IDMAP_AUTORID(8) System Administration tools IDMAP_AUTORID(8)

NAME

idmap_autorid - Samba's idmap_autorid Backend for Winbind

DESCRIPTION

The idmap_autorid backend provides a way to use an algorithmic
mapping scheme to map UIDs/GIDs and SIDs that is more deterministic
than idmap_tdb and easier to configure than idmap_rid.

The module works similar to idmap_rid, but it automatically
configures the range to be used for each domain, so there is no need
to specify a specific range for each domain in the forest, the only
configuration that is needed is the range of uid/gids that shall be
used for user/group mappings and an optional size of the ranges to be
used.

The mappings of which domain is mapped to which range is stored in
autorid.tdb, thus you should backup this database regularly.

Due to the algorithm being used, it is the module that is most easy
to use as it only requires a minimal configuration.

IDMAP OPTIONS

range = low - high
Defines the available matching uid and gid range for which the
backend is authoritative. Note that the range acts as a filter.
If algorithmically determined UID or GID fall outside the range,
they are ignored and the corresponding map is discarded. It is
intended as a way to avoid accidental UID/GID overlaps between
local and remotely defined IDs. Note that the range should be a
multiple of the rangesize and needs to be at least twice as large
in order to have sufficient id range space for the mandatory
BUILTIN domain. With a default rangesize of 100000 the range
needs to span at least 200000. This would be: range = 100000 -
299999.

rangesize = numberofidsperdomain
Defines the number of uids/gids available per domain range. The
minimum needed value is 2000. SIDs with RIDs larger than this
value will be mapped into extension ranges depending upon number
of available ranges. If the autorid backend runs out of available
ranges, mapping requests for new domains (or new extension ranges
for domains already known) are ignored and the corresponding map
is discarded.

Example: with rangesize set to 10000, users/groups with a RID up
to 10000 will be put into the first range for the domain. When
attempting to map the an object with a RID of 25000, an extension
range will be allocated that will then be used to map all RIDs
from 20000-29999.

One range will be used for local users and groups and for
non-domain well-known SIDs like Everyone (S-1-1-0) or Creator
Owner (S-1-3-0). A chosen list of well-known SIDs will be
preallocated on first start to create deterministic mappings for
those.

Thus the number of local users and groups that can be created is
limited by this option as well. If you plan to create a large
amount of local users or groups, you will need set this parameter
accordingly.

The default value is 100000.

read only = [ yes | no ]
Turn the module into read-only mode. No new ranges will be
allocated nor will new mappings be created in the idmap pool.
Defaults to no.

ignore builtin = [ yes | no ]
Ignore any mapping requests for the BUILTIN domain. Defaults to
no.

THE MAPPING FORMULAS

The Unix ID for a RID is calculated this way:

ID = REDUCED RID + IDMAP RANGE LOW VALUE + RANGE NUMBER * RANGE SIZE


where REDUCED RID = RID % RANGE_SIZE and a DOMAIN RANGE INDEX = RID /
RANGE_SIZE is used together with the domain sid to determine the
RANGE NUMBER (stored in the database).

Correspondingly, the formula for calculating the RID for a given Unix
ID is this:

RID = (ID - LOW ID) % RANGE SIZE + DOMAIN RANGE INDEX * RANGE SIZE


Where the DOMAIN RANGE INDEX is retrieved from the database along
with the domain sid by the RANGE NUMBER = (ID - LOW ID) / RANGE SIZE
.

EXAMPLES

This example shows you the minimal configuration that will work for
the principal domain and 19 trusted domains / range extensions.

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

idmap config * : backend = autorid
idmap config * : range = 1000000-1999999


This example shows how to configure idmap_autorid as default for all
domains with a potentially large amount of users plus a specific
configuration for a trusted domain that uses the SFU mapping scheme.
Please note that idmap ranges and sfu ranges are not allowed to
overlap.

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

idmap config * : backend = autorid
idmap config * : range = 1000000-19999999
idmap config * : rangesize = 1000000

idmap config TRUSTED : backend = ad
idmap config TRUSTED : range = 50000 - 99999
idmap config TRUSTED : schema_mode = sfu

AUTHOR

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.

Samba 4.18.11 03/13/2024 IDMAP_AUTORID(8)