Modifying the operating system Android often requires access to system files that are hidden from the average user. The key element of any firmware is the partition image systemcontaining libraries, applications and kernel settings. To make changes, add root access, or simply explore the contents, you need to unpack this image.
The process is not trivial, since device manufacturers use different compression formats and partition structures. Depending on the Android version and smartphone model, the file system.img can be packed in ext4, sparse or have a complex structure super. Understanding these differences is critical to successfully completing the operation without damaging data.
In this article, we will take a detailed look at the tools and methods that allow you to extract the contents of a system image. You will learn how to prepare a working environment, what utilities to use to convert formats, and how to avoid common mistakes that lead to a “bricked” device.
Preparing a working environment and tools
Before you start, you need to set up your computer, since mobile devices do not have enough power to process partition images. You will need a PC running Windows, Linux or macOS with sufficient free memory. It is recommended to have at least 10 GB of free disk space, since the unpacked image can take up a significant amount of space.
The main set of utilities is Android SDK Platform-Tools, which includes adb and fastboot. Without these components, interaction with the bootloader and debugging of the device is impossible. You will also need to install drivers for your specific smartphone so that the computer correctly recognizes the gadget in boot mode.
To directly work with file system images, you will need specialized utilities. In a Linux environment, these are standard tools like mount and unsparse, while Windows users will need third-party solutions such as UnpackImg or Simulator. It is critical to use a version of the utility that is compatible with Android version of your firmware, otherwise the directory structure may be broken.
⚠️ Attention: All manipulations with system images are performed at your own peril and risk. An error when mounting or writing a modified file can lead to loss of warranty and inoperability of the smartphone.
Before starting work, create a full backup of the current state of the device via TWRP or Fastboot, so that you can rollback in case of failure.
Analysis of the file structure system.img
Not every file with the extension .img can be opened with standard archiving tools. The file system.img often is an image of a block device rather than a simple archive. The first step is to determine the file system type and format for storing data inside the container.
There are several common formats. The most common ext4 is the standard file system for Linux and Android. However, manufacturers often use the format sparse (sparse image) to save space when flashing. Also, in modern devices with dynamic partitions, the data may be located inside an image super.imgthat requires preliminary extraction.
For analysis, you can use a utility file in the Linux terminal or specialized hex code viewers. If the utility reports the format Android sparse image, preliminary conversion to a raw image will be required. Ignoring this step will result in an error when attempting to mount or unpack.
- 📁 Raw Image: Full bitmap of the partition, ready to be mounted.
- 📦 Sparse Image: A compressed image that skips empty blocks requires conversion.
- 🗄️ Super Image: A container containing several logical partitions (system, product, vendor).
- 🔒 EROFS: Modern read-only file system used in new versions of Android.
Unpacking through the UnpackImg utility (Windows)
For operating system users Windows the most convenient solution is the tool UnpackImg. This utility has a graphical interface or works via the command line, automatically detecting the type of image and applying the desired unpacking algorithm. It supports working with sparse images and standard ext4.
The process begins by placing the file system.img in the folder with the executable file of the app. The launch occurs through the command line with administrator rights. The command usually looks simple: the name of the utility and the path to the file. The app will create a folder outwhere all system files will be extracted.
If automatic detection does not work, you can manually specify the image type. This is true for old firmware Samsung or LGthat used proprietary packaging formats. In such cases, it may be necessary to pre-process the file through img2simg or reverse conversion.
☑️ Checking readiness for unpacking
After the process is completed, you will have access to a full copy of the system partition. You will be able to view files, replace libraries .so or remove pre-installed software (bloatware). However, remember that simply copying the files back will not update the firmware - you will need to create a new image.
Method of mounting an image in Linux
Kernel-based operating systems Linux provide native capabilities for working with disk images. This method is considered the most reliable and transparent, as it allows you to use standard file system commands without third-party software. It is ideal for advanced users and developers.
The first step is to check whether the sparse image needs to be converted. If the file is compressed, it must be converted to raw format using the utility img2simg (for reverse conversion) or simg2img. The command is executed in the terminal and takes from several seconds to minutes depending on the file size.
simg2img system.img system_raw.imgAfter receiving the raw image, you need to create a mount point - an empty directory through which files will be accessed. Then the command is used mount indicating the file system type. Most often this is ext4, but for new devices it may be necessary erofs.
It is important to mount with superuser rights (sudo). After successful execution of the command, the contents of the image will become available in the specified folder as regular files. You can edit them, script changes and analyze the directory structure /bin, /lib and /etc.
⚠️ Attention: When running on Linux, make sure the image is not mounted read-only if you plan to make changes. Use the flag
-o rw, but be extremely careful with access rights.
