source: chapter10/grub.xml@ 5353a19

11.2 11.3 11.3-rc1 bdubbs/gcc13 multilib trunk xry111/arm64 xry111/clfs-ng xry111/glibc-2.37 xry111/kcfg-revise xry111/pip3 xry111/queue-11.3 xry111/rust-wip-20221008
Last change on this file since 5353a19 was 5353a19, checked in by Xi Ruoyao <xry111@…>, 9 months ago

grub: add a note about filesystem UUID and partition UUID usage

Text only change.

  • Property mode set to 100644
File size: 9.4 KB
1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3 "" [
4 <!ENTITY % general-entities SYSTEM "../general.ent">
5 %general-entities;
8<sect1 id="ch-bootable-grub" role="wrap">
9 <?dbhtml filename="grub.html"?>
11 <sect1info condition="script">
12 <productname>grub</productname>
13 <productnumber>&grub-version;</productnumber>
14 <address>&grub-url;</address>
15 </sect1info>
17 <title>Using GRUB to Set Up the Boot Process</title>
19 <note>
20 <para>
21 If your system has UEFI support and you wish to boot LFS with UEFI,
22 you should skip this page, and config GRUB with UEFI support
23 using the instructions provided in
24 <ulink url="&blfs-book;postlfs/grub-setup.html">the BLFS page</ulink>.
25 </para>
26 </note>
28 <sect2>
29 <title>Introduction</title>
31 <warning><para>Configuring GRUB incorrectly can render your system
32 inoperable without an alternate boot device such as a CD-ROM or bootable
33 USB drive. This section is not required to boot your LFS system. You may
34 just want to modify your current boot loader, e.g. Grub-Legacy, GRUB2, or
35 LILO.</para></warning>
37 <para> Ensure that an emergency boot disk is ready to <quote>rescue</quote>
38 the computer if the computer becomes unusable (un-bootable). If you do not
39 already have a boot device, you can create one. In order for the procedure
40 below to work, you need to jump ahead to BLFS and install
41 <userinput>xorriso</userinput> from the <ulink
42 url="&blfs-book;multimedia/libisoburn.html">
43 libisoburn</ulink> package.</para>
45<screen role="nodump"><userinput>cd /tmp
46grub-mkrescue --output=grub-img.iso
47xorriso -as cdrecord -v dev=/dev/cdrw blank=as_needed grub-img.iso</userinput></screen>
49 </sect2>
51 <sect2>
52 <title>GRUB Naming Conventions</title>
54 <para>GRUB uses its own naming structure for drives and partitions in
55 the form of <emphasis>(hdn,m)</emphasis>, where <emphasis>n</emphasis>
56 is the hard drive number and <emphasis>m</emphasis> is the partition
57 number. The hard drive number starts from zero, but the partition number
58 starts from one for normal partitions and five for extended partitions.
59 Note that this is different from earlier versions where
60 both numbers started from zero. For example, partition <filename
61 class="partition">sda1</filename> is <emphasis>(hd0,1)</emphasis> to
62 GRUB and <filename class="partition">sdb3</filename> is
63 <emphasis>(hd1,3)</emphasis>. In contrast to Linux, GRUB does not
64 consider CD-ROM drives to be hard drives. For example, if using a CD
65 on <filename class="partition">hdb</filename> and a second hard drive
66 on <filename class="partition">hdc</filename>, that second hard drive
67 would still be <emphasis>(hd1)</emphasis>.</para>
69 </sect2>
71 <sect2>
72 <title>Setting Up the Configuration</title>
74 <para>GRUB works by writing data to the first physical track of the
75 hard disk. This area is not part of any file system. The programs
76 there access GRUB modules in the boot partition. The default location
77 is /boot/grub/.</para>
79 <para>The location of the boot partition is a choice of the user that
80 affects the configuration. One recommendation is to have a separate small
81 (suggested size is 200 MB) partition just for boot information. That way
82 each build, whether LFS or some commercial distro, can access the same boot
83 files and access can be made from any booted system. If you choose to do
84 this, you will need to mount the separate partition, move all files in the
85 current <filename class="directory">/boot</filename> directory (e.g. the
86 linux kernel you just built in the previous section) to the new partition.
87 You will then need to unmount the partition and remount it as <filename
88 class="directory">/boot</filename>. If you do this, be sure to update
89 <filename>/etc/fstab</filename>.</para>
91 <para>Using the current lfs partition will also work, but configuration
92 for multiple systems is more difficult.</para>
94 <para>Using the above information, determine the appropriate
95 designator for the root partition (or boot partition, if a separate
96 one is used). For the following example, it is assumed that the root
97 (or separate boot) partition is <filename
98 class="partition">sda2</filename>.</para>
100 <para>Install the GRUB files into <filename
101 class="directory">/boot/grub</filename> and set up the boot track:</para>
103 <warning>
104 <para>The following command will overwrite the current boot loader. Do not
