347 lines
12 KiB
Python
347 lines
12 KiB
Python
"""Library for modification of disk image files.
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Image file modification includes extracting ISO archives, adding files to
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initrd-archives contained within the ISO, recalculating md5sum-files
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inside the ISO and rebuilding bootable ISOs from directories on the
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local filesystem.
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"""
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from pathlib import Path
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import re
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import subprocess
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def extract_iso(path_to_output_dir, path_to_input_file):
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"""Extracts the contents of the ISO-file into the specified directory.
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Source: https://wiki.debian.org/DebianInstaller/Preseed/EditIso#Extracting_the_Initrd_from_an_ISO_Image
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Parameters
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----------
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path_to_output_dir : str or pathlike object
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Path to the directory into which the contents of the ISO archive will
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be extracted.
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path_to_input_file : str or pathlike object
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Path to the file/archive which should be extracted.
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Raises
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------
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FileNotFoundError
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Raised if the input file does not exist or is not a file.
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NotADirectoryError
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Raised if the output directory does not exist or is not a directory.
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Example
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-------
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extract_iso("/tmp/isocontents", "/home/myuser/downloads/debian-11.iso")
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"""
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path_to_output_dir = Path(path_to_output_dir)
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path_to_input_file = Path(path_to_input_file)
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# check if paths are valid
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if not path_to_output_dir.is_dir():
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raise NotADirectoryError(f"No such directory: '{path_to_output_dir}'.")
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if not path_to_input_file.is_file():
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raise FileNotFoundError(f"No such file: '{path_to_input_file}'.")
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# extract file to destination
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try:
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subprocess.run(
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[
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"xorriso",
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"-osirrox", "on"
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"-indev", path_to_input_file.resolve(),
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"-extract", "/",
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path_to_output_dir.resolve()
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],
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check=True)
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except subprocess.CalledProcessError:
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raise RuntimeError(
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f"An error occurred while extracting '{path_to_input_file}'.")
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def append_file_contents_to_initrd_archive(path_to_initrd_archive,
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path_to_input_file):
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"""Appends the input file to the specified initrd archive.
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The initrd archive is extracted, the input file is appended, and
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the initrd is repacked again.
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Source: https://wiki.debian.org/DebianInstaller/Preseed/EditIso#Adding_a_Preseed_File_to_the_Initrd
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Parameters
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----------
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path_to_initrd_archive : str or pathlike object
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Path the the initrd archive to which the input file shall be
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appended. The initrd file must be called 'initrd.gz'.
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path_to_input_file : str or pathlike object
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Path to the input file which shall be added to the initrd
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archive.
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Raises
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------
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AssertionError
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Thrown if the initrd archive is not named 'initrd.gz'.
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FileNotFoundError
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Thrown if the initrd archive file or input file does not
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exist.
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Examples
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--------
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append_file_contents_to_initrd_archive(
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"/tmp/isofiles/install.386/initrd.gz",
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"/tmp/preseed.cfg")
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"""
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path_to_initrd_archive = Path(path_to_initrd_archive)
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path_to_input_file = Path(path_to_input_file)
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# check if initrd file exists and has the correct name
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if not path_to_initrd_archive.is_file():
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raise FileNotFoundError(f"No such file: '{path_to_initrd_archive}'.")
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if not path_to_initrd_archive.name == "initrd.gz":
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raise AssertionError(f"Does not seem to be an initrd.gz archive: "
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f"'{path_to_initrd_archive.name}'.")
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# check if input file exists
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if not path_to_input_file.is_file():
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raise FileNotFoundError(f"No such file: '{path_to_input_file}'.")
