source: postlfs/security/shadow.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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 shadow-download-http "https://github.com/shadow-maint/shadow/releases/download/&shadow-version;/shadow-&shadow-version;.tar.xz">
  <!ENTITY shadow-download-ftp  " ">
  <!ENTITY shadow-md5sum        "006b0856abd49b5e7b45b7cb78ca272a">
  <!ENTITY shadow-size          "1.7 MB">
  <!ENTITY shadow-buildsize     "39 MB">
  <!ENTITY shadow-time          "0.2 SBU">
]>

<sect1 id="shadow" xreflabel="Shadow-&shadow-version;">
  <?dbhtml filename="shadow.html"?>


  <title>Shadow-&shadow-version;</title>

  <indexterm zone="shadow">
    <primary sortas="a-Shadow">Shadow</primary>
  </indexterm>

  <sect2 role="package">
    <title>Introduction to Shadow</title>

    <para>
      <application>Shadow</application> was indeed installed in LFS and there is
      no reason to reinstall it unless you installed
      <application>CrackLib</application> or
      <application>Linux-PAM</application> after your LFS system was completed.
      If you have installed <application>CrackLib</application> after LFS, then
      reinstalling <application>Shadow</application> will enable strong password
      support. If you have installed <application>Linux-PAM</application>,
      reinstalling <application>Shadow</application> will allow programs such as
      <command>login</command> and <command>su</command> to utilize PAM.
    </para>

    &lfs121_checked;

    <bridgehead renderas="sect3">Package Information</bridgehead>
    <itemizedlist spacing="compact">
      <listitem>
        <para>
          Download (HTTP): <ulink url="&shadow-download-http;"/>
        </para>
      </listitem>
      <listitem>
        <para>
          Download (FTP): <ulink url="&shadow-download-ftp;"/>
        </para>
      </listitem>
      <listitem>
        <para>
          Download MD5 sum: &shadow-md5sum;
        </para>
      </listitem>
      <listitem>
        <para>
          Download size: &shadow-size;
        </para>
      </listitem>
      <listitem>
        <para>
          Estimated disk space required: &shadow-buildsize;
        </para>
      </listitem>
      <listitem>
        <para>
          Estimated build time: &shadow-time;
        </para>
      </listitem>
    </itemizedlist>
<!--
    <bridgehead renderas="sect3">Additional Downloads</bridgehead>
    <itemizedlist spacing="compact">
      <listitem>
        <para>
          Required patch:
          <ulink url="&patch-root;/shadow-&shadow-version;-useradd_segfault-1.patch"/>
        </para>
      </listitem>
    </itemizedlist>
-->
    <bridgehead renderas="sect3">Shadow Dependencies</bridgehead>

    <bridgehead renderas="sect4">Required</bridgehead>
    <para role="required">
      <xref linkend="linux-pam"/> or
      <xref role="nodep" linkend="cracklib"/>
    </para>

    <bridgehead renderas="sect4">Optional</bridgehead>
    <para role="optional">
      <ulink url="https://libbsd.freedesktop.org/wiki/">libbsd</ulink> and
      <ulink url="https://www.openwall.com/tcb/">tcb</ulink>
    </para>

  </sect2>

  <sect2 role="installation">
    <title>Installation of Shadow</title>

    <important>
      <para>
        The installation commands shown below are for installations where
        <application>Linux-PAM</application> has been installed and
        <application>Shadow</application> is being reinstalled to support the
        <application>Linux-PAM</application> installation.
      </para>

      <para>
        If you are reinstalling <application>Shadow</application> to provide
        strong password support using the <application>CrackLib</application>
        library without using <application>Linux-PAM</application>, ensure you
        add the <parameter>--with-libcrack</parameter> parameter to the
        <command>configure</command> script below and also issue the following
        command:
      </para>

<screen role="nodump"><userinput>sed -i 's@DICTPATH.*@DICTPATH\t/lib/cracklib/pw_dict@' etc/login.defs</userinput></screen>
    </important>

