7 Active Directory support #
Active Directory* (AD) is a directory-service based on LDAP, Kerberos, and other services. It is used by Microsoft* Windows* to manage resources, services, and people. In a Microsoft Windows network, Active Directory provides information about these objects, restricts access to them, and enforces policies. SUSE® Linux Enterprise Server lets you join existing Active Directory domains and integrate your Linux machine into a Windows environment.
7.1 Integrating Linux and Active Directory environments #
With a Linux client (configured as an Active Directory client) that is joined to an existing Active Directory domain, benefit from various features not available on a pure SUSE Linux Enterprise Server Linux client:
- Browsing shared files and directories with SMB
GNOME Files (previously called Nautilus) supports browsing shared resources through SMB.
- Sharing files and directories with SMB
GNOME Files supports sharing directories and files as in Windows.
- Accessing and manipulating user data on the Windows server
Through GNOME Files, users can access their Windows user data and can edit, create, and delete files and directories on the Windows server. Users can access their data without having to enter their password multiple times.
- Offline authentication
Users can log in and access their local data on the Linux machine even if they are offline or the Active Directory server is unavailable for other reasons.
- Windows password change
This port of Active Directory support in Linux enforces corporate password policies stored in Active Directory. The display managers and console support password change messages and accept your input. You can even use the Linux
passwd
command to set Windows passwords.- Single sign-on through kerberized applications
Many desktop applications are Kerberos-enabled (kerberized), which means they can transparently handle authentication for the user without the need for password reentry at Web servers, proxies, groupware applications, or other locations.
In Windows Server 2016 and later, Microsoft has removed the role IDMU/NIS Server and along with it the Unix Attributes plug-in for the Active Directory Users and Computers MMC snap-in.
However, Unix attributes can still be managed manually when Active Directory Users and Computers MMC snap-in. For more information, see https://blogs.technet.microsoft.com/activedirectoryua/2016/02/09/identity-management-for-unix-idmu-is-deprecated-in-windows-server/.
are enabled in theAlternatively, use the method described in Procedure 7.1, “Joining an Active Directory domain using to complete attributes on the client side (in particular, see ”Step 6.c).
The following section contains technical background for most of the previously named features.
7.2 Background information for Linux Active Directory support #
Many system components need to interact flawlessly to integrate a Linux client into an existing Windows Active Directory domain. The following sections focus on the underlying processes of the key events in Active Directory server and client interaction.
To communicate with the directory service, the client needs to share at least two protocols with the server:
- LDAP
LDAP is a protocol optimized for managing directory information. A Windows domain controller with Active Directory can use the LDAP protocol to exchange directory information with the clients. To learn more about LDAP, refer to Chapter 5, LDAP with 389 Directory Server.
- Kerberos
Kerberos is a third-party trusted authentication service. All its clients trust Kerberos authorization of another client's identity, enabling kerberized single sign-on (SSO) solutions. Windows supports a Kerberos implementation, making Kerberos SSO possible even with Linux clients. To learn more about Kerberos in Linux, refer to Chapter 6, Network authentication with Kerberos.
Depending on which YaST module you use to set up Kerberos authentication, different client components process account and authentication data:
- Solutions based on SSSD
The
sssd
daemon is the central part of this solution. It handles all communication with the Active Directory server.To gather name service information,
sssd_nss
is used.To authenticate users, the
pam_sss
module for PAM is used. The creation of user homes for the Active Directory users on the Linux client is handled bypam_mkhomedir
.For more information about PAM, see Chapter 2, Authentication with PAM.
- Solution based on Winbind (Samba)
The
winbindd
daemon is the central part of this solution. It handles all communication with the Active Directory server.To gather name service information,
nss_winbind
is used.To authenticate users, the
pam_winbind
module for PAM is used. The creation of user homes for the Active Directory users on the Linux client is handled bypam_mkhomedir
.For more information about PAM, see Chapter 2, Authentication with PAM.
Figure 7.1, “Schema of Winbind-based Active Directory authentication” highlights the most prominent components of Winbind-based Active Directory authentication.
Figure 7.1: Schema of Winbind-based Active Directory authentication #
Applications that are PAM-aware, like the login routines and the GNOME display manager, interact with the PAM and NSS layer to authenticate against the Windows server. Applications supporting Kerberos authentication (such as file managers, Web browsers, or e-mail clients) use the Kerberos credential cache to access user's Kerberos tickets, making them part of the SSO framework.
