[fcc02767] | 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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[1c16a05] | 19 | <note>
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| 20 | <para>
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[c84ec38] | 21 | This section assume your system has UEFI support and you wish to boot
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| 22 | LFS with UEFI and GRUB built following the instructions in Chapter 8.
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| 23 | </para>
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| 24 | <para>
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| 25 | If you've installed GRUB for UEFI with optional dependencies following
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[64e8131] | 26 | BLFS, you should skip the instructions in this page but still learn the
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[b59c9e9] | 27 | syntax of <filename>grub.cfg</filename> and the method to specify
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| 28 | a partition in the file from this page, and configure GRUB with UEFI
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[1c16a05] | 29 | using the instructions provided in
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[c0a0f25] | 30 | <ulink url="&blfs-book;postlfs/grub-setup.html">the BLFS page</ulink>,
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| 31 | but replace <parameter>--target=x86_64-efi</parameter> with
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| 32 | <parameter>--target=arm64-efi</parameter> for the ARM64 system.
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[1c16a05] | 33 | </para>
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[c84ec38] | 34 | <para>
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| 35 | If your system does not support UEFI or you don't want to use it,
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| 36 | you'll need to figure out how to configure the booting process of
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| 37 | the system on your own.
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| 38 | </para>
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[1c16a05] | 39 | </note>
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| 40 |
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[fcc02767] | 41 | <sect2>
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| 42 | <title>Introduction</title>
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| 43 |
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| 44 | <warning><para>Configuring GRUB incorrectly can render your system
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[37b5ac1] | 45 | inoperable without an alternate boot device such as a CD-ROM or bootable
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| 46 | USB drive. This section is not required to boot your LFS system. You may
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| 47 | just want to modify your current boot loader, e.g. Grub-Legacy, GRUB2, or
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[fcc02767] | 48 | LILO.</para></warning>
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| 49 |
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[c84ec38] | 50 | <para>Ensure that an emergency boot disk is ready to <quote>rescue</quote>
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[fcc02767] | 51 | the computer if the computer becomes unusable (un-bootable). If you do not
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[c84ec38] | 52 | already have a boot device, you can create one. To create a emergency
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| 53 | boot device for UEFI, consult section <quote>Create an Emergency Boot
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| 54 | Disk</quote> in
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| 55 | <ulink url="&blfs-book;postlfs/grub-setup.html">the BLFS page</ulink>.</para>
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[fcc02767] | 56 |
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[c84ec38] | 57 | </sect2>
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| 58 |
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| 59 | <sect2>
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| 60 | <title>Turn off Secure Boot</title>
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[fcc02767] | 61 |
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[c84ec38] | 62 | <para>LFS does not have the essential packages to support Secure Boot.
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| 63 | To set up the boot process following the instructions in this section,
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| 64 | Secure Boot must be turned off from the configuration interface of the
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| 65 | firmware. Read the documentation provided by the manufacturer of your
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| 66 | system to find out how.</para>
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[fcc02767] | 67 | </sect2>
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| 68 |
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| 69 | <sect2>
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| 70 | <title>GRUB Naming Conventions</title>
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| 71 |
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| 72 | <para>GRUB uses its own naming structure for drives and partitions in
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| 73 | the form of <emphasis>(hdn,m)</emphasis>, where <emphasis>n</emphasis>
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| 74 | is the hard drive number and <emphasis>m</emphasis> is the partition
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[8190ca0] | 75 | number. The hard drive numbers start from zero, but the partition numbers
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| 76 | start from one for normal partitions (from five for extended partitions).
