Chapter 12. Mapping MS Windows and UNIX Groups
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## Chapter 12. Mapping MS Windows and UNIX Groups

### Jean François Micouleau

### Gerald (Jerry) Carter

Samba Team

`<jerry@samba.org>`

### John H. Terpstra

Samba Team

`<jht@samba.org>`

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 / XP Professional MMC tools. Appropriate interface scripts should be provided in `smb.conf` if it is desired that UNIX / Linux system accounts should be automatically created when these tools are used. In the absence of these scripts, and so long as winbind is running, Samba accounts group accounts that are created using these tools will be allocated UNIX UIDs/GIDs from the parameters set by the `idmap uid`/`idmap gid` settings in the `smb.conf` file.

Figure 12.1. IDMAP groups

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 that group privileges necessary privileges to perform essential system tasks. eg: Ability to change the date and time or to kill (or close) any process 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 Admins" 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?

1. create a unix group (usually in `/etc/group`), let's call it domadm

2. 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

3. 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 parameter 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 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 create 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
    cp /etc/group /etc/group.bak
    cat /etc/group.bak | 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 Orks, Elves, 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 Orks
    groupadd Elves
    groupadd Gnomes

    net groupmap add ntgroup="Orks"       unixgroup=Orks         type=d
    net groupmap add ntgroup="Elves"      unixgroup=Elves        type=d
    net groupmap add ntgroup="Gnomes"     unixgroup=Gnomes       type=d

Of course it is expected that the administrator 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 account 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.

### Adding Domain Users to the Power Users group

“ What must I do to add Domain Users to the Power Users group? ”

The Power Users group is a group that is local to each Windows 200x / XP Professional workstation. You can not add the Domain Users group to the Power Users group automatically, this must be done on each workstation by logging in as the local workstation administrator and then using click on Start / Control Panel / Users and Passwords now click on the 'Advanced' tab, then on the 'Advanced' Button.

Now click on 'Groups', then double click on 'Power Users'. This will launch the panel to add users or groups to the local machine 'Power Uses' group. Click on the 'Add' button, select the domain from which the 'Domain Users' group is to be added, double click on the 'Domain Users' group, then click on the 'Ok' button. Note: If a logon box is presented during this process please remember to enter the connect as DOMAIN\UserName. ie: For the domain MIDEARTH and the user 'root' enter MIDEARTH\root.

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