if you want to get your operating system relase you have 2 ways to do that:
First: you can run the following command:
# lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 13.04 Release: 13.04 Codename: raring
Or you can cat the following file:
# lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 13.04 Release: 13.04 Codename: raring
the previous steps tested on LINUX UBUTNU