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 | <note>
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20 | <para>
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21 | If your system has UEFI support and you wish to boot LFS with UEFI,
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22 | you should skip this page, and config GRUB with UEFI support
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23 | using the instructions provided in
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24 | <ulink url="&blfs-book;postlfs/grub-setup.html">the BLFS page</ulink>.
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25 | </para>
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26 | </note>
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27 |
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28 | <sect2>
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29 | <title>Introduction</title>
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30 |
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31 | <warning><para>Configuring GRUB incorrectly can render your system
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32 | inoperable without an alternate boot device such as a CD-ROM or bootable
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33 | USB drive. This section is not required to boot your LFS system. You may
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34 | just want to modify your current boot loader, e.g. Grub-Legacy, GRUB2, or
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35 | LILO.</para></warning>
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36 |
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37 | <para> Ensure that an emergency boot disk is ready to <quote>rescue</quote>
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38 | the computer if the computer becomes unusable (un-bootable). If you do not
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39 | already have a boot device, you can create one. In order for the procedure
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40 | below to work, you need to jump ahead to BLFS and install
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41 | <userinput>xorriso</userinput> from the <ulink
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42 | url="&blfs-book;multimedia/libisoburn.html">
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43 | libisoburn</ulink> package.</para>
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44 |
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45 | <screen role="nodump"><userinput>cd /tmp
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46 | grub-mkrescue --output=grub-img.iso
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47 | xorriso -as cdrecord -v dev=/dev/cdrw blank=as_needed grub-img.iso</userinput></screen>
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48 |
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49 | </sect2>
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50 |
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51 | <sect2>
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52 | <title>GRUB Naming Conventions</title>
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53 |
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54 | <para>GRUB uses its own naming structure for drives and partitions in
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55 | the form of <emphasis>(hdn,m)</emphasis>, where <emphasis>n</emphasis>
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56 | is the hard drive number and <emphasis>m</emphasis> is the partition
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57 | number. The hard drive number starts from zero, but the partition number
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58 | starts from one for normal partitions and five for extended partitions.
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59 | Note that this is different from earlier versions where
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60 | both numbers started from zero. For example, partition <filename
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61 | class="partition">sda1</filename> is <emphasis>(hd0,1)</emphasis> to
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62 | GRUB and <filename class="partition">sdb3</filename> is
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63 | <emphasis>(hd1,3)</emphasis>. In contrast to Linux, GRUB does not
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64 | consider CD-ROM drives to be hard drives. For example, if using a CD
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65 | on <filename class="partition">hdb</filename> and a second hard drive
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66 | on <filename class="partition">hdc</filename>, that second hard drive
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67 | would still be <emphasis>(hd1)</emphasis>.</para>
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68 |
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69 | </sect2>
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70 |
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71 | <sect2>
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72 | <title>Setting Up the Configuration</title>
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73 |
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74 | <para>GRUB works by writing data to the first physical track of the
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75 | hard disk. This area is not part of any file system. The programs
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76 | there access GRUB modules in the boot partition. The default location
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77 | is /boot/grub/.</para>
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78 |
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79 | <para>The location of the boot partition is a choice of the user that
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80 | affects the configuration. One recommendation is to have a separate small
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81 | (suggested size is 200 MB) partition just for boot information. That way
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82 | each build, whether LFS or some commercial distro, can access the same boot
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83 | files and access can be made from any booted system. If you choose to do
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84 | this, you will need to mount the separate partition, move all files in the
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85 | current <filename class="directory">/boot</filename> directory (e.g. the
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86 | linux kernel you just built in the previous section) to the new partition.
