Introduction: The Criticality of Live Android Filesystem Acquisition

In the realm of mobile forensics, debugging, and security analysis, the ability to perform a live acquisition of an Android device’s filesystem is paramount. While non-rooted devices present significant challenges due to security restrictions like Verified Boot and SELinux, a rooted Android device offers a gateway to its entire internal storage. This access is invaluable for extracting critical evidence, analyzing malware, or performing deep system diagnostics. This article delves into advanced techniques and best practices for conducting a full filesystem extraction from a rooted Android device, focusing on methods that ensure data integrity and minimize system alteration.

A “live acquisition” refers to the process of extracting data from a device while it is powered on and running its operating system. This contrasts with “deadbox” forensics, where data is acquired from a powered-off device, often by removing storage chips. Live acquisition is particularly relevant for Android due to its volatile nature, active processes, and potentially encrypted storage that can only be decrypted while the system is operational.

Prerequisites for a Successful Acquisition

Before embarking on the acquisition process, ensure you have the following:

• Rooted Android Device: The target device must be rooted. Methods vary widely (e.g., Magisk, SuperSU) and are beyond the scope of this article, but root access (via su command in ADB shell) is non-negotiable for full filesystem access.
• ADB (Android Debug Bridge) Setup: Ensure ADB is installed and configured on your host machine. The device should be connected via USB debugging and authorized.
• Sufficient Host Storage: The extracted data can be substantial (tens to hundreds of gigabytes). Ensure your host machine has ample free disk space.
• Basic Linux Command-Line Knowledge: Familiarity with commands like ls, mount, dd, tar, cat, and netcat is essential.
• Forensic Workstation (Recommended): A dedicated machine with appropriate tools and isolation for forensic tasks.

Understanding Android Filesystem Layouts

Android devices typically utilize an ext4 filesystem for user data (/data) and system partitions. Other common partitions include:

• /system: Contains the Android operating system, framework, and pre-installed applications. Usually read-only.
• /data: User data, installed apps, user settings, databases, and private application files. This is often the primary target for acquisition.
• /boot: Contains the kernel and ramdisk, essential for booting the device.
• /recovery: A separate bootable partition used for system updates, factory resets, and recovery operations.
• /cache: Temporary storage for system processes and app caches.
• /storage/emulated/0 (or /sdcard): The primary external storage path, often an emulated partition within /data.

To identify the block devices corresponding to these partitions, you can use the mount command or examine /proc/partitions or /dev/block/platform/*/by-name/ on the device.

adb shellsumountls -l /dev/block/platform/*/by-name

Look for entries like /dev/block/mmcblk0pXX or /dev/block/sdaXX corresponding to data or userdata.

Techniques for Live Filesystem Acquisition

1. Using adb pull (Limited Utility for Full Acquisition)

While adb pull is convenient for specific files or directories, it has significant limitations for a full filesystem acquisition:

• Permissions Issues: Even with root, adb pull runs as the shell user, which may not have read access to all system files, especially those protected by SELinux contexts.
• Open Files: It can fail on files currently open or locked by other processes.
• Metadata Loss: File attributes like permissions, ownership, and timestamps might not be preserved accurately, or their preservation depends on the host OS’s filesystem.
• Slow and Inefficient: Pulling thousands of small files individually is very inefficient.

# Example: Pulling a specific directory (less ideal for full acquisition)adb pull /data/data/com.example.app/databases ./app_db_backup/

For these reasons, adb pull is generally not recommended for a forensically sound, full filesystem dump.

2. Imaging Block Devices with dd via ADB Shell

The dd command is the gold standard for creating raw disk images. By piping its output over netcat or directly to a host file, you can create a byte-for-byte copy of a partition.

Method A: Direct to Host using dd and netcat

This method is highly effective for imaging entire partitions. It requires netcat (nc) to be available on both the Android device (often present in /system/bin or available via Magisk module) and the host machine.

On your host machine (e.g., Linux/macOS):

First, start a netcat listener. Ensure port 1234 (or any chosen port) is not blocked by a firewall.

