source: postlfs/security/shadow.xml@ d64103f

<?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 shadow-download-http "http://pkg-shadow.alioth.debian.org/releases/shadow-&shadow-version;.tar.xz">
  <!ENTITY shadow-download-ftp  " ">
  <!ENTITY shadow-md5sum        "2bfafe7d4962682d31b5eba65dba4fc8">
  <!ENTITY shadow-size          "1.5 MB">
  <!ENTITY shadow-buildsize     "53 MB">
  <!ENTITY shadow-time          "0.2 SBU">
]>

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

  <sect1info>
    <othername>$LastChangedBy$</othername>
    <date>$Date$</date>
  </sect1info>

  <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>

    &lfs75_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">Shadow Dependencies</bridgehead>

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

    <para condition="html" role="usernotes">
      User Notes: <ulink url="&blfs-wiki;/shadow"/>
    </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 (with or
        without a <application>CrackLib</application> installation) 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><userinput>sed -i 's@DICTPATH.*@DICTPATH\t/lib/cracklib/pw_dict@' etc/login.defs</userinput></screen>
    </important>

    <para>
      Reinstall <application>Shadow</application> by running the following
      commands:
    </para>

<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;

sed -i -e 's@#ENCRYPT_METHOD DES@ENCRYPT_METHOD SHA512@' \
       -e 's@/var/spool/mail@/var/mail@' etc/login.defs &amp;&amp;

sed -i 's/1000/999/' etc/useradd &amp;&amp;

./configure --sysconfdir=/etc &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 install &amp;&amp;
mv -v /usr/bin/passwd /bin</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>: This
      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.
    </para>

    <para>
      <command>sed -i -e 's@#ENCRYPT_METHOD DES@ENCRYPT_METHOD SHA512@' -e
      's@/var/spool/mail@/var/mail@' etc/login.defs</command>: Instead of using
      the default 'DES' method, this command modifies the installation to use
      the more secure 'SHA512' method of hashing passwords, which also allows
      passwords longer than eight characters. It 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.
    </para>

    <para>
      <command>sed -i 's/1000/999/' etc/useradd</command>: Make a minor change 
      to make the default useradd consistent with the LFS groups file.
    </para>

    <para>
      <command>mv -v /usr/bin/passwd /bin</command>: The
      <command>passwd</command> program may be needed during times when the
      <filename class='directory'>/usr</filename> filesystem is not mounted so
      it is moved into the root partition.
    </para>
  </sect2>

  <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>CrackLib</application>, you can visit the following
        link:
      </para>

      <itemizedlist spacing="compact">
        <listitem>
          <para>
            <ulink url="http://www.deer-run.com/~hal/sysadmin/pam_cracklib.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, replace
          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>'system-account'</title>

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

account   required    pam_unix.so

# End /etc/pam.d/system-account</literal>
EOF</userinput></screen>
      </sect4>

      <sect4>
        <title>'system-auth'</title>

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

auth      required    pam_unix.so

# End /etc/pam.d/system-auth</literal>
EOF</userinput></screen>
      </sect4>

      <sect4>
        <title>'system-passwd' (with cracklib)</title>

<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   type=Linux retry=3 difok=5 \
                                        difignore=23 minlen=9 dcredit=1 \
                                        ucredit=1 lcredit=1 ocredit=1 \
                                        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, owing to credits, 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>
      </sect4>

      <sect4>
        <title>'system-passwd' (without cracklib)</title>

<screen role="root"><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>
      </sect4>

      <sect4>
        <title>'system-session'</title>

<screen role="root"><userinput>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</userinput></screen>
      </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 the default auth settings
auth      include     system-auth

# check access for the user
account   required    pam_access.so

# include the default 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 date of last login - Disabled by default
#session   optional    pam_lastlog.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 the default 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
auth      include     system-auth

# include the default account settings
account   include     system-account

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

# include system session defaults
session   include     system-session

# End /etc/pam.d/su</literal>
EOF</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 defaults for auth account and session
auth      include     system-auth
account   include     system-account
session   include     system-session

# Always permit for authentication updates
password  required    pam_permit.so

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

      <sect4>
        <title>'chfn', 'chgpasswd', 'chgpasswd', 'chsh', 'groupadd', 'groupdel',
        'groupmems', 'groupmod', 'newusers', 'useradd', 'userdel' and
        'usermod'</title>

<screen role="root"><userinput>for PROGRAM in chfn chgpasswd chpasswd chsh groupadd groupdel \
               groupmems groupmod newusers 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 a user, then <command>su</command> to
            <systemitem class="username">root</systemitem>. 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. 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>
        <title>Other</title>

        <para>
          Currently, <filename>/etc/pam.d/other</filename> is configured to
          allow anyone with an account on the machine to use PAM-aware programs
          without a configuration file for that program. After testing
          <application>Linux-PAM</application> for proper configuration, install
          a more restrictive <filename>other</filename> file so that
          program-specific configuration files are required:
        </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>
      </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>

<screen role="root"><userinput>[ -f /etc/login.access ] &amp;&amp; mv -v /etc/login.access{,.NOUSE}</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>[ -f /etc/limits ] &amp;&amp; mv -v /etc/limits{,.NOUSE}</userinput></screen>
      </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="http://www.linuxfromscratch.org/lfs/view/&lfs-version;/chapter06/shadow.html#contents-shadow"/>.
    </para>

  </sect2>

</sect1>