Using MultiROM - 走看看

MultiROM is capable of installing:

Android Primary ROMs (internal)
Android Secondary ROMs
Alternative Linux-based operating systems
Ubuntu Touch
ROMs on USB Drives (Supported devices only)

The instructions below are just general guides. Your device may differ, so check the device guides in the sidebar first.

Install Primary ROM (Internal)

You can still update and install your primary Android ROM as usual, with just one added step:

Boot to TWRP recovery.
Flash ROM's ZIP file as usual.
Run a factory reset if needed (it won't erase secondary ROMs).
Go to Advanced -> MultiROM in recovery and run Inject curr. boot sector.

(Editor's note: check if newer MultiROM versions do this automatically)

Installing Android Secondary ROMs

All devices support installing secondary Android ROMs. You can install as many as you'd like, as long as there is enough space. Typical Android 4.2 installations need more than 700 MB.

Make sure you have enough space.
Go to TWRP recovery, select Advanced -> MultiROM -> Add ROM.
Select the ROM's zip file and confirm.
Your secondary ROM will be installed. Now reboot, and you can use the MultiROM bootloader to load your secondary ROM.

Installing Alternative Operating Systems

Note: Ubuntu Touch has its own unique installation method, found in the next section.

If your device supports alternative Linux-based operating systems, you can also install them using MultiROM. That way, you can switch back to Android whenever you need to.

(FIXME: needs instructions)

Installing Ubuntu Touch

Ubuntu Touch requires 2.5 GB or at least 5% free space on your flash drive after installation.

Ubuntu touch installation can be done only via the MultiROM Manager Android app, all other methods are deprecated.

Installing to a USB drive (Supported devices only)

During installation, recovery lets you select install location. Plug in the USB drive, wait a while and press "refresh" so that it shows partitions on the USB drive. You just select the location (extX, NTFS and FAT32 partitions are supported) and proceed with the installation.

If you wanna use other than default FAT32 partition, just format it in PC. If you don't know how/don't know where to find out how, you probably should not try installing MultiROM.

If you are installing to NTFS or FAT32 partition, recovery asks you to set image size for all the partitions - this cannot be easilly changed afterward, so choose carefully. FAT32 is limited to maximum of 4095MB per image - it is limitation of the filesystem, I can do nothing about that.

Installation to USB drives takes a bit longer, because the flash drive is (usually) slower and it needs to create the images, so installation of Ubuntu to 4Gb image on my pretty fast USB drive takes about 20 minutes.

Enumerating USB drive can take a while in MultiROM menu, so when you press the "USB" button in MultiROM, wait a while (max. 30-45s) until it searches the USB drive. It does it by itself, no need to press something, just wait.

Uninstalling MultiROM

You will need to flash an uninstaller zip file in your custom recovery to get rid of MultiROM. This can be found in your device's guide in the sidebar.

You could also reflash TWRP recovery with an ordinary custom recovery, but there's no need to, since TWRP will work normally without MultiROM.