Ubuntu LDAP Installation

Resources

• How to Install OpenLDAP on Ubuntu 22.04 from HowToForge (works for Ubuntu 24.04)
  • Note: In this document, you can skip the steps of manually adding groups and users to LDAP before install LDAP Account Manager. Once LAM is configured, it will automatically add the default OUs for groups and users.
• LDAP & TLS from the Ubuntu Server Guide
• How Does HTTPS Work from kubucation on YouTube (a good overview of CAs and certificates)
• Core Networking Services - Security
• The Cloud - Certificates

Video Transcript

As we did earlier with setting up Active Directory on Windows, let’s take a look at the steps required to install and configure OpenLDAP on Linux. The goal of this video isn’t to show you all the steps of the process, but provide commentary on some of the more confusing steps you’ll perform.

For this example, I’m using the Ubuntu VM labelled Server from Lab 3. I have chosen to disable the DHCP server on this system, and instead have replaced it with the VMware DHCP server. In practice, that change should not affect any of this process. Also, I’ll generally be following the guide from DigitalOcean, which is linked in the resources section below the video.

At this point, I have also already performed the first steps of the guide, which is to install the slapd and ldap-utils packages on this system. Now, I’ll step through the configuration process for slapd and discuss the various options it presents.

sudo dpkg-reconfigure slapd

First, it will ask you if you want to omit the OpenLDAP server configuration. Make sure you select <No> for that option. You can use the arrow keys (← and →) to move the red-shaded selector to the option you’d like to select, then press ENTER to confirm it.

Next, it will ask for your domain name. For this example, I’ll just use ldap.cis527russfeld.cs.ksu.edu. You’ll need to adjust these settings to match the required configuration for the lab assignment. This matches the DNS configuration I made in Lab 3, which is very important later on in this process.

Next, it will also ask for your organization name. I’ll just use cis527 here.

Then, it will ask for your Administrator password. This is the equivalent of the root account within the domain. It is able to change all domain settings, and therefore the password for this account should be very complex and well protected. For this example, I’ll just use the same password we are using for everything else, but in practice you’ll want to carefully consider this password.

The next option is whether you want to have the database removed if you purge the slapd package. Selecting <yes> on this option would delete your LDAP database if you ever chose to reinstall the slapd package. For most uses, you’ll always want to select <no> here, which is what I’ll do.

Since there are some existing configuration files in place, the installer asks if you’d like those to be moved. Unless you are reinstalling slapd on an existing server, you can select <yes> for this option.

That should complete the configuration for the OpenLDAP server. For this example, I have disabled the firewall on this system, but for your lab assignment you’ll need to do a bit of firewall configuration at this point.

Finally, let’s add some encryption to this server to protect the information shared across the network. This step was not required in previous versions of this lab, but it has always been a good idea. Now that Ubuntu uses SSSD, or System Security Services Daemon, for authentication, it requires us to provide TLS encryption on our LDAP server. So, let’s do that now.

For these steps, we’ll be closely following the Ubuntu Server Guide linked below this video. We’ll be adjusting a few of the items to match our configuration, but most of the commands are exactly the same.

First, we’ll need to install a couple of packages to allow us to create and manipulate security certificates

sudo apt update
sudo apt install gnutls-bin ssl-cert

Next, we need to create our own certificate authority, or CA. In a production system, you would instead work with an actual CA to obtain a security certificate from them, but that can be time consuming and expensive. So, for this example, we’ll just create our own. Also, contrary to what your browser may lead you to believe, using your own CA certificates will result in an encrypted connection, it just may not be “trusted” since your browser doesn’t recognize the CA certificate.

If you want to know more about CAs and certificates, check out the handy YouTube video I’ve linked below this video. It gives a great description of how certificates work in much more detail. I’ve also included links to the lectures in Module 3 and Module 5 that deal with TLS certificates.

