[ONE General] GRMrGecko:
This guide will help you install the unofficial builds of CyanogenMod 12 and other Lollipop builds.

Disclaimer: These builds are not official and are very much pre-alpha builds. While many people have little issues, you may have issues yourself and without some knowledge of ROMing, you may end up bricking your device.

I and the people who built the ROMs are not responsible for you bricking your device or losing data.

Installation

Backup: If you do not backup your device, you will lose everything!

Install Titanium Backup and choose Backup all user apps from the backup batch actions

[IMG="TB Batch Backup"]http://g.gec.im/87fbfa357557f1622b15935247cd4cb1.png[/IMG]

Titanium Backup requires that you are rooted to work. If you are not rooted, use a tool such as Helium.

Be sure to copy your backup to your computer just in-case the data in the "SD Card" partition gets deleted. Use Android File Transfer or ADB to do so.

Unlock Bootloader: If you did not root your device, you likely have not unlocked your bootloader and you will need to unlock your device using the guide here.

Recovery: You need to also make sure you have a custom recovery such as the TWRP recovery which an installation guide is also available here.

Downloads: If you have done all of the above, you are ready to begin the installation process.

First you need to download all these files to your device.

Google Apps from https://s.basketbuild.com/gapps

SuperSu from http://download.chainfire.eu/593/SuperSU/BETA-SuperSU-v2.19.zip (optional for root)

Next you need to get a copy of CM12, you can do so in the following 2 ways.

Download a lollipop ROM. Choose from one of these known to work ROMs, build your own ROM, or find a ROM from someone else you trust (if you find another good ROM, let me know).

https://www.reddit.com/r/oneplus/comments/2moqig/cm12_nonscheduled_builds_discussionupdate_thread/

http://xdaforums.com/oneplus-one/development/rom-cm12-daily-builds-gapps-t2937887

Build your own copy by following this guide http://xdaforums.com/oneplus-one/development/guide-building-lollipop-oneplus-one-t2947949

Flashing: This guide is using TWRP. If you have a guide for using ClockworkMod or another custom recovery, let me know.

1. Reboot into recovery, ether by adb reboot recovery in terminal or by holding down the volume down button as you reboot.

2. Go into wipe, and swipe to factory reset. This erases your data but should not erase the "SD Card" partition.

3. Go back home if it doesn't automatically do so.

4. Go into reboot then choose Recovery.

5. After reboot, choose install and select the Lollipop ROM you downloaded.

6. Swipe to confirm flash.

7. After successful flash, go back home and back into install and flash both Google Apps and SuperSu.

8. Reboot device to system and you should have Lollipop.

Restoring Backup: Now that you're on Lollipop, you will want all your app settings and apps back.

If you used the Titanium Backup option, install Titanium Backup, and choose Restore missing apps with data.

[IMG="TB Restore"]http://g.gec.im/4147f7c2ee37411f1da63ae056520c83.png[/IMG]

Common Issues

Slow Boot: The solution people have used was to remove GPS and location services. This means you will not be able to use any map program to navigate anywhere.

Using ES File Explorer, go to /System/priv-app and remove com.Qualcomm.location

NFC and Bluetooth: There was some earlier ROMs that had these issues, go to a more recent ROM.

Enable on screen keys and disable hardware keys: Follow this guide http://xdaforums.com/showthread.php?t=2032117 and flash this to disable the backlight on the buttons https://drive.google.com/file/d/0Byxnqyony5AybHFOeWJhMmczS09pd0JNaGFwWHFybHlYRmNJ/view credit [MENTION=1995532]sd65[/MENTION]

MultiROM: MultiROM does not support Lollipop as of right now. There has been success in installing Lollipop then using CM11(S) as a secondary ROM.

I will update this as I find other common issues.

Restore CM11S (Stock firmware)

Make sure you backup using the instructions above.

Download original firmware from https://cyngn.com/products/oneplusone/ and extract it.

In terminal, cd into the extracted folder.

On your phone, unplug it from your computer and hold down volume up and the power button until you see the fastboot icon, then connect to your computer and run the commands in the terminal window.

fastboot flash boot boot.img
fastboot flash system system.img

If you wish to flash the original recovery:

fastboot flash recovery recovery.img

You can also try following this guide if you trust their download.

Once you are restored, so long as you didn't flash userdata, you should still have your backup from Titanium Backup in the "SD Card".