lfs-book/chapter06/glibc.xml

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

  <title>Glibc-&glibc-version;</title>

  <indexterm zone="ch-system-glibc">
    <primary sortas="a-Glibc">Glibc</primary>
  </indexterm>

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

    <para>The Glibc package contains the main C library. This library provides
    the basic routines for allocating memory, searching directories, opening and
    closing files, reading and writing files, string handling, pattern matching,
    arithmetic, and so on.</para>

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

      <seglistitem>
        <seg>&glibc-ch6-sbu;</seg>
        <seg>&glibc-ch6-du;</seg>
      </seglistitem>
    </segmentedlist>

  </sect2>

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

    <note>
      <para>Some packages outside of LFS suggest installing GNU libiconv in
      order to translate data from one encoding to another. The project's
      home page (<ulink url="http://www.gnu.org/software/libiconv/"/>) says
      <quote>This library provides an <function>iconv()</function>
      implementation, for use on systems which don't have one, or whose
      implementation cannot convert from/to Unicode.</quote> Glibc provides
      an <function>iconv()</function> implementation and can convert from/to
      Unicode, therefore libiconv is not required on an LFS system.</para>
    </note>

    <para>The Glibc build system is self-contained and will install
    perfectly, even though the compiler specs file and linker are still
    pointing at <filename class="directory">/tools</filename>. The specs
    and linker cannot be adjusted before the Glibc install because the
    Glibc autoconf tests would give false results and defeat the goal
    of achieving a clean build.</para>

    <para>The glibc-libidn tarball adds support for internationalized domain
    names (IDN) to Glibc. Many programs that support IDN require the full
    <filename class="libraryfile">libidn</filename> library, not this add-on (see
    <ulink url="&blfs-root;view/svn/general/libidn.html"/>).
    Unpack the tarball from within the Glibc source directory:</para>

<screen><userinput>tar -xvf ../glibc-libidn-&glibc-version;.tar.gz
mv glibc-libidn-&glibc-version; libidn</userinput></screen>

    <para>In the vi_VN.TCVN locale, <command>bash</command> enters an infinite loop
    at startup. It is unknown whether this is a <command>bash</command> bug or a
    Glibc problem. Disable installation of this locale in order to avoid the
    problem:</para>

<screen><userinput>sed -i '/vi_VN.TCVN/d' localedata/SUPPORTED</userinput></screen>

    <para>When running <command>make install</command>, a script called
    <filename>test-installation.pl</filename> performs a small sanity test on
    our newly installed Glibc. However, because our toolchain still points to
    the <filename class="directory">/tools</filename> directory, the sanity
    test would be carried out against the wrong Glibc. We can force the script
    to check the Glibc we have just installed with the following:</para>

<screen><userinput>sed -i \
's|libs -o|libs -L/usr/lib -Wl,-dynamic-linker=/lib/ld-linux.so.2 -o|' \
        scripts/test-installation.pl</userinput></screen>

    <para>The <command>ldd</command> shell script contains Bash-specific
    syntax. Change it's default program interpreter to <command>/bin/bash</command>
    in case another <command>/bin/sh</command> is installed as described in the
    <ulink url="&blfs-root;view/svn/postlfs/shells.html">Shells</ulink>
    chapter of the BLFS book:</para>

<screen><userinput>sed -i 's|@BASH@|/bin/bash|' elf/ldd.bash.in</userinput></screen>

    <para>The Glibc documentation recommends building Glibc outside of the source
    directory in a dedicated build directory:</para>

<screen><userinput>mkdir -v ../glibc-build
cd ../glibc-build</userinput></screen>

    <para>Prepare Glibc for compilation:</para>

<screen><userinput>../glibc-&glibc-version;/configure --prefix=/usr \
    --disable-profile --enable-add-ons \
    --enable-kernel=2.6.0 --libexecdir=/usr/lib/glibc</userinput></screen>

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

      <varlistentry>
        <term><parameter>--libexecdir=/usr/lib/glibc</parameter></term>
        <listitem>
          <para>This changes the location of the <command>pt_chown</command>
          program from its default of <filename
          class="directory">/usr/libexec</filename> to <filename
          class="directory">/usr/lib/glibc</filename>.</para>
        </listitem>
      </varlistentry>

    </variablelist>

    <para>Compile the package:</para>

<screen><userinput>make</userinput></screen>

    <important>
      <para>In this section, the test suite for Glibc is considered critical.
      Do not skip it under any circumstance.</para>
    </important>