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# temporarily extract initrd archive and append the input file's contents
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try:
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# make archive temporarily writable
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subprocess.run(["chmod", "+w", path_to_initrd_archive],
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check=True)
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# extract archive in-place
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subprocess.run(["gunzip", path_to_initrd_archive],
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check=True)
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# append contents of input_file to extracted archive using cpio
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subprocess.run(
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["echo", path_to_input_file,
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"|", "cpio", "-H", "newc", "-o", "-A",
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"-F", path_to_initrd_archive.with_suffix("")],
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shell=True,
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check=True)
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# repack archive
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subprocess.run(
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["gzip", path_to_initrd_archive.with_suffix("")],
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check=True)
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# remove write permissions from repacked archive
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subprocess.run(["chmod", "-w", path_to_initrd_archive],
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check=True)
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except subprocess.CalledProcessError:
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raise RuntimeError(f"Failed while appending contents of "
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f"'{path_to_input_file}' to "
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f"'{path_to_initrd_archive}'.")
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def regenerate_iso_md5sums_file(path_to_extracted_iso_root):
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"""Recalculates and rewrites the md5sum.txt file for the extracted ISO.
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Source: https://wiki.debian.org/DebianInstaller/Preseed/EditIso#Regenerating_md5sum.txt
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Parameters
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----------
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path_to_extracted_iso_root : str or pathlike object
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Path to the root folder containing an extracted ISO's
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contents.
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Raises
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------
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RuntimeError
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Raised if the recalculation/rewrite operation fails.
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NotADirectoryError
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Raised if the specified directory is not a directory or does
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not exist.
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Examples
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--------
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regenerate_iso_md5sums_file("/tmp/extracted_iso")
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"""
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path_to_extracted_iso_root = Path(path_to_extracted_iso_root)
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# check if input path exists
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if not path_to_extracted_iso_root.is_dir():
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raise NotADirectoryError(f"No such directory: "
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f"'{path_to_extracted_iso_root}'.")
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# recalculate and rewrite 'md5sum.txt' in ISO's root
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try:
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# make md5sum.txt temporarily writable
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subprocess.run(
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["chmod", "+w", path_to_extracted_iso_root/"md5sum.txt"],
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check=True)
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# find all files within ISO's root and regenerate md5sum.txt file
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subprocess.run(
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["find", path_to_extracted_iso_root,
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"-follow", "-type", "f", "!", "-name", "md5sum.txt", "-print0"
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"|", "xargs", "-0", "md5sum",
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">", path_to_extracted_iso_root/"md5sum.txt"],
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shell=True,
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check=True)
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# remove write permissions from md5sum.txt
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subprocess.run(
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["chmod", "-w", path_to_extracted_iso_root/"md5sum.txt"],
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check=True)
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except subprocess.CalledProcessError:
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raise RuntimeError(f"Failed while regenerating "
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f"'md5sum.txt' within "
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f"'{path_to_extracted_iso_root}'.")
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def extract_mbr_from_iso(path_to_output_file, path_to_source_iso):
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"""Extracts the MBR-data from the ISO and writes it into the outputfile.
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The source ISO file must be a BIOS-bootable '.iso'- or
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'.img'-file. You should use a "vanilla" debian installation ISO as
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the source file.
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Source: https://wiki.debian.org/RepackBootableISO#Determine_those_options_which_need_to_be_adapted_on_amd64_or_i386
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Parameters
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----------
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path_to_output_file : str or pathlike object
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Path to the file which will be created and contain the MBR
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data.
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path_to_source_iso : str or pathlike object
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Path to the source ISO whose MBR data will get extracted.
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Raises
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------
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RuntimeError
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Raised if the input ISO has the wrong file extension.
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FileNotFoundError
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Raised if the input ISO does not exist or is not a file.
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FileExistsError
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Raised if the output file already exists.
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Examples
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--------
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extract_mbr_from_iso("/tmp/mbr-data.bin", "/tmp/debian-11.0.4-netinst.iso")
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"""
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path_to_output_file = Path(path_to_output_file)
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path_to_source_iso = Path(path_to_source_iso)
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# make sure output file does not exist already
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if path_to_output_file.exists():
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raise FileExistsError(
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f"Outputfile exists and would get overwritten: "
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f"'{path_to_output_file}'.")
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# make sure input file exists and has the right extension
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if not path_to_source_iso.is_file():
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raise FileNotFoundError(f"No such file: '{path_to_source_iso}'.")
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if path_to_source_iso.suffix not in [".iso", ".img"]:
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raise RuntimeError(
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f"Input file is not an image file: '{path_to_source_iso}'.")
