GROUP-MAPPING-HOWTO.xml   [plain text]

<?xml version="1.0" encoding="iso8859-1"?>
<chapter id="groupmapping">
<chapterinfo>
	<author>
		<firstname>Jean François</firstname><surname>Micouleau</surname>
	</author>
	&author.jerry;
	&author.jht;
</chapterinfo>
<title>Mapping MS Windows and UNIX Groups</title>

<indexterm significance="preferred"><primary>groups</primary><secondary>mapping</secondary></indexterm>

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

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

<sect1>
<title>Features and Benefits</title>

	<para>
	Samba allows the administrator to create MS Windows NT4 / 200x group accounts and to
	arbitrarily associate them with UNIX/Linux group accounts.
	</para>

<indexterm><primary>UID</primary></indexterm>
<indexterm><primary>GID</primary></indexterm>
	<para>
	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 <smbconfoption><name>idmap uid</name></smbconfoption>/<smbconfoption><name>idmap gid</name></smbconfoption> settings
	in the &smb.conf; file.
	</para>


	<figure id="idmap-group-diag"><title>IDMAP groups</title>
	<mediaobject>
	<imageobject role="latex"><imagedata fileref="projdoc/imagefiles/idmap-groups" scale="50" scalefit="1"/></imageobject>
	<imageobject><imagedata fileref="projdoc/imagefiles/idmap-groups.png" scale="50" scalefit="1"/></imageobject>
	</mediaobject>
	</figure>

	<indexterm><primary>groupadd</primary></indexterm>
	<indexterm><primary>groupdel</primary></indexterm>

	<para>
	Administrators should be aware that where &smb.conf; group interface scripts make
	direct calls to the UNIX/Linux system tools (eg: the shadow utilities, <command>groupadd</command>,
	<command>groupdel</command>, <command>groupmod</command>) 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
	<ntgroup>Engineering Managers</ntgroup> will attempt to create an identically named
	UNIX/Linux group, an attempt that will of course fail!
	</para>


	<indexterm><primary>GID</primary></indexterm>
	<indexterm><primary>SID</primary></indexterm>

	<para>
	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.
	</para>

	<para>
	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 <command>net groupmap</command>
	tool to connect the two to each other.
	</para>

</sect1>

<sect1>
<title>Discussion</title>

	<para>
	When installing <application>MS Windows NT4 / 200x</application> on a computer, the installation
	program creates default users and groups, notably the <constant>Administrators</constant> 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.
	</para>
	
	<indexterm><primary>Administrator</primary></indexterm>
	<para>
	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'.
	</para>

	<para>
	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.
	</para>

	<para>
	The following steps describe how to make Samba PDC users members of the 'Domain Admins' group?
	</para>

	<orderedlist>
		<listitem><para>
		create a unix group (usually in <filename>/etc/group</filename>), let's call it domadm
		</para></listitem>

		<listitem><para>add to this group the users that must be Administrators. For example
		if you want joe, john and mary, your entry in <filename>/etc/group</filename> will
		look like:
		</para>

		<para><programlisting>
		domadm:x:502:joe,john,mary
		</programlisting>
		</para></listitem>

		<listitem><para>
		Map this domadm group to the "Domain Admins" group by running the command:
		</para>

		<para>
<screen>
&rootprompt;<userinput>net groupmap add ntgroup="Domain Admins" unixgroup=domadm</userinput>
</screen>
		</para>
		
		<indexterm><primary>"Domain Admins" group</primary></indexterm>
		<para>
		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 (=).
		</para></listitem>
	</orderedlist>

	<para>
	Now joe, john and mary are domain administrators!
	</para>

	<indexterm><primary>groups</primary><secondary>domain</secondary></indexterm>
	<para>
	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:
	</para>

	<para>
<screen>
&rootprompt;<userinput>net groupmap add rid=1000 ntgroup="Accounting" unixgroup=acct</userinput>
</screen>
	</para>

	<para>
	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.
	</para>

	<sect2>
	<title>Example Configuration</title>

		<para>
		You can list the various groups in the mapping database by executing 
		<command>net groupmap list</command>.  Here is an example:
		</para>

		<para>
<screen>
&rootprompt; <userinput>net groupmap list</userinput>
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
</screen>
		</para>

		<para>
		For complete details on <command>net groupmap</command>, refer to the net(8) man page.
		</para>

	</sect2>

</sect1>

<sect1>
<title>Configuration Scripts</title>

	<para>
	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). 
	</para>

	<sect2>
	<title>Sample &smb.conf; add group script</title>

		<para>
		A script to create complying group names for use by the Samba group interfaces:
		</para>

		<para>
<example>
	<title>smbgrpadd.sh</title>
<programlisting>

#!/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
</programlisting>
</example>
</para>

		<para>
		The &smb.conf; entry for the above script would look like:
		<smbconfblock>
<smbconfoption><name>add group script</name><value>/path_to_tool/smbgrpadd.sh %g</value></smbconfoption>
		</smbconfblock>
		</para>

	</sect2>
	
	<sect2>
	<title>Script to configure Group Mapping</title>

	<para>
		In our example we have created a UNIX/Linux group called <ntgroup>ntadmin</ntgroup>.
		Our script will create the additional groups <ntgroup>Orks</ntgroup>, <ntgroup>Elves</ntgroup>, <ntgroup>Gnomes</ntgroup>:
	</para>

<para>
<programlisting>
#!/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
</programlisting>
</para>

	<para>
	Of course it is expected that the administrator will modify this to suit local needs.
	For information regarding the use of the <command>net groupmap</command> tool please
	refer to the man page.
	</para>

	</sect2>

</sect1>

<sect1>
<title>Common Errors</title>

<para>
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.
</para>

	<sect2>
	<title>Adding Groups Fails</title>

		<para>
		This is a common problem when the <command>groupadd</command> is called directly
		by the Samba interface script for the <smbconfoption><name>add group script</name></smbconfoption> in
		the &smb.conf; file.
		</para>

		<para>
		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.
		</para>

		<para>
		There are three possible work-arounds. Firstly, use only group names that comply
		with the limitations of the UNIX/Linux <command>groupadd</command> 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.
		</para>

	</sect2>

	<sect2>
	<title>Adding MS Windows Groups to MS Windows Groups Fails</title>

	<indexterm><primary>groups</primary><secondary>nested</secondary></indexterm>

		<para>
		Samba-3 does NOT support nested groups from the MS Windows control environment.
		</para>

	</sect2>

	<sect2>
	<title>Adding <emphasis>Domain Users</emphasis> to the <emphasis>Power Users</emphasis> group</title>

		<para><quote>
		What must I do to add Domain Users to the Power Users group?
		</quote></para>

		<para>
		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 
		<emphasis>administrator</emphasis> and then using click on Start / Control Panel / Users and Passwords
		now click on the 'Advanced' tab, then on the 'Advanced' Button.
		</para>

<indexterm><primary>"Domain Users" group</primary></indexterm>
		<para>
		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.
		</para>	
	</sect2>

</sect1>

</chapter>