7.2.1 Domain join #
During domain join, the server and the client establish a secure relation. On the client, the following tasks need to be performed to join the existing LDAP and Kerberos SSO environment provided by the Windows domain controller. The entire join process is handled by the YaST Domain Membership module, which can be run during installation or in the installed system:
The Windows domain controller providing both LDAP and KDC (Key Distribution Center) services is located.
A machine account for the joining client is created in the directory service.
An initial ticket granting ticket (TGT) is obtained for the client and stored in its local Kerberos credential cache. The client needs this TGT to get further tickets allowing it to contact other services, like contacting the directory server for LDAP queries.
NSS and PAM configurations are adjusted to enable the client to authenticate against the domain controller.
During client boot, the winbind daemon is started and retrieves the initial Kerberos ticket for the machine account. winbindd automatically refreshes the machine's ticket to keep it valid. To keep track of the current account policies, winbindd periodically queries the domain controller.
7.2.2 Domain login and user homes #
The login manager of GNOME (GDM) has been extended to allow the handling of Active Directory domain login. Users can choose to log in to the primary domain the machine has joined or to one of the trusted domains with which the domain controller of the primary domain has established a trust relationship.
User authentication is mediated by several PAM modules as described in Section 7.2, “Background information for Linux Active Directory support”. If there are errors, the error codes are translated into user-readable error messages that PAM gives at login through any of the supported methods (GDM, console and SSH):
Password has expired
The user sees a message stating that the password has expired and needs to be changed. The system prompts for a new password and informs the user if the new password does not comply with corporate password policies (for example the password is too short, too simple, or already in the history). If a user's password change fails, the reason is shown and a new password prompt is given.
Account disabled
The user sees an error message stating that the account has been disabled and to contact the system administrator.
Account locked out
The user sees an error message stating that the account has been locked and to contact the system administrator.
Password has to be changed
The user can log in but receives a warning that the password needs to be changed soon. This warning is sent three days before that password expires. After expiration, the user cannot log in.
Invalid workstation
When a user is restricted to specific workstations and the current SUSE Linux Enterprise Server machine is not among them, a message appears that this user cannot log in from this workstation.
Invalid logon hours
When a user is only allowed to log in during working hours and tries to log in outside working hours, a message informs the user that logging in is not possible at that time.
Account expired
An administrator can set an expiration time for a specific user account. If that user tries to log in after expiration, the user gets a message that the account has expired and cannot be used to log in.
During a successful authentication, the client acquires a ticket granting ticket (TGT) from the Kerberos server of Active Directory and stores it in the user's credential cache. It also renews the TGT in the background, requiring no user interaction.
SUSE Linux Enterprise Server supports local home directories for Active Directory users. If configured through YaST as described in Section 7.3, “Configuring a Linux client for Active Directory”, user home directories are created when a Windows/Active Directory user first logs in to the Linux client. These home directories look and feel identical to standard Linux user home directories and work independently of the Active Directory Domain Controller.
Using a local user home, it is possible to access a user's data on this machine (even when the Active Directory server is disconnected) if the Linux client has been configured to perform offline authentication.
7.2.3 Offline service and policy support #
Users in a corporate environment must have the ability to become roaming users (for example, to switch networks or even work disconnected for some time). To enable users to log in to a disconnected machine, extensive caching was integrated into the winbind daemon. The winbind daemon enforces password policies even in the offline state. It tracks the number of failed login attempts and reacts according to the policies configured in Active Directory. Offline support is disabled by default and must be explicitly enabled in the YaST Domain Membership module.
When the domain controller has become unavailable, the user can still access network resources (other than the Active Directory server itself) with valid Kerberos tickets that have been acquired before losing the connection (as in Windows). Password changes cannot be processed unless the domain controller is online. While disconnected from the Active Directory server, a user cannot access any data stored on this server. When a workstation has become disconnected from the network entirely and connects to the corporate network again later, SUSE Linux Enterprise Server acquires a new Kerberos ticket when the user has locked and unlocked the desktop (for example, using a desktop screen saver).
7.3 Configuring a Linux client for Active Directory #
Before your client can join an Active Directory domain, adjustments must be made to your network setup to ensure the flawless interaction of client and server.
- DNS
Configure your client machine to use a DNS server that can forward DNS requests to the Active Directory DNS server. Alternatively, configure your machine to use the Active Directory DNS server as the name service data source.
