Red Hat Enterprise Linux 7

Windows Integration Guide

Integrating Linux Systems with Active Directory Environments

Tomáš Čapek

Red Hat Customer Content Services

tcapek@redhat.com

Aneta Petrová

Red Hat Customer Content Services

apetrova@redhat.com

Ella Deon Ballard

Red Hat Customer Content Services

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Abstract

Heterogeneous IT environments often contain various different domains and operating systems that need to be able to seamlessly communicate. Red Hat Enterprise Linux offers multiple ways to tightly integrate Linux domains with Active Directory (AD) on Microsoft Windows. The integration is possible on different domain objects that include users, groups, services, or systems. This guide also covers different integration scenarios, ranging from light-weight AD pass-through authentication to full-fledged Kerberos trusted realms.

⁠Chapter 1. Ways to Integrate Active Directory and Linux Environments

IT environments have a structure. The systems in them are arranged with a purpose. Integrating two separate infrastructures requires an assessment of the purpose of each of those environments and an understanding of how and where they interact.

⁠1.1. Defining Windows Integration

Windows integration can mean very different things, depending on the desired interaction between the Linux environment and the Windows environment. It could mean that individual Linux systems are enrolled into a Windows domain, it could mean that a Linux domain is configured to be a peer to the Windows domain, or it could simply mean that information is copied between environments.

There are several points of contact between a Windows domain and Linux systems. Each of these points revolve around identifying different domain objects (users, groups, systems, services) and the services which are used in that identification.

⁠User Identities and Authentication

Where are user accounts located; in a central authentication system running on Windows (AD domain) or in a central identity and authentication server running on Linux?

How are users authenticated on a Linux system; through a local Linux authentication system or a central authentication system running on Windows?

How is group membership configured for users? How is that group membership determined?

Will users authenticate using a username/password pair, Kerberos tickets, certificates, or a combination of methods?

POSIX attributes are required to access services on Linux machines. How are these attributes stored: are they set in the Windows domain, configured locally on the Linux system, or dynamically mapped (for UID/GID numbers and Windows SIDs)?

What users will be accessing what resources? Will Windows-defined users access Linux resources? Will Linux-defined users access Windows resources?

In most environments, the Active Directory domain is the central hub for user information, which means that there needs to be some way for Linux systems to access that user information for authentication requests. The real question then is how to obtain that user information and how much of that information is available to external systems. There also needs to be a balance between information required for Linux systems (POSIX attributes) and Linux users (certain application administrators) and how that information is managed.

⁠Host and Service Principals

What resources will be accessed?

What authentication protocols are required?

How will Kerberos tickets be obtained? How will SSL certificates be requested or verified?

Will users need access to a single domain or to both Linux and Windows domains?

⁠DNS Domains, Queries, and Name Resolution

What will be a DNS configuration?

Is there a single DNS domain? Are there subdomains?

How will system host names be resolved?

How will service discovery be configured?

⁠Security Policies

Where are access control instructions set?

What administrators are configured for each domain?

⁠Change Management

How frequently are systems added to the domain?

If the underlying configuration for something related to Windows integration is changed, for example the DNS service, how are those changes propagated?

Is configuration maintained through domain-related tools or a provisioning system?

Does the integration path require additional applications or configuration on the Windows server?

As important as which elements in the domains are integrated, is how that integration is maintained. If a particular instrument of integration is heavily manual, yet the environment has a large number of systems which are frequently updated, then that one instrument may not work for that environment from a maintenance standpoint.

The following sections outline the main scenarios for integration with Windows. In direct integration, Linux systems are connected to Active Directory without any additional intermediaries. Indirect integration, on the other hand, involves an identity server that centrally manages Linux systems and connects the whole environment to Active Directory of the server-to-server level.

⁠1.2. Direct Integration

You need two components to connect a Linux system to Active Directory (AD). One component interacts with the central identity and authentication source, which is AD in this case. The other component detects available domains and configures the first component to work with the right identity source. There are different options that can be used to retrieve information and perform authentication against AD. Among them are:

Native LDAP and Kerberos PAM and NSS modules

Among these modules are nss_ldap, pam_ldap, and pam_krb5. As PAM and NSS modules are loaded into every application process, they directly affect the execution environment. With no caching, offline support, or sufficient protection of access credentials, use of the basic LDAP and Kerberos modules for NSS and PAM is discouraged due to their limited functionality.

Samba Winbind

Samba Winbind had been a traditional way of connecting Linux systems to AD. Winbind emulates a Windows client on a Linux system and is able to communicate to AD servers. The recent versions of the System Security Services Daemon (SSSD) closed a feature gap between Samba Winbind and SSSD and SSSD can now be used as a replacement for Winbind. In certain corner cases, Winbind might still be necessary to use but it is no longer the first choice in general.

System Security Services Daemon (SSSD)

The primary function of SSSD is to access a remote identity and authentication resource through a common framework that provides caching and offline support to the system. SSSD is highly configurable; it provides PAM and NSS integration and a database to store local users, as well as core and extended user data retrieved from a central server. SSSD is the recommended component to connect a Linux system with an identity server of your choice, be it Active Directory, Identity Management (IdM) in Red Hat Enterprise Linux, or any generic LDAP and/or Kerberos server.

The main reason to transition from Winbind to SSSD is that SSSD can be used for both direct and indirect integration and allows to switch from one integration approach to another without significant migration costs. The most convenient way to configure SSSD or Winbind in order to directly integrate a Linux system with AD is to use the realmd service. It allows callers to configure network authentication and domain membership in a standard way. The realmd service automatically discovers information about accessible domains and realms and does not require advanced configuration to join a domain or realm.

Direct integration is a simple way to introduce Linux systems to AD environment. However, as the share of Linux systems grows, the deployments usually see the need for a better centralized management of the identity-related policies such as host-based access control, sudo, or SELinux user mappings. At first, the configuration of these aspects of the Linux systems can be maintained in local configuration files. With a growing number of systems though, distribution and management of the configuration files is easier with a provisioning system such as Red Hat Satellite. This approach creates an overhead of changing the configuration files and then distributing them. When direct integration does not scale anymore, it is more beneficial to consider indirect integration described in the next section.

⁠1.3. Indirect Integration

The main advantage of the indirect integration is to manage Linux systems and policies related to those systems centrally while enabling users from Active Directory (AD) domains to transparently access Linux systems and services. There are two different approaches to the indirect integration:

Trust-based solution

The recommended approach is to leverage Identity Management (IdM) in Red Hat Enterprise Linux as the central server to control Linux systems and then establish cross-realm Kerberos trust with AD, enabling users from AD to log on to and to use single sign-on to access Linux systems and resources. This solution uses the Kerberos capability to establish trusts between different identity sources. IdM presents itself to AD as a separate forest and takes advantage of the forest-level trusts supported by AD.

In complex environments, a single IdM forest can be connected to multiple AD forests. This setup enables better separation of duties for different functions in the organization. AD administrators can focus on users and policies related to users while Linux administrators have full control over the Linux infrastructure. In such a case, the Linux realm controlled by IdM is analogous to an AD resource domain or realm but with Linux systems in it.

Note

In Windows, every domain is a Kerberos realm and a DNS domain at the same time. Every domain managed by the domain controller needs to have its own dedicated DNS zone. The same applies when IdM is trusted by AD as a forest. AD expects IdM to have its own DNS domain. For the trust setup to work, the DNS domain needs to be dedicated to the Linux environment.

Synchronization-based solution

An alternative to a trust-based solution is to leverage user synchronization capability, also available in IdM or Red Hat Directory Server (RHDS), allowing user accounts (and with RHDS also group accounts) to be synchronized from AD to IdM or RHDS, but not in the opposite direction. User synchronization has certain limitations, including:

duplication of users

the need to synchronize passwords, which requires a special component on all domain controllers in an AD domain

to be able to capture passwords, all users must first manually change them

synchronization supports only a single domain

only one domain controller in AD can be used to synchronize data to one instance of IdM or RHDS

In some integration scenarios, the user synchronization may be the only available option, but in general, use of the synchronization approach is discouraged in favor of the cross-realm trust-based integration.

⁠Part I. Adding a Single Linux System to an Active Directory Domain

⁠Chapter 2. Using Active Directory as an Identity Provider for SSSD

The System Security Services Daemon (SSSD) provides access to different identity and authentication providers. This service ties a local system to a larger back-end system. That can be a simple LDAP directory, domains for Active Directory (AD) or Identity Management (IdM) in Red Hat Enterprise Linux, or Kerberos realms.

SSSD configures a way to connect to an identity store to retrieve authentication information and then uses that to create a local cache of users and credentials. SSSD can also pull in group information. Authorization information is gathered by SSSD by using host-based access control (HBAC) in IdM and group policy object (GPO) settings in AD.

⁠2.1. About SSSD

The SSSD service is an intermediary between local applications and any configured data store. This relationship brings a number of benefits for administrators:

Reduced load on identification and authentication servers. Rather than having every application service attempt to contact the identification server directly, each local application can contact SSSD, which in turn connects to the identification server or checks its cache.

Option for offline authentication. SSSD keeps a cache of user identities (and optionally also user credentials) that it retrieves from remote services. This allows users to authenticate even if the remote identification server or the local machine is offline.

Single user account. Users can have two or more user accounts. For example, one for their local system and another for the organizational system. This is necessary to connect to a virtual private network (VPN). Because SSSD supports caching and offline authentication, remote users can connect to network resources simply by authenticating to their local machine and then SSSD maintains their network credentials.

⁠2.1.1. SSSD Configuration

SSSD is a local service, which connects a system to a larger, external identity service. This is done by configuring domains in the SSSD configuration file. Each domain represents a different, external data source. Domains always represent an identity provider, which supplies user information, and, optionally, define other providers for different kinds of operations, such as authentication or password changes.

Note

SSSD allows all user identities to be created and maintained in a separate, external identity source. For Windows integration, an AD domain is typically used to manage user accounts. Local system users do not need to be created or synced with user accounts in AD – SSSD uses those Windows identities and lets the Windows users access the local system and local services.

SSSD also defines which services on the system use SSSD for credentials caching and user accounts. These relate to foundational security services such as the Name Service Switch (NSS) and Pluggable Authentication Modules (PAM), which are then used by higher-level applications.

⁠

Example 2.1. Simple sssd.conf File

​[sssd]
​domains = WIN.EXAMPLE.COM
​services = nss, pam
​config_file_version = 2
​
​[domain/WINDOWS]
​id_provider = ad
​auth_provider = ad
​access_provider = ad

⁠2.1.2. Active Directory Domain Configuration

As shown in Example 2.1, “Simple sssd.conf File”, the SSSD configuration file has two major sections: the first configures the SSSD service ([sssd]), the second configures configures the identity domains ([domain/NAME]). There might be additional sections that configure system services which use SSSD as an identity cache; for example [nss] or [pam].

By default, only the identity provider (id_provider) and authorization provider (access_provider) options need to be configured. The id_provider option is used for the authentication (auth_provider) and password provider (chpass_provider) options if no other types or servers are set. Active Directory can be configured as any kind of provider using the ad value.

​[domain/AD_EXAMPLE]
​id_provider = ad
​auth_provider = ad
​access_provider = ad
​chpass_provider = ad
​
​ad_server = dc1.example.com
​# only needed if DNS discovery is not working
​ad_hostname = client.example.com
​# only needed if the host name of the client machine is incorrect
​ad_domain = example.com
​# only needed if AD domain is named differently than SSSD domain

The connection information is required to identify what Active Directory server to use. Past the basic configuration, the Active Directory identity provider can be configured specifically for the Active Directory environment and specific features, such as whether to use POSIX attributes or mapping for Windows SIDs on the local system, failover servers, and account information such as home directories.

All of the LDAP domain parameters are available to the Active Directory provider, as well as Active Directory-specific configuration parameters. The complete lists are available in the sssd-ldap and sssd-ad man pages.

There is a number of options in the generic LDAP provider configuration which can be used to configure an Active Directory provider. Using the ad value is a shortcut which automatically pulls in the parameters and values to configure a given provider for Active Directory. For example, the shortcut for an access provider is:

​access_provider = ad

Using generic LDAP parameters, that configuration expands to:

​access_provider = ldap
​ldap_access_order = expire
​ldap_account_expire_policy = ad

Those settings are all set implicitly by using the ad provider type.

⁠2.2. Environments for SSSD

SSSD, for the most part, replaces older identity management services which were used for Windows integration, including NIS and Winbind. SSSD is a local system service, so configuring it manually is only feasible for environments with a small number of systems.

There are tools which can prepare the initial configuration for the SSSD Active Directory domain; The realmd suite edits all underlying configuration files automatically. It simplifies editing the configuration but must be run separately on each system. An IdM server can configure a client to work with an Active Directory-IdM trust, but that requires a configured and functioning IdM Linux domain and an already-configured trust environment.

⁠2.3. How SSSD Integrates with an Active Directory Environment

⁠2.3.1. Active Directory Identities on the Local System

There are inherent structural differences between how Windows and Linux handle system users. The user schemas used in Active Directory and standard LDAPv3 directory services also differ significantly. When using an Active Directory identity provider with SSSD to manage system users, it is necessary to reconcile Active Directory-style users to the new SSSD users. There are two ways to achieve it:

ID mapping in SSSD can create a map between Active Directory security IDs (SIDs) and the generated UIDs on Linux. ID mapping is the simplest option for most environments because it requires no additional packages or configuration on Active Directory.

Unix services can manage POSIX attributes on Windows user and group entries. This requires more configuration and information within the Active Directory environment, but it provides more administrative control over the specific UID/GID values and other POSIX attributes.

Active Directory can replicate user entries and attributes from its local directory into a global catalog, which makes the information available to other domains within the forest. Performance-wise, the global catalog replication is the recommended way for SSSD to get information about users and groups, so that SSSD has access to all user data for all domains within the topology. As a result, SSSD can be used by applications which need to query the Active Directory global catalog for user or group information.

⁠2.3.1.1. About Security ID Mapping

⁠The Mechanism of ID Mapping

Linux/Unix systems use a local user ID number (UID) and group ID number (GID) to identify users on the system. These UID:GID numbers are a simple integer, for example 501:501.

Microsoft Windows and Active Directory use a different user ID structure to identify users, groups, and machines. Each ID, also called a Security Identifier (SID) is constructed of different segments that identify the security version, the issuing authority type, the machine, and the identity itself. The third through sixth blocks are the machine identifier:

S-1-5-21-3623811015-3361044348-30300820-1013

The last block is the relative identifier (RID) which identifies the specific entity:

S-1-5-21-3623811015-3361044348-30300820-1013

A range of possible ID numbers is always assigned to SSSD. As this is a local range, it is the same for every machine. By default, this range is divided into 10,000 sections with each section allocated 200,000 IDs.

When a new Active Directory domain is detected, the SID is hashed. Then, SSSD takes the modulus of the hash and the number of available sections to determine which ID section to assign to the Active Directory domain. This is a consistent way of assigning ID sections, so the same ID range is assigned to the same Active Directory domain on all client machines.

|    AD     |    AD     |         |
| domain 1  | domain 2  |   ...   |
|___________|___________|_________|
|  slice 1  |  slice 2  |   ...   |
min ID                        max ID

Note

As long as all clients use SSSD for the ID mapping, the mapping will be consistent. However, if some clients use different software, ensure that the same mapping algorithm is used or use explicit POSIX attributes.

⁠ID Mapping Parameters

The ID mapping is enabled by default in the AD provider. The ldap_id_mapping parameter enables the mapping while the ldap_schema parameter configures which LDAP attribute is mapped to which SSSD attribute.

Note

When ID mapping is enabled, the uidNumber and gidNumber attributes are ignored. This prevents any manually-assigned values. If any values must be manually assigned, then all values must be manually assigned, and ID mapping should be disabled.

⁠Mapping Users

When an Active Directory user attempts to log into a local system for the first time, an entry for that user is created in the SSSD cache. The remote user is set up much like a system user:

A system UID is created for the user based on his SID and the ID range for that domain.

A GID is created for the user, which is identical to the UID.

A shell attribute is used according to SSSD settings.

If the user belongs to any groups in the Active Directory domain, SSSD uses the SID to add the user to those groups on the Linux system.

⁠2.3.1.2. About SSSD and POSIX Attributes

Active Directory can be configured to create and store POSIX attributes such as uidNumber, gidNumber, unixHomeDirectory, and loginShell. As with all user attributes, these are originally stored in the local domain, but they can be replicated to the global catalog. Once they are in the global catalog, they are available to SSSD and any application which uses SSSD for its identity information.

Replicating the attributes is beneficial for performance but is not required. SSSD tries to detect if POSIX attributes are present and if not, SSSD connects to the individual domain controllers directly on the LDAP port instead of requiring POSIX attributes to be replicated to the global catalog.

Note

Note that it is possible to use ID mapping even when POSIX attributes are defined on the server. In such a case, SSSD ignores the POSIX attributes.

To use existing POSIX attributes for the best performance, ensure the following:

publish the POSIX attributes to Active Directory's global catalog,

disable ID mapping in SSSD by setting ldap_id_mapping = False in the Active Directory domain entry.

⁠2.3.1.3. Accessing a CIFS share with SSSD

SSSD is able to handle ID mapping between Windows security IDs (SIDs) and POSIX IDs. An SSSD client can therefore access and fully use a Common Internet File System (CIFS) share.

Note

In order to use a CIFS share for proper access control, it is necessary to translate the Windows SIDs to Linux POSIX UIDs and GIDs. Previously, only Winbind provided this functionality. Now, SSSD clients are no longer required to run Winbind alongside SSSD for this purpose.

The CIFS file-sharing protocol is widely deployed on Windows machines; SSSD enables seamless use of CIFS in environments with a trust between Identity Management and Active Directory as if it was a standard Linux file system. The SID-to-ID or SID-to-name algorithm that the SSSD client uses for system identity information can now also be used for a CIFS share. For example, accessing the Access Control Lists (ACLs) no longer requires to run Winbind in parallel to SSSD.

It is recommended to use SSSD for accessing a CIFS share instead of Winbind. IdM clients use SSSD by default to map AD users to UNIX users; using SSSD for the CIFS mapping avoids the possibility of inconsistent mapping, which can occur when IdM clients use Winbind. If a Linux client uses SSSD instead of Winbind for general AD user mappings in an environment with direct AD integration, where the client is directly joined into an AD domain, the client should also use SSSD as the mapping service for CIFS.

On the server side, SSSD also enables SID-to-POSIX ID mapping, providing access to a CIFS share to clients. However, Winbind on the server side still provides certain services that SSSD cannot, such as support for authentication using the NT LAN Manager (NTLM) or NetBIOS name lookup. This does not pose a problem for IdM clients because in IdM domains, Kerberos authentication and DNS name lookup are available for the same purposes.

Note

If you require NTLM authentication or NetBIOS name lookup, use Winbind for accessing a CIFS share instead of SSSD.

⁠Configuring Samba for Accessing a CIFS Share with SSSD

To configure Samba to provide access to a CIFS share using SSSD, modify the [global] section of the /etc/samba/smb.conf file.

The following example of smb.conf is intended for environments with direct AD integration. The system keytab setting specifies that the keytab required for Kerberos access to the CIFS share is the same as the keytab that SSSD uses:

[global]
	security = ads
	workgroup = ADSHORTNAME
	realm = ADREALM
	kerberos method = system keytab

An example of smb.conf for environments with an AD trust, where the most-widely used solution is to specify a dedicated keytab for Samba:

[global]
	security = ads
	workgroup = IPA
	realm = IPA.TEST
	dedicated keytab file = FILE:/etc/samba/samba.keytab
	kerberos method = dedicated keytab

⁠Packages Required for Accessing a CIFS Share with SSSD

For a client to use SSSD to access a CIFS share, the following two packages are required.

sssd-client

The sssd-client package is installed automatically as an SSSD dependency. The package provides the SSSD plug-in for the cifs-utils package. This plug-in contains the libsss_nss_idmap.so library.

sssd-libwbclient

The sssd-libwbclient package is not installed automatically. To install it, run the following command:

# yum install sssd-libwbclient

The package provides the libwbclient.so.0.11-64 library, which is the SSSD alternative to the library provided by the libwbclient package used by the Winbind service.

After installing sssd-libwbclient, you can verify that your system uses the SSSD implementation with the alternatives tool. The tool displays the currently used alternative:

# alternatives --list | grep -E cifs\|libwbclient
cifs-idmap-plugin       auto     /usr/lib64/cifs-utils/cifs_idmap_sss.so
libwbclient.so.0.11-64 auto /usr/lib64/sssd/modules/libwbclient.so.0.11.0

⁠Switching Between SSSD and Winbind

To find out if you are currently using SSSD or Winbind for accessing a CIFS share, use the alternatives tool.

# alternatives --display cifs-idmap-plugin
cifs-idmap-plugin - status is auto.
 link currently points to /usr/lib/cifs-utils/cifs_idmap_sss.so
/usr/lib/cifs-utils/cifs_idmap_sss.so - priority 20
/usr/lib/cifs-utils/idmapwb.so - priority 10
Current `best' version is /usr/lib/cifs-utils/cifs_idmap_sss.so.

If the SSSD plug-in (cifs_idmap_sss.so) is installed, it has a higher priority than the Winbind plug-in (idmapwb.so) by default.

To switch to a different plug-in, run the alternatives --set cifs-idmap-plugin command and provide the path to the plug-in. For example, to switch to Winbind:

# alternatives --set cifs-idmap-plugin /usr/lib/cifs-utils/idmapwb.so

Important

It is recommended that IdM clients always use the SSSD plug-in.

If you want to switch to the Winbind plug-in, make sure that Winbind is running on the system. Similarly, if you want to switch to SSSD, make sure that SSSD is running.

⁠2.3.2. Active Directory Users and Range Retrieval Searches

Microsoft Active Directory has an attribute, MaxValRange, which sets a limit on how many values for a multi-valued attribute is returned. This is the range retrieval search extension. The extension runs multiple mini-searches, each returning a subset of the results within a given range, until all matches are returned.

For example, when doing a search for the member attribute, each entry could have multiple values, and there can be multiple entries with that attribute. If there are 1500 matching results or more, then MaxValRange limits how many are displayed at once. The given attribute has an additional flag set, showing which range in the set the result is in:

attribute:range=low-high:value

For example, to display results 100 to 500 in a search, use:

member:range=99-499: cn=John Smith...

SSSD supports range retrievals with Active Directory providers as part of user and group management, without any additional configuration.

When the search base in SSSD specifies a custom filter or scope, some LDAP provider attributes which are available to configure searches (such as ldap_user_search_base) cannot be used with range retrievals. When configuring search bases in the Active Directory provider domain, be aware what searches may trigger a range retrieval.

⁠2.3.3. Linux Clients and Active Directory DNS Sites

SSSD connects a local Linux system to a larger Active Directory environment. This requires SSSD to have an awareness of possible configurations within the Active Directory forest and work with them so that the Linux client is cleanly integrated.

Active Directory forests can be very large, with numerous different domain controllers, domains and subdomains, and physical sites. To increase client performance, Active Directory uses a special kind of DNS record to identify domain controllers within the same domain but at different physical locations. Clients connect to the closest domain controller.

