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git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@9336 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689
260 lines
11 KiB
XML
260 lines
11 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="ch-bootable-grub" role="wrap">
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<?dbhtml filename="grub.html"?>
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<sect1info condition="script">
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<productname>grub</productname>
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<productnumber>&grub-version;</productnumber>
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<address>&grub-url;</address>
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</sect1info>
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<title>Using GRUB to Set Up the Boot Process</title>
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<sect2>
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<title>Introduction</title>
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<para>Boot loading can be a complex area, so a few cautionary
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words are in order. Be familiar with the current boot loader and any other
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operating systems present on the hard drive(s) that need to be
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bootable. Make sure that an emergency boot disk is ready to
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<quote>rescue</quote> the computer if the computer becomes
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unusable (un-bootable).</para>
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<para>The procedure involves writing some special GRUB files to specific
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locations on the hard drive. We highly recommend creating a GRUB boot
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floppy diskette as a backup. Insert a blank floppy diskette and run the
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following commands:</para>
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<screen role="nodump"><userinput>cd /tmp
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grub-mkrescue --output=grub-img.iso
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dd if=grub-img.iso of=/dev/fd0 bs=1440 count=1</userinput></screen>
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<para>Alternatively, a boot CD can be created by using your host system's
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CD burning tools to burn the <filename>grub-img.iso</filename> on to a
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blank CD.</para>
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<para>GRUB uses its own naming structure for drives and partitions in
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the form of <emphasis>(hdn,m)</emphasis>, where <emphasis>n</emphasis>
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is the hard drive number and <emphasis>m</emphasis> is the partition
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number. The hard drive number starts from zero, but the partition number
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starts from one for normal partitions and five for extended partitions.
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Note that this is different from earlier versions where
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both numbers started from zero. For example, partition <filename
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class="partition">sda1</filename> is <emphasis>(hd0,1)</emphasis> to
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GRUB and <filename class="partition">sdb3</filename> is
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<emphasis>(hd1,3)</emphasis>. In contrast to Linux, GRUB does not
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consider CD-ROM drives to be hard drives. For example, if using a CD
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on <filename class="partition">hdb</filename> and a second hard drive
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on <filename class="partition">hdc</filename>, that second hard drive
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would still be <emphasis>(hd1)</emphasis>.</para>
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<para>You can determine what GRUB thinks your disk devices are by running:</para>
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<screen role="nodump"><userinput>grub-mkdevicemap --device-map=device.map
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cat device.map</userinput></screen>
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<para>The location of the boot partition is a choice of the user that
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affects the configuration. One recommendation is to have a separate small
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(suggested size is 100 MB) partition just for boot information. That way
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each build, whether LFS or some commercial distro, can access the same boot
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files and access can be made from any booted system. If you choose to do
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this, you will need to mount the separate partition, move all files in the
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current <filename class="directory">/boot</filename> directory (e.g. the
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linux kernel you just built in the previous section) to the new partition.
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You will then need to unmount the partition and remount it as <filename
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class="directory">/boot</filename>. If you do this, be sure to update
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<filename>/etc/fstab</filename>.</para>
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<para>Using the current lfs partition will also work, but configuration
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for multiple systems is more difficult.</para>
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</sect2>
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<sect2>
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<title>Setting Up the Configuration</title>
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<para>Using the above information, determine the appropriate
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designator for the root partition (or boot partition, if a separate
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one is used). For the following example, it is assumed that the root
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(or separate boot) partition is <filename
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class="partition">sda2</filename>.</para>
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<para>Install the GRUB files into <filename
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class="directory">/boot/grub</filename>:</para>
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<screen role="nodump"><userinput>grub-install --grub-setup=/bin/true /dev/sda</userinput></screen>
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<para>We use --grub-setup=/bin/true for now to prevent updating the
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Master Boot Record (MBR). In this way, we can test our installation
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before committing to a change that is hard to revert.</para>
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<para>Generate <filename>/boot/grub/grub.cfg</filename>:</para>
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<screen role="nodump"><userinput>grub-mkconfig -o /boot/grub/grub.cfg</userinput></screen>
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<para>Here <command>grub-mkconfig</command> uses the files in <filename
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class="directory">/etc/grub.d/</filename> to determine the contents
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of this file. The configuration file will look something like:</para>
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<screen><computeroutput>#
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# DO NOT EDIT THIS FILE
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#
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# It is automatically generated by /usr/sbin/grub-mkconfig using templates
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# from /etc/grub.d and settings from /etc/default/grub
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#
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### BEGIN /etc/grub.d/00_header ###
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set default=0
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set timeout=5
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### END /etc/grub.d/00_header ###
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### BEGIN /etc/grub.d/10_linux ###
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menuentry "GNU/Linux, Linux 2.6.34-lfs" {
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insmod ext2
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set root=(hd0,2)
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search --no-floppy --fs-uuid --set 915852a7-859e-45a6-9ff0-d3ebfdb5cea2
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linux /boot/vmlinux-&linux-version;-lfs-&version; root=/dev/sda2 ro
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}
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menuentry "GNU/Linux, Linux 2.6.30.2-lfs65 (recovery mode)" {
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insmod ext2
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set root=(hd0,2)
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search --no-floppy --fs-uuid --set 915852a7-859e-45a6-9ff0-d3ebfdb5cea2
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linux /boot/vmlinux-&linux-version;-lfs-&version; root=/dev/sda2 ro single
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}
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menuentry "GNU/Linux, Linux 2.6.28-11-server" {
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insmod ext2
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set root=(hd0,2)
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search --no-floppy --fs-uuid --set 6b4c0339-5501-4a85-8351-e398e5252be8
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linux /boot/vmlinuz-2.6.28-11-server root=UUID=6b4c0339-5501-4a85-8351-e398e5252be8 ro
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initrd /boot/initrd.img-2.6.28-11-server
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}
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menuentry "GNU/Linux, Linux 2.6.28-11-server (recovery mode)" {
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insmod ext2
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set root=(hd0,2)
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search --no-floppy --fs-uuid --set 6b4c0339-5501-4a85-8351-e398e5252be8
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linux /boot/vmlinuz-2.6.28-11-server root=UUID=6b4c0339-5501-4a85-8351-e398e5252be8 ro single
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initrd /boot/initrd.img-2.6.28-11-server
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}
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### END /etc/grub.d/10_linux ###
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### BEGIN /etc/grub.d/30_os-prober ###
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### END /etc/grub.d/30_os-prober ###
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### BEGIN /etc/grub.d/40_custom ###
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# This file provides an easy way to add custom menu entries. Simply type the
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# menu entries you want to add after this comment. Be careful not to change
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# the 'exec tail' line above.