- NTP
To succeed with Kerberos authentication, the client must have its time set accurately. It is recommended to use a central NTP time server for this purpose (this can be also the NTP server running on your Active Directory domain controller). If the clock skew between your Linux host and the domain controller exceeds a certain limit, Kerberos authentication fails and the client is logged in using the weaker NTLM (NT LAN Manager) authentication. For more details about using Active Directory for time synchronization, see Procedure 7.2, “Joining an Active Directory domain using . ”
- Firewall
To browse your network neighborhood, either disable the firewall entirely or mark the interface used for browsing as part of the internal zone.
To change the firewall settings on your client, log in as
root
and start the YaST firewall module. Select . Select your network interface from the list of interfaces and click . Select and apply your settings with . Leave the firewall settings with › . To disable the firewall, check the option, and leave the firewall module with › .- Active Directory account
You cannot log in to an Active Directory domain unless the Active Directory administrator has provided you with a valid user account for that domain. Use the Active Directory user name and password to log in to the Active Directory domain from your Linux client.
7.3.1 Choosing which YaST module to use for connecting to Active Directory #
YaST contains multiple modules that allow connecting to an Active Directory:
Use both an identity service (usually LDAP) and a user authentication service (usually Kerberos). This option is based on SSSD and in the majority of cases is best suited for joining Active Directory domains. .
This module is described in Section 7.3.2, “Joining Active Directory using . ”
Join an Active Directory (which entails use of Kerberos and LDAP). This option is based on .
winbind
and is best suited for joining an Active Directory domain if support for NTLM or cross-forest trusts is necessary.This module is described in Section 7.3.3, “Joining Active Directory using . ”
7.3.2 Joining Active Directory using #
The YaST module
supports authentication at an Active Directory. Additionally, it also supports the following related authentication and identification providers:- Identification providers
Support for legacy NSS providers via a proxy. .
FreeIPA and Red Hat Enterprise Identity Management provider. .
An LDAP provider. For more information about configuring LDAP, see .
man 5 sssd-ldap
.An SSSD-internal provider for local users. .
- Authentication providers
Relay authentication to another PAM target via a proxy. .
FreeIPA and Red Hat Enterprise Identity Management provider. .
An LDAP provider. .
Kerberos authentication. .
An SSSD-internal provider for local users. .
Disables authentication explicitly. .
To join an Active Directory domain using SSSD and the
module of YaST, proceed as follows:Open YaST.
To be able to use DNS auto-discovery later, set up the Active Directory Domain Controller (the Active Directory server) as the name server for your client.
In YaST, click
.Select
, then enter the IP address of the Active Directory Domain Controller into the text box .Save the setting with
.
From the YaST main window, start the module
.The module opens with an overview showing different network properties of your computer and the authentication method currently in use.
Figure 7.2: Main window of #To start editing, click
.Now join the domain.
Click
.In the appearing dialog, specify the correct
. Then specify the services to use for identity data and authentication: Select for both.Ensure that
is activated.Click
.(Optional) You can keep the default settings in the following dialog. However, there are reasons to make changes:
If the local host name does not match the host name set on the domain controller. Find out if the host name of your computer matches the name under which your computer is known to the Active Directory Domain Controller. In a terminal, run the command
hostname
, then compare its output to the configuration of the Active Directory Domain Controller.If the values differ, specify the host name from the Active Directory configuration under
. Otherwise, leave the appropriate text box empty.If you do not want to use DNS auto-discovery. Specify the that you want to use. If there are multiple Domain Controllers, separate their host names with commas.
To continue, click
.If not all software is installed already, the computer now installs missing software. It then checks whether the configured Active Directory Domain Controller is available.
If everything is correct, the following dialog should now show that it has discovered an
but that you are .In the dialog, specify the
and of the Active Directory administrator account (Administrator
).To make sure that the current domain is enabled for Samba, activate
.To enroll, click
.Figure 7.3: Enrolling into a domain #You should now see a message confirming that you have enrolled successfully. Finish with
.
