source: postlfs/security/linux-pam.xml@ dee8484

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
  <!ENTITY % general-entities SYSTEM "../../general.ent">
  %general-entities;

  <!ENTITY linux-pam-download-http "https://github.com/linux-pam/linux-pam/releases/download/v&linux-pam-version;/Linux-PAM-&linux-pam-version;.tar.xz">
  <!ENTITY linux-pam-download-ftp  " ">
  <!ENTITY linux-pam-md5sum        "895e8adfa14af334f679bbeb28503f66">
  <!ENTITY linux-pam-size          "966 KB">
  <!ENTITY linux-pam-buildsize     "39 MB (with tests)">
  <!ENTITY linux-pam-time          "0.4 SBU (with tests)">

  <!ENTITY linux-pam-docs-download "https://github.com/linux-pam/linux-pam/releases/download/v&linux-pam-version;/Linux-PAM-&linux-pam-docs-version;-docs.tar.xz">
  <!ENTITY linux-pam-docs-md5sum   "ceb3dc248cb2f49a40904b93cb91db1b">
  <!ENTITY linux-pam-docs-size     "433 KB">
  <!--
  <!ENTITY debian-pam-docs         "http://debian.securedservers.com/kernel/pub/linux/libs/pam">
  -->
]>

<sect1 id="linux-pam" xreflabel="Linux-PAM-&linux-pam-version;">
  <?dbhtml filename="linux-pam.html"?>


  <title>Linux-PAM-&linux-pam-version;</title>

  <indexterm zone="linux-pam">
    <primary sortas="a-Linux-PAM">Linux-PAM</primary>
  </indexterm>

  <sect2 role="package">
    <title>Introduction to Linux PAM</title>

    <para>
      The <application>Linux PAM</application> package contains
      Pluggable Authentication Modules used by the local
      system administrator to control how application programs authenticate
      users.
    </para>

    &lfs112_checked;

    <bridgehead renderas="sect3">Package Information</bridgehead>
    <itemizedlist spacing="compact">
      <listitem>
        <para>
          Download (HTTP): <ulink url="&linux-pam-download-http;"/>
        </para>
      </listitem>
      <listitem>
        <para>
          Download (FTP): <ulink url="&linux-pam-download-ftp;"/>
        </para>
      </listitem>
      <listitem>
        <para>
          Download MD5 sum: &linux-pam-md5sum;
        </para>
      </listitem>
      <listitem>
        <para>
          Download size: &linux-pam-size;
        </para>
      </listitem>
      <listitem>
        <para>
          Estimated disk space required: &linux-pam-buildsize;
        </para>
      </listitem>
      <listitem>
        <para>
          Estimated build time: &linux-pam-time;
        </para>
      </listitem>
    </itemizedlist>

    <bridgehead renderas="sect3">Additional Downloads</bridgehead>
    <itemizedlist spacing="compact">
    <title>Optional Documentation</title>
      <listitem>
        <para>
          Download (HTTP): <ulink url="&linux-pam-docs-download;"/>
        </para>
      </listitem>
      <listitem>
        <para>
          Download MD5 sum: &linux-pam-docs-md5sum;
        </para>
      </listitem>
      <listitem>
        <para>
          Download size &linux-pam-docs-size;
        </para>
      </listitem>
    </itemizedlist>

    <bridgehead renderas="sect3">Linux PAM Dependencies</bridgehead>

    <bridgehead renderas="sect4">Optional</bridgehead>
    <para role="optional">
      <xref linkend="db"/>,
      <xref linkend="libnsl"/>,
      <xref linkend="libtirpc"/>,
      <ulink url="https://github.com/linux-audit/audit-userspace">libaudit</ulink>, and
      <ulink url="https://www.prelude-siem.org">Prelude</ulink>
    </para>

    <bridgehead renderas="sect4">Optional (To Rebuild the Documentation)</bridgehead>
    <para role="optional">
      <xref linkend="DocBook"/>,
      <xref linkend="docbook-xsl"/>,
      <xref linkend="fop"/>,
      <xref linkend="libxslt"/> and either
      <xref linkend="lynx"/> or
      <ulink url="&w3m-url;">W3m</ulink>
    </para>

