We all knew today was going to be a jam packed day with Ubuntu news for the Nexus devices so let’s keep it going with installation instructions for your beloved Samsung Galaxy Nexus. If you’re new to the whole flashing, rooting and hacking process I suggest you sit this one out until the devs have worked out the kinks and make this as easy as possible for everyone. For those of you ready to take the plunge read on!
These instructions were posted by Lesicnik1 over at XDA -
1. Nandroid backup
2. Factory Reset
3. Grab quantal-preinstalled-armel+maguro.zip (MD5: e4c9c5601019ec7ce24f43f317361982) and quantal-preinstalled-phablet-armhf.zip from here: http://nexfiles.kjonigsen.net/ubuntu/
If those links are down, use this one to download the needed files: http://cdimage.ubuntu.com/ubuntu-tou…ntal/mwc-demo/
4. Flash quantal-preinstalled-armel+maguro.zip
5. Flash quantal-preinstalled-phablet-armhf.zip (this one will take a while, grab some coffee 
)
6. Reboot (screen will go black but after a few seconds Ubuntu is up)
7. Profit 
This install didn’t wiped my sdcard. I just restored my TWRP backup after a short Ubuntu testdrive.
If you are paranoid, just copy your stuf from SDCARD to your PC before flashing.
As always folks! Flash at your own risk! And READ, READ and READ more if you have any doubts or questions.
I will be running Ubuntu on the Galaxy Nexus, Nexus 7 and Nexus 10 for a week on each device. At the end of the 7 days I will give a full review of my experience using Ubuntu as my daily driver. So stay tuned folks!