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mkdiskimg

Create disk images with partitions and content from JSON configuration.

Usage

mkdiskimg config.json
mkdiskimg -h  # Show detailed help

Features

  • No root privileges or manual loop device setup required
  • JSON configuration with comment support (// and /* */)
  • Multiple partition table formats: MBR, GPT, hybrid, raw
  • Various filesystems: ext2/3/4, vfat, swap
  • Content population: tarballs, file uploads, raw writes
  • Path expansion: environment variables and glob patterns
  • Multiple image formats: raw, qcow2, vmdk, etc.

Configuration

Root Properties

  • name - Image filename (without extension)
  • size - Image size: 64M, 1G, or bytes (hex/decimal)
  • image_format - Format: raw (default), qcow2, vmdk, etc.
  • partition_table - Type: mbr (default), gpt, hybrid, raw
  • imgver - Optional version string appended to filename
  • parts - Array of partition definitions
  • binaries - Array of raw binary writes (disk level)

Partition Properties

Layout:

  • type - p (primary), l (logical), e (extended)
  • start - Start sector (auto if 0)
  • end - End sector (negative = offset from end)
  • size - Partition size (e.g., 32M, 1G)

Filesystem:

  • filesystem - Type: ext4 (default), ext3, vfat, swap, raw
  • block_size - Filesystem block size in bytes
  • label - Partition/filesystem label [GPT only]

Partition Table:

  • mbr_id - MBR type ID: 0x83 (Linux), 0x0b (FAT32), 0x05 (extended) [MBR only]
  • gpt_type - GPT type GUID (e.g., C12A7328-F81F-11D2-BA4B-00A0C93EC93B for EFI) [GPT/hybrid only]
  • active - Bootable flag [MBR only]

Content:

  • raw_image - Copy raw image file directly to partition
  • tarballs - Extract tarballs: [{"source": "rootfs.tar.gz", "target": "/"}]
  • uploads - Copy files: [{"source": "file.txt", "target": "/etc/"}]
  • writes - Create files: [{"target": "/etc/hostname", "content": "myhost"}]
  • binaries - Raw binary writes at partition level

Binary Write Properties

  • source - Source file path (supports ~ and $VAR)
  • source_offset - Byte offset in source (hex or decimal, default: 0)
  • target_offset - Byte offset in target (hex or decimal, default: 0)
  • size - Bytes to write (hex or decimal, default: entire file)
  • part - Partition number (for disk-level binaries only)

Example

Check mbr.md, gpt.md, hybrid.md for more configurations.

{
  // Disk configuration
  "name": "system",
  "size": "128M",
  "partition_table": "mbr",

  "parts": [
    {
      // Boot partition
      "type": "p",
      "filesystem": "vfat",
      "size": "32M",
      "mbr_id": "0x0b",
      "active": true,
      "label": "BOOT",
      "uploads": [
        {"source": "boot/*", "target": "/"}
      ]
    },
    {
      // Root filesystem
      "type": "p",
      "filesystem": "ext4",
      "size": "64M",
      "label": "rootfs",
      "tarballs": [
        {"source": "rootfs.tar.gz", "target": "/"}
      ],
      "writes": [
        {"target": "/etc/hostname", "content": "embedded-system"}
      ]
    }
  ],

  // Raw bootloader write
  "binaries": [
    {
      "source": "u-boot.bin",
      "target_offset": "0x8000"
    }
  ]
}

Installation

Dependencies

  • Python 3
  • libguestfs
# Fedora/RHEL/CentOS
sudo yum install python3-libguestfs

# Debian/Ubuntu
sudo apt-get install python3-guestfs

# Arch Linux
sudo pacman -S libguestfs

Install

chmod +x mkdiskimg
sudo cp mkdiskimg /usr/local/bin/

Notes

  • Default partition start is 1M (2048 sectors) for alignment
  • Tarball compression auto-detected: .gz, .bz, .xz, .Z, .lzo, .zst
  • Upload sources support glob patterns (*, ?)
  • Paths support environment variables ($VAR) and tilde (~)
  • Hybrid partition table: GPT with protective MBR for first 3 partitions

License

GPLv3