The idmap_tdb2 plugin is a substitute for the default idmap_tdb backend used by winbindd for storing SID/uid/gid mapping tables in clustered environments with Samba and CTDB.
In contrast to read only backends like idmap_rid, it is an allocating backend: This means that it needs to allocate new user and group IDs in order to create new mappings. The allocator can be provided by the idmap_tdb2 backend itself or by any other allocating backend like idmap_tdb or idmap_ldap. This is configured with the parameter idmap alloc backend.
Note that in order for this (or any other allocating) backend to function at all, the default backend needs to be writeable. The ranges used for uid and gid allocation are the default ranges configured by "idmap uid" and "idmap gid".
Furthermore, since there is only one global allocating backend responsible for all domains using writeable idmap backends, any explicitly configured domain with idmap backend tdb2 should have the same range as the default range, since it needs to use the global uid / gid allocator. See the example below.
range = low - high
The tdb2 idmap backend supports a script for performing id mappings through the smb.conf option idmap : script. The script should accept the following command line options.
SIDTOID S-1-xxxx IDTOSID UID xxxx IDTOSID GID xxxx
And it should return one of the following responses as a single line of text.
UID:yyyy GID:yyyy SID:yyyy ERR:yyyy
Note that the script should cover the complete range of SIDs that can be passed in for SID to Unix ID mapping, since otherwise SIDs unmapped by the script might get mapped to IDs that had previously been mapped by the script.
This example shows how tdb2 is used as a the default idmap backend. It configures the idmap range through the global options for all domains encountered. This same range is used for uid/gid allocation.
[global] idmap backend = tdb2 idmap uid = 1000000-2000000 idmap gid = 1000000-2000000
The original Samba software and related utilities were created by Andrew Tridgell. Samba is now developed by the Samba Team as an Open Source project similar to the way the Linux kernel is developed.