ID mapping in Samba is the mapping between Windows SIDs and Unix user and group IDs. This is performed by Winbindd with a configurable plugin interface. Samba's ID mapping is configured by options starting with the prefix. An idmap option consists of the prefix, followed by a domain name or the asterisk character (*), a colon, and the name of an idmap setting for the chosen domain. The idmap configuration is hence divided into groups, one group for each domain to be configured, and one group with the asterisk instead of a proper domain name, which specifies the default configuration that is used to catch all domains that do not have an explicit idmap configuration of their own. There are three general options available: backend = backend_name This specifies the name of the idmap plugin to use as the SID/uid/gid backend for this domain. The standard backends are tdb (idmap_tdb 8 ), tdb2 (idmap_tdb2 8), ldap (idmap_ldap 8), rid (idmap_rid 8), hash (idmap_hash 8), autorid (idmap_autorid 8), ad (idmap_ad 8) and nss (idmap_nss 8). The corresponding manual pages contain the details, but here is a summary. The first three of these create mappings of their own using internal unixid counters and store the mappings in a database. These are suitable for use in the default idmap configuration. The rid and hash backends use a pure algorithmic calculation to determine the unixid for a SID. The autorid module is a mixture of the tdb and rid backend. It creates ranges for each domain encountered and then uses the rid algorithm for each of these automatically configured domains individually. The ad backend uses unix ids stored in Active Directory via the standard schema extensions. The nss backend reverses the standard winbindd setup and gets the unix ids via names from nsswitch which can be useful in an ldap setup. range = low - high Defines the available matching uid and gid range for which the backend is authoritative. For allocating backends, this also defines the start and the end of the range for allocating new unique IDs. winbind uses this parameter to find the backend that is authoritative for a unix ID to SID mapping, so it must be set for each individually configured domain and for the default configuration. The configured ranges must be mutually disjoint. Note that the low value interacts with the option! read only = yes|no This option can be used to turn the writing backends tdb, tdb2, and ldap into read only mode. This can be useful e.g. in cases where a pre-filled database exists that should not be extended automatically. The following example illustrates how to configure the idmap_ad 8 backend for the CORP domain and the idmap_tdb 8 backend for all other domains. This configuration assumes that the admin of CORP assigns unix ids below 1000000 via the SFU extensions, and winbind is supposed to use the next million entries for its own mappings from trusted domains and for local groups for example. idmap config * : backend = tdb idmap config * : range = 1000000-1999999 idmap config CORP : backend = ad idmap config CORP : range = 1000-999999 min domain uid