How to check OS versions

For Redhat OS
Like centos ,fedora , debain etc.
#cat /etc/redhat-release
CloudLinux Server release 6.4

For Ubuntu OS
#cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=12.04
DISTRIB_CODENAME=precise
DISTRIB_DESCRIPTION="Ubuntu 12.04.2 LTS"