Hi and welcome to LQ.
FYI, there's no such thing as linux 6. I think you might be talking about Red Hat Enterprise Linux 6 or Debian 6. These are distributions (in short: distros)
Linux is the kernel of the system, which at the moment is at 2.6.39.2.
In the future, if you ask any question please kindly provide your distribution name and version.
Once again welcome to LQ and have fun.