Find the Ubuntu Version installed from terminal

From terminal type

lsb_release -a

It shows up information like

No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.2 LTS
Release: 16.04
Codename: xenial

If  you type

lsb_release -cs 

The sub-command prints specifically name of your Ubuntu version, like xenial or trusty.

Smooth!