Idmap config rid

Revision as of 12:05, 28 November 2018 by Hortimech (talk | contribs) (/* minor update)


The rid ID mapping back end implements a read-only API to retrieve account and group information from an Active Directory (AD) Domain Controller (DC) or NT4 primary domain controller (PDC). The back end assigns IDs from an individual per-domain range set in the smb.conf file and stores them in them in a local database. For details, how the local ID and the relative identifier (RID) are calculated, see the idmap_rid(8) man page. Because the rid back end is read-only, it is unable to assign new ID, such as for BUILTIN groups. Thus this back end cannot be set as idmap config * default ID mapping back end.

For alternatives, see Identity Mapping Back Ends.

Advantages and Disadvantages of the rid Back End


  • Easy to set up.
  • Used IDs are tracked automatically.
  • Requires only read access to domain controllers.
  • All domain's user accounts and groups are automatically available on the domain member.
  • No attributes need to be set for domain users and groups.


  • All users on the domain member get the same login shell and home directory base path assigned.
  • User and group IDs are only the same on other domain members using the rid back end, if the same ID ranges are configured for the domain.
  • All accounts and groups are automatically available on the domain member and individual entries cannot be excluded.
  • Not recommended for multi-domain environments because objects in different domains having the same relative identifier (RID) get the same ID assigned.

Planning the ID Ranges

Before configuring the rid back end in the smb.conf file, select unique ID ranges Samba can use 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.

Configuring the rid Back End

  • Set the following in the [global] section of your smb.conf file:
security = ADS
workgroup = SAMDOM

log file = /var/log/samba/%m.log
log level = 1

# Default ID mapping configuration for local BUILTIN accounts
# and groups on a domain member. The default (*) domain:
# - must not overlap with any domain ID mapping configuration!
# - must use a read-write-enabled back end, such as tdb.
# - Adding just this is not enough
# - You must set a DOMAIN backend configuration, see below
idmap config * : backend = tdb
idmap config * : range = 3000-7999

  • To configure the rid back end using the 10000-999999 ID range for the SAMDOM domain, you need to also add:
# idmap config for the SAMDOM domain
idmap config SAMDOM : backend = rid
idmap config SAMDOM : range = 10000-999999

  • Configure the template settings. For example, to set /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 are applied to all users in all domains. Samba resolves the %U variable to the session user name. For details, see the VARIABLE SUBSTITUTIONS section in the smb.conf(5) man page.

  • Reload Samba:
# smbcontrol all reload-config

For further details, see the smb.conf(5) and idmap_rid(8) man page.