Get bootloader type and (if available) the bootloader version. Only works on x86/x86-64 Linux.

get_x86_bootloader.sh

#!/bin/bash
set -euf -o pipefail

# Copyright (C) rany <ranygh@riseup.net>. All rights reserved.
#
# This software is licensed to you under the GNU General Public License,
# version 2 (GPLv2). There is NO WARRANTY for this software, express or
# implied, including the implied warranties of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. You should have received a copy of GPLv2
# along with this software; if not, see
# http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt.

# Where 0x15 is the bootloader type and 0x234 is the version,
# it is derived by doing: 0x15 << 4 | 0x234 & 0xf = 0x154.
# We use kernel.bootloader_version to get the full version type
# because bootloader_type only provides the last four bits.
bootloader_type=$(($(</proc/sys/kernel/bootloader_type) >> 4))
# Get the full bootloader version. If not written, it is zero.
# Source: https://www.kernel.org/doc/Documentation/x86/boot.rst
#         (ext_loader_ver section)
bootloader_version=$(</proc/sys/kernel/bootloader_version)
case $bootloader_type in
    # Source: https://www.kernel.org/doc/Documentation/x86/boot.rst
    #         (type_of_loader section)
    $((0x00)))
        if ((bootloader_version == 0)); then
            bootloader_type='pre-2.00 bootloader'
        else
            bootloader_type='LILO'
        fi
        ;;
    $((0x01))) bootloader_type='Loadlin';;
    $((0x02)))
        # Used by EFI Boot Stub:
        # https://github.com/torvalds/linux/blob/09a9639e56c01c7a00d6c0ca63f4c7c41abe075d/drivers/firmware/efi/libstub/x86-stub.c#L506
        if ((bootloader_version == 1)); then
            bootloader_type='EFI Boot Stub'
            bootloader_version='0'
        elif ((bootloader_version != 0)); then
            echo >&2 "Invalid type_of_loader and version combination. Only 0x20 and 0x21 are known to be used."
            exit 1
        else
            bootloader_type='bootsect-loader'
        fi
        ;;
    $((0x03))) bootloader_type='Syslinux';;
    $((0x04))) bootloader_type='Etherboot/gPXE/iPXE';;
    $((0x05))) bootloader_type='ELILO';;
    $((0x07))) bootloader_type='GRUB';;
    $((0x08))) bootloader_type='U-Boot';;
    $((0x09))) bootloader_type='Xen';;
    $((0x0A))) bootloader_type='Gujin';;
    $((0x0B))) bootloader_type='Qemu';;
    $((0x0C))) bootloader_type='Arcturus Networks uCbootloader';;
    $((0x0D))) bootloader_type='kexec-tools';;
    $((0x11))) bootloader_type='Minimal Linux Bootloader <http://sebastian-plotz.blogspot.de>';;
    $((0x12))) bootloader_type='OVMF UEFI virtualization stack';;
    $((0x13))) bootloader_type='barebox';;
    *)         echo >&2 "Unknown bootloader type ($bootloader_type). Please update this script."; exit 1;;
esac

printf %s "$bootloader_type"
(( bootloader_version > 0 )) && printf %s " (v$bootloader_version)"
printf '\n'