mirror of
https://git.linuxfromscratch.org/lfs.git
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33c17d128b
In the previous commit we've enabled the kernel to use the SimpleDRM driver on the VESA framebuffer. Now provide the VESA framebuffer to the kernel.
228 lines
10 KiB
XML
228 lines
10 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="ch-bootable-grub" role="wrap">
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<?dbhtml filename="grub.html"?>
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<sect1info condition="script">
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<productname>grub</productname>
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<productnumber>&grub-version;</productnumber>
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<address>&grub-url;</address>
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</sect1info>
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<title>Using GRUB to Set Up the Boot Process</title>
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<note>
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<para>
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If your system has UEFI support and you wish to boot LFS with UEFI,
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you should skip the instructions in this page but still learn the
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syntax of <filename>grub.cfg</filename> and the method to specify
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a partition in the file from this page, and configure GRUB with UEFI
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support using the instructions provided in
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<ulink url="&blfs-book;postlfs/grub-setup.html">the BLFS page</ulink>.
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</para>
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</note>
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<sect2>
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<title>Introduction</title>
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<warning><para>Configuring GRUB incorrectly can render your system
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inoperable without an alternate boot device such as a CD-ROM or bootable
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USB drive. This section is not required to boot your LFS system. You may
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just want to modify your current boot loader, e.g. Grub-Legacy, GRUB2, or
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LILO.</para></warning>
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<para> Ensure that an emergency boot disk is ready to <quote>rescue</quote>
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the computer if the computer becomes unusable (un-bootable). If you do not
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already have a boot device, you can create one. In order for the procedure
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below to work, you need to jump ahead to BLFS and install
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<userinput>xorriso</userinput> from the <ulink
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url="&blfs-book;multimedia/libisoburn.html">
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libisoburn</ulink> package.</para>
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<screen role="nodump"><userinput>cd /tmp
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grub-mkrescue --output=grub-img.iso
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xorriso -as cdrecord -v dev=/dev/cdrw blank=as_needed grub-img.iso</userinput></screen>
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</sect2>
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<sect2>
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<title>GRUB Naming Conventions</title>
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<para>GRUB uses its own naming structure for drives and partitions in
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the form of <emphasis>(hdn,m)</emphasis>, where <emphasis>n</emphasis>
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is the hard drive number and <emphasis>m</emphasis> is the partition
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number. The hard drive numbers start from zero, but the partition numbers
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start from one for normal partitions (from five for extended partitions).
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Note that this is different from earlier versions where
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both numbers started from zero. For example, partition <filename
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class="partition">sda1</filename> is <emphasis>(hd0,1)</emphasis> to
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GRUB and <filename class="partition">sdb3</filename> is
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<emphasis>(hd1,3)</emphasis>. In contrast to Linux, GRUB does not
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consider CD-ROM drives to be hard drives. For example, if using a CD
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on <filename class="partition">hdb</filename> and a second hard drive
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on <filename class="partition">hdc</filename>, that second hard drive
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would still be <emphasis>(hd1)</emphasis>.</para>
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</sect2>
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<sect2>
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<title>Setting Up the Configuration</title>
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<para>GRUB works by writing data to the first physical track of the
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hard disk. This area is not part of any file system. The programs
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there access GRUB modules in the boot partition. The default location
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is /boot/grub/.</para>
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<para>The location of the boot partition is a choice of the user that
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affects the configuration. One recommendation is to have a separate small
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(suggested size is 200 MB) partition just for boot information. That way
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each build, whether LFS or some commercial distro, can access the same boot
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files and access can be made from any booted system. If you choose to do
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this, you will need to mount the separate partition, move all files in the
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current <filename class="directory">/boot</filename> directory (e.g. the
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Linux kernel you just built in the previous section) to the new partition.
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You will then need to unmount the partition and remount it as <filename
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class="directory">/boot</filename>. If you do this, be sure to update
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<filename>/etc/fstab</filename>.</para>
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<para>Leaving <filename class="directory">/boot</filename> on
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the current LFS partition will also work, but configuration
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for multiple systems is more difficult.</para>
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<para>Using the above information, determine the appropriate
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designator for the root partition (or boot partition, if a separate
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one is used). For the following example, it is assumed that the root
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(or separate boot) partition is <filename
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class="partition">sda2</filename>.</para>
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<para>Install the GRUB files into <filename
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class="directory">/boot/grub</filename> and set up the boot track:</para>
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<warning>
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<para>The following command will overwrite the current boot loader. Do not
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run the command if this is not desired, for example, if using a third party
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boot manager to manage the Master Boot Record (MBR).</para>
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</warning>
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<screen role="nodump"><userinput>grub-install /dev/sda</userinput></screen>
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<note>
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<para>If the system has been booted using UEFI,
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<command>grub-install</command> will try to install files for the
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<emphasis>x86_64-efi</emphasis> target, but those files
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have not been installed in <xref linkend="chapter-building-system"/>.