Active Directory extends normal DNS SRV records to identify a specific physical location or site for its domain controllers. Clients such as SSSD can determine which domain controllers to use based on their own site configuration. SSSD can determine which domain controller to use by querying the Active Directory domain first for its site configuration, and then for the domain controller DNS records:

SSSD attempts to connect to the Active Directory domain and looks up any available domain controller through normal DNS discovery.

SSSD sends an LDAP search to a domain controller which looks for the DNS domain, domain SID, and version:

(&(&(DnsDomain=ad.domain)(DomainSid=S-1-5-21-1111-2222-3333))(NtVer=0x01000016))

This is used to retrieve the information about the client's site if one is configured.

If a site is configured for the client, then the reply contains extended DNS SRV records for the primary server, containing the site name (site-name._sites.):

_tcp._ldap.site-name._sites.domain.name

The backup server record is also sent, as a standard SRV record:

_tcp._ldap.domain.name

If no site is configured, then a standard SRV record is sent for all primary and backup servers.

SSSD retrieves a list of primary and fallback servers.

⁠2.4. Configuring an Active Directory Domain with ID Mapping

When configuring an Active Directory domain, the simplest configuration is to use the ad value for all providers (identity, access, password). Also, load the native Active Directory schema for user and group entries, rather than using the default RFC 2307.

Other configuration is available in the general LDAP provider configuration ⁠[1] and Active Directory-specific configuration ⁠[2]. This includes setting of LDAP filters for a specific user or group subtree, filters for authentication, and values for some account settings. Some additional configuration is covered in Section 2.6, “Additional Configuration Examples”.

Note

Note that the following procedure covers the manual configuration of an Active Directory domain. By using realmd, steps 3 to 7 below can be done automatically by using the realm join command. See Chapter 3, Using realmd to Connect to an Active Directory Domain for details.

Make sure that both the Active Directory and Linux systems have a properly configured environment.

Name resolution must be properly configured, particularly if service discovery is used with SSSD.

The clocks on both systems must be in sync for Kerberos to work properly.

On the Linux client, add the Active Directory domain to the client's DNS configuration so that it can resolve the domain's SRV records.

search adserver.example.com
nameserver 198.68.72.1

Set up the Linux system as an Active Directory client and enroll it within the Active Directory domain. This is done by configuring the Kerberos and Samba services on the Linux system.

Set up Kerberos to use the Active Directory Kerberos realm.

Open the Kerberos client configuration file.

[root@server ~]# vim /etc/krb5.conf

Configure the [logging] and [libdefaults] sections so that they connect to the Active Directory realm.

[logging]
 default = FILE:/var/log/krb5libs.log

[libdefaults]
 default_realm = EXAMPLE.COM
 dns_lookup_realm = true
 dns_lookup_kdc = true
 ticket_lifetime = 24h
 renew_lifetime = 7d
 rdns = false
 forwardable = yes

If auto-discovery is not used with SSSD, then also configure the [realms] and [domain_realm] sections to explicitly define the Active Directory server.

Configure the Samba server to connect to the Active directory server.

Open the Samba configuration file.

[root@server ~]# vim /etc/samba/smb.conf

Set the Active Directory domain information in the [global] section.

[global]
   workgroup = EXAMPLE
   client signing = yes
   client use spnego = yes
   kerberos method = secrets and keytab
   log file = /var/log/samba/%m.log
   password server = AD.EXAMPLE.COM
   realm = EXAMPLE.COM
   security = ads

Add the Linux machine to the Active Directory domain.

Obtain Kerberos credentials for a Windows administrative user.

[root@server ~]# kinit Administrator

Add the machine to the domain using the net command.

[root@server ~]# net ads join -k
Joined 'server' to dns domain 'example.com'

This creates a new keytab file, /etc/krb5.keytab.

List the keys for the system and check that the host principal is there.

[root@server ~]# klist -k

If necessary, install the oddjob-mkhomedir package to allow SSSD to create home directories for Active Directory users.

[root@server ~]# yum install oddjob-mkhomedir

Use authconfig to enable SSSD for system authentication. Use the --enablemkhomedir to enable SSSD to create home directories.

[root@server ~]# authconfig --update --enablesssd --enablesssdauth --enablemkhomedir

Open the SSSD configuration file.

[root@rhel-server ~]# vim /etc/sssd/sssd.conf

Configure the Active Directory domain.

In the [sssd] section, add the Active Directory domain to the list of active domains. This is the name of the domain entry that is set in [domain/NAME] in the SSSD configuration file.

Also, add pac to the list of services; this enables SSSD to set and use MS-PAC information on tickets used to communicate with the Active Directory domain.

[sssd]
config_file_version = 2
domains = ad.example.com
services = nss, pam, pac

Create a new domain section at the bottom of the file for the Active Directory domain. This section has the format domain/NAME, such as domain/ad.example.com. For each provider, set the value to ad, and give the connection information for the specific Active Directory instance to connect to.

[domain/ad.example.com]
id_provider = ad
auth_provider = ad
chpass_provider = ad
access_provider = ad

Enable credentials caching; this allows users to log into the local system using cached information, even if the Active Directory domain is unavailable.

cache_credentials = true

Restart the SSH service to load the new PAM configuration.

[root@server ~]# systemctl restart sshd.service

Restart SSSD after changing the configuration file.

[root@rhel-server ~]# systemctl restart sssd.service

⁠2.5. Configuring an Active Directory Domain with POSIX Attributes

Warning

The Identity Management for UNIX extension used in the following section is now deprecated. As explained on the Microsoft Developer Network, an attempt to upgrade a system running Identity Management for UNIX might fail with a warning suggesting you to remove the extension. No replacement to the extension is currently available.

It is recommended to avoid using Identity Management for UNIX and instead set POSIX information on the IdM server using the ID Views mechanism, described in Chapter 8, ID Views and Migrating Existing Environments to Trust.

To use Active Directory-defined POSIX attributes in SSSD, it is recommended to replicate them to the global catalog for better performance. Once they are in the global catalog, they are available to SSSD and any application which uses SSSD for its identity information. Additionally, if the POSIX attributes are used, ID mapping has to be disabled in SSSD, so the POSIX attributes are used from Active Directory rather than creating new settings locally.

Other configuration is available in the general LDAP provider configuration ⁠[3] and Active Directory-specific configuration ⁠[4]. This includes setting of LDAP filters for a specific user or group subtree, filters for authentication, and values for some account settings. Some additional configuration is covered in Section 2.6, “Additional Configuration Examples”.

Note

Note that the following procedure covers the manual configuration of an Active Directory domain. By using realmd, steps 4 to 11 below can be done automatically by using the realm join command. See Chapter 3, Using realmd to Connect to an Active Directory Domain for details.

Make sure that both the Active Directory and Linux systems have a properly configured environment.

Name resolution must be properly configured, particularly if service discovery is used with SSSD.

The clocks on both systems must be in sync for Kerberos to work properly.

In the Active Directory domain, set the POSIX attributes to be replicated to the global catalog.

Install Identity Management for UNIX Components on all primary and child domain controllers. This allows the POSIX attributes and related schema to be available to user accounts. These attributes are available in the UNIX Attributes tab in the entry's Properties menu.

Install the Active Directory Schema Snap-in to add attributes to be replicated to the global catalog.

For the relevant POSIX attributes (uidNumber, gidNumber, unixHomeDirectory, and loginShell), open the Properties menu, select the Replicate this attribute to the Global Catalog checkbox, and then click OK.

On the Linux client, add the Active Directory domain to the client's DNS configuration so that it can resolve the domain's SRV records.

search adserver.example.com
nameserver 198.68.72.1

Set up the Linux system as an Active Directory client and enroll it within the Active Directory domain. This is done by configuring the Kerberos and Samba services on the Linux system.

Set up Kerberos to use the Active Directory Kerberos realm.

Open the Kerberos client configuration file.

[root@server ~]# vim /etc/krb5.conf

Configure the [logging] and [libdefaults] sections so that they connect to the Active Directory realm.

[logging]
 default = FILE:/var/log/krb5libs.log

[libdefaults]
 default_realm = EXAMPLE.COM
 dns_lookup_realm = true
 dns_lookup_kdc = true
 ticket_lifetime = 24h
 renew_lifetime = 7d
 rdns = false
 forwardable = yes

If auto-discovery is not used with SSSD, then also configure the [realms] and [domain_realm] sections to explicitly define the Active Directory server.

Configure the Samba server to connect to the Active directory server.

Open the Samba configuration file.

[root@server ~]# vim /etc/samba/smb.conf

Set the Active Directory domain information in the [global] section.

[global]
   workgroup = EXAMPLE
   client signing = yes
   client use spnego = yes
   kerberos method = secrets and keytab
   log file = /var/log/samba/%m.log
   password server = AD.EXAMPLE.COM
   realm = EXAMPLE.COM
   security = ads

Add the Linux machine to the Active Directory domain.

Obtain Kerberos credentials for a Windows administrative user.

[root@server ~]# kinit Administrator

Add the machine to the domain using the net command.

[root@server ~]# net ads join -k
Joined 'server' to dns domain 'example.com'

This creates a new keytab file, /etc/krb5.keytab.

List the keys for the system and check that the host principal is there.

[root@server ~]# klist -ke

Test that users can search the global catalog, using an ldapsearch.

[root@server ~]# ldapsearch -H ldap://server.ad.example.com:3268 -Y GSSAPI -N -b "dc=ad,dc=example,dc=com" "(&(objectClass=user)(sAMAccountName=aduser))"

Install the sssd-ad package.

[root@server ~]# yum install sssd-ad

Start the SSSD service.

[root@server ~]# systemctl start sssd.service

Open the SSSD configuration file.

[root@rhel-server ~]# vim /etc/sssd/sssd.conf

Configure the Active Directory domain.

In the [sssd] section, add the Active Directory domain to the list of active domains. This is the name of the domain entry that is set in [domain/NAME] in the SSSD configuration file.

Create a new domain section at the bottom of the file for the Active Directory domain. This section has the format domain/NAME, such as domain/ad.example.com. For each provider, set the value to ad, and give the connection information for the specific Active Directory instance to connect to.

[domain/ad.example.com]
id_provider = ad
auth_provider = ad
chpass_provider = ad
access_provider = ad

Disable ID mapping. This tells SSSD to search the global catalog for POSIX attributes, rather than creating UID:GID numbers based on the Windows SID.

# disabling ID mapping
ldap_id_mapping = False

If home directory and a login shell are set in the user accounts, then comment out these lines to configure SSSD to use the POSIX attributes rather then creating the attributes based on the template.

# Comment out if the users have the shell and home dir set on the AD side
#default_shell = /bin/bash
#fallback_homedir = /home/%d/%u

Set whether to use short names or fully-qualified user names for Active Directory users. In complex topologies, using fully-qualified names may be necessary for disambiguation.

# Comment out if you prefer to user shortnames.
use_fully_qualified_names = True

Enable credentials caching; this allows users to log into the local system using cached information, even if the Active Directory domain is unavailable.

cache_credentials = true

Set the file permissions and owner for the SSSD configuration file.

[root@server ~]# chown root:root /etc/sssd/sssd.conf
[root@server ~]# chmod 0600 /etc/sssd/sssd.conf
[root@server ~]# restorecon /etc/sssd/sssd.conf

If necessary, install the oddjob-mkhomedir package to allow SSSD to create home directories for Active Directory users.

[root@server ~]# yum install oddjob-mkhomedir

Use authconfig to enable SSSD for system authentication. Use the --enablemkhomedir to enable SSSD to create home directories.

[root@server ~]# authconfig --update --enablesssd --enablesssdauth --enablemkhomedir

Restart the SSH service to load the new PAM configuration.

[root@server ~]# systemctl restart sshd.service

Restart SSSD after changing the configuration file.

[root@rhel-server ~]# systemctl restart sssd.service

Using authconfig automatically configured the NSS and PAM configuration files to use SSSD as their identity source.

For example, the nsswitch.conf file has SSSD (sss) added as a source for user, group, and service information.

passwd:         files sss
group:          files sss
...
services:       files sss
...
netgroup:       files sss

The different pam.d files add a line for the pam_sss.so module beneath every pam_unix.so line in the /etc/pam.d/system-auth and /etc/pam.d/password-auth files.

auth         sufficient    pam_sss.so use_first_pass
...
account      [default=bad success=ok user_unknown=ignore] pam_sss.so
...
password     sufficient    pam_sss.so use_authtok
...
session      optional      pam_mkhomedir.so
session      optional      pam_sss.so

⁠2.6. Additional Configuration Examples

⁠2.6.1. Account Settings

With Linux users, certain system preferences are set by default for new users. These system preferences either may not be set in the Windows user accounts or may be set to something incompatible with a Linux system. There are two such areas: the user home directory and default user shell.

⁠2.6.1.1. Setting a User Home Directory

Red Hat Enterprise Linux has a PAM library (pam_oddjob_mkhomedir.so) which automatically creates user directories when a user first logs in. This includes Active Directory users, when they first log into a Linux system.

With SSSD, the format of the user directory is retrieved from the identity provider. If the identity provider has a home directory format that is different than the format for the Linux system or if it does not supply a value, then SSSD can be configured to set the home directory attribute value using a template specified in its configuration. The template can be set globally in the NSS service section or per domain. There are two possible parameters:

fallback_homedir, which supplies a template if the identity provider does not supply one,

override_homedir, which sets a template to use regardless of what information is set in the identity provider.

Both can use variables within the template, such a %u for the login name and %d for the domain name:

[nss]
fallback_homedir = /home/%u
...
[domain/AD_EXAMPLE]
id_provider = ad
auth_provider = ad
...
override_homedir = /home/%d/%u

⁠2.6.1.2. Setting a User Shell

By default, SSSD attempts to retrieve information about user shells from the identity provider. In both Active Directory and LDAPv3 schema, this is defined in the loginShell attribute. However, this is an optional attribute, so it may not be defined for every user. For Active Directory users, the defined login shell may not be allowed on the Linux system.

There are a number of ways to handle shells in the SSSD configuration:

Set a fallback value if no shells are supplied using shell_fallback,

Set lists of allowed or blacklisted shells using allowed_shells and vetoed_shells,

Set a default value using default_shell,

Set a value to use, even if another value is given in the identity provider, using override_shell.

Note

The allowed_shells, vetoed_shells, and shell_fallback parameters can only be set as global settings, not per domain. However, these parameters do not affect local system users, only external users retrieved through SSSD identity providers. Using a general setting, such as /bin/rbash, is good for most external users.

Default values can be set per domain while some values, such as the white and blacklists for shells, must be set globally in the NSS service configuration. For example:

[nss]
shell_fallback = /bin/sh
allowed_shells =  /bin/sh,/bin/rbash,/bin/bash
vetoed_shells =  /bin/ksh
...

[domain/AD_EXAMPLE]
id_provider = ad
auth_provider = ad
...
default_shell = /bin/rbash

⁠2.6.2. Enabling Dynamic DNS Updates (Active Directory Only)

Active Directory allows its clients to refresh their DNS records automatically. Active Directory also actively maintains DNS records to make sure they are updated, including timing out (aging) and removing (scavenging) inactive records. Note that DNS scavenging is not enabled by default on the AD side.

SSSD allows the Linux system to imitate a Windows client by refreshing its DNS record, which also prevents its record from being marked inactive and removed from the DNS record. When dynamic DNS updates are enabled, then the client's DNS record is refreshed at several times:

When the identity provider comes online (always),

When the Linux system reboots (always),

At a specified interval (optional configuration).

Note

This can be set to the same interval as the DHCP lease, which means that the Linux client is renewed after the lease is renewed.

DNS updates are sent to the Active Directory server using Kerberos/GSSAPI for DNS (GSS-TSIG); this means that only secure connections need to be enabled.

The dynamic DNS configuration is set for each domain. For example:

[domain/ad.example.com]
id_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

⁠

Table 2.1. Options for Dynamic DNS Updates

Option | Description | Format
dyndns_update | Sets whether to update the DNS server dynamically with the client IP address. This requires secure updates and must be set to true for any other dynamic DNS setting to be enabled. The default value is true. | Boolean
dyndns_ttl | Sets a time-to-live for the client's DNS record. The default value is 3600 seconds. | Integer
dyndns_refresh_interval | Sets a frequency to perform an automatic DNS update, in addition to the update when the provider comes online. The default value is 86400 seconds (24 hours). | Integer
dyndns_update_ptr | Sets whether to update the PTR record when the client updates its DNS records. The default value is true. | Boolean

⁠2.6.3. Using a Filter with Access Controls

The Active Directory access provider is used as the source for authorization information. The following configuration parameter option is actually a combination of several other generic LDAP parameters:

access_provider = ad

This is the same as setting the following LDAP parameters:

access_provider = ldap
ldap_access_order = expire
ldap_account_expire_policy = ad

There is an additional option to identify which user accounts to grant access, based on an LDAP filter. First, accounts must match the filter, and then they must pass the expiration check, which is implicit in the access_provider = ad setting. For example, the following sets that only users which belong to the administrators group and have a unixHomeDirectory attribute match the access control check:

access_provider = ad
ad_access_filter = (&(memberOf=cn=admins,ou=groups,dc=example,dc=com)(unixHomeDirectory=*))

⁠2.7. Group Policy Object Access Control

Group Policy is a Microsoft Windows feature that enables administrators to centrally manage policies for users and computers in AD environments. A group policy object (GPO) is a collection of policy settings, such as name and value pairs, that are stored on a domain controller (DC) and can be applied to policy targets, such as computers and users.

GPO policy settings related to Windows logon rights are commonly used to manage computer-based access control in AD environments. SSSD can retrieve GPOs applicable to host systems and AD users; based on the retrieved GPO configuration, it determines if a user is allowed to log on to a particular host. Therefore, with the GPO-based access control provided by SSSD, the administrator can define login policies that are honored by both Red Hat Enterprise Linux and Windows clients centrally on the AD DC.

Note

SSSD only allows using GPO for the computer-based access control. Other GPO-related access control options are currently not supported.

Warning

Note that SSSD only handles rules that apply to a whole site, domain, or AD organizational unit (OU). If you want to apply the SSSD-supported GPO-based access control to a specific machine, you can create a new OU in the AD domain, move the machine to the OU, and then link the GPO to this OU.

⁠2.7.1. Configuring GPO-Based Access Control

GPO-based access control can be configured in the /etc/sssd/sssd.conf file. The ad_gpo_access_control option specifies the mode in which the GPO-based access control runs. It can be set to the following values:

ad_gpo_access_control = permissive

The permissive value specifies that GPO-based access control is evaluated but not enforced; a syslog message is recorded every time access would be denied. This is the default setting.

ad_gpo_access_control = enforcing

The enforcing value specifies that GPO-based access control is evaluated and enforced.

ad_gpo_access_control = disabled

The disabled value specifies that GPO-based access control is neither evaluated nor enforced.

Important

Before starting to use the GPO-based access control and setting ad_gpo_access_control to enforcing mode, it is recommended to ensure that ad_gpo_access_control is set to permissive mode and examine the logs. By reviewing the syslog messages, you can test and adjust the current GPO settings as necessary before finally setting the enforcing mode.

The following parameters related to the GPO-based access control can also be specified in the sssd.conf file:

The ad_gpo_map_* options and the ad_gpo_default_right option configure which PAM services are mapped to specific Windows logon rights.

The ad_gpo_cache_timeout option specifies the interval during which subsequent access control requests can reuse the files stored in the cache, instead of retrieving them from the DC anew.

For a detailed list of available GPO parameters as well as their descriptions and default values, see the sssd-ad(5) man page.

[1] See the sssd-ldap man page.

[2] See the sssd-ad man page.

[3] See the sssd-ldap man page.

[4] See the sssd-ad man page.

⁠Chapter 3. Using realmd to Connect to an Active Directory Domain

The realmd system provides a clear and simple way to discover and join identity domains. It does not connect to the domain itself but configures underlying Linux system services, such as SSSD or Winbind, to connect to the domain.

⁠3.1. About realmd

Chapter 2, Using Active Directory as an Identity Provider for SSSD describes how to use the System Security Services Daemon on a local system and Active Directory as a back-end identity provider. There are a number of different configuration parameters for each possible identity provider and for SSSD itself. All domain information must be available in advance and then properly formatted in the SSSD configuration for SSSD to integrate the local system with Active Directory. That can be a complex task and realmd simplifies that configuration; it can run a service discovery to identify available Active Directory and Red Hat Enterprise Linux Identity Management domains, and then join the domain and manage user access. SSSD as an underlying service supports multiple domains and realmd can therefore discover and support multiple domains as well.

⁠3.1.1. Types of Domains

The realmd system can discover the following types of identity domains:

Microsoft Active Directory

Red Hat Enterprise Linux Identity Management

You can use realmd to join an Active Directory or Identity Management domain; realmd properly configures the required system configuration files and services.

⁠3.1.2. Supported Domain Clients

The realmd system automatically configures the required client services that are used to connect to the given identity realm. There are two supported clients:

SSSD for both Red Hat Enterprise Linux Identity Management and Microsoft Active Directory

Winbind for Microsoft Active Directory

⁠3.2. realmd Commands

The realmd system has two major task areas: managing system enrollment in a domain and setting which domain users are allowed to access the local system resources. The central utility in realmd is called realm – this utility mostly specifies an action and the realm for which to perform that action.

realm command arguments

For example:

realm join ad.example.com
realm permit username

⁠

Table 3.1. realmd Commands

Command | Description
Realm Commands |
discover | Run a discovery scan for domains on the network.
join | Add the system to the specified domain.
leave | Removes the system from the specified domain.
list | Lists all configured realms for the system or all discovered and configured realms.
Login Commands |
permit | Enables access for specified users or for all users within a configured realm to access the local system.
deny | Restricts access for specified users or for all users within a configured realm to access the local system.

⁠3.3. Discovering and Joining Active Directory Domains

⁠3.3.1. Discovering Domains

The discovery process is handled by the discover command. It returns complete realm configuration and a list of packages that must be installed for the system to be enrolled in the realm.

Note

Note that the realm discover command requires NetworkManager to be running; in particular, it depends on the D-Bus interface of NetworkManager. If your system does not use NetworkManager, specify the realm name in the command, for example, realm discover ad.example.com.

[root@server ~]# realm discover
ad.example.com
  type: active-directory
  realm-name: AD.EXAMPLE.COM
  domain-name: ad.example.com
  configured: kerberos-member
  server-software: active-directory
  client-software: sssd
  required-package: oddjob
  required-package: oddjob-mkhomedir
  required-package: sssd
  login-formats: %D\%U
  login-policy: allow-realm-logins

realmd can discover both Active Directory and Identity Management domains. If both are in the environment, then it is possible to limit the discovery results to a specific type of server:

[root@server ~]# realm discover --server-software=active-directory

It is also possible to run a discovery for a specific domain, using the domain controller's host name or IP address:

[root@server ~]# realm discover ad.example.com

⁠3.3.2. Joining an Active Directory Domain

The join command only requires the realm name:

[root@server ~]# realm join ad.example.com
See: journalctl REALMD_OPERATION=r1088239.6316
realm: Joined ad.example.com domain

This performs the join as the default Windows administrator and, in most environments, will prompt for the password. The command can connect to the Active Directory environment as a different user, by using the -U option:

[root@server ~]# realm join ad.example.com -U AD.EXAMPLE.COM\jsmith

If Kerberos is properly configured on a Linux system, the join operation can also be performed with a Kerberos ticket for authentication. The realmd system can use the -U option to select, which principal to use, or can use the default credential cache or the KRB5_CCACHE variable.

