Solution x 1

As said in the official page, use:

lsb_release -a

Your version appears on the "Description" line.

If you want to check it through your desktop environment, you can check System Settings -> Details.

Solution x 2

cat /etc/*release

in my case produce the following output:

DISTRIB_ID=LinuxMint
DISTRIB_RELEASE=17.2
DISTRIB_CODENAME=rafaela
DISTRIB_DESCRIPTION="Linux Mint 17.2 Rafaela"
NAME="Ubuntu"
VERSION="14.04.3 LTS, Trusty Tahr"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 14.04.3 LTS"
VERSION_ID="14.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"

Reference

Original Link