debian/ubuntu uefi

systemctl reboot --firmware-setup

int efi_set_reboot_to_firmware(bool value) {
        int r;
        uint64_t b, b_new;

        r = get_os_indications(&b);
        if (r < 0)
                return r;

        if (value)
                b_new = b | EFI_OS_INDICATIONS_BOOT_TO_FW_UI;
        else
                b_new = b & ~EFI_OS_INDICATIONS_BOOT_TO_FW_UI;

        /* Avoid writing to efi vars store if we can due to firmware bugs. */
        if (b != b_new)
                return efi_set_variable(EFI_VENDOR_GLOBAL, "OsIndications", &b_new, sizeof(uint64_t));

        return 0;
}

static int get_os_indications(uint64_t *os_indication) {
        int r;
        size_t s;
        _cleanup_free_ void *v = NULL;

        r = efi_reboot_to_firmware_supported();
        if (r < 0)
                return r;

        r = efi_get_variable(EFI_VENDOR_GLOBAL, "OsIndications", NULL, &v, &s);
        if (r < 0)
                return r;
        else if (s != sizeof(uint64_t))
                return -EINVAL;

        *os_indication = *(uint64_t *)v;
        return 0;
}

#!/usr/bin/env python3
# -*- mode: python; coding: utf-8 -*-

assert str is not bytes

import os
import struct

EFI_VAR_PATH = '/sys/firmware/efi/efivars/OsIndications-8be4df61-93ca-11d2-aa0d-00e098032b8c'
EFI_OS_INDICATIONS_BOOT_TO_FW_UI = 0x0000000000000001
REAL_REBOOT_CMD = 'reboot'

def reboot_to_firmware():
    with open(EFI_VAR_PATH, mode='rb') as fd:
        raw_efi_value = fd.read()
    
    efi_struct_format = '=IQ'
    efi_prefix, efi_value = struct.unpack(efi_struct_format, raw_efi_value)
    new_efi_value = efi_value | EFI_OS_INDICATIONS_BOOT_TO_FW_UI
    new_raw_efi_value = struct.pack(efi_struct_format, efi_prefix, new_efi_value)
    
    with open(EFI_VAR_PATH, mode='wb') as fd:
        fd.write(new_raw_efi_value)
    
    os.system(REAL_REBOOT_CMD)

if __name__ == '__main__':
    reboot_to_firmware()

chmod +x reboot-to-firmware.py

./reboot-to-firmware.py