How to install aircrack on Ubuntu 12.04 [duplicate]

If you want to install it from source (though Naveens's answer would be easier) you must install libnl-dev.

To install from source you need to install the -dev packages for every library that the program you are compiling uses. Whenever a program you are compiling asks for a library look it up in synaptic (if you don't have it run apt-get install synaptic as root) then select the library's -dev package, which contains the headers that the program needs to compile to the library.

How to install without compiling
Execute this command in your Terminal:

sudo apt-get update
sudo apt-get install aircrack-ng