1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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5 | %general-entities;
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6 | ]>
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7 |
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8 | <sect1 id="ch-bootable-grub" role="wrap">
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9 | <?dbhtml filename="grub.html"?>
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10 |
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11 | <sect1info condition="script">
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12 | <productname>grub</productname>
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13 | <productnumber>&grub-version;</productnumber>
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14 | <address>&grub-url;</address>
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15 | </sect1info>
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16 |
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17 | <title>Using GRUB to Set Up the Boot Process</title>
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18 |
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19 | <sect2>
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20 | <title>Introduction</title>
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21 |
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22 | <para>Boot loading can be a complex area, so a few cautionary
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23 | words are in order. Be familiar with the current boot loader and any other
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24 | operating systems present on the hard drive(s) that need to be
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25 | bootable. Make sure that an emergency boot disk is ready to
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26 | <quote>rescue</quote> the computer if the computer becomes
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27 | unusable (un-bootable).</para>
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28 |
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29 | <para>The procedure involves writing some special GRUB files to specific
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30 | locations on the hard drive. We highly recommend creating a GRUB boot
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31 | floppy diskette as a backup. Insert a blank floppy diskette and run the
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32 | following commands:</para>
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33 |
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34 | <screen role="nodump"><userinput>cd /tmp
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35 | grub-mkrescue --output=grub-img.iso
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36 | dd if=grub-img.iso of=/dev/fd0 bs=1440 count=1</userinput></screen>
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37 |
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38 | <para>Alternatively, a boot CD can be created by using your host system's
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39 | CD burning tools to burn the <filename>grub-img.iso</filename> on to a
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40 | blank CD.</para>
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41 |
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42 | <para>GRUB uses its own naming structure for drives and partitions in
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43 | the form of <emphasis>(hdn,m)</emphasis>, where <emphasis>n</emphasis>
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44 | is the hard drive number and <emphasis>m</emphasis> is the partition
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45 | number. The hard drive number starts from zero, but the partition number
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46 | starts from one for normal partitions and five for extended partitions.
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47 | Note that this is different from earlier versions where
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48 | both numbers started from zero. For example, partition <filename
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49 | class="partition">sda1</filename> is <emphasis>(hd0,1)</emphasis> to
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50 | GRUB and <filename class="partition">sdb3</filename> is
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51 | <emphasis>(hd1,3)</emphasis>. In contrast to Linux, GRUB does not
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52 | consider CD-ROM drives to be hard drives. For example, if using a CD
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53 | on <filename class="partition">hdb</filename> and a second hard drive
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54 | on <filename class="partition">hdc</filename>, that second hard drive
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55 | would still be <emphasis>(hd1)</emphasis>.</para>
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56 |
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57 | <para>You can determine what GRUB thinks your disk devices are by running:</para>
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58 |
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59 | <screen role="nodump"><userinput>grub-mkdevicemap --device-map=device.map
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60 | cat device.map</userinput></screen>
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61 |
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62 | <para>The location of the boot partition is a choice of the user that
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63 | affects the configuration. One recommendation is to have a separate small
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64 | (suggested size is 100 MB) partition just for boot information. That way
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65 | each build, whether LFS or some commercial distro, can access the same boot
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66 | files and access can be made from any booted system. If you choose to do
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67 | this, you will need to mount the separate partition, move all files in the
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68 | current <filename class="directory">/boot</filename> directory (e.g. the
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69 | linux kernel you just built in the previous section) to the new partition.
