Integrate Ubuntu to Samba4 AD DC with SSSD and Realm – Part 15

This tutorial will guide you on how to join an Ubuntu Desktop machine into a Samba4 Active Directory domain with SSSD and Realmd services in order to authenticate users against an Active Directory.

Requirements:

1. Create an Active Directory Infrastructure with Samba4 on Ubuntu

Step 1: Initial Configurations

1. Before starting to join Ubuntu into an Active Directory make sure the hostname is properly configured. Use hostnamectl command to set the machine name or manually edit /etc/hostname file.

$ sudo hostnamectl set-hostname your_machine_short_hostname
$ cat /etc/hostname
$ hostnamectl

2. On the next step, edit machine network interface settings and add the proper IP configurations and the correct DNS IP server addresses to point to the Samba AD domain controller as illustrated in the below screenshot.

If you have configured a DHCP server at your premises to automatically assign IP settings for your LAN machines with the proper AD DNS IP addresses then you can skip this step and move forward.

On the above screenshot, 192.168.1.254 and 192.168.1.253 represents the IP addresses of the Samba4 Domain Controllers.

3. Restart the network services to apply the changes using the GUI or from command line and issue a series of ping command against your domain name in order to test if DNS resolution is working as expected. Also, use host command to test DNS resolution.

$ sudo systemctl restart networking.service
$ host your_domain.tld
$ ping -c2 your_domain_name
$ ping -c2 adc1
$ ping -c2 adc2

4. Finally, make sure that machine time is in sync with Samba4 AD. Install ntpdate package and sync time with the AD by issuing the below commands.

$ sudo apt-get install ntpdate
$ sudo ntpdate your_domain_name

Step 2: Install Required Packages

5. On this step install the necessary software and required dependencies in order to join Ubuntu into Samba4 AD DC: Realmd and SSSD services.

$ sudo apt install adcli realmd krb5-user samba-common-bin samba-libs samba-dsdb-modules sssd sssd-tools libnss-sss libpam-sss packagekit policykit-1 

6. Enter the name of the default realm with uppercases and press Enter key to continue the installation.

7. Next, create the SSSD configuration file with the following content.

$ sudo nano /etc/sssd/sssd.conf

Add following lines to sssd.conf file.

[nss]
filter_groups = root
filter_users = root
reconnection_retries = 3

[pam]
reconnection_retries = 3

[sssd]
domains = tecmint.lan
config_file_version = 2
services = nss, pam
default_domain_suffix = TECMINT.LAN


[domain/tecmint.lan]
ad_domain = tecmint.lan
krb5_realm = TECMINT.LAN
realmd_tags = manages-system joined-with-samba
cache_credentials = True
id_provider = ad
krb5_store_password_if_offline = True
default_shell = /bin/bash
ldap_id_mapping = True
use_fully_qualified_names = True
fallback_homedir = /home/%d/%u
access_provider = ad

auth_provider = ad
chpass_provider = ad
access_provider = ad
ldap_schema = ad
dyndns_update = true
dyndns_refresh_interval = 43200
dyndns_update_ptr = true
dyndns_ttl = 3600

Make sure you replace the domain name in following parameters accordingly:

domains = tecmint.lan
default_domain_suffix = TECMINT.LAN
[domain/tecmint.lan]
ad_domain = tecmint.lan
krb5_realm = TECMINT.LAN

8. Next, add the proper permissions for SSSD file by issuing the below command:

$ sudo chmod 700 /etc/sssd/sssd.conf

9. Now, open and edit Realmd configuration file and add the following lines.

$ sudo nano /etc/realmd.conf

Realmd.conf file excerpt:

[active-directory]
os-name = Linux Ubuntu
os-version = 17.04

[service]
automatic-install = yes

 [users]
default-home = /home/%d/%u
default-shell = /bin/bash

[tecmint.lan]
user-principal = yes
fully-qualified-names = no

10. The last file you need to modify belongs to Samba daemon. Open /etc/samba/smb.conf file for editing and add the following block of code at the beginning of the file, after the [global] section as illustrated on the image below.

 workgroup = TECMINT
   client signing = yes
   client use spnego = yes
   kerberos method = secrets and keytab
   realm = TECMINT.LAN
   security = ads

Make sure you replace the domain name value, especially the realm value to match your domain name and run testparm command in order to check if the configuration file contains no errors.

