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EFS partition contains a lot of important data about your phone, such as WiFi/Bluetooth MACs, IMEI, others.
Its highly recommended to backup EFS partition if you own a Samsung galaxy S5. If one day your phones EFS partition is corrupted, your phones IMEI will be changed to "NULL NULL" and you will face "Not Registered On Network" problem and you wont be able to use your phone correctly.

This tool will allow you to backup the whole EFS partition of the galaxy S5 in one file, to restore at anytime and fix "Not Registered On Network" problem.

Requirements :

• Rooted Samsung galaxy S5
• Installed mobile USB driver or Samsung Kies on your PC.
• EFS backup/restore tool
• PC, USB cable

Steps :

• Download and extract EFS backup/restore tool
• Enable USB debugging, then Connect your phone to PC via USB cable
• Open the extracted "EFS_Backup_Restore" folder and double click on "EFS.bat"
  
• For LTE variant : choose option (1) to backup and option (2) to restore.
  (SM-G900A, SM-G900F, SM-G900M, SM-G900P, SM-G900R4, SM-G900T, SM-G900V, SM-G900W8).
• For SM-G900H : choose option (3) to backup and option (4) to restore.
• For SM-G906S, SM-G901F : choose option (5) to backup and option (6) to restore. 

Notes :

• This tool works only for rooted devices
• Make sure you choose the correct option for your device while restoring EFS partition.
• Make sure you have ALL backup files in the same directory of "EFS.bat" file while restoring.
• Backup files will be saved in the same folder of *.bat file
• Use this tool at your own risk.

Downloads :

• Latest Samsung Mobile Driver HERE
• Latest Samsung Kies 2 HERE
• Latest Samsung Kies 3 HERE
• EFS Backup Restore tool HERE

Notes :
~ This process will not help if you didnt have a backup
~ The backup will be saved in the internal storage as "efs.img" and "efs.tar.gz"
~ KTool work only on Samsung galaxy S2/Note/Nexus/S3 (International I9300 - *NOT* US variants)
~ NEVER RESTORE IF YOU ALREADY DIDNT LOST THE IMEI
~ I am not responsible if something bad happened to your device (use this AT YOUR OWN RISK)

Downloads :
KTool app http://goo.gl/gcu66

IMEI is a unique identification number programmed onto your device and you can check the unique IMEI of your device by dialing *#06# or written on sticker under the battery. It is required in order to be correctly identified on a mobile network.
Without IMEI, you cannot make calls, send SMS or use mobile data.

EFS is a partition on the internal memory of your device which contain important data including the IMEI.
If the data in this partition gets corrupt, you will lose your IMEI

Requirements :
1. Samsung galaxy S4 device
2. "Android Terminal Emulator" app (Link below)

EFS Backing up Steps :
1. Open "Android Terminal Emulator" and type
Then enter
It will ask for root permission
Then enter
B.  For galaxy S4 all LTE and US variant Type :
Then enter

C.  For galaxy S3 all LTE and US variant Type :

dd if=/dev/block/mmcblk0p11 of=/sdcard/efs.img

dd if=/dev/block/mmcblk0p12 of=/sdcard/mod1.bin

dd if=/dev/block/mmcblk0p13 of=/sdcard/mod2.bin

Then enter

3. Backup the created files on your phones internal storage to your PC or the cloud.

EFS Restoring Steps :
1. Send the files (Step 3) to the internal storage of your device
2. Open "Android Terminal Emulator" and type :
Then enter
It will ask for root permission
3.A. For galaxy S4 GT-I9500 Type :
Then enter
B. For galaxy S4 all LTE and US variant Type :
Then enter

C. For galaxy S3 all LTE and US variant Type :

dd if=/sdcard/efs.img of=/dev/block/mmcblk0p11

dd if=/sdcard/mod1.bin of=/dev/block/mmcblk0p12

dd if=/sdcard/mod2.bin of=/dev/block/mmcblk0p13 

Then enter

4. Restart your device
Done !
Notes :
~ It wont delete your data
~ Make sure you choose the correct cmd in restoring process
~ This method will work only on ROOTED devices
~ Backing up EFS partition is highly recommended for users who use the custom Roms
~ Use it at your own risk
~ This method wont repair your device if you dont have a backup of the EFS partition, but you can to try this How to Fix "Not Registered on Network"/Wrong IMEI for Galaxy S3/S4/Note2
~ Every device has unique partition, so you cant use this if you have backup file from another device

Downloads :
Android Terminal Emulator App HERE