linux loves the nexus 7!
Yes there are linux ports for Android, but specifically for the Nexus 7 well that is a different story...
There are linux ports like debian linux, ubuntu linux, fedora linux, and arch linux that you can install with a very nice app called "complete linux installer" which can be downloaded from the google play store.
Now those versions of linux run on top of android in a chroot environment.
However, if you want a security based linux operating system then there is a really cool project going on right now called "kali pwnpad" which is based off of "PwnPad" from the great guys over at pwnie express -> https://www.pwnieexpress.com/penetra.../pwn-pad-2014/
Now if you are like me and don't have/want to spend $1,000+ dollars for a PwnPad tablet (basically a modified nexus 7 2013) then you can head over to the XDA thread for Kali PwnPad here -> http://forum.xda-developers.com/show....php?t=2577356
That thread will show you how to install Kali PwnPad on your Nexus 7 2013 tablet and you can go directly into Kali Linux (aka Backtrack Linux) through any of the apps which will put you into a chroot linux environment. A big bonus is you can use usb wifi devices or multiple usb devices with Kali PwnPad so you can use linux programs like, aircrack-ng, wifite, kismet, metasploit, openvas. social-engineering toolkit, and others!
That project is a lot of fun, and Kali PwnPad has just added bluetooth to its latest kernel so you can now use bluetooth usb devices for all of your bluetooth hacking needs. Devices like -> ubertooth-one, and the Parani-UD100
Also...don't be so quick to dispose of Ubuntu Touch. There is a lot of work being done with Ubuntu Touch for the Nexus 7 2013 and it is a lot of fun to use!
I hope this has been helpful. and if you have any questions on Kali PwnPad drop by thread and ask us a question!