Firmware Android

Some users while installing a custom ROM, downgrade recovery or unlocking bootloader might lose the IMEI of   there devices and this will lead to losing network
This Guide will help you to make a backup of  the EFS partition for your galaxy S3
And if one day you lost/changed your device's IMEI or become NULL NULL, with this backup you will be able to restore it easily without any problem.

Requirements :
Rooted Samsung galaxy S3
Installed "KTool" app in your device (Link below)

Backing up instructions :
1- Open "KTool" app and accept the root permission
2- Press on "Backup EFS to /sdcard/efs.img"
(if you want press "yes" to verify the backup files)
3- Open "My files" then sdcard (you will find the backed up files)
Save the two files to your computer or upload it to the cloud
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Restoring instructions : (ONLY IF YOU LOST THE IMEI)
1- Copy "efs.img" and "efs.tar.gz" files to the internal storage
2- Open "KTool" app and accept the root permission
3- Choose "Restore EFS from backup (DANGEROUS!)"
4- Tap on "Restore IMG"
after it finished restart you device