The idmap alloc backend provides a plugin interface for Winbind to use when allocating Unix uids/gids for Windows SIDs. This option refers to the name of the idmap module which will provide the id allocation functionality. Please refer to the man page for each idmap plugin to determine whether or not the module implements the allocation feature. The most common plugins are the tdb ( idmap_tdb8) and ldap (idmap_ldap 8) libraries. This parameter defaults to the value was set to, so by default winbind will allocate Unix IDs from the default backend. You will only need to set this parameter explicitly if you have an external source for Unix IDs, like a central database service somewhere in your company. Also refer to the option. tdb