    <note>
      <para role="required">
        <xref role="runtime" linkend="shadow"/>
        <phrase revision="systemd"> and <xref role="runtime" linkend="systemd"/>
        must</phrase><phrase revision="sysv">must</phrase> be reinstalled
        and reconfigured
        after installing and configuring <application>Linux PAM</application>.
      </para>

      <para role="recommended">
         With Linux-PAM-1.4.0 and higher, the pam_cracklib module is not
         installed by default. Use <xref role="runtime" linkend="libpwquality"/>
         to enforce strong passwords.
      </para>
    </note>

    <para condition="html" role="usernotes">User Notes:
      <ulink url="&blfs-wiki;/linux-pam"/>
    </para>
  </sect2>

  <sect2 role="installation">
    <title>Installation of Linux PAM</title>

    <para revision="sysv">
      First, prevent the installation of an unneeded systemd file:
    </para>

<screen revision="sysv"><userinput>sed -e /service_DATA/d \
    -i modules/pam_namespace/Makefile.am &amp;&amp;
autoreconf</userinput></screen>

    <para>
      If you downloaded the documentation, unpack the tarball by issuing
      the following command.
    </para>

<screen><userinput>tar -xf ../Linux-PAM-&linux-pam-docs-version;-docs.tar.xz --strip-components=1</userinput></screen>

    <para>
      If you want to regenerate the documentation yourself, fix the
      <command>configure</command> script so it will detect lynx:
    </para>

<screen><userinput>sed -e 's/dummy elinks/dummy lynx/'                                    \
    -e 's/-no-numbering -no-references/-force-html -nonumbers -stdin/' \
    -i configure</userinput></screen>

    <para>
      Compile and link <application>Linux PAM</application> by
      running the following commands:
    </para>

<screen><userinput>./configure --prefix=/usr                        \
            --sbindir=/usr/sbin                  \
            --sysconfdir=/etc                    \
            --libdir=/usr/lib                    \
            --enable-securedir=/usr/lib/security \
            --docdir=/usr/share/doc/Linux-PAM-&linux-pam-version; &amp;&amp;
make</userinput></screen>

    <para>
      To test the results, a suitable <filename>/etc/pam.d/other</filename>
      configuration file must exist.
    </para>

    <caution>
      <title>Reinstallation or Upgrade of Linux PAM</title>
      <para>
        If you have a system with Linux PAM installed and working, be careful
        when modifying the files in
        <filename class="directory">/etc/pam.d</filename>, since your system
        may become totally unusable. If you want to run the tests, you do not
        need to create another <filename>/etc/pam.d/other</filename> file. The
        existing file can be used for the tests.
      </para>

      <para>
         You should also be aware that <command>make install</command>
         overwrites the configuration files in
         <filename class="directory">/etc/security</filename> as well as
         <filename>/etc/environment</filename>. If you
         have modified those files, be sure to back them up.
      </para>
    </caution>

    <para>
      For a first-time installation, create a configuration file by issuing the
      following commands as the <systemitem class="username">root</systemitem>
      user:
    </para>

<screen role="root"><userinput>install -v -m755 -d /etc/pam.d &amp;&amp;

cat &gt; /etc/pam.d/other &lt;&lt; "EOF"
<literal>auth     required       pam_deny.so
account  required       pam_deny.so
password required       pam_deny.so
session  required       pam_deny.so</literal>
EOF</userinput></screen>

    <para>
      Now run the tests by issuing <command>make check</command>.
      Be sure the tests produced no errors before continuing the
      installation. Note that the tests are very long.
      Redirect the output to a log file, so you can inspect it thoroughly.
    </para>

    <para>
      For a first-time installation, remove the configuration file
      created earlier by issuing the following command as the
      <systemitem class="username">root</systemitem> user:
    </para>

