path: root/docs/Samba-HOWTO-Collection/Group-Mapping.xml

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<chapter id="groupmapping">
<chapterinfo>
	&author.jht;
	<author>
		<firstname>Jean François</firstname><surname>Micouleau</surname>
	</author>
	&author.jerry;
</chapterinfo>
<title>Group Mapping &smbmdash; MS Windows and UNIX</title>


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

	<para>
	The new facility for mapping NT Groups to UNIX system groups allows the administrator to decide
	which NT Domain Groups are to be exposed to MS Windows clients. Only those NT Groups that map
	to a UNIX group that has a value other than the default (<constant>-1</constant>) will be exposed
	in group selection lists in tools that access domain users and groups.
	</para>

	<warning>
	<para>
	<indexterm><primary>domain admin group</primary></indexterm>
	The <parameter>domain admin group</parameter> parameter has been removed in Samba-3 and should no longer
	be specified in &smb.conf;. In Samba-2.2.x, 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>

	<para>
<indexterm><primary>UID</primary></indexterm>
<indexterm><primary>GID</primary></indexterm>
<indexterm><primary>idmap uid</primary></indexterm>
	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 <command>winbindd</command> is running, Samba group accounts that are created using these
	tools will be allocated UNIX UIDs/GIDs from the ID range specified by the
	<smbconfoption><name>idmap uid</name></smbconfoption>/<smbconfoption><name>idmap gid</name></smbconfoption>
	parameters in the &smb.conf; file.
	</para>

	<image id="idmap-sid2gid">
		<description>IDMAP: group SID to GID resolution.</description>
		<imagefile scale="50">idmap-sid2gid</imagefile>
	</image>

	<image id="idmap-gid2sid"><description>IDMAP: GID resolution to matching SID.</description>
	<imagefile scale="50">idmap-gid2sid</imagefile>
	</image>

	<para>
	<indexterm><primary>IDMAP</primary></indexterm>
	In both cases, when winbindd is not running, only locally resolvable groups can be recognized. Please refer to
	<link linkend="idmap-sid2gid">IDMAP: group SID to GID resolution</link> and <link linkend="idmap-gid2sid">IDMAP: GID resolution to matching SID</link>. 
	The <command>net groupmap</command> is
	used to establish UNIX group to NT SID mappings as shown in <link linkend="idmap-store-gid2sid">IDMAP: storing group mappings</link>.
	</para>

	<image id="idmap-store-gid2sid"><description>IDMAP storing group mappings.</description>
	<imagefile scale="50">idmap-store-gid2sid</imagefile>
	</image>

	<para>
	<indexterm><primary>groupadd</primary></indexterm>
	<indexterm><primary>groupdel</primary></indexterm>
	Administrators should be aware that where &smb.conf; group interface scripts make
	direct calls to the UNIX/Linux system tools (the shadow utilities, <command>groupadd</command>,
	<command>groupdel</command>, and <command>groupmod</command>), 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>



	<para>
	<indexterm><primary>GID</primary></indexterm>
	<indexterm><primary>SID</primary></indexterm>
	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,
	such as the ability to change the date and time or to kill (or close) any process running on the
	local machine.
	</para>
	
	<para>
	<indexterm><primary>Administrator</primary></indexterm>
	The <constant>Administrator</constant> user is a member of the <constant>Administrators</constant> group, and thus inherits
	<constant>Administrators</constant> group privileges. If a <constant>joe</constant> user is created to be a member of the
	<constant>Administrators</constant> group, <constant>joe</constant> has exactly the same rights as the user,
	<constant>Administrator</constant>.
	</para>

	<para>
	When an MS Windows NT4/200x/XP machine is made a Domain Member, the <quote>Domain Admins</quote> group of the
	PDC is added to the local <constant>Administrators</constant> group of the workstation. Every member of the
	<constant>Domain Administrators</constant> group inherits the rights of the local <constant>Administrators</constant> group when
	logging on the workstation.
	</para>

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

	<orderedlist>
		<listitem><para>
		Create a UNIX group (usually in <filename>/etc/group</filename>), let's call it <constant>domadm</constant>.
		</para></listitem>

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

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

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

		<para>
	<screen>
	&rootprompt;<userinput>net groupmap add ntgroup=<quote>Domain Admins</quote> unixgroup=domadm</userinput>
	</screen>
	</para>
		
		<para>
		<indexterm><primary>Domain Admins group</primary></indexterm>
		The quotes around <quote>Domain Admins</quote> are necessary due to the space in the group name.
		Also make sure to leave no white-space surrounding the equal character (=).
		</para></listitem>
	</orderedlist>