What should you do if the mount fails?
If the mount command returns an error about an unknown file system type, the image may be encrypted or use a non-standard structure. Try updating the system kernel or using the FUSE utility for a custom mount.
Working with dynamic partitions and Super.img
Starting from Android 10, many manufacturers have switched to a dynamic partition scheme. In this architecture, individual images (system, product, system_ext) are combined into one large file super.img. It is impossible to unpack system directly from such a container without first extracting it.
To work with super.img use the utility lpunpackincluded in the Android SDK. It allows you to divide a single image into logical parts. The process requires specifying the specific partition you want to extract, for example system_a or system_b depending on the device slot.
| Image Type | Tool | Complexity | Features |
|---|---|---|---|
| system.img (ext4) | mount / UnpackImg | Low | Standard format, easy to mount |
| system.img (sparse) | simg2img | Medium | Requires conversion to raw before work |
| super.img | lpunpack | High | Contains several sections, sampling is required |
| dat.img / dat.br | Broli / Brotli | High | Strong compression, often used in OTA |
After extracting the desired piece from the super-image, you get a normal one system.img, which can be worked with using the methods described above. This step adds an extra operation, but is mandatory for modern smartphones Pixel, Xiaomi and Samsung.
For devices with dynamic partitions, always use lpunpack to extract the system first, otherwise the unpacking tools will not see the file system.
Reassembling and flashing the modified image
Making changes is only half the task. For the modifications to take effect, you need to pack the files back into the image format and write them to the device memory. Simply copying files to the phone is not enough, since the bootloader expects a strictly defined block structure.
For reverse conversion in Windows, use the utility mkuserimg_mke2fs or the functions of itself UnpackImgif they support repacking. In Linux, you can use the command mke2fs with parameters identical to the original image (block size, number of inodes). Failure to comply with the parameters will result in a bootloop error.
If you worked with a sparse image, after creating the raw image you need to compress it again using the utility img2simg. This will reduce the file size and speed up the flashing process via fastboot. The final stage is writing the image to the system partition with the command fastboot flash system system_new.img.
- 🔄 Conversion: Converting the folder with files into a raw image.
- 📉 Compression: Optional creation of a sparse image to save space.
- 🚀 Recording: Sending data to the phone via Fastboot mode.
- ✅ Verification: Checking checksums after recording.
⚠️ Attention: Interfaces of unpacking apps and image format may change with the release of new versions Android. Always check the current command parameters in the official documentation for the SDK or on the developer forums (XDA).
Is it possible to update the system after modifying system.img?
After manually replacing system files, the standard OTA update will most likely not be installed due to a violation of the integrity of the partition. You will need to reflash the device with a full firmware dump.
Frequent errors and ways to solve them
During the process of unpacking and modification, users often encounter technical problems. One of the most common is the “Permission denied” error when mounting in Linux. This can be solved by launching a terminal as root or checking the access rights to the image file.
Another common problem is the image size mismatch. If you create a new image that is larger than the original partition, writing via fastboot will fail. It is necessary to strictly ensure that the resulting file does not exceed the partition limits specified in the partition table (partition_table.xml).
It is also possible that the file system can be damaged if unmounted incorrectly. Always use the command umount before closing the terminal or turning off the computer. Ignoring this rule may lead to the image becoming unreadable and requiring re-extracting from the original.
Use the e2fsck utility to check the integrity of the ext4 image before mounting. This will help identify errors early and avoid recording failures.
Is it possible to extract system.img without a computer?
Theoretically, this is possible using terminal applications on a rooted device (for example, Termux), but the process is extremely complex, slow and requires the presence of all the utilities (simg2img, mount) inside Android. For stable operation, it is strongly recommended to use a PC.
What is the difference between system.img and boot.img?
system.img contains the file system with Android applications and libraries, and boot.img contains the Linux kernel (kernel) and ramdisk, necessary to start the system. They are unpacked using different tools and modifying boot.img requires knowledge about assembling kernels.
Is it safe to edit files inside system.img?
Editing system files carries risks. Deleting critical libraries or changing access rights can lead to an endless reboot of the phone. before making any changes.
Why does the UnpackImg utility give an error when opening a file?
Most often this is due to the fact that the file is a sparse image or encrypted. Try converting it first using simg2img or make sure that you are using the latest version of the utility that supports your version of Android.
Do you need to unlock the bootloader for unpacking?
For the unpacking procedure on the computer itself, unlocking the bootloader is not required. However, to write the modified image back to the phone, an unlocked bootloader is required, otherwise fastboot will reject the write command.