Introduction to System-as-Root (SAR)

The System-as-Root (SAR) partition layout, introduced with Android 9 (Pie), fundamentally changed how the Android operating system is structured on devices. Unlike previous layouts where a dedicated system partition held the read-only OS components and the ramdisk was part of the boot partition (with /system mounted separately), SAR integrates the system.img directly into the ramdisk. This unified approach means the root filesystem is now served from the system_root, which is part of the boot image itself or a logical partition within a `super` partition. This design offers benefits like simplified A/B updates and improved security but introduces new complexities for forensic analysis and low-level development.

The Forensics Challenge of SAR

For developers and forensic analysts, SAR presents unique challenges. The traditional separation of boot and system partitions is blurred. The kernel, ramdisk, and system image are all bundled together, or the `system` image is treated as the initial root partition. This means that:

• There is no longer a distinct /system block device that can be directly mounted and analyzed in isolation.
• The root filesystem (/) is directly derived from the system.img contents within the `boot` image or a dynamic partition.
• Tools and techniques designed for older partition layouts often fail or provide incomplete results when confronted with SAR.
• `dm-verity` and full-disk encryption (FDE) or file-based encryption (FBE) are often tightly integrated, adding layers of protection that must be addressed.

Understanding how to correctly identify, extract, and analyze data from SAR layouts is crucial for advanced debugging, vulnerability research, and digital forensics.

Identifying a SAR Layout

Before proceeding with extraction, it’s essential to confirm if a device utilizes a SAR layout. Several indicators can help determine this:

1. Checking System Properties via ADB

The easiest way is to query system properties using ADB (Android Debug Bridge):

adb shell getprop ro.build.system_root_image

If the output is true, the device uses a SAR layout. If it’s empty or false, it likely uses a traditional or A/B non-SAR layout.

2. Analyzing the Filesystem Structure

Once you have an ADB shell, examine the root directory and the /system mount point:

adb shell ls -l /adb shell mount | grep ' /system '

In a SAR setup, /system will typically be a symlink to /system_root/system or similar, and the root directory (/) will contain traditional system directories like /bin, /etc, /sbin, etc., directly from the system image rather than separate partition mounts.

Methods for Data Extraction

Extracting data from a SAR device requires careful consideration of its state (live, recovery, or offline) and protection mechanisms.

1. Live Device Extraction (via ADB)

For a live, rooted device, you can use adb pull, but direct pulling of entire system trees can be slow or encounter permission issues. A more robust approach involves packaging the data on the device first:

adb shell "cd /system_root && tar -czvf /sdcard/system_root.tar.gz ."adb pull /sdcard/system_root.tar.gz .adb shell rm /sdcard/system_root.tar.gz

This command archives the entire /system_root directory (which effectively contains the system image) into a compressed tarball on the device’s internal storage, then pulls it to your host machine, and finally cleans up the temporary file.

2. Recovery Mode Extraction (via Custom Recovery like TWRP)

If you have access to a custom recovery, extraction becomes more straightforward as it bypasses the running Android OS’s restrictions.

1. Boot the device into TWRP recovery.
2. Connect your device to your computer via USB.
3. In TWRP, navigate to
   
   Android Mobile Specs & Compare Directory

   Are you researching mobile hardware properties, processor SoCs, GPU chipsets, or RAM configurations? Access our complete specs catalog to compare up to 5 devices side-by-side!

   Compare Devices Specs →