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In this lesson,

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you're going to learn about GRUB 2,

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which is a popular boot loader in Linux.

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We've previously discussed

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the various essential components

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that make up the Linux boot process.

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Your existing knowledge of those concepts

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are going to help you leverage boot options

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as well as gain control over a how Linux boots.

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So now that you're familiar with the role of a boot loader

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inside the boot process,

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you can now be able to learn

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how to configure the primary Linux boot loader,

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which at the time of this recording is known as GRUB 2.

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Understanding how to configure GRUB and GRUB 2

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is really important for you to be able to recover from

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or to circumvent various types of problems and issues

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you may encounter as a system administrator.

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There are several boot loaders out there,

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but Linux usually uses GRUB,

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which is the GNU GRand Unified Bootloader.

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This is by far the most popular boot loader out there.

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And there's various versions of it,

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known as GRUB and GRUB 2.

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GRUB enables users to choose which operating system

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or kernel version they want to boot

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inside this multi-platform environment.

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Although the original version of GRUB

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was the primary boot loader for Linux distributions,

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it had several limitations,

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and eventually, it was phased out

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in favor of the new version of GRUB known as GRUB 2.

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Now, GRUB 2 is usually just called GRUB

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and it's more than just a simple newer version

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of GRUB, though.

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It's also a completely redesigned and rewritten version

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of the GRUB system.

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GRUB 2 offers administrators

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with more control over the boot process,

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the boot devices, and the boot behavior.

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GRUB 2 supports non-86 architecture platforms,

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things like RISC processors and ARM processors,

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as well as supports booting an OS from storage media

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and running the OS entirely in memory.

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You can do this

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without even installing the Linux operating system

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and run the entire thing from RAM.

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That's one of the things that GRUB 2 offers.

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It also supports partition UUIDs

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and supports loading modules

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to extend GRUB's functionality.

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In addition to all that, GRUB 2 also has the ability

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to configure the boot loader

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through the use of scripts.

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And it will attempt to fix boot issues

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like corrupted and missing configurations,

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as well as having other features

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to customize your user experience.

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This includes things like background wallpapers,

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different font, and more things like that

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to personalize your system.

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Because of these improvements,

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GRUB 2 has become the default boot loader

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on almost all modern Linux distributions.

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GRUB 2 can also be installed

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even if you're currently booting into the OS.

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Just execute the grub2-install command

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against the device or the partition you desire.

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It'll copy over the GRUB 2 files

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into the /boot/GRUB2 directory,

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and on some platforms,

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it'll install GRUB 2 into the boot sector.

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However, grub2-install applies to BIOS-based systems,

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not UEFI systems.

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If you want to install GRUB 2 on a UEFI system,

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you're going to have to use a package manager

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to install the grub2-efi package.

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Installing this package will copy GRUB 2 files

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onto the EFI system partition or the ESP

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inside of the /boot/efi directory.

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Now, to use grub2-install,

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you have to use the right syntax,

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and the syntax for this is grub2-install, the options,

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and the device name.

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Now, there's several different options you can use

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with the grub2-install command.

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For example, you can use --modules in the module names.

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This option will allow you

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to reload the specified kernel modules

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with the GRUB 2 boot loader.

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If you use the --install-modules and module names option,

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this is going to be used to install only the specified modules

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and their dependencies

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rather than the default of installing all available modules.

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If you use --directory and the directory name option,

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this is going to be used to install files

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from the specified directory

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rather than from the default directory.

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If you use --target and the target platform option,

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this is going to be used to specify the target platform

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that you want to install GRUB 2 for

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instead of using the platform

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that you're currently running on.

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The --boot-directory, directory name option

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is going to be used to specify the boot directory

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that you want to install GRUB 2 files to

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rather than using the default /bootdirectory or /boot/GRUB2.

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The -force option is going to be used to install GRUB 2

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regardless of any detected issues.

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Now, the main configuration file

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for your GRUB 2 boot loader is known as grub.cfg.

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This is a file that you're going to use on BIOS systems,

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and it's going to be located in /boot/grub2.

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If you're on a UEFI system,

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it's going to be located in /boot/efi/EFI

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and then you're going to have your file there.

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Now, this file is an executable shell script

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that is not recommended to be edited directly,

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because it's generated using specific commands

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that leverage configuration scripts stored elsewhere

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on the file system.

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Another important directory is the /etc/grub.d directory.

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This contains scripts

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that are used to build the main grub.config file.

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Each script provides various functions to GRUB 2,

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and it's numbered so that the scripts can execute

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in a sequence.

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It's usually not a good idea to edit the existing scripts

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in this directory.

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If you want to add a custom script,

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you should place this in the directory

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with a number number underscore as a file name prefixed,

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depending on the order you want the script to be executed in

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within your current directory.

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You could also add your script

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to the existing 40_custom file,

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because that way, it will execute last by default.

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Now, speaking of this 40_custom file,

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this is going to be located

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at /etc/grub.d/40_custom.

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And this file enables the customization of the menu

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that's presented to the user

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during the boot process.

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The GRUB 2 system is going to offer the user a menu

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of installed operating systems to choose from.

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This choice is really useful

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if you're multi booting your system

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and you have more than one operating system

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on the computer.

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For example,

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you might have different Linux kernels there,

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or you have Linux and Windows on the same system,

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or you might want to boot into rescue mode.

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The menu contents here can be customized

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by editing the /etc/grub.d/40_custom file

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and enabling an administrator

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to specify the order of the menu choices,

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provide user friendly names,

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and password protect different menu entries.

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You can also generate a password hash

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to protect your boot menu

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by using grub2-mkpasswd

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pbkdf2 at the command line.

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The /etc/default/grub file

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is going to contain the GRUB 2 display menu settings

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that are read by the /etc/grub.d scripts.

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And they're going to be built in to your grub.config file.

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It's going to enable you to change options

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such as how many seconds the GRUB 2 loader is going to wait

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before it automatically selects the default boot option,

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whether or not the GRUB 2

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will actually order kernel versions

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in a sub menu

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or whether or not GRUB 2 will display the menu

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in a graphical terminal

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and many other options.

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The grub2-mkconfig command or the make config command

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will generate a new GRUB configuration file

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or update the existing GRUB configuration file.

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This command is going to combine

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the configuration file templates

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inside of the /etc/grub.d directory

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with the settings in the /etc/default/grub,

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as well as to generate the grub.cfg configuration file.

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To run this, type grub2-mkconfig-o and the file name.

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If you simply need to update your GRUB 2 configuration file

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instead of making a new one,

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you can use the update-grub2 command too.