OpenLDAP

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.

Related articles

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 a good introduction that is easy to understand and that will get you started, even if you are new to LDAP.

Installation

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

Configuration

The server
Note:
  • If you have an obsolete slapd.conf configuration, you can simply convert it into the new cn=config database using
$ slaptest -f /etc/openldap/slapd.conf -F /etc/openldap/slapd.d/
  • If you already have an OpenLDAP database on your machine and would like to remove it, then it can be removed by deleting everything inside of /var/lib/openldap/openldap-data/. So, backup your DB_CONFIG.

Slapd, the server, stores its configuration directly inside its database. Thus, we need to write our configuration as an LDIF file and import it.

First, create a file config.ldif containing the following minimal sane configuration. This file declares the basic configuration structure and a database stored at /var/lib/openldap/openldap-data.

There are a few options you will need to change:

  • Every occurence of must be replaced with a valid DN. If you own a domain you will most likely want to choose .
  • $PASSWD must be replaced by a salted and hashed password, which you may generate by running slappasswd.

Additionally, you might consider to add further schemas and create additional indexes to tune the performance of your database. The specifics will depend on your use case, but here are a few recommendations. For LDAP authentication, you should include the three schemas below to be able to use the object class used for storing users.

To import these settings as the user using sudo:

# sudo -u ldap slapadd -n 0 -F /etc/openldap/slapd.d/ -l ./config.ldif

Alternatively, you may also run this directly as . However, if you do, make sure is accessible by :

# slapadd -n 0 -F /etc/openldap/slapd.d/ -l ./config.ldif
# chown -R ldap:ldap /etc/openldap/*

By default, OpenLDAP will listen unencrypted on all interfaces. To make it only listen on local IP interfaces, you may edit the environment file read by :

Finally, start the slapd daemon by starting .

The client

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

It is quite simple: you will only have to alter to reflect the suffix of the server, and 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 entry has to conform with the slapd configuration
  • If you decide to use TLS, add a line to
  • If you use a signed certificate from a CA, add the line in .

Create initial entry

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

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

Test your new OpenLDAP installation

This is easy, just run the command below:

$ ldapsearch -x '(objectclass=*)' -b 'dc=example,dc=com'

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

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

Now you should see some information about your database.

OpenLDAP over TLS

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.

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. must be world readable because it contains the public key. 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 configuration to tell LDAP where the certificate files reside by executing the following command:

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 :

SSLv2/v3

Disable SSLv2/v3 and use strong ciphers.

TLSProtocolMin specifies the minimum version in wire format, so "3.3" actually means TLSv1.2.

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 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'.

Start slapd with SSL

You will have to edit the environment file read by to change the protocol slapd listens on:

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

SLAPD_URLS="ldap://127.0.0.1 ldaps:///"

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

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.

Backup LDAP

It is imperative that we have a backup of our LDAP database and configuration in case we ever need to restore for any number of reasons.

Export configuration

 
$ sudo -u ldap slapcat -vF /etc/openldap/slapd.d -n 0 -l "$(hostname)-ldap-mdb-config-$(date '+%F').ldif"

Export database

 
$ sudo -u ldap slapcat -v -n 1 -l "$(hostname)-ldap-database-$(date '+%F').ldif"

Import configuration

 
$ sudo -u ldap slapadd -v -n 0 -F /etc/openldap/slapd.d -l <filename from config export>

Import database

 
$ sudo -u ldap slapadd -v -n 1 -F /etc/openldap/slapd.d -l <filename from database export>

Troubleshooting

slapd configuration checking

You can check configuration settings with

$ slaptest -F /etc/openldap/slapd.d/ -v

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 -R ldap:ldap /var/lib/openldap

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

LDAP server does not 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
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See also
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