[root@server ~]# kinit jsmith
[root@server ~]# realm join ad.example.com -U jsmith

During joining, the realmd system checks for the DNS SRV record:

_ldap._tcp.domain.example.com. // for IdM records
_ldap._tcp.dc._msdcs.domain.example.com. // for Active Directory records

The DNS SRV record is created by default when Active Directory is configured, which enables it to be found by the service discovery. realmd uses the domain assigned through DHCP to discover any LDAP servers on the network.

The actual join command configures both the local system services and the entries in the Active Directory domain by performing these steps:

Runs a discovery scan for the specified realm.

Installs any required packages to join the system to the domain. This includes SSSD and the PAM home directory job packages. Note that the automatic installation of packages requires the PackageKit suite to be running.

Note

If PackageKit is disabled, the system prompts you for the missing packages. You will be required to install them manually using the yum utility.

Attempts to join the Active Directory domain as the administrator unless a different user is specified with the -U option. The command first attempts to connect without credentials, but it prompts for a password if required.

Note

For Active Directory, the administrator account is called Administrator, for IdM, it is called admin.

Once it connects to the domain, it creates an account entry for the system in the directory.

Creates the /etc/krb5.keytab host keytab file.

Configures the domain in SSSD and restarts the service.

Enables domain users for the system services in PAM configuration and the /etc/nsswitch.conf file.

One of the attributes returned in the discovery search is login-policy, which shows if domain users are allowed to log in as soon as the join is complete. If logins are not allowed by default, then they can be manually allowed by the permit command. For details, see Section 3.4, “Managing User Logins from Active Directory”.

⁠3.3.3. Removing a System from the Active Directory Domain

If a system should ever be removed from an Active Directory domain, this is done with the leave command. This removes the domain configuration from SSSD and the local system:

[root@server ~]# realm leave ad.example.com

This command performs the removal as the default administrator account (admin in Identity Management; Administrator in Active Directory). The script may prompt for a password or, depending on how the system was joined to the domain, it may require performing the operation as a different user. A user can be specified with the -U option.

[root@server ~]# realm leave ad.example.com -U AD.EXAMPLE.COM\jsmith

Note

When a client leaves a domain, the computer object is not deleted; the local client is only deconfigured. If you want to delete it, run the command with the --remove option specified.

⁠3.3.4. Listing Domains

The list command lists every configured domain for the system, and the full details and default configuration for that domain. This is the same information as is returned for the realm discovery, only for a domain that is already in the system configuration.

[root@server ~]# realm list
linux.example.com
  type: kerberos
  realm-name: LINUX.EXAMPLE.COM
  domain-name: linux.example.com
  configured: kerberos-member
  server-software: ipa
  client-software: sssd
  required-package: ipa-client
  required-package: oddjob
  required-package: oddjob-mkhomedir
  required-package: sssd
  login-formats: %U
  login-policy: allow-realm-logins

The --all option includes discovered domains (Active Directory, Identity Management, and Kerberos) as well as configured domains. The --name-only limits the results to the domain name, without the configuration details.

[root@server ~]# realm list --all --name-only
linux.example.com
example.com
ad.example.com

⁠3.4. Managing User Logins from Active Directory

By default, login policies for domain users are defined in the domain itself. This can be overridden in the realm configuration so that client-side access control is used – that is, the local policies only define who is allowed to login. If a machine is joined to multiple domains, only one of them can apply domain access control; the other domains have to employ client-side access control.

The realmd command allows you to configure basic allow or deny access rules for users from a specific domain. You can specify these permissions only if you are applying the client-side access control.

Note

These access rules either allow all access to the system or no access. Finer-grained access rules must be set on a specific system resource or in the domain.

There are two commands that set access rules:

The realm deny command simply prevents access to all users within the realm. Use this command with the --all option.

The realm permit command, on the other hand, grants access to either all users by using --all, to only specified users, or it can withdraw permission from specified users by using -x.

For example, the following command adds an allow rule for every user within the ad.example.com domain, and then withdraws login permission from the jsmith user.

[root@server ~]# realm permit ad.example.com --all
[root@server ~]# realm permit ad.example.com -x AD.EXAMPLE.COM\jsmith

Important

It is recommended that you use permit to allow access instead of permit -x to deny it. It is much safer to allow access to specifically selected users or groups than to deny access to some, thus enabling it to everyone else.

Because SSSD is currently not capable to inform realmd about available subdomains and user logins must contain the domain name, allowing access works for users in primary domains but not for users in trusted domains.

⁠3.5. Adding Default User Configuration

The /etc/realmd.conf configuration file can add custom configuration for global logged-in user settings. Some POSIX attributes may not be set in the Windows user accounts or may be set to something different than other users on the local system. There are two such areas:

The user home directory

A default user shell

User settings are defined in the [users] section of the /etc/realmd.conf file.

The default-shell parameter can be any supported system shell.

The default-home parameter sets a template to use to create a home directory if none is defined in the realm. A common format is /home/%d/%u, where %d is the domain name and %u is the user name.

For example:

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

⁠3.6. Additional Configuration for the Active Directory Domain Entry

Each individual domain can have custom settings in the realm entry of the /etc/realmd.conf configuration file. Each realm can have its own configuration section:

[realm.name]
attribute = value
attribute = value

Each attribute can be set by manually adding them to the configuration file or by passing them as arguments when the system is joined to the realm.

⁠

Table 3.2. Realm Configuration Options

Parameter | Description
computer-ou | Sets the directory location for adding computer accounts to the domain. This can be the full DN or an RDN, relative to the root entry. The subtree must already exist.
user-principal | Sets whether to create a host principal for the system.
automatic-id-mapping | Sets whether to enable dynamic ID mapping or disable the mapping and use POSIX attributes configured in Active Directory.
manage-system | Sets whether certain login policies are set in the local system or by Active Directory.

The following example disables ID mapping, enables the host principal, and adds the system to the specified subtree.

[domain.example.com]
computer-ou = OU=Linux Computers,DC=domain,DC=example,DC=com
user-principal = yes
automatic-id-mapping = no
manage-system = no

These same parameters can be passed when the system is joined to the domain:

[root@server ~]# realm join --computer-ou="ou=Linux Computers," --automatic-id-mapping=no --user-principal=yes

⁠Chapter 4. Using Samba, Kerberos, and Winbind

The Samba standard Windows interoperability suite of utilities allows Linux systems to join an Active Directory environment by making them appear to be Windows clients. As a means of systems integration, Samba allows a Linux client to join an Active Directory Kerberos realm and to use Active Directory as its identity store.

Winbind is a component of the Samba suite to provide unified logon. It uses a UNIX implementation of Microsoft RPC calls, Pluggable Authentication Modules (PAMs), and the Name Service Switch (NSS) to allow Windows domain users to appear and operate as UNIX users on a UNIX system.

⁠4.1. About Samba and Active Directory Authentication

While the core functionality of Samba is to perform client-server networking for file and printer sharing and associated operations, this chapter only focuses on one aspect of using Samba to interact with Windows: allowing Linux clients to authenticate by using Active Directory.

⁠4.1.1. Samba, Kerberos, and Active Directory Domains

Active Directory is the domain controller for a number of services in Windows environments, including Kerberos realms and DNS domains. Samba supports the full range of protocols used in Active Directory, including Kerberos, DNS, NTLMSSP, or DCE/RPC. Intergration with Active Directory means configuring a security environment that uses Kerberos as the native security context in Active Directory.

Several different system services should be configured on the Linux client to use Active Directory as a domain controller:

Samba – for users and authentication

DNS – to set the Active Directory server as the name server

Kerberos – to use the Active Directory KDC

PAM – to use Winbind

NSS – to use Winbind

⁠4.1.1.1. Samba

There are several different ways how a Samba server can join an Active Directory domain. In SMB/CIFS networking, there are two types of security: user-level and share level. Samba provides four ways to use user-level security. Collectively, we call them the security modes. Only two of them are important for Windows integration:

ads configures the local Samba server as a domain member within an Active Directory domain. It also enables support for the internal usage of LDAP queries and Kerberos authentication. This is the preferred security mode.

domain configures the Samba server as a domain member server within an Active Directory domain by using the DCE/RPC protocol.

The necessary configuration is located in the the [global] section of /etc/samba/smb.conf. The essential settings include the security type (security); the name of the Active Directory Kerberos realm (realm), which is resolved by DNS discovery; and the Samba workgroup (workgroup):

#================= Global Settings ====================

[global]
    workgroup = ADEXAMPLE
    security = ads
    realm = ADEXAMPLE.COM

...

⁠4.1.1.2. Kerberos

Kerberos must be configured to use the Active Directory server as its KDC. It allows users to use Kerberos tickets for authentication. Additionally, Samba must be configured to use the Active Directory Kerberos realm, which allows Winbind to manage the Kerberos principals.

The Active Directory realm should be set as the default domain in the [libdefaults] section of the /etc/krb5.conf file, and then as a KDC in the [realms] section. The [domain_realm] section should define the Active Directory domain.

For seamless Kerberos experience, ensure the Winbind Kerberos locator plug-in is installed from the samba-winbind-krb5-locator package. It ensures that Winbind and all its users and the Kerberos library and all its users use the same KDC all the time.

[libdefaults]
...

  default_realm = ADEXAMPLE.COM

[realms]
  ADEXAMPLE.COM = {
    kdc = kdc.adexample.com
}

[domain_realm]
 adexample.com = ADEXAMPLE.COM
  .adexample.com = ADEXAMPLE.COM

⁠4.1.1.3. DNS

The local DNS service must be configured to use Active Directory as its domain controller. DNS is critical for proper resolution of host names and domains for Kerberos. While many systems have proper DNS settings so that the Samba-Active Directory integration could work well without configuring Active Directory as a name server, using Active Directory as a name server avoids any potential resolution problems. The domain should also be added as a search directive, so that the Active Directory domain is used for searches and discovery.

DNS settings are configured in the /etc/resolv.conf file.

nameserver 1.2.3.4
search adexample.com

⁠4.1.1.4. PAM and NSS

PAM and NSS allow local applications to use the Kerberos credentials provided by Active Directory, which enables single sign-on for system applications and domain users. For ease of use, offline caching of credentials, and other features, it is recommended to use Winbind.

For PAM, the Winbind libraries are set for authentication, account, password, and optionally session management. This is configured in the /etc/pam.d/system-auth file:

auth        required      pam_env.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 500 quiet
auth sufficient pam_winbind.so use_first_pass
auth        required      pam_deny.so

account     required      pam_unix.so broken_shadow
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 500 quiet
account [default=bad success=ok user_unknown=ignore] pam_winbind.so
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3 type=
password    sufficient    pam_unix.so sha512 shadow nullok try_first_pass use_authtok
password sufficient pam_winbind.so use_authtok
password    required      pam_deny.so

session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so
session     optional      pam_krb5.so
session optional pam_winbind.so use_first_pass

Another important configuration file is /etc/security/pam_winbind.conf. In it, various parameters and defaults are set, including Kerberos authentication, offline authentication, or automatic home directory creation. For further details, see the pam_winbind.conf(5) man page.

For NSS, Active Directory can be used for passwords, shadow (users), and groups by setting Winbind as an option. Additionally, you can add the WINS service option to use the configuration also for hosts. Always use files as the first location to check for accounts; this allows local system users and services to be able to log in and access resources.

NSS settings are configured in the /etc/nsswitch.conf file:

passwd:     files winbind
shadow:     files winbind
group:      files winbind

hosts:      files dns wins

Note

Note that PAM and NSS should not configured manually for integration with Active Directory. Instead, use the authconfig utility. See Section 4.3, “Configuring a Domain Member Using authconfig” for details.

⁠4.1.2. Authentication Using Winbind and Samba

There are two important tasks when managing files: to establish the proper ownership and to control access to appropriate parties. Both relate to an effective way to identify and authenticate users. Winbind provides three related but separate capabilities:

Authenticate users using local PAM configuration,

Resolve IDs, user names, and groups using NSS look-ups,

Create a database of mapped Active Directory SIDs and local UID/GID numbers.

Winbind is part of Samba and connects directly to the Active Directory domain. The local Linux system is a full domain member in Windows terminology, represented with a complete machine account stored in AD. PAM and NSS are configured to use Winbind for user identities on the local system.

Among other aspects of using Windbind are:

Winbind primarily maintains the machine account credentials (the Linux machine representation as a machine account in Active Directory). Among other functions, it can be used to update the machine account credentials or to update (or comply to) local stores of password policies.

Winbind supports POSIX attributes in the form of RFC 2307 attributes or in the form of "Microsoft Services for Unix" extensions (both version 3.5 and 3.0). See the idmap_ad(8) man page for details.

Joining the domain is done with utilities provided by Samba (via commands such as net ads join). Kerberos ticket management is done by Winbind, including ticket refresh and ticket re-acquisition.

The smb.conf file is the only location for defining ID mappings.

Note

In Red Hat Enterprise Linux, it is recommended to use SSSD as a capable alternative for direct integration with Active Directory. See Chapter 2, Using Active Directory as an Identity Provider for SSSD for more information.

⁠4.2. Summary of Configuration Files, Options, and Packages

⁠

Table 4.1. System Configuration Files, Required Options, and Required Packages

Service
Configuration File
Required Parameters
Required Packages

Samba
/etc/samba/smb.conf

[global]
    workgroup = ADEXAMPLE
    security = ads
    realm = ADEXAMPLE.COM

samba

Winbind
/etc/security/pam_winbind.conf

samba-winbind

Kerberos
/etc/krb5.conf

[libdefaults]
  default_realm = ADEXAMPLE.COM

[realms]
  ADEXAMPLE.COM = {
    kdc = kdc.adexample.com
}

[domain_realm]
 adexample.com = ADEXAMPLE.COM
  .adexample.com = ADEXAMPLE.COM

krb5-workstation

PAM
/etc/pam.d/system-auth or /etc/pam.d/system-auth-ac (with authconfig)

auth      sufficient   pam_winbind.so use_first_pass
account   [default=bad success=ok user_unknown=ignore] pam_winbind.so
password  sufficient   pam_winbind.so use_authtok
session   optional     pam_winbind.so use_first_pass

NSS
/etc/nsswitch.conf

#required
passwd:     files winbind
shadow:     files winbind
group:      files winbind

#optional
hosts:      files dns wins

DNS
/etc/resolv.conf

nameserver IPaddress
search domainName

⁠4.3. Configuring a Domain Member Using authconfig

All of the configuration outlined in Section 4.2, “Summary of Configuration Files, Options, and Packages” can be done automatically using the authconfig utility, with the exception of the DNS configuration. Configuration files can also be backed up by authconfig.

⁠4.3.1. Arguments and Configuration Parameters of authconfig

The Authentication Configuration utility automatically updates the required configuration files for Samba, Kerberos, and Active Directory integration when it is used to configure Winbind as the authentication store for the local system. Table 4.2, “authconfig Arguments and Configuration File Parameters” shows what parameters are set with each command option.

⁠

Table 4.2. authconfig Arguments and Configuration File Parameters

Service
CLI Option
GUI Field
Configuration File
Configuration Parameter

Samba
--smbsecurity
Security Model
/etc/samba/smb.conf
security

Samba
--smbworkgroup
Winbind Domain
/etc/samba/smb.conf
workgroup

Samba

Kerberos

--smbrealm
Winbind ADS Realm

Samba

/etc/samba/smb.conf

Kerberos

/etc/krb5.conf

Samba

realm in [global]

Kerberos

default_realm in [libdefaults]

realm entry (REALMNAME = {...}) in [realms]

Kerberos
--smbservers
Winbind Domain Controllers
/etc/krb5.conf
The KDC in the realm entry (e.g., REALMNAME {...}) in [realms]

Kerberos
--krb5realm

/etc/krb5.conf
The domain entry in [domain_realm]

PAM
--enablewinbindauth

/etc/pam.d/system-auth
auth, account, password, sessions

NSS
--enablewinbind

/etc/nsswitch.conf
passwd, shadow, group

NSS
--enablewins

/etc/nsswitch.conf
hosts

Winbind
--enablecache

Winbind
--enablewinbindkrb5

Winbind
--enablewinbindoffline

Important

The value of the --krb5realm option must be identical to the value given in --smbrealm for the domain to be configured properly.

⁠4.3.2. CLI Configuration of Active Directory Authentication with authconfig

Install the samba-winbind package. It is required for Windows integration features in Samba services, but is not installed by default:

[root@server ~]# yum install samba-winbind

Install the krb5-workstation package. It is required to connect to a Kerberos realm and manage principals and tickets:

[root@server ~]# yum install krb5-workstation

Install the samba-winbind-krb5-locator package. It contains a plug-in for the system Kerberos library to allow the local Kerberos library to use the same KDC as Samba and Winbind use.

[root@server ~]# yum install samba-winbind-krb5-locator

Edit the DNS configuration in the /etc/resolv.conf file to use the Active Directory domain as a name server and for search:

nameserver 1.2.3.4
search adexample.com

The authconfig utility does not set any requirements for what options must be invoked at a given time, since it can be used to modify configuration as well as to define new configuration.

The following example shows all required parameters for Samba, Kerberos, PAM, and NSS. It also includes options for Winbind, which allow offline access, and for the local system, which allow system accounts to continue to work. The example command is split into multiple lines and annotated for better readability.

​[root@server ~]# authconfig
​      // NSS
​      --enablewinbind
​      --enablewins
​      // PAM
​      --enablewinbindauth
​      // Samba
​      --smbsecurity ads
​      --smbworkgroup=ADEXAMPLE
​      --smbrealm ADEXAMPLE.COM
​      // Kerberos
​      --smbservers=ad.example.com
​      --krb5realm=ADEXAMPLE.COM
​      // winbind
​      --enablewinbindoffline
​      --enablewinbindkrb5
​      --winbindtemplateshell=/bin/sh
​      // general
​      --winbindjoin=admin
​      --update
​      --enablelocauthorize
​      --savebackup=/backups
​
​[/usr/bin/net join -w ADEXAMPLE -S ad.example.com -U admin]

The --winbindjoin option automatically runs the net join command to add the system to the Active Directory domain.

The --enablelocalauthorize option sets local authorization operations to check the /etc/passwd file. This allows local accounts to be used to authenticate users as well as the Active Directory domain.

Note

The --savebackup option is recommended but not required. It backs up the configuration files to the specified directory before making the changes. If there is a configuration error or the configuration is later changed, authconfig can use the backups to revert the changes.

⁠4.3.3. Configuring Active Directory Authentication in the authconfig GUI

There are fewer configuration options in the authconfig GUI than are in the CLI. For example, it is possible to configure Samba, NSS, Winbind, and to join the domain, but it does not configure Kerberos or PAM. Those must be configured manually if using the UI.

Note

The authconfig command-line utilities are installed by default, but the GUI requires the authconfig-gtk package, which is not available by default.

Install the samba-winbind package. It is required for Windows integration features in Samba services, but is not installed by default.

[root@se yum install samba-winbind

Install the krb5-workstation package. It is required to connect to a Kerberos realm and manage principals and tickets.

[root@se yum install krb5-workstation

Configure the Active Directory Kerberos realm as the default realm and KDC for the local system.

[root@se vim /etc/krb5.conf

[libdefaults]
...

  default_realm PLE.COM

[realms]
  ADEXAMPLE.COM
    kdc = kdc.adcom
}

[domain_realm]
 adexample.com =LE.COM
  .adexample.comMPLE.COM

Edit the DNS configuration in the /etc/resolv.conf file to use the Active Directory domain as a name server and for search:

nameserver 1.2.3
search adexample

Open the Authentication Configuration Tool.

[root2se authconfig-gtk

In the Identity & Authentication tab, select Winbind in the User Account Database drop-down menu.

Set the information that is required to connect to the Microsoft Active Directory domain controller.

Winbind Domain gives the Windows work group. The entry inthis field needs to be in the Windows 2000 format, such as DOMAIN.

Security Model sets the security model to use for Samba clients. The correct value is ads that configures Samba to act as a domain member in an Active Directory Server realm.

Winbind ADS Realm gives the Active Directory realm that the Samba server will join.

Winbind Domain Controllers gives the host name or IP address of the domain controller to use.

Template Shell sets which login shell to use for Windows user account settings. This setting is optional.

Allow offline login allows authentication information to be stored in a local cache. The cache is referenced when a user attempts to authenticate to system resources while the system is offline.

Click the Join Domain button to run the net ads join command and join the Active Directory domain. This action is to join the domain immediately; the configuration can be saved and then the net ads join command can be run manually later.

Click the Apply button to save the configuration.

⁠Part II. Integrating a Linux Domain with an Active Directory Domain

⁠Chapter 5. Creating Cross-forest Trusts with Active Directory and Identity Management

Kerberos implements a concept of trust. In a trust, a principal from one Kerberos realm can request a ticket to a service in another Kerberos realm. Using this ticket, the principal can authenticate against resources on machines belonging to the other realm.

Kerberos also has the ability to create a relationship between two otherwise separate Kerberos realms: a cross-realm trust. Realms joined in a trust create a shared ticket and key; a member of one realm then counts as a member of both realms.

Red Hat Identity Management supports configuring a cross-forest trust between an IdM domain and an Active Directory domain.

⁠5.1. Introduction to Cross-forest Trusts

Kerberos realm only concerns authentication. Other services and protocols are involved in complementing identity and authorization for resources running on the machines in the Kerberos realm.

As such, establishing Kerberos cross-realm trust is not enough to allow users from one realm to access resources in the other realm; a support is required at other levels of communication as well.

⁠5.1.1. The Architecture of a Trust Relationship

Both Active Directory and Identity Management manage a variety of core services such as Kerberos, LDAP, DNS, or certificate services. To transparently integrate these two diverse environments, all core services must interact seamlessly with one another.

⁠Active Directory Trusts, Forests, and Cross-forest Trusts

Kerberos cross-realm trust plays an important role in authentication between Active Directory environments. All activities to resolve user and group names in a trusted AD domain require authentication, regardless of how access is performed: using LDAP protocol or as part of the Distributed Computing Environment/Remote Procedure Calls (DCE/RPC) on top of the Server Message Block (SMB) protocol. Because there are more protocols involved in organizing access between two different Active Directory domains, trust relationship has a more generic name, Active Directory trust.

Multiple AD domains can be organized together into an Active Directory forest. A root domain of the forest is the first domain created in the forest. Identity Management domain cannot be part of existing AD forest, thus it is always seen as a separate forest.

When trust relationship is established between two separate forest root domains, allowing users and services from different AD forests to communicate, a trust is called Active Directory cross-forest trust.

