Integrating open source software in the enterprise Chapter 1: Creating a network file share with Linux and Samba authenticating against Active Directory

Integrating open source software in the enterprise is a series of posts that show you how to deploy open source software tools in an enterprise setting, interoperating with established commercial software such as Windows Server and Active Directory.

In this procedure we create a network file share by integrating the open source program Samba running on Linux with Active Directory to authenticate access to the network file share.

Business case

A computer running Linux and Samba can create a network file share authenticating against a company’s Active Directory. This means that a Linux server and Samba network file share software can replace a Windows server for the network file share role in the enterprise, reducing software licensing costs and improving security and stability.

This procedure was tested on Ubuntu Linux 22.04 LTS

This procedure was tested on Ubuntu Linux 22.04 LTS

Understanding the test network

This procedure was tested on a network of 3 virtual machines, each running in bridge mode, on different hypervisor hosts.

sudburyWindows Server 2019 acting as Active Directory controller for the clarkcounty.gordonbuchan.com domain.
sandiegoUbuntu Linux 22.04LTS desktop joined to the clarkcounty.gordonbuchan.com domain, authenticating access to a network file share enabled by Samba and Winbind against the Active Directory controller for the domain clarkcounty.gordonbuchan.com on sudbury.
hamiltonWindows 10 Pro workstation joined to the clarkcounty.gordonbuchan.com domain.

Understanding Active Directory

Active Directory is commercial software developed by Microsoft that runs primarily on Windows Server. Active Directory can authenticate users and groups of users, and can control access to resources like network file shares and “Single Sign-On” (SSO) login to computers connected to the network.

Understanding Samba

Samba is open source free software that enables a Linux server to provide a network file share that can be accessed by Windows computers.

A note re Samba’s included Active Directory functionality

Samba itself is able to act as an Active Directory controller and can implement a subset of Active Directory’s features. This post assumes that you are authenticating against an Active Directory controller running on Windows Server.

Understanding Winbind

Winbind is software that enables Samba to integrate with Active Directory to authenticate access to a network file share.

Understanding System Security Services Daemon (SSSD)

SSSD is a technology that enables Active Directory integration for Linux workstations. In practice, it is difficult to integrate SSSD with Samba for Active Directory authentication in a stable fashion. There are some approaches to SSSD which incorporate Winbind for a hybrid approach. This procedure will focus on using Winbind, and without using SSSD.

Choosing Winbind over SSSD for a network file share authenticaticated against Active Directory

This procedure will use Winbind to enable Samba to integrate with Active Directory to create a network file share authenticated against Active Directory.

Objectives

  • Access to the network file share authenticated against Active Directory.
  • The network file share must be accessible to workstations with “Enable insecure guest logins” set to “Disabled.”
  • The network file share must observe ACL and allow overrides by Windows clients for ownership and permissions.

(Single-Sign-On (SSO) and SSSD will be addressed in a later procedure.)

Creating the Active Directory group example_group and adding members to the group

Entering commands as root

This procedure assumes that you are logged in as the root user of the Linux server.

Escalate to the root user:

sudo su

Replacing the example realm/domain name with your realm/domain name

Please replace the sample realm/domain name clarkcounty.gordonbuchan.com with your realm/domain name.

Setting the system hostname

hostnamectl set-hostname sandiego.clarkcounty.gordonbuchan.com

Configuring the /etc/hosts file

Associate the host name of your Linux server with its IP address:

cd /etc
nano hosts
192.168.33.110   sandiego
192.168.33.110   sandiego.clarkcounty.gordonbuchan.com

Setting DNS

Disable systemd-resolved service:

systemctl stop systemd-resolved
systemctl disable systemd-resolved

Unlink the symbolic link /etc/resolv.conf:

cd /etc
unlink resolv.conf

Creating a new /etc/resolv.conf file

Ensure that the first nameserver entry is the IP address of the Active Directory server.

nano resolv.conf
nameserver 192.168.33.80
nameserver 8.8.8.8
search clarkcounty.gordonbuchan.com
reboot

Installing software

apt install acl samba winbind libnss-winbind krb5-user

Note: for the files /etc/krb5.conf and /etc/samba/smb.conf, the realm/domain name must be in UPPERCASE letters

The realm/domain name must be in UPPERCASE letters. This includes the long version CLARKCOUNTY.GORDONBUCHAN.COM and short version CLARKCOUNTY of the realm/domain name.

Configuring Kerberos

cd /etc
cp krb5.conf krb5.conf.orig
nano krb5.conf
[libdefaults]
default_realm = CLARKCOUNTY.GORDONBUCHAN.COM
dns_lookup_realm = false
dns_lookup_kdc = true

Configuring Nsswitch

cd /etc
cp nsswitch.conf nsswitch.conf.orig
nano nsswitch.conf
passwd: files winbind
group: files winbind
hosts: files dns wins
chmod 550 nsswitch.conf

Configuring Samba (1/2)

cd /etc/samba
cp smb.conf smb.conf.orig
nano smb.conf
[global]
   realm = CLARKCOUNTY.GORDONBUCHAN.COM
   security = ADS
   workgroup = CLARKCOUNTY

   idmap config SAMDOM : range = 10000 - 999999
   idmap config SAMDOM : backend = rid
   idmap config * : range = 3000-7999
   idmap config * : backend = tdb

   map acl inherit = Yes
   vfs objects = acl_xattr

   dedicated keytab file = /etc/krb5.keytab
   kerberos method = secrets and keytab
   winbind refresh tickets = Yes

Obtaining a Kerberos ticket

kinit admingordon
klist

Joining the Active Directory domain

net ads info testjoin
net ads -v join -U admingordon
net ads info

Restarting services (1/2)

systemctl restart smbd nmbd winbind

Creating the share folder

cd /home
mkdir example_share
chmod -R 2770 example_share
chown -R "CLARKCOUNTY\admingordon":"CLARKCOUNTY\example_group" example_share

Configuring Samba (2/2)

cd /etc/samba
cp smb.conf smb.conf.orig
nano smb.conf
   [Share]
   acl_xattr:ignore system acl = Yes
   acl allow execute always = Yes
   acl group control = Yes
   inherit acls = Yes
   inherit owner = windows and unix
   inherit permissions = Yes
   path = /media/share
   read only = No

Restarting services (2/2)

systemctl restart smbd nmbd winbind

Mapping sid==5-1-5-32-546 to nogroup

This SID must be mapped to the UNIX group nogroup:

net groupmap add sid=S-1-5-32-546 unixgroup=nogroup type=builtin

Connecting to the network file share from a Windows computer joined to the domain

Applying Windows Access Control Lists (ACLs) from a Windows computer joined to the domain

References

http://blog.jrg.com.br/2021/02/01/ubuntu-focal-fossa-samba-domain-member-shares-1/
https://docs.vmware.com/en/VMware-Horizon-7/7.13/linux-desktops-setup/GUID-F8F0CFCF-C4D6-4784-85FF-E7C6DF575F49.html
https://ubuntu.com/server/docs/service-sssd-ad
https://wiki.samba.org/index.php/Setting_up_Samba_as_a_Domain_Member
https://www.jurisic.org/post/2021/11/24/SAMBA-Domain-Member-as-File-Server
https://www.moderndeployment.com/windows-server-2019-active-directory-installation-beginners-guide/
https://www.reddit.com/r/Ubuntu/comments/h01i2w/cheat_sheet_on_how_to_configure_a_smb_file_server/