How to backup the EFS¶

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.

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.

Instructions¶

We will backup the modem partition from the Replicant recovery.

This is to make sure that the modem data partition is not being modified when we are doing the backup.

Enable root access through adb in Replicant¶

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 install adb and get a root shell on your device.

This will enable you to also be able to get a root shell in the recovery.

Reboot in the recovery¶

Once this is done you need to reboot in the Replicant recovery.

This is to make sure that the modem data partition is not being modified when we are doing the backup.

To do that:
1. Make sure that your device is booted under Replicant.
2. Press the power button until a menu appears
3. Press "Reboot"
4. Select "Recovery" and then press "ok"
5. The device will then reboot to the Replicant recovery

Enable root access through adb in the recovery¶

In the recovery:
1. Select Advanced
2. Select "Mount /system"

Backup the modem data partition on your computer¶

For the Galaxy SIII (I9300), run the following commands to do that:

mkdir backup_efs
cd backup_efs
adb pull /efs/ efs
adb shell "cat /dev/block/platform/*/by-name/EFS" > EFS.img 

For the Galaxy Nexus (I9250), run the following commands to do that:

mkdir backup_efs
cd backup_efs
adb pull /factory/ factory
adb shell "cat /dev/block/platform/*/*/by-name/efs" > efs.img 

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.