Idmap config ad

Introduction

The ad ID mapping back end implements a read-only API to read account and group information from Active Directory (AD). The back end is based on RFC 2307. For further details, see https://www.rfc-editor.org/rfc/rfc2307.txt.

Alternatives to the ad back end:

• idmap config rid
• idmap config autorid

Advantages and Disadvantages of the ad Back End

Advantages:

• Central administration of IDs inside Active Directory (AD).
• Consistent IDs on all Samba clients and servers using the ad back end.
• The required attributes only need creating once, this can be done when the user or group is created
• IDs are not stored in a local database that can corrupt and thus file ownerships are not lost.

Disadvantages:

• If the Windows Active Directory Users and Computers (ADUC) program is not used, you have to manual track ID values to avoid duplicates.
• The values for the RFC2307 attributes must be set manually.

winbind NSS info mode-specific features:

• rfc2307: Individual login shells and home directory paths for users.
• template: The login shells and home directory base paths are the same for all users.

Planning the ID Ranges

Before configuring the ad back end in the smb.conf file, you must select unique ID ranges for each domain. The ranges must be continuous and big enough to enable Samba to assign an ID for every future user and group created in the domain.

The ID ranges of the * default domain and all other domains configured in the smb.conf file must not overlap.

Prerequisites

To enable Samba to retrieve user and group information from Active Directory (AD):

• Users must have at least the uidNumber and groups the gidNumber attribute set. When using the rfc2307 winbind NSS info mode, user accounts must also have the loginShell, unixHomeDirectory and primaryGroupID set.
• The user and group IDs must be within the range configured in the smb.conf for this domain.
• If the Active Directory Users and Groups (ADUC) utility is used to assign the UNIX attributes, the NIS extensions have to be installed. For details, see Setting up RFC2307 in AD.
• User IDs must be unique for all users and group IDs for all groups. Duplicate IDs or reusing IDs of previously deleted accounts enable the new user or group to access files created by the previous ID owner. When using the ADUC utility, the IDs are automatically tracked inside AD and incremented when creating a new user or group.
• The primary user group of user accounts, normally the Domain Users group, must have a gidNumber attribute set. If the attribute is not set for the primary group, the users will not be visible on the machine having the ad ID mapping back end configured.

The RFC2307 and template winbind NSS info mode options

The ad ID mapping back end supports two modes, set in the winbind nss info parameter in the [global] section of the smb.conf file:

• winbind nss info = rfc2307: All information is read from Active Directory (AD):

• Users: Account name, UID, login shell, home directory path, and primary group.
• Groups: Group name and GID.

• winbind nss info = template: Only the following values are read from AD:

• Users: Account name, UID, and primary group.

The login shell and home directory are automatically set by user-independent settings in the smb.conf file.

• Groups: Group name and GID

Configuring the ad Back End

• Set the following in the [global] section of your smb.conf file:

• If no back end for local BUILTIN accounts and groups on the domain member is configured, add the tdb back end for the * default domain and set an ID range. For example:

# Default idmap config for local BUILTIN accounts and groups
idmap config * : backend = tdb
idmap config * : range = 3000-7999

Setting the default back end is mandatory.

• To configure the ad back end using the 10000-999999 ID range for the SAMDOM domain:

# idmap config for the SAMDOM domain
idmap config SAMDOM:backend = ad
idmap config SAMDOM:schema_mode = rfc2307
idmap config SAMDOM:range = 10000-999999

You must set these parameters for each and every domain, except the * default domain. The ID ranges of the * default domain and all other domains configured in the smb.conf file must not overlap.

• Configure the Winbind NSS info mode:

• To enable the template mode and set, for example, /bin/bash as shell and /home/%U as home directory path:

# Template settings for login shell and home directory
winbind nss info = template
template shell = /bin/bash
template homedir = /home/%U

The values will be applied to all users in all domains that have the schema_mode = template parameter set. Samba resolves the %U variable to the session user name. For details, see the VARIABLE SUBSTITUTIONS section in the smb.conf(5) man page.

• To enable the rfc2307 mode, set:

winbind nss info = rfc2307

• Reload Samba:

# smbcontrol all reload-config

For further details, see the smb.conf(5) and idmap_ad(5) man page.

Using the ad Back End on a Samba AD Domain Controller

Samba 4.0 and 4.1 used a new Winbind implementation built into the samba command. However, this implementation never worked correctly. For this reason, Samba 4.2 enabled the winbindd utility to be used on domain controllers (DC).

If you run a Samba version prior 4.2, update to a supported version before using the ad back end on a Samba Active Directory (AD) DC. For details, see Updating Samba.

To set up the ad ID mapping back end locally on a Samba AD DC, verify that you are not using the unsupported samba built-in Winbind implementation. If the server services parameter in your smb.conf file lists the option winbind, replace it with winbindd:

server services = ..., winbind, winbindd,...

If you do not have the server services parameter in your smb.conf file or it already lists the winbindd option, Samba automatically starts the winbindd service on Samba 4.2 and later when the samba service is started.

To verify that the winbindd service is started as a subprocess of the samba process, enter:

# ps axf
...
2156 ?        Ss     0:00 /usr/local/samba/sbin/samba -D
2158 ?        S      0:00  \_ /usr/local/samba/sbin/samba -D
2172 ?        R      0:00      \_ /usr/local/samba/sbin/winbindd -D --option=server role check:inhibit=yes --foreground
...

Do not start the winbindd service manually on a Samba AD DC.