server by using a simple web browser. Although this package is covered under the open source license there is a small fee for "commercial" users, but its still totally free for home use.

The package firstly needs to be downloaded from the phpLDAPadmin site and saved somewhere on the server; the package is available for download as a 'tarball' (a .tar.gz file). Use the following commands to extract the archive into the "/var/www" directory, remember to replace ?.?.? with the version number you have downloaded.

[bash]# tar -xzvf phpldapadmin-?.?.?.tar.gz -C /var/www/
[bash]# chown -R root.root /var/www/phpldapadmin-?.?.?/

The application has now been extracted and needs to be configured with the details of the local LDAP server. Normally there is only an example configuration file available in the package, this should be copied over as the main configuration file, then adjusted to suit your needs.

When when configured the Apache web server a few chapters ago, we created an SSL certificate and used the rewrite module to force SSL connections. It is recommended that SSL also be forced on the phpLDAPamin application so that any logon details and database queries are executed confidentially.

[bash]# cp /var/www/phpldapadmin-?.?.?/config/config.php.example /var/www/phpldapadmin-?.?.?/config/config.php

The following details in the configuration file are the basic requirements needed for simple LDAP access and administration by the web application. There are further details which can be configured, but not needed for simple address book management; you may configure these further options if you would like to use them though.

[bash]# vi /var/www/phpldapadmin-?.?.?/config.php

//$config->custom->debug['level'] = 255;
//$config->custom->debug['file'] = '/tmp/pla_debug.log';

/* Define your LDAP servers in this section  */

$ldapservers = new LDAPServers;
$ldapservers->SetValue($i,'server','name','My LDAP Server');
$ldapservers->SetValue($i,'login','pass','password');                   <-- set your Manager password here
$ldapservers->SetValue($i,'server','tls',true);                         <-- set to false if not using SSL certs


The archive for the phpLDAPadmin application was originally extracted into the "/var/www/phpldapadmin", while the Apache web server has its "DocumentRoot" directive set to "/var/www/html" which means the phpLDAPadmin application is located outside of the "DocumentRoot" and the contents are not yet accessible to the web server.

We can create a configuration file for the phpLDAPadmin application so Apache can access the resources that are required. The configuration below is using the AuthType directive from Apache, ensuring that the access is restricted to only those users that have a valid username and password.

[bash]# vi /etc/httpd/conf.d/phpLDAPadmin.conf
Alias /ldap "/var/www/phpldapadmin-?.?.?"

<Location "/ldap">
    AuthType Basic
    AuthName "Private Area - LDAP Administrator"
    AuthUserFile /etc/httpd/conf/authusers
    AuthGroupFile /etc/httpd/conf/authgroups
    Require group ldapusers
    Require valid-user

If SSL certificates where created for the Apache web server, then it should be configured to force the phpLDAPadmin application into SSL mode to keep it secure. This configuration uses the rewrite module configuration we created in Chapter 13.

[bash]# vi /etc/httpd/conf.d/mod-rewrite.conf
RewriteRule ^/ldap/(.*) https://%{SERVER_NAME}/ldap/$1 [R,L]

The Apache web server needs to be restarted before the settings will be implemented.

[bash]# /etc/init.d/httpd restart

If everything has gone well you should now be able to access the phpLDAPadmin application on the local server at: https://localhost/ldap.

Email Client Settings

The last steps in setting up the shared address book is to configure the users email clients to access the LDAP server.

The following table contains some of the information needed to configure the client applications. Note the username will need to be written as the complete "distinguished name" value so the server knows which object to authenticate.

Remember, not all clients can write to the address book, so use the phpLDAPadmin application to add and manage the entries as needed.

LDAP Server:
Search Base:
Login Method:
use distinguished name (if listed)
As entered in useraccount.ldif file (plain text version)
Secure Connection:
Never (unless encryption has been configured)

If you configured SquirrelMail on your server during Chapter 13, you will be pleased to hear that SquirrelMail is able to be configured to use an LDAP address book.

You can use the following commands to configure SquirrelMail to use your new LDAP address book.

[bash]# cd /usr/share/squirrelmail/config
[bash]# ./

The following list of client configurations should be used as a guide only, they may differ between versions and operating systems.

If you are aware of extra client settings that are not listed below, please send me the connection details to have them added.

Linux Clients

- Evolution (Ver 2.0):
      (can read and write)
1.   Press "CTRL+SHIFT+B", this opens "Add Address Book"
2.   Select "Type: On LDAP Servers"
3.   Enter configuration details then save and close

- Thunderbird (Ver 1.5x):
      (read only)
1.   Press "CTRL+2", this opens "Add Address Book"
2.   Select "Edit" --> "Preferences" --> "Composition" --> "Addressing"
3.   Select "Directory Server" check box, then click "Edit Directories"
4.   Enter configuration details then save and close

Microsoft Clients

- Microsoft Outlook 2003:
      (read only)
1.   Select "Tools" --> "E-mail Accounts" --> "Add a new directory or address book" --> "Internet Directory Service (LDAP)"
2.   Enter configuration details then select "More Settings.."
3.   Enter the search base then save and close

- Microsoft Outlook Express (Version 6.0):
      (read only)
1.   Select "Tools" --> "Accounts" --> "Add" --> "Directory Service"
2.   Enter simple configuration details from wizard
3.   Highlight the new address book, select "Properties"
4.   Enter login and search base details, save and close

 - Mozilla Thunderbird (Ver 1.0):
      (read only)
1.    Select "Tools" --> "Options" --> "Composition"
2.   Under "Address Autocompletion", tick "Directory Server", then select "Edit Directories"
3.   Select "Add", enter configuration details then save and close

Other Clients

??? Anyone ?

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