After enrolling, configure the client using the window
.Figure 7.4: Configuration window of #To allow logging in to the computer using login data provided by Active Directory, activate
.(Optional) Optionally, under , activate additional data sources such as information on which users are allowed to use
sudo
or which network drives are available.To allow Active Directory users to have home directories, activate
. The path for home directories can be set in multiple ways—on the client, on the server, or both ways:To configure the home directory paths on the Domain Controller, set an appropriate value for the attribute
UnixHomeDirectory
for each user. Additionally, make sure that this attribute replicated to the global catalog. For information on achieving that under Windows, see https://support.microsoft.com/en-us/kb/248717.To configure home directory paths on the client in such a way that precedence is given to the path set on the domain controller, use the option
fallback_homedir
.To configure home directory paths on the client in such a way that the client setting overrides the server setting, use
override_homedir
.
As settings on the Domain Controller are outside of the scope of this documentation, only the configuration of the client-side options is described in the following.
From the side bar, select
› , then click . From that window, select eitherfallback_homedir
oroverride_homedir
, then click .Specify a value. To have home directories follow the format
/home/USER_NAME
, use/home/%u
. For more information about possible variables, see the man pagesssd.conf
(man 5 sssd.conf
), section override_homedir.Click
.
Save the changes by clicking
. Then make sure that the values displayed now are correct. To leave the dialog, click .
7.3.3 Joining Active Directory using #
To join an Active Directory domain using winbind
and the
module of YaST, proceed as
follows:
Log in as
root
and start YaST.Start
› .Enter the domain to join at Figure 7.5, “Determining Windows domain membership”). If the DNS settings on your host are properly integrated with the Windows DNS server, enter the Active Directory domain name in its DNS format (
in the screen (seemydomain.mycompany.com
). If you enter the short name of your domain (also known as the pre–Windows 2000 domain name), YaST must rely on NetBIOS name resolution instead of DNS to find the correct domain controller.Figure 7.5: Determining Windows domain membership #To use the SMB source for Linux authentication, activate
.To automatically create a local home directory for Active Directory users on the Linux machine, activate
.Check
to allow your domain users to log in even if the Active Directory server is temporarily unavailable, or if you do not have a network connection.To change the UID and GID ranges for the Samba users and groups, select
. Let DHCP retrieve the WINS server only if you need it. This is the case when certain machines are resolved only by the WINS system.Configure NTP time synchronization for your Active Directory environment by selecting
and entering an appropriate server name or IP address. This step is obsolete if you have already entered the appropriate settings in the stand-alone YaST NTP configuration module.Click
and confirm the domain join when prompted for it.Provide the password for the Windows administrator on the Active Directory server and click Figure 7.6, “Providing administrator credentials”).
(seeFigure 7.6: Providing administrator credentials #
After you have joined the Active Directory domain, you can log in to it from your workstation using the display manager of your desktop or the console.
Joining a domain may not succeed if the domain name ends with
.local
. Names ending in .local
cause conflicts with Multicast DNS (MDNS) where
.local
is reserved for link-local host names.
Only a domain administrator account, such as
Administrator
, can join SUSE Linux Enterprise Server into Active
Directory.
7.3.4 Checking Active Directory connection status #
To check whether you are successfully enrolled in an Active Directory domain, use the following commands:
klist
shows whether the current user has a valid Kerberos ticket.getent passwd
shows published LDAP data for all users.
7.4 Logging in to an Active Directory domain #
Provided your machine has been configured to authenticate against Active Directory and you have a valid Windows user identity, you can log in to your machine using the Active Directory credentials. Login is supported for GNOME, the console, SSH and any other PAM-aware application.
SUSE Linux Enterprise Server supports offline authentication, allowing you to log in to your client machine even when it is offline. See Section 7.2.3, “Offline service and policy support” for details.
7.4.1 GDM #
To authenticate a GNOME client machine against an Active Directory server, proceed as follows:
Click
.In the text box
, enter the domain name and the Windows user name in this form:DOMAIN_NAME\USER_NAME
.Enter your Windows password.
If configured to do so, SUSE Linux Enterprise Server creates a user home directory on the local machine on the first login of each user authenticated via Active Directory. This allows you to benefit from the Active Directory support of SUSE Linux Enterprise Server while still having a fully functional Linux machine at your disposal.
7.4.2 Console login #
Besides logging in to the Active Directory client machine using a graphical front-end, you can log in using the text-based console or even remotely using SSH.
To log in to your Active Directory client from a console, enter
DOMAIN_NAME\USER_NAME
at the login:
prompt and provide the password.
