Group mapping HOWTO

+ Starting with Samba-3, new group mapping functionality is available to create associations + between Windows group SIDs and UNIX groups. The groupmap subcommand + included with the net tool can be used to manage these associations. +

Warning

+ The first immediate reason to use the group mapping on a Samba PDC, is that + the domain admin group has been removed and should no longer + be specified in smb.conf. This parameter was used to give the listed users membership + in the Domain Admins Windows group which gave local admin rights on their workstations + (in default configurations). +

Features and Benefits

+ Samba allows the administrator to create MS Windows NT4 / 200x group accounts and to + arbitrarily associate them with Unix/Linux group accounts. +

+ Group accounts can be managed using the MS Windows NT4 or MS Windows 200x MMC tools + so long as appropriate interface scripts have been provided to smb.conf +

+ Administrators should be aware that where smb.conf group interface scripts make + direct calls to the Unix/Linux system tools (eg: the shadow utilities, groupadd, + groupdel, groupmod) then the resulting Unix/Linux group names will be subject + to any limits imposed by these tools. If the tool does NOT allow upper case characters + or space characters, then the creation of an MS Windows NT4 / 200x style group of + Engineering Managers will attempt to create an identically named + Unix/Linux group, an attempt that will of course fail! +

+ There are several possible work-arounds for the operating system tools limitation. One + method is to use a script that generates a name for the Unix/Linux system group that + fits the operating system limits, and that then just passes the Unix/Linux group id (GID) + back to the calling samba interface. This will provide a dynamic work-around solution. +

+ Another work-around is to manually create a Unix/Linux group, then manually create the + MS Windows NT4 / 200x group on the Samba server and then use the net groupmap + tool to connect the two to each other. +

Discussion

+ When installing MS Windows NT4 / 200x on a computer, the installation + program creates default users and groups. Notably the Administrators group, + and gives to that group privileges necessary privilidges to perform essential system tasks. + eg: Ability to change the date and time or to kill any process (or close too) running on the + local machine. +

+ The 'Administrator' user is a member of the 'Administrators' group, and thus inherits + 'Administrators' group privileges. If a 'joe' user is created to be a member of the + 'Administrator' group, 'joe' has exactly the same rights as 'Administrator'. +

+ When an MS Windows NT4 / W200x is made a domain member, the "Domain Adminis" group of the + PDC is added to the local 'Administrators' group of the workstation. Every member of the + 'Domain Administrators' group inherits the rights of the local 'Administrators' group when + logging on the workstation. +

+ The following steps describe how to make samba PDC users members of the 'Domain Admins' group? +

+ create a unix group (usually in /etc/group), let's call it domadm +
add to this group the users that must be Administrators. For example + if you want joe,john and mary, your entry in /etc/group will + look like: +
```
+		domadm:x:502:joe,john,mary
+		
```
+
+ Map this domadm group to the "Domain Admins" group by running the command: +
+
```
+		root# net groupmap add ntgroup="Domain Admins" unixgroup=domadm
+		
```
+
+ The quotes around "Domain Admins" are necessary due to the space in the group name. + Also make sure to leave no whitespace surrounding the equal character (=). +

+ Now joe, john and mary are domain administrators! +

+ It is possible to map any arbitrary UNIX group to any Windows NT4 / 200x group as well as + making any UNIX group a Windows domain group. For example, if you wanted to include a + UNIX group (e.g. acct) in a ACL on a local file or printer on a domain member machine, + you would flag that group as a domain group by running the following on the Samba PDC: +

+	root# net groupmap add rid=1000 ntgroup="Accounting" unixgroup=acct
+

+ Be aware that the RID parmeter is a unsigned 32 bit integer that should + normally start at 1000. However, this rid must not overlap with any RID assigned + to a user. Verifying this is done differently depending on on the passdb backend + you are using. Future versions of the tools may perform the verification automatically, + but for now the burden is on you. +

Example Configuration

+ You can list the various groups in the mapping database by executing + net groupmap list. Here is an example: +

