IDMAP_SCRIPT(8) System Administration tools IDMAP_SCRIPT(8)

NAME

idmap_script - Samba's idmap_script Backend for Winbind

DESCRIPTION

The idmap_script plugin is a substitute for the idmap_tdb2 backend
used by winbindd for storing SID/uid/gid mapping tables in clustered
environments with Samba and CTDB. It is a read only backend that uses
a script to perform mapping.

It was developed out of the idmap_tdb2 back end and does not store
SID/uid/gid mappings in a TDB, since the winbind_cache tdb will store
the mappings once they are provided.

IDMAP OPTIONS

range = low - high
Defines the available matching uid and gid range for which the
backend is authoritative.

script
This option can be used to configure an external program for
performing id mappings.

IDMAP SCRIPT

The tdb2 idmap backend supports an external program for performing id
mappings through the ${prefix}/etc/smb.conf option idmap config * :
script or its deprecated legacy form idmap : script.

The mappings obtained by the script are then stored in the idmap tdb2
database instead of mappings created by the incrementing id counters.
It is therefore important that the script covers 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.

The script should accept the following command line options.

SIDTOID S-1-xxxx
IDTOSID UID xxxx
IDTOSID GID xxxx
IDTOSID XID xxxx


And it should return one of the following responses as a single line
of text.

UID:yyyy
GID:yyyy
XID:yyyy
SID:ssss
ERR:yyyy


XID indicates that the ID returned should be both a UID and a GID.
That is, it requests an ID_TYPE_BOTH, but it is ultimately up to the
script whether or not it can honor that request. It can choose to
return a UID or a GID mapping only.

EXAMPLES

This example shows how script is used as a the default idmap backend
using an external program via the script parameter:

[global]
idmap config * : backend = script
idmap config * : range = 1000000-2000000
idmap config * : script = /usr/local/samba/bin/idmap_script.sh


This shows a simple script to partially perform the task:

#!/bin/sh
#
# Uncomment this if you want some logging
#echo $@ >> /tmp/idmap.sh.log
if [ "$1" == "SIDTOID" ]
then
# Note. The number returned has to be within the range defined
#echo "Sending UID:1000005" >> /tmp/idmap.sh.log
echo "UID:1000005"
exit 0
else
#echo "Sending ERR: No idea what to do" >> /tmp/idmap.sh.log
echo "ERR: No idea what to do"
exit 1
fi


Clearly, this script is not enough, as it should probably use wbinfo
to determine if an incoming SID is a user or group SID and then look
up the mapping in a table or use some other mechanism for mapping
SIDs to UIDs and etc.

Please be aware that the script is called with the _NO_WINBINDD
environment variable set to 1. This prevents recursive calls into
winbind from the script both via explicit calls to wbinfo and via
implicit calls via nss_winbind. For example a call to ls -l could
trigger such an infinite recursion.

It is safe to call wbinfo -n and wbinfo -s from within an idmap
script. To do so, the script must unset the _NO_WINBINDD environment
variable right before the call to wbinfo and set it to 1 again right
after wbinfo has returned to protect against the recursion.

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_SCRIPT(8)