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Arch Linux Working On Unified Kernel Image

What is a Unified Kernel Image?

A Unified Kernel Image (UKI) is a single executable file that combines:

  • The Linux kernel
  • An initramfs (initial RAM filesystem)
  • The kernel command line
  • UEFI stub (for direct UEFI booting)
  • Optional secure boot signatures

UKIs simplify the boot process by bundling everything needed into one file, making it easier to manage and sign for Secure Boot compatibility.

Generating UKIs

Arch linux mkinitcpio will assemble the UKI itself unless systemd-ukify is installed.

Using mkinitcpio

mkinitcpio preset file for the linux package at /etc/mkinitcpio.d/linux.preset

ESP_DIR="/efi/EFI/ArchLinux"

ALL_kver="/boot/vmlinuz-linux${SUFFIX}"

PRESETS=('default') # this is not for a fallback

default_image="/boot/initramfs-linux${SUFFIX}.img"
default_uki="${ESP_DIR}/arch-linux${SUFFIX}.efi"
default_options="--cmdline /etc/kernel/cmdline"

This code can be helpfull when creating a template i.e. for linux-lts e.g. in /etc/mkinitcpio.d/linux-lts.preset

SUFFIX="-lts"
source /etc/mkinitcpio.d/linux.preset

Kernel command line

mkinitcpio supports reading kernel parameters from command line files in the /etc/cmdline.d directory. mkinitcpio will concatenate the contents of all files with a .conf extension in this directory and use them to generate the kernel command line. Or /etc/kernel/cmdline can also be used as illustrated in above code.

rd.luks.name=fe30dd04-9v8a-4817-q10e-0999ece7oo31=archlinux root=/dev/mapper/archlinux rootflags=noatime,ssd,compress=zstd:1,space_cache=v2,discard=async,subvol=@ rw quiet splash loglevel=3 systemd.show_status=auto rd.udev.log_level=3

Additional info

mkinitcpio.conf contains hooks e.g.

HOOKS=(base systemd plymouth autodetect microcode modconf kms keyboard sd-vconsole block sd-encrypt filesystems fsck)

Note

Please give a proper read unified_kernel_image and mkinitcpio.


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