[Device Reviews and Information] euroclie:
Hi all,

After a couple of days desperately waiting for a free slot in my schedule to apply the latest OTA upgrade, I decided to make the big jump today!

I was using the latest (05/17) version of the official MM ROM, so I did get the OTA notification, but since I had rooted my Ulefone Power, I knew it wouldn't be as simple as accepting the OTA update when prompted. I still downloaded the file (I have it around if someone need it, its a nice big 37.4 Mb file), but did nothing else... until this afternoon.

Here's what I did:

TL;DR;: unroot, OTA update, TWRP, systemless root

1) First, a full TRWP backup on the SD card, and I copied the file from the SD card to my PC, just in case. Backing up never hurts... ;)

2) Then, using SPFlashTool 5.1532, I reflashed the boot, recovery and system partitions:

* boot partition : probably not needed, I think that SuperSU in system mode doesn't change the boot partition.

* recovery partition : to erase TWRP

* system partition : to remove any trace of root in the system partition

I used the scatter file from the latest official MM ROM (05/17), in "Download only" mode, without any alteration except unchecking all the partition except boot, recovery and system. See attached screenshot.

3) After a successful reflash, I rebooted, waited for the application optimisation, and had a working, unrooted phone again.

4) I applied the OTA upgrade. The installation itself was quite fast (about five minutes), but on the following reboot I had again to wait for application optimisation, this time it took nearly half an hour.

5) Since I knew I'd need the zip files to get root again, once my phone was useable again I connected it to my computer via USB, and copied the xposed framework & supersu files on the phone. You'll need them once TWRP is installed.

6) I then used SPFlashTool again to reflash the latest TWRP from MegTheBest (thanks again, dude, impressive and essential piece of software!), still with SPFlashTool in "Download only" mode, this time using the scatter file from the TWRP bundle, so only the recovery partition is checked in the partition list.

7) On the next reboot, I forgot to boot first in Recovery Mode, which means that somehow during the normal boot the recovery partition was reset to normal... No big deal, I just reflashed TWRP a second time.

8) Once the TWRP recovery flash is completed, disconnect your phone from the computer, then boot in recovery (volume up + power buttons pressed until the menu appears). The menu is really tiny, you'll find a zoomed picture of it in the attached files. The first (top) menu item is "Recovery Mode", the second "Fastboot Mode", and the third "Normal Boot". Pressing the "Volume Up" key scrolls down one line (then loops to the first), and pressing the "Volume Down" key selects the mode which the arrow is pointing. Just make sure to select "Recovery Mode".

9) Once you're in TWRP, if you've chosen systemless root, keep the system partition read-only when prompted by TWRP. Normally, for a system root, you'd mount the system partition read-write to install superSU, otherwise your phone stays rooted only until the next boot, but in systemless root, it's the boot partition that gets changed, not the system partition, so you can keep that one read-only. The supposed benefit is that you might be able to use the next OTA update without having to unroot first, since the system partition will be "clean".

10) Install the latest SuperSU zip file. In my case, the file was BETA-SuperSU-v2.74-2-20160519174328.zip, but I'm pretty sure that by the time someone else reads this, there will be a new beta. Anyway, just make sure to download it from this XDA thread: http://xdaforums.com/apps/supersu/2014-09-02-supersu-v2-05-t2868133

A word of warning, though: this is beta software, so it's safe to consider that it's broken, and that if it works it's only temporary unless you're extremely lucky... 8)

11) The systemless root zip was installed without error message, so I wiped the cache/dalvik and rebooted the phone.

12) I needed a root-enabled application to test root, so I launched Titanium Backup. Initially it froze on a screen indicating it was trying to get root permission. It stayed frozen for quite some time (10/15 seconds?), so I pressed the "Home" button to exit the application, thinking that the root wasn't working, but just after going back to the launcher, the SuperSU permission request popup windows was displayed. I granted Titanium Backup the root permission, and after that everything was back to normal, root operations... :D

13) Rebooted to TWRP to install Xposed Framework (xposed-v85-sdk23-arm64 from this link: http://dl-xda.xposed.info/framework/sdk23/arm64/ ). The installation was quick and painless, and after reboot I launched Xposed Installer from the launcher, and updated GravityBox to the latest version (6.1.4, I was using 6.1.2 before).

Now I'm fully back in business! No error message yet, I'll post if I encounter any bug...

Bottom line: it's a bit long and boring, but if you're patient and careful, it is quite easy. I do expect some hicups in the future, using systemless root for the first time, but so far it seems to be working fine.

I hope this can help people who still hesitate to update to the latest OTA version because they're rooted!

Happy hacking to you all.