source: chapter10/grub.xml@ fcc02767

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Last change on this file since fcc02767 was fcc02767, checked in by Bruce Dubbs <bdubbs@…>, 18 months ago

Initial commit of alternative cross LFS

git-svn-id: http://svn.linuxfromscratch.org/LFS/branches/cross2@11897 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

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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="&blfs-book;multimedia/libisoburn.html">
35 libisoburn</ulink> package.</para>
36
37<screen role="nodump"><userinput>cd /tmp
38grub-mkrescue --output=grub-img.iso
39xorriso -as cdrecord -v dev=/dev/cdrw blank=as_needed grub-img.iso</userinput></screen>
40
41 <note>
42 <para>
43 To boot LFS on host systems that have UEFI enabled, the kernel needs to
44 have been built with the CONFIG_EFI_STUB capabality described in the
45 previous section. However, LFS can be booted using GRUB2 without such
46 an addition. To do this, the UEFI Mode and Secure Boot capabilities in
47 the host system's BIOS need to be turned off. For details, see <ulink
48 url="&hints-root;lfs-uefi.txt">
49 the lfs-uefi.txt hint</ulink> at
50 &hints-root;lfs-uefi.txt.
51 </para>
52 </note>
53
54 </sect2>
55
56 <sect2>
57 <title>GRUB Naming Conventions</title>
58
59 <para>GRUB uses its own naming structure for drives and partitions in
60 the form of <emphasis>(hdn,m)</emphasis>, where <emphasis>n</emphasis>
61 is the hard drive number and <emphasis>m</emphasis> is the partition
62 number. The hard drive number starts from zero, but the partition number
63 starts from one for normal partitions and five for extended partitions.
64 Note that this is different from earlier versions where
65 both numbers started from zero. For example, partition <filename
66 class="partition">sda1</filename> is <emphasis>(hd0,1)</emphasis> to
67 GRUB and <filename class="partition">sdb3</filename> is
68 <emphasis>(hd1,3)</emphasis>. In contrast to Linux, GRUB does not
69 consider CD-ROM drives to be hard drives. For example, if using a CD
70 on <filename class="partition">hdb</filename> and a second hard drive
71 on <filename class="partition">hdc</filename>, that second hard drive
72 would still be <emphasis>(hd1)</emphasis>.</para>
73
74 </sect2>
75
76 <sect2>
77 <title>Setting Up the Configuration</title>
78
79 <para>GRUB works by writing data to the first physical track of the
80 hard disk. This area is not part of any file system. The programs
81 there access GRUB modules in the boot partition. The default location
82 is /boot/grub/.</para>
83
84 <para>The location of the boot partition is a choice of the user that
85 affects the configuration. One recommendation is to have a separate small
86 (suggested size is 100 MB) partition just for boot information. That way
87 each build, whether LFS or some commercial distro, can access the same boot
88 files and access can be made from any booted system. If you choose to do
89 this, you will need to mount the separate partition, move all files in the
90 current <filename class="directory">/boot</filename> directory (e.g. the
91 linux kernel you just built in the previous section) to the new partition.
92 You will then need to unmount the partition and remount it as <filename
93 class="directory">/boot</filename>. If you do this, be sure to update
94 <filename>/etc/fstab</filename>.</para>
95
96 <para>Using the current lfs partition will also work, but configuration
97 for multiple systems is more difficult.</para>
98
99 <para>Using the above information, determine the appropriate
100 designator for the root partition (or boot partition, if a separate
101 one is used). For the following example, it is assumed that the root
102 (or separate boot) partition is <filename
103 class="partition">sda2</filename>.</para>
104
105 <para>Install the GRUB files into <filename
106 class="directory">/boot/grub</filename> and set up the boot track:</para>
107
108 <warning>
109 <para>The following command will overwrite the current boot loader. Do not
110 run the command if this is not desired, for example, if using a third party
111 boot manager to manage the Master Boot Record (MBR).</para>
112 </warning>
113
114<screen role="nodump"><userinput>grub-install /dev/sda</userinput></screen>
115
116 <note>
117 <para>If the system has been booted using UEFI,
118 <command>grub-install</command> will try to install files for the
119 <emphasis>x86_64-efi</emphasis> target, but those files
120 have not been installed in chapter 6. If this is the case, add
121 <option>--target i386-pc</option> to the command above.</para>
122 </note>
123
124<!-- This does not seem to be true any more
125 <note><para><application>grub-install</application> is a script and calls another
126 program, grub-probe, that may fail with a message "cannot stat `/dev/root'".
127 If so, create a temporary symbolic link from your root partition to /dev/root:</para>
128
129<screen role="nodump"><userinput>ln -sv /dev/sda2 /dev/root</userinput></screen>
130
131 <para>The symbolic link will only be present until the system is rebooted.
132 The link is only needed for the installation procedure.
133 </para></note>
134-->
135 </sect2>
136
137 <sect2 id="grub-cfg">
138 <title>Creating the GRUB Configuration File</title>
139
140 <para>Generate <filename>/boot/grub/grub.cfg</filename>:</para>
141
142 <screen revision="sysv"><userinput>cat &gt; /boot/grub/grub.cfg &lt;&lt; "EOF"
143<literal># Begin /boot/grub/grub.cfg
144set default=0
145set timeout=5
146
147insmod ext2
148set root=(hd0,2)
149
150menuentry "GNU/Linux, Linux &linux-version;-lfs-&version;" {
151 linux /boot/vmlinuz-&linux-version;-lfs-&version; root=/dev/sda2 ro
152}</literal>
153EOF</userinput></screen>
154
155 <screen revision="systemd"><userinput>cat &gt; /boot/grub/grub.cfg &lt;&lt; "EOF"
156<literal># Begin /boot/grub/grub.cfg
157set default=0
158set timeout=5
159
160insmod ext2
161set root=(hd0,2)
162
163menuentry "GNU/Linux, Linux &linux-version;-lfs-&versiond;" {
164 linux /boot/vmlinuz-&linux-version;-lfs-&versiond; root=/dev/sda2 ro
165}</literal>
166EOF</userinput></screen>
167
168
169 <note><para>From <application>GRUB</application>'s perspective, the
170 kernel files are relative to the partition used. If you
171 used a separate /boot partition, remove /boot from the above
172 <emphasis>linux</emphasis> line. You will also need to change the
173 <emphasis>set root</emphasis> line to point to the boot partition.
174 </para></note>
175
176 <para>GRUB is an extremely powerful program and it provides a tremendous
177 number of options for booting from a wide variety of devices, operating
178 systems, and partition types. There are also many options for customization
179 such as graphical splash screens, playing sounds, mouse input, etc. The
180 details of these options are beyond the scope of this introduction.</para>
181
182 <caution><para>There is a command, <application>grub-mkconfig</application>, that
183 can write a configuration file automatically. It uses a set of scripts in
184 /etc/grub.d/ and will destroy any customizations that you make. These scripts
185 are designed primarily for non-source distributions and are not recommended for
186 LFS. If you install a commercial Linux distribution, there is a good chance
187 that this program will be run. Be sure to back up your grub.cfg file.</para></caution>
188
189 </sect2>
190
191</sect1>
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