h1. How to backup the EFS

h1. Introduction

Many devices supported by Replicant have a partition with the modem data (IMEI, etc) which is called EFS.

It's a good idea to do a backup of this partition, to make it easier to restore it if it becomes corrupted, as "it can sometimes happen with Replicant":https://redmine.replicant.us/issues/1869.

Only the following devices that are supported by Replicant have a modem data partition (EFS):
* Galaxy S 2 (I9100)
* Galaxy S 3 (I9300)
* Galaxy S 3 4G (I9305)
* Galaxy Nexus (I9250)
* Galaxy Note (N7000)
* Galaxy Note 2 (N7100)
* Galaxy Tab 2 7.0 (P3100)
* Galaxy Tab 2 10.1 (P5100)
* Galaxy Note 8.0 (N5100)

If you have a device that is not mentioned in the list above, it most probably doesn't have a modem data partition, so you don't need to make a backup.

h2. Instructions

First make sure that you have adb setup correctly and that it gives you a root shell on the device by following the wiki page that explains how to [[ADB|install adb and get a root shell]] on your device.

Once this is done you can then backup the EFS.

For the Galaxy SIII (I9300), run the following commands to do that:
<pre>
mkdir backup_efs
cd backup_efs
adb pull /efs/ efs
adb shell "cat /dev/block/platform/*/by-name/EFS" > EFS.img 
</pre>

For the Galaxy Nexus (I9250), run the following commands to do that:
<pre>
mkdir backup_efs
cd backup_efs
adb pull /factory/ factory
adb shell "cat /dev/block/platform/*/*/by-name/efs" > efs.img 
</pre>


This will create a copy of the contents of /efs in the backup_efs directory. It will also backup the full partition.
Keep these files around as a backup in case anything goes wrong.