Normally you know which version of a given distro you are running if you are on your machine, but what if you are on a rented server, or a friend’s machine.

If you want to know which version of Debian or Ubuntu you are running, you can always check the /etc/apt/sources.list there you will see the version you are running but a better way is to run this on a terminal:

lsb_release -a

The output in my Debian Box is:

Distributor ID: Debian
Description:    Debian GNU/Linux 5.0 (lenny)
Release:        5.0
Codename:       lenny

You can also run this in a Debian Linux.

cat /etc/debian_version

In my Debian box this is the output:

5.0

I do not have an Ubuntu machine now, but I can remember that if you run this on an Ubuntu Linux, you will get

sid

As the output, as Ubuntu is based on Debian sid.