So, we’ll first create a private key for our CA:

sudo certtool --generate-privkey --bits 4096 --outfile /etc/ssl/private/mycakey.pem

Then, we’ll create a template file that contains the options we need for creating this certificate. Notice here that I’ve modified this information from what is provided in the Ubuntu Server Guide document to match our setup:

sudo nano /etc/ssl/ca.info

and put the following text into that file.

cn = CIS 527
ca
cert_signing_key
expiration_days = 3650

Then, we can use that template to create our self-signed certificate authority certificate:

sudo certtool --generate-self-signed --load-privkey /etc/ssl/private/mycakey.pem --template /etc/ssl/ca.info --outfile /usr/local/share/ca-certificates/mycacert.crt

This will create a certificate called mycacert.crt that is stored in /usr/local/share/ca-certificates/. This is our self-signed CA certificate. So, whenever we want any system to trust one of our self-signed certificates that we make from our CA, we’ll need to make sure that system has a copy of this CA certificate in its list of trusted certificates.

To do that, we simply place the certificate in /usr/local/share/ca-certificates/, and then run the following command to add it to the list of trusted certificates:

sudo update-ca-certificates

If that command works correctly, it should tell us that it has added 1 certificate to our list.

Before we move on, let’s make a copy of our mycacert.crt file in our cis527 users’s home directory. We’ll use this file in the next part of this lab when we are configuring our client system to authenticate using LDAP.

cp /usr/local/share/ca-certificates/mycacert.crt ~/

Now that we’ve created our own self-signed CA, we can use it to create a certificate for our LDAP server. So, we’ll start by creating yet another private key:

sudo certtool --generate-privkey --bits 2048 --outfile /etc/ldap/ldap01_slapd_key.pem

Then, we’ll create another template file to give the information about the certificate that we’d like to create:

sudo nano /etc/ssl/ldap01.info

and place the following tex in that file:

organization = CIS 527
cn = ldap.cis527russfeld.cs.ksu.edu
tls_www_server
encryption_key
signing_key
expiration_days = 365

Notice that in that file, we entered the fully qualified domain name for our LDAP server on the second line. This is the most important part that makes all of this work. On our client machine, we must have a DNS entry that links this domain name to our LDAP server’s IP address, and then the certificate the server uses must match that domain name. So, if we don’t get this step right, the whole system may not work correctly until we fix it!

Finally, we can use this long and complex command to create and sign our server’s certificate:

sudo certtool --generate-certificate --load-privkey /etc/ldap/ldap01_slapd_key.pem --load-ca-certificate /etc/ssl/certs/mycacert.pem --load-ca-privkey /etc/ssl/private/mycakey.pem --template /etc/ssl/ldap01.info --outfile /etc/ldap/ldap01_slapd_cert.pem

Once the certificate has been created, we just need to do a couple of tweaks so that it has the correct permissions. This will allow the LDAP server to properly access the file:

sudo chgrp openldap /etc/ldap/ldap01_slapd_key.pem
sudo chmod 0640 /etc/ldap/ldap01_slapd_key.pem

Finally, at long last, we are ready to tell our LDAP server to use the certificate. To do that, we’ll create an LDIF file:

nano ~/certinfo.ldif

and in that file we’ll put the information about our certificate:

dn: cn=config
add: olcTLSCACertificateFile
olcTLSCACertificateFile: /etc/ssl/certs/mycacert.pem
-
add: olcTLSCertificateFile
olcTLSCertificateFile: /etc/ldap/ldap01_slapd_cert.pem
-
add: olcTLSCertificateKeyFile
olcTLSCertificateKeyFile: /etc/ldap/ldap01_slapd_key.pem

Once that file is created, we can use the ldapmodify tool to import it into our server:

sudo ldapmodify -Y EXTERNAL -H ldapi:/// -f certinfo.ldif

Whew! That was a lot of work! Now, if we did everything correctly, we should be able to query this LDAP server using TLS. The best way to check that is by using the following command:

ldapwhoami -x -ZZ -h ldap.cis527russfeld.cs.ksu.edu

The -ZZ part of that command tells it to use TLS, and if it works correctly it should return anonymous as the result. If this step fails, then you may need to do some troubleshooting to see what the problem is.

That should do it! In the next video, I’ll show how to configure another Ubuntu VM to use this LDAP server for authentication.