update-systemd.sh

#!/bin/sh
#
# This is a simple kernel hook to populate the systemd-boot entries
# whenever kernel images are added or removed.
# Author: https://p5r.uk/blog/2020/using-systemd-boot-on-debian-bullseye.html


# The disk containing the root partition; also see `sudo blkid`
root_disk="UUID=$(findmnt / -o UUID -n)"

# The linux kernel arguments
flags="ro quiet"

prog_name=`basename $0`
boot_dir="/boot"
sd_boot_dir="loader/entries"
sd_boot_path="$boot_dir/efi/$sd_boot_dir"
title=
prefix=
force=0
verbose=0


usage() {
    echo "$prog_name [OPTIONS]"
}

help() {
    usage
    echo
    echo "OPTIONS"
    echo "  -h          show this help page"
    echo "  -f          force overwrite"
    echo "  -v          make verbose"
}

while getopts hfv opt; do
    case "$opt" in
        h)  help
            exit 0;;
        f)  force=1;;
        v)  verbose=1;;
        \?)     # unknown flag
            usage >&2
            exit 1;;
    esac
done
shift `expr $OPTIND - 1`

if [ $# -ne 0 ]; then
    echo >&2 "No extra argument allowed"
    exit 1
fi


sd_boot_entry() {
    cat <<-EOF
	title   $title
	version $version
	linux   /$sd_boot_dir/vmlinuz-$version
	initrd  /$sd_boot_dir/initrd.img-$version
	options root=$root_disk $flags
	EOF
}


if [ ! -h "/dev/disk/by-uuid/${root_disk#UUID=}" ]; then
    echo >&2 "error: root disk '$root_disk' not found"
    exit 1
fi

if [ ! -d "$sd_boot_path" ]; then
    echo >&2 "error: directory '$sd_boot_path' not found"
    exit 1
fi

if [ ! -f /etc/machine-id ]; then
    echo >&2 "error: machine id file '/etc/machine-id' not found"
    exit 1
fi
prefix="`cat /etc/machine-id`-v"

if [ -f /etc/os-release ]; then
    title=`sed -ne '/^PRETTY_NAME=/s/.*"\(.*\)".*/\1/p' /etc/os-release`
else
    title=Debian
fi


echo "Updating Systemd boot entries"

# Copy images from the Debian install directory to the EFI partition
find "$boot_dir" -maxdepth 1 -type f -name '*.dpkg-tmp' -prune -o -name 'vmlinuz-*' -exec cp -u {} "$sd_boot_path" \;
find "$boot_dir" -maxdepth 1 -type f -name '*.dpkg-tmp' -prune -o -name 'initrd.img-*' -exec cp -u {} "$sd_boot_path" \;

# Remove files from the EFI if they are missing from the Debian install directory
find "$sd_boot_path" -maxdepth 1 -type f -name 'vmlinuz-*' | while read i; do
    kernel="$boot_dir/`basename $i`"
    if [ ! -f "$kernel" ]; then
        rm -f "$i"
    fi
done
find "$sd_boot_path" -maxdepth 1 -type f -name 'initrd.img-*' | while read i; do
    initrd="$boot_dir/`basename $i`"
    if [ ! -f "$initrd" ]; then
        rm -f "$i"
    fi
done

# Remove the conf file
find "$sd_boot_path" -maxdepth 1 -type f -name "$prefix*.conf" | sort -Vr | while read i; do
    version=`basename $i | sed -e "s/$prefix//; s/.conf$//"`
    kernel="$sd_boot_path/vmlinuz-$version"
    initrd="$sd_boot_path/initrd.img-$version"
    if [ ! -f "$kernel" -o ! -f "$initrd" ]; then
        echo "Removing kernel v$version"
        rm -f "$i" "$kernel" "$initrd"
    fi
done

# Add new kernel entries
find "$boot_dir" -maxdepth 1 -type f -name '*.dpkg-tmp' -prune -o -name 'vmlinuz-*' -print | sort -Vr | while read i; do
    version=`basename $i | sed -e 's/vmlinuz-//'`
    initrd="$boot_dir/initrd.img-$version"
    file="$sd_boot_path/$prefix$version.conf"
    echo "Found kernel `basename $i`"
    if [ ! -f "$initrd" ]; then
        echo "Ignoring $i"
    elif [ $force -eq 1 -o ! -f "$file" ]; then
        echo "Adding $file"
        sd_boot_entry "$version" > "$file"
        cp -v $i "$initrd" "$sd_boot_path"
    fi
done