One of the primary reasons I use Ubuntu is to crack wireless networks whenever I get the opportunity. I recently moved to Ubuntu 12.04 and found that aircrack-ng was NOT in the repository.
In the process of compiling aircrack-ng from source, I hit a lot of errors mostly to do with a variable called –Werror. This is what you need to do to compile aircrack-ng without the pesky errors.
sudo apt-get install build-essential
sudo apt-get install libssl-dev
tar -zxvf aircrack-ng-1.1.tar.gz