From: "Ben Seattle" <icd-AT-communism.org> Subject: M-I: The Cathedral and the Bazaar (parts 7 - 13) Date: Mon, 2 Feb 1998 23:50:32 -0800 [continued from parts 1 - 6] ====================================================7. Fetchmail Grows Up ==================================================== There I was with a neat and innovative design, code that I knew worked well because I used it every day, and a burgeoning beta list. It gradually dawned on me that I was no longer engaged in a trivial personal hack that might happen to be useful to few other people. I had my hands on a program every hacker with a Unix box and a SLIP/PPP mail connection really needs. With the SMTP forwarding feature, it pulled far enough in front of the competition to potentially become a "category killer", one of those classic programs that fills its niche so competently that the alternatives are not just discarded but almost forgotten. I think you can't really aim or plan for a result like this. You have to get pulled into it by design ideas so powerful that afterward the results just seem inevitable, natural, even foreordained. The only way to try for ideas like that is by having lots of ideas -- or by having the engineering judgment to take other peoples' good ideas beyond where the originators thought they could go. Andrew Tanenbaum had the original idea to build a simple native Unix for the 386, for use as a teaching tool. Linus Torvalds pushed the Minix concept further than Andrew probably thought it could go -- and it grew into something wonderful. In the same way (though on a smaller scale), I took some ideas by Carl Harris and Harry Hochheiser and pushed them hard. Neither of us was `original' in the romantic way people think is genius. But then, most science and engineering and software development isn't done by original genius, hacker mythology to the contrary. The results were pretty heady stuff all the same -- in fact, just the kind of success every hacker lives for! And they meant I would have to set my standards even higher. To make fetchmail as good as I now saw it could be, I'd have to write not just for my own needs, but also include and support features necessary to others but outside my orbit. And do that while keeping the program simple and robust. The first and overwhelmingly most important feature I wrote after realizing this was multidrop support -- the ability to fetch mail from mailboxes that had accumulated all mail for a group of users, and then route each piece of mail to its individual recipients. I decided to add the multidrop support partly because some users were clamoring for it, but mostly because I thought it would shake bugs out of the single-drop code by forcing me to deal with addressing in full generality. And so it proved. Getting RFC822 parsing right took me a remarkably long time, not because any individual piece of it is hard but because it involved a pile of interdependent and fussy details. But multidrop addressing turned out to be an excellent design decision as well. Here's how I knew: 14. Any tool should be useful in the expected way, but a *great* tool lends itself to uses you never expected. The unexpected use for multi-drop fetchmail is to run mailing lists with the list kept, and alias expansion done, on the client side of the SLIP/PPP connection. This means someone running a personal machine through an ISP account can manage a mailing list without continuing access to the ISP's alias files. Another important change demanded by my beta testers was support for 8-bit MIME operation. This was pretty easy to do, because I had been careful to keep the code 8-bit clean. Not because I anticipated the demand for this feature, but rather in obedience to another rule: 15. When writing gateway software of any kind, take pains to disturb the data stream as little as possible -- and *never* throw away information unless the recipient forces you to! Had I not obeyed this rule, 8-bit MIME support would have been difficult and buggy. As it was, all I had to do is read RFC 1652 and add a trivial bit of header-generation logic. Some European users bugged me into adding an option to limit the number of messages retrieved per session (so they can control costs from their expensive phone networks). I resisted this for a long time, and I'm still not entirely happy about it. But if you're writing for the world, you have to listen to your customers -- this doesn't change just because they're not paying you in money. ====================================================8. A Few More Lessons From Fetchmail ==================================================== Before we go back to general software-engineering issues, there are a couple more specific lessons from the fetchmail experience to ponder. The rc file syntax includes optional `noise' keywords that are entirely ignored by the parser. The English-like syntax they allow is considerably more readable than the traditional terse keyword-value pairs you get when you strip them all out. These started out as a late-night experiment when I noticed how much the rc file declarations were beginning to resemble an imperative minilanguage. (This is also why I changed the original popclient `server' keyword to `poll'). It seemed to me that trying to make that imperative minilanguage more like English