command to check Operating system version for CentOS and Ubuntu

Solution :

If you already know you’re running Ubuntu or CentOS but don’t know the version.

CentOS

To find the CentOS version, enter the following command in Terminal:

cat /etc/*release*

The following sample output shows you’re running CentOS 6.5 (you can ignore most of the output):

CentOS release 6.5 (Final)
LSB_VERSION=base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
cat: /etc/lsb-release.d: Is a directory
CentOS release 6.5 (Final)
CentOS release 6.5 (Final)

Ubuntu

To find the Ubuntu version, enter the following command in Terminal:

lsb_release -a

The following sample output shows you’re running Ubuntu 14:

No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 14.04.1 LTS
Release:        14.04
Codename:       trusty