<screen role="root"><userinput>rm -fv /etc/pam.d/other</userinput></screen>

    <para>
      Now, as the <systemitem class="username">root</systemitem>
      user:
    </para>

<screen role="root"><userinput>make install &amp;&amp;
chmod -v 4755 /usr/sbin/unix_chkpwd</userinput></screen>

  </sect2>

  <sect2 role="commands">
    <title>Command Explanations</title>

    <para>
      <parameter>--enable-securedir=/usr/lib/security</parameter>:
      This switch sets the installation location for the
      <application>PAM</application> modules.
    </para>

    <para>
      <option>--disable-regenerate-docu</option> : If the needed dependencies
      (<xref linkend="DocBook"/>, <xref linkend="docbook-xsl"/>, <xref
      linkend="libxslt"/>, and <xref linkend="lynx"/> or <ulink
      url="&w3m-url;">W3m</ulink>) are installed, the manual pages, and the
      html and text documentation files, are generated and installed.
      Furthermore, if <xref linkend="fop"/> is installed, the PDF
      documentation is generated and installed. Use this switch if you do not
      want to rebuild the documentation.
    </para>

    <para>
      <command>chmod -v 4755 /usr/sbin/unix_chkpwd</command>:
      The setuid bit for the <command>unix_chkpwd</command> helper program must be 
      turned on, so that non-<systemitem class="username">root</systemitem>
      processes can access the shadow file.
    </para>

  </sect2>

  <sect2 role="configuration">
    <title>Configuring Linux-PAM</title>

    <sect3 id="pam-config">
      <title>Configuration Files</title>

      <para>
        <filename>/etc/security/*</filename> and
        <filename>/etc/pam.d/*</filename>
      </para>

      <indexterm zone="linux-pam pam-config">
        <primary sortas="e-etc-security">/etc/security/*</primary>
      </indexterm>

      <indexterm zone="linux-pam pam-config">
        <primary sortas="e-etc-pam.d">/etc/pam.d/*</primary>
      </indexterm>

    </sect3>

    <sect3>
      <title>Configuration Information</title>

      <para>
        Configuration information is placed in
        <filename class="directory">/etc/pam.d/</filename>.
        Here is a sample file:
      </para>

<screen><literal># Begin /etc/pam.d/other

auth            required        pam_unix.so     nullok
account         required        pam_unix.so
session         required        pam_unix.so
password        required        pam_unix.so     nullok

# End /etc/pam.d/other</literal></screen>

      <para>
        Now create some generic configuration files.  As the
        <systemitem class="username">root</systemitem> user:
      </para>

<screen role="root"><userinput>install -vdm755 /etc/pam.d &amp;&amp;
cat &gt; /etc/pam.d/system-account &lt;&lt; "EOF" &amp;&amp;
<literal># Begin /etc/pam.d/system-account

account   required    pam_unix.so

# End /etc/pam.d/system-account</literal>
EOF

cat &gt; /etc/pam.d/system-auth &lt;&lt; "EOF" &amp;&amp;
<literal># Begin /etc/pam.d/system-auth

auth      required    pam_unix.so

# End /etc/pam.d/system-auth</literal>
EOF

cat &gt; /etc/pam.d/system-session &lt;&lt; "EOF"
<literal># Begin /etc/pam.d/system-session

session   required    pam_unix.so

# End /etc/pam.d/system-session</literal>
EOF
cat &gt; /etc/pam.d/system-password &lt;&lt; "EOF"
<literal># Begin /etc/pam.d/system-password

# use sha512 hash for encryption, use shadow, and try to use any previously
# defined authentication token (chosen password) set by any prior module
# Use the same number of rounds as shadow.
password  required    pam_unix.so       sha512 shadow try_first_pass \
                                        rounds=500000

# End /etc/pam.d/system-password</literal>
EOF
</userinput></screen>

     <para>
       If you wish to enable strong password support, install
       <xref linkend="libpwquality"/>, and follow the
       instructions on that page to configure the pam_pwquality
       PAM module with strong password support.
     </para>

<!-- With the removal of the pam_cracklib module, we're supposed to be using
     libpwquality. That already includes instructions in its configuration
     information page, so we'll use those instead.