might make it easier to use. Now, although I'm a convinced partisan of the "make it a language" school of design as exemplified by Emacs and HTML and many database engines, I am not normally a big fan of "English-like" syntaxes. Traditionally programmers have tended to favor control syntaxes that are very precise and compact and have no redundancy at all. This is a cultural legacy from when computing resources were expensive, so parsing stages had to be as cheap and simple as possible. English, with about 50% redundancy, looked like a very inappropriate model then. This is not my reason for fighting shy of English-like syntaxes; I mention it here only to demolish it. With cheap cycles and core, terseness should not be an end in itself. Nowadays it's more important for a language to be convenient for humans than to be cheap for the computer. There are, however, good reasons to be wary. One is the complexity cost of the parsing stage -- you don't want to raise that to the point where it's a significant source of bugs and user confusion in itself. Another is that trying to make a language syntax English-like often demands that the "English" it speaks be bent seriously out of shape, so much so that the superficial resemblance to natural language is as confusing as a traditional syntax would have been. (You see this in a lot of 4GLs and commercial database-query languages.) The fetchmail control syntax seems to avoid these problems because the language domain is extremely restricted. It's nowhere near a general- purpose language; the things it says simply are not very complicated, so there's little potential for confusion in moving mentally between a tiny subset of English and the actual control language. I think there may be a wider lesson here: 16. When your language is nowhere near Turing-complete, syntactic sugar can be your friend. Another lesson is about security by obscurity. Some fetchmail users asked me to change the software to store passwords encrypted in the rc file, so snoopers wouldn't be able to casually see them. I didn't do it, because this doesn't actually add protection. Anyone who's acquired permissions to read your rc file will be able to run fetchmail as you anyway -- and if it's your password they're after, they'd be able to rip the necessary decoder out of the fetchmail code itself to get it. All .fetchmailrc password encryption would have done is give a false sense of security to people who don't think very hard. The general rule here is: 17. A security system is only as secure as its secret. Beware of pseudo-secrets. ====================================================9. Necessary Preconditions for the Bazaar Style ==================================================== Early reviewers and test audiences for this paper consistently raised questions about the preconditions for successful bazaar-style development, including both the qualifications of the project leader and the state of code at the time one goes public and starts to try to build a co-developer community. It's fairly clear that one cannot code from the ground up in bazaar style. One can test, debug and improve in bazaar style, but it would be very hard to originate a project in bazaar mode. Linus didn't try it. I didn't either. Your nascent developer community needs to have something runnable and testable to play with. When you start community-building, what you need to be able to present is a plausible promise. Your program doesn't have to work particularly well. It can be crude, buggy, incomplete, and poorly documented. What it must not fail to do is convince potential co- developers that it can be evolved into something really neat in the foreseeable future. Linux and fetchmail both went public with strong, attractive basic designs. Many people thinking about the bazaar model as I have presented it have correctly considered this critical, then jumped from it to the conclusion that a high degree of design intuition and cleverness in the project leader is indispensable. But Linus got his design from Unix. I got mine initially from the ancestral popmail (though it would later change a great deal, much more proportionately speaking than has Linux). So does the leader/coordinator for a bazaar-style effort really have to have exceptional design talent, or can he get by on leveraging the design talent of others? I think it is not critical that the coordinator be able to originate designs of exceptional brilliance, but it is absolutely critical that he/she be able to recognize good design ideas from others. Both the Linux and fetchmail projects show evidence of this. Linus, while not (as previously discussed) a spectacularly original designer, has displayed a powerful knack for recognizing good design and integrating it into the Linux kernel. And I have already described how the single most powerful design idea in fetchmail (SMTP forwarding) came from somebody else. Early audiences of this paper complimented me by suggesting that I am prone to undervalue design originality in bazaar projects because I have a lot of it myself, and therefore take it for granted. There may be some truth to this; design (as opposed to coding or debugging) is certainly my strongest skill. But the problem with being clever and original in software design is that it gets to be a habit -- you