lfs/chapter08/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;
]>

<sect1 id="ch-system-shadow" role="wrap">
  <?dbhtml filename="shadow.html"?>

  <sect1info condition="script">
    <productname>shadow</productname>
    <productnumber>&shadow-version;</productnumber>
    <address>&shadow-url;</address>
  </sect1info>

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

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

  <sect2 role="package">
    <title/>

    <para>The Shadow package contains programs for handling passwords in a secure
    way.</para>

    <segmentedlist>
      <segtitle>&buildtime;</segtitle>
      <segtitle>&diskspace;</segtitle>

      <seglistitem>
        <seg>&shadow-fin-sbu;</seg>
        <seg>&shadow-fin-du;</seg>
      </seglistitem>
    </segmentedlist>

  </sect2>

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

    <important>
      <para>
        If you've installed Linux-PAM, you should follow
        <ulink url='&blfs-book;postlfs/shadow.html'>the BLFS
        instruction</ulink> instead of this page to build (or, rebuild or
        upgrade) shadow.
      </para>
    </important>

    <note>
      <para>If you would like to enforce the use of strong passwords,
      <ulink url='&blfs-book;postlfs/linux-pam.html'>install and configure
      Linux-PAM</ulink> first.  Then
      <ulink url='&blfs-book;postlfs/shadow.html'>install and configure
      shadow with the PAM support</ulink>.  Finally
      <ulink url='&blfs-book;postlfs/libpwquality.html'>install
      libpwquality and configure PAM to use it</ulink>.</para>
    </note>

    <para>Disable the installation of the <command>groups</command> program
    and its man pages, as Coreutils provides a better version. Also,
    prevent the installation of manual pages that were already installed in
    <xref linkend="ch-system-man-pages"/>:</para>

<screen><userinput remap="pre">sed -i 's/groups$(EXEEXT) //' src/Makefile.in
find man -name Makefile.in -exec sed -i 's/groups\.1 / /'   {} \;
find man -name Makefile.in -exec sed -i 's/getspnam\.3 / /' {} \;
find man -name Makefile.in -exec sed -i 's/passwd\.5 / /'   {} \;</userinput></screen>

    <para id="shadow-login_defs">Instead of using the default
    <emphasis>crypt</emphasis> method, use the much more secure
    <emphasis>YESCRYPT</emphasis> method of password encryption, which also
    allows passwords longer than 8 characters.
    It is also necessary to change
    the obsolete <filename class="directory">/var/spool/mail</filename> location
    for user mailboxes that Shadow uses by default to the <filename
    class="directory">/var/mail</filename> location used currently. And,
    remove <filename class="directory">/bin</filename> and
    <filename class="directory">/sbin</filename> from the <envar>PATH</envar>,
    since they are simply symlinks to their counterparts in
    <filename class="directory">/usr</filename>.</para>

    <warning>
      <para>Including <filename class="directory">/bin</filename>
      and/or <filename class="directory">/sbin</filename> in
      the <envar>PATH</envar> variable may cause some BLFS packages fail to
      build,<!-- known example: SPIRV-LLVM-Translator --> so don't do that
      in the <filename>.bashrc</filename> file or anywhere else.</para>
    </warning>

<screen><userinput remap="pre">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</userinput></screen>

<!--
    <para>Make a minor change to make the first group number generated
    by useradd 1000:</para>

<screen><userinput remap="pre">sed -i 's/1000/999/' etc/useradd</userinput></screen>
-->
<!--
    <para>Fix a simple programming error by modifying a file with following command:</para>

<screen><userinput remap="pre">sed -e "224s/rounds/min_rounds/" -i libmisc/salt.c</userinput></screen>
-->
    <para>Prepare Shadow for compilation:</para>

<screen><userinput remap="configure">touch /usr/bin/passwd
./configure --sysconfdir=/etc   \
            --disable-static    \
            --with-{b,yes}crypt \
            --without-libbsd    \
            --with-group-name-max-length=32</userinput></screen>

    <variablelist>
      <title>The meaning of the new configuration options:</title>

      <varlistentry>
        <term><command>touch /usr/bin/passwd</command></term>
        <listitem>
          <para>The file <filename>/usr/bin/passwd</filename> needs
          to exist because its location is hardcoded in some programs; 
          if it does not already exist, the installation script will 
          create it in the wrong place.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><parameter>--with-{b,yes}crypt</parameter></term>
        <listitem>
          <para>The shell expands this to two switches,
          <parameter>--with-bcrypt</parameter> and
          <parameter>--with-yescrypt</parameter>.  They allow shadow to use
          the Bcrypt and Yescrypt algorithms implemented by
          <application>Libxcrypt</application> for hashing passwords.
          These algorithms are more secure (in particular, much more
          resistant to GPU-based attacks) than the traditional SHA
          algorithms.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><parameter>--with-group-name-max-length=32</parameter></term>
        <listitem>
          <para>The longest permissible user name is 32 characters.  Make the maximum
          length of a group name the same.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><parameter>--without-libbsd</parameter></term>
        <listitem>
           <para>Do not use the readpassphrase function from libbsd which
           is not in LFS.  Use the internal copy instead.</para>
        </listitem>
      </varlistentry>