    <warning>
      <para>
        If reinstalling shadow for a version update, be sure to 
        reaccomplish the Linux-PAM configuration below.  The installation
        of shadow overwrites many of the files in 
        <filename class="directory">/etc/pam.d/</filename>.
      </para>
    </warning>

    <para>
      Reinstall <application>Shadow</application> by running the following
      commands:
    </para>
<!--
<screen><userinput>patch -Np1 -i ../shadow-4.10-useradd_segfault-1.patch &amp;&amp;
-->
<screen><userinput>sed -i 's/groups$(EXEEXT) //' src/Makefile.in          &amp;&amp;

find man -name Makefile.in -exec sed -i 's/groups\.1 / /'   {} \; &amp;&amp;
find man -name Makefile.in -exec sed -i 's/getspnam\.3 / /' {} \; &amp;&amp;
find man -name Makefile.in -exec sed -i 's/passwd\.5 / /'   {} \; &amp;&amp;

sed -e 's@#ENCRYPT_METHOD DES@ENCRYPT_METHOD YESCRYPT@' \
    -e 's@/var/spool/mail@/var/mail@'                   \
    -e '/PATH=/{s@/sbin:@@;s@/bin:@@}'                  \
    -i etc/login.defs                                   &amp;&amp;

./configure --sysconfdir=/etc   \
            --disable-static    \
            --without-libbsd    \
            --with-{b,yes}crypt &amp;&amp;<!--
This is the default:            - -with-group-name-max-length=32 &amp;&amp;-->
make</userinput></screen>

    <para>
      This package does not come with a test suite.
    </para>

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

<screen role="root"><userinput>make exec_prefix=/usr pamddir= install</userinput></screen>

    <para>
      The man pages were installed in LFS, but if reinstallation is
      desired, run (as the <systemitem class="username">root</systemitem> user):
    </para>

<screen role="root"><userinput>make -C man install-man</userinput></screen>

  </sect2>

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

    <para>
      <command>sed -i 's/groups$(EXEEXT) //' src/Makefile.in</command>: This sed
      is used to suppress the installation of the <command>groups</command>
      program as the version from the <application>Coreutils</application>
      package installed during LFS is preferred.
    </para>

    <para>
      <command>find man -name Makefile.in -exec ... {} \;</command>: The
      first command is used to suppress the installation of the
      <command>groups</command> man pages so the existing ones installed from
      the <application>Coreutils</application> package are not replaced.
      The two other commands prevent installation of manual pages that
      are already installed by <application>Man-pages</application> in LFS.
    </para>

    <para>
      <command>sed -e 's@#ENCRYPT_METHOD DES@ENCRYPT_METHOD YESCRYPT@' -e
        's@/var/spool/mail@/var/mail@' -e '/PATH=/{s@/sbin:@@;s@/bin:@@}'
        -i etc/login.defs</command>: Instead of using the default 'DES'
      method, this command modifies the installation to use the much more
      secure 'YESCRYPT' method of hashing passwords, which also allows
      passwords longer than eight characters.  The command also changes the
      obsolete <filename class="directory">/var/spool/mail</filename> location
      for user mailboxes that <application>Shadow</application> uses by
      default to the <filename class="directory">/var/mail</filename>
      location. It also changes the default path to be consistent with that
      set in LFS.
    </para>

    <para>
      <parameter>--without-libbsd</parameter>: Prevents looking for the
      <command>readpassphrase</command> function, which can be found only in
      <filename class="libraryfile">libbsd</filename>, which we do not
      have in BLFS. An internal implementation of
      <command>readpassphrase</command> is used instead.
    </para>

    <para>
      <parameter>pamddir=</parameter>: Prevents installation of the shipped
      PAM configuration files into
      <filename class='directory'>/etc/pam.d</filename>. The shipped
      configuration does not work with the BLFS PAM configuration and we
      will create these configuration files explicitly.
    </para>