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### END /etc/grub.d/40_custom ###
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</computeroutput></screen>
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<note>
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<itemizedlist>
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<listitem><para>Even though there is a warning not to edit the file, you
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can do so as long as you do not re-run
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<command>grub-mkconfig</command>.</para></listitem>
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<listitem><para>The <emphasis>search</emphasis> lines are generally not
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useful for LFS systems as that command only sets an internal GRUB
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variable used to find the kernel image. The <emphasis>set root</emphasis>
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command provides the same capability without the overhead of
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searching.</para></listitem>
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<listitem><para>The <emphasis>set root</emphasis> and
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<emphasis>insmod ext2</emphasis> commands can be moved out of the
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<emphasis>menuentry</emphasis> sections to apply to all sections of the file.
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This leads to a simple section like:</para></listitem>
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</itemizedlist>
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<screen><computeroutput>menuentry "Linux &linux-version;-lfs-&version;" {
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linux /boot/vmlinux-&linux-version;-lfs-&version; root=/dev/sda2 ro
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}
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</computeroutput></screen>
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<itemizedlist>
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<listitem><para>Passing a UUID to the kernel requires an initial ram disk
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(initrd) not built by LFS.</para></listitem>
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<listitem><para>If the <filename>/boot</filename> partition is installed
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on a separate partition, the linux and initrd lines should not have the
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string <emphasis>/boot</emphasis> prefixed to the file
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names.</para></listitem>
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<listitem><para>In this example the kernel files for a Ubuntu
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installation are also found in <filename
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class="directory">/boot</filename>.</para></listitem>
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</itemizedlist>
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</note>
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</sect2>
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<sect2>
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<title>Testing the Configuration</title>
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<para>The core image of GRUB is also a Multiboot kernel, so if you already
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have GRUB Legacy loaded you can load GRUB-&grub-version; through your old
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boot loader. To accomplish this, you will need to exit the
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<command>chroot</command> environment and re-enter it to finish the
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few remaining portions of the book.</para>
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<screen role="nodump"><userinput>/sbin/reboot
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...
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grub> root (hd0,1)
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grub> kernel /boot/grub/core.img
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grub> boot</userinput></screen>
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<para>Note that the GRUB commands above are assumed to be GRUB Legacy.
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At this point the GRUB prompt will appear (very similar to GRUB Legacy) and
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you can explore the interface or boot to one of the systems in the grub.cfg
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file.</para>
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</sect2>
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<sect2>
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<title>Updating the Master Boot Record</title>
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<para>If you tested the GRUB configuration as specified above, re-enter
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the <command>chroot</command> environment.</para>
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<warning>
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<para>The following command will overwrite the current boot loader. Do not
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run the command if this is not desired, for example, if using a third party
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boot manager to manage the Master Boot Record (MBR).</para>
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</warning>
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<para>Update the MBR with:</para>
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<screen role="nodump"><userinput>grub-setup '<DEVICE>'</userinput></screen>
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<para>Change the DEVICE above to your boot disk, normally '(hd0)' or /dev/sda.
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If using (hd0) be sure to escape the parentheses with backslashes or single
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quotes to prevent the shell from interpreting them as a sub-shell.</para>
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<para>This program uses the following defaults and are correct if you did not
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deviate from the instructions above:</para>
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<itemizedlist>
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<listitem><para>boot image - boot.img </para></listitem>
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<listitem><para>core image - core.img </para></listitem>
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<listitem><para>directory - /boot/grub</para></listitem>
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<listitem><para>device map - device.map</para></listitem>
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<listitem><para>default root setting - guessed</para></listitem>
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</itemizedlist>
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<note><para>The root setting is the default value if a 'set root'
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instruction is not found in grub.cfg. This is the partition that is
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searched for the kernel and other supporting files. It is different from
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the 'root=' parameter on the 'linux' line in the configuration line. The
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latter is the partition the kernel mounts as '/'. In the example grub.cfg
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above, both values point to /dev/sda2, but if there is a separate boot
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partition, they will be different.</para></note>
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</sect2>
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</sect1>
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