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[fcc02767] | 77 | Note that this is different from earlier versions where
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| 78 | both numbers started from zero. For example, partition <filename
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| 79 | class="partition">sda1</filename> is <emphasis>(hd0,1)</emphasis> to
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| 80 | GRUB and <filename class="partition">sdb3</filename> is
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| 81 | <emphasis>(hd1,3)</emphasis>. In contrast to Linux, GRUB does not
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| 82 | consider CD-ROM drives to be hard drives. For example, if using a CD
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| 83 | on <filename class="partition">hdb</filename> and a second hard drive
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| 84 | on <filename class="partition">hdc</filename>, that second hard drive
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| 85 | would still be <emphasis>(hd1)</emphasis>.</para>
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| 86 |
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| 87 | </sect2>
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| 88 |
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| 89 | <sect2>
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| 90 | <title>Setting Up the Configuration</title>
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| 91 |
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[c84ec38] | 92 | <para>GRUB works by creating an EFI executable in the EFI System
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| 93 | Partition (ESP). You can find the ESP with:</para>
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| 94 |
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| 95 | <screen role="nodump"><userinput>fdisk -l | grep 'EFI System'</userinput></screen>
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| 96 |
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| 97 | <para>If no ESP exists on your hard drive (for example, you are building
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| 98 | LFS on a fresh new system with a Live CD as the host distro), read
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| 99 | <ulink url="&blfs-book;postlfs/grub-setup.html">the BLFS page</ulink>
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| 100 | for the instruction to create an ESP on your hard drive.</para>
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| 101 |
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| 102 | <para>If the ESP is not mounted at
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| 103 | <filename class="directory">/boot/efi</filename> (in the chroot),
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| 104 | mount it now:</para>
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| 105 |
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[c0a0f25] | 106 | <screen role="nodump"><userinput>mkdir -pv /boot/efi
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| 107 | mount /boot/efi</userinput></screen>
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[c84ec38] | 108 |
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| 109 | <note>
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| 110 | <para>The path to the device node is intentionally omitted in the
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| 111 | command. We expect the entry for mounting the ESP to
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| 112 | <filename class="directory">/boot/efi</filename> is already in
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| 113 | <filename>/etc/fstab</filename>. Add the entry before running the
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| 114 | command if you forgot to create an entry for the ESP in
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| 115 | <xref linkend="ch-bootable-fstab"/>.</para>
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| 116 | </note>
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[fcc02767] | 117 |
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| 118 | <para>The location of the boot partition is a choice of the user that
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| 119 | affects the configuration. One recommendation is to have a separate small
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[37b5ac1] | 120 | (suggested size is 200 MB) partition just for boot information. That way
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[fcc02767] | 121 | each build, whether LFS or some commercial distro, can access the same boot
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| 122 | files and access can be made from any booted system. If you choose to do
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| 123 | this, you will need to mount the separate partition, move all files in the
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| 124 | current <filename class="directory">/boot</filename> directory (e.g. the
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[8190ca0] | 125 | Linux kernel you just built in the previous section) to the new partition.
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[fcc02767] | 126 | You will then need to unmount the partition and remount it as <filename
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| 127 | class="directory">/boot</filename>. If you do this, be sure to update
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| 128 | <filename>/etc/fstab</filename>.</para>
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| 129 |
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[c7f74cd] | 130 | <para>Leaving <filename class="directory">/boot</filename> on
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[8190ca0] | 131 | the current LFS partition will also work, but configuration
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[fcc02767] | 132 | for multiple systems is more difficult.</para>
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| 133 |
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| 134 | <para>Using the above information, determine the appropriate
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| 135 | designator for the root partition (or boot partition, if a separate
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| 136 | one is used). For the following example, it is assumed that the root
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| 137 | (or separate boot) partition is <filename
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| 138 | class="partition">sda2</filename>.</para>
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| 139 |
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| 140 | <para>Install the GRUB files into <filename
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[c84ec38] | 141 | class="directory">/boot/grub</filename> and the GRUB EFI executable into
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[53415749] | 142 | <filename class="directory">/boot/efi/EFI/BOOT/BOOTAA64.EFI</filename>:</para>
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[fcc02767] | 143 |
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| 144 | <warning>
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[c84ec38] | 145 | <para>The following command will overwrite
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| 146 | <filename>BOOTAA64.EFI</filename>. Do not run the command if this is
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| 147 | not desired, for example, if it contains a third party boot manager.
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| 148 | You can backup it with <command>cp</command> as it's a regular
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| 149 | file.</para>
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[fcc02767] | 150 | </warning>
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| 151 |
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[c84ec38] | 152 | <screen role="nodump"><userinput>grub-install --removable</userinput></screen>
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[fcc02767] | 153 |
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| 154 | <note>
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[c84ec38] | 155 | <para>
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| 156 | <parameter>--removable</parameter> may seem strange here. The UEFI
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| 157 | firmware searches EFI executables for boot loaders in a hardcoded
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[53415749] | 158 | path, <filename>EFI/BOOT/BOOTAA64.EFI</filename> in the ESP, and other
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[c84ec38] | 159 | boot loader paths listed in the EFI variables. We've not installed
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| 160 | the utilities for manipulating EFI variables so we need to install
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| 161 | the EFI executable into the hardcoded path. The hardcoded path is
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| 162 | usually used by removable devices (for example, USB thumb devices)
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| 163 | so the <command>grub-install</command> option for this purpose is
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| 164 | named <parameter>--removable</parameter>.