To remotely log in to your Active Directory client machine using SSH, proceed as follows:
At the login prompt, enter:
>
ssh DOMAIN_NAME\\USER_NAME@HOST_NAMEThe
\
domain and login delimiter is escaped with another\
sign.Provide the user's password.
7.5 Changing passwords #
SUSE Linux Enterprise Server helps the user choose a suitable new password that meets the corporate security policy. The underlying PAM module retrieves the current password policy settings from the domain controller and informs the user by a message on login about the specific password quality requirements a user account typically has. Like its Windows counterpart, SUSE Linux Enterprise Server presents a message describing:
Password history settings
Minimum password length requirements
Minimum password age
Password complexity
The password change process cannot succeed unless all requirements have been successfully met. Feedback about the password status is given both through the display managers and the console.
GDM provides feedback about password expiration and the prompt for new passwords in an interactive mode. To change passwords in the display managers, provide the password information when prompted.
To change your Windows password, you can use the standard Linux utility,
passwd
, instead of having to manipulate this data on
the server. To change your Windows password, proceed as follows:
Log in at the console.
Enter
passwd
.Enter your current password when prompted.
Enter the new password.
Reenter the new password for confirmation. If your new password does not comply with the policies on the Windows server, this feedback is given to you and you are prompted for another password.
To change your Windows password from the GNOME desktop, proceed as follows:
Click the
icon on the left edge of the panel.Select
.From the
section, select › .Enter your old password.
Enter and confirm the new password.
Leave the dialog with
to apply your settings.
7.6 Active Directory certificate auto-enrollment #
Certificate auto-enrollment enables network devices to automatically
enroll certificates from Active Directory Certificate Services, including
SUSE Linux Enterprise Server devices, with no user intervention. This is managed by Active Directory's
Group Policy, using Samba's samba-gpupdate
command.
7.6.1 Configuring certificate auto-enrollment on the server #
The Windows server roles Certification Authority
,
Certificate Enrollment Policy Web Service
,
Certificate Enrollment Web Service
and
Network Device Enrollment Service
all must be installed
and configured on the Active Directory server.
Configure Group Policy auto-enrollment as described in this Microsoft documentation: https://docs.microsoft.com/en-us/windows-server/networking/core-network-guide/cncg/server-certs/configure-server-certificate-autoenrollment#configure-server-certificate-auto-enrollment.
7.6.2 Enable certificate auto-enrollment on the client #
Follow the steps in the following procedure to enable certificate on your clients.
Install the samba-gpupdate package. This automatically installs the certmonger, cepces and sscep dependencies. Samba uses
sscep
to download the Certificate Authority root chain, then uses thecertmonger
paired withcepces
to monitor the host certificate templates.Join to an Active Directory domain (one where the CA has been previously configured as explained in Section 7.6.1, “Configuring certificate auto-enrollment on the server”).
On Winbind-joined machines, set the
smb.conf
global parameter by adding the lineapply group policies = yes
.For SSSD-joined machines, install oddjob-gpupdate from https://github.com/openSUSE/oddjob-gpupdate.
Then verify that certificate auto-enrollment is correctly configured by running the following command on the client:
>
/usr/sbin/samba-gpupdate --rsop
If you see output like the following example, it is correctly configured:
Resultant Set of Policy Computer Policy GPO: Default Domain Policy ========================================================== CSE: gp_cert_auto_enroll_ext ----------------------------------------------------------- Policy Type: Auto Enrollment Policy ----------------------------------------------------------- [ <CA NAME> ] = [ CA Certificate ] = ----BEGIN CERTIFICATE---- <CERTIFICATE> ----END CERTIFICATE---- [ Auto Enrollment Server ] = <DNS NAME>
Use the following command to display installed certificates:
>
getcert list
Number of certificates and requests being tracked: 1. Request ID 'Machine': status: MONITORING stuck: no key pair storage: type=FILE,location='/var/lib/samba/private/certs/Machine.key' certificate: type=FILE,location='/var/lib/samba/certs/Machine.crt' CA: <CA NAME> issuer: CN=<CA NAME> subject: CN=<HOSTNAME> expires: 2017-08-15 17:37:02 UTC dns: <hostname> key usage: digitalSignature,keyEncipherment eku: id-kp-clientAuth,id-kp-serverAuth certificate template/profile: Machine
Certificates are installed in /var/lib/samba/certs
and private keys are installed in
/var/lib/samba/private
/certs.
For more information, see man samba-gpupdate
.