64-bit: How do I determine whether I am already running a 64-bit Linux OS?

If you are trying to figure out whether you can run 64-bit Linux on your computer, see this post.

Whether you are running a 64-bit OS is easy to find. Just open a terminal window on your computer running Linux, and run the following command:

uname -m

If the output you get is i686, then you are running a 32-bit OS.
However, if the output is x86_64 or amd64, then you are running 64-bit Linux.

(This post assumes that you are running Linux on a x86-based machine. Never, ever, have I seen a general purpose computer running Linux on a non-x86 processor, though I know it works.)