OpenLDAP

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OpenLDAP is an open-source implementation of the LDAP protocol. An LDAP server basically is a non-relational database which is optimised for accessing, but not writing, data. It is mainly used as an address book (for e.g. email clients) or authentication backend to various services (such as Samba, where it is used to emulate a domain controller, or Linux system authentication, where it replaces /etc/passwd) and basically holds the user data.

Note: Commands related to OpenLDAP that begin with ldap (like ldapsearch) are client-side utilities, while commands that begin with slap (like slapcat) are server-side.

This page is a starting point for a basic OpenLDAP installation and a sanity check.

Tip: Directory services are an enormous topic. Configuration can therefore be complex. If you are totally new to those concepts, this is an good introduction that is easy to understand and that will get you started, even if you are new to everything LDAP.

Installation

OpenLDAP contains both a LDAP server and client. Install it with the package openldap.

Configuration

The server

Note: If you already have an OpenLDAP database on your machine, remove it by deleting everything inside /var/lib/openldap/openldap-data/.

The server configuration file is located at /etc/openldap/slapd.conf.

Edit the suffix and rootdn. The suffix typically is your domain name but it does not have to be. It depends on how you use your directory. We will use example for the domain name, and com for the tld. The rootdn is your LDAP administrator's name (we will use root here).

suffix     "dc=example,dc=com"
rootdn     "cn=root,dc=example,dc=com"

Now we delete the default root password and create a strong one:

# sed -i "/rootpw/ d" /etc/openldap/slapd.conf #find the line with rootpw and delete it
# echo "rootpw    $(slappasswd)" >> /etc/openldap/slapd.conf  #add a line which includes the hashed password output from slappasswd

You will likely want to add some typically used schemas to the top of slapd.conf:

Note: currently missing: cp /usr/share/doc/samba/examples/LDAP/samba.schema /etc/openldap/schema
include         /etc/openldap/schema/cosine.schema
include         /etc/openldap/schema/inetorgperson.schema
include         /etc/openldap/schema/nis.schema
#include         /etc/openldap/schema/samba.schema

You will likely want to add some typically used indexes to the bottom of slapd.conf:

index   uid             pres,eq
index   mail            pres,sub,eq
index   cn              pres,sub,eq
index   sn              pres,sub,eq
index   dc              eq

Now prepare the database directory. You will need to copy the default config file and set the proper ownership:

# cp /etc/openldap/DB_CONFIG.example /var/lib/openldap/openldap-data/DB_CONFIG
# chown ldap:ldap /var/lib/openldap/openldap-data/DB_CONFIG
Note: With OpenLDAP 2.4 the configuration of slapd.conf is deprecated. From this version on all configuration settings are stored in /etc/openldap/slapd.d/.

To store the recent changes in slapd.conf to the new /etc/openldap/slapd.d/ configuration settings, we have to delete the old configuration files first, do this every time you change the configuration:

# rm -rf /etc/openldap/slapd.d/*


(if you do not have a database yet, you might need to create one by starting and stopping the slapd.service using systemd )

Then we generate the new configuration with:

# slaptest -f /etc/openldap/slapd.conf -F /etc/openldap/slapd.d/

The above command has to be run every time you change slapd.conf. Check if everything succeeded. Ignore message "bdb_monitor_db_open: monitoring disabled; configure monitor database to enable".

Change ownership recursively on the new files and directory in /etc/openldap/slapd.d:

# chown -R ldap:ldap /etc/openldap/slapd.d


Note: Index the directory after you populate it. You should stop slapd before doing this.
# slapindex
# chown ldap:ldap /var/lib/openldap/openldap-data/*

or just

$ sudo -u ldap slapindex

Finally, start the slapd daemon with slapd.service using systemd.

The client

The client config file is located at /etc/openldap/ldap.conf.

It is quite simple: you will only have to alter BASE to reflect the suffix of the server, and URI to reflect the address of the server, like:

/etc/openldap/ldap.conf
BASE            dc=example,dc=com
URI             ldap://localhost

If you decide to use SSL:

  • The protocol (ldap or ldaps) in the URI entry has to conform with the slapd configuration
  • If you decide to use self-signed certificates, add a TLS_REQCERT allow line to ldap.conf
  • If you use a signed certificate from a CA, add the line TLS_CACERTDIR /usr/share/ca-certificates/trust-source in ldap.conf.

Create initial entry

Once your client is configured, you probably want to create the root entry, and an entry for the root role:

$ ldapadd -x -D 'cn=root,dc=example,dc=com' -W
dn: dc=example,dc=com
objectClass: dcObject
objectClass: organization
dc: example
o: Example
description: Example directory

dn: cn=root,dc=example,dc=com
objectClass: organizationalRole
cn: root
description: Directory Manager
^D

The text after the first line is entered on stdin, or could be read from a file either with the -f option or a file redirect.

Test your new OpenLDAP installation

This is easy, just run the command below:

$ ldapsearch -x '(objectclass=*)'

Or authenticating as the rootdn (replacing -x by -D <user> -W), using the example configuration we had above:

$ ldapsearch -D "cn=root,dc=example,dc=com" -W '(objectclass=*)'

Now you should see some information about your database.

