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decode kernel panic from QR Code photo

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decode-kernel-panic.py

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#!/usr/bin/env python3

"""

Scan a Linux panic QR code with ZXingReader and decompress its crash log.

./decode-kernel-panic.py screenshot.png -o panic.log

"""

import argparse

import json

from pathlib import Path

import subprocess

import sys

from urllib.parse import parse_qs, urlsplit

import zlib

def decode_panic_url(url):

"""Decode the kernel's z parameter: 17 decimal digits per 7 little-endian bytes.

Format reference: https://github.com/kdj0c/panic_report

"""

parts = urlsplit(url)

parameters = parse_qs(parts.query, keep_blank_values=True)

if "z" not in parameters:

parameters = parse_qs(parts.fragment.lstrip("?"), keep_blank_values=True)

if "z" not in parameters:

raise ValueError("QR code URL has no compressed panic data (z parameter)")

if len(parameters["z"]) != 1:

raise ValueError("QR code URL has multiple z parameters")

digits = parameters["z"][0]

if not digits or not digits.isascii() or not digits.isdecimal():

raise ValueError("panic data must contain only decimal digits")

A final, partial group uses fewer digits and bytes.

byte_counts = {3: 1, 5: 2, 8: 3, 10: 4, 13: 5, 15: 6, 17: 7}

compressed = bytearray()

for offset in range(0, len(digits), 17):

chunk = digits[offset:offset + 17]

if len(chunk) not in byte_counts:

raise ValueError("invalid length of encoded panic data")

try:

compressed.extend(int(chunk).to_bytes(byte_counts[len(chunk)], "little"))

except OverflowError as exc:

raise ValueError("encoded panic data contains an out-of-range chunk") from exc

return zlib.decompress(compressed)

def scan_image(image):

if not image.is_file():

raise ValueError(f"image does not exist or is not a file: {image}")

try:

result = subprocess.run(

["ZXingReader", "-formats", "QRCode", "-json", str(image.resolve())],

capture_output=True,

text=True,

)

except FileNotFoundError as exc:

raise ValueError("ZXingReader is required; install it and put it on PATH") from exc

if result.returncode != 0:

detail = result.stderr.strip() or "no readable QR code found"

raise ValueError(f"ZXingReader failed: {detail}")

if not result.stdout.strip():

raise ValueError("no readable QR code found")

try:

qr = json.loads(result.stdout)

except json.JSONDecodeError as exc:

raise ValueError("expected one QR code in ZXingReader's JSON output") from exc

if not isinstance(qr, dict) or not isinstance(qr.get("Text"), str):

raise ValueError("ZXingReader returned no QR code text")

return qr["Text"]

def main():

parser = argparse.ArgumentParser(

description="Scan a Linux panic screenshot with ZXingReader and decompress its log.",

epilog="Requires Python 3 and ZXingReader. Decoding runs locally without network access.",

)

parser.add_argument("image", type=Path, help="screenshot or photo containing the panic QR code")

parser.add_argument("-o", "--output", type=Path, help="write the log to a file instead of stdout")

args = parser.parse_args()

try:

if args.output and args.output.resolve() == args.image.resolve():

raise ValueError("output must differ from the input image")

log = decode_panic_url(scan_image(args.image))

if args.output:

args.output.write_bytes(log)

else:

sys.stdout.buffer.write(log)

except BrokenPipeError:

Allow commands such as decode-kernel-panic screenshot.png | head.

import os

os.dup2(os.open(os.devnull, os.O_WRONLY), sys.stdout.fileno())

return 0

except (OSError, ValueError, zlib.error) as exc:

print(f"{parser.prog}: {exc}", file=sys.stderr)

return 1

return 0

if name == "main":

sys.exit(main())

skorotkiewicz

commented

Oct 30, 2026

•

edited

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