#MultiROM for Nexus 7 MultiROM is multi-boot solution for Nexus 7. It can boot android ROM while keeping the one in internal memory intact or boot Ubuntu without formating the whole device. MultiROM can boot either from internal memory of the device or from USB flash drive.
More info in the XDA thread: http://forum.xda-developers.com/showthread.php?t=2011403
###Build
Clone repo to some folder inside Android 4.1.x source tree, I use /system/extras/multirom. Then just
. build/envsetup.h
lunch full_grouper-userdebug
make multirom trampoline -j4