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<h3 class="appendixsec">C.4 Specific advice for GNU/Linux systems</h3>

<p><a name="index-upgrading-from-libc5-3818"></a><a name="index-kernel-header-files-3819"></a>
If you are installing GNU libc on a GNU/Linux system, you need to have the
header files from a 2.2 or newer kernel around for reference.  For some
architectures, like ia64, sh and hppa, you need at least headers from
kernel 2.3.99 (sh and hppa) or 2.4.0 (ia64).  You do not need to use
that kernel, just have its headers where glibc can access at them.  The
easiest way to do this is to unpack it in a directory such as
<samp><span class="file">/usr/src/linux-2.2.1</span></samp>.  In that directory, run &lsquo;<samp><span class="samp">make config</span></samp>&rsquo;
and accept all the defaults.  Then run &lsquo;<samp><span class="samp">make
include/linux/version.h</span></samp>&rsquo;.  Finally, configure glibc with the option
&lsquo;<samp><span class="samp">--with-headers=/usr/src/linux-2.2.1/include</span></samp>&rsquo;.  Use the most recent
kernel you can get your hands on.

   <p>An alternate tactic is to unpack the 2.2 kernel and run &lsquo;<samp><span class="samp">make
config</span></samp>&rsquo; as above; then, rename or delete <samp><span class="file">/usr/include</span></samp>, create a
new <samp><span class="file">/usr/include</span></samp>, and make symbolic links of
<samp><span class="file">/usr/include/linux</span></samp> and <samp><span class="file">/usr/include/asm</span></samp> into the kernel
sources.  You can then configure glibc with no special options.  This
tactic is recommended if you are upgrading from libc5, since you need to
get rid of the old header files anyway.

   <p>After installing GNU libc, you may need to remove or rename
<samp><span class="file">/usr/include/linux</span></samp> and <samp><span class="file">/usr/include/asm</span></samp>, and replace them
with copies of <samp><span class="file">include/linux</span></samp> and
<samp><span class="file">include/asm-$</span><var>ARCHITECTURE</var></samp> taken from the Linux source
package which supplied kernel headers for building the library. 
<var>ARCHITECTURE</var> will be the machine architecture for which the
library was built, such as &lsquo;<samp><span class="samp">i386</span></samp>&rsquo; or &lsquo;<samp><span class="samp">alpha</span></samp>&rsquo;.  You do not need
to do this if you did not specify an alternate kernel header source
using &lsquo;<samp><span class="samp">--with-headers</span></samp>&rsquo;.  The intent here is that these directories
should be copies of, <strong>not</strong> symlinks to, the kernel headers used to
build the library.

   <p>Note that <samp><span class="file">/usr/include/net</span></samp> and <samp><span class="file">/usr/include/scsi</span></samp> should
<strong>not</strong> be symlinks into the kernel sources.  GNU libc provides its
own versions of these files.

   <p>GNU/Linux expects some components of the libc installation to be in
<samp><span class="file">/lib</span></samp> and some in <samp><span class="file">/usr/lib</span></samp>.  This is handled automatically
if you configure glibc with &lsquo;<samp><span class="samp">--prefix=/usr</span></samp>&rsquo;.  If you set some other
prefix or allow it to default to <samp><span class="file">/usr/local</span></samp>, then all the
components are installed there.

   <p>If you are upgrading from libc5, you need to recompile every shared
library on your system against the new library for the sake of new code,
but keep the old libraries around for old binaries to use.  This is
complicated and difficult.  Consult the Glibc2 HOWTO at
<a href="http://www.imaxx.net/~thrytis/glibc">http://www.imaxx.net/~thrytis/glibc</a> for details.

   <p>You cannot use <code>nscd</code> with 2.0 kernels, due to bugs in the
kernel-side thread support.  <code>nscd</code> happens to hit these bugs
particularly hard, but you might have problems with any threaded
program.

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