1.11. Linux PackagingLinus and his group of volunteer programmers developed a kernel, which is the core part of the operating system. But if you installed a kernel on a machine without the hundreds of tools, utilities, and applications that users require, it would not be of much use to most people. To complement the Linux kernel, the UNIX-like tools developed by the Free Software Foundation can be added to the kernel code and packaged as a distribution of open source software. The distinction between the Linux kernel and the GNU utilities is an important one. While most people refer to a complete system as Linux, this is strictly not correct. Linux is technically only the kernel itself; most of the command utilities and applications come from the GNU Project. Many companies and organizations have created their own distributions of Linux and the GNU utilities, as we will see in Chapter 2, "Installing Your Linux System." When you receive a Linux distribution from a vendor, it was packaged and perhaps modified or added to by that vendor, but contains code from Linus and his kernel team and the FSF GNU Project. Because it is all covered by the GNU GPL, you are free to use and modify all of the code in any way you wish, as long as, if you redistribute it, you do so also under the terms of the GNU GPL (thus allowing anyone else to use and modify any code you might have added). More information on Linux, Linux distributions, download locations, and documentation, can be found on the following web site:
|
1.12. The Linux and UNIX PhilosophySo what is Linux? Let's be clear, Linux is not UNIX. It shares no code with UNIX. But because both operating systems adhere to the same POSIX standard, they look and act almost alike, so for most people, the fact that they are not the same thing is only a technicality. But it is an extremely important technicality! Linux is a complete reimplementation. Because it shares no common code with any version of UNIX, it does not connect into the UNIX "family tree." Even so, Linux has strong philosophical connections and design influences derived from virtually all versions of UNIX. When one talks about the philosophy of Linux and GNU utilities, it is truly to talk about the UNIX philosophy. The original UNIX system was lean and mean. It had a very small number of utilities and virtually no network or security functionality. The original designers of UNIX had some pretty strong notions about how utilities should be written: a program should do one thing, do it well, and complex tasks should be performed by using these utilities together. To this end, they built a special mechanism called a "pipe" into the heart of UNIX to support their vision. A pipe allows a user to specify that the output of one process is to be used as the input to another process. Two or more processes may be connected in this fashion, resulting in a "pipeline" of data flowing from the first process through to the last (Figure 1-4). Figure 1-4. A pipeline.
The nice thing about pipelines is that many problems can be solved by such an arrangement of processes. Each process in the pipeline performs a set of operations upon the data and then passes the results on to the next process for further processing. For example, imagine that you wish to obtain a sorted list of all the users on the system. There is a utility called who that outputs an unsorted list of the users, and another utility called sort that outputs a sorted version of its input. These two utilities may be connected together with a pipe so that the output from who passes directly into sort , resulting in a sorted list of users (Figure 1-5). Figure 1-5. A pipeline that sorts.
This is a more powerful approach to solving problems than writing a fresh program from scratch every time or using two programs but having to store the intermediate data in a temporary file in order for the next program to have access to it. The UNIX (and therefore Linux) philosophy for solving problems can thus be stated:
Inside Linux is hidden another more subtle philosophy that is slowly eroding. The original system was designed by programmers who liked to have the power to access data or code anywhere in the system, regardless of who owned it. To support this capability, they built the concept of a "super-user" into UNIX, which meant that certain privileged individuals could have special access rights. For example, the system administrator of a UNIX system always has the capability of becoming a super-user so that he/she may perform cleanup tasks such as terminating rogue processes or removing unwanted users from the system. The concept of super-user has security implications that are a little frightening. Anyone with the right password could potentially wipe out an entire system, or extract top-security data with relative ease. |
