[OnePlus X General] Sachin7843:
OnePlus Team has finally rolled out long-awaited Marshmallow Update. This time, it isn't community build or beta, it is a STABLE update!

This post will guide you to upgrade from 2.2.2 to 3.1.2 for both non-rooted and rooted users.

Disclaimer:

* I am not responsible for bricked devices, dead SD cards,
* thermonuclear war, or you getting fired because the alarm app failed. Please
* do some research if you have any concerns about features included in this ROM
* before flashing it! YOU are choosing to make these modifications, and if
* you point the finger at me for messing up your device, I will laugh at you.

For non-rooted, unmodified system users (who haven't tinkered anything with the device's software):

1a. You must have received a notification to update to OOS 2.2.3

Download it, and hit reboot now! This will automatically install the update which will prepare your device to install MM update.

1b. If you haven't received the update notification for 2.2.3 then download it manually from here - https://goo.gl/NkZm2I

Place it in the root directory of Internal Storage (not inside any folder, just directly on Internal storage) and then enter recovery mode by turning off your phone and then pressing Power button + volume down button at the same time. Once you get into recovery, select Install from Internal Storage and the select your file and flash it!

Congratulations, now you are on OOS 2.2.3!

Download MM OOS 3.1.2 from here - http://s3.amazonaws.com/oxygenos.on...OTA_017_all_201609231354_e675a52db5a044e7.zip

and place it on your SD card again, like above, go to recovery and flash the file!

You are now on Official Oxygen OS 3.1.2 MM Update!

For rooted users, who have modified system:

1. Download the zip http://s3.amazonaws.com/oxygenos.on...OTA_017_all_201609231354_e675a52db5a044e7.zip and place it on your SD Card or Internal Storage

2. Go to your recovery (TWRP is preferred)

3. Wipe System, Data, Cache, and Dalvik Cache

4. Select Install and navigate to your file location, select your file and flash it!

5. Flash https://drive.google.com/file/d/0B4K5cvm1zdldcmZpc3RuVnRjUUE/view to get root access!

6. Reboot! Enjoy your MM Update!

(Optional) These are steps I followed for a safer install:

1. Took the whole backup of 2.2.2 from official TWRP

2. Flashed Whole 2.2.2 zip from here - http://downloads.oneplus.net/oneplus-x/oneplus_x_oxygenos_2.2.2/ which I had already downloaded

3. Flashed Stock Lollipop recovery

4. Unrooted my phone

5. Locked and unlocked my bootloader (don't know why I was getting locked bootloader error while flashing blu-spark twrp so did it)

6. Unrooted my phone

7. Flashed 3.1.2 zip from stock lollipop recovery

8. Flashed blu-spark TWRP using fastboot

9. Flashed modified SuperSU

10. Restored just data partition from my 2.2.2 backup and wiped cached.

This way is long and tedious but ensures you get the data, which was important for me.

Edit: Above process can be applied to install Oxygen OS 3.1.3 (link below) Directly! Hope you have a pleasant experience on Marshmallow, cause I'm definitely loving it :)

Feel free to ask any queries!

Useful Links: -

1. Stock Lollipop Recovery - https://s3.amazonaws.com/oxygenos.oneplus.net/OPX_recovery.img

2. Official TWRP Recovery - https://dl.twrp.me/onyx/

3. Blu Spark Recovery - http://xdaforums.com/devdb/project/dl/?id=20236

4. SuperSU for OOS 3.x.x - https://drive.google.com/file/d/0B4K5cvm1zdldcmZpc3RuVnRjUUE/view

5. Unbrick Guide - http://xdaforums.com/oneplus-x/general/guide-mega-unbrick-guide-hard-bricked-t3272108

6. Official Oxygen OS 3.1.2 link - http://s3.amazonaws.com/oxygenos.on...OTA_017_all_201609231354_e675a52db5a044e7.zip

7. SD Card Writable fix in MM - http://xdaforums.com/android/software/fix-extsd-fix-v1-0b-2016-01-18-t3296266

6. Official Oxygen OS 3.1.3 link - http://downloads.oneplus.net/oneplus-x/oneplus_x_oxygenos_3.1.3/

Credits: Joshwin Aranha, OnePlus Team, Google and everyone who I forgot to mention

Hit Thanks if this post helped you!