105 run the command if this is not desired, for example, if using a third party
106 boot manager to manage the Master Boot Record (MBR).</para>
107 </warning>
109<screen role="nodump"><userinput>grub-install /dev/sda</userinput></screen>
111 <note>
112 <para>If the system has been booted using UEFI,
113 <command>grub-install</command> will try to install files for the
114 <emphasis>x86_64-efi</emphasis> target, but those files
115 have not been installed in <xref linkend="chapter-building-system"/>.
116 If this is the case, add <option>--target i386-pc</option> to the
117 command above.</para>
118 </note>
120<!-- This does not seem to be true any more
121 <note><para><application>grub-install</application> is a script and calls another
122 program, grub-probe, that may fail with a message "cannot stat `/dev/root'".
123 If so, create a temporary symbolic link from your root partition to /dev/root:</para>
125<screen role="nodump"><userinput>ln -sv /dev/sda2 /dev/root</userinput></screen>
127 <para>The symbolic link will only be present until the system is rebooted.
128 The link is only needed for the installation procedure.
129 </para></note>
131 </sect2>
133 <sect2 id="grub-cfg">
134 <title>Creating the GRUB Configuration File</title>
136 <para>Generate <filename>/boot/grub/grub.cfg</filename>:</para>
138 <screen><userinput>cat &gt; /boot/grub/grub.cfg &lt;&lt; "EOF"
139<literal># Begin /boot/grub/grub.cfg
140set default=0
141set timeout=5
143insmod ext2
144set root=(hd0,2)
146menuentry "GNU/Linux, Linux &linux-version;-lfs-&version;" {
147 linux /boot/vmlinuz-&linux-version;-lfs-&version; root=/dev/sda2 ro
151 <note><para>From <application>GRUB</application>'s perspective, the
152 kernel files are relative to the partition used. If you
153 used a separate /boot partition, remove /boot from the above
154 <emphasis>linux</emphasis> line. You will also need to change the
155 <emphasis>set root</emphasis> line to point to the boot partition.
156 </para></note>
158 <note>
159 <para>The GRUB designator for a partition may change if you added or
160 removed some disks (including removable disks like USB thumb devices).
161 The change may cause boot failure because
162 <filename>grub.cfg</filename> refers to some <quote>old</quote>
163 designators. If you wish to avoid such a problem, you may use
164 the UUID of partition and filesystem instead of GRUB designator to
165 specify a partition.
166 Run <command>lsblk -o UUID,PARTUUID,PATH,MOUNTPOINT</command> to show
167 the UUID of your filesystems (in <literal>UUID</literal> column) and
168 partitions (in <literal>PARTUUID</literal> column). Then replace
169 <literal>set root=(hdx,y)</literal> with
170 <literal>search --set=root --fs-uuid <replaceable>&lt;UUID of the filesystem where the kernel is installed&gt;</replaceable></literal>, and replace
171 <literal>root=/dev/sda2</literal> with
172 <literal>root=PARTUUID=<replaceable>&lt;UUID of the partition where LFS is built&gt;</replaceable></literal>.</para>
173 <para>Note that the UUID of a partition and the UUID of the filesystem
174 in this partition is completely different. Some online resources may
175 instruct you to use
176 <literal>root=UUID=<replaceable>&lt;filesystem UUID&gt;</replaceable></literal>
177 instead of
178 <literal>root=PARTUUID=<replaceable>&lt;partition UUID&gt;</replaceable></literal>,
179 but doing so will require an initramfs which is beyond the scope of
180 LFS.</para>
181 <para>The name of the device node for a partition in
182 <filename class='directory'>/dev</filename> may also change (more
183 unlikely than GRUB designator change though). You can also replace
184 paths to device nodes like <literal>/dev/sda1</literal> with
185 <literal>PARTUUID=<replaceable>&lt;partition UUID&gt;</replaceable></literal>,
186 in <filename>/etc/fstab</filename>, to avoid a potential boot failure
187 in case the device node name has changed.</para>
188 </note>
190 <para>GRUB is an extremely powerful program and it provides a tremendous
191 number of options for booting from a wide variety of devices, operating
192 systems, and partition types. There are also many options for customization
193 such as graphical splash screens, playing sounds, mouse input, etc. The
194 details of these options are beyond the scope of this introduction.</para>
196 <caution><para>There is a command, <application>grub-mkconfig</application>, that
197 can write a configuration file automatically. It uses a set of scripts in
198 /etc/grub.d/ and will destroy any customizations that you make. These scripts
199 are designed primarily for non-source distributions and are not recommended for
200 LFS. If you install a commercial Linux distribution, there is a good chance
201 that this program will be run. Be sure to back up your grub.cfg file.</para></caution>
203 </sect2>
Note: See TracBrowser for help on using the repository browser.