lfs-book/chapter06/glibc.xml

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<sect1 id="ch-system-glibc" role="wrap">
<title>Glibc-&glibc-version;</title>
<?dbhtml filename="glibc.html"?>

<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>16.7 SBU</seg><seg>500 MB</seg></seglistitem>
</segmentedlist>

<segmentedlist>
<segtitle>&dependencies;</segtitle>
<seglistitem><seg>Bash, Binutils, Coreutils, Diffutils,
Gawk, GCC, Gettext, Grep, Make, Perl, Sed, and Texinfo</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 libidn library (see
<ulink url="&blfs-root;view/svn/general/libidn.html"/>),
not this add-on.
Unpack the tarball from within the Glibc source
directory:</para>

<screen><userinput>tar -xf ../glibc-libidn-&glibc-version;.tar.bz2</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 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>

<para>The meaning of the new configure options:</para>

<variablelist>
<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 &gt;glibc-check-log 2&gt;&amp;1
grep Error glibc-check-log</userinput></screen>

<para>On at least i686 you can expect to see failures in the <emphasis>test-double
</emphasis> and <emphasis>test-idouble</emphasis> math tests with
gcc-&gcc-version;, as well as an expected (ignored) failure in <emphasis>
posix/annexc</emphasis>.  These two failures in the math tests appear to be
harmless.</para>

<para>The Glibc test suite is highly dependent on certain functions of
the host system, in particular the kernel. In certain circumstances,
some failures are unavoidable. This is a list of the most common
issues:</para>

<itemizedlist>
<listitem><para>The <emphasis>math</emphasis> tests sometimes fail in other tests
when running
on systems where the CPU is not a relatively new genuine Intel or authentic AMD.
Certain optimization settings are also known to be a factor here.</para></listitem>

<listitem><para>The <emphasis>gettext</emphasis> test sometimes fails due to
host system issues. The exact reasons are not yet clear.</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, 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 misssing, testuites 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>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>EST5EDT</emphasis> or <emphasis>Canada/Eastern</emphasis>).
Then create the <filename>/etc/localtime</filename> file by
running:</para>

<screen><userinput>cp -v --remove-destination /usr/share/zoneinfo/<replaceable>[xxx]</replaceable> \
    /etc/localtime</userinput></screen>

<para>Replace <replaceable>[xxx]</replaceable> with the name of the time zone
that <command>tzselect</command> provided (e.g., Canada/Eastern).</para>

<para>The meaning of the cp option:</para>

<variablelist>
<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, nscd_nischeck, 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, 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="nscd_nischeck">
<term><command>nscd_nischeck</command></term>
<listitem>
<para>Checks whether or not secure mode is necessary for NIS+ lookup</para>
<indexterm zone="ch-system-glibc nscd_nischeck"><primary sortas="b-nscd_nischeck">nscd_nischeck</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 Berkey 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>