Ever since Canonical announced and subsequently released the images and source for Ubuntu on the Nexus 7, all of us tinkerers have been looking for a way to get the operating systems dual booting. Now thanks to XDA developer Tasssadar this, and more, is possible. Not only can you boot into additional installs of Android and Linux but the system Tasssadar has developed also allows you to boot from a connected USB drive. Tasssadar’s thread can be found on XDA forums if you want to read more and see how others have progressed with this.
Performing the mod is a relatively simple affair: Flash a modified recovery, kernel and the MultiROM files. What is even more impressive is that your current ROM will continue to work unaffected (except for running the modded kernel).
For the purpose of this guide, I am assuming that you already have root, ‘adb’ and ‘fastboot’ installed and know how to access them on your machine. We will start by downloading the required files.
Now select the kernel that suits your current ROM.
Once you have downloaded all your files, copy the MultiROM zip and the kernel zip to your Nexus 7’s internal memory and then reboot to bootloader. If your ROM does not have this as an option on the power menu switch it off, and then powerback on holding the vol down button. Once the bootloader screen appears connect your N7 to your PC. Open a terminal (Linux) or a command prompt (windows) and navigate to the folder where you downloaded the above files and flash the modded recovery.
Fastboot flash recovery TWRP_multirom_n7_20121220-2.img
(remember and use sudo on Linux)
Once complete, use the volume buttons to navigate to recovery on the N7 and use power to select. Now flash the two files that were previously copied onto the tablet. In recovery press ‘Install’ and navigate to the multirom_v6_n7_signed.zip file and select it. Now press ‘Add More Zips’, select the modded kernel you copied and swipe to confirm the flash. Congratulations, you now have a multi-boot enabled Nexus 7. If you reboot the recovery and select ‘Advanced’ you will see a new option, ‘MultiROM’.
In the MultiROM menu you have five options:
- Add ROM – Add a new internal or external ROM.
- List ROMs – List and manage installed ROMs.
- Inject boot.imf file – Used to inject MultiROM to kernels supplied as boot.img files.
- Inject curr. boot sector – Used to re-inject MultiROM to the boot sector after a kernel update etc.
- Settings – Allows you to setup a default OS to boot into on power on and adjust the time delay before doing so.
When you enter the ‘Add ROM’ sub menu you need to select the correct settings for your flash. These are fairly simple to do, choose between Android or Ubuntu (use this option for Bodhi and Plasma Active as well) and internal or external. The ROM you are installing must be on the medium you are installing to, so if you are installing to an external USB drive, the ROM zip file must be located there.
To install a Linux distro you need to have the install in a .img.gz format. The download for Ubuntu 13.03 can be found here. The file you want will be the largest there (around the 560MB mark) and the description will include ‘preinstalled SD Card image’.
If you decide you want to use an external drive (possibly the most useful feature) then the drive can be formatted as EXT, NTFS or FAT32 (please note that a FAT32 partition is limited to 4096MB).
To remove the MultiROM feature and also any secondary ROM files is also a simple task. Secondary ROM files are located in /sdcard/multirom so simply remove this folder using a file manager. Now you need to flash your normal boot.img for your ROM, this will be located in the ROM .zip file so extract it and flash with the following command from either a Linux terminal or Windows command prompt.
fastboot flash boot boot.img
(again remembering sudo on Linux)
Now we have covered how to use MultiROM I suppose I should say a little on why you might wish to use it. For some people (like myself) there is a pleasure in pushing your hardware to do as much as possible and this certainly fits into that category. Others simply want functionality from their device. MultiROM allows you to keep your main ROM as is and still enjoy trying other ROMs or even operating systems. I mentioned how many folk wanted a dual boot system with Android and Ubuntu, this allows you that pleasure with out sacrificing your current working setup. By allowing you to boot from an external device you don’t even lose valuable storage space.