There are a couple of ways to find the CentOS version from the command line. The most accurate way is to check the installed centos-release rpm another option would be to cat the contents of /etc/redhat-release (not recommended as any application could potentially change the contents of this file).

CentOS Version Command

The most accurate way to check the CentOS version:

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[root@li468-203 ~]# rpm -q centos-release
centos-release-6-3.el6.centos.9.i686

A far less reliable way of checking would be:

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[root@centos ~]# cat /etc/redhat-release
CentOS release 6.2 (Final)

Below is a video tutorial on how to find the CentOS version: