path: root/data/samples/wrapped/en/the_cathedral_and_the_bazaar.eric_s_raymond.sst

% SiSU 4.0

@title: The Cathedral and the Bazaar

@creator:
 :author: Raymond, Eric S.

@date:
 :published: 2002-08-02
 :created: 1997-05-21
 :issued: 1997-05-21
 :available: 1997-05-21
 :modified: 2002-08-02

@rights:
 :copyright: Copyright © 2000 Eric S. Raymond.
 :license: Permission is granted to copy, distribute and/or modify this document under the terms of the Open Publication License, version 2.0.

@classify:
 :topic_register: SiSU markup sample:book:discourse;programming;software:open source software;open source software:development

@identifier:
 :oclc: 45835582

@notes:
 :abstract: I anatomize a successful open-source project, fetchmail, that was run as a deliberate test of the surprising theories about software engineering suggested by the history of Linux. I discuss these theories in terms of two fundamentally different development styles, the "cathedral" model of most of the commercial world versus the "bazaar" model of the Linux world. I show that these models derive from opposing assumptions about the nature of the software-debugging task. I then make a sustained argument from the Linux experience for the proposition that "Given enough eyeballs, all bugs are shallow", suggest productive analogies with other self-correcting systems of selfish agents, and conclude with some exploration of the implications of this insight for the future of software.

@links:
 { The Cathedral and the Bazaar, Source }http://www.catb.org/~esr/writings/cathedral-bazaar/cathedral-bazaar/
 { @ Wikipedia }http://en.wikipedia.org/wiki/The_Cathedral_and_the_Bazaar
 { CatB @ Amazon.com }http://www.amazon.com/Wealth-Networks-Production-Transforms-Markets/dp/0596001088/
 { CatB @ Barnes & Noble }http://search.barnesandnoble.com/booksearch/isbnInquiry.asp?isbn=0596001088

@make:
 :breaks: new=:C; break=1
 :home_button_text: {The Cathedral and the Bazaar}http://www.catb.org/esr/writings/homesteading/; {Eric S. Raymond}http://www.catb.org/~esr/
 :footer: {The Cathedral and the Bazaar}http://www.catb.org/esr/writings/homesteading/; {Eric S. Raymond}http://www.catb.org/~esr/

:A~ @title @author

1~ The Cathedral and the Bazaar

Linux is subversive. Who would have thought even five years ago (1991) that a
world-class operating system could coalesce as if by magic out of part-time
hacking by several thousand developers scattered all over the planet, connected
only by the tenuous strands of the Internet?

Certainly not I. By the time Linux swam onto my radar screen in early 1993, I
had already been involved in Unix and open-source development for ten years. I
was one of the first GNU contributors in the mid-1980s. I had released a good
deal of open-source software onto the net, developing or co-developing several
programs (nethack, Emacs's VC and GUD modes, xlife, and others) that are still
in wide use today. I thought I knew how it was done.

Linux overturned much of what I thought I knew. I had been preaching the Unix
gospel of small tools, rapid prototyping and evolutionary programming for
years. But I also believed there was a certain critical complexity above which
a more centralized, a priori approach was required. I believed that the most
important software (operating systems and really large tools like the Emacs
programming editor) needed to be built like cathedrals, carefully crafted by
individual wizards or small bands of mages working in splendid isolation, with
no beta to be released before its time.

Linus Torvalds's style of development—release early and often, delegate
everything you can, be open to the point of promiscuity—came as a surprise. No
quiet, reverent cathedral-building here—rather, the Linux community seemed to
resemble a great babbling bazaar of differing agendas and approaches (aptly
symbolized by the Linux archive sites, who'd take submissions from anyone) out
of which a coherent and stable system could seemingly emerge only by a
succession of miracles.

The fact that this bazaar style seemed to work, and work well, came as a
distinct shock. As I learned my way around, I worked hard not just at
individual projects, but also at trying to understand why the Linux world not
only didn't fly apart in confusion but seemed to go from strength to strength
at a speed barely imaginable to cathedral-builders.

