Q: How can we check the current running linux version?
A: The following commands are somehow distro-specific which means they may not work on all linux distros, so try them all. The distros which the following commands are tested has mentioned.
Fedora, CentOS, Red Hat, Ubuntu
cat /etc/ issue
Mac OSX, Fedora, CentOS, Red Hat, Ubuntu
You can also access more data about the distribution you are using by the following command which works on Mac OSX, Fedora, CentOS, Red Hat and Ubuntu