[Galaxy S III Original Android Development] curiousrom:
EFS Partition Backup - No Service, No IMEI & No SIM Card Fix

EFS Partition Backup

[IMG="Belt & Suspenders"]https://i.imgur.com/6gyP1Zc.png[/IMG]

"Can't say I know what an EFI partition is..." - [MENTION=6705442]Simon_29[/MENTION] meant the EFS partition on our S3. It's crucial to your phone & if corrupted while messing around with ROMs & custom Recovery you get a beautiful brick so back it up.

"Efs partition contains: IMEI number, Mac address of Wireless devices, important files of internet and product code etc."

From this thread:

BACKGROUND: AKA "WHAT IS THE EFS AND WHY DO I EVEN CARE"

EFS stands for Encrypted File System. Imagine the EFS as a big folder containing all of the important stuff that makes the "phone" part of your phone (i.e. what lets you communicate from one person with a phone to another) tick. It contains your IMEI, lots of files revolving around your SIM card and Wifi/Bluetooth (this includes your MAC address for all the radios of your phone), and lots of other things that should never ever under any circumstance be deleted or touched. It's sensitive, it's devastatingly important, and it's a huge pain. If you lose your EFS folder, you lose pretty much any chance of your phone being able to use data, Wifi, Bluetooth, and (in my case) your phone will just not wanna respond and reboot quite a lot.

TWRP > Backup > select only EFS > Select Storage > to external Micro SD card (so it does not get erased when flashing a new ROM & Formatting Data) > Name: EFS_Backup (for example) > Swipe to Backup. (screenshots)

The EFS Partition backup folder created is small (5-10MB) so I copy it to computer also. TWRP creates efs.ext4.win, efs.ext4.win.sha2, efs.info & recovery.log files.

You can also create full Nandroid backups with TWRP including the EFS Partition but having an extra EFS specific small backup is a good thing IMO. Note: If you are restoring a full TWRP backup & you do not have any No Service, No IMEI & No SIM Card problems then do not restore EFS as per the principle: if it ain't broke, don't fix it!

Restoring your EFS partition backup using TWRP may fix a No Service or no SIM card or no IMEI problem:

TWRP > Restore > Select Storage (where your backup is located) > Select Package to Restore > Select Partitions to Restore > EFS (do not select Enable Digest) > Swipe to Restore. Reboot to System without doing anything else in TWRP.

If you are running LIneageOS or an other custom ROM and you have this problem and no EFS backup or no full backup from which to restore the EFS partition then install the S3 i9300 Samsung stock firmware 4.3 & if the SIM problem is solved then install TWRP recovery as described in that post & make a EFS partition backup before flashing LineageOS or an other ROM.

I also use the free Partitions Backup & Restore app (requires ROOT, screenshot) which creates efs_backup.img & efs_backup.tar.gz files. The app can also backup Radio (modem), Boot.img, etc. The current app version can only backup to internal memory on LineageOS so make sure to copy that backup to external SD card & computer.

With both belt & suspenders I figure I won't loose my pants. :good:

Edit 2020-10-11: A S5 G900V user reported here that he could not restore the EFS partition with TWRP 3.4 but could with TWRP 3.3.

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Cell Data Not Working & APN T-Mobile US

Oops, what is your exact S3 phone model number? Settings > About phone > Device model?

To rule out any mistakes & be 100% sure (if the motherboard was not changed): turn off the phone & look at the top left of the sticker under the battery.

This thread is about the Official LineageOS 14.1 version for the S3 GT-I9300 which does not support the 4G LTE band.

So my guess is either you tried the wrong version of LineageOS for your phone model or you have the wrong APN setting in LOS which could explain your no cellular data problem.

From this official T-Mobile APN Settings Support page: > Android APN settings > APN: Fast.t-mobile.com (for LTE devices) or epc.tmobile.com (for non-LTE devices).

Just curious: what is the exact name of that ArchiDroid. ROM & post a link to that thread if you can.

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