[OnePlus 5 Guides, News, & Discussion] shadowstep:
Introduction

Hello everyone! In the past few days, I was approached by a few people wanting to know the steps I take to successfully flash a ROM as a secondary ROM in MultiROM. Since there seems to be many people interested in trying out new ROMs while still keeping their daily-driver primary ROM untouched, I decided to make this thread for those interested. The following is a tutorial to modify a TWRP flashable ROM zip to make it compatible with MultiROM and then flashing it as a secondary ROM. Let's get straight to it then!

Compatibility

Device(s)

OnePlus 5

ROM(s)

Mostly All ROMs (in theory, at least, hence mostly)

Android Version(s)

Android Nougat 7.x.x

Android Oreo 8.x.x

Prerequisites

Basic knowledge about TWRP flashing, fastboot flashing, zip editing, MultiROM usage, etc.

A working fastboot interface on your computer

Zip-editor installed on your computer (I prefer Bandizip)

Unlocked bootloader (how-to guide here)

Unencrypted/decrypted system (how-to guide here)

Steps To Follow

Step 1: Create a new folder on desktop (or wherever you prefer) and download the following stuff in it:

The flashable ROM zip that you wish to modify to use a secondary ROM in MultiROM

update-binary.zip (attached at the end of this post)

The latest MultiROM recovery and MultiROM zip (available here)

An updated copy of the latest SuperSU (available here)

Step 2: Extract the update-binary.zip file after which you will get the modified update-binary file that we have to use

Step 3: Open the downloaded ROM zip in the zip program that you use and inside it, navigate to META-INF\com\google\android

Step 4: Delete the existing update-binary that you see there and replace it with the update-binary that you extracted in step 2

Step 5: Save the modified zip (this is now the modified ROM zip that can be flashed as a secondary ROM via MultiROM)

Step 6: Copy the modified ROM zip, the SuperSU zip and the MultiROM zip that you downloaded in step 1 to your phone's internal storage

Step 7: Reboot your phone to the bootloader mode and connect it to your computer

Step 8: Open command prompt and navigate to the folder where you've downloaded the MultiROM TWRP image file

Step 8: Run the following command to flash MultiROM TWRP to your phone's recovery partition:

fastboot flash recovery TWRP_multirom_cheeseburger_20170919-03.img

Step 10: Once the flashing is successful, reboot to the bootloader mode again using the command:

fastboot reboot-bootloader

Step 11: Press the volume down button until you see "Recovery mode" on your phone's screen and then press the power button to boot to recovery

Step 12: Once you're in the recovery mode (running MultiROM TWRP), flash the MultiROM zip first and then reboot your phone to recovery

Step 13: Once the phone has rebooted to the recovery mode, open the MultiROM menu (three parallel horizontal lines on the top right of your phone's screen) and click on the "Add ROM" option

Step 14: Select the modified ROM zip and flash it (choose the "internal memory" option if it prompts for a partition to flash the secondary ROM in)

Step 15: Once done, hit back to open the MultiROM menu, then click on the "List ROMs" option and select the ROM that you just installed

Step 16: Once you select the ROM that you just installed, select the "Install Zip" option and flash the SuperSU zip

Step 17: Once the SuperSU zip is flashed, reboot your phone to system and you will notice a new selection menu is now displayed before the phone boots into the system

Step 18: Select the new ROM that you just flashed as the secondary ROM to boot to it

Step 19: The phone will bootloop a couple of times - DON'T WORRY, THIS IS NORMAL AFTER FLASHING SUPERSU - and in between the reboots if you see the ROM selection menu appear again, just select the newly flashed ROM and let it continue

Step 20: It should boot into your secondary ROM after a couple of bootloops/reboots!

Disclaimers

You are doing this at your own risk. 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 are unsure of how to go about something. Also, please don't forget to make a full nandroid backup via TWRP in case anything goes wrong.

The above method works for me 99% of the time, but there are a few ROMs that I wasn't able to boot as secondary no matter what I tried. If a ROM doesn't boot as secondary for you using the tutorial above, I'll try my best to help you, but I may or may not succeed.

I haven't tried the above method with Magisk instead of SuperSU. If you wish to try, feel free to do so at your own risk.

Flashing of the secondary ROM will most probably corrupt your primary ROM's password/pin (if you have one setup). If you can't get into your primary ROM after flashing the secondary ROM using your password/pin, flash this zip in TWRP which will remove your lockscreen security settings (but won't touch your fingerprints, if you have any setup).

Thanks To

[MENTION=4139665]martinusbe[/MENTION] for adapting MultiROM (recovery, installer zip, manager application, uninstallation zip) to OnePlus 5

[MENTION=631273]Chainfire[/MENTION] for SUperSU and all the work he's ever done for the community

All of you guys for viewing this thread

Changelog

December 26, 2017 - Initial post

OP Update Information

Created: December 26, 2017

Last Updated: December 26, 2017