    <para>Test the results:</para>

<screen><userinput>make -k check 2&gt;&amp;1 | tee glibc-check-log
grep Error glibc-check-log</userinput></screen>

    <para>You will probably see an expected (ignored) failure in the
    <emphasis>posix/annexc</emphasis> test.  In addition the Glibc test suite
    is somewhat dependent on the host system.  This is a list of the most
    common issues:</para>

    <itemizedlist>
      <!-- Check again after updating from gcc-4.1.x -->
      <listitem>
        <para>The <emphasis>nptl/tst-cancel1</emphasis> test will fail when
        using the 4.1 series of GCC.</para>
      </listitem>
      <!-- Was true in glibc-2.3.6 -->
      <listitem>
        <para>The <emphasis>nptl/tst-clock2</emphasis> and
        <emphasis>tst-attr3</emphasis> tests sometimes
        fail.  The reason is not completely understood, but indications
        are that a heavy system load can trigger these failures.</para>
      </listitem>
      <listitem>
        <para>The math tests sometimes fail when running on
        systems where the CPU is not a relatively new genuine Intel or
        authentic AMD processor.</para>
      </listitem>
      <listitem>
        <para>If you have mounted the LFS partition with the
        <parameter>noatime</parameter> option, the <emphasis>atime</emphasis>
        test will fail. As mentioned in <xref linkend="space-mounting"/>, do not
        use the <parameter>noatime</parameter> option while building LFS.</para>
      </listitem>
      <listitem>
        <para>When running on older and slower hardware or on systems under
        load, some tests can fail because of test timeouts being exceeded.</para>
      </listitem>
    </itemizedlist>

    <para>Though it is a harmless message, the install stage of Glibc will
    complain about the absence of <filename>/etc/ld.so.conf</filename>.
    Prevent this warning with:</para>

<screen><userinput>touch /etc/ld.so.conf</userinput></screen>

    <para>Install the package:</para>

<screen><userinput>make install</userinput></screen>

    <para>The locales that can make the system respond in a different language
    were not installed by the above command. None of the locales are required,
    but if some of them are missing, testsuites of the future packages would
    skip important testcases.</para>

    <para>Individual locales can be installed using the
    <command>localedef</command> program. E.g., the first
    <command>localedef</command> command below combines the
    <filename>/usr/share/i18n/locales/de_DE</filename>
    charset-independent locale definition with the
    <filename>/usr/share/i18n/charmaps/ISO-8859-1.gz</filename>
    charmap definition and appends the result to the
    <filename>/usr/lib/locale/locale-archive</filename> file.
    The following instructions will install the minimum set of
    locales necessary for the optimal coverage of tests:</para>

<screen role="nodump"><userinput>mkdir -pv /usr/lib/locale
localedef -i de_DE -f ISO-8859-1 de_DE
localedef -i de_DE@euro -f ISO-8859-15 de_DE@euro
localedef -i en_HK -f ISO-8859-1 en_HK
localedef -i en_PH -f ISO-8859-1 en_PH
localedef -i en_US -f ISO-8859-1 en_US
localedef -i en_US -f UTF-8 en_US.UTF-8
localedef -i es_MX -f ISO-8859-1 es_MX
localedef -i fa_IR -f UTF-8 fa_IR
localedef -i fr_FR -f ISO-8859-1 fr_FR
localedef -i fr_FR@euro -f ISO-8859-15 fr_FR@euro
localedef -i fr_FR -f UTF-8 fr_FR.UTF-8
localedef -i it_IT -f ISO-8859-1 it_IT
localedef -i ja_JP -f EUC-JP ja_JP</userinput></screen>

    <para>In addition, install the locale for your own country, language and
    character set.</para>

    <para>Alternatively, install all locales listed in the
    <filename>glibc-&glibc-version;/localedata/SUPPORTED</filename> file
    (it includes every locale listed above and many more) at once with the
    following time-consuming command:</para>

<screen><userinput>make localedata/install-locales</userinput></screen>

    <para>Then use the <command>localedef</command> command to create and
    install locales not listed in the
    <filename>glibc-&glibc-version;/localedata/SUPPORTED</filename> file
    in the unlikely case if you need them.</para>
    <!-- The Live CD patches the localedata/SUPPORTED file instead of
    running localedef, the results are equivalent -->