⁠Trust Flow and One-way Trusts

A trust establishes an access relationship between two domains. Active Directory environments can be complex so there are different possible types and arrangements for Active Directory trusts, between subdomains, root domains, or forests. A trust is a path from one domain to another. The way that identities and information move between the domains is called a trust flow.

The trusted domain contains users, and the trusting domain allows access to resources. In a one-way trust, trust flows only in one direction: users can access the trusting domain's resources but users in the trusting domain cannot access resources in the trusted domain. In Figure 5.1, “One-way Trust”, Domain A is trusted by Domain B, but Domain B is not trusted by Domain A.

⁠

Figure 5.1. One-way Trust

IdM allows the administrator to configure both one-way and two-way trusts. For more information on how to achieve this, see Section 5.3.1, “One-Way and Two-Way Trusts”.

⁠Transitive and Non-transitive Trusts

Trusts can be transitive so that a domain trusts another domain and any other domain trusted by that second domain.

⁠

Figure 5.2. Transitive Trusts

Trusts can also be non-transitive which means the trust is limited only to the explicitly included domains.

⁠Cross-forest Trust in Active Directory and Identity Management

Within an Active Directory forest, trust relationships between domains are normally two-way and transitive by default.

Because trust between two AD forests is a trust between two forest root domains, it can also be two-way or one-way. The transitivity of the cross-forest trust is explicit: any domain trust within an AD forest that leads to the root domain of the forest is transitive over the cross-forest trust. However, separate cross-forest trusts are not transitive. An explicit cross-forest trust must be established between each AD forest root domain to another AD forest root domain.

From the perspective of AD, Identity Management represents a separate AD forest with a single AD domain. When cross-forest trust between an AD forest root domain and an IdM domain is established, users from the AD forest domains can interact with Linux machines and services from the IdM domain.

⁠

Figure 5.3. Trust Direction

⁠5.1.2. Active Directory Security Objects and Trust

An application can use Kerberos as the protocol to process authentication requests. Kerberos interacts with the Net Logon layer in Active Directory, from which process for accessing domain objects is the same. Each AD server maintains a local security authority (LSA), which include all locally-defined security policies and provides a way to identify local users and identifiers, tickets and PACs, and other security data.

⁠Active Directory Global Catalog

All Kerberos communication for both AD and IdM for trusts uses GSS-API. Past the local security authority, there is the larger AD configuration. The domain system container holds all security information, including principles, user, and group information for all objects in a domain. At the root of the domain is a global catalog of all users, groups, and objects within the entire forest. With a trust, information about Windows users can be retrieved from the system container or from the global catalog.

⁠Global Catalog and POSIX Attributes

The global catalog only contains information about users, groups, and other objects that are part of the context of the forest. Some types of groups are only valid withing a specific server or specific domain. These groups are not part of the global catalog service. AD servers always evaluate access permissions based on the specifics of access context, which means that server-local or domain-local groups are not visible beyond the context of their definition.

Note that the cross-forest trust context is wider than a single domain. Therefore, some of these server-local or domain-local security group memberships from a trusted forest might not be visible to IdM servers. In addition, the global catalog only replicates a minimal subset of user and group attributes from the forest domains. If any of the users and groups in AD have POSIX attributes defined, these attributes are not replicated to the global catalog by default. If it is required to use POSIX attributes defined in AD, Red Hat strongly recommends to replicate them to the global catalog service, as mentioned in Section 2.3.1.2, “About SSSD and POSIX Attributes”.

⁠5.1.3. Trust Architecture in IdM

On the Identity Management side, the IdM server has to be able to recognize Active Directory identities and appropriately process their group membership for access controls. The Microsoft PAC (MS-PAC, Privilege Account Certificate) contains the required information about the user; their security ID, domain user name, and group memberships. Identity Management has two components to analyze data in the PAC on the Kerberos ticket:

SSSD, to perform identity lookups on Active Directory and to retrieve user and group security identifiers (SIDs) for authorization. SSSD also caches user, group, and ticket information for users and maps Kerberos and DNS domains,

Identity Management (Linux domain management), to associate the Active Directory user with an IdM group for IdM policies and access.

Note

Access control rules and policies for Linux domain administration, such as SELinux, sudo, and host-based access controls, are defined and applied through Identity Management. Any access control rules set on the Active Directory side are not evaluated or used by IdM; the only Active Directory configuration which is relevant is group membership.

⁠Trusts with Different Active Directory Forests

IdM can also be part of trust relationships with different AD forests. Once a trust is established, additional trusts with other forests can be added later, following the same commands and procedures. IdM can trust multiple entirely unrelated forests at the same time, allowing users from such unrelated AD forests access to resources in the same shared IdM domain.

⁠5.1.3.1. Active Directory PACs and IdM Tickets

Group information in Active Directory is stored in a list of identifiers in the Privilege Attribute Certificate (MS-PAC or PAC) data set. The PAC contains various authorization information, such as group membership or additional credentials information. It also includes security identifiers (SIDs) of users and groups in the Active Directory domain. SIDs are identifiers assigned to Active Directory users and groups when they are created. In trust environments, group members are identified by SIDs, rather than by names or DNs.

A PAC is embedded in the Kerberos service request ticket for Active Directory users as a way of identifying the entity to other Windows clients and servers in the Windows domain. IdM maps the group information in the PAC to the Active Directory groups and then to the corresponding IdM groups to determine access.

When an Active Directory user requests a ticket for a service on IdM resources, the process goes as follows:

The request for a service contains the PAC of the user. The IdM KDC analyzes the PAC by comparing the list of Active Directory groups to memberships in IdM groups.

For SIDs of the Kerberos principal defined in the MS-PAC, the IdM KDC evalues external group memberships defined in the IdM LDAP. If additional mappings are available for an SID, the MS-PAC record is extended with other SIDs of the IdM groups to which the SID belongs. The resulting MS-PAC is signed by the IdM KDC.

The service ticket is returned to the user with the updated PAC signed by the IdM KDC. Users belonging to AD groups known to the IdM domain can now be recognized by SSSD running on the IdM clients based on the MS-PAC content of the service ticket. This allows to reduce identity traffic to discover group memberships by the IdM clients.

When the IdM client evaluates the service ticket, the process includes the following steps:

The Kerberos client libraries used in the evaluation process send the PAC data to the SSSD PAC responder.

The PAC responder verifies the group SIDs in the PAC and adds the user to the corresponding groups in the SSSD cache. SSSD stores multiple TGTs and tickets for each user as new services are accessed.

Users belonging to the verified groups can now access the required services on the IdM side.

⁠5.1.3.2. Active Directory Users and Identity Management Groups

When managing Active Directory users and groups, you can add individual AD users and whole AD groups to Identity Management groups.

For a description of how to configure IdM groups for AD users, see Section 5.4, “Creating IdM Groups for Active Directory Users”.

⁠Non-POSIX External Groups and SID Mapping

Group membership in the IdM LDAP is expressed by specifying a distinguished name (DN) of an LDAP object that is a member of a group. AD entries are not synchronized or copied over to IdM, which means that AD users and groups have no LDAP objects in the IdM LDAP. Therefore, they cannot be directly used to express group membership in the IdM LDAP.

For this reason, IdM creates non-POSIX external groups: proxy LDAP objects that contain references to SIDs of AD users and groups as strings. Non-POSIX external groups are then referenced as normal IdM LDAP objects to signify group membership for AD users and groups in IdM.

SIDs of non-POSIX external groups are processed by SSSD; SSSD maps SIDs of groups to which an AD user belongs to POSIX groups in IdM. The SIDs on the AD side are associated with user names. When the user name is used to access IdM resources, SSSD in IdM resolves that user name to its SID, and then looks up the information for that SID within the AD domain, as described in Section 5.1.3.1, “Active Directory PACs and IdM Tickets”.

⁠ID Ranges

When a user is created in Linux, it is assigned a user ID number. In addition, a private group is created for the user. The private group ID number is the same as the user ID number. In Linux environment, this does not create a conflict. On Windows, however, the security ID number must be unique for every object in the domain.

Trusted AD users require a UID and GID number on a Linux system. This UID and GID number can be generated by IdM, but if the AD entry already has UID and GID numbers assigned, assigning different numbers creates a conflict. To avoid such conflicts, it is possible to use the AD-defined POSIX attributes, including the UID and GID number and preferred login shell.

Note

AD stores a subset of information for all objects within the forest in a global catalog. The global catalog includes every entry for every domain in the forest. If you want to use AD-defined POSIX attributes, Red Hat strongly recommends that you first replicate the attributes to the global catalog, as mentioned in Section 2.3.1.2, “About SSSD and POSIX Attributes”.

When a trust is created, IdM automatically detects what kind of ID range to use and creates a unique ID range for the AD domain added to the trust. You can also choose this manually by passing one of the following options to the ipa trust-add command:

ipa-ad-trust

This range option is used for IDs algorithmically generated by IdM based on the SID.

If IdM generates the SIDs using SID-to-POSIX ID mapping, the ID ranges for AD and IdM users and groups must have unique, non-overlapping ID ranges available.

ipa-ad-trust-posix

This range option is used for IDs defined in POSIX attributes in the AD entry.

IdM obtains the POSIX attributes, including uidNumber and gidNumber, from the global catalog in AD or from the directory controller. If the AD domain is managed correctly and without ID conflicts, the ID numbers generated in this way are unique. In this case, no ID validation or ID range is required.

For example:

ipa trust-add --range-type=ipa-ad-trust-posix

⁠5.1.3.3. Active Directory Users and IdM Policies and Configuration

Several IdM policy definitions, such as SELinux, host-based access control, sudo, and netgroups, rely on user groups to identify how the policies are applied.

⁠

Figure 5.4. Active Directory Users and IdM Groups and Policies

Active Directory users are external to the IdM domain, but they can still be added as group members to IdM groups, as long as those groups are configured as external groups described in Section 5.1.3.2, “Active Directory Users and Identity Management Groups”. In such cases, the sudo, host-based access controls, and other policies are applied to the external POSIX group and, ultimately, to the AD user when accessing IdM domain resources.

The user SID in the PAC in the ticket is resolved to the AD identity. This means that Active Directory users can be added as group members using their fully-qualified user name or their SID.

⁠5.1.4. Potential Behavior Issues with Active Directory Trust

⁠5.1.4.1. Active Directory Users and IdM Administration

Active Directory users exist only within the AD domain. Because they do not existin within IdM, they cannot be administrators for IdM. They also cannot use any IdM administrative tools, including the IdM web UI and command-line utilities.

Additionally, AD users currently cannot manage their own ID overrides. Only IdM users can add and manage ID overrides.

⁠5.1.4.2. Authenticating Deleted Active Directory Users

By default, every IdM client uses the SSSD service to cache user identities and credentials. If the IdM or AD back-end provider is temporarily unavailable, SSSD enables the local system to reference identities for users who have already logged in successfully once.

Because SSSD maintains a list of users locally, changes that are made on the back end might not be immediately visible to clients that run SSSD offline. On such clients, users who have previously logged into IdM resources and whose hashed passwords are stored in the SSSD cache are able to log in again even if their user accounts have been deleted in AD.

If the above conditions are met, the user identity is cached in SSSD, and the AD user is able to log into IdM resources even if the user account is deleted AD. This problem will persist until SSSD becomes online and is able to verify AD user logon against AD domain controllers.

If the client system runs SSSD online, the password provided by the user is validated by an AD domain controller. This ensures that deleted AD users are not allowed to log in.

⁠5.1.4.3. Credential Cache Collections and Selecting Active Directory Principals

The Kerberos credentials cache attempts to match a client principal to a server principal based on the following identifiers in this order:

service name

host name

realm name

When the client and server mapping is based on the host name or real name and credential cache collections are used, unexpected behavior can occur in binding as an AD user. This is because the realm name of the Active Directory user is different than the realm name of the IdM system.

If an AD user obtains a ticket using the kinit utility and then uses SSH to connect to an IdM resource, the principal is not selected for the resource ticket. an IdM principal is used because the IdM principal matches the realm name of the resource.

For example, if the AD user is Administrator and the domain is ADEXAMPLE.ADREALM, the principal is Administrator@ADEXAMPLE.ADREALM.

[root@server ~]# kinit Administrator@ADEXAMPLE.ADREALM
Password for Administrator@ADEXAMPLE.ADREALM:
[root@server ~]# klist
Ticket cache: KEYRING:persistent:0:0
Default principal: Administrator@ADEXAMPLE.ADREALM

Valid starting       Expires              Service principal
27.11.2015 11:25:23  27.11.2015 21:25:23  krbtgt/ADEXAMPLE.ADREALM@ADEXAMPLE.ADREALM
	renew until 28.11.2015 11:25:16

This is set as the default principal in the Active Directory ticket cache. However, if any IdM user also has a Kerberos ticket (such as admin), then there is a separate IdM credentials cache, with an IdM default principal. That IdM default principal is selected for a host ticket if the Active Directory user uses SSH to connect to a resource.

[root@vm-197 ~]# ssh -l Administrator@adexample.adrealm ipaclient.example.com
Administrator@adexample.adrealm@ipaclient.example.com's password:

[root@vm-197 ~]# klist -A
Ticket cache: KEYRING:persistent:0:0
Default principal: Administrator@ADEXAMPLE.ADREALM

Valid starting       Expires              Service principal
27.11.2015 11:25:23  27.11.2015 21:25:23  krbtgt/ADEXAMPLE.ADREALM@ADEXAMPLE.ADREALM
	renew until 28.11.2015 11:25:16

Ticket cache: KEYRING:persistent:0:0
Default principal: admin@EXAMPLE.COM >>>>> IdM user

Valid starting       Expires              Service principal
27.11.2015 11:25:18  28.11.2015 11:25:16  krbtgt/EXAMPLE.COM@EXAMPLE.COM
27.11.2015 11:25:48 28.11.2015 11:25:16 host/ipaclient.example.com@EXAMPLE.COM >>>>> host principal

This is because the realm name of the IdM principal matches the realm of the IdM resource.

⁠5.1.4.4. Resolving Group SIDs

⁠Losing Kerberos Tickets

Running a command to obtain a SID from the Samba service, such as net getlocalsid or net getdomainsid, removes any existing admin ticket from the Kerberos cache.

Note

You are not required to run commands such as net getlocalsid or net getdomainsid in order to use Active Directory trusts.

⁠Cannot Verify Group Membership for Users

It is not possible to verify that a specific trusted user is associated with a specific IdM group, external or POSIX.

⁠Cannot Display Remote Active Directory Group Memberships for an Active Directory User

Important

Note that this problem no longer occurs if the IdM server and client run on Red Hat Enterprise Linux 7.1 or later.

The id utlity can be used to display local group associations for Linux system users. However, id does not display Active Directory group memberships for Active Directory users, even though Samba tools do display them.

To work around this, you can use the ssh utility to log into an IdM client machine as the given AD user. After the AD user logs in successfully for the first time, the id search detects and displays the AD group memberships:

[root@ipaserver ~]# id ADDOMAIN\jsmith
uid=1921801107(jsmith@adexample.com) gid=1921801107(jsmith@adexample.com) groups=1921801107(jsmith@adexample.com),129600004(ad_users),1921800513(domain users@adexample.com)

⁠5.2. Environment and Machine Requirements to Set up Trusts

Before configuring a trust agreement, make sure that both the Active Directory and Identity Management servers, machines, and environments meet the requirements and settings described in this section.

⁠5.2.1. Supported Windows Platforms

Trust relationships can be configured with these Windows server versions:

Windows Server 2008

Windows Server 2008 R2

Windows Server 2012

Windows Server 2012 R2

⁠5.2.2. DNS and Realm Settings

To establish a trust, Active Directory and Identity Management require specific DNS configuration:

Unique primary DNS domains

Each system must have its own unique primary DNS domain configured; for example, ad.example.com for AD and idm.example.com for IdM. The most convenient management solution is an environment where each DNS domain is managed by integrated DNS servers, but it is possible to use any other standard-compliant DNS server as well.

It is not possible for AD or IdM to share the primary DNS domain with another system for identity management. For more information, see documentation for host name and DNS configuration requirements in the Linux Domain Identity, Authentication, and Policy Guide.

Kerberos realm names as upper-case versions of primary DNS domain names

Kerberos realm names must be the same as the primary DNS domain names, with all letters uppercase. For example, if the domain names are ad.example.com for AD and idm.example.com for IdM, the Kerberos realm names are required to be AD.EXAMPLE.COM and IDM.EXAMPLE.COM.

DNS records resolvable from all DNS domains in the trust

All machines must be able to resolve DNS records from all DNS domains involved in the trust relationship. When configuring IdM DNS, follow the instructions described in the section on configuring DNS services within the IdM domain and section on managing DNS forwarding in the Linux Domain Identity, Authentication, and Policy Guide. If you are using IdM without integrated DNS, follow the instructions described in the section describing basic interactive installation.

No overlap between IdM and AD DNS Domains

Machines joined to IdM can be distributed over multiple DNS domains. DNS domains containing IdM clients must not overlap with DNS domains containing machines joined to AD. The primary IdM DNS domain must have proper SRV records to support AD trusts.

For other DNS domains that are part of the same IdM realm, it is not required for the SRV records to be configured when the trust to AD is configured. The reason is that AD domain controllers do not use SRV records to discover KDCs but rather base the KDC discovery on name suffix routing information for the trust.

⁠Verifying the DNS Configuration

Before configuring trust, verify that the Identity Management and Active Directory servers can resolve themselves and also each other.

If running the commands described below does not display the expected results, inspect the DNS configuration on the host where the commands were executed. If the host configuration seems correct, make sure that DNS delegations from the parent to child domains are set up correctly.

Note that AD caches the results of DNS lookups, and changes you make in DNS are therefore sometimes not visible immediately. You can delete the current cache by running the ipconfig /flushdns command.

⁠Verify that the IdM-hosted services are resolvable from the IdM domain server used for establishing trust

Run a DNS query for the Kerberos over UDP and LDAP over TCP service records.

[root@ipaserver ~]# dig +short -t SRV _kerberos._udp.ipa.example.com.
0 100 88 ipamaster1.ipa.example.com.

[root@ipaserver ~]# dig +short -t SRV _ldap._tcp.ipa.example.com.
0 100 389 ipamaster1.ipa.example.com.

The commands are expected to list all IdM servers.

Run a DNS query for the TXT record with the IdM Kerberos realm name. The obtained value is expected to match the Kerberos realm that you specified when installing IdM.

[root@ipaserver ~]# dig +short -t TXT _kerberos.ipa.example.com.
IPA.EXAMPLE.COM

After you execute the ipa-adtrust-install utility, as described in Section 5.3.3.1, “Preparing the IdM Server for Trust”, run a DNS query for the MS DC Kerberos over UDP and LDAP over TCP service records.

[root@ipaserver ~]# dig +short -t SRV _kerberos._udp.dc._msdcs.ipa.example.com.
0 100 88 ipamaster1.ipa.example.com.

[root@ipaserver ~]# dig +short -t SRV _ldap._tcp.dc._msdcs.ipa.example.com.
0 100 389 ipamaster1.ipa.example.com.

The commands are expected to list all IdM servers on which ipa-adtrust-install has been executed. Note that the output is empty if ipa-adtrust-install has not been executed on any IdM server, which is typically before establishing the very first trust relationship.

⁠Verify that IdM is able to resolve service records for AD

Run a DNS query for the Kerberos over UDP and LDAP over TCP service records.

[root@ipaserver ~]# dig +short -t SRV _kerberos._udp.dc._msdcs.ad.example.com.
0 100 88 addc1.ad.example.com.

[root@ipaserver ~]# dig +short -t SRV _ldap._tcp.dc._msdcs.ad.example.com.
0 100 389 addc1.ad.example.com.

These commands are expected to return the names of AD domain controllers.

Verify that the IdM-hosted services are resolvable from the AD server

On the AD server, set the nslookup.exe utility to look up service records.

C:\>nslookup.exe
> set type=SRV

Enter the domain name for the Kerberos over UDP and LDAP over TCP service records.

> _kerberos._udp.ipa.example.com.
_kerberos._udp.ipa.example.com.       SRV service location:
    priority                = 0
    weight                  = 100
    port                    = 88
    svr hostname   = ipamaster1.ipa.example.com
> _ldap._tcp.ipa.example.com
_ldap._tcp.ipa.example.com       SRV service location:
    priority                = 0
    weight                  = 100
    port                    = 389
    svr hostname   = ipamaster1.ipa.example.com

The expected output contains the same set of IdM servers as displayed in Verify that the IdM-hosted services are resolvable from the IdM domain server used for establishing trust.

Change the service type to TXT and run a DNS query for the TXT record with the IdM Kerberos realm name.

C:\>nslookup.exe
> set type=TXT
> _kerberos.ipa.example.com.
_kerberos.ipa.example.com.        text =

    "IPA.EXAMPLE.COM"

The output is expected to contain the same value as displayed in Verify that the IdM-hosted services are resolvable from the IdM domain server used for establishing trust.

After you execute the ipa-adtrust-install utility, as described in Section 5.3.3.1, “Preparing the IdM Server for Trust”, run a DNS query for the MS DC Kerberos over UDP and LDAP over TCP service records.

C:\>nslookup.exe
> set type=SRV
> _kerberos._udp.dc._msdcs.ipa.example.com.
_kerberos._udp.dc._msdcs.ipa.example.com.        SRV service location:
    priority = 0
    weight = 100
    port = 88
    svr hostname = ipamaster1.ipa.example.com
> _ldap._tcp.dc._msdcs.ipa.example.com.
_ldap._tcp.dc._msdcs.ipa.example.com.        SRV service location:
    priority = 0
    weight = 100
    port = 389
    svr hostname = ipamaster1.ipa.example.com

The command is expected to list all IdM servers on which the ipa-adtrust-install utility has been executed. Note that the output is empty if ipa-adtrust-install has not been executed on any IdM server, which is typically before establishing the very first trust relationship.

Verify that AD services are resolvable from the AD server

On the AD server, set the nslookup.exe utility to look up service records.

C:\>nslookup.exe
> set type=SRV

Enter the domain name for the Kerberos over UDP and LDAP over TCP service records.

> _kerberos._udp.dc._msdcs.ad.example.com.
_kerberos._udp.dc._msdcs.ad.example.com. 	SRV service location:
    priority = 0
    weight = 100
    port = 88
    svr hostname = addc1.ad.example.com
> _ldap._tcp.dc._msdcs.ad.example.com.
_ldap._tcp.dc._msdcs.ad.example.com. 	SRV service location:
    priority = 0
    weight = 100
    port = 389
    svr hostname = addc1.ad.example.com

The expected output contains the same set of AD servers as displayed in Verify that IdM is able to resolve service records for AD.

⁠5.2.3. NetBIOS Names

The NetBIOS name is critical for identifying the AD domain and, if the IdM domain is within a subdomain of Active Directory DNS, for identifying the IdM domain and services. The IdM domain and Active Directory domain must have different NetBIOS names.

Note

The NetBIOS name is usually the far-left component of the domain name. For example, if the domain is linux.example.com, the NetBIOS name is linux. If the domain name is example.com, the NetBIOS name is example.

The maximum length of the NetBIOS name is 15 characters.

