Booting Void Linux using the EFI boot stub

When the kernel is compiled with the EFI boot stub like the one packaged in Void, UEFI firmware can load the kernel directly as an EFI executable, eliminating the need for a bootloader.

In the following, we set up a simple Void system on a drive, with an encrypted root partition and an unencrypted EFI system partition. We will refer to the drive as /dev/sd<X>.

(I originally wrote this article for the Void Linux handbook, but it seems like they have long-term plans to turn their installation tutorials into a structured reference.)

Provisioning

On the drive, create a GPT partition table with the following partitions:

No.SizeType
1512MiBEFI System
2rest of the driveLinux filesystem

Create a FAT 32 filesystem on the EFI System Partition, optionally giving it a label.

# mkfs.fat -F 32 -n efi /dev/sd<X>1

Initialize the LUKS device.

# cryptsetup luksFormat /dev/sd<X>2 --type luks2 --label luks

Open the LUKS device.

# cryptsetup open --type luks /dev/sd<X>2 root

Create the desired file system.

# mkfs.ext4 -L root /dev/mapper/root

Installation

With the LUKS device still open, mount the root filesystem, the EFI system partition and the necessary directories to /mnt.

# mount /dev/mapper/root /mnt
# mkdir /mnt/boot
# mount /dev/sd<X>1 /mnt/boot
# for dir in dev proc sys run; do
> mkdir /mnt/$dir
> mount --rbind --make-rslave /$dir /mnt/$dir
> done

Install the Void Linux base system, cryptsetup and efibootmgr.

# xbps-install -S -R https://alpha.de.repo.voidlinux.org/current -r /mnt base-system cryptsetup efibootmgr

Change the filesystem root to enter the new system.

# chroot /mnt

Set the filesystem permissions, root password and hostname.

# chown root:root /
# chmod 755 /
# passwd root
# echo void > /etc/hostname

Void Linux uses dracut to manage early userspace. Configure it to open and mount the LUKS device and mount the EFI variables and system partition. To this end, edit /etc/crypttab.

# <name>    <device>                  <password>  <options>
root        /dev/disk/by-uuid/<UUID>  none

The UUID of /dev/sd<X>2 can be determined with lsblk -f. We'd like to write /dev/disk/by-label/luks instead, but it seems udev doesn't support LUKS labels yet. The password field is a path to a file containing the password or none to prompt during boot.

Now, edit /etc/fstab.

# <file system>	        <dir> <type>  <options>             <dump>  <pass>
tmpfs                   /tmp  tmpfs   defaults,nosuid,nodev 0       0
efivarfs  /sys/firmware/efi/efivars  efivarfs  defaults     0       0
/dev/disk/by-label/root /     ext4    defaults              0       1
/dev/disk/by-label/efi  /boot vfat    defaults              0       2

Create /etc/dracut.conf.d/30.conf to configure dracut.

hostonly="yes"
use_fstab="yes"
install_items+=" /etc/crypttab "
add_drivers+=" vfat nls_cp437 nls_iso8859_1 "

Create a symbolic link from /etc/fstab.sys to /etc/fstab to indicate that dracut should mount all the file systems listed. Then, to omit mounting them again in runit stage 1, disable the corresponding core service.

# mv /etc/runit/core-services/03-filesystems.sh{,.bak}

Edit /etc/xbps.d/xbps.conf to prevent the service from being added back by an update to runit-void.

noextract=/etc/runit/core-services/03-filesystems.sh

We are choosing dracut to mount our filesystems because otherwise the filesystems core service will try to open the encrypted drive a second time. Another option would be to stop dracut from mounting anything at all.

Edit the configuration for efibootmgr's kernel hook in /etc/default/efiboomgr-kernel-hook for it to add boot entries. Kernel command-line parameters may be added with OPTIONS.

MODIFY_EFI_ENTRIES="1"
DISK="/dev/sd<X>"
PART="1"

Invoke dracut and efibootmgr by reconfiguring the kernel. You can determine the installed kernel version by listing the dependencies of the linux meta-package using xbps-query.

# xbps-reconfigure -f linux<major>.<minor>

As needed, modify the boot order using efibootmgr. To determine the current boot order and entries, invoke it without any arguments. To set the bootorder, use --bootorder XXXX,XXXX,....

Exit the chroot, unmount the filesystems and reboot.

# exit
# umount -R /mnt
# reboot