OpenLDAP over TLS

Note: upstream documentation is much more useful/complete than this section

If you access the OpenLDAP server over the network and especially if you have sensitive data stored on the server you run the risk of someone sniffing your data which is sent clear-text. The next part will guide you on how to setup an SSL connection between the LDAP server and the client so the data will be sent encrypted.

In order to use TLS, you must have a certificate. For testing purposes, a self-signed certificate will suffice. To learn more about certificates, see OpenSSL.

Warning: OpenLDAP cannot use a certificate that has a password associated to it.

Create a self-signed certificate

To create a self-signed certificate, type the following:

$ openssl req -new -x509 -nodes -out slapdcert.pem -keyout slapdkey.pem -days 365

You will be prompted for information about your LDAP server. Much of the information can be left blank. The most important information is the common name. This must be set to the DNS name of your LDAP server. If your LDAP server's IP address resolves to example.org but its server certificate shows a CN of bad.example.org, LDAP clients will reject the certificate and will be unable to negotiate TLS connections (apparently the results are wholly unpredictable).

Now that the certificate files have been created copy them to /etc/openldap/ssl/ (create this directory if it does not exist) and secure them. slapdcert.pem must be world readable because it contains the public key. slapdkey.pem on the other hand should only be readable for the ldap user for security reasons:

# mv slapdcert.pem slapdkey.pem /etc/openldap/ssl/
# chmod -R 755 /etc/openldap/ssl/
# chmod 400 /etc/openldap/ssl/slapdkey.pem
# chmod 444 /etc/openldap/ssl/slapdcert.pem
# chown ldap /etc/openldap/ssl/slapdkey.pem

Configure slapd for SSL

Edit the daemon configuration file (/etc/openldap/slapd.conf) to tell LDAP where the certificate files reside by adding the following lines:

# Certificate/SSL Section
TLSCipherSuite DEFAULT
TLSCertificateFile /etc/openldap/ssl/slapdcert.pem
TLSCertificateKeyFile /etc/openldap/ssl/slapdkey.pem

If you are using a signed SSL Certificate from a certification authority such as Let’s Encrypt, you will also need to specify the path to the root certificates database and your intermediary certificate. You will also need to change ownership of the .pem files and intermediary directories to make them readable to the user ldap:

# Certificate/SSL Section
TLSCipherSuite DEFAULT
TLSCertificateFile /etc/letsencrypt/live/ldap.my-domain.com/cert.pem
TLSCertificateKeyFile /etc/letsencrypt/live/ldap.my-domain.com/privkey.pem
TLSCACertificateFile /etc/letsencrypt/live/ldap.my-domain.com/chain.pem
TLSCACertificatePath /usr/share/ca-certificates/trust-source

The TLSCipherSuite specifies a list of OpenSSL ciphers from which slapd will choose when negotiating TLS connections, in decreasing order of preference. In addition to those specific ciphers, you can use any of the wildcards supported by OpenSSL. NOTE: DEFAULT is a wildcard. See man ciphers for description of ciphers, wildcards and options supported.

Note: To see which ciphers are supported by your local OpenSSL installation, type the following: openssl ciphers -v ALL:COMPLEMENTOFALL. Always test which ciphers will actually be enabled by TLSCipherSuite by providing it to OpenSSL command, like this: openssl ciphers -v 'DEFAULT'

Regenerate the configuration directory:

# rm -rf /etc/openldap/slapd.d/*                                  # erase old config settings
# slaptest -f /etc/openldap/slapd.conf -F /etc/openldap/slapd.d/  # generate new config directory from config file
# chown -R ldap:ldap /etc/openldap/slapd.d                        # Change ownership recursively to ldap on the config directory

Start slapd with SSL

You will have to edit slapd.service to change to protocol slapd listens on.

Create the override unit:

systemctl edit slapd.service
[Service]
ExecStart=
ExecStart=/usr/bin/slapd -u ldap -g ldap -h "ldaps:///"

Localhost connections do not need to use SSL. So, if you want to access the server locally you should change the ExecStart line to:

ExecStart=/usr/bin/slapd -u ldap -g ldap -h "ldap://127.0.0.1 ldaps:///"

Then restart slapd.service. If it was enabled before, reenable it now.

Note: If you created a self-signed certificate above, be sure to add TLS_REQCERT allow to /etc/openldap/ldap.conf on the client, or it will not be able connect to the server.

Next Steps

You now have a basic LDAP installation. The next step is to design your directory. The design is heavily dependent on what you are using it for. If you are new to LDAP, consider starting with a directory design recommended by the specific client services that will use the directory (PAM, Postfix, etc).

A directory for system authentication is the LDAP authentication article.

A nice web frontend is phpLDAPadmin.

Troubleshooting

Client Authentication Checking

If you cannot connect to your server for non-secure authentication

$ ldapsearch -x -H ldap://ldaservername:389 -D cn=Manager,dc=example,dc=exampledomain

and for TLS secured authentication with:

$ ldapsearch -x -H ldaps://ldaservername:636 -D cn=Manager,dc=example,dc=exampledomain

LDAP Server Stops Suddenly

If you notice that slapd seems to start but then stops, try running:

# chown ldap:ldap /var/lib/openldap/openldap-data/*

to allow slapd write access to its data directory as the user "ldap".

LDAP Server Doesn't Start

Try starting the server from the command line with debugging output enabled:

# slapd -u ldap -g ldap -h ldaps://ldaservername:636 -d Config,Stats

See Also