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70 | You will then need to unmount the partition and remount it as <filename
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71 | class="directory">/boot</filename>. If you do this, be sure to update
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72 | <filename>/etc/fstab</filename>.</para>
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73 |
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74 | <para>Using the current lfs partition will also work, but configuration
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75 | for multiple systems is more difficult.</para>
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76 | </sect2>
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77 |
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78 | <sect2>
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79 | <title>Setting Up the Configuration</title>
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80 |
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81 | <para>Using the above information, determine the appropriate
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82 | designator for the root partition (or boot partition, if a separate
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83 | one is used). For the following example, it is assumed that the root
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84 | (or separate boot) partition is <filename
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85 | class="partition">sda2</filename>.</para>
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86 |
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87 | <para>Install the GRUB files into <filename
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88 | class="directory">/boot/grub</filename>:</para>
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89 |
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90 | <screen role="nodump"><userinput>grub-install --grub-setup=/bin/true /dev/sda</userinput></screen>
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91 |
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92 | <para>We use --grub-setup=/bin/true for now to prevent updating the
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93 | Master Boot Record (MBR). In this way, we can test our installation
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94 | before committing to a change that is hard to revert.</para>
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95 |
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96 | <para>Generate <filename>/boot/grub/grub.cfg</filename>:</para>
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97 |
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98 | <screen role="nodump"><userinput>grub-mkconfig -o /boot/grub/grub.cfg</userinput></screen>
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99 |
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100 | <para>Here <command>grub-mkconfig</command> uses the files in <filename
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101 | class="directory">/etc/grub.d/</filename> to determine the contents
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102 | of this file. The configuration file will look something like:</para>
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103 | <screen><computeroutput>#
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104 | # DO NOT EDIT THIS FILE
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105 | #
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106 | # It is automatically generated by /usr/sbin/grub-mkconfig using templates
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107 | # from /etc/grub.d and settings from /etc/default/grub
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108 | #
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109 |
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110 | ### BEGIN /etc/grub.d/00_header ###
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111 | set default=0
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112 | set timeout=5
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113 | ### END /etc/grub.d/00_header ###
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114 |
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115 | ### BEGIN /etc/grub.d/10_linux ###
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116 | menuentry "GNU/Linux, Linux &linux-version;-lfs-&version;" {
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117 | insmod ext2
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118 | set root=(hd0,2)
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119 | search --no-floppy --fs-uuid --set 915852a7-859e-45a6-9ff0-d3ebfdb5cea2
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120 | linux /boot/vmlinux-&linux-version;-lfs-&version; root=/dev/sda2 ro
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121 | }
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122 | menuentry "GNU/Linux, Linux &linux-version;-lfs-&version;" (recovery mode)" {
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123 | insmod ext2
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124 | set root=(hd0,2)
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125 | search --no-floppy --fs-uuid --set 915852a7-859e-45a6-9ff0-d3ebfdb5cea2
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126 | linux /boot/vmlinux-&linux-version;-lfs-&version; root=/dev/sda2 ro single
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127 | }
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128 | menuentry "GNU/Linux, Linux 2.6.28-11-server" {
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129 | insmod ext2
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130 | set root=(hd0,2)
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131 | search --no-floppy --fs-uuid --set 6b4c0339-5501-4a85-8351-e398e5252be8
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132 | linux /boot/vmlinuz-2.6.28-11-server root=UUID=6b4c0339-5501-4a85-8351-e398e5252be8 ro
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133 | initrd /boot/initrd.img-2.6.28-11-server
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134 | }
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135 | menuentry "GNU/Linux, Linux 2.6.28-11-server (recovery mode)" {
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136 | insmod ext2
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137 | set root=(hd0,2)
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138 | search --no-floppy --fs-uuid --set 6b4c0339-5501-4a85-8351-e398e5252be8
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139 | linux /boot/vmlinuz-2.6.28-11-server root=UUID=6b4c0339-5501-4a85-8351-e398e5252be8 ro single
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140 | initrd /boot/initrd.img-2.6.28-11-server
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141 | }
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142 | ### END /etc/grub.d/10_linux ###
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143 |
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144 | ### BEGIN /etc/grub.d/30_os-prober ###
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145 | ### END /etc/grub.d/30_os-prober ###
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146 |
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147 | ### BEGIN /etc/grub.d/40_custom ###
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148 | # This file provides an easy way to add custom menu entries. Simply type the
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149 | # menu entries you want to add after this comment. Be careful not to change
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150 | # the 'exec tail' line above.
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151 | ### END /etc/grub.d/40_custom ###
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152 | </computeroutput></screen>
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153 |
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154 | <note>
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155 | <itemizedlist>
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156 | <listitem><para>Even though there is a warning not to edit the file, you
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157 | can do so as long as you do not re-run
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158 | <command>grub-mkconfig</command>.</para></listitem>
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159 |
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160 | <listitem><para>The <emphasis>search</emphasis> lines are generally not
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161 | useful for LFS systems as that command only sets an internal GRUB
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162 | variable used to find the kernel image. The <emphasis>set root</emphasis>
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163 | command provides the same capability without the overhead of
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164 | searching.</para></listitem>
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165 |
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166 | <listitem><para>The <emphasis>set root</emphasis> and
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167 | <emphasis>insmod ext2</emphasis> commands can be moved out of the
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168 | <emphasis>menuentry</emphasis> sections to apply to all sections of the file.
