source: chapter08/grub.xml@ bf58c1e

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Last change on this file since bf58c1e was bf58c1e, checked in by Bruce Dubbs <bdubbs@…>, 8 years ago

Rewrite and reorganize Chapter 7.
Update systemd customization.

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1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4 <!ENTITY % general-entities SYSTEM "../general.ent">
5 %general-entities;
6]>
7
8<sect1 id="ch-bootable-grub" role="wrap">
9 <?dbhtml filename="grub.html"?>
10
11 <sect1info condition="script">
12 <productname>grub</productname>
13 <productnumber>&grub-version;</productnumber>
14 <address>&grub-url;</address>
15 </sect1info>
16
17 <title>Using GRUB to Set Up the Boot Process</title>
18
19 <sect2>
20 <title>Introduction</title>
21
22 <warning><para>Configuring GRUB incorrectly can render your system
23 inoperable without an alternate boot device such as a CD-ROM. This
24 section is not required to boot your LFS system. You may just
25 want to modify your current boot loader, e.g. Grub-Legacy, GRUB2, or
26 LILO.</para></warning>
27
28
29 <para> Ensure that an emergency boot disk is ready to <quote>rescue</quote>
30 the computer if the computer becomes unusable (un-bootable). If you do not
31 already have a boot device, you can create one. In order for the procedure
32 below to work, you need to jump ahead to BLFS and install
33 <userinput>xorriso</userinput> from the <ulink
34 url="http://www.linuxfromscratch.org/blfs/view/svn/multimedia/libisoburn.html">
35 libisoburn</ulink> package.</para>
36
37<screen role="nodump"><userinput>cd /tmp &amp;&amp;
38grub-mkrescue --output=grub-img.iso &amp;&amp;
39xorriso -as cdrecord -v dev=/dev/cdrw blank=as_needed grub-img.iso</userinput></screen>
40
41 </sect2>
42
43 <sect2>
44 <title>GRUB Naming Conventions</title>
45
46 <para>GRUB uses its own naming structure for drives and partitions in
47 the form of <emphasis>(hdn,m)</emphasis>, where <emphasis>n</emphasis>
48 is the hard drive number and <emphasis>m</emphasis> is the partition
49 number. The hard drive number starts from zero, but the partition number
50 starts from one for normal partitions and five for extended partitions.
51 Note that this is different from earlier versions where
52 both numbers started from zero. For example, partition <filename
53 class="partition">sda1</filename> is <emphasis>(hd0,1)</emphasis> to
54 GRUB and <filename class="partition">sdb3</filename> is
55 <emphasis>(hd1,3)</emphasis>. In contrast to Linux, GRUB does not
56 consider CD-ROM drives to be hard drives. For example, if using a CD
57 on <filename class="partition">hdb</filename> and a second hard drive
58 on <filename class="partition">hdc</filename>, that second hard drive
59 would still be <emphasis>(hd1)</emphasis>.</para>
60
61 </sect2>
62
63 <sect2>
64 <title>Setting Up the Configuration</title>
65
66 <para>GRUB works by writing data to the first physical track of the
67 hard disk. This area is not part of any file system. The programs
68 there access GRUB modules in the boot partition. The default location
69 is /boot/grub/.</para>
70
71 <para>The location of the boot partition is a choice of the user that
72 affects the configuration. One recommendation is to have a separate small
73 (suggested size is 100 MB) partition just for boot information. That way
74 each build, whether LFS or some commercial distro, can access the same boot
75 files and access can be made from any booted system. If you choose to do
76 this, you will need to mount the separate partition, move all files in the
77 current <filename class="directory">/boot</filename> directory (e.g. the
78 linux kernel you just built in the previous section) to the new partition.
79 You will then need to unmount the partition and remount it as <filename
80 class="directory">/boot</filename>. If you do this, be sure to update
81 <filename>/etc/fstab</filename>.</para>
82
83 <para>Using the current lfs partition will also work, but configuration
84 for multiple systems is more difficult.</para>
85
86 <para>Using the above information, determine the appropriate
87 designator for the root partition (or boot partition, if a separate
88 one is used). For the following example, it is assumed that the root
89 (or separate boot) partition is <filename
90 class="partition">sda2</filename>.</para>
91
92 <para>Install the GRUB files into <filename
93 class="directory">/boot/grub</filename> and set up the boot track:</para>
94
95 <warning>
96 <para>The following command will overwrite the current boot loader. Do not
97 run the command if this is not desired, for example, if using a third party
98 boot manager to manage the Master Boot Record (MBR).</para>
99 </warning>
100
101<screen role="nodump"><userinput>grub-install /dev/sda</userinput></screen>
102
103<!-- This does not seem to be true any more
104 <note><para><application>grub-install</application> is a script and calls another
105 program, grub-probe, that may fail with a message "cannot stat `/dev/root'".
106 If so, create a temporary symbolic link from your root partition to /dev/root:</para>
107
108<screen role="nodump"><userinput>ln -sv /dev/sda2 /dev/root</userinput></screen>
109
110 <para>The symbolic link will only be present until the system is rebooted.
111 The link is only needed for the installation procedure.
112 </para></note>
113-->
114 </sect2>
115
116 <sect2 id="grub-cfg">
117 <title>Creating the GRUB Configuration File</title>
118
119 <para>Generate <filename>/boot/grub/grub.cfg</filename>:</para>
120
121 <screen><userinput>cat &gt; /boot/grub/grub.cfg &lt;&lt; "EOF"
122<literal># Begin /boot/grub/grub.cfg
123set default=0
124set timeout=5
125
126insmod ext2
127set root=(hd0,2)
128
129menuentry "GNU/Linux, Linux &linux-version;-lfs-&version;" {
130 linux /boot/vmlinuz-&linux-version;-lfs-&version; root=/dev/sda2 ro
131}</literal>
132EOF</userinput></screen>
133
134 <note><para>From <application>GRUB</application>'s perspective, the
135 kernel files are relative to the partition used. If you
136 used a separate /boot partition, remove /boot from the above
137 <emphasis>linux</emphasis> line. You will also need to change the
138 <emphasis>set root</emphasis> line to point to the boot partition.
139 </para></note>
140
141 <para>GRUB is an extremely powerful program and it provides a tremendous
142 number of options for booting from a wide variety of devices, operating
143 systems, and partition types. There are also many options for customization
144 such as graphical splash screens, playing sounds, mouse input, etc. The
145 details of these options are beyond the scope of this introduction.</para>
146
147 <caution><para>There is a command, <application>grub-mkconfig</application>, that
148 can write a configuration file automatically. It uses a set of scripts in
149 /etc/grub.d/ and will destroy any customizations that you make. These scripts
150 are designed primarily for non-source distributions and are not recommended for
151 LFS. If you install a commercial Linux distribution, there is a good chance
152 that this program will be run. Be sure to back up your grub.cfg file.</para></caution>
153
154 </sect2>
155
156</sect1>
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