⁠5.2.4. Firewalls and Ports

For a trust relationship, the Active Directory server and the IdM server must have all of the ports required for an IdM server installation and for trust open:

For a list of the ports required by IdM, see the corresponding chapter in the Linux Domain Identity, Authentication, and Policy Guide.

The ports required for a trust relationship to work are listed in Table 5.1, “Ports Required for a Trust”.

⁠

Table 5.1. Ports Required for a Trust

Service | Ports | Type
NetBIOS-DGM | 138 | TCP and UDP
NetBIOS-SSN | 139 | TCP and UDP
LDAP | 389 | UDP
Microsoft-DS | 445 | TCP and UDP

Active Directory domain controllers and IdM masters must be able to communicate together using the services described in Table 5.1, “Ports Required for a Trust”, as well as using Kerberos, LDAP, and also DNS if the IdM master is running DNS. Ports required for these last three services are listed in in the Linux Domain Identity, Authentication, and Policy Guide.

⁠Opening the Required Ports

Opening ports requires the firewalld service to be running. To start firewalld as well as to configure it to start automatically when the system boots:

[root@server ~]# systemctl start firewalld.service
[root@server ~]# systemctl enable firewalld.service

Note

You can determine whether firewalld is currently running using the systemctl status firewalld.service command.

To open the ports using firewalld, assuming the default firewalld zone is used:

⁠

Open the ports to services required by IdM.

[root@server ~]# firewall-cmd --permanent --add-port={80/tcp,443/tcp,389/tcp,636/tcp,88/tcp,464/tcp,53/tcp,88/udp,464/udp,53/udp,123/udp}

Open the ports to services required for a trust relationship.

[root@server ~]# firewall-cmd --permanent --add-port={138/tcp,139/tcp,445/tcp,138/udp,139/udp,389/udp,445/udp}

Reload the firewalld configuration, so that the change is applied immediately.

[root@server ~]# firewall-cmd --reload

⁠5.2.5. IPv6 Settings

The IdM system must have the IPv6 protocol enabled in the kernel. If IPv6 is disabled, then the CLDAP plug-in used by the IdM services fails to initialize.

⁠5.2.6. Clock Settings

Both the Active Directory server and the IdM server must have their clocks in sync.

⁠5.2.7. Supported User Name Formats

IdM performs user name mapping in the local SSSD client. The default user name format supported by SSSD is name@domain. Active Directory supports several different kinds of name formats: username, username@domain.name, and DOMAIN\username.

To identify the user name and the domain to which the user name belongs, SSSD uses a regular expression defined in the re_expression option. The regular expression is used for IdM back ends or AD back ends and supports all the mentioned formats:

re_expression = (((?P<domain>[^\\]+)\\(?P<name>.+$))|((?P<name>[^@]+)@(?P<domain>.+$))|(^(?P<name>[^@\\]+)$))

⁠5.3. Creating Trusts

The following sections describe creating trusts in various configuration scenarios. Section 5.3.3, “Creating a Trust from the Command Line” contains the full procedure for configuring a trust from the command line. The other sections describe the steps which are different from this basic configuration scenario and reference the basic procedure for all other steps.

⁠5.3.1. One-Way and Two-Way Trusts

IdM supports two types of trust agreements, depending on whether the entities that can establish connection to services in IdM are limited to only AD or can include IdM entities as well.

One-way trust

One-way trust enables users and groups in Active Directory to access resources in IdM but not the other way around. The IdM domain trusts the Active Directory forest using the AD cross-forest trust feature, but the AD forest does not trust the IdM domain.

One-way trust is the default mode for creating a trust. Running the ipa trust-add command without the --two-way option automatically sets up a one-way trust.

Two-way trust

Two-way trust enables AD users and groups to access resources in IdM, and it also enables IdM users and groups to access resources in AD. The IdM domain and the AD forest both trust each other.

Note that the two-way trust in IdM does not give the users any additional rights compared to the one-way trust solution in AD. Both solutions are considered equally secure because of default cross-forest trust SID filtering settings.

To set up a two-way trust, pass the --two-way=true option with the ipa trust-add command.

After a trust is established, it is not possible to modify its type. If you require a different type of trust, run the ipa trust-add command again; by doing this, you can delete the existing trust and establish a new one.

⁠5.3.2. Trust Controllers and Trust Agents

To allow full flexibility for different use cases, Identity Management allows to choose from three types of master servers with regards to support of trust to Active Directory:

Normal IdM masters

Normal IdM master servers run the LDAP server, Kerberos KDC server, IdM management framework, SSSD, and a number of optional services, such as the CA, KRA, or DNS. These servers do not support trust to AD.

Trust agents

Trust agents are IdM masters allowed to perform identity lookups against AD domain controllers. Only IdM clients enrolled into trust agents can look up users and groups from trusted AD forests.

Trust agents are typically used to resolve AD users and groups but not to manage the trust.

Trust controllers

Trust controllers are implicitly trust agents as well, but in addition, they also run the Samba suite to allow AD domain controllers to communicate with IdM when trust to AD is established and verified.

Trust controllers can be used for trust management operations, such as adding trust agreements and enabling or disabling separate domains from a trusted forest to access IdM resources. Additionally, AD domain controllers contact trust controllers when validating the trust.

Red Hat recommends to reduce the number of trust controllers in a cross-forest trust deployment. Because trust controllers are required only for management purposes, trust agents should be used instead for enrolling IdM clients designed to run services accessible by users from trusted AD forests. Trust controllers run an increased amount of network-facing services compared to trust agents, and thus present a greater attack surface for potential intruders.

When setting up a trust to an AD forest, at least one IdM trust controller is required. To set up a normal IdM server as a trust controller, configure the trust by using the ipa-adtrust-install utility without adding the --add-agents option.

To turn a normal IdM master into a trust agent, run the ipa-adtrust-install --add-agents command on a trust controller. The command then enters interactive configuration session and prompts you for the information required to set up the agent. After setting up a trust agent, restart the LDAP service. For more information about the --add-agents option, see the ipa-adtrust-install(1) man page.

⁠5.3.3. Creating a Trust from the Command Line

Creating a trust relationship between the IdM and Active Directory Kerberos realms involves the following steps:

Preparing the IdM server for the trust, described in Section 5.3.3.1, “Preparing the IdM Server for Trust”

Creating a trust agreement, described in Section 5.3.3.2, “Creating a Trust Agreement”

Verifying the Kerberos configuration, described in Section 5.3.3.3, “Verifying the Kerberos configuration”

⁠5.3.3.1. Preparing the IdM Server for Trust

To set up the IdM server for a trust relationship with AD, follow these steps:

Install the required IdM, trust, and Samba packages:

[root@ipaserver ]# yum install ipa-server "*ipa-server-trust-ad" samba

Configure the IdM server to enable trust services:

Run the ipa-adtrust-install utility. The utility adds DNS service records required for AD trusts. These records are created automatically if IdM was installed with an integrated DNS server.

If IdM was installed without an integrated DNS server, ipa-adtrust-install prints a list of service records that must be manually added to DNS before you can continue.

Important

Red Hat strongly recommends to verify the DNS configuration as described in Section 5.2.2, “Verifying the DNS Configuration” every time after running ipa-adtrust-install, especially if IdM or AD do not use integrated DNS servers.

The script prompts to configure the slapi-nis plug-in, a compatibility plug-in that allows older Linux clients to work with trusted users.

Do you want to enable support for trusted domains in Schema Compatibility plugin?
This will allow clients older than SSSD 1.9 and non-Linux clients to work with trusted users.

Enable trusted domains support in slapi-nis? [no]: y

At least one user (the IdM administrator) exists when the directory is first installed. The SID generation task can create a SID for any existing users, to support the trust environment. This is a resource-intensive task; for a high-number of users, this can be run separately.

Do you want to run the ipa-sidgen task? [no]: yes

Make sure that DNS is properly configured, as described in Section 5.2.2, “DNS and Realm Settings”.

Use the smbclient utility to verify that Samba responds to Kerberos authentication from the IdM side.

[root@ipaserver ~]# smbclient -L ipaserver.ipaexample.com -k
lp_load_ex: changing to config backend registry
Domain=[IPAEXAMPLE] OS=[Unix] Server=[Samba 4.0.0rc4]
    Sharename       Type      Comment
    ---------       ----      -------
    IPC$            IPC       IPC Service (Samba 4.0.0rc4)
Domain=[IPAEXAMPLE] OS=[Unix] Server=[Samba 4.0.0rc4]
    Server               Comment
    ---------            -------
    Workgroup            Master
    ---------            -------

⁠5.3.3.2. Creating a Trust Agreement

Create a trust agreement for the Active Directory domain and the IdM domain by using the ipa trust-add command:

ipa trust-add --type=type ad_domain_name --admin ad_admin_username --password

For example:

[root@ipaserver ~]# ipa trust-add --type=ad adexample.com --admin Administrator --password
Active directory domain administrator's password:
------------------------------------------------------
Added Active Directory trust for realm "adexample.com"
------------------------------------------------------
  Realm name: adexample.com
  Domain NetBIOS name: ADEXAMPLE
  Domain Security Identifier: S-1-5-21-1689615952-3716327440-3249090444
  Trust direction: Two-way trust
  Trust type: Active Directory domain
  Trust status: Established and verified

⁠5.3.3.3. Verifying the Kerberos configuration

To verify the Kerberos configuration, test if it is possible to obtain a ticket for an IdM user and if the IdM user can request service tickets:

Request a ticket for an IdM user:

[root@ipaserver ~]# kinit user

Request service tickets for service within the IdM domain:

[root@ipaserver ~]# kvno -S host ipaserver.example.com

Request service tickets for services within the AD domain:

[root@ipaserver ~]# kvno -S cifs adserver.example.com

If the AD service ticket is successfully granted, there is a cross-realm ticket-granting ticket (TGT) listed with all of the other requested tickets. The TGT is named krbtgtAD.DOMAIN@IPA.DOMAIN.

[root@ipaserver ]# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: jsmith@IPA.DOMAIN

Valid starting     Expires            Service principal
06/15/12 12:13:04  06/16/12 12:12:55  krbtgt/IPA.DOMAIN@IPA.DOMAIN
06/15/12 12:13:13  06/16/12 12:12:55  host/ipaserver.ipaexample.com@IPA.DOMAIN
06/15/12 12:13:23 06/16/12 12:12:55 krbtgt/AD.DOMAIN@IPA.DOMAIN
06/15/12 12:14:58  06/15/12 22:14:58  cifs/adserver.adexample.com@AD.DOMAIN

If the localauth plug-in for mapping Kerberos principals to local SSSD user names is enabled, AD users can automatically use Kerberos for authentication.

Note

For more information about the plug-in, see Section 5.8.1, “Using SSH Without Passwords”.

⁠5.3.4. Creating a Trust with a Shared Secret

A shared secret is a password that is known to trusted peers and can be used by other domains to join the trust. Trusts within Active Directory can be configured with a shared secret. In AD, the shared secret is stored as a trusted domain object (TDO) within the trust configuration.

IdM supports creating a trust using a shared secret instead of the AD administrator credentials. Setting up such trust requires the administrator to create the shared secret in AD and manually validate the trust on the AD side.

To create a trust with a shared secret:

⁠

Prepare the IdM server for the trust, as described in Section 5.3.3.1, “Preparing the IdM Server for Trust”.

Configure a trust in the Active Directory Domains and Trusts console. Select the appropriate domain, and create a new trust. Use these settings:

The Trust Type is Forest trust.

The Direction of Trust is One-way.

The Sides of Trust is This domain only.

The Outgoing Trust Authentication Level is Forest-wide authentication.

Set the Trust Password.

Note

The same password must be used when configuring the trust in IdM.

When asked to confirm outgoing or incoming trust, select No.

Create a trust agreement, as described in Section 5.3.3.2, “Creating a Trust Agreement”. When running the ipa trust-add command, use the --type and --trust-secret options, and omit the --admin option. For example:

[root@ipaserver ~]# ipa trust-add --type=ad adexample.com --trust-secret
Shared secret for the trust:
--------------------------------------------------
Added Active Directory trust for realm "adexample.com"
--------------------------------------------------
  Realm name: adexample.com
  Domain NetBIOS name: ADEXAMPLE
  Domain Security Identifier: S-1-5-21-1910160501-511572375-3625658879
  SID blacklist incoming: S-1-0, S-1-1, S-1-2, S-1-3, S-1-5-1, S-1-5-2, S-1-5-3, S-1-5-4, S-1-5-5, S-1-5-6, S-1-5-7, S-1-5-8, S-1-5-9, S-1-5-10, S-1-5-11, S-1-5-12, S-1-5-13, S-1-5-14, S-1-5-15, S-1-5-16,
                          S-1-5-17, S-1-5-18, S-1-5-19, S-1-5-20
  SID blacklist outgoing: S-1-0, S-1-1, S-1-2, S-1-3, S-1-5-1, S-1-5-2, S-1-5-3, S-1-5-4, S-1-5-5, S-1-5-6, S-1-5-7, S-1-5-8, S-1-5-9, S-1-5-10, S-1-5-11, S-1-5-12, S-1-5-13, S-1-5-14, S-1-5-15, S-1-5-16,
                          S-1-5-17, S-1-5-18, S-1-5-19, S-1-5-20
  Trust direction: Two-way trust
  Trust type: Active Directory domain
  Trust status: Waiting for confirmation by remote side

In the Domains and Trusts console on the AD server, refresh name suffix routing for the IdM server.

⁠

Figure 5.5. Refreshing the Name Suffix Routing

On the IdM server, verify that the trust relationship is established by using the ipa trust show command.

[root@ipaserver ~]# ipa trust show adexample.com

  Realm name: adexample.com
  Domain NetBIOS name: AD
  Domain Security Identifier: S-1-5-21-91314187-2404433721-1858927112
  Trust direction: One-way trust
  Trust type: Active Directory domain

Verify the Kerberos configuration, as described in Section 5.3.3.3, “Verifying the Kerberos configuration”.

⁠5.3.5. Creating a Trust on an Existing IdM Instance

When configuring a trust for an existing IdM instance, certain settings for the IdM server and entries within its domain are already configured. However, you must set the DNS configuration for the Active Directory domain and assign Active Directory SIDs to all existing IdM users and groups.

⁠

Prepare the IdM server for the trust, as described in Section 5.3.3.1, “Preparing the IdM Server for Trust”.

Create a trust agreement, as described in Section 5.3.3.2, “Creating a Trust Agreement”.

Generate SIDs for each IdM user.

Note

Do not perform this step if the SIDs were generated when the ipa-adtrust-install utility was used to establish the trust.

Add a new ipaNTSecurityIdentifier attribute, containing a SID, automatically for each entry by running the ipa-sidgen-task operation on the backend LDAP directory.

[root@ipaserver ]# ldapmodify -x -H ldap://ipaserver.ipaexample.com:389 -D "cn=directory manager" -w password -f

dn: cn=sidgen,cn=ipa-sidgen-task,cn=tasks,cn=config
changetype: add
objectClass: top
objectClass: extensibleObject
cn: sidgen
nsslapd-basedn: dc=ipadomain,dc=com
delay: 0

adding new entry "cn=sidgen,cn=ipa-sidgen-task,cn=tasks,cn=config"

After the task completes successfully, a message is recorded in the error logs that the SID generation task (Sidgen task) finished with a status of zero (0).

[root@ipaserver ]# grep "sidgen_task_thread" /var/log/dirsrv/slapd-IPALAB-QE/errors
[20/Jul/2012:18:17:16 +051800] sidgen_task_thread - [file ipa_sidgen_task.c, line 191]: Sidgen task starts ...
[20/Jul/2012:18:17:16 +051800] sidgen_task_thread - [file ipa_sidgen_task.c, line 196]: Sidgen task finished [0].

Verify the Kerberos configuration, as described in Section 5.3.3.3, “Verifying the Kerberos configuration”.

⁠5.3.6. Adding a Second Trust

When adding a trust on an IdM server that already has one or more trust agreements configured, certain general IdM trust settings, such as installing the trust-related packages or configuring SIDs, is no longer required. To add an additional trust, you only must configure DNS and establish a trust agreement.

⁠

Make sure that DNS is properly configured, as described in Section 5.2.2, “DNS and Realm Settings”.

Create a trust agreement, as described in Section 5.3.3.2, “Creating a Trust Agreement”.

⁠5.3.7. Creating a Trust in the Web UI

Before creating a trust in the web UI, prepare the IdM server for the trust. This trust configuration is easiest to perform from the command line, as described in Section 5.3.3.1, “Preparing the IdM Server for Trust”.

Once the initial configuration is set, a trust agreement can be added in the IdM web UI:

Open the IdM web UI:

https://ipaserver.example.com

Open the IPA Server main tab, and select the Trusts subtab.

In the Trusts subtab, click Add to open the new trust configuration window.

Fill in the required information about the trust:

Provide the AD domain name in the Domain field.

To set up the trust as two-way, select the Two-way trust check box. To set up the trust as one-way, leave Two-way trust unselected.

For more information about one-way and two-way trusts, see Section 5.3.1, “One-Way and Two-Way Trusts”.

The Establish using section defines how the trust is to be established:

To establish the trust using the AD administrator's user name and password, select Administrative account and provide the required credentials.

Alternatively, to establish the trust with a shared password, select Pre-shared password and provide the trust password.

Define the ID configuration for the trust:

The Range type option allows you to choose the ID range type. If you want IdM to automatically detect what kind of ID range to use, select Detect.

To define the starting ID of the ID range, use the Base ID field. To define the size of the ID range, use the Range size field. If you want IdM to use default values for the ID range, do not specify these options.

For more information about ID ranges, see Section 5.1.3.2, “ID Ranges”.

⁠

Figure 5.6. Adding a Trust in the Web UI

Click Add to save the new trust.

After this, verify the Kerberos configuration, as described in Section 5.3.3.3, “Verifying the Kerberos configuration”.

⁠5.4. Creating IdM Groups for Active Directory Users

User groups are required to set access permissions, host-based access control, sudo rules, and other controls on IdM users. These groups are what grant access to IdM domain resources, as well as restricting access.

Both AD users and AD groups can be added directly to IdM user groups. To do that, first add the AD users or groups to a non-POSIX IdM external group and then to a local IdM POSIX group. The POSIX group can then be used for user and role management of the AD users. The principles of handling non-POSIX groups in IdM are described in Section 5.1.3.2, “Active Directory Users and Identity Management Groups”.

Note

It is also possible to add AD user groups as members to IdM external groups. This might make it easier to define policies for Windows users, by keeping the user and group management within the single AD realm.

Optional. Create or select the group in the AD domain to use to manage AD users in the IdM realm. Multiple groups can be used and added to different groups on the IdM side.

Create an external group in the IdM domain for the Active Directory users by adding the --external option to the ipa group-add command. The --external option indicates that this group is intended to contain members from outside the IdM domain. For example:

[root@ipaserver ~]# ipa group-add --desc='AD users external map' ad_users_external --external
-------------------------------
Added group "ad_users_external"
-------------------------------
  Group name: ad_users_external
  Description: AD users external map

Create a new IdM POSIX group or select an existing one for administering the IdM policies. For example, to create a new group:

[root@ipaserver ~]# ipa group-add --desc='AD users' ad_users
----------------------
Added group "ad_users"
----------------------
  Group name: ad_users
  Description: AD users
  GID: 129600004

Add the AD users or groups to the IdM external group as an external member. The AD member is identified by its fully-qualified name, such as DOMAIN\group_name or DOMAIN\username. The AD identity is then mapped to the Active Directory SID for the user or group.

For example, for an AD group:

[root@ipaserver ~]# ipa group-add-member ad_users_external --external "AD\Domain Users"
 [member user]:
 [member group]:
  Group name: ad_users_external
  Description: AD users external map
  External member: S-1-5-21-3655990580-1375374850-1633065477-513 SID_DOM_GROUP (2)
-------------------------
Number of members added 1
-------------------------

Add the external IdM group to the POSIX IdM group as a member. For example:

[root@ipaserver ~]# ipa group-add-member ad_users --groups ad_users_external
  Group name: ad_users
  Description: AD users
  GID: 129600004
  Member groups: ad_users_external
-------------------------
Number of members added 1
-------------------------

⁠5.5. Maintaining Trusts

Trust management involves several areas, such as global trust configuration, Kerberos trust configuration, DNS realm configuration, or ID ranges assignment to Active Directory users.

⁠5.5.1. Editing the Global Trust Configuration

The ipa-adtrust-install utility automatically automatically configures background information for the IdM domain which is required to create a trust with the Active Directory domain.

The global trust configuration contains five attributes:

A Windows-style security ID (SID); this attribute is autogenerated and cannot be modified

A domain GUID; this attribute is autogenerated and cannot be modified

A Kerberos domain name; this attribute comes from the IdM configuration and cannot be modified

The default group to which to add IdM users; this attribute can be modified

The NetBIOS name; it is not recommended to modify this attribute

The trust configuration is stored in the cn=domain,cn=ad,cn=etc,dc=example,dc=com subtree.

⁠5.5.1.1. Changing the NetBIOS Name

Important

Changing the NetBIOS name in most cases requires to re-establish all existing trusts. Therefore, Red Hat recommends not to change the attribute.

A NetBIOS name compatible within an Active Directory topology is configured for the IdM server when running the ipa-adtrust-install utility. To change it later, run ipa-adtrust-install again and specify the new NetBIOS name using the --netbios-name option:

[root@ipaserver ]# ipa-adtrust-install --netbios-name=NEWBIOSNAME

⁠5.5.1.2. Changing the Default Group for Windows Users

When Identity Management is configured to trust an Active Directory forest, an MS-PAC record is added to the Kerberos tickets of IdM users. An MS-PAC record contains security identifiers (SIDs) of the groups to which an IdM user belongs. If the primary group of the IdM user has no SID assigned, the value of the security identifier defined for the Default SMB Group will be used. The same logic is applied by the Samba suite when the AD domain controller requests user information from the IdM trust controller.

The Default SMB Group is a fallback group created automatically by the ipa-adtrust-install utility. The default group cannot be deleted, but you can use the global trust configuration to specify another IdM group to be used as a fallback for the primary group of the IdM users.

To set the default group from the command line, use the ipa trustconfig-mod command:

[root@server ~]# kinit admin
[root@server ~]# ipa trustconfig-mod --fallback-primary-group="Example Windows Group"

To set the default group from the IdM web UI:

Open the IdM web UI.

https://ipaserver.example.com

Open the IPA Server main tab, and then select the Trusts subtab.

In the Global Configuration subtab, select a new group from all of the IdM groups listed in the Fallback primary group.

Click the Update link to save the new configuration.

⁠5.5.2. Discovering, Enabling, and Disabling Trust Domains

A transitive trust means that the trust path can follow a chain of domains. It is described in more detail in Section 5.1.1, “The Architecture of a Trust Relationship”.

IdM has a trust with the root domain in a forest, and due to transitivity, all of its subdomains and trusted domains are implicitly included in that trust. IdM follows that topology as Windows users from anywhere in the forest attempt to access IdM resources. Each domain and subdomain is a trust domain in the IdM trust configuration. Each domain is stored in its own entry, cn=subdomain,cn=trust_name,cn=ad,cn=trusts,dc=example,dc=com in the trusts subtree.