  </sect2>

  <sect2 id="conf-glibc" role="configuration">
    <title>Configuring Glibc</title>

    <indexterm zone="conf-glibc">
      <primary sortas="e-/etc/nsswitch.conf">/etc/nsswitch.conf</primary>
    </indexterm>

    <indexterm zone="conf-glibc">
      <primary sortas="e-/etc/localtime">/etc/localtime</primary>
    </indexterm>

    <para>The <filename>/etc/nsswitch.conf</filename> file needs to be created
    because, although Glibc provides defaults when this file is missing or corrupt,
    the Glibc defaults do not work well in a networked environment. The time zone
    also needs to be configured.</para>

    <para>Create a new file <filename>/etc/nsswitch.conf</filename> by running the
    following:</para>

<screen><userinput>cat &gt; /etc/nsswitch.conf &lt;&lt; "EOF"
<literal># Begin /etc/nsswitch.conf

passwd: files
group: files
shadow: files

hosts: files dns
networks: files

protocols: files
services: files
ethers: files
rpc: files

# End /etc/nsswitch.conf</literal>
EOF</userinput></screen>

    <para>One way to determine the local time zone, run the following
    script:</para>

<screen role="nodump"><userinput>tzselect</userinput></screen>

    <para>After answering a few questions about the location, the script will
    output the name of the time zone (e.g.,
    <emphasis>America/Edmonton</emphasis>). There are also some other possible
    timezones listed in <filename
    class='directory'>/usr/share/zoneinfo</filename> such as
    <emphasis>Canada/Eastern</emphasis> or <emphasis>EST5EDT</emphasis> that
    are not identified by the script but can be used.</para>

    <para>Then create the <filename>/etc/localtime</filename> file by
    running:</para>

<screen><userinput>cp -v --remove-destination /usr/share/zoneinfo/<replaceable>&lt;xxx&gt;</replaceable> \
    /etc/localtime</userinput></screen>

    <para>Replace <replaceable>&lt;xxx&gt;</replaceable> with the name of the
    time zone selected (e.g., Canada/Eastern).</para>

    <variablelist>
      <title>The meaning of the cp option:</title>

      <varlistentry>
        <term><parameter>--remove-destination</parameter></term>
        <listitem>
          <para>This is needed to force removal of the already existing symbolic
          link. The reason for copying the file instead of using a symlink is to
          cover the situation where <filename class="directory">/usr</filename>
          is on a separate partition. This could be important when booted into
          single user mode.</para>
        </listitem>
      </varlistentry>

    </variablelist>

  </sect2>

  <sect2 id="conf-ld" role="configuration">
    <title>Configuring the Dynamic Loader</title>

    <indexterm zone="conf-ld">
      <primary sortas="e-/etc/ld.so.conf">/etc/ld.so.conf</primary>
    </indexterm>

    <para>By default, the dynamic loader (<filename
    class="libraryfile">/lib/ld-linux.so.2</filename>) searches through
    <filename class="directory">/lib</filename> and <filename
    class="directory">/usr/lib</filename> for dynamic libraries that are
    needed by programs as they are run. However, if there are libraries in
    directories other than <filename class="directory">/lib</filename> and
    <filename class="directory">/usr/lib</filename>, these need to be added
    to the <filename>/etc/ld.so.conf</filename> file in order for the
    dynamic loader to find them. Two directories that are commonly known
    to contain additional libraries are <filename
    class="directory">/usr/local/lib</filename> and <filename
    class="directory">/opt/lib</filename>, so add those directories to the
    dynamic loader's search path.</para>

    <para>Create a new file <filename>/etc/ld.so.conf</filename> by running the
    following:</para>

<screen><userinput>cat &gt; /etc/ld.so.conf &lt;&lt; "EOF"
<literal># Begin /etc/ld.so.conf

/usr/local/lib
/opt/lib

# End /etc/ld.so.conf</literal>
EOF</userinput></screen>

  </sect2>

  <sect2 id="contents-glibc" role="content">
    <title>Contents of Glibc</title>

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

      <seglistitem>
        <seg>catchsegv, gencat, getconf, getent, iconv, iconvconfig, ldconfig,
        ldd, lddlibc4, locale, localedef, mtrace, nscd, pcprofiledump,
        pt_chown, rpcgen, rpcinfo, sln, sprof, tzselect, xtrace,
        zdump, and zic</seg>
        <seg>ld.so, libBrokenLocale.{a,so}, libSegFault.so, libanl.{a,so},
        libbsd-compat.a, libc.{a,so}, libcidn.so, libcrypt.{a,so}, libdl.{a,so},
        libg.a, libieee.a, libm.{a,so}, libmcheck.a, libmemusage.so,
        libnsl.{a,so},  libnss_compat.so, libnss_dns.so, libnss_files.so,
        libnss_hesiod.so, libnss_nis.so, libnss_nisplus.so, libpcprofile.so,
        libpthread.{a,so}, libresolv.{a,so}, librpcsvc.a, librt.{a,so},
        libthread_db.so, and libutil.{a,so}</seg>
      </seglistitem>
    </segmentedlist>

