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1.6 The Design and Philosophy of Linux


  When new users encounter Linux, they often have a few misconceptions and false expectations of the system. Linux is a unique operating system, and it is important to understand its philosophy and design in order to use it effectively. Time enough for a soapbox. Even if you are an aged UNIX guru, what follows is probably of interest to you.

  In commercial UNIX development houses, the entire system is developed with a rigorous policy of quality assurance, source and revision control systems, documentation, and bug reporting and resolution. Developers are not allowed to add features or to change key sections of code on a whim: they must validate the change as a response to a bug report and consequently ``check in'' all changes to the source control system, so that the changes can be backed out if necessary. Each developer is assigned one or more parts of the system code, and only that developer may alter those sections of the code while it is ``checked out''.

Internally, the quality assurance department runs rigorous regression test suites on each new pass of the operating system, and reports any bugs. It is the responsibility of the developers to fix these bugs as reported. A complicated system of statistical analysis is employed to ensure that a certain percentage of bugs are fixed before the next release, and that the operating system as a whole passes certain release criteria.

In all, the process used by commercial UNIX developers to maintain and support their code is very complicated, and quite reasonably so. The company must have quantitative proof that the next revision of the operating system is ready to be shipped; hence, the gathering and analysis of statistics about the operating system's performance. It is a big job to develop a commercial UNIX system, often large enough to employ hundreds (if not thousands) of programmers, testers, documentors, and administrative personel. Of course, no two commercial UNIX vendors are alike, but you get the general picture.

With Linux, you can throw out the entire concept of organized development, source control systems, structured bug reporting, or statistical analysis. Linux is, and more than likely always will be, a hacker's   operating system.gif

Linux is primarily developed as a group effort by volunteers on the Internet from all over the world. Across the Internet and beyond, anyone with enough know-how has the opportunity to aid in developing and debugging the kernel, porting new software, writing documentation, or helping new users. There is no single organization responsible for developing the system. For the most part, the Linux community communicates via various mailing lists and USENET newsgroups. A number of conventions have sprung up around the development effort: for example, anyone wishing to have their code included in the ``official'' kernel should mail it to Linus Torvalds,   which he will test and include in the kernel (as long as it doesn't break things or go against the overall design of the system, he will more than likely include it).

  The system itself is designed with a very open-ended, feature-minded approach. While recently the number of new features and critical changes to the system have diminished, the general rule is that a new version of the kernel will be released about every few months (sometimes even more frequently than this). Of course, this is a very rough figure: it depends on a several factors including the number of bugs to be fixed, the amount of feedback from users testing pre-release versions of the code, and the amount of sleep that Linus has had this week.

    Let it suffice to say that not every single bug has been fixed, and not every problem ironed out between releases. As long as the system appears to be free of critical or oft-manifesting bugs, it is considered ``stable'' and new revisions will be released. The thrust behind Linux development is not an effort to release perfect, bug-free code: it is to develop a free implementation of UNIX. Linux is for the developers, more than anyone else.

Anyone who has a new feature or software application to add to the system generally makes it available in an ``alpha''     stage---that is, a stage for testing by those brave or unwary users who want to bash out problems with the initial code. Because the Linux community is largely based on the Internet, alpha software is usually uploaded to one or more of the various Linux FTP sites (see Appendix C) and a message posted to one of the Linux USENET newsgroups about how to get and test the code. Users who download and test alpha software can then mail results, bug fixes, or questions to the author.

After the initial problems in the alpha code have been fixed, the code enters a ``beta'' stage,     in which it is usually considered stable but not complete (that is, it works, but not all of the features may be present). Otherwise, it may go directly to a ``final'' stage in which the software is considered complete and usable. For kernel code, once it is complete the developer may ask Linus to include it in the standard kernel, or as an optional add-on feature to the kernel.

Keep in mind that these are only conventions---not   rules. Some people feel so confident with their software that they don't need to release an alpha or test version. It is always up to the developer to make these decisions.

You might be amazed that such a nonstructured system of volunteers, programming and debugging a complete UNIX system, could get anything done at all. As it turns out, it is one of the most efficient and motivated development efforts ever employed. The entire Linux kernel was written from scratch, without employing any code from proprietary sources. A great deal of work was put forth by volunteers to port all of the free software under the sun to the Linux system. Libraries were written and ported, filesystems developed, and hardware drivers written for many popular devices.

The Linux software is generally released as a distribution,     which is a set of pre-packaged software making up an entire system. It would be quite difficult for most users to build a complete system from the ground up, starting with the kernel, adding utilities, and installing all of the necessary software by hand. Instead, there are a number of software distributions including everything that you need to install and run a complete system. Again, there is no standard distribution---there are many, each with their own advantages and disadvantages. We'll talk more about the various available Linux distributions in Section 2.1.

Despite the completeness of the Linux software, you will still need a bit of UNIX know-how to install and run a complete system. No distribution of Linux is completely bug-free, so you may be required to fix small problems by hand after installation. Running a UNIX system is not an easy task, not even for commercial versions of UNIX. If you're serious about Linux, bear in mind that it will take a considerable amount of effort and attention on your part to keep the system running and take care of things: this is true of any UNIX system, and Linux is no exception. Because of the diversity of the Linux community and the many needs which the software is attempting to meet, not eveything can be taken care of for you all of the time.

next up previous contents index
Next: 1.6.1 Hints for UNIX Up: 1 Introduction to Linux Previous: 1.5 About Linux's Copyright

Matt Welsh