Bootloaders: How Linux is Loaded

• GRUB 2 - The Most Widely Used
  • Configuration
    • Files Used for Configuration
    • Editing GRUB Configuration in /etc/default/grub
    • Sample GRUB Configuration (/etc/default/grub)
    • Make Configuration files
  • Installation
    • EFI Installation
    • BIOS Legacy Installation
  • GRUB Videos
• Systemd Boot - Minimal Built-In boot
  • Configuraiton
    • General Configuration
    • Adding Boot Entries
  • Installation
• Limine - Modern Multiprotocol Bootloader
  • Configuration
    • Basic limine.conf Structure
  • Installation

There are many bootloaders available, but this chapter focuses on three common choices in 2026: GRUB 2, systemd-boot, and Limine.

Rule of thumb: Use GRUB 2 for dual-boot or multiboot setups, and for any system where you want theme support and a boot menu. Use systemd-boot for single-OS EFI systems where you prefer a minimal, fast bootloader without extra packages.

GRUB 2 - The Most Widely Used

GRUB 2 is the most popular bootloader for Linux. It supports themes, multiboot setups, rescue modes, and a wide range of configuration options. For Windows/Linux dual-boot systems, GRUB 2 is the recommended choice.

Resource: GRUB Manual Table of Contents

Configuration

Before installing or updating GRUB, you need to generate configuration files. The authoritative reference is the Gentoo GRUB2 Wiki.

Files Used for Configuration

Editing GRUB Configuration in /etc/default/grub

Common settings in /etc/default/grub:

• GRUB_DEFAULT — Default boot entry. 0 selects the first entry, 1 the second, and so on.
• GRUB_TIMEOUT_STYLE — menu shows the boot menu; hidden skips it (controlled by GRUB_HIDDEN_TIMEOUT).
• GRUB_TIMEOUT — Seconds to display the menu before auto-booting. -1 waits indefinitely for user input.
• GRUB_CMDLINE_LINUX_DEFAULT — Kernel options passed on boot. Common values:
  • quiet splash — hides boot output and shows a splash screen
  • nomodeset — disables kernel modesetting; useful for installing NVIDIA drivers
  • single — boots into single-user mode for maintenance or password resets
• GRUB_DISABLE_RECOVERY — Set to true to hide recovery entries from the menu.

Resource: Full list of GRUB configuration variables

Sample GRUB Configuration (/etc/default/grub)

Example with no boot menu (instant boot to default entry):

GRUB_DEFAULT="0"
GRUB_TIMEOUT_STYLE="hidden"
GRUB_TIMEOUT="0"
GRUB_DISTRIBUTOR="`lsb_release -i -s 2> /dev/null || echo Debian`"
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""
GRUB_DISABLE_RECOVERY="true"
GRUB_DISABLE_LINUX_RECOVERY="true"

Make Configuration files

After editing /etc/default/grub, regenerate the main GRUB configuration file:

grub-mkconfig -o /boot/grub/grub.cfg

On Debian-based systems you can also use the shorthand:

update-grub

Installation

Once configuration files are ready, install GRUB onto your disk. First, confirm whether your system uses EFI or Legacy BIOS:

ls /sys/firmware/efi

If the command lists files, you are on EFI. If it errors with “No such file or directory,” you are on Legacy BIOS.

EFI Installation

EFI systems require a dedicated EFI System Partition (ESP) mounted at /boot/efi. Make sure the partition is mounted before running the installer:

grub-install --efi-directory=/boot/efi

BIOS Legacy Installation

Warning: Only use Legacy BIOS installation on hardware that does not support EFI. For all modern hardware, prefer EFI.

On a typical single-drive Legacy setup, run:

grub-install /dev/sda

Replace /dev/sda with your actual target disk. Use lsblk or blkid to identify the correct drive if you are unsure.

For the full grub-install reference: https://www.gnu.org/software/grub/manual/grub/html_node/Installing-GRUB-using-grub_002dinstall.html

GRUB Videos

• How to Repair Linux with Boot Failure
• Fix Multi-Boot Systems running GRUB and Windows
• Using SuperGRUBDisk to repair GRUB
• Custom Bootloader Themes Project
• Using GRUB Rescue

Systemd Boot - Minimal Built-In boot

Systemd-boot is shipping with more distributions as a lightweight alternative to GRUB for single-OS EFI systems.