By mid-1996 I thought I was beginning to understand. Chance handed me a perfect
way to test my theory, in the form of an open-source project that I could
consciously try to run in the bazaar style. So I did—and it was a significant
success.

This is the story of that project. I'll use it to propose some aphorisms about
effective open-source development. Not all of these are things I first learned
in the Linux world, but we'll see how the Linux world gives them particular
point. If I'm correct, they'll help you understand exactly what it is that
makes the Linux community such a fountain of good software—and, perhaps, they
will help you become more productive yourself.

1~ The Mail Must Get Through

Since 1993 I'd been running the technical side of a small free-access Internet
service provider called Chester County InterLink (CCIL) in West Chester,
Pennsylvania. I co-founded CCIL and wrote our unique multiuser bulletin-board
software—you can check it out by telnetting to locke.ccil.org. Today it
supports almost three thousand users on thirty lines. The job allowed me
24-hour-a-day access to the net through CCIL's 56K line—in fact, the job
practically demanded it!

I had gotten quite used to instant Internet email. I found having to
periodically telnet over to locke to check my mail annoying. What I wanted was
for my mail to be delivered on snark (my home system) so that I would be
notified when it arrived and could handle it using all my local tools.

The Internet's native mail forwarding protocol, SMTP (Simple Mail Transfer
Protocol), wouldn't suit, because it works best when machines are connected
full-time, while my personal machine isn't always on the Internet, and doesn't
have a static IP address. What I needed was a program that would reach out over
my intermittent dialup connection and pull across my mail to be delivered
locally. I knew such things existed, and that most of them used a simple
application protocol called POP (Post Office Protocol). POP is now widely
supported by most common mail clients, but at the time, it wasn't built in to
the mail reader I was using.

I needed a POP3 client. So I went out on the Internet and found one. Actually,
I found three or four. I used one of them for a while, but it was missing what
seemed an obvious feature, the ability to hack the addresses on fetched mail so
replies would work properly.

The problem was this: suppose someone named `joe' on locke sent me mail. If I
fetched the mail to snark and then tried to reply to it, my mailer would
cheerfully try to ship it to a nonexistent `joe' on snark. Hand-editing reply
addresses to tack on <@ccil.org> quickly got to be a serious pain.

This was clearly something the computer ought to be doing for me. But none of
the existing POP clients knew how! And this brings us to the first lesson:

_1 1. Every good work of software starts by scratching a developer's personal
itch.

Perhaps this should have been obvious (it's long been proverbial that
"Necessity is the mother of invention") but too often software developers spend
their days grinding away for pay at programs they neither need nor love. But
not in the Linux world—which may explain why the average quality of software
originated in the Linux community is so high.

So, did I immediately launch into a furious whirl of coding up a brand-new POP3
client to compete with the existing ones? Not on your life! I looked carefully
at the POP utilities I had in hand, asking myself "Which one is closest to what
I want?" Because:

_1 2. Good programmers know what to write. Great ones know what to rewrite (and
reuse).

While I don't claim to be a great programmer, I try to imitate one. An
important trait of the great ones is constructive laziness. They know that you
get an A not for effort but for results, and that it's almost always easier to
start from a good partial solution than from nothing at all.

Linus Torvalds, for example, didn't actually try to write Linux from scratch.
Instead, he started by reusing code and ideas from Minix, a tiny Unix-like
operating system for PC clones. Eventually all the Minix code went away or was
completely rewritten—but while it was there, it provided scaffolding for the
infant that would eventually become Linux.

In the same spirit, I went looking for an existing POP utility that was
reasonably well coded, to use as a development base.

The source-sharing tradition of the Unix world has always been friendly to code
reuse (this is why the GNU project chose Unix as a base OS, in spite of serious
reservations about the OS itself). The Linux world has taken this tradition
nearly to its technological limit; it has terabytes of open sources generally
available. So spending time looking for some else's almost-good-enough is more
likely to give you good results in the Linux world than anywhere else.

And it did for me. With those I'd found earlier, my second search made up a
total of nine candidates—fetchpop, PopTart, get-mail, gwpop, pimp, pop-perl,
popc, popmail and upop. The one I first settled on was `fetchpop' by Seung-Hong
Oh. I put my header-rewrite feature in it, and made various other improvements
which the author accepted into his 1.9 release.