<!-- This is the default
    <para>
      <parameter>-\-with-group-name-max-length=32</parameter>: The maximum
      user name is 32 characters. Make the maximum group name the same.
    </para>
    -->
<!--
    <para>
      <parameter>-\-without-su</parameter>: Don't reinstall
      <command>su</command> because upstream recommends using the
      <command>su</command> command from <xref linkend='util-linux'/>
      when <application>Linux-PAM</application> is available.
    </para>
-->
  </sect2>

<!-- Now, /etc/default/useradd is not reinstalled anymore, and this
     configuration has been done in lfs
  <sect2 role="configuration">
    <title>Configuring Shadow</title>

    <para>
      <application>Shadow</application>'s stock configuration for the
      <command>useradd</command> utility may not be desirable for your
      installation. One default parameter causes <command>useradd</command> to
      create a mailbox file for any newly created user.
      <command>useradd</command> will make the group ownership of this file to
      the <systemitem class="groupname">mail</systemitem> group with 0660
      permissions. If you would prefer that these mailbox files are not created
      by <command>useradd</command>, issue the following command as the
      <systemitem class="username">root</systemitem> user:
    </para>

<screen role="root"><userinput>sed -i 's/yes/no/' /etc/default/useradd</userinput></screen>
  </sect2>
-->
  <sect2 role="configuration">
    <title>Configuring Linux-PAM to Work with Shadow</title>

    <note>
      <para>
        The rest of this page is devoted to configuring
        <application>Shadow</application> to work properly with
        <application>Linux-PAM</application>. If you do not have
        <application>Linux-PAM</application> installed, and you reinstalled
        <application>Shadow</application> to support strong passwords via the
        <application>CrackLib</application> library, no further configuration is
        required.
      </para>
    </note>

    <sect3 id="pam.d">
      <title>Config Files</title>

      <para>
        <filename>/etc/pam.d/*</filename> or alternatively
        <filename>/etc/pam.conf</filename>,
        <filename>/etc/login.defs</filename> and
        <filename>/etc/security/*</filename>
      </para>

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

      <indexterm zone="shadow pam.d">
        <primary sortas="e-etc-pam.conf">/etc/pam.conf</primary>
      </indexterm>

      <indexterm zone="shadow pam.d">
        <primary sortas="e-etc-login.defs">/etc/login.defs</primary>
      </indexterm>

      <indexterm zone="shadow pam.d">
        <primary sortas="e-etc-security">/etc/security/*</primary>
      </indexterm>
    </sect3>

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

      <para>
        Configuring your system to use <application>Linux-PAM</application> can
        be a complex task. The information below will provide a basic setup so
        that <application>Shadow</application>'s login and password
        functionality will work effectively with
        <application>Linux-PAM</application>. Review the information and links
        on the <xref linkend="linux-pam"/> page for further configuration
        information. For information specific to integrating
        <application>Shadow</application>, <application>Linux-PAM</application>
        and <application>libpwquality</application>, you can visit the
        following link:
      </para>

      <itemizedlist spacing="compact">
        <listitem>
          <!-- Old URL redirects to here. -->
          <para>
            <ulink url="https://deer-run.com/users/hal/linux_passwords_pam.html"/>
          </para>
        </listitem>
      </itemizedlist>

      <sect4 id="pam-login-defs">
        <title>Configuring /etc/login.defs</title>

        <para>
          The <command>login</command> program currently performs many functions
          which <application>Linux-PAM</application> modules should now handle.
          The following <command>sed</command> command will comment out the
          appropriate lines in <filename>/etc/login.defs</filename>, and stop
          <command>login</command> from performing these functions (a backup
          file named <filename>/etc/login.defs.orig</filename> is also created
          to preserve the original file's contents). Issue the following
          commands as the <systemitem class="username">root</systemitem> user:
        </para>

        <indexterm zone="shadow pam-login-defs">
          <primary sortas="e-etc-login.defs">/etc/login.defs</primary>
        </indexterm>

