Active Directory Authentication with Samba

Prerequisites¶

Some understanding of Active Directory
Some understanding of LDAP

Introduction¶

In most enterprises, Microsoft's Active Directory (AD) is the default authentication system for Windows systems and for external, LDAP-connected services. It allows you to configure users and groups, access control, permissions, auto-mounting, and more.

While connecting Linux to an AD cluster cannot support all of the features mentioned, it can handle users, groups, and access control. It is possible (through some configuration tweaks on the Linux side and some advanced options on the AD side) to distribute SSH keys using AD.

The default way of using Active Directory on Rocky Linux is using SSSD, but Samba is a more full-featured alternative. For instance, file sharing can be done with Samba but not SSSD. This guide, however, will cover configuring authentication against Active Directory using Samba and will not include any extra configuration on the Windows side.

Discovering and joining AD using Samba¶

Note

The domain name ad.company.local throughout this guide will represent the Active Directory domain. To follow this guide, replace it with your AD domain's name.

The first step to joining a Linux system into AD is to discover your AD cluster, to ensure the network configuration is correct on both sides.

Preparation¶

Ensure the following ports are open to your Linux host on your domain controller:

Service	Port(s)	Notes
DNS	53 (TCP+UDP)
Kerberos	88, 464 (TCP+UDP)	Used by `kadmin` for setting & updating passwords
LDAP	389 (TCP+UDP)
LDAP-GC	3268 (TCP)	LDAP Global Catalog - allows you to source user IDs from AD

Ensure you have configured your AD domain controller as a DNS server on your Rocky Linux host:

With NetworkManager:

# where your primary NetworkManager connection is 'System eth0' and your AD
# server is accessible on the IP address 10.0.0.2.
[root@host ~]$ nmcli con mod 'System eth0' ipv4.dns 10.0.0.2

Ensure that the time on both sides (AD host and Linux system) is synchronized (see chronyd)

To check the time on Rocky Linux:

[user@host ~]$ date
Wed 22 Sep 17:11:35 BST 2021

Install the required packages for AD connection on the Linux side:

[user@host ~]$ sudo dnf install samba samba-winbind samba-client

Discovery¶

You should now be able to successfully discover your AD server(s) from your Linux host.

[user@host ~]$ realm discover ad.company.local
ad.company.local
  type: kerberos
  realm-name: AD.COMPANY.LOCAL
  domain-name: ad.company.local
  configured: no
  server-software: active-directory
  client-software: sssd
  required-package: oddjob
  required-package: oddjob-mkhomedir
  required-package: sssd
  required-package: adcli
  required-package: samba-common

The relevant SRV records stored in your Active Directory DNS service will allow discovery.

Joining¶

Once you have successfully discovered your Active Directory installation from the Linux host, you should be able to use realmd to join the domain, which will orchestrate the configuration of Samba using adcli and some other such tools.

[user@host ~]$ sudo realm join -v --membership-software=samba --client-software=winbind ad.company.local

You will be prompted to enter your domain's administrator password so input it.

If this process complains about encryption with KDC has no support for encryption type, try updating the global crypto policy to allow older encryption algorithms:

[user@host ~]$ sudo update-crypto-policies --set DEFAULT:AD-SUPPORT

If this process succeeds, you should now be able to pull passwd information for an Active Directory user.

[user@host ~]$ sudo getent passwd administrator@ad.company.local
AD\administrator:*:1450400500:1450400513:Administrator:/home/administrator@ad.company.local:/bin/bash

Note

getent get entries from Name Service Switch libraries (NSS). It means that, contrary to passwd or dig for example, it will query different databases, including /etc/hosts for getent hosts or from samba in the getent passwd case.

realm provides some interesting options that you can use:

Option	Observation
--computer-ou='OU=LINUX,OU=SERVERS,dc=ad,dc=company.local'	The OU where to store the server account
--os-name='rocky'	Specify the OS name stored in the AD
--os-version='8'	Specify the OS version stored in the AD
-U admin_username	Specify an admin account

Attempting to authenticate¶

Now your users should be able to authenticate to your Linux host against Active Directory.

On Windows 10: (which provides its own copy of OpenSSH)

C:\Users\John.Doe> ssh -l john.doe@ad.company.local linux.host
Password for john.doe@ad.company.local:

Activate the web console with: systemctl enable --now cockpit.socket

Last login: Wed Sep 15 17:37:03 2021 from 10.0.10.241
[john.doe@ad.company.local@host ~]$

If this succeeds, you have successfully configured Linux to use Active Directory as an authentication source.

Eliminating the domain name in usernames¶

In a completely default setup, you will need to log in with your AD account by specifying the domain in your username (e.g., john.doe@ad.company.local). If this is not the desired behavior and you instead want to be able to omit the default domain name at authentication time you can configure Samba to default to a specific domain.

This is a relatively straightforward process, requiring a configuration tweak in your SSSD configuration file.

[user@host ~]$ sudo vi /etc/samba/smb.conf
[global]
...
winbind use default domain = yes

By adding the winbind use default domain, you are instructing Samba to infer that the user is trying to authenticate as a user from the ad.company.local domain. This allows you to authenticate as something like john.doe instead of john.doe@ad.company.local.

To make this configuration change take effect, you must restart the smb and winbind services with systemctl.

[user@host ~]$ sudo systemctl restart smb winbind

In the same way, if you do not want your home directories suffixed with the domain name, you can add those options into your configuration file /etc/samba/smb.conf:

[global]
template homedir = /home/%U

Do not forget to restart the smb and winbind services.

Author: Neel Chauhan

Contributors: Steven Spencer, Ganna Zhyrnova