     Linux-PAM must be installed prior to libpwquality so that PAM support
     is built in, and the PAM module is built.
-->
<!-- WARNING: If for any reason the instructions below are reinstated be
     careful with the number of rounds, which should match the one in shadow.
      <para>
        The remaining generic file depends on whether <xref
        linkend="cracklib"/> is installed.  If it is installed, use:
      </para>

<screen role="root"><userinput>cat &gt; /etc/pam.d/system-password &lt;&lt; "EOF"
<literal># Begin /etc/pam.d/system-password

# check new passwords for strength (man pam_cracklib)
password  required    pam_cracklib.so    authtok_type=UNIX retry=1 difok=5 \
                                         minlen=9 dcredit=1 ucredit=1 \
                                         lcredit=1 ocredit=1 minclass=0 \
                                         maxrepeat=0 maxsequence=0 \
                                         maxclassrepeat=0 \
                                         dictpath=/lib/cracklib/pw_dict
# use sha512 hash for encryption, use shadow, and use the
# authentication token (chosen password) set by pam_cracklib
# above (or any previous modules)
password  required    pam_unix.so        sha512 shadow use_authtok

# End /etc/pam.d/system-password</literal>
EOF</userinput></screen>

      <note>
        <para>
          In its default configuration, pam_cracklib will
          allow multiple case passwords as short as 6 characters, even with
          the <parameter>minlen</parameter> value set to 11. You should review
          the pam_cracklib(8) man page and determine if these default values
          are acceptable for the security of your system.
        </para>
      </note>

      <para>
        If <xref linkend="cracklib"/> is <emphasis>NOT</emphasis> installed,
        use:
      </para>

<screen role="nodump"><userinput>cat &gt; /etc/pam.d/system-password &lt;&lt; "EOF"
<literal># Begin /etc/pam.d/system-password

# use sha512 hash for encryption, use shadow, and try to use any previously
# defined authentication token (chosen password) set by any prior module
password  required    pam_unix.so       sha512 shadow try_first_pass

# End /etc/pam.d/system-password</literal>
EOF</userinput></screen>
-->
      <para>
        Next, add a restrictive <filename>/etc/pam.d/other</filename>
        configuration file.  With this file, programs that are PAM aware will
        not run unless a configuration file specifically for that application
        exists.
      </para>

<screen role="root"><userinput>cat &gt; /etc/pam.d/other &lt;&lt; "EOF"
<literal># Begin /etc/pam.d/other

auth        required        pam_warn.so
auth        required        pam_deny.so
account     required        pam_warn.so
account     required        pam_deny.so
password    required        pam_warn.so
password    required        pam_deny.so
session     required        pam_warn.so
session     required        pam_deny.so

# End /etc/pam.d/other</literal>
EOF</userinput></screen>

      <para>
        The <application>PAM</application> man page (<command>man
        pam</command>) provides a good starting point to learn
        about the several fields, and allowable entries.
        <!-- not accessible 2022-09-08 -->
        <!-- it's available at a different address 2022-10-23-->
        The
        <ulink url="https://www.docs4dev.com/docs/en/linux-pam/1.1.2/reference/Linux-PAM_SAG.html">
          Linux-PAM System Administrators' Guide
        </ulink> is recommended for additional information.
      </para>

      <important>
        <para>
          You should now reinstall the <xref linkend="shadow"/>
          <phrase revision="sysv">package</phrase>
          <phrase revision="systemd"> and <xref linkend="systemd"/>
          packages</phrase>.
        </para>
      </important>

    </sect3>

  </sect2>

  <sect2 role="content">
    <title>Contents</title>

    <segmentedlist>
      <segtitle>Installed Program</segtitle>
      <segtitle>Installed Libraries</segtitle>
      <segtitle>Installed Directories</segtitle>

