Working with system images of the operating system Android often becomes a necessity for customizing a device, creating your own assemblies, or in-depth analysis of the file structure. Developers and modification enthusiasts are constantly faced with the imgformat, which is a bitwise copy of a memory section. Understanding how to properly extract the contents of such a container opens the door to editing system applications, replacing fonts, or fixing bugs in the kernel.
The unpacking process is not a trivial mouse click, as images often have complex header and compression structures. Unlike conventional archives ZIP or RAR, this requires specialized software that can correctly interpret the metadata of the bootloader and file systems. Errors at the stage of structure analysis can lead to data damage, so the procedure should be approached with the utmost care and the availability of backup copies.
In this article we will analyze in detail the algorithms of actions, the necessary tools and the nuances of working with various types of images found in the ecosystem. Android. You will learn how standard boot images differ from system partitions and which utilities best cope with the task of decompression depending on the version of the operating system and processor architecture.
Analysis of the image structure and preparation of tools
Before you begin to directly extract files, you need to understand what type of image you are dealing with. Files with the extension .img can contain different file systems, such as ext4, yaffs2 or squashfs, and also have specific headers specific to Qualcomm or MediaTek bootloaders. Incorrect identification of the format will result in the unpacking utility throwing an error or creating an empty folder.
To get started, you will need a computer running Windows, Linux or macOS, as well as an installed package Python version 3.x, which is necessary for many scripts to work unpacking. A critical element is the availability of the original firmware file, obtained either through dumps from the device or downloaded from the official resources of the manufacturer. Always check the integrity of the file through checksums before starting manipulations.
⚠️ Attention: Never try to mount images of system partitions directly in Windows Explorer without first checking the file system. This can lead to incorrect data reading or accidental garbage writing to the image structure.
There are several key tools that have proven to be reliable solutions for this task. The choice of specific software depends on the complexity of the image structure and your personal preferences regarding the graphical interface or command line.
- 🛠️ Android Image Kitchen - a powerful GUI solution for Windows that supports automatic format detection.
- 💻 unpackbootimg - a classic command line utility, ideal for working with boot images and kernels.
- 🐧 SIMG2IMG - a specialized converter for working with sparse Android images, often found in OTA updates.
Using Android Image Kitchen for automatic unpacking
The most convenient way for users who do not want to dive into the jungle of the command line is the application of the utility Android Image Kitchen. This app automatically parses the file header and applies the appropriate decompression algorithm, be it extracting the kernel, RAM disk or system partition. The process begins by launching the executable file AndroidImageKitchen.bat in the root of the app folder.
After launching the interface, you need to drag the target file .img to the designated area of the window or use the file selection button. The app will instantly scan the structure and offer available options. If the image contains several layers of compression, the utility will offer to perform multi-stage unpacking, which significantly saves the user's time compared to manually trying out methods.
It is important to note that Android Image Kitchen creates a separate directory with the name of the unpacked image, where all extracted files are stored. In this folder you will find both the file system itself in disassembled form, and individual components, such as ramdisk and kernelif they were built into the image. This allows you to modify each element independently before reassembling it.
If the app gives an error when opening the file, try renaming the file, removing all spaces and special characters from its name, leaving only Latin letters.
However, it is worth remembering that automation has its limits. In cases with heavily modified firmware from Chinese manufacturers or outdated versions, the algorithm may not recognize the format correctly. In such situations, you have to turn to manual methods or look for specialized scripts for a specific device. Android, the algorithm may not recognize the format correctly. In such situations, you have to resort to manual methods or look for specialized scripts for a specific device.
Android Image Kitchen saves time by automatically detecting the format, but may not cope with unique or heavily modified firmware images.
Manual unpacking via unpackbootimg and the command line
For those who prefers complete control over the process or works in the Linuxenvironment, the utility unpackbootimg remains the gold standard. This tool is specifically designed to parse bootloader images created by the utility mkbootimg, which is standard for the ecosystem Android. Working with the console requires basic skills in navigating the file system and entering commands.
The process begins with compiling the utility from source code, if your repository does not have a ready-made binary file, or downloading a pre-compiled version. After placing the executable file in the same directory with the image, you need to open the terminal and execute the unpacking command, specifying the name of the input file and the desired output directory.
./unpackbootimg -i boot.img -o output_folderExecution of this command will lead to the creation of a folder output_folder, which will contain separately extracted components: the kernel (kernel), the second stage of the bootloader (second), ramotisk (ramdisk) and kernel tags (dtb). Each of these files can be further analyzed or modified. For example, ramotisk often requires additional unpacking, since it itself is an archive cpiocompressed via gzip or lz4.
⚠️ Attention: When working with the command line, carefully monitor file access rights. Running scripts as a superuser (
root) can unnecessarily change the rights to the extracted files, which will complicate their subsequent packaging back.
If the standard utility cannot cope with the header format, which often happens on devices Sony or HTC, there are forks project unpackbootimg with support for specific offsets and structures. Using such versions requires knowledge of the exact device model and bootloader version in order to select the correct patch or repository branch.
☑️ Checking readiness for manual unpacking
Working with sparse images and SIMG2IMG conversion
Modern devices are increasingly using the sparse image mechanism (sparse images) to optimize space when transferring firmware over the air (OTA). Such files have an extension .img, but inside they contain metadata about empty blocks that do not take up physical space on the disk. An attempt to unpack such a file using standard methods will result in a structure error or receiving broken data.
