Developers often use uname -a to get the version of operating system.
Though 'uname -a' gives the system information it doesnt give the details about the Ubuntu version.
just type in command:
output looks like this:
No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 13.04 Release: 13.04 Codename: raring
As you can see in the output, it clearly provides the Ubuntu version in the description field.