+		root#  net groupmap list
+		System Administrators (S-1-5-21-2547222302-1596225915-2414751004-1002) -> sysadmin
+		Domain Admins (S-1-5-21-2547222302-1596225915-2414751004-512) -> domadmin
+		Domain Users (S-1-5-21-2547222302-1596225915-2414751004-513) -> domuser
+		Domain Guests (S-1-5-21-2547222302-1596225915-2414751004-514) -> domguest
+

+ For complete details on net groupmap, refer to the net(8) man page. +

Configuration Scripts

+ Everyone needs tools. Some of us like to create our own, others prefer to use canned tools + (ie: prepared by someone else for general use). +

Sample `smb.conf` add group script

+ A script to great complying group names for use by the samba group interfaces: +

Example 12.1. smbgrpadd.sh

+
+#!/bin/bash
+
+# Add the group using normal system groupadd tool.
+groupadd smbtmpgrp00
+
+thegid=`cat /etc/group | grep smbtmpgrp00 | cut -d ":" -f3`
+
+# Now change the name to what we want for the MS Windows networking end
+cat /etc/group | sed s/smbtmpgrp00/$1/g > /etc/group
+
+# Now return the GID as would normally happen.
+echo $thegid
+exit 0
+

+ The smb.conf entry for the above script would look like: +

+		add group script = /path_to_tool/smbgrpadd.sh %g
+

Script to configure Group Mapping

+ In our example we have created a Unix/Linux group called ntadmin. + Our script will create the additional groups Engineers, Marketoids, Gnomes: +

+#!/bin/bash
+
+net groupmap modify ntgroup="Domain Admins" unixgroup=ntadmin
+net groupmap modify ntgroup="Domain Users" unixgroup=users
+net groupmap modify ntgroup="Domain Guests" unixgroup=nobody
+net groupmap modify ntgroup="Administrators" unixgroup=root
+net groupmap modify ntgroup="Users" unixgroup=users
+net groupmap modify ntgroup="Guests" unixgroup=nobody
+net groupmap modify ntgroup="System Operators" unixgroup=sys
+net groupmap modify ntgroup="Account Operators" unixgroup=root
+net groupmap modify ntgroup="Backup Operators" unixgroup=bin
+net groupmap modify ntgroup="Print Operators" unixgroup=lp
+net groupmap modify ntgroup="Replicators" unixgroup=daemon
+net groupmap modify ntgroup="Power Users" unixgroup=sys
+
+#groupadd Engineers
+#groupadd Marketoids
+#groupadd Gnomes
+
+#net groupmap add ntgroup="Engineers"  unixgroup=Engineers    type=d
+#net groupmap add ntgroup="Marketoids" unixgroup=Marketoids   type=d
+#net groupmap add ntgroup="Gnomes"     unixgroup=Gnomes       type=d
+

+ Of course it is expected that the admininstrator will modify this to suit local needs. + For information regarding the use of the net groupmap tool please + refer to the man page. +

Common Errors

+At this time there are many little surprises for the unwary administrator. In a real sense +it is imperative that every step of automated control scripts must be carefully tested +manually before putting them into active service. +

Adding Groups Fails

+ This is a common problem when the groupadd is called directly + by the samba interface script for the add group script in + the smb.conf file. +

+ The most common cause of failure is an attempt to add an MS Windows group acocunt + that has either an upper case character and/or a space character in it. +

+ There are three possible work-arounds. Firstly, use only group names that comply + with the limitations of the Unix/Linux groupadd system tool. + The second involves use of the script mentioned earlier in this chapter, and the + third option is to manually create a Unix/Linux group account that can substitute + for the MS Windows group name, then use the procedure listed above to map that group + to the MS Windows group. +

Adding MS Windows Groups to MS Windows Groups Fails

+ Samba-3 does NOT support nested groups from the MS Windows control environment. +

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Chapter 21. Group mapping HOWTO

Chapter 12. Mapping MS Windows and Unix Groups

Jean François Micouleau

Gerald (Jerry) Carter

John H. Terpstra