mbtamuli/EFISTUB.md

## EFISTUB.md

      
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              EFISTUB.md
            
          
    Why

We don't want extra stuff
What

We want to boot Linux without installing a boot loader
How


We need to create an entry in the UEFI NVRAM entries list.
We can use the bcfg tool for that. But we need a unified kernel image(something with .efi).
We use the objcopy utility to do generate the unified kernel image.
Finally, we need to setup Pacman hooks to have the unified kernel image every time we upgrade linux.

Partition scheme

Depending on your partition scheme, you might need to change the paths in the steps.
lsblk
NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
nvme0n1     259:0    0 476.9G  0 disk 
├─nvme0n1p1 259:1    0   529M  0 part 
├─nvme0n1p2 259:2    0   100M  0 part /boot
├─nvme0n1p3 259:3    0    16M  0 part 
├─nvme0n1p4 259:4    0 298.8G  0 part 
├─nvme0n1p5 259:5    0   581M  0 part 
└─nvme0n1p6 259:6    0 176.9G  0 part /

/etc/fstab
UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx	/         	ext4      	rw,relatime	0 1
UUID=xxxx-xxxx      	/boot     	vfat      	rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro	0 2

Steps


Install binutils package, as we need the objcopy utility
pacman -S binutils


Get PARTUUID using lsblk command
lsblk --output=PATH,PARTUUID


Create a file with your kernel command line parameters
cat <<EOF > kernel-command-line.txt
root=PARTUUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx rw
EOF


Create and place linux.efi at /boot/EFI/Linux/linux.efi
objcopy \
    --add-section .osrel="/usr/lib/os-release" --change-section-vma .osrel=0x20000 \
    --add-section .cmdline="kernel-command-line.txt" --change-section-vma .cmdline=0x30000 \
    --add-section .splash="/usr/share/systemd/bootctl/splash-arch.bmp" --change-section-vma .splash=0x40000 \
    --add-section .linux="/boot/vmlinuz-linux" --change-section-vma .linux=0x2000000 \
    --add-section .initrd="/boot/initramfs-linux.img" --change-section-vma .initrd=0x3000000 \
    "/usr/lib/systemd/boot/efi/linuxx64.efi.stub" "linux.efi"
mkdir -p /boot/EFI/Linux/
cp linux.efi /boot/EFI/Linux/


Use the bcfg command in UEFI Shell v2 (i.e., from the Arch Linux live iso).
bcfg boot add 0 fs2:\EFI\Linux\linux.efi "Arch Linux"


Create the hook file /etc/pacman.d/hooks/90-update-efistub.hook with content
[Trigger]
Operation = Install
Operation = Upgrade
Type = Path
Target = usr/src/*/dkms.conf
Target = usr/lib/modules/*/build/include/
Target = usr/lib/modules/*/modules.alias

[Action]
Description = Updating linux efistub...
When = PostTransaction
Depends = linux
Depends = binutils
Depends = util-linux
Exec = /etc/pacman.d/scripts/efistub-update
NeedsTargets


Also create the corresponding script /etc/pacman.d/scripts/efistub-update with content

note: You might need to change the path according to your setup /boot/EFI/Linux/linux.efi
#!/bin/bash -e

SCRIPT_TMPDIR=$(mktemp -d)
ROOT_PARTUUID="$(findmnt --noheadings --output PARTUUID --target /)"

trap "{ rm -rf $SCRIPT_TMPDIR; }" EXIT HUP INT QUIT TERM STOP PWR

pushd "$SCRIPT_TMPDIR" > /dev/null

cat <<EOF > kernel-command-line.txt
root=PARTUUID=$ROOT_PARTUUID rw
EOF

objcopy \
    --add-section .osrel="/usr/lib/os-release" --change-section-vma .osrel=0x20000 \
    --add-section .cmdline="kernel-command-line.txt" --change-section-vma .cmdline=0x30000 \
    --add-section .splash="/usr/share/systemd/bootctl/splash-arch.bmp" --change-section-vma .splash=0x40000 \
    --add-section .linux="/boot/vmlinuz-linux" --change-section-vma .linux=0x2000000 \
    --add-section .initrd="/boot/initramfs-linux.img" --change-section-vma .initrd=0x3000000 \
    "/usr/lib/systemd/boot/efi/linuxx64.efi.stub" "linux.efi"
rm --force /boot/EFI/Linux/linux.efi
cp linux.efi /boot/EFI/Linux/

popd > /dev/null


Make the script executable
chmod +x /etc/pacman.d/scripts/efistub-update