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87 | You will then need to unmount the partition and remount it as <filename
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88 | class="directory">/boot</filename>. If you do this, be sure to update
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89 | <filename>/etc/fstab</filename>.</para>
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90 |
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91 | <para>Using the current lfs partition will also work, but configuration
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92 | for multiple systems is more difficult.</para>
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93 |
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94 | <para>Using the above information, determine the appropriate
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95 | designator for the root partition (or boot partition, if a separate
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96 | one is used). For the following example, it is assumed that the root
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97 | (or separate boot) partition is <filename
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98 | class="partition">sda2</filename>.</para>
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99 |
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100 | <para>Install the GRUB files into <filename
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101 | class="directory">/boot/grub</filename> and set up the boot track:</para>
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102 |
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103 | <warning>
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104 | <para>The following command will overwrite the current boot loader. Do not
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105 | run the command if this is not desired, for example, if using a third party
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106 | boot manager to manage the Master Boot Record (MBR).</para>
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107 | </warning>
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108 |
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109 | <screen role="nodump"><userinput>grub-install /dev/sda</userinput></screen>
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110 |
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111 | <note>
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112 | <para>If the system has been booted using UEFI,
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113 | <command>grub-install</command> will try to install files for the
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114 | <emphasis>x86_64-efi</emphasis> target, but those files
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115 | have not been installed in <xref linkend="chapter-building-system"/>.
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116 | If this is the case, add <option>--target i386-pc</option> to the
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117 | command above.</para>
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118 | </note>
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119 |
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120 | <!-- This does not seem to be true any more
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121 | <note><para><application>grub-install</application> is a script and calls another
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122 | program, grub-probe, that may fail with a message "cannot stat `/dev/root'".
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123 | If so, create a temporary symbolic link from your root partition to /dev/root:</para>
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124 |
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125 | <screen role="nodump"><userinput>ln -sv /dev/sda2 /dev/root</userinput></screen>
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126 |
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127 | <para>The symbolic link will only be present until the system is rebooted.
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128 | The link is only needed for the installation procedure.
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129 | </para></note>
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130 | -->
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131 | </sect2>
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132 |
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133 | <sect2 id="grub-cfg">
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134 | <title>Creating the GRUB Configuration File</title>
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135 |
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136 | <para>Generate <filename>/boot/grub/grub.cfg</filename>:</para>
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137 |
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138 | <screen revision="sysv"><userinput>cat > /boot/grub/grub.cfg << "EOF"
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139 | <literal># Begin /boot/grub/grub.cfg
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140 | set default=0
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141 | set timeout=5
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142 |
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143 | insmod ext2
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144 | set root=(hd0,2)
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145 |
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146 | menuentry "GNU/Linux, Linux &linux-version;-lfs-&version;" {
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147 | linux /boot/vmlinuz-&linux-version;-lfs-&version; root=/dev/sda2 ro
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148 | }</literal>
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149 | EOF</userinput></screen>
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150 |
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151 | <screen revision="systemd"><userinput>cat > /boot/grub/grub.cfg << "EOF"
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152 | <literal># Begin /boot/grub/grub.cfg
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153 | set default=0
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154 | set timeout=5
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155 |
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156 | insmod ext2
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157 | set root=(hd0,2)
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158 |
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159 | menuentry "GNU/Linux, Linux &linux-version;-lfs-&version;" {
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160 | linux /boot/vmlinuz-&linux-version;-lfs-&version; root=/dev/sda2 ro
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161 | }</literal>
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162 | EOF</userinput></screen>
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163 |
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164 |
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165 | <note><para>From <application>GRUB</application>'s perspective, the
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166 | kernel files are relative to the partition used. If you
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167 | used a separate /boot partition, remove /boot from the above
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168 | <emphasis>linux</emphasis> line. You will also need to change the
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169 | <emphasis>set root</emphasis> line to point to the boot partition.
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170 | </para></note>
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171 |
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172 | <para>GRUB is an extremely powerful program and it provides a tremendous
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173 | number of options for booting from a wide variety of devices, operating
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174 | systems, and partition types. There are also many options for customization
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175 | such as graphical splash screens, playing sounds, mouse input, etc. The
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176 | details of these options are beyond the scope of this introduction.</para>
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177 |
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178 | <caution><para>There is a command, <application>grub-mkconfig</application>, that
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179 | can write a configuration file automatically. It uses a set of scripts in
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180 | /etc/grub.d/ and will destroy any customizations that you make. These scripts
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181 | are designed primarily for non-source distributions and are not recommended for
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182 | LFS. If you install a commercial Linux distribution, there is a good chance
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183 | that this program will be run. Be sure to back up your grub.cfg file.</para></caution>
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184 |
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185 | </sect2>
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186 |
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187 | </sect1>
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