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<?xml version="1.0" encoding="UTF-8"?>
<!-- $Header: $ -->
<!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
<guide disclaimer="draft" link="/doc/en/grub-2-guide.xml" lang="en">
<title>GRUB 2 Guide</title>
<author title="Author">
<mail link="matej@laitl.cz">Matěj Laitl</mail>
</author>
<author title="Author">
<mail link="scarabeus"/>
</author>
<abstract>
This guide shows you how to install and configure GRUB 2 bootloader.
</abstract>
<!-- The content of this document is licensed under the CC-BY-SA license -->
<!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
<license/>
<version>1</version>
<date>2011-08-26</date>
<chapter>
<title>About</title>
<section>
<body>
<p>
GRUB 2 is next generation bootloader that brings many long awaited features
that were not availible in Grub Legacy (0.9*).
</p>
<p>
Some examples of new features:
</p>
<ul>
<li>Booting from boot partition stored on LVM</li>
<li>Booting from encrypted boot partition</li>
<li>Booting from UEFI</li>
<li>Support for native screen resolution and theming</li>
</ul>
</body>
</section>
</chapter>
<chapter>
<title>Installation</title>
<section>
<title>Setting Useflags</title>
<body>
<p>
By default grub tries to detect the desired platform during configure from your
toolchain and CPU. If you want support for other platforms or just don't want
to use the autodetection you should use GRUB_PLATFORMS use expand. This variable
should be set in /etc/make.conf.
</p>
<p>Description of mostly used values for GRUB_PLATFORMS as of =sys-boot/grub-1.99:</p>
<ol>
<li>pc: normal BIOS pc</li>
<li>efi-64: EFI systems, their latest 64b version</li>
<li>coreboot: Coreboot replacement of BIOS</li>
<li>qemu: support for QEMU booting</li>
<li>yeelong: Support for MIPS loongson</li>
</ol>
<note>
Most users should just rely on platform detection or just use
GRUB_PLATFORMS="pc"
</note>
<warn>
One should be really carefull with custom-cflags IUSE, as some CFLAGS can
easily render your system impossible to boot.
</warn>
</body>
</section>
<section>
<title>Configuring GRUB</title>
<body>
<impo>
Gentoo installs grub renamed to grub2. So if you read any other guide you
should replace all grub mentions with grub2 <i>(grub-mkconfig -> grub2-mkconfig)</i>.
</impo>
<p>
Compared to grub-legacy current grub uses automatic generation to generate
all the required entries for you to boot. This is handled by <i>grub2-mkconfig</i>
command that probes your system for all the required data. Cooperating with
<i>sys-boot/os-prober</i> it detects even other OSes on all disks.
</p>
<impo>
If you updated from grub-legacy then your <path>/boot/grub/menu.lst</path>
Was converted to <path>/boot/grub2/grub.cfg</path> to ensure that your system
can boot even if you forget to generate the config. Never the less you should
take time and migrate the configuration to be automatically generated, because
next time grub2 is installed it will use automatic generation and ignore
grub-legacy files.
</impo>
<pre caption="Generating the grub2 config">
grub2-mkconfig -o /boot/grub2/grub.cfg
</pre>
<p>
Tweaking the options is to be done in the <path>/etc/defaults/grub</path> file.
Simple text file configuration with description of some default values.
All the options are described in grub2 info pages.
</p>
<note>
This file is created by Gentoo and if you find interesting option not used
in there just open bugreport (possibly with a patch).
</note>
<p>
Sometimes if automatic detection of grub does not suffice the file <path>
/etc/grub.d/40_custom</path> should be used to store custom finder. Full
description how to configure such with example can be find in grub2 info
pages.
</p>
<pre caption="Custom menu entry">
menuentry "My Shiny Gentoo Kernel" {
set root=(hd0,1)
search --no-floppy --fs-uuid --set <UUID>
linux /boot/gentookernel-5.3.2-generic root=UUID=<UUID>
initrd /boot/initrd.img-5.3.2
}
</pre>
<warn>
Remember to replace the <i><UUID></i> with your device UUID.
</warn>
</body>
</section>
<section>
<title>Pre-Configuring GRUB to use EFI</title>
<body>
<p>
Some newer PCs (and all Intel Macs) come with
<uri link="http://en.wikipedia.org/wiki/Extensible_Firmware_Interface">EFI</uri>
(UEFI to be correct) as a replacement for lagacy
and aging BIOS firmware. EFI usually can emulate BIOS environment for OS, but
that also hides some unique features of EFI such as faster boot times, support
for GPT partition tables etc. EFI firmware comes in two flavours - 32bit and
64bit and unless you have early Intel-based Mac with 32bit processor, your
firmware will be likely 64bit. Please note that unlike in user-space, <b>64bit
EFI firmware cannot run 32bit EFI bootloader.</b> This section will guide you
through installing GRUB 2 on such EFI-capable boards; it assumes that your
firmware adheres to UEFI 2.0 standard or newer (virtually every PC with EFI
support; Intel Macs do not entirely conform to the specification and may need
special treatment in some places)
</p>
<p>First thing you need is EFI-enabled Linux kernel with
<c>CONFIG_EFI</c> and <c>CONFIG_EFI_PARTITION</c> options enabled,
<c>CONFIG_FB_EFI</c> and <c>CONFIG_EFI_VARS</c> being optional but recommended.