IdM attempts to discover and map the full Active Directory topology when the trust is first configured, although in some cases it is required or beneficial to retrieve that topology manually. That is done with the trust-fetch-domains command:

[root@ipaserver ~]# kinit admin
[root@ipaserver ~]# ipa trust-fetch-domains adexample.com
--------------------------------------------
List of trust domains successfully refreshed
--------------------------------------------
  Realm name: test.adexample.com
  Domain NetBIOS name: TEST
  Domain Security Identifier: S-1-5-21-87535643-5658642561-5780864324

  Realm name: users.adexample.com
  Domain NetBIOS name: USERS
  Domain Security Identifier: S-1-5-21-91314187-2404433721-1858927112

  Realm name: prod.adexample.com
  Domain NetBIOS name: PROD
  Domain Security Identifier: S-1-5-21-46580863-3346886432-4578854233
----------------------------
Number of entries returned 3
----------------------------

Note

When adding a trust with a shared secret, you need to manually retrieve topology of the AD forest. After running the "ipa trust-add ad.domain --trust-secret" command, validate incoming trust at AD side using forest trust properties in the AD Domains and Trusts tool. Then, run the "ipa trust-fetch-domains ad.domain" command. IdM will receive information about the trust, which will then be usable.

Once the topology is retrieved (through automatic or manual discovery), individual domains and subdomains in that topology can be enabled, disabled, or removed entirely within the IdM trust configuration.

For example, to disallow users from a specific subdomain from using IdM resources, disable that trust domain:

[root@ipaserver ~]# kinit admin
[root@ipaserver ~]# ipa trustdomain-disable test.adexample.com
------------------------------------------
Disabled trust domain "test.adexample.com"
------------------------------------------

That trust domain can be re-enabled using the trustdomain-enable command.

If a domain should be permanently removed from the topology, than it can be deleted from the IdM trust configuration.

[root@ipaserver ~]# kinit admin
[root@ipaserver ~]# ipa trustdomain-del prod.adexample.com
-------------------------------------------------------------------
Removed information about the trusted domain " "prod.adexample.com"
-------------------------------------------------------------------

⁠5.5.3. Viewing and Managing DNS Realms

When a trust is created, the Active Directory DNS configuration is added to the IdM DNS configuration, with each realm being added as a special realm domain. Each domain is stored in the cn=Realm Domains,cn=ipa,cn=etc,dc=example,dc=com subtree in the IdM directory.

Since these realm domains are added automatically, the DNS zones do not generally need to be added or modified. The list of configured realm domains can be displayed (instead of listing all DNS zones configured in IdM) using the realmdomains-show command.

[root@ipaserver ~]# kinit admin
[root@ipaserver ~]# ipa realmdomains-show
 Domain: ipa.example.org, ipa.example.com, example.com

If a single realm domain should be added to the configuration, this can be done with the --add-domain option.

[root@ipaserver ~]# kinit admin
[root@ipaserver ~]# ipa realmdomains-mod --add-domain=adexample.com
 Domain: ipa.example.org, ipa.example.com, example.com, adexample.com

A single domain can be removed using the --del-domain option.

If there are multiple changes to be made to the list of domains, the list itself can be modified and replaced using the --domain option.

[root@ipaserver ~]# ipa realmdomains-mod --domain={ipa.example.org,adexample.com}

⁠5.5.4. Adding Ranges for UID and GID Numbers in a Transitive Trust

Creating ID ranges at the time when a trust is originally configured is described in Section 5.1.3.2, “ID Ranges”. To add an ID range later, use the ipa idrange-add command with the following options:

the --base-id option sets the base ID for the POSIX range, which is the starting number

the --range-size option sets the size of the range

the --rid-base option sets the starting number of the RID, which is the far-right number in the SID; the value represents the range to add to the base ID to prevent conflicts

the --dom-sid option sets the domain SID, because there can be multiple domains configured for trusts

In the following example, the base ID is 1,200,000 and the RID is 1,000. The resulting ID number is then 1,201,000.

[root@server ~]$ kinit admin
[root@server ~]$ ipa idrange-add --base-id=1200000 --range-size=200000 --rid-base=0 --dom-sid=S-1-5-21-123-456-789 trusted_dom_range

Important

Make sure that the manually defined ID range does not overlap with the ID range used by IdM.

⁠5.6. Setting PAC Types for Services

On IdM resources, if an Active Directory user requests a ticket for a service, then IdM forwards the request to Active Directory to retrieve the user information. Access data, associated with the Active Directory group assignments for the user, is sent back by Active Directory and embedded in the Kerberos ticket.

Group information in Active Directory is stored in a list of identifiers in each Kerberos ticket for Active Directory users in a special data set called privileged access certificates or MS-PAC. The group information in the PAC has to be mapped to the Active Directory groups and then to the corresponding IdM groups to help determine access.

IdM services can be configured to generate PACs for each authentication request when a user first attempts to authenticate to a domain service.

⁠5.6.1. Setting Default PAC Types

The IdM server configuration defines which PAC types are generated by default for a service. The global settings can be overridden by changing the local settings on a specific service.

Open the IPA Server tab.

Select the Configuration subtab.

Scroll to the Service Options area.

⁠

Figure 5.7. The Service Options Area

To use PAC, select the MS-PAC check box, which adds a certificate that can be used by AD services. If no check box is selected, then no PAC is added to Kerberos tickets.

If you select the nfs:NONE check box, the MS-PAC record will not be added to the service tickets issued against NFS servers.

Note

You can ignore the PAD check box. This functionality is not yet available in IdM.

Click the Update link at the top of the page to save the changes.

⁠5.6.2. Setting PAC Types for a Service

The global policy sets what PAC types to use for a service if nothing is set explicitly for that service. However, the global settings can be overridden on the local service configuration.

To change the PAC setting from the command line, use the ipa service-mod command with the --pac-type option. For information on how to use the command, run it with the --help option added:

$ ipa service-mod --help
Usage: ipa [global-options] service-mod PRINCIPAL [options]

Modify an existing IPA service.
Options:
-h, --help            show this help message and exit
...

To change the PAC setting in the web UI:

Open the Identity tab, and select the Services subtab.

Click the name of the service to edit.

In the Service Settings area, check the Override inherited settings option and then select the MS-PAC check box to add a certificate that can be used by AD services.

⁠

Figure 5.8. The Service Settings Area

If no check box is selected, then no PACs are added to Kerberos tickets.

Note

You can ignore the PAD check box. This functionality is not yet available in IdM.

Click the Update link at the top of the page to save the changes.

⁠5.7. Transferring POSIX Attributes from Active Directory

Important

The client must be enrolled with an IdM server based on Red Hat Enterprise Linux 7.1 or later to benefit from this functionality.

SSSD is able to read the following attribute values from an Active Directory server in a trust relationship with IdM:

the loginShell attribute, which specifies the AD user's shell

the unixHomeDirectory attribute, which specifies the AD user's home directory

When a custom shell or home directory value is defined on the AD server using these attributes, the custom value is then displayed to the IdM client for the AD user. Therefore, the same user shell is displayed for the AD user both on the AD side and on the IdM side.

Note that to display the AD user's home directory to the IdM client, the subdomain_homedir option in the [domain] section of the /etc/sssd/sssd.conf file on the IdM server must be set to %o. The %o value represents the home directory retrieved from the identity provider. For example:

[domain/example.com]
subdomain_homedir = %o

If the AD administrator modifies loginShell or unixHomeDirectory on the AD side, the change is automatically reflected on the IdM side as well. If the attributes are not defined on the AD server, SSSD uses a template default value. This default value is then displayed to the IdM client.

⁠5.8. Using SSH from Active Directory Machines for IdM Resources

When a trust is configured, Active Directory users can access machines, services, and files on IdM hosts using SSH and their AD credentials.

⁠5.8.1. Using SSH Without Passwords

The localauth Kerberos plug-in for local authorization ensures that Kerberos principals are automatically mapped to local SSSD user names. With localauth, Windows users from a trusted AD domain are not prompted for a password when logging in using Kerberos and can therefore use SSH without passwords.

The plug-in provides a reliable mapping mechanism across multiple realms and trusts: it obtains the Kerberos principal and the POSIX user name from the sshd service and maps them to an SSSD-provided user entry. The localauth plug-in is enabled by default on Red Hat Enterprise Linux 7 systems running Red Hat Enterprise Linux 7.1 and later.

Note

On systems with localauth, it is not required to set the auth_to_local option in the /etc/krb5.conf file or list Kerberos principals in the .k5login file. The localauth plug-in makes this previously-used configuration for passwordless login obsolete.

⁠Kerberos Authentication for AD Users on Red Hat Enterprise Linux 7.0 Systems

On systems running Red Hat Enterprise Linux 7.0, the localauth plug-in is not present. On these systems, using SSH still prompts for a user password for Active Directory domain users even if the user obtains a proper Kerberos ticket.

To enable Active Directory users to use Kerberos for authentication in this situation, configure the auth_to_local option in the /etc/krb5.conf file or list the user Kerberos principals in the .k5login file in the home directory of the user.

Configuring /etc/krb5.conf

The following procedure describes how to configure realm mapping in the Kerberos configuration.

⁠

Open the /etc/krb5.conf file.

In the [realms] section, identify the IdM realm by name, and then add two auth_to_local lines to define the Kerberos principal name mapping:

In one rule, include a rule to map different Active Directory user name formats and the specific Active Directory domain.

In the other rule, set the value of DEFAULT, for standard Unix user names.

For example:

[realms]
IDM = {
....
auth_to_local = RULE:[1:$1@$0](^.*@ADDOMAIN$)s/@ADDOMAIN/@addomain/
auth_to_local = DEFAULT
}

Restart the KDC service.

[root@server ~]# systemctl restart krb5kdc.service

Note that if you configure Kerberos authentication using the auth_to_local option, the user name used for SSH access must meet the following criteria:

The user name must have the format ad_user@ad_domain.

The domain name must be lower-case.

The case of the user name must match the case of the user name in Active Directory. For example, user and User are considered different users because of the different cases.

For more information about setting auth_to_local, see the krb5.conf(5) man page.

Configuring .k5login

The following procedure configures the system to find the Kerberos principal name for a local user name.

⁠

Create the .k5login file in the user's home directory.

List the Kerberos principals used by the user in the file.

If the authenticating user matches the principal in an existing Kerberos ticket, the user is allowed to log in using the ticket and is not prompted for a password.

Note that if you configure Kerberos authentication using the .k5login configuration, the user name used for SSH access must have the format ad_user@ad_domain.

For more information about configuring the .k5login file, see the .k5login(5) man page.

Either one of these configuration procedures results in AD users being able to log in using Kerberos.

⁠5.9. Using Trust with Kerberized Web Applications

Any existing web application can be configured to use Kerberos authentication, which references the trusted Active Directory and IdM Kerberos realms. For the full Kerberos configuration directives, see the Configuration page for the mod_auth_kerb module.

Note

After changing the Apache application configuration, restart the Apache service:

[root@ipaserver ~]# systemctl restart httpd.service

For example, for an Apache server, there are several options that define how the Apache server connects to the IdM Kerberos realm:

KrbAuthRealms

The KrbAuthRealms option gives the application location to the name of the IdM domain. This is required.

Krb5Keytab

The Krb5Keytab option gives the location for the IdM server keytab. This is required.

KrbServiceName

The KrbServiceName option sets the Kerberos service name used for the keytab (HTTP). This is recommended.

KrbMethodK5Passwd and KrbMethodNegotiate

The KrbMethodK5Passwd Kerberos method option enables password-based authentication for valid users. The KrbMethodNegotiate option enables single sign-on (SSO) if a valid Kerberos ticket is available.

These options are recommended for ease of use for many users.

KrbLocalUserMapping

The KrbLocalUserMapping option enables normal web logins (which are usually the UID or common name of the account) to be mapped to the fully-qualified username (which has a format of user@REALM.COM).

This option is strongly recommended. Without the domain name/login name mapping, the web login appears to be a different user account than the domain user. This means that users cannot see their expected data.

For information on supported user name formats, see Section 5.2.7, “Supported User Name Formats”.

⁠

Example 5.1. Kerberos Configuration in an Apache Web Application

​<Location "/mywebapp">
​   AuthType Kerberos
​   AuthName "IPA Kerberos authentication"
​   KrbMethodNegotiate on
​   KrbMethodK5Passwd on
​   KrbServiceName HTTP
​   KrbAuthRealms IDM_DOMAIN
​   Krb5Keytab /etc/httpd/conf/ipa.keytab
​   KrbLocalUserMapping on
​   KrbSaveCredentials off
​   Require valid-user
​</Location>

⁠5.10. Active Directory Trust for Legacy Linux Clients

Linux clients running Red Hat Enterprise Linux with SSSD version 1.8 or earlier (legacy clients) do not provide native support for IdM cross-forest trusts with Active Directory. Therefore, for AD users to be able to access services provided by the IdM server, the legacy Linux clients and the IdM server have to be properly configured.

Instead of using SSSD version 1.9 or later to communicate with the IdM server to obtain LDAP information, legacy clients use other utilities for this purpose, for example nss_ldap, nss-pam-ldapd, or SSSD version 1.8 or earlier. Clients running the following versions of Red Hat Enterprise Linux do not use SSSD 1.9 and are therefore considered to be legacy clients:

Red Hat Enterprise Linux 5.7 or later

Red Hat Enterprise Linux 6.0 – 6.3

Important

Do not use the configuration described in this section for non-legacy clients, that is, clients running SSSD version 1.9 or later. SSSD 1.9 or later provides native support for IdM cross-forest trusts with AD, meaning AD users can properly access services on IdM clients without any additional configuration.

When a legacy client joins the domain of an IdM server in a trust relationship with AD, a compat LDAP tree provides the required user and group data to AD users. However, the compat tree enables the AD users to access only a limited number of IdM services.

Legacy clients do not provide access to the following services:

Kerberos authentication

host-based access control (HBAC)

SELinux user mapping

sudo rules

Access to the following services is provided even in case of legacy clients:

information look-up

password authentication

⁠5.10.1. Server-Side Configuration for AD Trust for Legacy Clients

Make sure the IdM server meets the following configuration requirements:

The ipa-server package for IdM and the ipa-server-trust-ad package for the IdM trust add-on have been installed.

The ipa-server-install utility has been run to set up the IdM server.

The ipa-adtrust-install --enable-compat command has been run, which ensures that the IdM server supports trusts with AD domains and that the compat LDAP tree is available.

If you have already run ipa-adtrust-install without the --enable-compat option in the past, run it again, this time adding --enable-compat.

The ipa trust-add ad.example.org command has been run to establish the AD trust.

If the host-based access control (HBAC) allow_all rule is disabled, enable the system-auth service on the IdM server, which allows authentication of the AD users.

You can determine the current status of allow_all directly from the command line using the ipa hbacrule-show command. If the rule is disabled, Enabled: FALSE is displayed in the output:

[user@server ~]$ kinit admin
[user@server ~]$ ipa hbacrule-show allow_all
  Rule name: allow_all
  User category: all
  Host category: all
  Service category: all
  Description: Allow all users to access any host from any host
  Enabled: FALSE

Note

For information on disabling and enabling HBAC rules, see the Linux Domain Identity, Authentication, and Policy Guide.

To enable system-auth on the IdM server, create an HBAC service named system-auth and add an HBAC rule using this service to grant access to IdM masters. Adding HBAC services and rules is described in the Linux Domain Identity, Authentication, and Policy Guide. Note that HBAC services are PAM service names; if you add a new PAM service, make sure to create an HBAC service with the same name and then grant access to this service through HBAC rules.

⁠5.10.2. Client-Side Configuration Using the ipa-advise Utility

The ipa-advise utility provides the configuration instructions to set up a legacy client for an AD trust.

To display the complete list of scenarios for which ipa-advise can provide configuration instructions, run ipa-advise without any options. Running ipa-advise prints the names of all available sets of configuration instructions along with the descriptions of what each set does and when it is recommended to be used.

[root@server ~]# ipa-advise
config-redhat-nss-ldap		: Instructions for configuring a system
				  with nss-ldap as a IPA client.
				  This set of instructions is targeted
				  for platforms that include the
				  authconfig utility, which are all
				  Red Hat based platforms.
config-redhat-nss-pam-ldapd	: Instructions for configuring a system
(...)

To display a set of instructions, run the ipa-advise utility with an instruction set as a parameter:

[root@server ~]# ipa-advise config-redhat-nss-ldap
#!/bin/sh
# ----------------------------------------------------------------------
# Instructions for configuring a system with nss-ldap as a IPA client.
# This set of instructions is targeted for platforms that include the
# authconfig utility, which are all Red Hat based platforms.
# ----------------------------------------------------------------------
# Schema Compatibility plugin has not been configured on this server. To
# configure it, run "ipa-adtrust-install --enable-compat"
# Install required packages via yum
yum install -y wget openssl nss_ldap authconfig

# NOTE: IPA certificate uses the SHA-256 hash function. SHA-256 was
# introduced in RHEL5.2. Therefore, clients older than RHEL5.2 will not
# be able to interoperate with IPA server 3.x.
# Please note that this script assumes /etc/openldap/cacerts as the
# default CA certificate location. If this value is different on your
# system the script needs to be modified accordingly.
# Download the CA certificate of the IPA server
mkdir -p -m 755 /etc/openldap/cacerts
wget http://vm-093.idm.lab.eng.brq.redhat.com/ipa/config/ca.crt -O /etc/openldap/cacerts/ipa.crt
(...)

You can configure a Linux client using the ipa-advise utility by running the displayed instructions as a shell script or by executing the instructions manually.

To run the instructions as a shell script:

⁠

Create the script file.

[root@server ~]# ipa-advise config-redhat-nss-ldap > setup_script.sh

Add execute permissions to the file using the chmod utility.

[root@server ~]# chmod +x setup_script.sh

Copy the script to the client using the scp utility.

[root@server ~]# scp setup_script.sh root@client

Run the script on the client.

[root@client ~]# ./setup_script.sh

Important

Always read and review the script file carefully before you run it on the client.

To configure the client manually, follow and execute the instructions displayed by ipa-advise from the command line.

⁠Chapter 6. Setting up Kerberos Cross-Realm Authentication

Kerberos v5 creates a realm of clients. That realm can be trust and integrate with an Active Directory domain, as well as other Kerberos domains. Kerberos itself is system-agnostic, so it can work in a number of different environments, systems, and applications.

A lot of Linux environments (and mixed environments) will already have a Kerberos realm deployed for single sign-on, application authentication, and user management. That makes Kerberos a potentially common integration path for mixed Windows-Linux environments, particularly if the Linux environment is not using a more structured domain configuration like Identity Management.

⁠6.1. A Trust Relationship

Kerberos implements a concept of trust. In a trust, a principal from one Kerberos realm can request a ticket to a service in another Kerberos realm. Using this ticket, the principal can authenticate against resources on machines belonging to the other realm.

This is achieved by creating a shared key for a single principal that is held in common by both domains.

⁠

Figure 6.1. Basic Trust

In Figure 6.1, “Basic Trust”, the shared principal would belong to Domain B (krbtgt/B.EXAMPLE.COM@A.EXAMPLE.COM). When that principal is also added to Domain A, then the clients in Domain A can access the resources in Domain B. The configured principal exists in both realms. That shared principal has three characteristics:

It exists in both realms.

When a key is created, the same password is used in both realms.

The key has the same key version number (kvno).

A cross-realm trust is unidirectional by default. This trust is not automatically reciprocated so that the B.EXAMPLE.COM realm are trusted to authenticate to services in the A.EXAMPLE.COM realm. To establish trust in the other direction, both realms would need to share keys for the krbtgt/A.EXAMPLE.COM@B.EXAMPLE.COM service — an entry with a reverse mapping from the previous example.

A realm can have multiple trusts, both realms that it trusts and realms it is trusted by. With Kerberos trusts, the trust can flow in a chain. If Realm A trusts Realm B and Realm B trusts Realm C, Realm A implicity trusts Realm C, as well. The trust flows along realms; this is a transitive trust.

⁠

Figure 6.2. Transitive Trust

The direction of a transitive trust is the trust flow. The trust flow has to be defined, first by recognizing to what realm a service belongs and then by identifying what realms a client must contact to access that service.

A Kerberos principal name is structured in the format service/hostname@REALM. The service is generally a protocol, such as LDAP, IMAP, HTTP, or host. The hostname is the fully-qualified domain name of the host system, and the REALM is the Kerberos realm to which it belongs. Clients usually map the hostname or DNS domain name to the realm. The realm, then, somewhat related to the DNS domain name (unless a realm is explicitly defined in the domain_realm section of /etc/krb5.conf).

When traversing a trust, Kerberos assumes that each realm is structured like a hierarchical DNS domain, with a root domain and subdomains. This means that the trust flows up to a shared root. Each step, or hop, has a shared key. In Figure 6.3, “Trusts in the Same Domain”, A shares a key with EXAMPLE.COM, and EXAMPLE.COM shares a key with B.

⁠

Figure 6.3. Trusts in the Same Domain

The client treats the relam name as a DNS name, and it determines its trust path by stripping off elements of its own realm name until it reaches the root name. It then begins prepending names until it reaches the service's realm.

⁠

Figure 6.4. Child/Parent Trusts in the Same Domain

This is a nature of trusts being transitive. SITE.SALES.EXAMPLE.COM only has a single shared key, with SALES.EXAMPLE.COM. But because of a series of small trusts, there is a large trust flow that allows trust to go from SITE.SALES.EXAMPLE.COM to EVERYWHERE.EXAMPLE.COM.

That trust flow can even go between completely different domains by creating a shared key at the domain level, where the sites share no common suffix.

⁠

Figure 6.5. Trusts in Different Domains

It is also possible to reduce the number of hops and represent very complex trust flows by explicitly defining the flow. The capaths section of the /etc/krb5.conf file defines the trust flow between different realms.

The format of the capaths section is relatively straightforward: there is a main entry for each realm where a client has a principal, and then inside each realm section is a list of intermediate realms from which the client must obtain credentials.

For example, this has the realm of A.EXAMPLE.COM, and a set of hops from A to D. A client in Realm A must obtain credentials first from Realm B (the . means that it can obtain credentials directly, without any intermmediate hops; otherwise, it would attempt to gain credentials by going through a hierarchy). It must then use the B credentials to obtain credentials from C, and then use the C credentials to obtain credentials for D.

​[capaths]
​A.EXAMPLE.COM = {
​B.EXAMPLE.COM = .
​C.EXAMPLE.COM = B.EXAMPLE.COM
​D.EXAMPLE.COM = C.EXAMPLE.COM
​}

⁠6.2. Setting up a Realm Trust

In this example, the Kerberos realm is KRB.EXAMPLE.COM, and the Active Directory domain is AD.EXAMPLE.COM.

Create the entry for the shared principal in Kerberos, using kadmin.

