lfs-book/chapter08/grub.xml

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<sect1 id="ch-bootable-grub">
<title>Making the LFS System Bootable</title>
<?dbhtml filename="grub.html"?>

<indexterm zone="ch-bootable-grub">
<primary sortas="a-Grub">GRUB</primary>
<secondary>configuring</secondary></indexterm>

<para>Your shiny new LFS system is almost complete. One of the last
things to do is to ensure that the system can be properly booted. The
instructions below apply only to computers of IA-32 architecture,
meaning mainstream PCs. Information on <quote>boot loading</quote> for
other architectures should be available in the usual resource-specific
locations for those architectures.</para>

<para>Boot loading can be a complex area, so a few cautionary
words are in order. Be familiar with the current boot loader and any other
operating systems present on the hard drive(s) that need to be
bootable. Make sure that an emergency boot disk is ready to
<quote>rescue</quote> the computer if the computer becomes
unusable (un-bootable).</para>

<para>Earlier, we compiled and installed the GRUB boot loader software
in preparation for this step. The procedure involves writing some
special GRUB files to specific locations on the hard drive. We highly
recommend creating a GRUB boot floppy diskette as a backup. Insert a
blank floppy diskette and run the following commands:</para>

<screen><userinput>dd if=/boot/grub/stage1 of=/dev/fd0 bs=512 count=1
dd if=/boot/grub/stage2 of=/dev/fd0 bs=512 seek=1</userinput></screen>

<para>Remove the diskette and store it somewhere safe. Now, run the
<command>grub</command> shell:</para>

<screen><userinput>grub</userinput></screen>

<para>GRUB uses its own naming structure for drives and partitions in
the form of <emphasis>(hdn,m)</emphasis>, where <emphasis>n</emphasis>
is the hard drive number and <emphasis>m</emphasis> is the partition
number, both starting from zero. For example, partition <filename
class="partition">hda1</filename> is <emphasis>(hd0,0)</emphasis> to
GRUB and <filename class="partition">hdb3</filename> is
<emphasis>(hd1,2)</emphasis>. In contrast to Linux, GRUB does not
consider CD-ROM drives to be hard drives. For example, if using a CD
on <filename class="partition">hdb</filename> and a second hard drive
on <filename class="partition">hdc</filename>, that second hard drive
would still be <emphasis>(hd1)</emphasis>.</para>

<para>Using the above information, determine the appropriate
designator for the root partition (or boot partition, if a separate
one is used). For the following example, it is assumed that the root
(or separate boot) partition is <filename
class="partition">hda4</filename>.</para>

<para>Tell GRUB where to search for its
<filename>stage{1,2}</filename> files. The Tab key can be used
everywhere to make GRUB show the alternatives:</para>

<screen><userinput>root (hd0,3)</userinput></screen>

<warning><para>The following command will overwrite the current boot
loader. Do not run the command if this is not desired, for example, if
using a third party boot manager to manage the Master Boot Record
(MBR). In this scenario, it would make more sense to install
GRUB into the <quote>boot sector</quote> of the LFS partition. In this
case, this next command would become <userinput>setup
(hd0,3)</userinput>.</para></warning>

<para>Tell GRUB to install itself into the MBR of
<filename class="partition">hda</filename>:</para>

<screen><userinput>setup (hd0)</userinput></screen>

<para>If all went well, GRUB will have reported finding its files in
<filename class="directory">/boot/grub</filename>. That's all there is
to it. Quit the <command>grub</command> shell:</para>

<screen><userinput>quit</userinput></screen>

<para>Create a <quote>menu list</quote> file defining GRUB's boot menu:</para>

<screen><userinput>cat &gt; /boot/grub/menu.lst &lt;&lt; "EOF"
<literal># Begin /boot/grub/menu.lst

# By default boot the first menu entry.
default 0

# Allow 30 seconds before booting the default.
timeout 30

# Use prettier colors.
color green/black light-green/black

# The first entry is for LFS.
title LFS &version;
root (hd0,3)
kernel /boot/lfskernel-&linux-version; root=/dev/hda4</literal>
EOF</userinput></screen>

<para>Add an entry for the host distribution if desired. It might look
like this:</para>

<screen><userinput>cat &gt;&gt; /boot/grub/menu.lst &lt;&lt; "EOF"
<literal>title Red Hat
root (hd0,2)
kernel /boot/kernel-2.6.5 root=/dev/hda3
initrd /boot/initrd-2.6.5</literal>
EOF</userinput></screen>

<para>If dual-booting Windows, the following entry will allow
booting it:</para>

<screen><userinput>cat &gt;&gt; /boot/grub/menu.lst &lt;&lt; "EOF"
<literal>title Windows
rootnoverify (hd0,0)
chainloader +1</literal>
EOF</userinput></screen>

<para>If <command>info grub</command> does not provide all necessary material, additional
information regarding GRUB is located on its website at:
<ulink url="http://www.gnu.org/software/grub/"/>.</para>

<para>The FHS stipulates that GRUB's <filename>menu.lst</filename> file should be symlinked to
<filename class="symlink">/etc/grub/menu.lst</filename>.  To satisfy this requirement, issue the 
following command:</para>

<screen><userinput>mkdir /etc/grub &amp;&amp;
ln -s /boot/grub/menu.lst /etc/grub</userinput></screen>

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