Check what Debian version you are running on your Linux system

The easiest way on how to check what Debian version you are running is to simply read a content of /etc/issue file. Example:

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

However, the above command may not show the current Debian update point releases. Thus you may get more accurate info with the following command:

root@debian:~# cat /etc/debian_version
7.7

An alternative way is by use of lsb_release command. This command may be missing by default so you may need to install it first:

# apt-get install lsb-release

Once you install the above package run the following command to see what debian version you are running on your debian box:

# lsb_release -da
No LSB modules are available.
Distributor ID: Debian
Description: Debian GNU/Linux 7.7 (wheezy)
Release: 7.7
Codename: wheezy

For systemd debian version you may also use hostnamectl:

# hostnamectl 
   Static hostname: debian
         Icon name: computer-vm
           Chassis: vm
        Machine ID: 4c983dae19f6403ca2c555c3867beb14
           Boot ID: 3b399eb976d04569a8514a1d666a4d81
    Virtualization: oracle
  Operating System: Debian GNU/Linux 8 (jessie)
            Kernel: Linux 3.16.0-4-amd64
      Architecture: x86-64

https://linuxconfig.org/check-what-debian-version-you-are-running-on-your-linux-system