​[root@server ~]# kadmin -r KRB.EXAMPLE.COM
​kadmin: add_principal krbtgt/AD.EXAMPLE.COM@KRB.EXAMPLE.COM
​Enter password for principal "krbtgt/AD.EXAMPLE.COM@KRB.EXAMPLE.COM":
​Re-enter password for principal "krbtgt/AD.EXAMPLE.COM@KRB.EXAMPLE.COM":
​Principal "krbtgt/AD.EXAMPLE.COM@KRB.EXAMPLE.COM" created.
​quit

A realm trust is configured in the Active Directory Domains and Trusts console. Select the appropriate domain, and create a new trust. These are the settings to use:

The Trust Type is Realm.

The Transitivity of Trust can be either transitive or non-transitive.

The Direction of Trust is One-way: incoming. This trusts Active Directory users in the Kerberos realm.

This creates a unidirectional trust, where Active Directory users are trusted in the Kerberos realm. To create a two-way trust, set the direction of trust to two-way. This is described in the Microsoft TechNet documentation.

The Sides of Trust is This domain only.

The Trust Password can be anything. This must be used when configuring the trust in Kerberos.

⁠Chapter 7. Synchronizing Active Directory and Identity Management Users

Red Hat Enterprise Linux Identity Management uses active synchronization to combine the user data stored in an Active Directory domain and the user data stored in the IdM domain. Critical user attributes, including passwords, are copied and synchronized between the services.

Entry synchronization is performed through a process similar to replication, which uses hooks to connect to and retrieve directory data from the Windows server. This is functionality is available immediately in Identity Management, with no additional configuration in the Active Directory domain.

Password synchronization is performed through a Windows service which is installed on the Windows server and then communicates to the Identity Management server.

⁠7.1. Supported Windows Platforms

Synchronization are supported with these Windows servers:

Windows Server 2008 R2

Windows Server 2012 R2

The version of the password sync service which works with Windows is 1.1.5. This is available in the Red Hat Directory Server downloads part of Red Hat Network.

⁠7.2. About Active Directory and Identity Management

Within the IdM domain, information is shared among servers and replicas by copying that information, reliably and predictably, between data masters (servers and replicas). This process is replication.

A similar process can be used to share data between the IdM domain and a Microsoft Active Directory domain. This is synchronization.

Synchronization is the process of copying user data back and forth between Active Directory and Identity Management.

⁠

Figure 7.1. Active Directory and IdM Synchronization

Synchronization is defined in an agreement between an IdM server and an Active Directory domain controller. The sync agreement defines all of the information required to identify sync-able user entries (like the subtree to synchronize and requisite object classes in the user entries) as well as defining how account attributes are handled. The sync agreements are created with default values which can be tweaked to meet the needs of a specific domain. When two servers are involved in synchronization, they are called peers.

⁠

Table 7.1. Information in a Sync Agreement

Windows Information
IdM Information

User subtree (cn=Users,$SUFFIX)

Connection information

Active Directory administrator username and password

Password Sync Service password

CA certificate

User subtree (ou=People,$SUFFIX)

Synchronization is most commonly bi-directional. Information is sent back and forth between the IdM domain and the Windows domain in a process that is very similar to how IdM servers and replicas share information among themselves. It is possible to configure synchronization to only sync one way. That is uni-directional synchronization.

To prevent the risk of data conflicts, only one directory should originate or remove user entries. This is typically the Windows directory, which is the primary identity store in the IT environment, and then new accounts or account deletions are synced to the Identity Management peer. Either directory can modify entries.

Synchronization, then, is configured between one Identity Management server and one Active Directory domain controller. The Identity Management server propagates throughout to the IdM domain, while the domain controller propagates changes throughout the Windows domain.

⁠

Figure 7.2. Synchronization Topology

There are some key features to IdM synchronization:

A synchronization operation runs every five minutes.

Synchronization can only be configured with one Active Directory domain.

Synchronization can only be configured with one Active Directory domain controller.

Only user information is synchronized.

Both user attributes and passwords can be synchronized.

While modifications are bi-directional (going both from Active Directory to IdM and from IdM to Active Directory), creating accounts is only uni-directional, from Active Directory to Identity Management. New accounts created in Active Directory are synchronized over to IdM automatically. However, user accounts created in IdM must also be created in Active Directory before they will be synchronized.

Account lock information is synchronized by default, so a user account which is disabled in one domain is disabled in the other.

Password synchronization changes take effect immediately. If a user password is added or changed on one peer, that change is immediately propagated to the other peer server.

The Password Sync client synchronizes new passwords or password updates.

Existing passwords, which are stored in a hashed form in both IdM and Active Directory, cannot be decrypted or synchronized when the Password Sync client is installed, so existing passwords are not synchronized. User passwords must be changed to initiate synchronization between the peer servers.

When Active Directory users are synchronized over to IdM, certain attributes (including Kerberos and POSIX attributes) will have IPA attributes are automatically added to the user entries. These attributes are used by IdM within its domain. They are not synchronized back over the corresponding Active Directory user entry.

Some of the data in synchronization can be modified as part of the synchronization process. For examples, certain attributes can be automatically added to Active Directory user accounts when they are synced over to the IdM domain. These attribute changes are defined as part of the synchronization agreement and are described in Section 7.5.3, “Changing the Behavior for Syncing User Account Attributes”.

⁠7.3. About Synchronized Attributes

Identity Management synchronizes a subset of user attributes between IdM and Active Directory user entries. Any other attributes present in the entry, either in Identity Management or in Active Directory, are ignored by synchronization.

NOTE

Most POSIX attributes are not synchronized.

Although there are significant schema differences between the Active Directory LDAP schema and the 389 Directory Server LDAP schema used by Identity Management, there are many attributes that are the same. These attributes are simply synchronized between the Active Directory and IdM user entries, with no changes to the attribute name or value format.

⁠

User Schema That Are the Same in Identity Management and Windows Servers

cn ⁠[5]

physicalDeliveryOfficeName

description

postOfficeBox

destinationIndicator

postalAddress

facsimileTelephoneNumber

postalCode

givenname

registeredAddress

homePhone

sn

homePostalAddress

st

initials

street

l

telephoneNumber

mail

teletexTerminalIdentifier

mobile

telexNumber

o

title

ou

userCertificate

pager

x121Address

Some attributes have different names but still have direct parity between IdM (which uses 389 Directory Server) and Active Directory. These attributes are mapped by the synchronization process.

⁠

Table 7.2. User Schema Mapped between Identity Management and Active Directory

Identity Management
Active Directory

cn ⁠[a]
name

nsAccountLock
userAccountControl

ntUserDomainId
sAMAccountName

ntUserHomeDir
homeDirectory

ntUserScriptPath
scriptPath

ntUserLastLogon
lastLogon

ntUserLastLogoff
lastLogoff

ntUserAcctExpires
accountExpires

ntUserCodePage
codePage

ntUserLogonHours
logonHours

ntUserMaxStorage
maxStorage

ntUserProfile
profilePath

ntUserParms
userParameters

ntUserWorkstations
userWorkstations

[a] The cn is mapped directly (cn to cn) when syncing from Identity Management to Active Directory. When syncing from Active Directory cn is mapped from the name attribute in Active Directory to the cn attribute in Identity Management.

⁠7.3.1. User Schema Differences between Identity Management and Active Directory

Even though attributes may be successfully synced between Active Directory and IdM, there may still be differences in how Active Directory and Identity Management define the underlying X.500 object classes. This could lead to differences in how the data are handled in the different LDAP services.

This section describes the differences in how Active Directory and Identity Management handle some of the attributes which can be synchronized between the two domains.

⁠7.3.1.1. Values for cn Attributes

In 389 Directory Server, the cn attribute can be multi-valued, while in Active Directory this attribute must have only a single value. When the Identity Management cn attribute is synchronized, then, only one value is sent to the Active Directory peer.

What this means for synchronization is that,potentially, if a cn value is added to an Active Directory entry and that value is not one of the values for cn in Identity Management, then all of the Identity Management cn values are overwritten with the single Active Directory value.

One other important difference is that Active Directory uses the cn attribute as its naming attribute, where Identity Management uses uid. This means that there is the potential to rename the entry entirely (and accidentally) if the cn attribute is edited in the Identity Management. If that cn change is written over to the Active Directory entry, then the entry is renamed, and the new named entry is written back over to Identity Management.

⁠7.3.1.2. Values for street and streetAddress

Active Directory uses the attribute streetAddress for a user's postal address; this is the way that 389 Directory Server uses the street attribute. There are two important differences in the way that Active Directory and Identity Management use the streetAddress and street attributes, respectively:

In 389 Directory Server, streetAddress is an alias for street. Active Directory also has the street attribute, but it is a separate attribute that can hold an independent value, not an alias for streetAddress.

Active Directory defines both streetAddress and street as single-valued attributes, while 389 Directory Server defines street as a multi-valued attribute, as specified in RFC 4519.

Because of the different ways that 389 Directory Server and Active Directory handle streetAddress and street attributes, there are two rules to follow when setting address attributes in Active Directory and Identity Management:

The synchronization process maps streetAddress in the Active Directory entry to street in Identity Management. To avoid conflicts, the street attribute should not be used in Active Directory.

Only one Identity Management street attribute value is synced to Active Directory. If the streetAddress attribute is changed in Active Directory and the new value does not already exist in Identity Management, then all street attribute values in Identity Management are replaced with the new, single Active Directory value.

⁠7.3.1.3. Constraints on the initials Attribute

For the initials attribute, Active Directory imposes a maximum length constraint of six characters, but 389 Directory Server does not have a length limit. If an initials attribute longer than six characters is added to Identity Management, the value is trimmed when it is synchronized with the Active Directory entry.

⁠7.3.1.4. Requiring the surname (sn) Attribute

Active Directory allows person entries to be created without a surname attribute. However, RFC 4519 defines the person object class as requiring a surname attribute, and this is the definition used in Directory Server.

If an Active Directory person entry is created without a surname attribute, that entry will not be synced over to IdM since it fails with an object class violation.

⁠7.3.2. Active Directory Entries and POSIX Attributes

Windows uses unique, random security IDs (SIDs) to identify users. These SIDs are assigned in blocks or ranges, identifying different system user types within the Windows domain. When users are synchronized between Identity Management and Active Directory, Windows SIDs for users are mapped to the Unix UIDs used by the Identity Management entry. Another way of saying this is that the Windows SID is the only ID within the Windows entry which is used as an identifier in the corresponding Unix entry, and then it is used in a mapping.

When Active Directory domains interact with Unix-style applications or domains, then the Active Directory domain may use Services for Unix or IdM for Unix to enable Unix-style uidNumber and gidNumber attributes. This allows Windows user entries to follow the specifications for those attributes in RFC 2307.

However, the uidNumber and gidNumber attributes are not actually used as the uidNumber and gidNumber attributes for the Identity Management entry. The Identity Management uidNumber and gidNumber attributes are generated when the Windows user is synced over.

NOTE

The uidNumber and gidNumber attributes defined and used in Identity Management are not the same uidNumber and gidNumber attributes defined and used in the Active Directory entry, and the numbers are not related.

⁠7.4. Setting up Active Directory for Synchronization

Synchronizing user accounts alone is enabled within IdM, so all that is necessary is to set up a sync agreement (Section 7.5.2, “Creating Synchronization Agreements”). However, the Active Directory does need to be configured in a way that allows the Identity Management server to connect to it.

⁠7.4.1. Creating an Active Directory User for Sync

On the Windows server, it is necessary to create the user that the IdM server will use to connect to the Active Directory domain.

The process for creating a user in Active Directory is covered in the Windows server documentation at http://technet.microsoft.com/en-us/library/cc732336.aspx. The new user account must have the proper permissions:

Grant the sync user account Replicating directory changes rights to the synchronized Active Directory subtree. Replicator rights are required for the sync user to perform synchronization operations.

Replicator rights are described in http://support.microsoft.com/kb/303972.

Add the sync user as a member of the Account Operator and Enterprise Read-Only Domain controller groups. It is not necessary for the user to belong to the full Domain Admin group.

⁠7.4.2. Setting up an Active Directory Certificate Authority

The Identity Management server connects to the Active Directory server using a secure connection. This requires that the Active Directory server have an available CA certificate or CA certificate chain available, which can be imported into the Identity Management security databases, so that the Windows server is a trusted peer.

While this could technically be done with an external (to Active Directory) CA, most deployments should use the Certificate Services available with Active Directory.

The procedure for setting up and configuring certificate services on Active Directory is covered in the Microsoft documentation at http://technet.microsoft.com/en-us/library/cc772393(v=WS.10).aspx.

⁠7.5. Managing Synchronization Agreements

⁠7.5.1. Trusting the Active Directory and IdM CA Certificates

Both Active Directory and Identity Management use certificates for server authentication. For the Active Directory and IdM SSL server certificates to be trusted by each other, both servers need to trust the CA certificate for the CA which issued those certificates. This means that the Active Directory CA certificate needs to be imported into the IdM database, and the IdM CA certificate needs to be imported into the Active Directory database.

On the Active Directory server, download the IdM server's CA certificate from http://ipa.example.com/ipa/config/ca.crt.

Install the IdM CA certificate in the Active Directory certificate database. This can be done using the Microsoft Management Console or the certutil utility.

Right-click on the executable, and select Run as administrator, then run certutil with the -installcert option. For example:

C:\Windows\system32\certutil -installcert -v -config "ipaserver.example.com\Example Domain CA" c:\path\to\ca.crt

This command must be run as an administrative account, or it will fail because it cannot access the certificate database.

For more details on installing certificates, see the Active Directory documentation.

Export the Active Directory CA certificate.

In My Network Places, open the CA distribution point.

Double-click the security certificate file (.crt file) to display the Certificate dialog box.

On the Details tab, click Copy to File to start the Certificate Export Wizard.

Click Next, and then select Base-64 encoded X.509 (.CER).

Specify a suitable directory and file name for the exported file. Click Next to export the certificate, and then click Finish.

Copy the Active Directory certificate over to the IdM server machine.

Download the IdM server's CA certificate from http://ipa.example.com/ipa/config/ca.crt.

Copy both the Active Directory CA certificate and the IdM CA certificate into the /etc/openldap/cacerts/ directory.

Update the hash symlinks for the certificates.

cacertdir_rehash /etc/openldap/cacerts/

Edit the /etc/openldap/ldap.conf file, and add the information to point to and use the certificates in the /etc/openldap/cacerts/ directory.

TLS_CACERTDIR /etc/openldap/cacerts/
TLS_REQCERT allow

⁠7.5.2. Creating Synchronization Agreements

Synchronization agreements are created on the IdM server using the ipa-replica-manage connect command because it creates a connection to the Active Directory domain. The options to create the synchronization agreement are listed in Table 7.3, “Synchronization Agreement Options”.

Make sure that the Active Directory and IdM servers trust each other's CA certificates, as in Section 7.5.1, “Trusting the Active Directory and IdM CA Certificates”.

Remove any existing Kerberos credentials on the IdM server.

$ kdestroy

Use the ipa-replica-manage command to create a Windows synchronization agreement. This requires the --winsync option. If passwords will be synchronized as well as user accounts, then also use the --passsync option and set a password to use for Password Sync.

The --binddn and--bindpwd options give the username and password of the system account on the Active Directory server that IdM will use to connect to the Active Directory server.

$ ipa-replica-manage connect --winsync
	--binddn cn=administrator,cn=users,dc=example,dc=com
	--bindpw Windows-secret
	--passsync secretpwd
	--cacert /etc/openldap/cacerts/windows.cer
	adserver.example.com -v

When prompted, enter the Directory Manager password.

Optional. Configure Password Synchronization, as in Section 7.6.2, “Setting up Password Synchronization”. Without the Password Sync client, user attributes are synchronized between the peer servers, but passwords are not.

NOTE

The Password Sync client captures password changes and then synchronizes them between Active Directory and IdM. This means that it synchronizes new passwords or password updates.

Existing passwords, which are stored in a hashed form in both IdM and Active Directory, cannot be decrypted or synchronized when the Password Sync client is installed, so existing passwords are not synchronized. User passwords must be changed to initiate synchronization between the peer servers.

⁠

Table 7.3. Synchronization Agreement Options

Option | Description
--winsync | Identifies this as a synchronization agreement.
--binddn | Gives the full user DN of the synchronization identity. This is the user DN that the IdM LDAP server uses to bind to Active Directory. This user must exist in the Active Directory domain and must have replicator, read, search, and write permissions on the Active Directory subtree.
--bindpw | Gives the password for the sync user.
--passsync | Gives the password for the Windows user account which is involved in synchronization.
--cacert | Gives the full path and file name of the Active Directory CA certificate. This certificate is exported in Section 7.5.1, “Trusting the Active Directory and IdM CA Certificates”.
--win-subtree | Gives the DN of the Windows subtree containing the users to synchronize. The default value is cn=Users,$SUFFIX.
AD_server_name | Gives the hostname of the Active Directory domain controller.

⁠7.5.3. Changing the Behavior for Syncing User Account Attributes

When the sync agreement is created, it has certain default behaviors defined for how the synchronization process handles the user account attributes during synchronization. The types of behaviors are things like how to handle lockout attributes or how to handle different DN formats. This behavior can be changed by editing the synchronization agreement. The list of attribute-related parameters are in Table 7.4, “Synced Attribute Settings”.

The sync agreement exists as a special plug-in entry in the LDAP server and each attribute behavior is set through an LDAP attribute. To change the sync behavior, use the ldapmodify command to modify the LDAP server entry directly.

For example, account lockout attributes are synchronized between IdM and Active Directory by default, but this can be disabled by editing the ipaWinSyncAcctDisable attribute. (Changing this means that if an account is disabled in Active Directory, it is still active in IdM and vice versa.)

[jsmith@ipaserver ~]$ ldapmodify -x -D "cn=directory manager" -w password

dn: cn=ipa-winsync,cn=plugins,cn=config
changetype: modify
replace: ipaWinSyncAcctDisable
ipaWinSyncAcctDisable: none

modifying entry "cn=ipa-winsync,cn=plugins,cn=config"

⁠

Table 7.4. Synced Attribute Settings

Parameter
Description
Possible Values

General User Account Parameters

ipaWinSyncNewEntryFilter
Sets the search filter to use to find the entry which contains the list of object classes to add to new user entries.
The default is (cn=ipaConfig).

ipaWinSyncNewUserOCAttr
Sets the attribute in the configuration entry which actually contains the list of object classes to add to new user entries.
The default is ipauserobjectclasses.

ipaWinSyncHomeDirAttr
Identifies which attribute in the entry contains the default location of the POSIX home directory.
The default is ipaHomesRootDir.

ipaWinSyncUserAttr
Sets an additional attribute with a specific value to add to Active Directory users when they are synced over from the Active Directory domain. If the attribute is multi-valued, then it can be set multiple times, and the sync process adds all of the values to the entry.

NOTE

This only sets the attribute value if the entry does not already have that attribute present. If the attribute is present, then the entry's value is used when the Active Directory entry is synced over.

ipaWinSyncUserAttr: attributeName attributeValue

ipaWinSyncForceSync
Sets whether to check existing IdM users which match an existing Active Directory user should be automatically edited so they can be synchronized. If an IdM user account has a uid parameter which is identical to the sAMAccountName in an existing Active Directory user, then that account is not synced by default. This attribute tells the sync service to add the ntUser and ntUserDomainId to the IdM user entries automatically, which allows them to be synchronized.
true | false

User Account Lock Parameters

ipaWinSyncAcctDisable
Sets which way to synchronize account lockout attributes. It is possible to control which account lockout settings are in effect. For example, to_ad means that when account lockout attribute is set in IdM, its value is synced over to Active Directory and overrides the local Active Directory value. By default, account lockout attributes are synced from both domains.

both (default)

to_ad

to_ds

none

ipaWinSyncInactivatedFilter
Sets the search filter to use to find the DN of the group used to hold inactivated (disabled) users. This does not need to be changed in most deployments.
The default is (&(cn=inactivated)(objectclass=groupOfNames)).

ipaWinSyncActivatedFilter
Sets the search filter to use to find the DN of the group used to hold active users. This does not need to be changed in most deployments.
The default is (&(cn=activated)(objectclass=groupOfNames)).

Group Parameters

ipaWinSyncDefaultGroupAttr
Sets the attribute in the new user account to reference to see what the default group for the user is. The group name in the entry is then used to find the gidNumber for the user account.
The default is ipaDefaultPrimaryGroup.

ipaWinSyncDefaultGroupFilter
Sets the search filter to map the group name to the POSIX gidNumber.
The default is (&(gidNumber=*)(objectclass=posixGroup)(cn=groupAttr_value)).

Realm Parameters

ipaWinSyncRealmAttr
Sets the attribute which contains the realm name in the realm entry.
The default is cn.

ipaWinSyncRealmFilter
Sets the search filter to use to find the entry which contains the IdM realm name.
The default is (objectclass=krbRealmContainer).

⁠7.5.4. Changing the Synchronized Windows Subtree

Creating a synchronization agreement automatically sets the two subtrees to use as the synchronized user database. In IdM, the default is cn=users,cn=accounts,$SUFFIX, and for Active Directory, the default is CN=Users,$SUFFIX.

The value for the Active Directory subtree can be set to a non-default value when the sync agreement is created by using the --win-subtree option. After the agreement is created, the Active Directory subtree can be changed by using the ldapmodify command to edit the nsds7WindowsReplicaSubtree value in the sync agreement entry.

Get the name of the sync agreement, using ldapsearch. This search returns only the values for the dn and nsds7WindowsReplicaSubtree attributes instead of the entire entry.

[jsmith@ipaserver ~]$ ldapsearch -xLLL -D "cn=directory manager" -w password -p 389 -h ipaserver.example.com -b cn=config objectclass=nsdswindowsreplicationagreement dn nsds7WindowsReplicaSubtree

dn: cn=meToWindowsBox.example.com,cn=replica,cn=dc\3Dexample\2Cdc\3Dcom,cn=mapping tree,cn=config
nsds7WindowsReplicaSubtree: cn=users,dc=example,dc=com

... 8< ...

Modify the sync agreement

[jsmith@ipaserver ~]$ ldapmodify -x -D "cn=directory manager" -W -p 389 -h ipaserver.example.com <<EOF
 dn: cn=meToWindowsBox.example.com,cn=replica,cn=dc\3Dexample\2Cdc\3Dcom,cn=mapping tree,cn=config
 changetype: modify
 replace: nsds7WindowsReplicaSubtree
 nsds7WindowsReplicaSubtree: cn=alternateusers,dc=example,dc=com
 EOF

 modifying entry "cn=meToWindowsBox.example.com,cn=replica,cn=dc\3Dexample\2Cdc\3Dcom,cn=mapping tree,cn=config"

The new subtree setting takes effect immediately. If a sync operation is currently running, then it takes effect as soon as the current operation completes.

⁠7.5.5. Configuring Uni-Directional Sync

By default, all modifications and deletions are bi-directional. A change in Active Directory is synced over to Identity Management, and a change to an entry in Identity Management is synced over to Active Directory. This is essentially an equitable, multi-master relationship, where both Active Directory and Identity Management are equal peers in synchronization and are both data masters.

However, there can be some data structure or IT designs where only one domain should be a data master and the other domain should accept updates. This changes the sync relationship from a multi-master relationship (where the peer servers are equal) to a master-consumer relationship.