To work with such files, you must first convert them to the "raw" format (raw image), using the utility simg2img. This app is included Android SDK Platform Tools or can be installed separately through package managers in Linux. Conversion restores the complete structure of the file system, making the image suitable for further mounting or unpacking.
The command for conversion is as follows and is executed in the terminal:
simg2img sparse_system.img raw_system.imgAfter successful execution, you will receive a file raw_system.imgthat can be opened through Android Image Kitchen or mounted in the operating room system. It is important to consider that the file size after conversion may increase significantly, since all empty blocks will be filled with zeros. Make sure there is enough free space on the disk before starting the process.
| Image type | File extension | Required tool | Complexity |
|---|---|---|---|
| Boot image | boot.img | unpackbootimg | Low |
| System partition | system.img | Android Image Kitchen | Medium |
| Sparse image | system_sparse.img | simg2img +.unpack | High |
| Recovery image | recovery.img | unpackbootimg | Low |
It is worth noting that some manufacturers use their own compression formats on top of standard sparse images. In such cases, an additional stage of decompression may be required using utilities like lpunpack to work with dynamic partitions implemented in Android 10 and newer.
What are dynamic partitions?
Starting with Android 10, Google has implemented the system dynamic partitions, which allows you to resize system volumes without re-partitioning the disk. This complicates the unpacking process, requiring the use of the lpunpack utility before standard extraction.
Extracting contents from Ramdisk and the kernel
After successfully unpacking the main container, you will often find a file ramdisk.cpio.gz or similar inside. Ramdisk is a temporary file system loaded into RAM when the device starts, containing critical initialization scripts and drivers. Its modification allows you to change boot parameters, access rights, or implement root access at an early stage.
To extract files from a ramdisk in the environment Linux it is most convenient to use the built-in capabilities of the utility cpio. The file must first be decompressed if it is compressed, and then the data stream must be passed to the extract command. This process requires caution, since violation of the access rights structure (chmod, chown) inside the ramdisk can lead to a bootloop of the device.
gunzip -c ramdisk.cpio.gz | cpio -idmvIn the environment Windows for these purposes, Android Image Kitchenis again suitable, which automatically recognizes nested archives and unpacks them into a separate folder ramdisk. Inside you will find scripts init.rcthat control the launch of services. Editing these files requires an understanding of the syntax init language and the consequences of each change for the boot process Android.
⚠️ Warning: Changing files in the ramdisk without preserving the original permissions and SELinux context is guaranteed to make the system unable to boot. Always make a backup before editing.
The kernel (kernel) extracted from the image is usually a compressed binary file. Its direct editing is impossible without disassembling and reassembling, which is a task for experts at the level of kernel developers. However, it can be replaced with a custom kernel with support for overclocking or additional drivers if the architecture and version are the same.
The ramdisk contains critical initialization scripts; any change in access rights inside it can turn the device into a “brick.”
Reassembly and data integrity check
After making all the necessary changes to the firmware files, the reverse assembly stage begins. This process is no less important than unpacking, as it requires strict adherence to the heading structure and block order. To build boot images, a utility is used mkbootimg, which takes as arguments the path to the kernel, ramdisk and memory addressing parameters.
If you used Android Image Kitchen, the process is simplified by clicking the "Repack" button, but manual assembly gives more flexibility. You will need to know the base memory addresses (--base), the kernel address (--kernel_offset) and other parameters that can be found from the unpacking log or the device specification. A mismatch between these addresses will result in the bootloader refusing to accept the new image.
The final step is to verify the signature and integrity of the assembled image. Some devices require a cryptographic signature of the firmware, without which the mode fastboot will refuse to execute the firmware command. In such cases, it is necessary to use tools for signing images or disable signature verification in the bootloader, which is only possible on unlocked devices.
- ✅ Check the size of the assembled image - it should not exceed the size of the original memory partition.
- ✅ Check the checksum (MD5/SHA1) with the expected values, if known.
- ✅ Test the image on an emulator or a spare device before installing it on your main smartphone.
Remember that tool interfaces and compression methods may change with the release of new versions Android. Always check the latest build parameters for your specific OS version in the developer documentation or on specialized forums.
Use a hex editor utility to check the first bytes of the assembled image. The title should begin with magic numbers corresponding to the type of image (for example, ANDROID! for boot.img).
Is it possible to unpack the firmware on a smartphone without a computer?
Theoretically, this is possible using applications like Termux and unpacking packages installed inside, but the process is extremely inconvenient and is risky due to limited resources and the lack of a full-fledged file system for working with temporary files.
What to do if the "Unknown magic" error occurs during unpacking?
This error means that the utility did not recognize the file header. Most likely, the file is in the manufacturer's proprietary format or is corrupted. Try using other tools or finding a dump for a specific device model.
Is it safe to edit system.img files?
Editing system files carries a high risk. An error may void your warranty, prevent OTA updates from working, or cause your device to become completely inoperable. Always have a working dump of stock firmware on hand for recovery.
Why do you need to convert sparse img to raw img?
Sparse images contain only useful data, skipping empty blocks. Standard unpacking tools cannot work with such a structure on the fly, so preliminary conversion into a continuous data stream is required.