source: vendor/current/docs-xml/smbdotconf/security/serverrole.xml

<samba:parameter name="server role"
                 context="G"
                 type="enum"
                 function="_server_role"
                 enumlist="enum_server_role"
                 xmlns:samba="http://www.samba.org/samba/DTD/samba-doc">
<description>
    <para>This option determines the basic operating mode of a Samba
    server and is one of the most important settings in the <filename
    moreinfo="none"> smb.conf</filename> file.</para>

    <para>The default is <command moreinfo="none">server role = auto</command>, as causes
    Samba to operate according to the <smbconfoption name="security"/> setting, or if not
    specified as a simple file server that is not connected to any domain.</para>

    <para>The alternatives are
    <command moreinfo="none">server role = standalone</command> or <command moreinfo="none">server role = member server
    </command>, which support joining Samba to a Windows domain, along with <command moreinfo="none">server role = domain controller</command>, which run Samba as a Windows domain controller.</para>

    <para>You should use <command moreinfo="none">server role = standalone</command> and 
    <smbconfoption name="map to guest"/> if you 
    want to mainly setup shares without a password (guest shares). This 
    is commonly used for a shared printer server. </para>
                
    <para><anchor id="AUTO"/><emphasis>SERVER ROLE = AUTO</emphasis></para>

    <para>This is the default server role in Samba, and causes Samba to consult
    the <smbconfoption name="security"/> parameter (if set) to determine the server role, giving compatible behaviours to previous Samba versions.</para>

    <para><anchor id="STANDALONE"/><emphasis>SERVER ROLE = STANDALONE</emphasis></para>

    <para>If <smbconfoption name="security"/> is also not specified, this is the default security setting in Samba. 
    In standalone operation, a client must first &quot;log-on&quot; with a 
    valid username and password (which can be mapped using the <smbconfoption name="username map"/> 
    parameter) stored on this machine. Encrypted passwords (see the <smbconfoption name="encrypted passwords"/> parameter) are by default
    used in this security mode. Parameters such as <smbconfoption name="user"/> and <smbconfoption
        name="guest only"/> if set      are then applied and 
    may change the UNIX user to use on this connection, but only after 
    the user has been successfully authenticated.</para>

    <para><anchor id="MEMBER SERVER"/><emphasis>SERVER ROLE = MEMBER SERVER</emphasis></para>

    <para>This mode will only work correctly if <citerefentry><refentrytitle>net</refentrytitle>
    <manvolnum>8</manvolnum></citerefentry> has been used to add this
    machine into a Windows Domain. It expects the <smbconfoption name="encrypted passwords"/>
        parameter to be set to <constant>yes</constant>. In this 
    mode Samba will try to validate the username/password by passing
    it to a Windows or Samba Domain Controller, in exactly 
    the same way that a Windows Server would do.</para>

    <para><emphasis>Note</emphasis> that a valid UNIX user must still 
    exist as well as the account on the Domain Controller to allow 
    Samba to have a valid UNIX account to map file access to.  Winbind can provide this.</para>

    <para><anchor id="PDC"/><emphasis>SERVER ROLE = CLASSIC PRIMARY DOMAIN CONTROLLER</emphasis></para>

    <para>This mode of operation runs a classic Samba primary domain
    controller, providing domain logon services to Windows and Samba
    clients of an NT4-like domain.  Clients must be joined to the domain to
    create a secure, trusted path across the network.  There must be
    only one PDC per NetBIOS scope (typcially a broadcast network or
    clients served by a single WINS server).</para>

    <para><anchor id="BDC"/><emphasis>SERVER ROLE = CLASSIC BACKUP DOMAIN CONTROLLER</emphasis></para>

    <para>This mode of operation runs a classic Samba backup domain
    controller, providing domain logon services to Windows and Samba
    clients of an NT4-like domain.  As a BDC, this allows
    multiple Samba servers to provide redundant logon services to a
    single NetBIOS scope.</para>

    <para><anchor id="AD-DC"/><emphasis>SERVER ROLE = ACTIVE DIRECTORY DOMAIN CONTROLLER</emphasis></para>

    <para>This mode of operation runs Samba as an active directory
    domain controller, providing domain logon services to Windows and
    Samba clients of the domain.  This role requires special
    configuration, see the <ulink
    url="http://wiki.samba.org/index.php/Samba4/HOWTO">Samba4
    HOWTO</ulink></para>

</description>

<related>security</related>
<related>realm</related>
<related>encrypt passwords</related>

<value type="default">AUTO</value>
<value type="example">ACTIVE DIRECTORY DOMAIN CONTROLLER</value>
</samba:parameter>