Ok, sometimes after some kind of flashing error/corruption, you end up with your Samsung S4 mini LTE (GT-i9195) returning error E:failed to mount /efs (Invalid argument) in various recovery tool (TWRP and others).
If you check your /efs with a root level explorer, you will find out the folder is empty. Technically this cause my phone to : loose bluetooth pairing after turning it off or turning off bluetooth stack. Also cannot install Lollipop, stuck on the loop boot with Cyanogenmod or other updates.
Here is the fix for it :
– Flash TWRP recovery and root your device using recovery method by installing UPDATE-SuperSU-vX.XX.zip file.
– Install ADB on your computer.
– Boot your device into recovery mode (Vol Up+Home+Power).
– Connect your device to PC via USB cable wait until windows update the driver.
– In the recovery mode choose “Mount /System”
– Open ADB command window and type the following command (from windows command line, from the folder ADB is installed into):
mount -w -t ext4 /dev/block/mmcblk0p10
These instructions are quite similar to what you find around on Internet with S3, however here please note that the block is the N°10, different from the instructions you find googlig around. At this stage the phone should reboot itself.
If you encounter some « can’t mount /fstab » error, this is because you have NOT applied correctly the root UPDATE-Super-SU patch on the device.
By following the above command, it will create a generic EFS files on your device. Your IMEI number will NOT be changed or reset, as this is stored in a different place on a Samsung GT-i9195 (on the p11 and p12 blocks apparently).
Reboot, and voilà you should not hit this /efs folder issue anymore, and if you browse the /efs folder, you should now see something with folders named « drm », « imei » « lost+found » and « wifi ».