Some platforms (namely many boards designed for <e>Intel Sandy Bridge</e>
processor generation) have <uri link="https://lkml.org/lkml/2011/5/19/377">
buggy EFI implementations</uri> and require at least kernel versions 2.6.39.1
or 3.0 in order to successfully boot.
</p>
<p>
One big difference between BIOS and EFI is that EFI is able to read partition
table (both MBR and GPT formats should be supported) and to read from specially
labelled FAT32 partition called <b>EFI System Partition</b>. During bootup, EFI
fimrmware can execute <e>EFI applications</e> stored in files in EFI System
Partition. One special EFI application is a bootloader. You may use the EFI
System Partition as your <c>/boot</c> partition if you don't mind limitations
of FAT32 filesystem such as no support for symlinks and per-file owner and
permissions. The rest of this section assumes that you use <c>/boot</c> for
mounting EFI System Partition.
</p>
<p>
If you don't already have EFI System Partition, let's create one. The procedure is
different for GPT and MBR-formatted disks. The partition need not be the first
one on disk as in our examples. In case it is GPT-partitioned you'll need one
of the <c>gdisk</c> (CLI, sys-apps/gptfdisk), <c>parted</c> (CLI,
sys-block/parted) or <c>gparted</c> (GUI, sys-block/gparted) partitioning
tools; <c>fdisk</c>, <c>cfdisk</c> and <c>sfdisk</c> do not currently support
GPT. In the GPT case, create a partition at least 100 MiB in size with
<c>boot</c> flag (shown by (g)parted) or <c>EF00</c> Code (shown by gdisk).
</p>
<note>
Replace <c>/dev/sda</c> with disk you want to have EFI System Partition on and
<c>/dev/sda1</c> with partition designated for it in all following samples.
</note>
<pre caption="EFI System Partion on GPT disk as shown by gdisk">
# <i>gdisk -l <keyword>/dev/sda</keyword></i>
<comment>(...)</comment>
Number Start (sector) End (sector) Size Code Name
<ident> 1 34 411647 201.0 MiB EF00 </ident>
</pre>
<pre caption="EFI System Partion on GPT disk as shown by parted">
# <i>parted -l</i>
<comment>(...)</comment>
Number Start End Size File system Name Flags
<ident> 1 17.4kB 211MB 211MB fat32 boot</ident> <comment># you may have File system field empty</comment>
</pre>
<p>
In case the disk partition scheme is MBR (MS-DOS), EFI System Partition should
have type <c>EF</c>. Create or re-type it, again it should be at least 100 MiB
large.
</p>
<pre caption="EFI System Partion on MBR disk as shown by fdisk">
# <i>fdisk -l <keyword>/dev/sda</keyword></i>
<comment>(...)</comment>
Device Boot Start End Blocks Id System
<ident>/dev/sda1 2048 206847 102400 ef EFI (FAT-12/16/32)</ident>
</pre>
<p>
Next create FAT32 filesystem on it if you already haven't done so. From now on,
procedure is the same for both GPT and MBR-formatted disks. Program
<c>mkdosfs</c> is from package <c>sys-fs/dosfstools</c>.
</p>
<pre caption="Creating FAT32 filesystem on EFI System Partition">
# <i>mkdosfs -F 32 -n efi-boot <keyword>/dev/sda1</keyword></i>
mkdosfs 3.0.9 (31 Jan 2010)
</pre>
<warn>
This command erases everything that previously was on <c>/dev/sda1</c>.
</warn>
<p>
The <c>-F 32</c> option tells mkdosfs to create FAT32 filesystem and <c>-n
efi-boot</c> option tells mkdosfs to set partition label to <c>efi-boot</c>.
You may use atrbitrary string up to 11 characters long for label or you may not
use it at all.
</p>
<p>
After you prepared your HDDs you can easily proceed with generating the
configuration.
</p>
</body>
</section>
<section>
<title>Configuring with LVM</title>
<body>
<p>
Grub2 itself detects the LVM correctly, with no aditional setup required.
</p>
<impo>
If you placed your root and boot partitions inside LVM make sure that disk
you plan to use as booting one has at least few MBs of space before first
partition, because grub2 needs more space to store lvm loader. In other
words if you install it with not enough space it will just break your
partition.
</impo>
</body>
</section>
</chapter>
<chapter>
<title>Installation of grub2</title>
<section>
<title>Installing on some MBR/GPT directly</title>
<body>
<p>
Installation of grub2 is similar to installation of grub-legacy.
</p>
<pre caption="Installing grub2 on /dev/sda">
grub2-install --no-floppy /dev/sda
</pre>
<impo>
If you get ANY errors during this step do not reboot your computer,
but make sure it is fixed. Your computer won't boot if installation
fail.
</impo>
</body>
</section>
</chapter>
</guide>
|
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