$ sudo testparm

11. After you’ve made all the required changes, test Kerberos authentication using an AD administrative account and list the ticket by issuing the below commands.

$ sudo kinit [email protected]
$ sudo klist

Step 3: Join Ubuntu to Samba4 Realm

12. To join Ubuntu machine to Samba4 Active Directory issue following series of commands as illustrated below. Use the name of an AD DC account with administrator privileges in order for the binding to realm to work as expected and replace the domain name value accordingly.

$ sudo realm discover -v DOMAIN.TLD
$ sudo realm list
$ sudo realm join TECMINT.LAN -U ad_admin_user -v
$ sudo net ads join -k

13. After the domain binding took place, run the below command to assure that all domain accounts are permitted to authenticate on the machine.

$ sudo realm permit --all

Subsequently, you can allow or deny access for a domain user account or a group using realm command as presented on the below examples.

$ sudo realm deny -a
$ realm permit --groups ‘domain.tld\Linux Admins’
$ realm permit [email protected]
$ realm permit DOMAIN\\User2

14. From a Windows machine with RSAT tools installed you can open AD UC and navigate to Computers container and check if an object account with the name of your machine has been created.

Step 4: Configure AD Accounts Authentication

15. In order to authenticate on Ubuntu machine with domain accounts you need to run pam-auth-update command with root privileges and enable all PAM profiles including the option to automatically create home directories for each domain account at the first login.

Check all entries by pressing [space] key and hit ok to apply configuration.

$ sudo pam-auth-update

16. On systems manually edit /etc/pam.d/common-account file and the following line in order to automatically create homes for authenticated domain users.

session    required    pam_mkhomedir.so    skel=/etc/skel/    umask=0022

17. If Active Directory users can’t change their password from command line in Linux, open /etc/pam.d/common-password file and remove the use_authtok statement from password line to finally look as on the below excerpt.

password       [success=1 default=ignore]      pam_winbind.so try_first_pass

18. Finally, restart and enable Realmd and SSSD service to apply changes by issuing the below commands:

$ sudo systemctl restart realmd sssd
$ sudo systemctl enable realmd sssd

19. In order to test if the Ubuntu machine was successfully integrated to realm run install winbind package and run wbinfo command to list domain accounts and groups as illustrated below.

$ sudo apt-get install winbind
$ wbinfo -u
$ wbinfo -g

20. Also, check Winbind nsswitch module by issuing the getent command against a specific domain user or group.

$ sudo getent passwd your_domain_user
$ sudo getent group ‘domain admins’

21. You can also use Linux id command to get info about an AD account as illustrated on the below command.

$ id tecmint_user

22. To authenticate on Ubuntu host with a Samba4 AD account use the domain username parameter after su – command. Run id command to get extra info about the AD account.

$ su - your_ad_user

Use pwd command to see your domain user current working directory and passwd command if you want to change password.

23. To use a domain account with root privileges on your Ubuntu machine, you need to add the AD username to the sudo system group by issuing the below command:

$ sudo usermod -aG sudo [email protected]

Login to Ubuntu with the domain account and update your system by running apt update command to check root privileges.

24. To add root privileges for a domain group, open end edit /etc/sudoers file using visudo command and add the following line as illustrated.

%domain\ [email protected]       		 ALL=(ALL:ALL) ALL

25. To use domain account authentication for Ubuntu Desktop modify LightDM display manager by editing /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf file, append the following two lines and restart lightdm service or reboot the machine apply changes.

greeter-show-manual-login=true
greeter-hide-users=true

Log in to Ubuntu Desktop with a domain account using either your_domain_username or your_domain_username@your_domain.tld syntax.

26. To use short name format for Samba AD accounts, edit /etc/sssd/sssd.conf file, add the following line in [sssd] block as illustrated below.

full_name_format = %1$s

and restart SSSD daemon to apply changes.

$ sudo systemctl restart sssd

You will notice that the bash prompt will change to the short name of the AD user without appending the domain name counterpart.

27. In case you cannot login due to enumerate=true argument set in sssd.conf you must clear sssd cached database by issuing the below command:

$ rm /var/lib/sss/db/cache_tecmint.lan.ldb

That’s all! Although this guide is mainly focused on integration with a Samba4 Active Directory, the same steps can be applied in order to integrate Ubuntu with Realmd and SSSD services into a Microsoft Windows Server Active Directory.