start reflexively making things cute and complicated when you should be keeping them robust and simple. I have had projects crash on me because I made this mistake, but I managed not to with fetchmail. So I believe the fetchmail project succeeded partly because I restrained my tendency to be clever; this argues (at least) against design originality being essential for successful bazaar projects. And consider Linux. Suppose Linus Torvalds had been trying to pull off fundamental innovations in operating system design during the development; does it seem at all likely that the resulting kernel would be as stable and successful as what we have? A certain base level of design and coding skill is required, of course, but I expect almost anybody seriously thinking of launching a bazaar effort will already be above that minimum. The free-software community's internal market in reputation exerts subtle pressure on people not to launch development efforts they're not competent to follow through on. So far this seems to have worked pretty well. There is another kind of skill not normally associated with software development which I think is as important as design cleverness to bazaar projects -- and it may be more important. A bazaar project coordinator or leader must have good people and communications skills. This should be obvious. In order to build a development community, you need to attract people, interest them in what you're doing, and keep them happy about the amount of work they're doing. Technical sizzle will go a long way towards accomplishing this, but it's far from the whole story. The personality you project matters, too. It is not a coincidence that Linus is a nice guy who makes people like him and want to help him. It's not a coincidence that I'm an energetic extrovert who enjoys working a crowd and has some of the delivery and instincts of a stand-up comic. To make the bazaar model work, it helps enormously if you have at least a little skill at charming people. ====================================================10. The Social Context of Free Software ==================================================== It is truly written: the best hacks start out as personal solutions to the author's everyday problems, and spread because the problem turns out to be typical for a large class of users. This takes us back to the matter of rule 1, restated in a perhaps more useful way: 18. To solve an interesting problem, start by finding a problem that is interesting to you. So it was with Carl Harris and the ancestral popclient, and so with me and fetchmail. But this has been understood for a long time. The interesting point, the point that the histories of Linux and fetchmail seem to demand we focus on, is the next stage -- the evolution of software in the presence of a large and active community of users and co-developers. In "The Mythical Man-Month", Fred Brooks observed that programmer time is not fungible; adding developers to a late software project makes it later. He argued that the complexity and communication costs of a project rise with the square of the number of developers, while work done only rises linearly. This claim has since become known as "Brooks's Law" and is widely regarded as a truism. But if Brooks's Law were the whole picture, Linux would be impossible. A few years later Gerald Weinberg's classic "The Psychology Of Computer Programming" supplied what, in hindsight, we can see as a vital correction to Brooks. In his discussion of "egoless programming", Weinberg observed that in shops where developers are not territorial about their code, and encourage other people to look for bugs and potential improvements in it, improvement happens dramatically faster than elsewhere. Weinberg's choice of terminology has perhaps prevented his analysis from gaining the acceptance it deserved -- one has to smile at the thought of describing Internet hackers as "egoless". But I think his argument looks more compelling today than ever. The history of Unix should have prepared us for what we're learning from Linux (and what I've verified experimentally on a smaller scale by deliberately copying Linus's methods). That is, that while coding remains an essentially solitary activity, the really great hacks come from harnessing the attention and brainpower of entire communities. The developer who uses only his or her own brain in a closed project is going to fall behind the developer who knows how to create an open, evolutionary context in which bug-spotting and improvements get done by hundreds of people. But the traditional Unix world was prevented from pushing this approach to the ultimate by several factors. One was the legal contraints of various licenses, trade secrets, and commercial interests. Another (in hindsight) was that the Internet wasn't yet good enough. Before cheap Internet, there were some geographically compact communities where the culture encouraged Weinberg's "egoless" programming, and a developer could easily attract a lot of skilled kibitzers and co-developers. Bell Labs, the MIT AI Lab, UC Berkeley -- these became the home of innovations that are legendary and still potent. Linux was the first project to make a conscious and successful effort to use the entire world as its talent pool. I don't think it's a coincidence that the