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

	<para>
	<indexterm><primary>groups</primary><secondary>domain</secondary></indexterm>
	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 an 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. Verification for 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>Important Administrative Information</title>

	<para>
	Administrative rights are necessary in two specific forms:
	</para>

	<orderedlist>
		<listitem><para>For Samba-3 Domain Controllers and 
				Domain Member Servers/Clients.</para></listitem>
		<listitem><para>To manage Domain Member Windows workstations.</para></listitem>
	</orderedlist>

	<para>
	Administrative tasks on UNIX/Linux systems, such as adding users or groups, requires <constant>root</constant>
	level privilege. The addition of a Windows client to a Samba Domain involves the addition of a user account
	for the Windows client.
	</para>

	<para>
	Many UNIX administrators continue to request the Samba Team make it possible to add Windows workstations, or 
	to ability to add/delete or modify user accounts, without requiring <constant>root</constant> privileges. 
	Such a request violates every understanding of basic UNIX system security.
	</para>

	<para>
	There is no safe way to provide access on a UNIX/Linux system without providing <constant>root</constant>
	level privilege. Provision of <constant>root</constant> privileges can be done either by logging onto
	the Domain as the user <constant>root</constant>, or by permitting particular users to use a UNIX account
	that has a UID=0 in the <filename>/etc/passwd</filename> database. Users of such accounts can use tools
	like the NT4 Domain User Manager, and the NT4 Domain Server Manager to manage user and group accounts as
	well as Domain Member server and client accounts. This level of privilege is also needed to manage share
	level ACLs.
	</para>

	<para>
	Administrative tasks on a Windows Domain Member workstation, can be done by anyone who is a member of the
	<constant>Domain Admins</constant> group. This group can be mapped to any convenient UNIX group.
	</para>

	</sect2>

	<sect2>
	<title>Default Users, Groups and Relative Identifiers</title>

	<para>
<indexterm><primary>Relative Identifier</primary><see>RID</see></indexterm>
<indexterm><primary>RID</primary></indexterm>
	When first installed, Microsoft Windows NT4/200x/XP are pre-configured with certain User, Group, and
	Alias entities. Each has a well-known Relative Identifier (RID). These must be preserved for continued
	integrity of operation. Samba must be provisioned with certain essential Domain Groups that require
	the appropriate RID value. When Samba-3 is configured to use <constant>tdbsam</constant> the essential
	Domain Groups are automatically created. It is the LDAP administrators' responsibility to create
	(provision) the default NT Groups.
	</para>

	<para>
	Each essential Domain Group must be assigned its respective well-known RID. The default Users, Groups,
	Aliases, and RIDs are shown in <link linkend="WKURIDS">Well-Known User Default RIDs</link> table.
	</para>

	<para><note>
	When the <parameter>passdb backend</parameter> uses LDAP (<constant>ldapsam</constant>) it is the
	administrators' responsibility to create the essential Domain Groups, and to assign each its default RID.
	</note></para>

	<para>
	It is permissible to create any Domain Group that may be necessary, just make certain that the essential
	Domain Groups (well known) have been created and assigned its default RID. Other groups you create may
	be assigned any arbitrary RID you care to use.
	</para>

	<para>
	Be sure to map each Domain Group to a UNIX system group. That is the only way to ensure that the group
	will be available for use as an NT Domain Group.
	</para>