    </variablelist>

    <para>Compile the package:</para>

    <screen><userinput remap="make">make</userinput></screen>

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

    <para>Install the package:</para>

    <screen><userinput remap="install">make exec_prefix=/usr install
make -C man install-man</userinput></screen>

  </sect2>

  <sect2 id="conf-shadow" role="configuration">
    <title>Configuring Shadow</title>

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

    <para>This package contains utilities to add, modify, and delete users and
    groups; set and change their passwords; and perform other administrative
    tasks. For a full explanation of what <emphasis>password shadowing</emphasis>
    means, see the <filename>doc/HOWTO</filename> file within the unpacked
    source tree. If you use Shadow support, keep in mind that programs which need
    to verify passwords (display managers, FTP programs, pop3 daemons, etc.)
    must be Shadow-compliant. That is, they must be able to work with
    shadowed passwords.</para>

    <para>To enable shadowed passwords, run the following command:</para>

<screen><userinput>pwconv</userinput></screen>

    <para>To enable shadowed group passwords, run:</para>

<screen><userinput>grpconv</userinput></screen>

    <para>Shadow's default configuration for the <command>useradd</command>
    utility needs some explanation. First, the default
    action for the <command>useradd</command> utility is to create the user and
    a group with the same name as the user. By default the user ID (UID) and
    group ID (GID) numbers will begin at 1000. This means if you don't pass
    extra parameters to <command>useradd</command>, each user will be a member of a
    unique group on the system. If this behavior is undesirable, you'll need
    to pass either the <parameter>-g</parameter> or <parameter>-N</parameter>
    parameter to <command>useradd</command>, or else change the setting of
    <parameter>USERGROUPS_ENAB</parameter> in
    <filename>/etc/login.defs</filename>. See <ulink role='man'
    url='&man;useradd.8'>useradd(8)</ulink> for more information.</para>

    <para>Second, to change the default parameters, the file
    <filename>/etc/default/useradd</filename> must be created and tailored
    to suit your particular needs. Create it with:</para>

<screen><userinput>mkdir -p /etc/default
useradd -D --gid 999</userinput></screen>

    <variablelist>
      <title><filename>/etc/default/useradd</filename> parameter explanations</title>

      <varlistentry>
        <term><parameter>GROUP=999</parameter></term>
        <listitem>
          <para>This parameter sets the beginning of the group numbers used in
          the <filename>/etc/group</filename> file. The particular value 999
          comes from the <parameter>--gid</parameter> parameter above.  You
          may set it to any desired value.

          Note that <command>useradd</command> will never reuse a UID or GID.
          If the number identified in this parameter is used, it will use the
          next available number. Note also that if you don't have a group with
          an ID equal to this number on your system, then the first time you use
          <command>useradd</command> without the <parameter>-g</parameter>
          parameter, an error message will be generated&mdash;<computeroutput>useradd:
          unknown GID 999</computeroutput>,
          even though the account has been created correctly. That is why we
          created the group <systemitem class="groupname">users</systemitem>
          with this group ID in
          <xref linkend='ch-tools-createfiles' role='.'/></para>

        </listitem>
      </varlistentry>
      <varlistentry>
        <term><parameter>CREATE_MAIL_SPOOL=yes</parameter></term>
        <listitem>
          <para>This parameter causes <command>useradd</command> to create a
          mailbox file for each new user. <command>useradd</command>
          will assign the group ownership of this file to the
          <systemitem class="groupname">mail</systemitem> group with 0660
          permissions. If you would rather not create these files,
          issue the following command:</para>

<screen><userinput>sed -i '/MAIL/s/yes/no/' /etc/default/useradd</userinput></screen>
        </listitem>
      </varlistentry>

    </variablelist>

  </sect2>

  <sect2 role="configuration">
    <title>Setting the Root Password</title>

    <para>Choose a password for user <emphasis>root</emphasis> and set it
    by running:</para>

<screen role="nodump"><userinput>passwd root</userinput></screen>

  </sect2>

  <sect2 id="contents-shadow" role="content">
    <title>Contents of Shadow</title>

    <segmentedlist>
      <segtitle>Installed programs</segtitle>
      <segtitle>Installed directories</segtitle>
      <segtitle>Installed libraries</segtitle>