<screen role="root"><userinput>install -v -m644 /etc/login.defs /etc/login.defs.orig &amp;&amp;
for FUNCTION in FAIL_DELAY               \
                FAILLOG_ENAB             \
                LASTLOG_ENAB             \
                MAIL_CHECK_ENAB          \
                OBSCURE_CHECKS_ENAB      \
                PORTTIME_CHECKS_ENAB     \
                QUOTAS_ENAB              \
                CONSOLE MOTD_FILE        \
                FTMP_FILE NOLOGINS_FILE  \
                ENV_HZ PASS_MIN_LEN      \
                SU_WHEEL_ONLY            \
                CRACKLIB_DICTPATH        \
                PASS_CHANGE_TRIES        \
                PASS_ALWAYS_WARN         \
                CHFN_AUTH ENCRYPT_METHOD \
                ENVIRON_FILE
do
    sed -i "s/^${FUNCTION}/# &amp;/" /etc/login.defs
done</userinput></screen>
      </sect4>

      <sect4>
        <title>Configuring the /etc/pam.d/ Files</title>

        <para>
          As mentioned previously in the <application>Linux-PAM</application>
          instructions, <application>Linux-PAM</application> has two supported
          methods for configuration. The commands below assume that you've
          chosen to use a directory based configuration, where each program has
          its own configuration file.  You can optionally use a single
          <filename>/etc/pam.conf</filename> configuration file by using the
          text from the files below, and supplying the program name as an
          additional first field for each line.
        </para>

        <para>
          As the <systemitem class="username">root</systemitem> user, create
          the following <application>Linux-PAM</application> configuration files
          in the <filename class="directory">/etc/pam.d/</filename> directory
          (or add the contents to the <filename>/etc/pam.conf</filename> file)
          using the following commands:
        </para>
      </sect4>

      <sect4>
        <title>'login'</title>

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

# Set failure delay before next prompt to 3 seconds
auth      optional    pam_faildelay.so  delay=3000000

# Check to make sure that the user is allowed to login
auth      requisite   pam_nologin.so

# Check to make sure that root is allowed to login
# Disabled by default. You will need to create /etc/securetty
# file for this module to function. See man 5 securetty.
#auth      required    pam_securetty.so

# Additional group memberships - disabled by default
#auth      optional    pam_group.so

# include system auth settings
auth      include     system-auth

# check access for the user
account   required    pam_access.so

# include system account settings
account   include     system-account

# Set default environment variables for the user
session   required    pam_env.so

# Set resource limits for the user
session   required    pam_limits.so

# Display the message of the day - Disabled by default
#session   optional    pam_motd.so

# Check user's mail - Disabled by default
#session   optional    pam_mail.so      standard quiet

# include system session and password settings
session   include     system-session
password  include     system-password

# End /etc/pam.d/login</literal>
EOF</userinput></screen>
      </sect4>

      <sect4>
        <title>'passwd'</title>

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

password  include     system-password

# End /etc/pam.d/passwd</literal>
EOF</userinput></screen>
      </sect4>

      <sect4>
        <title>'su'</title>

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

# always allow root
auth      sufficient  pam_rootok.so

# Allow users in the wheel group to execute su without a password
# disabled by default
#auth      sufficient  pam_wheel.so trust use_uid

# include system auth settings
auth      include     system-auth

# limit su to users in the wheel group
# disabled by default
#auth      required    pam_wheel.so use_uid

# include system account settings
account   include     system-account

# Set default environment variables for the service user
session   required    pam_env.so

# include system session settings
session   include     system-session

# End /etc/pam.d/su</literal>
EOF</userinput></screen>
      </sect4>

      <sect4>
        <title>'chpasswd' and 'newusers'</title>

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

# always allow root
auth      sufficient  pam_rootok.so

# include system auth and account settings
auth      include     system-auth
account   include     system-account
password  include     system-password

# End /etc/pam.d/chpasswd</literal>
EOF

sed -e s/chpasswd/newusers/ /etc/pam.d/chpasswd >/etc/pam.d/newusers</userinput></screen>
      </sect4>