      <seglistitem>
        <seg>
          faillock, mkhomedir_helper, pam_namespace_helper,
          pam_timestamp_check, pwhistory_helper, unix_chkpwd and
          unix_update
        </seg>
        <seg>
          libpam.so, libpamc.so and libpam_misc.so
        </seg>
        <seg>
          /etc/security,
          /usr/lib/security,
          /usr/include/security and
          /usr/share/doc/Linux-PAM-&linux-pam-version;
        </seg>
      </seglistitem>
    </segmentedlist>

    <variablelist>
      <bridgehead renderas="sect3">Short Descriptions</bridgehead>
      <?dbfo list-presentation="list"?>
      <?dbhtml list-presentation="table"?>

      <varlistentry id="faillock">
        <term><command>faillock</command></term>
        <listitem>
          <para>
            displays and modifies the authentication failure record files
          </para>
          <indexterm zone="linux-pam faillock">
            <primary sortas="b-faillock">faillock</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="mkhomedir_helper">
        <term><command>mkhomedir_helper</command></term>
        <listitem>
          <para>
            is a helper binary that creates home directories
          </para>
          <indexterm zone="linux-pam mkhomedir_helper">
            <primary sortas="b-mkhomedir_helper">mkhomedir_helper</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="pam_namespace_helper">
        <term><command>pam_namespace_helper</command></term>
        <listitem>
          <para>
            is a helper program used to configure a private namespace for a
            user session
          </para>
          <indexterm zone="linux-pam pam_namespace_helper">
            <primary sortas="b-pam_namespace_helper">pam_namespace_helper</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="pwhistory_helper">
        <term><command>pwhistory_helper</command></term>
        <listitem>
          <para>
            is a helper program that transfers password hashes from passwd or
            shadow to opasswd
          </para>
          <indexterm zone="linux-pam pwhistory_helper">
            <primary sortas="b-pwhistory_helper">pwhistory_helper</primary>
          </indexterm>
        </listitem>
      </varlistentry>
<!-- Removed with the removal of the pam_tally{,2} module
      <varlistentry id="pam_tally">
        <term><command>pam_tally</command></term>
        <listitem>
          <para>
            is used to interrogate and manipulate the login counter file.
          </para>
          <indexterm zone="linux-pam pam_tally">
            <primary sortas="b-pam_tally">pam_tally</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="pam_tally2">
        <term><command>pam_tally2</command></term>
        <listitem>
          <para>
            is used to interrogate and manipulate the login counter file, but
            does not have some limitations that <command>pam_tally</command>
            does.
          </para>
          <indexterm zone="linux-pam pam_tally2">
            <primary sortas="b-pam_tally2">pam_tally2</primary>
          </indexterm>
        </listitem>
      </varlistentry>
-->

      <varlistentry id="pam_timestamp_check">
        <term><command>pam_timestamp_check</command></term>
        <listitem>
          <para>
            is used to check if the default timestamp is valid
          </para>
          <indexterm zone="linux-pam pam_timestamp_check">
            <primary sortas="b-pam_timestamp_check">pam_timestamp_check</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="unix_chkpwd">
        <term><command>unix_chkpwd</command></term>
        <listitem>
          <para>
            is a helper binary that verifies the password of the current user
          </para>
          <indexterm zone="linux-pam unix_chkpwd">
            <primary sortas="b-unix_chkpwd">unix_chkpwd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="unix_update">
        <term><command>unix_update</command></term>
        <listitem>
          <para>
            is a helper binary that updates the password of a given user
          </para>
          <indexterm zone="linux-pam unix_update">
            <primary sortas="b-unix_update">unix_update</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libpam">
        <term><filename class="libraryfile">libpam.so</filename></term>
        <listitem>
          <para>
            provides the interfaces between applications and the
            PAM modules
          </para>
          <indexterm zone="linux-pam libpam">
            <primary sortas="c-libpam">libpam.so</primary>
          </indexterm>
        </listitem>
      </varlistentry>

    </variablelist>

  </sect2>

</sect1>