A few weeks later, though, I stumbled across the code for popclient by Carl
Harris, and found I had a problem. Though fetchpop had some good original ideas
in it (such as its background-daemon mode), it could only handle POP3 and was
rather amateurishly coded (Seung-Hong was at that time a bright but
inexperienced programmer, and both traits showed). Carl's code was better,
quite professional and solid, but his program lacked several important and
rather tricky-to-implement fetchpop features (including those I'd coded
myself).

Stay or switch? If I switched, I'd be throwing away the coding I'd already done
in exchange for a better development base.

A practical motive to switch was the presence of multiple-protocol support.
POP3 is the most commonly used of the post-office server protocols, but not the
only one. Fetchpop and the other competition didn't do POP2, RPOP, or APOP, and
I was already having vague thoughts of perhaps adding IMAP (Internet Message
Access Protocol, the most recently designed and most powerful post-office
protocol) just for fun.

But I had a more theoretical reason to think switching might be as good an idea
as well, something I learned long before Linux.

_1 3. "Plan to throw one away; you will, anyhow." (Fred Brooks, The Mythical
Man-Month, Chapter 11)

Or, to put it another way, you often don't really understand the problem until
after the first time you implement a solution. The second time, maybe you know
enough to do it right. So if you want to get it right, be ready to start over
at least once [JB].

Well (I told myself) the changes to fetchpop had been my first try. So I
switched.

After I sent my first set of popclient patches to Carl Harris on 25 June 1996,
I found out that he had basically lost interest in popclient some time before.
The code was a bit dusty, with minor bugs hanging out. I had many changes to
make, and we quickly agreed that the logical thing for me to do was take over
the program.

Without my actually noticing, the project had escalated. No longer was I just
contemplating minor patches to an existing POP client. I took on maintaining an
entire one, and there were ideas bubbling in my head that I knew would probably
lead to major changes.

In a software culture that encourages code-sharing, this is a natural way for a
project to evolve. I was acting out this principle:

_1 4. If you have the right attitude, interesting problems will find you.

But Carl Harris's attitude was even more important. He understood that

_1 5. When you lose interest in a program, your last duty to it is to hand it
off to a competent successor.

Without ever having to discuss it, Carl and I knew we had a common goal of
having the best solution out there. The only question for either of us was
whether I could establish that I was a safe pair of hands. Once I did that, he
acted with grace and dispatch. I hope I will do as well when it comes my turn.

1~ The Importance of Having Users

And so I inherited popclient. Just as importantly, I inherited popclient's user
base. Users are wonderful things to have, and not just because they demonstrate
that you're serving a need, that you've done something right. Properly
cultivated, they can become co-developers.

Another strength of the Unix tradition, one that Linux pushes to a happy
extreme, is that a lot of users are hackers too. Because source code is
available, they can be effective hackers. This can be tremendously useful for
shortening debugging time. Given a bit of encouragement, your users will
diagnose problems, suggest fixes, and help improve the code far more quickly
than you could unaided.

_1 6. Treating your users as co-developers is your least-hassle route to rapid
code improvement and effective debugging.

The power of this effect is easy to underestimate. In fact, pretty well all of
us in the open-source world drastically underestimated how well it would scale
up with number of users and against system complexity, until Linus Torvalds
showed us differently.

In fact, I think Linus's cleverest and most consequential hack was not the
construction of the Linux kernel itself, but rather his invention of the Linux
development model. When I expressed this opinion in his presence once, he
smiled and quietly repeated something he has often said: "I'm basically a very
lazy person who likes to get credit for things other people actually do." Lazy
like a fox. Or, as Robert Heinlein famously wrote of one of his characters, too
lazy to fail.

In retrospect, one precedent for the methods and success of Linux can be seen
in the development of the GNU Emacs Lisp library and Lisp code archives. In
contrast to the cathedral-building style of the Emacs C core and most other GNU
tools, the evolution of the Lisp code pool was fluid and very user-driven.
Ideas and prototype modes were often rewritten three or four times before
reaching a stable final form. And loosely-coupled collaborations enabled by the
Internet, a la Linux, were frequent.

