What version is this Live CD / Live USB?

I often have a number of Live CDs sitting around (actually USBs) and I'm not always sure which version is which. Is there some quick way to find out the Ubuntu version I'm looking at? Perhaps a file I can look at on the CD, or some executable I can run or something?

There will be a hidden folder called .disk. So, if you are in Nautilus hit Ctrl + H to show hidden files.

Inside .disk there is a file called info which if you open, will tell you the Ubuntu version, including the architecture (32-bit or 64-bit).

A 'quick' way to find out the info is to open a terminal and type:

cat <mount-point-of-usb>/README.diskdefines

Replace <mount-point-of-usb> accordingly.

Look at dists/[release name]/Release. Here is an example of the head for Ubuntu 14.04:

Origin: Ubuntu
Label: Ubuntu
Suite: trusty
Version: 14.04
Codename: trusty
Date: Thu, 08 May 2014 14:19:09 UTC
Architectures: amd64 i386
Components: main restricted
Description: Ubuntu Trusty 14.04

At the root of your Live CD, there is a README.diskdefines file with the version of the distro in it. You can also check the dists folder.

The other answers were related to when you aren't running the live CD. If you are running it already, lsb_release -a shows this information like this:

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 14.04.3 LTS
Release:    14.04
Codename:   trusty