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<h3 class="appendixsec">C.2 Installing the C Library</h3>

<p><a name="index-installing-3815"></a>
To install the library and its header files, and the Info files of the
manual, type <code>env LANGUAGE=C LC_ALL=C make install</code>.  This will
build things, if necessary, before installing them; however, you should
still compile everything first.  If you are installing glibc as your
primary C library, we recommend that you shut the system down to
single-user mode first, and reboot afterward.  This minimizes the risk
of breaking things when the library changes out from underneath.

   <p>If you're upgrading from Linux libc5 or some other C library, you need to
replace the <samp><span class="file">/usr/include</span></samp> with a fresh directory before installing
it.  The new <samp><span class="file">/usr/include</span></samp> should contain the Linux headers, but
nothing else.

   <p>You must first build the library (&lsquo;<samp><span class="samp">make</span></samp>&rsquo;), optionally check it
(&lsquo;<samp><span class="samp">make check</span></samp>&rsquo;), switch the include directories and then install
(&lsquo;<samp><span class="samp">make install</span></samp>&rsquo;).  The steps must be done in this order.  Not moving
the directory before install will result in an unusable mixture of header
files from both libraries, but configuring, building, and checking the
library requires the ability to compile and run programs against the old
library.

   <p>If you are upgrading from a previous installation of glibc 2.0 or 2.1,
&lsquo;<samp><span class="samp">make install</span></samp>&rsquo; will do the entire job.  You do not need to remove
the old includes &ndash; if you want to do so anyway you must then follow the
order given above.

   <p>You may also need to reconfigure GCC to work with the new library.  The
easiest way to do that is to figure out the compiler switches to make it
work again (&lsquo;<samp><span class="samp">-Wl,--dynamic-linker=/lib/ld-linux.so.2</span></samp>&rsquo; should work on
GNU/Linux systems) and use them to recompile gcc.  You can also edit the specs
file (<samp><span class="file">/usr/lib/gcc-lib/</span><var>TARGET</var><span class="file">/</span><var>VERSION</var><span class="file">/specs</span></samp>), but that
is a bit of a black art.

   <p>You can install glibc somewhere other than where you configured it to go
by setting the <code>install_root</code> variable on the command line for
&lsquo;<samp><span class="samp">make install</span></samp>&rsquo;.  The value of this variable is prepended to all the
paths for installation.  This is useful when setting up a chroot
environment or preparing a binary distribution.  The directory should be
specified with an absolute file name.

   <p>Glibc 2.2 includes a daemon called <code>nscd</code>, which you
may or may not want to run.  <code>nscd</code> caches name service lookups; it
can dramatically improve performance with NIS+, and may help with DNS as
well.

   <p>One auxiliary program, <samp><span class="file">/usr/libexec/pt_chown</span></samp>, is installed setuid
<code>root</code>.  This program is invoked by the <code>grantpt</code> function; it
sets the permissions on a pseudoterminal so it can be used by the
calling process.  This means programs like <code>xterm</code> and
<code>screen</code> do not have to be setuid to get a pty.  (There may be
other reasons why they need privileges.)  If you are using a 2.1 or
newer Linux kernel with the <code>devptsfs</code> or <code>devfs</code> filesystems
providing pty slaves, you don't need this program; otherwise you do. 
The source for <samp><span class="file">pt_chown</span></samp> is in <samp><span class="file">login/programs/pt_chown.c</span></samp>.

   <p>After installation you might want to configure the timezone and locale
installation of your system.  The GNU C library comes with a locale
database which gets configured with <code>localedef</code>.  For example, to
set up a German locale with name <code>de_DE</code>, simply issue the command
&lsquo;<samp><span class="samp">localedef -i de_DE -f ISO-8859-1 de_DE</span></samp>&rsquo;.  To configure all locales
that are supported by glibc, you can issue from your build directory the
command &lsquo;<samp><span class="samp">make localedata/install-locales</span></samp>&rsquo;.

   <p>To configure the locally used timezone, set the <code>TZ</code> environment
variable.  The script <code>tzselect</code> helps you to select the right value. 
As an example, for Germany, <code>tzselect</code> would tell you to use
&lsquo;<samp><span class="samp">TZ='Europe/Berlin'</span></samp>&rsquo;.  For a system wide installation (the given
paths are for an installation with &lsquo;<samp><span class="samp">--prefix=/usr</span></samp>&rsquo;), link the
timezone file which is in <samp><span class="file">/usr/share/zoneinfo</span></samp> to the file
<samp><span class="file">/etc/localtime</span></samp>.  For Germany, you might execute &lsquo;<samp><span class="samp">ln -s
/usr/share/zoneinfo/Europe/Berlin /etc/localtime</span></samp>&rsquo;.

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