There are times debian or ubuntu users and admins want to find which version of debian and ubuntu linux version is running on their machines.This is very useful for those who is helping their customers and they want to know which version they are running and if you took over new system admin job you want to know which version is running on your servers or desktops.
Find or identify which version of Debian Linux you are running
This can be checked in /etc/debian_version file
Find or identify which version of ubuntu Linux you are running
You can find in different ways in ubuntu
The file /etc/issue holds the version of Ubuntu installed on your system