      <seglistitem>
        <seg>chage, chfn, chgpasswd, chpasswd, chsh, expiry, faillog,
        getsubids, gpasswd, groupadd, groupdel, groupmems, groupmod, grpck,
        grpconv, grpunconv, login, logoutd, newgidmap, newgrp,
        newuidmap, newusers, nologin, passwd, pwck, pwconv, pwunconv,
        sg (link to newgrp), su, useradd, userdel, usermod,
        vigr (link to vipw), and vipw</seg>
      <seg>/etc/default and /usr/include/shadow</seg>
        <seg>libsubid.so</seg>
      </seglistitem>
    </segmentedlist>

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

      <varlistentry id="chage">
        <term><command>chage</command></term>
        <listitem>
          <para>Used to change the maximum number of days between obligatory
          password changes</para>
          <indexterm zone="ch-system-shadow chage">
            <primary sortas="b-chage">chage</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="chfn">
        <term><command>chfn</command></term>
        <listitem>
          <para>Used to change a user's full name and other information</para>
          <indexterm zone="ch-system-shadow chfn">
            <primary sortas="b-chfn">chfn</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="chgpasswd">
        <term><command>chgpasswd</command></term>
        <listitem>
          <para>Used to update group passwords in batch mode</para>
          <indexterm zone="ch-system-shadow chgpasswd">
            <primary sortas="b-chgpasswd">chgpasswd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="chpasswd">
        <term><command>chpasswd</command></term>
        <listitem>
          <para>Used to update user passwords in batch mode</para>
          <indexterm zone="ch-system-shadow chpasswd">
            <primary sortas="b-chpasswd">chpasswd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="chsh">
        <term><command>chsh</command></term>
        <listitem>
          <para>Used to change a user's default login shell</para>
          <indexterm zone="ch-system-shadow chsh">
            <primary sortas="b-chsh">chsh</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="expiry">
        <term><command>expiry</command></term>
        <listitem>
          <para>Checks and enforces the current password expiration policy</para>
          <indexterm zone="ch-system-shadow expiry">
            <primary sortas="b-expiry">expiry</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="faillog">
        <term><command>faillog</command></term>
        <listitem>
          <para>Is used to examine the log of login failures, to set a maximum
          number of failures before an account is blocked, and to reset the
          failure count</para>
          <indexterm zone="ch-system-shadow faillog">
            <primary sortas="b-faillog">faillog</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="getsubids">
        <term><command>getsubids</command></term>
        <listitem>
          <para>Is used to list the subordinate id ranges for a user</para>
          <indexterm zone="ch-system-shadow getsubids">
            <primary sortas="b-getsubids">getsubids</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="gpasswd">
        <term><command>gpasswd</command></term>
        <listitem>
          <para>Is used to add and delete members and administrators to
          groups</para>
          <indexterm zone="ch-system-shadow gpasswd">
            <primary sortas="b-gpasswd">gpasswd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="groupadd">
        <term><command>groupadd</command></term>
        <listitem>
          <para>Creates a group with the given name</para>
          <indexterm zone="ch-system-shadow groupadd">
            <primary sortas="b-groupadd">groupadd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="groupdel">
        <term><command>groupdel</command></term>
        <listitem>
          <para>Deletes the group with the given name</para>
          <indexterm zone="ch-system-shadow groupdel">
            <primary sortas="b-groupdel">groupdel</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="groupmems">
        <term><command>groupmems</command></term>
        <listitem>
          <para>Allows a user to administer his/her own group membership list
          without the requirement of super user privileges.</para>
          <indexterm zone="ch-system-shadow groupmems">
            <primary sortas="b-groupmems">groupmems</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="groupmod">
        <term><command>groupmod</command></term>
        <listitem>
          <para>Is used to modify the given group's name or GID</para>
          <indexterm zone="ch-system-shadow groupmod">
            <primary sortas="b-groupmod">groupmod</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="grpck">
        <term><command>grpck</command></term>
        <listitem>
          <para>Verifies the integrity of the group files
          <filename>/etc/group</filename> and
          <filename>/etc/gshadow</filename></para>
          <indexterm zone="ch-system-shadow grpck">
            <primary sortas="b-grpck">grpck</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="grpconv">
        <term><command>grpconv</command></term>
        <listitem>
          <para>Creates or updates the shadow group file from the normal
          group file</para>
          <indexterm zone="ch-system-shadow grpconv">
            <primary sortas="b-grpconv">grpconv</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="grpunconv">
        <term><command>grpunconv</command></term>
        <listitem>
          <para>Updates <filename>/etc/group</filename> from
          <filename>/etc/gshadow</filename> and then deletes the latter</para>
          <indexterm zone="ch-system-shadow grpunconv">
            <primary sortas="b-grpunconv">grpunconv</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="login">
        <term><command>login</command></term>
        <listitem>
          <para>Is used by the system to let users sign on</para>
          <indexterm zone="ch-system-shadow login">
