Configure OpenLDAP

This material is work-in-progress ... Do not follow instructions here until this notice is removed. (Last edited by Dhorton on 4 May 2022.)

Lightweight Directory Access Protocol (LDAP) is often employed as an authentication mechanism, providing a common username and password across many different applications. This tutorial shows how to install and configure the OpenLDAP package on Alpine Linux.

Installing Packages

There is an Alpine package for OpenLDAP. However, simply adding the openldap apk is not enough to get you up and running. You'll also need to install a backend database and some LDAP command-line tools.

Here's how:

 apk add openldap openldap-back-mdb openldap-clients

But, before you start up the slapd service and go, there's a bit of configuration to do.

Customizing Configuration for OpenLDAP 2.3+

The Alpine OpenLDAP package can use either a configuration directory (slapd.d) or a configuration file (slapd.conf). Since OpenLDAP version 2.3, the preferred method is to use the slapd.d configuration directory. Any official OpenLDAP documentation, including their quickstart guide, will use this configuration method.

First, create the slapd.d directory with the proper ownership and permissions.

 install -m 755 -o ldap -g ldap -d /etc/openldap/slapd.d

Next, edit the slapd startup configuration to use the directory instead of the file.

1. Open up /etc/conf.d/slapd in your favorite editor
2. Comment out cfgfile="/etc/openldap/slapd.conf"
3. Uncomment cfgdir="/etc/openldap/slapd.d"

Finally, get rid of the included slapd.conf file.

 rm /etc/openldap/slapd.conf

Updating Shared Libraries Filenames

Open up /etc/openldap/slapd.ldif in your favorite editor. Search for the filenames ending with .la and change the extension to .so

Or, you can do...

 sed -i s/\.la$/.so/g slapd.ldif

Customizing Configuration for Your Domain

Your LDAP domain can be the same as your DNS domain or it can be completely different. Whatever you choose, be sure to use the LDAP naming convention of dc=domain,dc=tld rather than the dot separated DNS style of domain.tld

1. Edit slapd.ldif again.
2. Find olcSuffix:
3. Change to match your domain
4. Find olcRootDN:
5. Change to match your domain

Or, assuming your domain is 'contoso.com' you can do...

 sed -i s/dc=my-domain,dc=com/dc=contoso,dc=com/g /etc/openldap/slapd.ldif

Import the Configuration

Before starting the slapd service, import the configuration into the backend database.

Use the slapadd command like this:

 slapadd -n 0 -F /etc/openldap/slapd.d -l /etc/openldap/slapd.ldif

There should be no errors, only a "Closing DB..." message.

Change ownership on the files or the slapd service will refuse to start.

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

Configuring the slapd Service

The pid directory is missing. We'll need to create it or the service won't start.

 install -m 755 -o ldap -g ldap -d /var/lib/openldap/run
 

Testing

ldapsearch -x -b -s base '(objectclass=*)' namingContexts

You should see your domain.

You can also test with `slapcat -n 0` This will dump the entire config database in LDIF format. Combine with grep to search for your domain.

>When using grep, remember LDAP uses the format dc=domain,dc=com and not the more familiar domain.com.

Reference

https://openldap.org/doc/admin26/quickstart.html