Wednesday, June 21, 2017

Tarballing Android files and partitions over adb

Some time back I was recovering a phone, and before I made something irreversible, I opted for a low-level backup. This copy of old data helped somewhat in migration of program configs to my next phone, too -- although changes between Android 4 and Android 6 did not make this an easy task, clobbering everything with security features ;)

Of course, this adventure required a lot of googling, and posting back as I learned, so I want to save as a cheat-sheet a solution I used:

Note that this was done using a Windows PC and corresponding tools and drivers, and the Linux side might have different caveats. And of course Android side was rooted, USB debugging allowed, busybox installed, etc. - thanks to a handy habit to do this early, while deploying a new phone.

So, a slightly edited copy of my post from SO follows:

First thing to note is that the adb shell generally sets up a text terminal (so can convert single end-of-line characters to CRLF, mangling binary data like partition images or TAR archives). While you can work around this in Unix/Linux versions of adb (e.g. add stty raw to your shelled command) or use some newer adb with exec-out option, on Windows it still writes CRLF to its output. The neat trick is to pass data through base64 encoding and decoding (binaries are available for Windows en-masse, google them). Also note that errors or verbose messages printed to stderr in shell end up on stdout of the adb shell program in the host system - so you want to discard those after inevitable initial experimentation.

Here goes (note that in command examples below, long command lines are wrapped for readability - you will need to unwrap them back while copy-pasting... not that my examples would match your phones exactly anyway):

adb shell "su -c 'cat /dev/block/mmcblk0p25 | base64' 2>/dev/null" \
  | base64 -d > s3-mmcblk0p25.img

Can be easily scripted by Windows cmd.exe shell to cover all the partitions (one can look the list up by ls -la /dev/block/ and/or by cat /proc/diskstats or by cat /proc/partitions), e.g.:

for /L %P in (1,1,25) do ..\platform-tools\adb shell \
  "su -c 'cat /dev/block/mmcblk0p%P | base64' 2>/dev/null" \
  | base64 -d > s3-mmcblk0p%P.img

(Note to use %%P in pre-created and saved CMD batch files, or %P in interactive shell).

Don't forget that there are also mmcblk0boot[01] partitions, and that the mmcblk0 overall contains all those partitions in a GPT wrapping, just like any other harddisk or impersonator of one :)

To estimate individual partition sizes, you can look at the output of:

fdisk -u -l /dev/block/mmcblk0*

Unfortunately, I did not quickly and easily manage to tar cf - mmcblkp0* and get the partition contents, so I could pipe it to e.g. 7z x -si and get the data out as multiple files in a portable one-liner as well.

To tar some files you can:

adb shell "su -c 'cd /mnt/data && tar czf - ./ | base64' \
  2>/dev/null" | base64 -d > s3-mmcblk0p25-userdata.tar.gz

Of course this solution is not perfect due to increase of transferal time by one third, but given that for recovery purposes grasping for any straws that can help is good enough... well... :) In any case, if I send a whole partition for export like this, I do not really care if it takes an hour vs hour and a half, as long as it reliably does the job. Also if, as some others have documented, the Windows variant of adb.exe does effectively always output CRLF separated text, there seems little we can do but abuse it with ASCII-friendly encapsulation. Alternately, adb exec-out might be the solution - but for some reason did not work well for me.

Hope this helps someone else, Jim Klimov

1 comment:

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