Important: systemd-boot is EFI only. Verify before proceeding: ls /sys/firmware/efi

Dual-boot and multiboot setups are possible with systemd-boot, but configuration is more cumbersome than GRUB. For multiboot systems, use GRUB.

• systemd.io — Booting section
• Arch Wiki — systemd-boot

Configuraiton

Directory layout for systemd-boot:

General Configuration

/boot/efi/loader/loader.conf options:

• default — Default boot entry filename or wildcard (e.g., arch-*.conf)
• timeout — Seconds to show the menu; omit to show menu only on keypress
• editor — yes (default) allows editing boot entries at startup; set to no on shared or public systems
• auto-entries — 1 shows automatic Windows/EFI Shell entries; 0 hides them
• console-mode — auto picks a suitable display mode; max uses the highest available

Example /boot/efi/loader/loader.conf:

default  arch.conf
timeout  4
console-mode max
editor   no

Adding Boot Entries

Each file in /boot/efi/loader/entries/ defines one boot entry.

Key fields:

• title — OS name displayed in the menu (required)
• linux — Path to the kernel image (required unless using efi)
• initrd — Path to initramfs and optional CPU microcode images
• options — Kernel parameters; root= is required for Linux

To find the UUID of your root partition:

sudo blkid

Example Arch Linux entry /boot/efi/loader/entries/arch.conf:

title   Arch Linux
linux   /vmlinuz-linux
initrd  /intel-ucode.img
initrd  /initramfs-linux.img
options root="LABEL=arch" rw

Example Windows 10 entry /boot/efi/loader/entries/win10.conf:

title Windows 10
efi /EFI/Microsoft/Boot/bootmgfw.efi

Resource: All kernel parameters reference

Installation

Install systemd-boot with:

bootctl install

To update after adding new entries manually:

bootctl update

Limine - Modern Multiprotocol Bootloader

Limine is a modern, advanced, multiprotocol bootloader and boot manager that has become more popular in 2026, including as a default in distributions such as CachyOS and Omarchy.

Compared with GRUB and systemd-boot, Limine is often chosen for modern setups that want clean configuration, broad protocol support, and strong Secure Boot and measured boot capabilities.

• Limine GitHub Repository
• Limine Configuration Reference (CONFIG.md)
• Limine Usage Reference (USAGE.md)
• Arch Wiki — Limine
• CachyOS Wiki — Limine

Configuration

Limine uses a plain-text configuration file named limine.conf.

Common config file locations (from the Limine docs):

• On EFI, Limine first checks for limine.conf next to the EFI executable.
• If not found there (or on BIOS), it scans standard paths such as /boot/limine/limine.conf and /limine.conf.

Basic limine.conf Structure

The config contains:

• Global options like timeout: and default_entry:
• Menu entries beginning with /Entry Name
• Per-entry options like protocol:, path:, and cmdline:

Example Linux entry:

timeout: 5
default_entry: 1

/Linux
protocol: linux
path: boot():/vmlinuz-linux
module_path: boot():/initramfs-linux.img
cmdline: root=UUID=REPLACE_WITH_ROOT_UUID rw quiet

Important syntax notes:

• Limine options use name: value format.
• Menu entries begin with / and can be nested using additional / characters.
• boot():/ points to the partition containing limine.conf; if your kernel/initramfs live on a different partition, use uuid(<PARTUUID>):/path (as documented on Arch Wiki).
• In Secure Boot mode, Limine enforces stronger integrity checks; see CONFIG.md for file-hash requirements and editor restrictions.

Installation

Limine installation differs from distro to distro. In general:

1. Install the limine package from your distribution or use official release binaries.
2. Place Limine files on the target disk/ESP according to the official usage docs.
3. Create or update limine.conf.
4. Reboot and validate boot entries.

For exact, up-to-date commands, follow:

• INSTALL.md
• USAGE.md

Tip: If you need traditional Linux/Windows dual-boot convenience and broad distro documentation, GRUB is still usually easier. If you want a modern boot manager with a clean config model and strong Secure Boot features, Limine is an excellent option.