Indeed, my own most successful single hack previous to fetchmail was probably
Emacs VC (version control) mode, a Linux-like collaboration by email with three
other people, only one of whom (Richard Stallman, the author of Emacs and
founder of the Free Software Foundation) I have met to this day. It was a
front-end for SCCS, RCS and later CVS from within Emacs that offered
"one-touch" version control operations. It evolved from a tiny, crude sccs.el
mode somebody else had written. And the development of VC succeeded because,
unlike Emacs itself, Emacs Lisp code could go through release/test/improve
generations very quickly.

The Emacs story is not unique. There have been other software products with a
two-level architecture and a two-tier user community that combined a
cathedral-mode core and a bazaar-mode toolbox. One such is MATLAB, a commercial
data-analysis and visualization tool. Users of MATLAB and other products with a
similar structure invariably report that the action, the ferment, the
innovation mostly takes place in the open part of the tool where a large and
varied community can tinker with it.

1~ Release Early, Release Often

Early and frequent releases are a critical part of the Linux development model.
Most developers (including me) used to believe this was bad policy for larger
than trivial projects, because early versions are almost by definition buggy
versions and you don't want to wear out the patience of your users.

This belief reinforced the general commitment to a cathedral-building style of
development. If the overriding objective was for users to see as few bugs as
possible, why then you'd only release a version every six months (or less
often), and work like a dog on debugging between releases. The Emacs C core was
developed this way. The Lisp library, in effect, was not—because there were
active Lisp archives outside the FSF's control, where you could go to find new
and development code versions independently of Emacs's release cycle [QR].

The most important of these, the Ohio State Emacs Lisp archive, anticipated the
spirit and many of the features of today's big Linux archives. But few of us
really thought very hard about what we were doing, or about what the very
existence of that archive suggested about problems in the FSF's
cathedral-building development model. I made one serious attempt around 1992 to
get a lot of the Ohio code formally merged into the official Emacs Lisp
library. I ran into political trouble and was largely unsuccessful.

But by a year later, as Linux became widely visible, it was clear that
something different and much healthier was going on there. Linus's open
development policy was the very opposite of cathedral-building. Linux's
Internet archives were burgeoning, multiple distributions were being floated.
And all of this was driven by an unheard-of frequency of core system releases.

Linus was treating his users as co-developers in the most effective possible
way:

_1 7. Release early. Release often. And listen to your customers.

Linus's innovation wasn't so much in doing quick-turnaround releases
incorporating lots of user feedback (something like this had been Unix-world
tradition for a long time), but in scaling it up to a level of intensity that
matched the complexity of what he was developing. In those early times (around
1991) it wasn't unknown for him to release a new kernel more than once a day!
Because he cultivated his base of co-developers and leveraged the Internet for
collaboration harder than anyone else, this worked.

But how did it work? And was it something I could duplicate, or did it rely on
some unique genius of Linus Torvalds?

I didn't think so. Granted, Linus is a damn fine hacker. How many of us could
engineer an entire production-quality operating system kernel from scratch? But
Linux didn't represent any awesome conceptual leap forward. Linus is not (or at
least, not yet) an innovative genius of design in the way that, say, Richard
Stallman or James Gosling (of NeWS and Java) are. Rather, Linus seems to me to
be a genius of engineering and implementation, with a sixth sense for avoiding
bugs and development dead-ends and a true knack for finding the minimum-effort
path from point A to point B. Indeed, the whole design of Linux breathes this
quality and mirrors Linus's essentially conservative and simplifying design
approach.

So, if rapid releases and leveraging the Internet medium to the hilt were not
accidents but integral parts of Linus's engineering-genius insight into the
minimum-effort path, what was he maximizing? What was he cranking out of the
machinery?

Put that way, the question answers itself. Linus was keeping his hacker/users
constantly stimulated and rewarded—stimulated by the prospect of having an
ego-satisfying piece of the action, rewarded by the sight of constant (even
daily) improvement in their work.

