source: postlfs/security/shadow.xml@ bbffefa5

<?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.bz2 ">
  <!ENTITY shadow-download-ftp  " ">
  <!ENTITY shadow-md5sum        "b8608d8294ac88974f27b20f991c0e79">
  <!ENTITY shadow-size          "1.8 MB">
  <!ENTITY shadow-buildsize     "30 MB">
  <!ENTITY shadow-time          "0.3 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>

    &lfs70_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_fix-2.patch"/></para>
      </listitem>
    </itemizedlist> -->

    <bridgehead renderas="sect3">Shadow Dependencies</bridgehead>

    <bridgehead renderas="sect4">Required</bridgehead>
    <para role="required"><xref linkend="linux-pam"/> and/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/ ko//' -e 's/ zh_CN zh_TW//' man/Makefile.in       &amp;&amp;

sed -i -e 's@#ENCRYPT_METHOD DES@ENCRYPT_METHOD SHA512@' \
       -e 's@/var/spool/mail@/var/mail@' etc/login.defs         &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 command 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 '...' -e '...' man/Makefile.in</command>: This
    command disables the installation of Chinese and Korean manual pages, since
    <application>Man-DB</application> cannot format them properly.</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 'crypt' 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>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, /etc/login.defs, and
      /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
      links:</para>

      <itemizedlist spacing="compact">
      <listitem>
        <para><ulink
        url="http://www.kernel.org/pub/linux/libs/pam/Linux-PAM-html/sag-pam_cracklib.html"/></para>
      </listitem>
      <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 LASTLOG_ENAB MAIL_CHECK_ENAB \
                PORTTIME_CHECKS_ENAB CONSOLE \
                MOTD_FILE NOLOGINS_FILE PASS_MIN_LEN \
                SU_WHEEL_ONLY MD5_CRYPT_ENAB \
                CONSOLE_GROUPS ENVIRON_FILE \
                ULIMIT ENV_TZ ENV_HZ ENV_SUPATH \
                ENV_PATH QMAIL_DIR MAIL_DIR MAIL_FILE \
                CHFN_AUTH FAILLOG_ENAB QUOTAS_ENAB FTMP_FILE \
                OBSCURE_CHECKS_ENAB CRACKLIB_DICTPATH \
                PASS_CHANGE_TRIES PASS_ALWAYS_WARN ISSUE_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 perviously
# 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
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

# Use xauth keys (if available)
session   optional    pam_xauth.so

# 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

# Use xauth keys (if available)
session   optional    pam_xauth.so

# 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>if [ -f /etc/login.access ]; then
    mv -v /etc/login.access /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 /etc/limits.NOUSE
fi</userinput></screen>

      </sect4>

      <sect4 id="pam-env">
        <title>Configuring Default Environment</title>

          <para>During previous configuration, several items were removed from
          <filename>/etc/login.defs</filename>.  Some of these items are now
          controlled by the <filename class='libraryfile'>pam_env.so</filename>
          module and the <filename>/etc/security/pam_env.conf</filename>
          configuration file.  In particular, the default path has been
          changed.  To recover your default path, execute the following
          commands:</para>

<screen role="root"><userinput>ENV_PATH=`grep '^ENV_PATH' /etc/login.defs.orig | \
    awk '{ print $2 }' | sed 's/PATH=//'` &amp;&amp;
echo 'PATH        DEFAULT='`echo "${ENV_PATH}"`\
'        OVERRIDE=${PATH}' \
    >> /etc/security/pam_env.conf &amp;&amp;
unset ENV_PATH</userinput></screen>

          <note>
            <para>The ENV_SUPATH option used to modify root's default path
            does not work with PAM. You have to set the path in root's login
            scripts instead.
            </para>
          </note>

      </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;/chapter06/shadow.html#contents-shadow"/>.</para>

  </sect2>

</sect1>