gestation period of Linux coincided with the birth of the World Wide Web, and that Linux left its infancy during the same period in 1993-1994 that saw the takeoff of the ISP industry and the explosion of mainstream interest in the Internet. Linus was the first person who learned how to play by the new rules that pervasive Internet made possible. While cheap Internet was a necessary condition for the Linux model to evolve, I think it was not by itself a sufficient condition. Another vital factor was the development of a leadership style and set of cooperative customs that could allow developers to attract co- developers and get maximum leverage out of the medium. But what is this leadership style and what are these customs? They cannot be based on power relationships -- and even if they could be, leadership by coercion would not produce the results we see. Weinberg quotes the autobiography of the 19th-century Russian anarchist Kropotkin's "Memoirs of a Revolutionist") to good effect on this subject: "Having been brought up in a serf-owner's family, I entered active life, like all young men of my time, with a great deal of confidence in the necessity of commanding, ordering, scolding, punishing and the like. But when, at an early stage, I had to manage serious enterprises and to deal with [free] men, and when each mistake would lead at once to heavy consequences, I began to appreciate the difference between acting on the principle of command and discipline and acting on the principle of common understanding. The former works admirably in a military parade, but it is worth nothing where real life is concerned, and the aim can be achieved only through the severe effort of many converging wills." The "severe effort of many converging wills" is precisely what a project like Linux requires -- and the "principle of command" is effectively impossible to apply among volunteers in the anarchist's paradise we call the Internet. To operate and compete effectively, hackers who want to lead collaborative projects have to learn how to recruit and energize effective communities of interest in the mode vaguely suggested by Kropotkin's "principle of understanding". They must learn to use Linus's Law. Earlier I referred to the "Delphi effect" as a possible explanation for Linus's Law. But more powerful analogies to adaptive systems in biology and economics also irresistably suggest themselves. The Linux world behaves in many respects like a free market or an ecology, a collection of selfish agents attempting to maximize utility which in the process produces a self-correcting spontaneous order more elaborate and efficient than any amount of central planning could achieve. Here, then, is the place to seek the "principle of understanding". The "utility function" Linux hackers are maximizing is not classically economic, but is the intangible of their own ego satisfaction and reputation among other hackers. (One may call their motivation "altruistic", but this ignores the fact that altruism is itself a form of ego satisfaction for the altruist). Voluntary cultures that work this way are not actually uncommon; one other in which I have long participated is science fiction fandom, which unlike hackerdom explicitly recognizes "egoboo" (the enhancement of one's reputation among other fans) as the basic drive behind volunteer activity. Linus, by successfully positioning himself as the gatekeeper of a project in which the development is mostly done by others, and nurturing interest in the project until it became self-sustaining, has shown an acute grasp of Kropotkin's "principle of shared understanding". This quasi-economic view of the Linux world enables us to see how that understanding is applied. We may view Linus's method as an way to create an efficient market in "egoboo" -- to connect the selfishness of individual hackers as firmly as possible to difficult ends that can only be achieved by sustained cooperation. With the fetchmail project I have shown (albeit on a smaller scale) that his methods can be duplicated with good results. Perhaps I have even done it a bit more consciously and systematically than he. Many people (especially those who politically distrust free markets) would expect a culture of self-directed egoists to be fragmented, territorial, wasteful, secretive, and hostile. But this expectation is clearly falsified by (to give just one example) the stunning variety, quality and depth of Linux documentation. It is a hallowed given that programmers hate documenting; how is it, then, that Linux hackers generate so much of it? Evidently Linux's free market in egoboo works better to produce virtuous, other-directed behavior than the massively-funded documentation shops of commercial software producers. Both the fetchmail and Linux kernel projects show that by properly rewarding the egos of many other hackers, a strong developer/coordinator can use the Internet to capture the benefits of having lots of co-developers without having a project collapse into a chaotic mess. So to Brooks's Law I counter-propose the following: 19: Provided the development coordinator has a medium at least as good as the Internet, and knows how to lead without coercion, many heads are inevitably better than one. I think the future of free software will increasingly belong to people