EFI Stub

this articles is about booting your linux system without a bootload (grub, lilo...), traditionally we use bootloaders to load the kernel and initramfs, but if you have an uefi system, you could skip bootloaders entirely, and use uefi to load the kernel.

1. Verify

to check if you have a uefi run:

ls /sys/firmware/efi/efivars

the directory should exist and contains some entries.

2. Setup ESP

to make use of uefi, you need to create a separate partition, to hold efi files, it should be at least 100MiB, use fdisk(or any tool you like) to create it:

doas fdisk /dev/sda

here replace /dev/sda, with the disk you want to use.

then format the partition you just created:

doas mkfs.fat -F32 /dev/sda1

I assume it is /dev/sda1, replace it w/ whatever you have.

then mount it:

doas mkdir -p /boot/efi
doas mount /dev/sda1 /boot/efi

now your partition is ready, if you like you can add it to /etc/fstab, but it is not mandatory:

# /dev/sda1
UUID=YOUR-UUID          /boot/efi           vfat            rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro   0 2

3. Install EFI Entry

first you need to install efibootmgr

doas pacman -S efibootmgr

then copy your kernel, and initramfs to ESP partition.

doas mkdir -p /boot/efi/EFI/arch
doas cp -v /boot/{vmlinuz-linux, initramfs-linux.img} /boot/efi/EFI/arch

finally add an entry to the uefi:

doas efibootmgr --verbose --create --disk /dev/sda --part 1 --loader "\EFI\arch\vmlinuz-linux" --unicode "initrd=\EFI\arch\initramfs-linux.img root=/dev/sda2 rw"

finally reboot to make sure it works:

doas reboot now

and that's it. if you booted directly with your kernel, without going through the bootloader menu, you successfully did it.

4. Notes

if you don't use an initramfs as I have explained here, you don't need to pass initrd argument to the kernel.

5. Common Problems

some times this method efibootmgr doesn't work, because it is not compatible with your machine uefi implementations.

in that case you can try uefi shell that comes with archlinux iso, boot it, and run the following commands:

bcfg boot add N FS0:\EFI\arch\vmlinuz-linux

where N is boot entry number, to see the next available boot number run:

bcfg boot dump -v

and FS0 is the ESP partition you can use cd, ls utilities to find it. now we will add arguments to our kernel, by creating file that contains them.

edit FS0:\boot.config

add the same arguments we use before, then save and quit the file.

finally read args and add them to the entry

bcfg boot -opt N FS0:\boot.config

then exit

exit

now the entry should appear in uefi firmware menu, and you could boot properly.