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

      <varlistentry id="catchsegv">
        <term><command>catchsegv</command></term>
        <listitem>
          <para>Can be used to create a stack trace when a program
          terminates with a segmentation fault</para>
          <indexterm zone="ch-system-glibc catchsegv">
            <primary sortas="b-catchsegv">catchsegv</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="gencat">
        <term><command>gencat</command></term>
        <listitem>
          <para>Generates message catalogues</para>
          <indexterm zone="ch-system-glibc gencat">
            <primary sortas="b-gencat">gencat</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="getconf">
        <term><command>getconf</command></term>
        <listitem>
          <para>Displays the system configuration values for file system
          specific variables</para>
          <indexterm zone="ch-system-glibc getconf">
            <primary sortas="b-getconf">getconf</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="getent">
        <term><command>getent</command></term>
        <listitem>
          <para>Gets entries from an administrative database</para>
          <indexterm zone="ch-system-glibc getent">
            <primary sortas="b-getent">getent</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="iconv">
        <term><command>iconv</command></term>
        <listitem>
          <para>Performs character set conversion</para>
          <indexterm zone="ch-system-glibc iconv">
            <primary sortas="b-iconv">iconv</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="iconvconfig">
        <term><command>iconvconfig</command></term>
        <listitem>
          <para>Creates fastloading <command>iconv</command> module configuration
          files</para>
          <indexterm zone="ch-system-glibc iconvconfig">
            <primary sortas="b-iconvconfig">iconvconfig</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ldconfig">
        <term><command>ldconfig</command></term>
        <listitem>
          <para>Configures the dynamic linker runtime bindings</para>
          <indexterm zone="ch-system-glibc ldconfig">
            <primary sortas="b-ldconfig">ldconfig</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ldd">
        <term><command>ldd</command></term>
        <listitem>
          <para>Reports which shared libraries are required
          by each given program or shared library</para>
          <indexterm zone="ch-system-glibc ldd">
            <primary sortas="b-ldd">ldd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="lddlibc4">
        <term><command>lddlibc4</command></term>
        <listitem>
          <para>Assists <command>ldd</command> with object files</para>
          <indexterm zone="ch-system-glibc lddlibc4">
            <primary sortas="b-lddlibc4">lddlibc4</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="locale">
        <term><command>locale</command></term>
        <listitem>
          <para>Prints various information about the current locale</para>
          <indexterm zone="ch-system-glibc locale">
            <primary sortas="b-locale">locale</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="localedef">
        <term><command>localedef</command></term>
        <listitem>
          <para>Compiles locale specifications</para>
          <indexterm zone="ch-system-glibc localedef">
            <primary sortas="b-localedef">localedef</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="mtrace">
        <term><command>mtrace</command></term>
        <listitem>
          <para>Reads and interprets a memory trace file and displays a summary
          in human-readable format</para>
          <indexterm zone="ch-system-glibc mtrace">
            <primary sortas="b-mtrace">mtrace</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="nscd">
        <term><command>nscd</command></term>
        <listitem>
          <para>A daemon that provides a cache for the most common name
          service requests</para>
          <indexterm zone="ch-system-glibc nscd">
            <primary sortas="b-nscd">nscd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="pcprofiledump">
        <term><command>pcprofiledump</command></term>
        <listitem>
          <para>Dumps information generated by PC profiling</para>
          <indexterm zone="ch-system-glibc pcprofiledump">
            <primary sortas="b-pcprofiledump">pcprofiledump</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="pt_chown">
        <term><command>pt_chown</command></term>
        <listitem>
          <para>A helper program for <command>grantpt</command> to set the owner,
          group and access permissions of a slave pseudo terminal</para>
          <indexterm zone="ch-system-glibc pt_chown">
            <primary sortas="b-pt_chown">pt_chown</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="rpcgen">
        <term><command>rpcgen</command></term>
        <listitem>
          <para>Generates C code to implement the Remote Procecure Call (RPC)
          protocol</para>
          <indexterm zone="ch-system-glibc rpcgen">
            <primary sortas="b-rpcgen">rpcgen</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="rpcinfo">
        <term><command>rpcinfo</command></term>