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| 165 | </para>
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| 166 | <para>
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| 167 | UEFI implementation usually prefers the boot loaders with paths
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| 168 | recorded in an EFI variable, to the boot loader with the hardcoded
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| 169 | search path. You may need to invoke the boot device selection menu
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| 170 | or setting interface of your EFI firmware on next boot to explicitly
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| 171 | select the bootloader.
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| 172 | </para>
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| 173 | <para>
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| 174 | Some UEFI implementation may completely skip the hardcoded path if
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| 175 | there are other boot loaders in the same hard drive with paths
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| 176 | recorded in an EFI variable. Then you need to create an EFI
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| 177 | variable for the newly installed boot loader. Install
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| 178 | <ulink url="&blfs-book;postlfs/efibootmgr.html">efibootmgr</ulink>,
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| 179 | then run the following commands:
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[c0a0f25] | 180 |
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[c84ec38] | 181 | <screen role="nodump"><userinput>mount -v -t efivarfs efivarfs /sys/firmware/efi/efivars
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[c0a0f25] | 182 | efibootmgr -B -L LFS || true
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[8f641ee] | 183 | efibootmgr -c -L LFS -l '\EFI\BOOT\BOOTAA64.EFI' -d /dev/sda
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[c0a0f25] | 184 | umount /sys/firmware/efi/efivars</userinput></screen>
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| 185 |
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[c84ec38] | 186 | Replace <filename>/dev/sda</filename> with the device node of the
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[c0a0f25] | 187 | hard drive where you are installing GRUB into. For some UEFI
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| 188 | firmwares, <option>-e 3</option> option may be needed for the
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| 189 | <command>efibootmgr -c</command> command.
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[c84ec38] | 190 | </para>
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[fcc02767] | 191 | </note>
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| 192 |
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| 193 | <!-- This does not seem to be true any more
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| 194 | <note><para><application>grub-install</application> is a script and calls another
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| 195 | program, grub-probe, that may fail with a message "cannot stat `/dev/root'".
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| 196 | If so, create a temporary symbolic link from your root partition to /dev/root:</para>
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| 197 |
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| 198 | <screen role="nodump"><userinput>ln -sv /dev/sda2 /dev/root</userinput></screen>
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| 199 |
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| 200 | <para>The symbolic link will only be present until the system is rebooted.
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| 201 | The link is only needed for the installation procedure.
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| 202 | </para></note>
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| 203 | -->
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| 204 | </sect2>
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| 205 |
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| 206 | <sect2 id="grub-cfg">
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| 207 | <title>Creating the GRUB Configuration File</title>
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| 208 |
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| 209 | <para>Generate <filename>/boot/grub/grub.cfg</filename>:</para>
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| 210 |
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[3d7b4f6] | 211 | <screen><userinput>cat > /boot/grub/grub.cfg << "EOF"
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[fcc02767] | 212 | <literal># Begin /boot/grub/grub.cfg
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| 213 | set default=0
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| 214 | set timeout=5
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| 215 |
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[67ca5ef] | 216 | insmod part_gpt
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[fcc02767] | 217 | insmod ext2
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| 218 | set root=(hd0,2)
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| 219 |
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[0ebfdf7e] | 220 | insmod all_video
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| 221 |
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[fcc02767] | 222 | menuentry "GNU/Linux, Linux &linux-version;-lfs-&version;" {
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| 223 | linux /boot/vmlinuz-&linux-version;-lfs-&version; root=/dev/sda2 ro
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| 224 | }</literal>
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| 225 | EOF</userinput></screen>
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| 226 |
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[93ec8b3] | 227 | <para>
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| 228 | The <command>insmod</command> commands load the
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| 229 | <application>GRUB</application> modules named
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| 230 | <filename>part_gpt</filename> and <filename>ext2</filename>.
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| 231 | Despite the naming, <filename>ext2</filename> actually supports
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| 232 | <systemitem class='filesystem'>ext2</systemitem>,
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| 233 | <systemitem class='filesystem'>ext3</systemitem>, and
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| 234 | <systemitem class='filesystem'>ext4</systemitem> filesystems.