This is done by setting the oneWaySync parameter on the sync agreement. The possible values are fromWindows (for Active Directory to Identity Management sync) and toWindows (for Identity Management to Active Directory sync).

For example, to sync changes from Active Directory to Identity Management:

[jsmith@ipaserver ~]$ ldapmodify -x -D "cn=directory manager" -w password -p 389 -h ipaserver.example.com

dn: cn=meToWindowsBox.example.com,cn=replica,cn=dc\3Dexample\2Cdc\3Dcom,cn=mapping tree,cn=config
changetype: modify
add: oneWaySync
oneWaySync: fromWindows

IMPORTANT

Enabling uni-directional sync does not automatically prevent changes on the un-synchronized server, and this can lead to inconsistencies between the sync peers between sync updates. For example, uni-directional sync is configured to go from Active Directory to Identity Management, so Active Directory is (in essence) the data master. If an entry is modified or even deleted on the Identity Management, then the Identity Management information is different then the information and those changes are never carried over to Active Directory. During the next sync update, the edits are overwritten on the Directory Server and the deleted entry is re-added.

⁠7.5.6. Deleting Synchronization Agreements

Synchronization can be stopped by deleting the sync agreement which disconnects the IdM and Active Directory servers. In the inverse of creating a sync agreement, deleting a sync agreement uses the ipa-replica-manage disconnect command and then the hostname of the Active Directory server.

Delete the sync agreement.

# ipa-replica-manage disconnect adserver.example.com

Remove the Active Directory CA certificate from the IdM server database:

# certutil -D -d /etc/dirsrv/slapd-EXAMPLE.COM/ -n "Imported CA"

⁠7.5.7. Winsync Agreement Failures

⁠

Creating the sync agreement fails because it cannot connect to the Active Directory server.

One of the most common sync agreement failures is that the IdM server cannot connect to the Active Directory server:

"Update failed! Status: [81  - LDAP error: Can't contact LDAP server]

This can occur if the wrong Active Directory CA certificate was specified when the agreement was created. This creates duplicate certificates in the IdM LDAP database (in the /etc/dirsrv/slapd-DOMAIN/ directory) with the name Imported CA. This can be checked using certutil:

$ certutil -L -d /etc/dirsrv/slapd-DOMAIN/

Certificate Nickname                                         Trust Attributes
SSL,S/MIME,JAR/XPI

CA certificate                                               CTu,u,Cu
Imported CA                                                  CT,,C
Server-Cert                                                  u,u,u
Imported CA                                                  CT,,C

To resolve this issue, clear the certificate database:

# certutil -d /etc/dirsrv/slapd-DOMAIN-NAME -D -n "Imported CA"

This deletes the CA certificate from the LDAP database.

There are errors saying passwords are not being synced because it says the entry exists

For some entries in the user database, there may be an informational error message that the password is not being reset because the entry already exists:

"Windows PassSync entry exists, not resetting password"

This is not an error. This message occurs when an exempt user, the Password Sync user, is not being changed. The Password Sync user is the operational user which is used by the service to change the passwords in IdM.

⁠7.6. Managing Password Synchronization

Synchronizing user entries is configured with the sync agreement. However, passwords in both Active Directory and Identity Management are not part of the normal user synchronization process. A separate client must be installed on the Active Directory servers to capture passwords as user accounts are created or passwords are changed, and then to forward that password information with the sync updates.

NOTE

The Password Sync client captures password changes and then synchronizes them between Active Directory and IdM. This means that it synchronizes new passwords or password updates.

Existing passwords, which are stored in a hashed form in both IdM and Active Directory, cannot be decrypted or synchronized when the Password Sync client is installed, so existing passwords are not synchronized. User passwords must be changed to initiate synchronization between the peer servers.

⁠7.6.1. Setting up the Windows Server for Password Synchronization

Synchronizing passwords requires two things:

Active Directory must be running in SSL.

The Password Sync Service must be installed on each Active Directory domain controller.

The Password Sync Service records password changes and synchronizes them, over a secure connection, to the IdM entry.

TIP

Install the Microsoft Certificate System in Enterprise Root Mode. Active Directory will then automatically enroll to retrieve its SSL server certificate.

Make sure that the Active Directory password complexity policies are enabled so that the Password Sync service will run.

Run secpol.msc from the command line.

Select Security Settings.

Open Account Policies, and then open Password Policy.

Enable the Password must meet complexity requirements option and save.

If SSL is not already enabled, set up SSL on the Active Directory server. Setting up LDAPS is explained in more detail in the Microsoft knowledgebase at http://support.microsoft.com/kb/321051.

Install a certificate authority in the Windows Components section in Add/Remove Programs.

Select the Enterprise Root CA option.

Reboot the Active Directory server. If IIS web services are running, the CA certificate can be accessed by opening http://servername/certsrv.

Set up the Active Directory server to use the SSL server certificate.

Create a certificate request .inf, using the fully-qualified domain name of the Active Directory as the certificate subject. For example:

;----------------- request.inf -----------------

[Version]

Signature="$Windows NT$

[NewRequest]

Subject = "CN=ad.server.example.com, O=Engineering, L=Raleigh, S=North Carolina, C=US"
KeySpec = 1
KeyLength = 2048
Exportable = TRUE
MachineKeySet = TRUE
SMIME = False
PrivateKeyArchive = FALSE
UserProtected = FALSE
UseExistingKeySet = FALSE
ProviderName = "Microsoft RSA SChannel Cryptographic Provider"
ProviderType = 12
RequestType = PKCS10
KeyUsage = 0xa0

[EnhancedKeyUsageExtension]

OID=1.3.6.1.5.5.7.3.1

;-----------------------------------------------

For more information on the .inf request file, see the Microsoft documentation, such as http://technet.microsoft.com/en-us/library/cc783835.aspx.

Generate the certificate request.

certreq -new request.inf request.req

Submit the request to the Active Directory CA. For example:

certreq -submit request.req certnew.cer

NOTE

If the command-line tool returns an error message, then use the Web browser to access the CA and submit the certificate request. If IIS is running, then the CA URL is http://servername/certsrv.

Accept the certificate request. For example:

certreq -accept certnew.cer

Make sure that the server certificate is present on the Active Directory server.

In the File menu, click Add/Remove, then click Certificates and Personal>Certificates.

Import the CA certificate from Directory Server into Active Directory. Click Trusted Root CA, then Import, and browse for the Directory Server CA certificate.

Reboot the domain controller.

⁠7.6.2. Setting up Password Synchronization

Install the Password Sync Service on every domain controller in the Active Directory domain in order to synchronize Windows passwords.

Download the PassSync.msi file to the Active Directory machine.

Log into the Customer Portal.

Click the Downloads tab.

Click the Red Hat Enterprise Linux downloads button in the middle of the page.

Filter the downloads by using a search term such as Directory Server, and then expand one of the Red Hat Enterprise Linux versions.

Click the Directory Server link.

On the Directory Server page, download the appropriate version of the WinSync Installer. This is the Password Sync MSI file (RedHat-PassSync-1.1.5-arch.msi).

NOTE

Regardless of the Red Hat Enterprise Linux architecture, there are two PassSync packages available, one for 32-bit Windows servers and one for 64-bit. Make sure to select the appropriate packages for your Windows platform.

Double-click the Password Sync MSI file to install it.

The Password Sync Setup window appears. Hit Next to begin installing.

Fill in the information to establish the connection to the IdM server.

The IdM server connection information, including the hostname and secure port number.

The username of the system user which Active Directory uses to connect to the IdM machine. This account is configured automatically when sync is configured on the IdM server. The default account is uid=passsync,cn=sysaccounts,cn=etc,dc=example,dc=com.

The password set in the --passsync option when the sync agreement was created.

The search base for the people subtree on the IdM server. The Active Directory server connects to the IdM server similar to an ldapsearch or replication operation, so it has to know where in the IdM subtree to look for user accounts. The user subtree is cn=users,cn=accounts,dc=example,dc=com.

The certificate token is not used at this time, so that field should be left blank.

Hit Next, then Finish to install Password Sync.

Import the IdM server's CA certificate into the Active Directory certificate store.

Download the IdM server's CA certificate from http://ipa.example.com/ipa/config/ca.crt.

Copy the IdM CA certificate to the Active Directory server.

Install the IdM CA certificate in the Password Sync database. For example:

cd "C:\Program Files\Red Hat Directory Password Synchronization"

certutil.exe -d . -A -n "IPASERVER.EXAMPLE.COM IPA CA" -t CT,, -a -i ipaca.crt

Reboot the Windows machine to start Password Sync.

NOTE

The Windows machine must be rebooted. Without the rebooting, PasswordHook.dll is not enabled, and password synchronization will not function.

If passwords for existing accounts should be synchronized, reset the user passwords.

NOTE

The Password Sync client captures password changes and then synchronizes them between Active Directory and IdM. This means that it synchronizes new passwords or password updates.

Existing passwords, which are stored in a hashed form in both IdM and Active Directory, cannot be decrypted or synchronized when the Password Sync client is installed, so existing passwords are not synchronized. User passwords must be changed to initiate synchronization between the peer servers.

The first attempt to synchronize passwords, which happened when the Password Sync application is installed, will always fail because of the SSL connection between the Directory Server and Active Directory sync peers. The tools to create the certificate and key databases is installed with the .msi.

⁠7.6.3. Allowing Users to Change Other Users' Passwords Cleanly

By default, every time an administrator changes a user password, that user is required to reset the password at the next login. However, this behavior can be changed to allow administrators to reset a password without requiring an immediate password reset.

The passSyncManagersDNs attribute lists administrator accounts which are allowed to perform password change operations and which will not then require a password reset.

IMPORTANT

This is required for password synchronization because, otherwise, whenever a password is synchronized, the IdM server would interpret that as a password change operation and then require a password change at the next login.

Edit the password synchronization entry, cn=ipa_pwd_extop,cn=plugins,cn=config, and add the passSyncManagersDNs attribute with the name of the user. This attribute is multi-valued. For example:

$ ldapmodify -x -D "cn=Directory Manager" -w secret -h ldap.example.com -p 389

dn: cn=ipa_pwd_extop,cn=plugins,cn=config
changetype: modify
add: passSyncManagersDNs
passSyncManagersDNs: uid=admin,cn=users,cn=accounts,dc=example,dc=com

WARNING

Be careful to limit the listed DNs only to administrator accounts which require the ability to set user passwords. Any user listed here is given access to all user passwords, which is extremely powerful.

[5] The cn is treated differently than other synced attributes. It is mapped directly (cn to cn) when syncing from Identity Management to Active Directory. When syncing from Active Directory to Identity Management, however, cn is mapped from the name attribute on Windows to the cn attribute in Identity Management.

⁠Chapter 8. ID Views and Migrating Existing Environments to Trust

The ID Views mechanism that is part of Red Hat Identity Management enables you to specify POSIX attributes for users or groups. When you create a new ID view, you can define what user or group attributes it should override; these newly defined attributes are then applied to the user or group. By allowing this, ID views provide a solution to preserve existing environments during migration from other identity management and system integration solutions.

After running the ipa-adtrust-install command, the Default Trust View is created. The Default Trust View is always applied to Active Directory users and groups, which allows you to define POSIX attributes for AD users and groups regardless of how AD itself defined them. If you add a host-specific ID view that overrides the AD users or groups, the attributes from the host-specific ID view are applied on top of the Default Trust View. While the new ID view overrides the Default Trust View, you cannot delete the default view itself. If no specific ID view is applied to a client, the Default Trust View always applies.

Note

If you do not run ipa-adtrust-install, you can still use the ID Views feature in a pure IdM environment to manage ID views and overrides for IdM users.

In a setup with a synchronization-based AD integration, all users are copied to the IdM server with generated POSIX attributes, such as login name, UID, GID, or shell. As explained in Section 1.3, “Indirect Integration”, the synchronization-based approach is generally discouraged, and it is recommended to use the trust-based approach instead. By enabling the administrator to modify the POSIX attributes that AD previously generated for AD users, the ID Views feature provides a solution to migrate existing environments to a trust-based AD integration.

Use cases covered by ID Views include:

Store POSIX attributes and SSH keys for AD users

Define POSIX attributes or SSH keys and SSH login information for AD users, and let them be applied when an AD user authenticates to clients running SSSD with ID Views support or when the AD user authenticates using a compat LDAP tree, which offers a simplified LDAP tree with user and group data for legacy clients.

This capability is useful for migration from a synchronization-based solution or in a situation when a Linux administrator would like to manually define POSIX attributes for AD users but the AD policy does not allow it.

Migrate from a synchronization-based to a trust-based integration

Configure the POSIX attributes for users that are in a synchronization-based environment by creating an ID view override specifying previously used UID or other tools. Then move the users back to AD.

Perform per-host group override of the IdM user POSIX attributes

NIS-based infrastructure that is being migrated to an IdM integration with AD still often requires that the original POSIX data remain unchanged on some NIS domains or the company policies might prevent setting the original POSIX data in AD directly. In these situations, you can use ID Views to configure the POSIX data directly on the Identity Management server.

Set different POSIX attributes or SSH keys for different environments

Set different POSIX attributes or different user SSH public keys for different production environments – such as development, testing, or production – depending on the corresponding host groups.

⁠8.1. User Overrides and Group Overrides

Every ID view is a collection of user overrides and group overrides that applies to specified hosts. An override provides a new user or group attribute that overrides the previous one; this enables you to, for example, replace a previously generated attribute with a new one. Every override is related to an AD or IdM user or group.

Note

Non-IdM integration systems can generate the UID and GID attributes using an algorithm that is different from the algorithm used in IdM. By overriding the previously generated attributes so that they are in compliance with the IdM system, a client that used to be a member of another integration system can be fully integrated with IdM.

The following user attributes can be overridden in an ID view:

uid: user login name

uidNumber: user UID number

gidNumber: user GID number

loginShell: user login shell

gecos: user GECOS entry

homeDirectory: user home directory

ipaSshPubkey: user SSH public key or keys

The following group attributes can be overridden in an ID view:

cn: group name

gidNumber: group GID number

Note

IdM uses ID ranges to avoid collisions of POSIX IDs from different domains. POSIX IDs in ID Views do not use a special range type because IdM must allow overlaps with other kinds of ID ranges: for example, AD users created through synchronization have POSIX IDs from the same ID range as IdM users. If a collision occurs, it can be easily fixed by changing the conflicting IDs because POSIX IDs are managed manually in ID Views on the IdM side.

⁠8.2. Managing ID Views

ID views can be added, modified, or deleted. You can define what ID attributes an ID view should override and to which client hosts it should apply.

For AD users, overrides from the Default Trust View are always applied. If an ID view assigned to the host overrides the values present in the Default Trust View or the original values from AD for some attributes, these overridden values are visible on the host. If an ID view does not override a value present in the Default Trust View, all clients assigned to this other ID view see the Default Trust View value.

Default Trust View accepts only AD user overrides; you cannot add overrides of IdM users or groups to the Default Trust View. For IdM users, the default view is represented by the values defined in their corresponding IdM user records.

IdM servers and replicas always apply the Default Trust View without any ID view overrides; you cannot assign a different ID view to them. The default view is also always applied to AD users or groups.

⁠8.2.1. ID Views and SSSD

If the administrator applies another ID view on a client, the client and all the other clients applying this ID view must restart the SSSD service. Moreover, if the new ID view changes a UID or GID, the client and all the other clients applying the ID view must clear the SSSD cache.

Note

Applying an ID view can have a negative impact on SSSD performance because certain optimizations and ID views cannot run at the same time.

For example, ID views prevent SSSD from optimizing the process of looking up groups on the server. With ID views, SSSD must check every member on the returned list of group member names if the group name is overridden. Without ID views, SSSD can only collect the user names from the member attribute of the group object. This negative effect will most likely become apparent when the SSSD cache is empty or when all entries are invalid, that is, after clearing the cache.

ID views are applied on the client side, which means that clients running earlier versions of IdM only see the Default Trust View. If a client requires a different ID view, update SSSD on the client to a version with ID View support or have the client use the compat LDAP tree.

⁠8.2.2. Managing ID Views from the Web UI

To manage ID views from the IdM Web UI, open the IPA Server main tab and then select the ID Views subtab.

To add a new ID view:

Click Add above the list of all ID views.

⁠

Figure 8.1. Adding a New ID View

Fill out the information about the new ID view in the form that shows up.

⁠

Figure 8.2. Form for Adding a New ID View

Click the Add button under the form.

To define the properties of an ID view:

Click on the name of the ID view in the list of ID views, and then choose the appropriate tab.

⁠

Figure 8.3. ID View Tabs

Users shows the list of users whose user attributes the ID view overrides.

⁠

Figure 8.4. Adding a User Override

Click Add to create a new user override; you will be asked to fill out the new values for the user attributes.

⁠

Figure 8.5. Adding a User Override

Click Delete to remove selected user overrides.

User Groups shows the list of user groups whose group attributes the ID view overrides.

⁠

Figure 8.6. User Groups Tab

Click Add to create a new user group override; you will be asked to fill out the new values for the group attributes.

⁠

Figure 8.7. Adding a Group Override

Click Delete to remove selected user group overrides.

Hosts shows the list of hosts or host groups to which the ID view applies.

⁠

Figure 8.8. Hosts Tab

Click Apply to hosts or Apply to host groups to add a new host or to add hosts belonging to a host group. In the form that shows up, move the required hosts or hosts group from the Available to Prospective column and click Apply.

⁠

Figure 8.9. Applying an ID View to a Host

Un-apply removes the ID view from specified hosts. Un-apply from host groups enables you to remove the ID view from specified host groups.

Settings enables you to modify the ID view description.

⁠

Figure 8.10. Settings Tab

⁠8.2.3. Managing ID Views from the command line

To manage ID views on the command line, use the following commands:

ipa idview-add adds a new ID view

ipa idview-apply applies an ID view to specified hosts or host groups; any previously applied ID view is overridden

ipa idview-del deletes an ID view

ipa idview-find searches for a specified ID view

ipa idview-mod modifies an ID view

ipa idview-show displays information about an ID view

ipa idview-unapply removes an ID view from specified hosts or host groups

To manage group and user ID overrides, use the following commands:

ipa idoverridegroup-add adds a new group ID override

ipa idoverrideuser-add adds a new user ID override

ipa idoverridegroup-del deletes a group ID override

ipa idoverrideuser-del deletes a user ID override

ipa idoverridegroup-find searches for a specified group ID override

ipa idoverrideuser-find searches for a specified user ID override

ipa idoverridegroup-mod modifies a group ID override

ipa idoverrideuser-mod modifies a user ID override

ipa idoverridegroup-show displays information about a group ID override

ipa idoverrideuser-show displays information about a user ID override

For detailed information on what options can be passed to these commands, see the corresponding man pages or run one of them with the --help option added.

⁠

Example 8.1. Storing POSIX Attributes and SSH Keys for AD Users Using a Host-Specific ID View

To change the UID of the testuser user to 6666:

Add a new host-specific ID view using ipa idview-add and supply the required values.

[user@client ~]$ ipa idview-add testview --desc "Our new host-specific view"
---------------------------------------------
Added ID View "testview"
---------------------------------------------
  ID View Name: testview
  Description: Our new host-specific view

Add an ID override to the ID view by running ipa idoverrideuser-add and supplying the required values.

[user@client ~]$ ipa idoverrideuser-add testview testuser@example.com --uid 6666
---------------------------------------------
Added User ID override "testuser@example.com"
---------------------------------------------
  Anchor to override: testuser@example.com
  UID: 6666

Apply the ID view to a specific host by running ipa idview-apply and supplying the host using the --hosts option.

[user@client ~]$ ipa idview-apply testview --hosts examplehost.com
---------------------------------------------
Applied ID View "testview"
---------------------------------------------
  hosts: examplehost.com
---------------------------------------------
Number of hosts the ID View was applied to: 1

You can override the GID and other attributes using a similar procedure. For more information, run the ipa idoverrideuser-add --help command.

Note

The --hostgroups option applies the ID view to hosts belonging in a specified host group and can be used in the same way as the --hosts option. The --hostgroups option does not associate the ID view with the host group itself; it expands the members of the specified host group and applies --hosts individually to every one of them.

⁠8.3. Migrating from the Synchronization-Based to the Trust-Based Solution

In an environment that uses the synchronization-based integration, you can migrate to the trust-based integration by following these steps:

Create a trust with the synchronized domain. For information about creating trusts, see Chapter 5, Creating Cross-forest Trusts with Active Directory and Identity Management.

For every synchronized user or group, individually create an ID override in a host-specific view or in the Default Trust View to preserve the UID and GID generated by IdM. For an example on how to do this, see Example 8.1, “Storing POSIX Attributes and SSH Keys for AD Users Using a Host-Specific ID View”.

Make a backup copy of the original synchronized user or group entry.

Delete all the original synchronized user or group entries.

⁠Index

A

Active Directory

schema differences between Identity Management, User Schema Differences between Identity Management and Active Directory

Active Directory

global catalog, Active Directory Identities on the Local System

S

schema

differences between Identity Management and Active Directory, User Schema Differences between Identity Management and Active Directory

cn, Values for cn Attributes

initials, Constraints on the initials Attribute

sn, Requiring the surname (sn) Attribute

street and streetAddress, Values for street and streetAddress

SSSD

Active Directory

global catalog, Active Directory Identities on the Local System

Microsoft Active Directory domain, Configuring an Active Directory Domain with ID Mapping

⁠Appendix A. Revision History

Note that revision numbers relate to the edition of this manual, not to version numbers of Red Hat Enterprise Linux.

Revision History

Revision 7.0-21
Fri Nov 13 2015
Aneta Petrová

Version for 7.2 GA release with minor updates.

Revision 7.0-20
Thu Nov 12 2015
Aneta Petrová

Version for 7.2 GA release.

Revision 7.0-19
Fri Sep 18 2015
Tomáš Čapek

Updated the splash page sort order.

Revision 7.0-18
Thu Sep 10 2015
Aneta Petrová

Updated the output format.

Revision 7.0-17
Mon Jul 27 2015
Aneta Petrová

Async update to include GPO-based access control and a number of minor changes.

Revision 7.0-16
Thu Apr 02 2015
Tomáš Čapek

Async update to include ipa-advise, additional information on accessing a CIFS share with SSSD, and admonition for the Identity Management for UNIX extension.

Revision 7.0-15
Fri Mar 13 2015
Tomáš Čapek

Async update with last-minute edits for 7.1.

Revision 7.0-13
Wed Feb 25 2015
Tomáš Čapek

Version for 7.1 GA release.

Revision 7.0-11
Fri Dec 05 2014
Tomáš Čapek

Rebuild to update the sort order on the splash page.

Revision 7.0-7
Mon Sep 15 2014
Tomáš Čapek

Section 5.3 Creating Trusts temporarily removed for content updates.

Revision 7.0-5
June 27, 2014
Ella Deon Ballard

Improving Samba+Kerberos+Winbind chapters.

Revision 7.0-4
June 13, 2014
Ella Deon Ballard

Adding Kerberos realm chapter.

Revision 7.0-3
June 11, 2014
Ella Deon Ballard

Initial release.