        <listitem>
          <para>Makes an RPC call to an RPC server</para>
          <indexterm zone="ch-system-glibc rpcinfo">
            <primary sortas="b-rpcinfo">rpcinfo</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="sln">
        <term><command>sln</command></term>
        <listitem>
          <para>A statically linked <command>ln</command> program</para>
          <indexterm zone="ch-system-glibc sln">
            <primary sortas="b-sln">sln</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="sprof">
        <term><command>sprof</command></term>
        <listitem>
          <para>Reads and displays shared object profiling data</para>
          <indexterm zone="ch-system-glibc sprof">
            <primary sortas="b-sprof">sprof</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="tzselect">
        <term><command>tzselect</command></term>
        <listitem>
          <para>Asks the user about the location of the system and reports
          the corresponding time zone description</para>
          <indexterm zone="ch-system-glibc tzselect">
            <primary sortas="b-tzselect">tzselect</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="xtrace">
        <term><command>xtrace</command></term>
        <listitem>
          <para>Traces the execution of a program by printing the currently
          executed function</para>
          <indexterm zone="ch-system-glibc xtrace">
            <primary sortas="b-xtrace">xtrace</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="zdump">
        <term><command>zdump</command></term>
        <listitem>
          <para>The time zone dumper</para>
          <indexterm zone="ch-system-glibc zdump">
            <primary sortas="b-zdump">zdump</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="zic">
        <term><command>zic</command></term>
        <listitem>
          <para>The time zone compiler</para>
          <indexterm zone="ch-system-glibc zic">
            <primary sortas="b-zic">zic</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ld.so">
        <term><filename class="libraryfile">ld.so</filename></term>
        <listitem>
          <para>The helper program for shared library executables</para>
          <indexterm zone="ch-system-glibc ld.so">
            <primary sortas="c-ld.so">ld.so</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libBrokenLocale">
        <term><filename class="libraryfile">libBrokenLocale</filename></term>
        <listitem>
          <para>Used internally by Glibc as a gross hack to get broken programs
          (e.g., some Motif applications) running. See comments in
          <filename>glibc-&glibc-version;/locale/broken_cur_max.c</filename>
          for more information</para>
          <indexterm zone="ch-system-glibc libBrokenLocale">
            <primary sortas="c-libBrokenLocale">libBrokenLocale</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libSegFault">
        <term><filename class="libraryfile">libSegFault</filename></term>
        <listitem>
          <para>The segmentation fault signal handler, used by
          <command>catchsegv</command></para>
          <indexterm zone="ch-system-glibc libSegFault">
            <primary sortas="c-libSegFault">libSegFault</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libanl">
        <term><filename class="libraryfile">libanl</filename></term>
        <listitem>
          <para>An asynchronous name lookup library</para>
          <indexterm zone="ch-system-glibc libanl">
            <primary sortas="c-libanl">libanl</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libbsd-compat">
        <term><filename class="libraryfile">libbsd-compat</filename></term>
        <listitem>
          <para>Provides the portability needed in order to run certain
          Berkeley Software Distribution (BSD) programs under Linux</para>
          <indexterm zone="ch-system-glibc libbsd-compat">
            <primary sortas="c-libbsd-compat">libbsd-compat</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libc">
        <term><filename class="libraryfile">libc</filename></term>
        <listitem>
          <para>The main C library</para>
          <indexterm zone="ch-system-glibc libc">
            <primary sortas="c-libc">libc</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libcidn">
        <term><filename class="libraryfile">libcidn</filename></term>
        <listitem>
          <para>Used internally by Glibc for handling internationalized domain
          names in the <function>getaddrinfo()</function> function</para>
          <indexterm zone="ch-system-glibc libcrypt">
            <primary sortas="c-libcrypt">libcrypt</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libcrypt">
        <term><filename class="libraryfile">libcrypt</filename></term>
        <listitem>
          <para>The cryptography library</para>
          <indexterm zone="ch-system-glibc libcrypt">
            <primary sortas="c-libcrypt">libcrypt</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libdl">
        <term><filename class="libraryfile">libdl</filename></term>
        <listitem>
          <para>The dynamic linking interface library</para>
          <indexterm zone="ch-system-glibc libdl">
            <primary sortas="c-libdl">libdl</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libg">
