First to clarify
- Root directory
/ of Android devices is a read-only pseudo (temporary) filesystem (
rootfs) that lives in RAM and is vanished when device is powered off. When device is powered on, it's again extracted from
initramfs that lives in
boot partition along with kernel.
On newer devices with system-as-root,
system partition is mounted at root
/data directory is a mountpoint, where largest partition, usually named
userdata is mounted. This partition contains all user apps, their data (settings, databases, caches, temporary files etc.), system apps' data and all other configurations we make through
/data/media/0 is the directory that we see as
/storage/emulated/0 through emulation.
... there was a file in the /data directory which I need. Is it possible to create an image (.img or something similar) of the root directory ...
If a file is deleted from
/data, you need to create a dump of
data partition, not that of root directory.
You can do that in multiple ways described below. All require root access.
But first of all see this answer to make sure your data is recoverable.
In short, recovery is more or less possible only if (1):
- Your deleted data hasn't been
- And you haven't done a factory reset on encrypted
What you should do immediately:
- Switch off phone to make sure the deleted dats isn't overwritten.
- Don't install data recovery apps on device, it can do more harm than good.
- Mount the filesystem (if required) in recovery mode (or on PC) only with
FINDING BLOCK DEVICE:
In order to access
userdata partition, you need to find its block device. If you have root access, you can do so from mounted partitions:
~# mount | grep 'on /data'
/dev/block/mmcblk0p... on /data type f2fs (rw,nosuid,nodev,...)
On Qualcomm devices, it's located at
/dev/block/bootdevice/by-name/userdata (symlink). For MediaTek (
MTK) and other SoCs, the path is slightly different. You can find all block devices or
by-name directory using
~# find /dev -type b
~# find /dev -type d -name 'by-name'
Or by hit and trial:
~# ls -d /dev/*/by-name
~# ls -d /dev/*/*/by-name
~# ls -d /dev/*/*/*/by-name
Note: If your
/data partition has Full Disk Encryption (FDE) and you unencrypted it in recovery, DMCrypt will create block device at dev/block/dm-0. Use this instead of
CREATING PARTITION DUMP:
DISK DUMP (
Once the block device is known, you can use
dd command from:
- ADB shell (OS or custom recovery)
- A terminal emulator app like Termux
userdata partition is the largest partition (all other partitions hardly using 5GB out of total storage), you can't dump it to your internal memory. An external SD card with larger capacity is needed.
To create dump:
~# dd if=/dev/block/bootdevice/by-name/userdata of=/path/to/ext_sdcard/data.img
To prevent any data loss, recommended is to create dump when partition is not mounted i.e. in recovery mode.
If you don't want to use external SD card, you can also dump the partition directly to PC. First you need a working
adb setup, running as root. Then it can be used in multiple ways:
~$ adb exec-out dd if=/dev/block/bootdevice/by-name/userdata > data.img
* Make sure your
adb binary (on Windows or Linux) supports exec-out.
But you may end up with corrupted data when writing a whole large-sized partition to
STDOUT of terminal because there are issues with line break types (
STDERR could possibly be added to file if not directed to
/dev/null. See this question for reference.
To avoid unwanted characters, use
~$ adb shell 'stty raw && dd if=/dev/block/bootdevice/by-name/userdata' > data.img
But the most straightforward way is:
~$ adb pull /dev/block/bootdevice/by-name/userdata data.img
See this answer for more details.
USB MASS STORAGE (UMS)
This method is useful if you don't want to create a dump of partition, instead access partition directly on PC.
UMS is disabled by default on newer Android devices and only MTP is enabled. However you can enable that in custom recovery mode:
~# mountpoint /data && umount /data
~# echo '0' >/sys/class/android_usb/android0/enable
~# echo '/dev/block/bootdevice/by-name/userdata' >/sys/class/android_usb/android0/f_mass_storage/lun/file
~# echo 'mass_storage' >/sys/class/android_usb/android0/functions
~# echo '1' >/sys/class/android_usb/android0/enable
* Kernel should be built with
* Paths may vary depending on device
userdata will appear as a partition on Linux PC just as we connect a USB drive. If
/dev/sda is the hard disk drive, usually
/dev/sdb will be the
userdata partition. You can find that by using
~# blkid | grep userdata
/dev/sdb: PARTLABEL="userdata" PARTUUID="..."
You can run recovery progam directly on block device or mount the filesystem (if needed) or may also create a dump.
HOW TO RECOVER DATA?
There are basically two ways to recover deleted data as mentioned in this answer: carving method and through filesystem.
Recovery tools mostly don't need mounting filesystems but if it's required, it needs to be done on Linux PC because Windows doesn't support
f2fs natively, hence the tools aren't easily available AFAIK.
If anyone has been able to successfully make block/journal level access to Linux/Android filesystem for data recovery on Windows through Ext3Fsd or any other driver, let me know so that I can update the answer.
On Linux you can use tools like extundelete to recover data using filesystem journal:
~# extundelete --restore-all data.img
Or to recover data directly with UMS:
~# extundelete --restore-all /dev/sdb
Since you have done a factory reset which erases filesystem, consider carving method using tools like testdisk or
~# testdisk data.img
In the same way you can use any other data recovery tools.