Active Directory Authentication¶
- Some understanding of Active Directory
- Some understanding of LDAP
Microsoft's Active Directory (AD) is, in most enterprises, the de facto 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.
Now, while connecting Linux to an AD cluster cannot support all of the features mentioned, it can handle users, groups, and access control. It is even possible (through some configuration tweaks on the Linux side and some advanced options on the AD side) to distribute SSH keys using AD.
This guide, however, will just cover configuring authentication against Active Directory, and will not include any extra configuration on the Windows side.
Discovering and joining AD using SSSD¶
Throughout this guide, the domain name
ad.company.local will be used to
represent the Active Directory domain. To follow this guide, replace it with
the actual domain name your AD domain uses.
The first step along the way to join a Linux system into AD is to discover your AD cluster, to ensure that the network configuration is correct on both sides.
- Ensure the following ports are open to your Linux host on your domain controller:
|Kerberos||88, 464 (TCP+UDP)||Used by
|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:
# 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
Manually editing the /etc/resolv.conf:
# Edit the resolv.conf file [user@host ~]$ sudo vi /etc/resolv.conf search lan nameserver 10.0.0.2 nameserver 188.8.131.52 # replace this with your preferred public DNS (as a backup) # Make the resolv.conf file unwritable, preventing NetworkManager from # overwriting it. [user@host ~]$ sudo chattr +i /etc/resolv.conf
- Ensure that the time on both sides (AD host and Linux system) is synchronized
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 realmd oddjob oddjob-mkhomedir sssd adcli krb5-workstation
Now, you should 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
This will be discovered using the relevant SRV records stored in your Active Directory DNS service.
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
adcli and some other such
[user@host ~]$ sudo realm join ad.company.local
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
for an Active Directory user.
[user@host ~]$ sudo getent passwd email@example.com firstname.lastname@example.org:*:1450400500:1450400513:Administrator:/email@example.com:/bin/bash
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 firstname.lastname@example.org linux.host Password for email@example.com: Activate the web console with: systemctl enable --now cockpit.socket Last login: Wed Sep 15 17:37:03 2021 from 10.0.10.241 [firstname.lastname@example.org@host ~]$
If this succeeds, you have successfully configured Linux to use Active Directory as an authentication source.
Setting the default domain¶
In a completely default setup, you will need to log in with your AD account by
specifying the domain in your username (e.g.
this is not the desired behaviour, and you instead want to be able to omit the
domain name at authentication time, you can configure SSSD to default to a
This is actually a relatively simple process, and just requires a configuration tweak in your SSSD configuration file.
[user@host ~]$ sudo vi /etc/sssd/sssd.conf [sssd] ... default_domain_suffix = ad.company.local
By adding the
default_domain_suffix, you are instructing SSSD to (if no
other domain is specified) infer that the user is trying to authenticate as a
user from the
ad.company.local domain. This allows you to authenticate as
john.doe instead of
To make this configuration change take effect, you must restart the
sssd.service unit with
[user@host ~]$ sudo systemctl restart sssd
Author: Hayden Young
Contributors: Steven Spencer, Sambhav Saggi