        <term><filename class="libraryfile">libg</filename></term>
        <listitem>
          <para>Dummy library containing no functions. Previously was a runtime
          library for <command>g++</command></para>
          <indexterm zone="ch-system-glibc libg">
            <primary sortas="c-libg">libg</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libieee">
        <term><filename class="libraryfile">libieee</filename></term>
        <listitem>
          <para>Linking in this module forces error handling rules for math
          functions as defined by the Institute of Electrical and Electronic
          Engineers (IEEE). The default is POSIX.1 error handling</para>
          <indexterm zone="ch-system-glibc libieee">
            <primary sortas="c-libieee">libieee</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libm">
        <term><filename class="libraryfile">libm</filename></term>
        <listitem>
          <para>The mathematical library</para>
          <indexterm zone="ch-system-glibc libm">
            <primary sortas="c-libm">libm</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libmcheck">
        <term><filename class="libraryfile">libmcheck</filename></term>
        <listitem>
          <para>Turns on memory allocation checking when linked to</para>
          <indexterm zone="ch-system-glibc libmcheck">
            <primary sortas="c-libmcheck">libmcheck</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libmemusage">
        <term><filename class="libraryfile">libmemusage</filename></term>
        <listitem>
          <para>Used by <command>memusage</command> to help collect
          information about the memory usage of a program</para>
          <indexterm zone="ch-system-glibc libmemusage">
            <primary sortas="c-libmemusage">libmemusage</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libnsl">
        <term><filename class="libraryfile">libnsl</filename></term>
        <listitem>
          <para>The network services library</para>
          <indexterm zone="ch-system-glibc libnsl">
            <primary sortas="c-libnsl">libnsl</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libnss">
        <term><filename class="libraryfile">libnss</filename></term>
        <listitem>
          <para>The Name Service Switch libraries, containing functions for
          resolving host names, user names, group names, aliases, services,
          protocols, etc.</para>
          <indexterm zone="ch-system-glibc libnss">
            <primary sortas="c-libnss">libnss</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libpcprofile">
        <term><filename class="libraryfile">libpcprofile</filename></term>
        <listitem>
          <para>Contains profiling functions used to track the amount of CPU
          time spent in specific source code lines</para>
          <indexterm zone="ch-system-glibc libpcprofile">
            <primary sortas="c-libpcprofile">libpcprofile</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libpthread">
        <term><filename class="libraryfile">libpthread</filename></term>
        <listitem>
          <para>The POSIX threads library</para>
          <indexterm zone="ch-system-glibc libpthread">
            <primary sortas="c-libpthread">libpthread</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libresolv">
        <term><filename class="libraryfile">libresolv</filename></term>
        <listitem>
          <para>Contains functions for creating, sending, and interpreting
          packets to the Internet domain name servers</para>
          <indexterm zone="ch-system-glibc libresolv">
            <primary sortas="c-libresolv">libresolv</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="librpcsvc">
        <term><filename class="libraryfile">librpcsvc</filename></term>
        <listitem>
          <para>Contains functions providing miscellaneous RPC services</para>
          <indexterm zone="ch-system-glibc librpcsvc">
            <primary sortas="c-librpcsvc">librpcsvc</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="librt">
        <term><filename class="libraryfile">librt</filename></term>
        <listitem>
          <para>Contains functions providing most of the interfaces specified
          by the POSIX.1b Realtime Extension</para>
          <indexterm zone="ch-system-glibc librt">
            <primary sortas="c-librt">librt</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libthread_db">
        <term><filename class="libraryfile">libthread_db</filename></term>
        <listitem>
          <para>Contains functions useful for building debuggers for
          multi-threaded programs</para>
          <indexterm zone="ch-system-glibc libthread_db">
            <primary sortas="c-libthread_db">libthread_db</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="libutil">
        <term><filename class="libraryfile">libutil</filename></term>
        <listitem>
          <para>Contains code for <quote>standard</quote> functions used in
          many different Unix utilities</para>
          <indexterm zone="ch-system-glibc libutil">
            <primary sortas="c-libutil">libutil</primary>
          </indexterm>
        </listitem>
      </varlistentry>

    </variablelist>

  </sect2>

</sect1>