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How to extract, create or edit android adb backups

Android Software and Hacking General - xda-developers - forum.xda-developers.com
What is an android adb backup?

An adb backup is a file with ab extension, generated by android's backup manager when we request it via adb shell. This allows you to backup some data of the phone, but is not a replacement of a clockworkmod backup:

- Each application files may be backed up or not depending on its policies. In some cases, the apk itself is never backed up even if requested.

- Usually for restoring an application's data it requires you to have it installed first.

- Inside an ab file is a tar file, which contains files and folders in a certain order. You have you respect that order in order to create a valid tar file.

- Inside the tar file, directories must not have trailing slash, for that reason pax, star or equivalent has to be used.

- There are some bugs present in the android source code.

- 'adb backup' or 'adb restore' are pretty slow, no matter what computer or phone you have, because the android debugging bridge has a maximum internal speed of about 1 MBps. So, each gigabyte can take about 15 minutes to backup or restore.

You can use java or perl, although with perl can be more complicated because requires downloading some modules from cpan and some ssl headers.

To know more information about types of android backups:

[Guide Types of Android backups]

Software needed

The entire process can be done from Windows, but is better to use a unix-like operating system, like Linux, OS X or BSD, since we should extract the files on a filesystem that preservers file permissions and owners and repack the tar archive. Furthermore some tools like star are easier to get for linux. In such cases, using Virtualbox or VMWare Workstation is highly recommended. Using Windows should work in any case whatsoever.

Java 7 or higher

- Java 7 or OpenJDK 7 (more builds here)

- Oracle Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files 7 if you are going to work with password encrypted backups.

You need to install the files local_policy.jar and US_export_policy.jar under jre's lib/security folder, for example:

- For Windows:

- C:\Program Files\Java\jdk1.7.0_09\jre\lib\security\

- C:\Program Files\Java\jre7\lib\security\

- C:\Program Files (x86)\Java\jdk1.7.0_07\jre\lib\security\

- C:\Program Files (x86)\Java\jre7\lib\security\

- For Linux or BSD:

/usr/local/jdk1.7/jre/lib/security/

/usr/lib/jvm/java-7-openjdk-*/jre/lib/security/

/usr/local/openjdk7/jre/lib/security/

- For OS X:

- /Library/Java/JavaVirtualMachines/jdk1.7.0_09.jdk/Contents/Home/jre/lib/security/

Perl

- Perl is available for several operating systems

- libssl or openssl headers. If you are using Linux or Cygwin is much more easier

- cpan modules required by use functions

pax or star

pax is an archiving utility that compresses in ustar by default. In this case is extremely useful because stores directories without trailing slash. Is available for all operating systems, and in windows can be installed via cygwin's setup.exe or download a native version like gnuwin32 (sometimes available via bsdtar with pax option).

star allows storing directories without trailing slash. You can get the ubuntu version 1.5 here. There is no version of star for Windows or Cygwin, and other versions like tar, gtar or bsdtar don't implement the option. So, the only option is to user another operating system, installing it or running it from VMWare Workstation or Virtualbox, and share a folder. See here images.

Android Backup Extractor

Android Backup Extractor is the java application that does all the job. It includes the perl scripts.

How it works, better with an example

I will use an example to demonstrate how it works, with java version. If you like to use perl, just grab the perl scripts and is nearly the same.

This is extracted from the readme file, and will extract a whole adb backup and repack only the data for the game Grand Theft Auto III for android.

1) Convert the original adb backup to tar format:

Code:

java -jar abe.jar unpack nexus7.ab nexus7.tar <password>

2) Extract the contents of the tar archive. This should be done on a filesystem where the permissions of the files inside the tar are preserved, for example using linux, mac or bsd. Up to two folders may appear, apps and shared:

Code:

tar -xvf nexus7.tar

3) Make a list of all the contents of the original archive in the order they are archived:

Code:

tar -tf nexus7.tar > nexus7.list

4) Create a new list only with the files and folders you want, in proper order. For example for the GTA 3 (you can try savegames instead of all data):

Code:

cat nexus7.list | grep com.rockstar.gta3 > gta3.list

5) Create the new tar archive. The directories stored on tar shouldn't contain trailing slashes, so I use pax or star instead of tar:

Code:

cat gta.list | pax -wd > gta3.tar

OR

Code:

star -c -v -f gta3.tar -no-dirslash list=gta3.list

6) Create the adb backup from the tar archive. Password is optional:

Code:

java -jar abe.jar pack gta3.tar gta3.ab <password>

Note: if the backup is not encrypted zlib can be used instead for both unpack and pack the ab archive:

- Quick unpacking:

Code:

dd if=nexus7.ab bs=24 skip=1 | openssl zlib -d > nexus7.tar

- Quick packing:

Code:

dd if=nexus7.ab bs=24 count=1 of=gta3.ab ; openssl zlib -in gta3.tar >> gta3.ab

Links

Android Backup Extractor (@ Sourceforge)

Android Backup Extractor (@ GitHub)

Documentation at Blogspot

[Guide Types of Android backups]

Perl scripts to encrypt/decrypt adb backup files

[GUIDE Full Phone Backup without Unlock or Root]

Related adb backup and restore bugs:

Issue 28303: adb backup doesn't respect -noshared flag

Issue 32830: adb restore errors not displayed on device

Issue 34311: Galaxy Nexus gets stuck when restoring adb backup

Issue 25780: BackupManager causes reboot when BackupAgent missing
Date: Dec 26, 2012   


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