# Start netcat listener on the host to receive the imagecb -l -p 1234 > data.img

On the Android device (via adb shell with su):

Identify the data partition’s block device. Let’s assume it’s /dev/block/mmcblk0p42 for this example (replace with your device’s actual partition!). Port forward the netcat connection, then execute dd.

# In a new terminal on your host, forward the portadb forward tcp:1234 tcp:1234# Now, on the adb shell (as root)su dd if=/dev/block/mmcblk0p42 | nc 127.0.0.1 1234

The dd command will read the raw partition data and pipe it through netcat to your host machine, which saves it as data.img. Repeat for other critical partitions like /system if necessary.

Method B: Imaging to Internal Storage then adb pull (Less Ideal)

You can also image to a file on the device’s internal storage first, then pull that file. This requires significant free space on the device and adds an extra step.

adb shellsu dd if=/dev/block/mmcblk0p42 of=/sdcard/data_partition.imgexitadb pull /sdcard/data_partition.img ./

This method is slower due to two write/read cycles on the device and is less forensically sound as it modifies the device’s storage by writing the image file.

3. Archiving Directories with tar via ADB Shell

The tar utility is excellent for archiving entire directory structures, preserving permissions, timestamps, and ownership. This is particularly useful for /data when you want a file-level backup rather than a raw block image (e.g., when the partition is already mounted and actively used).

On your host machine:

Start a netcat listener to receive the tarball:

nc -l -p 1235 > data_filesystem.tar

On the Android device (via adb shell with su):

Forward the port, then use tar to create an archive of the desired directory, piping it to netcat.

# In a new terminal on your host, forward the portadb forward tcp:1235 tcp:1235# On the adb shell (as root)su tar -cvf - /data 2>/dev/null | nc 127.0.0.1 1235

• -c: Create an archive.
• -v: Verbose output (can be removed for quieter operation).
• -f -: Write to standard output (stdout).
• /data: The directory to archive.
• 2>/dev/null: Redirects stderr (errors, warnings) to null, keeping stdout clean for netcat.

This method captures the files as they exist on the mounted filesystem, respecting file and directory structure, and metadata. It’s often preferred for /data when a file-level representation is needed.

Best Practices for Forensic Integrity

• Minimize Device Alterations: Every action taken on a live device can modify evidence. Use read-only tools where possible, and avoid writing to the device. The dd and tar pipe methods via netcat are excellent for this as they avoid intermediate files on the device.
• Document Everything: Record every command, its output, timestamps, and any observations about the device (battery level, network state, apps running).
• Calculate Hashes: After acquisition, compute cryptographic hashes (SHA256, MD5) of the acquired image or tarball. If possible, compute a hash of the source partition before acquisition (e.g., dd if=/dev/block/mmcblk0p42 bs=4M | md5sum and compare with hash of data.img). Note: Hashing a live, active partition will result in a different hash than the acquired image due to ongoing writes. Focus on verifying the transfer integrity.
• Working with Encrypted Devices: If the /data partition is FDE (Full Disk Encrypted) or FBE (File-Based Encrypted), a live acquisition (while the device is unlocked) is often the only way to get decrypted data. Once acquired, the data.img will contain decrypted data.
• Isolate the Device: Disconnect from networks (Wi-Fi, cellular) to prevent remote wipes or further data modification by active network connections.
• Time Synchronization: Ensure your host machine’s time is synchronized for accurate timestamping of acquired files.

Conclusion

Live acquisition of rooted Android filesystems is a powerful technique for mobile forensics and advanced debugging. While challenges exist, utilizing tools like dd and tar in conjunction with netcat provides robust and forensically sound methods for extracting complete filesystem images or archives. By adhering to best practices such as minimizing device alterations, thorough documentation, and integrity verification, investigators and analysts can ensure the reliability and admissibility of their acquired data. Mastering these techniques opens up a wealth of information previously locked away by Android’s security architecture, enabling deeper insights into device activity and data remnants.