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If this is the case, add <option>--target i386-pc</option> to the
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command above.</para>
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</note>
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</sect2>
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<sect2 id="grub-cfg">
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<title>Creating the GRUB Configuration File</title>
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<para>Generate <filename>/boot/grub/grub.cfg</filename>:</para>
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<screen><userinput>cat > /boot/grub/grub.cfg << "EOF"
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<literal># Begin /boot/grub/grub.cfg
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set default=0
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set timeout=5
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insmod part_gpt
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insmod ext2
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set root=(hd0,2)
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set gfxpayload=1024x768x32
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menuentry "GNU/Linux, Linux &linux-version;-lfs-&version;" {
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linux /boot/vmlinuz-&linux-version;-lfs-&version; root=/dev/sda2 ro
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}</literal>
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EOF</userinput></screen>
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<para>
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The <command>insmod</command> commands load the
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<application>GRUB</application> modules named
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<filename>part_gpt</filename> and <filename>ext2</filename>.
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Despite the naming, <filename>ext2</filename> actually supports
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<systemitem class='filesystem'>ext2</systemitem>,
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<systemitem class='filesystem'>ext3</systemitem>, and
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<systemitem class='filesystem'>ext4</systemitem> filesystems.
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The <command>grub-install</command> command has embedded some modules
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into the main <application>GRUB</application> image (installed into
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the MBR or the GRUB BIOS partition) to access the other modules
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(in <filename class='directory'>/boot/grub/i386-pc</filename>) without
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a chicken-or-egg issue, so with a typical configuration these two
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modules are already embedded and those two <command>insmod</command>
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commands will do nothing. But they do no harm anyway, and they may
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be needed with some rare configurations.
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</para>
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<para>
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The <command>set gfxpayload=1024x768x32</command> command sets the
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resolution and color depth of the VESA framebuffer to be passed to the
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kernel. It's necessary for the kernel SimpleDRM driver to use the
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VESA framebuffer. You can use a different resolution or color depth
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value which better suits for your monitor.
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</para>
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<note><para>From <application>GRUB</application>'s perspective, the
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kernel files are relative to the partition used. If you
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used a separate /boot partition, remove /boot from the above
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<emphasis>linux</emphasis> line. You will also need to change the
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<emphasis>set root</emphasis> line to point to the boot partition.
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</para></note>
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<note>
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<para>The GRUB designator for a partition may change if you added or
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removed some disks (including removable disks like USB thumb devices).
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The change may cause boot failure because
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<filename>grub.cfg</filename> refers to some <quote>old</quote>
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designators. If you wish to avoid such a problem, you may use
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the UUID of a partition and the UUID of a filesystem instead of a GRUB designator to
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specify a device.
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Run <command>lsblk -o UUID,PARTUUID,PATH,MOUNTPOINT</command> to show
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the UUIDs of your filesystems (in the <literal>UUID</literal> column) and
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partitions (in the <literal>PARTUUID</literal> column). Then replace
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<literal>set root=(hdx,y)</literal> with
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<literal>search --set=root --fs-uuid <replaceable><UUID of the filesystem
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where the kernel is installed></replaceable></literal>, and replace
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<literal>root=/dev/sda2</literal> with
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<literal>root=PARTUUID=<replaceable><UUID of the partition where LFS
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is built></replaceable></literal>.</para>
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<para>Note that the UUID of a partition is completely different from the
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UUID of the filesystem in this partition. Some online resources may
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instruct you to use
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<literal>root=UUID=<replaceable><filesystem UUID></replaceable></literal>
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instead of
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<literal>root=PARTUUID=<replaceable><partition UUID></replaceable></literal>,
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but doing so will require an initramfs, which is beyond the scope of
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LFS.</para>
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<para>The name of the device node for a partition in
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<filename class='directory'>/dev</filename> may also change (this is less
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likely than a GRUB designator change). You can also replace
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paths to device nodes like <literal>/dev/sda1</literal> with
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<literal>PARTUUID=<replaceable><partition UUID></replaceable></literal>,
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in <filename>/etc/fstab</filename>, to avoid a potential boot failure
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in case the device node name has changed.</para>
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</note>
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<para>GRUB is an extremely powerful program and it provides a tremendous
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number of options for booting from a wide variety of devices, operating
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systems, and partition types. There are also many options for customization
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such as graphical splash screens, playing sounds, mouse input, etc. The
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details of these options are beyond the scope of this introduction.</para>
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<caution><para>There is a command, <application>grub-mkconfig</application>, that
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can write a configuration file automatically. It uses a set of scripts in
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/etc/grub.d/ and will destroy any customizations that you make. These scripts
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are designed primarily for non-source distributions and are not recommended for
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LFS. If you install a commercial Linux distribution, there is a good chance
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that this program will be run. Be sure to back up your grub.cfg file.</para></caution>
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</sect2>
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</sect1>
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