iso-to-usb

#!/bin/bash
set -euo pipefail

# See also https://github.com/jsamr/bootiso

run() {
    echo >&2 "+ $*"
    "$@"
}

cleanup() {
    if [ -d "${loop_path-}" ]; then
        run umount "$loop_path"
        run rmdir "$loop_path"
    fi
    if [ -d "${tmpdir-}" ]; then
        run rmdir "$tmpdir"
    fi
}

usage() {
    cat >&2 <<EOM
usage: $(basename "$0") [options] ISO_FILE MOUNTED_USB_PATH

Burn ISO_FILE to a USB drive mounted at MOUNTED_USB_PATH.

Options:
    -h, --help              Print this help message
    --delete                Delete unknown files from MOUNTED_USB_PATH
    --delete-exclude DIR    Delete all files from MOUNTED_USB_PATH except DIR

EOM
}

check_dependencies() {
    for dep in findmnt install-mbr mount mv rmdir rsync sync syslinux umount
    do
        if ! which "$dep" >/dev/null; then
            echo >&2 "Failed to find dependency on PATH: $dep"
            return 1
        fi
    done
}

mount_iso() {
    local iso_file mount_path
    iso_file="$1"
    mount_path="$2"
    mkdir -v "$mount_path"
    run mount -o loop "$iso_file" "$mount_path"
}

device_for_mount_point() {
    run findmnt -n --output=source "$1"
}

copy_files() {
    local rsync_opts
    rsync_opts=("-v")

    if [ -n "$delete" ]; then
        rsync_opts+=("--del")
    fi
    if [ -n "$delete_exclude" ]; then
        rsync_opts+=("--exclude" "$delete_exclude")
    fi

    run rsync "${rsync_opts[@]}" -c -rpt "$loop_path/" "$mounted_usb_path/"
}

setup_boot() {
    run mv -vT "$mounted_usb_path/isolinux" "$mounted_usb_path/syslinux"
    run mv -vT "$mounted_usb_path/syslinux/"{iso,sys}linux.cfg
    run syslinux -s "$usb_partition"
}

check_partition_bootable_and_install_mbr() {
    local disk partition
    partition="$1"
    disk="/dev/$(run lsblk -no pkname "$partition")"

    run install-mbr "$disk"

    if run parted -m -s "$disk" print | grep boot; then
        echo "Looks like disk is bootable"
    else
        echo "Doesn't look like partition $partition is bootable!"
        echo "Please make sure that it has the boot partition flag"
    fi
}

delete=
delete_exclude=

while [ $# -gt 0 ] && [[ $1 == -* ]]; do
    case "$1" in
        --delete)
            delete=1
            ;;
        --delete-exclude)
            delete=1
            delete_exclude="$2"
            shift
            ;;
        -h|--help)
            usage
            exit
            ;;
        *)
            usage
            echo >&2 "Unknown option $1"
            exit 1
            ;;
    esac
    shift
done

if [ $# -ne 2 ]; then
    usage
    exit 1
fi

iso_file="$1"
mounted_usb_path="$2"

if [ "$(id -u)" -ne 0 ]; then
    echo >&2 "error: This script must be run as root"
    exit 1
fi

check_dependencies

usb_partition="$(device_for_mount_point "$mounted_usb_path")"

trap cleanup EXIT

tmpdir="$(mktemp -d)"

loop_path="$tmpdir/iso"

mount_iso "$iso_file" "$loop_path"

copy_files

setup_boot

check_partition_bootable_and_install_mbr "$usb_partition"

trap - EXIT
cleanup

run sync -f "$mounted_usb_path"

echo "All done!"