The following are how to know the version of some popular Linux Distro:
UBUNTU: "lsb_release -a"
DEBIAN: "cat /etc/debian_version"
SLACKWARE: "cat /etc/slackware-version"
SUSE: "cat /etc/SuSE-release"
REDHAT: "cat /etc/redhat-release"
CENTOS: "cat /etc/redhat-release"
FEDORA: "cat /etc/fedora-release"
GENTOO: "cat /etc/gentoo-release"
Linux