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# extract the MBR (first 432 Bytes) of the source ISO file
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with open(path_to_source_iso, mode="r+b") as iso_file:
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with open(path_to_output_file, mode="w+b") as mbr_file:
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mbr_file.write(iso_file.read(432))
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def repack_iso(path_to_output_iso,
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path_to_mbr_data_file,
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path_to_input_files_root_dir,
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created_iso_filesystem_name):
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"""Rebuilds a bootable ISO image using the input files.
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The input files root directory contains the contents of a previously
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extracted ISO file, with its contents possibly modified.
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The MBR data file used should contain MBR data extracted from the
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originially extracted ISO.
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The given filesystem name written into the modified ISO appears when
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the ISO gets mounted. It may only contain alphanumeric characters,
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hyphens, underscores or periods.
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Source: https://wiki.debian.org/RepackBootableISO#Determine_those_options_which_need_to_be_adapted_on_amd64_or_i386
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Parameters
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----------
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path_to_output_iso : str or pathlike object
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Path to the file as which the created ISO file will be saved.
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path_to_mbr_data_file : str or pathlike object
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Path to an existing file containing MBR data.
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path_to_input_files_root_dir : str or pathlike object
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Path to the root directory of those files which will be repacked into
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the new ISO file.
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created_iso_filesystem_name : str
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Name of the filesystem which the created ISO will have upon
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mounting it.
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Raises
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------
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RuntimeError
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Raised if the ISO packing process fails.
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NotADirectoryError
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Raised if the specified input files root directory does not
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exist or is not a directory.
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FileNotFoundError
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Raised if the MBR data file does not exist or is not a file.
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FileExistsError
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Raised if the output file already exists.
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Examples
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--------
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repack_iso("/tmp/debian-11.0.4-modified.iso",
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"/tmp/mbr-data.bin",
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"/tmp/extracted-iso",
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"Debian 11.0.4 installation image")
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"""
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path_to_output_iso = Path(path_to_output_iso)
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path_to_mbr_data_file = Path(path_to_mbr_data_file)
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path_to_input_files_root_dir = Path(path_to_input_files_root_dir)
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# make sure output file does not exist yet
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if path_to_output_iso.exists():
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raise FileExistsError(f"Existing file would get overwritten: "
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f"'{path_to_output_iso}'.")
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# make sure input files exist
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if not path_to_mbr_data_file.is_file():
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raise FileNotFoundError(f"No such file: '{path_to_mbr_data_file}'.")
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if not path_to_input_files_root_dir.is_dir():
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raise NotADirectoryError(f"No such directory: "
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f"'{path_to_input_files_root_dir}'.")
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# make sure specified filesystem name contains no illegal characters:
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# only alphanumeric, ' ', '.', '_' and '-' are allowed.
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filesystem_name_invalid_char_regex = re.compile(r"[^\w .-]")
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invalid_char_match = filesystem_name_invalid_char_regex.search(
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created_iso_filesystem_name)
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if invalid_char_match is not None:
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raise RuntimeError(f"Invalid character in filesystem name: "
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f"'{invalid_char_match.group()[0]}'.")
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# repack the ISO using xorriso
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try:
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subprocess.run(
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["xorriso", "-as", "mkisofs",
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"-r", "-V", created_iso_filesystem_name,
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"-o", path_to_output_iso,
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"-J", "-J", "-joliet-long", "-cache-inodes",
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"-isohybrid-mbr", path_to_mbr_data_file,
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"-b", "isolinux/isolinux.bin",
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"-c", "isolinux/boot.cat",
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"-boot-load-size", "4", "-boot-info-table", "-no-emul-boot",
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"-eltorito-alt-boot",
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"-e", "boot/grub/efi.img", "-no-emul-boot",
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"-isohybrid-gpt-basdat", "-isohybrid-apm-hfsplus",
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path_to_input_files_root_dir],
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check=True)
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except subprocess.CalledProcessError:
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raise RuntimeError(f"Failed while repacking ISO from source files: "
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f"'{path_to_input_files_root_dir}'.")
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