I'd just like to interject for a moment. What you're refering to as Linux, is in fact, GNU/Linux, or as I've recently taken to calling it, GNU plus Linux. Linux is not an operating system unto itself, but rather another free component of a fully functioning GNU system made useful by the GNU corelibs, shell utilities and vital system components comprising a full OS as defined by POSIX.
Many computer users run a modified version of the GNU system every day, without realizing it. Through a peculiar turn of events, the version of GNU which is widely used today is often called Linux, and many of its users are not aware that it is basically the GNU system, developed by the GNU Project.
There really is a Linux, and these people are using it, but it is just a part of the system they use. Linux is the kernel: the program in the system that allocates the machine's resources to the other programs that you run. The kernel is an essential part of an operating system, but useless by itself; it can only function in the context of a complete operating system. Linux is normally used in combination with the GNU operating system: the whole system is basically GNU with Linux added, or GNU/Linux. All the so-called Linux distributions are really distributions of GNU/Linux!
I'd just wike to intewject fow a moment. What you'we wefewing to as Linux, is in fact, GNU/Linux, ow as I've wecentwy taken to cawwing it, GNU pwus Linux. Linux is not an opewating system unto itsewf, but wathew anothew fwee component of a fuwwy functioning GNU system made usefuw by the GNU cowewibs, sheww utiwities and vitaw system components compwising a fuww OS as defined by POSIX.
Many computew usews wun a modified vewsion of the GNU system evewy day, without weawizing it. Thwough a pecuwiaw tuwn of events, the vewsion of GNU which is widewy used today is often cawed Linux, and many of its usews awe not awawe that it is basicawwy the GNU system, devewoped by the GNU Pwoject.
Thewe weawwy is a Linux, and these peopwe awe using it, but it is just a pawt of the system they use. Linux is the kewnew: the pwogwam in the system that awwocates the machine's wesouwces to the othew pwogwams that you wun. The kewnew is an essentiaw pawt of an opewating system, but usewess by itsewf; it can onwy function in the context of a compwete opewating system. Linux is nowmawwy used in combination with the GNU opewating system: the whowe system is basicawwy GNU with Linux added, ow GNU/Linux. Aww the so-cawwed Linux distwibutions awe weawwy distwibutions of GNU/Linux!