	<para>
	<table frame="all" id="WKURIDS">
	<title>Well-Known User Default RIDs</title>
		<tgroup cols="4" align="left">
			<colspec align="left"/>
			<colspec align="left"/>
			<colspec align="left"/>
			<colspec align="center"/>
			<thead>
				<row>
					<entry>Well-Known Entity</entry>
					<entry>RID</entry>
					<entry>Type</entry>
					<entry>Essential</entry>
				</row>
			</thead>
			<tbody>
				<row>
					<entry>Domain Administrator</entry>
					<entry>500</entry>
					<entry>User</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Domain Guest</entry>
					<entry>501</entry>
					<entry>User</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Domain KRBTGT</entry>
					<entry>502</entry>
					<entry>User</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Domain Admins</entry>
					<entry>512</entry>
					<entry>Group</entry>
					<entry>Yes</entry>
				</row>
				<row>
					<entry>Domain Users</entry>
					<entry>513</entry>
					<entry>Group</entry>
					<entry>Yes</entry>
				</row>
				<row>
					<entry>Domain Guests</entry>
					<entry>514</entry>
					<entry>Group</entry>
					<entry>Yes</entry>
				</row>
				<row>
					<entry>Domain Computers</entry>
					<entry>515</entry>
					<entry>Group</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Domain Controllers</entry>
					<entry>516</entry>
					<entry>Group</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Domain Certificate Admins</entry>
					<entry>517</entry>
					<entry>Group</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Domain Schema Admins</entry>
					<entry>518</entry>
					<entry>Group</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Domain Enterprise Admins</entry>
					<entry>519</entry>
					<entry>Group</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Domain Policy Admins</entry>
					<entry>520</entry>
					<entry>Group</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Builtin Admins</entry>
					<entry>544</entry>
					<entry>Alias</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Builtin users</entry>
					<entry>545</entry>
					<entry>Alias</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Builtin Guests</entry>
					<entry>546</entry>
					<entry>Alias</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Builtin Power Users</entry>
					<entry>547</entry>
					<entry>Alias</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Builtin Account Operators</entry>
					<entry>548</entry>
					<entry>Alias</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Builtin System Operators</entry>
					<entry>549</entry>
					<entry>Alias</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Builtin Print Operators</entry>
					<entry>550</entry>
					<entry>Alias</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Builtin Backup Operators</entry>
					<entry>551</entry>
					<entry>Alias</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Builtin Replicator</entry>
					<entry>552</entry>
					<entry>Alias</entry>
					<entry>No</entry>
				</row>
				<row>
					<entry>Builtin RAS Servers</entry>
					<entry>553</entry>
					<entry>Alias</entry>
					<entry>No</entry>
				</row>
			</tbody>
		</tgroup>
	</table>
	</para>

	</sect2>

	<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>

<indexterm><primary>net</primary><secondary>groupmap</secondary></indexterm>

		<para>
<screen>
&rootprompt; <userinput>net groupmap list</userinput>
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
	(i.e., 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
		is provided in <link linkend="smbgrpadd.sh">smbgrpadd.sh</link>.
		</para>

<indexterm><primary>smbgrpadd.sh</primary></indexterm>
		<para>
<example id="smbgrpadd.sh">
	<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 be something like that in <link linkend="smbgrpadd">the following example</link>.
<smbconfexample id="smbgrpadd">
<title>Configuration of &smb.conf; for the add group script.</title>
<smbconfsection>[global]</smbconfsection>
<member>...</member>
<smbconfoption><name>add group script</name><value>/path_to_tool/smbgrpadd.sh &quot;%g&quot;</value></smbconfoption>
<member>...</member>
</smbconfexample>
		</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>, and <ntgroup>Gnomes</ntgroup>.
		It is a good idea to save this shell script for later re-use just in case you ever need to rebuild your mapping database.
		For the sake of convenience we elect to save this script as a file called <filename>initGroups.sh</filename>.
		This script is given in <link linkend="set-group-map">intGroups.sh</link>.
	</para>

<para>
<indexterm><primary>initGroups.sh</primary></indexterm>
<example id="set-group-map">
	<title>Script to Set Group Mapping</title>
<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

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>
</example>
</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. First, use only group names that comply
		with the limitations of the UNIX/Linux <command>groupadd</command> system tool.
		Second, it involves the use of the script mentioned earlier in this chapter, and
		third is the 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>

<indexterm><primary>Domain Users group</primary></indexterm>

		<para>
		The Power Users group is a group that is local to each Windows 200x/XP Professional workstation.
		You cannot add the Domain Users group to the Power Users group automatically, it must be done on
		each workstation by logging in as the local workstation <emphasis>administrator</emphasis> and
		then using the following procedure:
		</para>

		<procedure>
			<step><para>
			Click <guimenu>Start -> Control Panel -> Users and Passwords</guimenu>.
			</para></step>

			<step><para>
			Click the <guimenuitem>Advanced</guimenuitem> tab.
			</para></step>

			<step><para>
			Click the <guibutton>Advanced</guibutton> button.
			</para></step>

			<step><para>
			Click <constant>Groups</constant>.
			</para></step>

			<step><para>
			Double click <constant>Power Users</constant>. This will launch the panel to add users or groups
			to the local machine <constant>Power Uses</constant> group.
			</para></step>

			<step><para>
			Click the <guibutton>Add</guibutton> button.
			</para></step>

			<step><para>
			Select the domain from which the <constant>Domain Users</constant> group is to be added.
			</para></step>

			<step><para>
			Double click the <constant>Domain Users</constant> group.
			</para></step>

			<step><para>
			Click the <guibutton>Ok</guibutton> button. If a logon box is presented during this process 
			please remember to enter the connect as <constant>DOMAIN\UserName</constant>. i.e., For the
			domain <constant>MIDEARTH</constant> and the user <constant>root</constant> enter
			<constant>MIDEARTH\root</constant>.
			</para></step>
		</procedure>
	</sect2>

</sect1>

</chapter>