            <primary sortas="b-login">login</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="logoutd">
        <term><command>logoutd</command></term>
        <listitem>
          <para>Is a daemon used to enforce restrictions on log-on time
          and ports</para>
          <indexterm zone="ch-system-shadow logoutd">
            <primary sortas="b-logoutd">logoutd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="newgidmap">
        <term><command>newgidmap</command></term>
        <listitem>
          <para>Is used to set the gid mapping of a user namespace</para>
          <indexterm zone="ch-system-shadow newgidmap">
            <primary sortas="b-newgidmap">newgidmap</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="newgrp">
        <term><command>newgrp</command></term>
        <listitem>
          <para>Is used to change the current GID during a login session</para>
          <indexterm zone="ch-system-shadow newgrp">
            <primary sortas="b-newgrp">newgrp</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="newuidmap">
        <term><command>newuidmap</command></term>
        <listitem>
          <para>Is used to set the uid mapping of a user namespace</para>
          <indexterm zone="ch-system-shadow newuidmap">
            <primary sortas="b-newuidmap">newuidmap</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="newusers">
        <term><command>newusers</command></term>
        <listitem>
          <para>Is used to create or update an entire series of user
          accounts</para>
          <indexterm zone="ch-system-shadow newusers">
            <primary sortas="b-newusers">newusers</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="nologin">
        <term><command>nologin</command></term>
        <listitem>
          <para>Displays a message saying an account is not available; it is designed
          to be used as the default shell for disabled accounts</para>
          <indexterm zone="ch-system-shadow nologin">
            <primary sortas="b-nologin">nologin</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="passwd">
        <term><command>passwd</command></term>
        <listitem>
          <para>Is used to change the password for a user or group account</para>
          <indexterm zone="ch-system-shadow passwd">
            <primary sortas="b-passwd">passwd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="pwck">
        <term><command>pwck</command></term>
        <listitem>
          <para>Verifies the integrity of the password files
          <filename>/etc/passwd</filename> and
          <filename>/etc/shadow</filename></para>
          <indexterm zone="ch-system-shadow pwck">
            <primary sortas="b-pwck">pwck</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="pwconv">
        <term><command>pwconv</command></term>
        <listitem>
          <para>Creates or updates the shadow password file from the normal
          password file</para>
          <indexterm zone="ch-system-shadow pwconv">
            <primary sortas="b-pwconv">pwconv</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="pwunconv">
        <term><command>pwunconv</command></term>
        <listitem>
          <para>Updates <filename>/etc/passwd</filename> from
          <filename>/etc/shadow</filename> and then deletes the latter</para>
          <indexterm zone="ch-system-shadow pwunconv">
            <primary sortas="b-pwunconv">pwunconv</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="sg">
        <term><command>sg</command></term>
        <listitem>
          <para>Executes a given command while the user's GID
          is set to that of the given group</para>
          <indexterm zone="ch-system-shadow sg">
            <primary sortas="b-sg">sg</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="su">
        <term><command>su</command></term>
        <listitem>
          <para>Runs a shell with substitute user and group IDs</para>
          <indexterm zone="ch-system-shadow su">
            <primary sortas="b-su">su</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="useradd">
        <term><command>useradd</command></term>
        <listitem>
          <para>Creates a new user with the given name, or updates the default
          new-user information</para>
          <indexterm zone="ch-system-shadow useradd">
            <primary sortas="b-useradd">useradd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="userdel">
        <term><command>userdel</command></term>
        <listitem>
          <para>Deletes the specified user account</para>
          <indexterm zone="ch-system-shadow userdel">
            <primary sortas="b-userdel">userdel</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="usermod">
        <term><command>usermod</command></term>
        <listitem>
          <para>Is used to modify the given user's login name, user
          identification (UID), shell, initial group, home directory, etc.</para>
          <indexterm zone="ch-system-shadow usermod">
            <primary sortas="b-usermod">usermod</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="vigr">
        <term><command>vigr</command></term>
        <listitem>
          <para>Edits the <filename>/etc/group</filename> or
          <filename>/etc/gshadow</filename> files</para>
          <indexterm zone="ch-system-shadow vigr">
            <primary sortas="b-vigr">vigr</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="vipw">
        <term><command>vipw</command></term>
        <listitem>
          <para>Edits the <filename>/etc/passwd</filename> or
          <filename>/etc/shadow</filename> files</para>
          <indexterm zone="ch-system-shadow vipw">
            <primary sortas="b-vipw">vipw</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libsubid">
        <term><filename class='libraryfile'>libsubid</filename></term>
        <listitem>
          <para>library to handle subordinate id ranges for users and groups</para>
          <indexterm zone="ch-system-shadow libsubid">
            <primary sortas="c-libsubid">libsubid</primary>
          </indexterm>
        </listitem>
      </varlistentry>

    </variablelist>

  </sect2>

</sect1>