who know how to play Linus's game, people who leave behind the cathedral and embrace the bazaar. This is not to say that individual vision and brilliance will no longer matter; rather, I think that the cutting edge of free software will belong to people who start from individual vision and brilliance, then amplify it through the effective construction of voluntary communities of interest. And perhaps not only the future of free software. No commercial developer can match the pool of talent the Linux community can bring to bear on a problem. Very few could afford even to hire the more than two hundred people who have contributed to fetchmail! Perhaps in the end the free-software culture will triumph not because cooperation is morally right or software "hoarding" is morally wrong (assuming you believe the latter, which neither Linus nor I do), but simply because the commercial world cannot win an evolutionary arms race with free-software communities that can put orders of magnitude more skilled time into a problem. ====================================================11. Acknowledgements ==================================================== This paper was improved by conversations with a large number of people who helped debug it. Particular thanks to Jeff Dutky <dutky-AT-wam.umd.edu>, who suggested the "debugging is parallelizable" formulation, and helped developed the analysis that proceeds from it. Also to Nancy Lebovitz <nancyl-AT-universe.digex.net> for her suggestion that I emulate Weinberg by quoting Kropotkin. Perceptive criticisms also came from Joan Eslinger <wombat-AT-kilimanjaro.engr.sgi.com> and Marty Franz <marty-AT-net-link.net> of the General Technics list. Paul Eggert <eggert-AT-twinsun.com> noticed the conflict between GPL and the bazaar model. I'm grateful to the members of PLUG, the Philadelphia Linux User's group, for providing the first test audience for the first public version of this paper. Finally, Linus Torvalds's comments were helpful and his early endorsement very encouraging. ====================================================12. For Further Reading ==================================================== I quoted several bits from Frederick P. Brooks's classic The Mythical Man-Month because, in many respects, his insights have yet to be improved upon. I heartily recommend the 25th Anniversary addition from Addison-Wesley (ISBN 0-201-83595-9), which adds his 1986 "No Silver Bullet" paper. The new edition is wrapped up by an invaluable 20-years-later retrospective in which Brooks forthrightly admits to the few judgements in the original text which have not stood the test of time. I first read the retrospective after this paper was substantially complete, and was surprised to discover that Brooks attributes bazaar- like practices to Microsoft! Gerald P. Weinberg's The Psychology Of Computer Programming (New York, Van Nostrand Reinhold 1971) introduced the rather unfortunately- labeled concept of "egoless programming". While he was nowhere near the first person to realize the futility of the "principle of command", he was probably the first to recognize and argue the point in particular connection with software development. Richard P. Gabriel, contemplating the Unix culture of the pre-Linux era, reluctantly argued for the superiority of a primitive bazaar-like model in his 1989 paper Lisp: Good News, Bad News, and How To Win Big. Though dated in some respects, this essay is still rightly celebrated among Lisp fans (including me). A correspondent reminded me that the section titled "Worse Is Better" reads almost as an anticipation of Linux. The paper is accessible on the World Wide Web at "http://alpha-bits.ai.mit.edu/articles/good-news/good-news.html". De Marco and Lister's Peopleware: Productive Projects and Teams (New York; Dorset House, 1987; ISBN 0-932633-05-6) is an underappreciated gem which I was delighted to see Fred Brooks cite in his retrospective. While little of what the authors have to say is directly applicable to the Linux or free-software communities, the authors' insight into the conditions necessary for creative work is acute and worthwhile for anyone attempting to import some of the bazaar model's virtues into a more commercial context. Finally, I must admit that I very nearly called this paper "The Cathedral and the Agora", the latter term being the Greek for an open market or public meeting place. The seminal "agoric systems" papers by Mark Miller and Eric Drexler, by describing the emergent properties of market-like computational ecologies, helped prepare me to think clearly about analogous phenomena in the free-software culture when Linux rubbed my nose in them five years later. These papers are available on the Web at "http://www.agorics.com/agorpapers.html". ====================================================13. Version and Change History: ==================================================== $Id: cathedral-paper.sgml,v 1.29 1998/01/30 22:29:31 esr Exp $ I gave 1.16 at the Linux Kongress, May 21 1997. I added the bibliography July 7 1997 in 1.20. I added the Perl Conference anecdote November 18 1997 in 1.27. Other revision levels incorporate minor editorial and markup fixes. --- from list marxism-international-AT-lists.village.virginia.edu ---
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