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169 | This leads to a simple section like:</para></listitem>
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170 |
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171 | </itemizedlist>
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172 | <screen><computeroutput>menuentry "Linux &linux-version;-lfs-&version;" {
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173 | linux /boot/vmlinux-&linux-version;-lfs-&version; root=/dev/sda2 ro
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174 | }
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175 | </computeroutput></screen>
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176 |
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177 | <itemizedlist>
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178 |
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179 | <listitem><para>Passing a UUID to the kernel requires an initial ram disk
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180 | (initrd) not built by LFS.</para></listitem>
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181 |
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182 | <listitem><para>If the <filename>/boot</filename> partition is installed
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183 | on a separate partition, the linux and initrd lines should not have the
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184 | string <emphasis>/boot</emphasis> prefixed to the file
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185 | names.</para></listitem>
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186 |
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187 | <listitem><para>In this example the kernel files for a Ubuntu
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188 | installation are also found in <filename
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189 | class="directory">/boot</filename>.</para></listitem>
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190 |
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191 | </itemizedlist>
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192 | </note>
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193 |
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194 | </sect2>
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195 |
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196 | <sect2>
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197 | <title>Testing the Configuration</title>
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198 |
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199 | <para>The core image of GRUB is also a Multiboot kernel, so if you already
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200 | have GRUB Legacy loaded you can load GRUB-&grub-version; through your old
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201 | boot loader. To accomplish this, you will need to exit the
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202 | <command>chroot</command> environment and re-enter it to finish the
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203 | few remaining portions of the book.</para>
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204 |
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205 | <screen role="nodump"><userinput>/sbin/reboot
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206 | ...
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207 | grub> root (hd0,1)
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208 | grub> kernel /boot/grub/core.img
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209 | grub> boot</userinput></screen>
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210 |
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211 | <para>Note that the GRUB commands above are assumed to be GRUB Legacy.
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212 | At this point the GRUB prompt will appear (very similar to GRUB Legacy) and
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213 | you can explore the interface or boot to one of the systems in the grub.cfg
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214 | file.</para>
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215 |
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216 | </sect2>
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217 |
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218 | <sect2>
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219 | <title>Updating the Master Boot Record</title>
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220 |
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221 | <para>If you tested the GRUB configuration as specified above, re-enter
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222 | the <command>chroot</command> environment.</para>
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223 |
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224 | <warning>
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225 | <para>The following command will overwrite the current boot loader. Do not
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226 | run the command if this is not desired, for example, if using a third party
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227 | boot manager to manage the Master Boot Record (MBR).</para>
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228 | </warning>
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229 |
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230 | <para>Update the MBR with:</para>
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231 |
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232 | <screen role="nodump"><userinput>grub-setup '<DEVICE>'</userinput></screen>
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233 |
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234 | <para>Change the DEVICE above to your boot disk, normally '(hd0)' or /dev/sda.
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235 | If using (hd0) be sure to escape the parentheses with backslashes or single
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236 | quotes to prevent the shell from interpreting them as a sub-shell.</para>
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237 |
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238 | <para>This program uses the following defaults and are correct if you did not
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239 | deviate from the instructions above:</para>
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240 |
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241 | <itemizedlist>
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242 | <listitem><para>boot image - boot.img </para></listitem>
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243 | <listitem><para>core image - core.img </para></listitem>
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244 | <listitem><para>directory - /boot/grub</para></listitem>
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245 | <listitem><para>device map - device.map</para></listitem>
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246 | <listitem><para>default root setting - guessed</para></listitem>
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247 | </itemizedlist>
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248 |
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249 | <note><para>The root setting is the default value if a 'set root'
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250 | instruction is not found in grub.cfg. This is the partition that is
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251 | searched for the kernel and other supporting files. It is different from
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252 | the 'root=' parameter on the 'linux' line in the configuration line. The
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253 | latter is the partition the kernel mounts as '/'. In the example grub.cfg
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254 | above, both values point to /dev/sda2, but if there is a separate boot
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255 | partition, they will be different.</para></note>
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256 |
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257 | </sect2>
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258 |
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259 | </sect1>
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