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<?xml version='1.0' encoding='utf-8' ?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % BOOK_ENTITIES SYSTEM "Fedora_Multiboot_Guide.ent">
%BOOK_ENTITIES;
]>
<section id="GRUB-configuration">
<title>Configuring the GRUB Bootloader</title>
<para>
GRUB configuration files can be found in several places:
</para>
<formalpara>
<title><filename>/etc/default/grub</filename></title>
<para>
Configuration for GRUB itself is defined in <filename>/etc/default/grub</filename>. The default options used when creating new entries for Fedora can also be found here.
</para>
</formalpara>
<formalpara>
<title><filename class="directory">/etc/grub.d/</filename></title>
<para>
Files in <filename class="directory">/etc/grub.d</filename> are used as templates for creating new GRUB entries as well as custom boot entries.
</para>
</formalpara>
<formalpara>
<title><filename class="directory">/boot</filename></title>
<para>
The <filename class="directory">/boot</filename> directory contains Fedora's kernel and <systemitem class="filesystem">initramfs</systemitem>.
</para>
</formalpara>
<para>
On BIOS systems, this directory also contains the configuration for GRUB itself.
</para>
<formalpara>
<title><filename class="directory">/boot/efi/EFI</filename></title>
<para>
This directory is only found on UEFI systems, and is within the UEFI System Partition. Both GRUB configuration files and the GRUB executable can be found in <filename class="directory">/boot/efi/EFI</filename>.
</para>
</formalpara>
<section id="GRUB-configuration-permanent_arg">
<title>Permanently adding to Fedora boot entries</title>
<para>
The options that GRUB passes to Fedora when booting are generated from the discovered filesystems and from the value of <parameter>GRUB_CMDLINE_LINUX</parameter> in <filename>/etc/default/grub</filename>.
</para>
<para>
Adding a parameter to the end of <parameter>GRUB_CMDLINE_LINUX</parameter> and regenerating <filename>grub.cfg</filename> will apply the parameter to all current and future Fedora boot entries.
</para>
<example id="GRUB-configuration-permanent_arg-backlight_example">
<title>In practice: Fixing backlight issues with kernel parameters</title>
<para>
Some laptops have problems with the display backlight using the default configuration. The screen might be too bright, too dim, flicker, or even appear to be completely black.
</para>
<para>
The issue can often be resolved by directing the system to prefer vendor-specific drivers for the backlight using the <parameter>acpi_backlight=vendor</parameter> parameter.
</para>
<procedure>
<step>
<para>
With root permissions, open the file <filename>/etc/default/grub</filename>.
<screen>
<command>nano /etc/default/grub</command>
<computeroutput>
GRUB_TIMEOUT=0
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="vconsole.font=latarcyrheb-sun16 $([ -x /usr/sbin/rhcrashkernel-param ] && /usr/sbin/rhcrashkernel-param || :) vconsole.keymap=us rhgb quiet"
GRUB_DISABLE_RECOVERY="true"
</computeroutput>
</screen>
</para>
</step>
<step>
<para>
Add the parameter to the end of <parameter>GRUB_CMDLINE_LINUX</parameter> and save the file.
<screen>
<computeroutput>
GRUB_TIMEOUT=0
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="vconsole.font=latarcyrheb-sun16 $([ -x /usr/sbin/rhcrashkernel-param ] && /usr/sbin/rhcrashkernel-param || :) vconsole.keymap=us rhgb quiet acpi_backlight=vendor"
GRUB_DISABLE_RECOVERY="true"
</computeroutput>
</screen>
</para>
</step>
<step>
<para>
Regenerate the GRUB configuration to apply the new changes.
</para>
<substeps>
<step>
<para>
For BIOS systems:
<screen>
<command>grub2-mkconfig -o /boot/grub/grub2.cfg</command>
</screen>
</para>
</step>
<step>
<para>
For UEFI systems:
<screen>
<command>grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg</command>
</screen>
</para>
</step>
</substeps>
</step>
</procedure>
</example>
</section>
</section>
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