With many UNIX systems that are around, the user is unaware that the operating system is a UNIX system. Many companies have point-of-sales systems hooked up to a UNIX host. For example, the users at the cash register may never see what is being run. Therefore, there is really no need to go into details about the system other than for pure curiosity assuming that users find out that they are running on a UNIX system.

On the other hand, if you do have access to the command line or interact with the system by some other means, knowing how the system is put together is useful information. Knowing how things interact helps expand your knowledge. Knowing what’s on your system is helpful in figuring out just what your system can do.

That’s what this chapter is about: what’s out there. We’re going to talk about what makes up Linux. This brings up the question “What is Linux?” There are more than a dozen versions commercially available, in several different countries, all with their own unique characteristics. How can you call any one of them the Linux distribution?

The answer is you can’t. What I will do instead is to synthesize all the different versions into a single pseudo-version that we can talk about. Although there are differences in the different versions, the majority of the components are the same. There has been a great deal of effort in the past few years to standardize Linux, with a great deal of success. I will therefore address this standard Linux and then mention those areas where specific versions diverge.