Check Debian version

There are a few ways to check what version of Debian or Debian-based Linux (Ubuntu, etc) that you are using.

cat /etc/debian_version

cat /etc/issue

lsb_release -a

This file may not be available.
cat /etc/lsb-release

Output will look like this

root@unknown_server:~# cat /etc/debian_version
7.5

root@unknown_server:~# cat /etc/issue
Debian GNU/Linux 7 \n \l

root@unknown_server:~# lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 7.5 (wheezy)
Release:        7.5
Codename:       wheezy