My GRUB linux boot entry generation script

grub_linux_manual.py

#!/usr/bin/env python3
#exec tail -n +3 $0
# Be careful not to change
# the 'exec tail' line above.

# This script lives in /etc/grub.d/

# 2015,2022 Ralph Versteegen
# The menuentry template was orginally generated by /etc/grub.d/10_linux

import os
import glob
import re
import sys
import subprocess

def tell(*args):
    print(*args, file = sys.stderr)

def run(cmd):
    tell(cmd)
    ret = subprocess.check_output(cmd.split()).decode('utf-8').rstrip()
    tell(" ->", ret)
    return ret

# Don't use initrd; the kernel image has it builtin and this breaks it
# I blame the patch applied in the SlackBuild to GRUB2 which makes it look for /boot/initrd.gz...

#################### bootflags

# Useful kernel params:
# 	rootdelay=	[KNL] Delay (in seconds) to pause before attempting to
#			mount the root filesystem
#	S		[KNL] Run init in single mode
#	libata.force=1.00:1.5,norst,udma4  or udma3 pio4 etc


bootflags = "rootflags=subvol=root rootfstype=btrfs ro"

#################### disks

# Find HDD and SSD devices which have mounted partitions
disks = {}
for part in ("/mnt/btrfs_ssd", "/mnt/btrfs_pool", "/mnt/btrfs_hdd"):
    if not os.path.isdir(part):
        continue
    part_dev = run("findmnt -vfn -o SOURCE " + part)
    if part not in disks:
        # Trim the partition number, to get disk's device
        disks[part] = re.match("[^0-9]*", part_dev).group(0)

tell("Found disks:", disks)

#################### Entry for each disk

for disk_path,disk_dev in disks.items():

    # PARTUUID of the root's btrfs partition
    # PARTUUID shown by "lsblk -f -o +PARTUUID,SIZE", and by gdisk 'i' (information) as "Partition unique GUID"
    # It is stored in MBR or GPT
    root_partuuid = run("findmnt -vfn -o PARTUUID " + disk_path)

    # Check fstab for a /mnt/boot entry
    # It's also possible to search HDD for LABEL=boot using blkid
    #boot_dev = run("findmnt -vfn -o UUID /mnt/boot")

    # Check for a partition labelled "boot"
    try:
        boot_dev = run("blkid -t LABEL=boot -o device " + " ".join(glob.glob(disk_dev + "*")))
        #if boot_dev:
        tell("Found boot partition " + boot_dev)

        boot_uuid = run("lsblk -n -o UUID " + boot_dev)
    #else:
    except subprocess.CalledProcessError:
        # No boot partition, using /boot

        # UUID aka FS UUID is stored in the FS itself
        boot_uuid = run("findmnt -vfn -o UUID " + disk_path)


    template = """
    menuentry 'Slackware GNU/Linux {NAME}' --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-new' {{
            load_video
            insmod gzio
            insmod part_msdos
            insmod part_gpt
            insmod btrfs
            insmod ext2
            echo   'Searching for boot partition...'
            search.fs_uuid {BOOTUUID} root
            echo	'Loading Linux from' $root
            linux	/root/boot/{IMAGE} {BOOTFLAGS} root=PARTUUID={ROOTPARTUUID}
    }}
    """

    for image_name in ("vmlinuz", "vmlinuz-backup"):
        image_path = disk_path + "/root/boot/" + image_name
        if os.path.isfile(image_path):
            name = os.readlink(image_path) + " on " + disk_path

            print(template.format(ROOTPARTUUID = root_partuuid,
                                  BOOTUUID = boot_uuid,
                                  BOOTFLAGS = bootflags,
                                  IMAGE = image_name,
                                  NAME = name))