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

<samba:parameter name="security"
                 context="G"
                 type="enum"
                 function="_security"
                 enumlist="enum_security"
                 xmlns:samba="http://www.samba.org/samba/DTD/samba-doc">
<when_value value="security">
    <requires option="encrypted passwords">/(yes|true)/</requires>
</when_value>
<description>
    <para>This option affects how clients respond to 
    Samba 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">security = user</command>, as this is
    the most common setting, used for a standalone file server or a DC.</para>

    <para>The alternatives are
    <command moreinfo="none">security = ads</command> or <command moreinfo="none">security = domain
    </command>, which support joining Samba to a Windows domain</para>

    <para>You should use <command moreinfo="none">security = user</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>The different settings will now be explained.</para>


    <para><anchor id="SECURITYEQUALSAUTO"/><emphasis>SECURITY = AUTO</emphasis></para>

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

    <para><anchor id="SECURITYEQUALSUSER"/><emphasis>SECURITY = USER</emphasis></para>

    <para>If <smbconfoption name="server role"/> is not specified, this is the default security setting in Samba. 
    With user-level security 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). Encrypted passwords (see the <smbconfoption name="encrypted passwords"/> parameter) can also
    be 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><emphasis>Note</emphasis> that the name of the resource being 
    requested is <emphasis>not</emphasis> sent to the server until after 
    the server has successfully authenticated the client. This is why 
    guest shares don't work in user level security without allowing 
    the server to automatically map unknown users into the <smbconfoption name="guest account"/>. 
    See the <smbconfoption name="map to guest"/> parameter for details on doing this.</para>

    <para><anchor id="SECURITYEQUALSDOMAIN"/><emphasis>SECURITY = DOMAIN</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 NT 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 NT Primary or Backup Domain Controller, in exactly 
    the same way that a Windows NT 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.</para>

    <para><emphasis>Note</emphasis> that from the client's point 
    of view <command moreinfo="none">security = domain</command> is the same 
    as <command moreinfo="none">security = user</command>. It only 
    affects how the server deals with the authentication, 
    it does not in any way affect what the client sees.</para>

    <para><emphasis>Note</emphasis> that the name of the resource being 
    requested is <emphasis>not</emphasis> sent to the server until after 
    the server has successfully authenticated the client. This is why 
    guest shares don't work in user level security without allowing 
    the server to automatically map unknown users into the <smbconfoption name="guest account"/>. 
    See the <smbconfoption name="map to guest"/> parameter for details on doing this.</para>

    <para>See also the <smbconfoption name="password server"/> parameter and
         the <smbconfoption name="encrypted passwords"/> parameter.</para>


    <para><emphasis>Note</emphasis> that the name of the resource being 
    requested is <emphasis>not</emphasis> sent to the server until after 
    the server has successfully authenticated the client. This is why 
    guest shares don't work in user level security without allowing 
    the server to automatically map unknown users into the <smbconfoption name="guest account"/>. 
    See the <smbconfoption name="map to guest"/> parameter for details on doing this.</para>

    <para>See also the <smbconfoption name="password server"/> parameter and the 
        <smbconfoption name="encrypted passwords"/> parameter.</para>

        <para><anchor id="SECURITYEQUALSADS"/><emphasis>SECURITY = ADS</emphasis></para>
        
        <para>In this mode, Samba will act as a domain member in an ADS realm. To operate 
                in this mode, the machine running Samba will need to have Kerberos installed 
                and configured and Samba will need to be joined to the ADS realm using the 
                net utility. </para>
        
        <para>Note that this mode does NOT make Samba operate as a Active Directory Domain 
                Controller. </para>

        <para>Note that this forces <smbconfoption name="require strong key">yes</smbconfoption>
        and <smbconfoption name="client schannel">yes</smbconfoption> for the primary domain.</para>

        <para>Read the chapter about Domain Membership in the HOWTO for details.</para>
</description>

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

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