      <sect4>
        <title>'chage'</title>

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

# always allow root
auth      sufficient  pam_rootok.so

# include system auth and account settings
auth      include     system-auth
account   include     system-account

# End /etc/pam.d/chage</literal>
EOF</userinput></screen>
      </sect4>

      <sect4>
        <title>Other shadow utilities</title>

<screen role="root"><userinput>for PROGRAM in chfn chgpasswd chsh groupadd groupdel \
               groupmems groupmod useradd userdel usermod
do
    install -v -m644 /etc/pam.d/chage /etc/pam.d/${PROGRAM}
    sed -i "s/chage/$PROGRAM/" /etc/pam.d/${PROGRAM}
done</userinput></screen>

        <warning>
          <para>
            At this point, you should do a simple test to see if
            <application>Shadow</application> is working as expected. Open
            another terminal and log in as
            <systemitem class="username">root</systemitem>, and then run
            <command>login</command> and login as another user.  If you do
            not see any errors, then all is well and you should proceed with
            the rest of the configuration. If you did receive errors, stop
            now and double check the above configuration files manually.
            Any error is the sign of an error in the above procedure.
            You can also run the
            test suite from the <application>Linux-PAM</application> package
            to assist you in determining the problem. If you cannot find and
            fix the error, you should recompile
            <application>Shadow</application> adding the
            <option>--without-libpam</option> switch to the
            <command>configure</command> command in the above instructions
            (also move the <filename>/etc/login.defs.orig</filename> backup
            file to <filename>/etc/login.defs</filename>). If you fail to do
            this and the errors remain, you will be unable to log into your
            system.
          </para>
        </warning>
      </sect4>

      <sect4 id="pam-access">
        <title>Configuring Login Access</title>

        <para>
          Instead of using the <filename>/etc/login.access</filename> file for
          controlling access to the system, <application>Linux-PAM</application>
          uses the <filename class='libraryfile'>pam_access.so</filename> module
          along with the <filename>/etc/security/access.conf</filename> file.
          Rename the <filename>/etc/login.access</filename> file using the
          following command:
        </para>

        <indexterm zone="shadow pam-access">
          <primary sortas="e-etc-security-access.conf">/etc/security/access.conf</primary>
        </indexterm>
<!-- to editors: it is a common belief that:
        if <condition>; then <command>; fi
     is equivalent to:
        <condition> && <command>
     This is not true in bash; try:
        ([ 0 = 1 ] && echo not reachable); echo $? # echoes 1
     vs
        (if [ 0 = 1 ]; then echo not reachable; fi); echo $? # echoes 0
     So in scripts that may call subshells (for example through sudo) and
     that need error reporting, the outcome _is_ different. In all
     cases, for bash, the "if" form should be preferred.-->
<screen role="root"><userinput>if [ -f /etc/login.access ]; then mv -v /etc/login.access{,.NOUSE}; fi</userinput></screen>
      </sect4>

      <sect4 id="pam-limits">
        <title>Configuring Resource Limits</title>

        <para>
          Instead of using the <filename>/etc/limits</filename> file for
          limiting usage of system resources,
          <application>Linux-PAM</application> uses the
          <filename class='libraryfile'>pam_limits.so</filename> module along
          with the <filename>/etc/security/limits.conf</filename> file. Rename
          the <filename>/etc/limits</filename> file using the following command:
        </para>

        <indexterm zone="shadow pam-limits">
          <primary sortas="e-etc-security-limits.conf">/etc/security/limits.conf</primary>
        </indexterm>

<screen role="root"><userinput>if [ -f /etc/limits ]; then mv -v /etc/limits{,.NOUSE}; fi</userinput></screen>

        <caution>
          <para>
          Be sure to test the login capabilities of the system before logging
          out.  Errors in the configuration can cause a permanent
          lockout requiring a boot from an external source to correct the
          problem.
          </para>
        </caution>

      </sect4>
    </sect3>

  </sect2>

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

    <para>
      A list of the installed files, along with their short descriptions can be
      found at
      <ulink url="&lfs-root;/chapter08/shadow.html#contents-shadow"/>.
    </para>

  </sect2>

</sect1>