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| 235 | The <command>grub-install</command> command has embedded some modules
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| 236 | into the main <application>GRUB</application> image (installed into
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| 237 | the MBR or the GRUB BIOS partition) to access the other modules
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| 238 | (in <filename class='directory'>/boot/grub/i386-pc</filename>) without
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| 239 | a chicken-or-egg issue, so with a typical configuration these two
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| 240 | modules are already embedded and those two <command>insmod</command>
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| 241 | commands will do nothing. But they do no harm anyway, and they may
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| 242 | be needed with some rare configurations.
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| 243 | </para>
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| 244 |
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[fcc02767] | 245 | <note><para>From <application>GRUB</application>'s perspective, the
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| 246 | kernel files are relative to the partition used. If you
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| 247 | used a separate /boot partition, remove /boot from the above
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| 248 | <emphasis>linux</emphasis> line. You will also need to change the
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| 249 | <emphasis>set root</emphasis> line to point to the boot partition.
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| 250 | </para></note>
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| 251 |
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[5353a19] | 252 | <note>
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| 253 | <para>The GRUB designator for a partition may change if you added or
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| 254 | removed some disks (including removable disks like USB thumb devices).
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| 255 | The change may cause boot failure because
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| 256 | <filename>grub.cfg</filename> refers to some <quote>old</quote>
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| 257 | designators. If you wish to avoid such a problem, you may use
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[8190ca0] | 258 | the UUID of a partition and the UUID of a filesystem instead of a GRUB designator to
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| 259 | specify a device.
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[5353a19] | 260 | Run <command>lsblk -o UUID,PARTUUID,PATH,MOUNTPOINT</command> to show
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[8190ca0] | 261 | the UUIDs of your filesystems (in the <literal>UUID</literal> column) and
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| 262 | partitions (in the <literal>PARTUUID</literal> column). Then replace
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[5353a19] | 263 | <literal>set root=(hdx,y)</literal> with
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[8190ca0] | 264 | <literal>search --set=root --fs-uuid <replaceable><UUID of the filesystem
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| 265 | where the kernel is installed></replaceable></literal>, and replace
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[5353a19] | 266 | <literal>root=/dev/sda2</literal> with
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[8190ca0] | 267 | <literal>root=PARTUUID=<replaceable><UUID of the partition where LFS
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| 268 | is built></replaceable></literal>.</para>
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| 269 | <para>Note that the UUID of a partition is completely different from the
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| 270 | UUID of the filesystem in this partition. Some online resources may
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[5353a19] | 271 | instruct you to use
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| 272 | <literal>root=UUID=<replaceable><filesystem UUID></replaceable></literal>
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| 273 | instead of
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| 274 | <literal>root=PARTUUID=<replaceable><partition UUID></replaceable></literal>,
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[8190ca0] | 275 | but doing so will require an initramfs, which is beyond the scope of
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[5353a19] | 276 | LFS.</para>
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| 277 | <para>The name of the device node for a partition in
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[8190ca0] | 278 | <filename class='directory'>/dev</filename> may also change (this is less
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| 279 | likely than a GRUB designator change). You can also replace
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[5353a19] | 280 | paths to device nodes like <literal>/dev/sda1</literal> with
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| 281 | <literal>PARTUUID=<replaceable><partition UUID></replaceable></literal>,
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| 282 | in <filename>/etc/fstab</filename>, to avoid a potential boot failure
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| 283 | in case the device node name has changed.</para>
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| 284 | </note>
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| 285 |
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[fcc02767] | 286 | <para>GRUB is an extremely powerful program and it provides a tremendous
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| 287 | number of options for booting from a wide variety of devices, operating
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| 288 | systems, and partition types. There are also many options for customization
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| 289 | such as graphical splash screens, playing sounds, mouse input, etc. The
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| 290 | details of these options are beyond the scope of this introduction.</para>
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| 291 |
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| 292 | <caution><para>There is a command, <application>grub-mkconfig</application>, that
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| 293 | can write a configuration file automatically. It uses a set of scripts in
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| 294 | /etc/grub.d/ and will destroy any customizations that you make. These scripts
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| 295 | are designed primarily for non-source distributions and are not recommended for
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| 296 | LFS. If you install a commercial Linux distribution, there is a good chance
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| 297 | that this program will be run. Be sure to back up your grub.cfg file.</para></caution>
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| 298 |
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| 299 | </sect2>
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| 300 |
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| 301 | </sect1>
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