Linus was directly aiming to maximize the number of person-hours thrown at
debugging and development, even at the possible cost of instability in the code
and user-base burnout if any serious bug proved intractable. Linus was behaving
as though he believed something like this:

_1 8. Given a large enough beta-tester and co-developer base, almost every
problem will be characterized quickly and the fix obvious to someone.

Or, less formally, "Given enough eyeballs, all bugs are shallow." I dub this:
"Linus's Law".

My original formulation was that every problem "will be transparent to
somebody". Linus demurred that the person who understands and fixes the problem
is not necessarily or even usually the person who first characterizes it.
"Somebody finds the problem," he says, "and somebody else understands it. And
I'll go on record as saying that finding it is the bigger challenge." That
correction is important; we'll see how in the next section, when we examine the
practice of debugging in more detail. But the key point is that both parts of
the process (finding and fixing) tend to happen rapidly.

In Linus's Law, I think, lies the core difference underlying the
cathedral-builder and bazaar styles. In the cathedral-builder view of
programming, bugs and development problems are tricky, insidious, deep
phenomena. It takes months of scrutiny by a dedicated few to develop confidence
that you've winkled them all out. Thus the long release intervals, and the
inevitable disappointment when long-awaited releases are not perfect.

In the bazaar view, on the other hand, you assume that bugs are generally
shallow phenomena—or, at least, that they turn shallow pretty quickly when
exposed to a thousand eager co-developers pounding on every single new release.
Accordingly you release often in order to get more corrections, and as a
beneficial side effect you have less to lose if an occasional botch gets out
the door.

And that's it. That's enough. If "Linus's Law" is false, then any system as
complex as the Linux kernel, being hacked over by as many hands as the that
kernel was, should at some point have collapsed under the weight of unforseen
bad interactions and undiscovered "deep" bugs. If it's true, on the other hand,
it is sufficient to explain Linux's relative lack of bugginess and its
continuous uptimes spanning months or even years.

Maybe it shouldn't have been such a surprise, at that. Sociologists years ago
discovered that the averaged opinion of a mass of equally expert (or equally
ignorant) observers is quite a bit more reliable a predictor than the opinion
of a single randomly-chosen one of the observers. They called this the Delphi
effect. It appears that what Linus has shown is that this applies even to
debugging an operating system—that the Delphi effect can tame development
complexity even at the complexity level of an OS kernel. [CV]

One special feature of the Linux situation that clearly helps along the Delphi
effect is the fact that the contributors for any given project are
self-selected. An early respondent pointed out that contributions are received
not from a random sample, but from people who are interested enough to use the
software, learn about how it works, attempt to find solutions to problems they
encounter, and actually produce an apparently reasonable fix. Anyone who passes
all these filters is highly likely to have something useful to contribute.

Linus's Law can be rephrased as "Debugging is parallelizable". Although
debugging requires debuggers to communicate with some coordinating developer,
it doesn't require significant coordination between debuggers. Thus it doesn't
fall prey to the same quadratic complexity and management costs that make
adding developers problematic.

In practice, the theoretical loss of efficiency due to duplication of work by
debuggers almost never seems to be an issue in the Linux world. One effect of a
"release early and often" policy is to minimize such duplication by propagating
fed-back fixes quickly [JH].

Brooks (the author of The Mythical Man-Month) even made an off-hand observation
related to this: "The total cost of maintaining a widely used program is
typically 40 percent or more of the cost of developing it. Surprisingly this
cost is strongly affected by the number of users. More users find more bugs."
[emphasis added].

More users find more bugs because adding more users adds more different ways of
stressing the program. This effect is amplified when the users are
co-developers. Each one approaches the task of bug characterization with a
slightly different perceptual set and analytical toolkit, a different angle on
the problem. The "Delphi effect" seems to work precisely because of this
variation. In the specific context of debugging, the variation also tends to
reduce duplication of effort.

So adding more beta-testers may not reduce the complexity of the current
"deepest" bug from the developer's point of view, but it increases the
probability that someone's toolkit will be matched to the problem in such a way
that the bug is shallow to that person.

Linus coppers his bets, too. In case there are serious bugs, Linux kernel
version are numbered in such a way that potential users can make a choice
either to run the last version designated "stable" or to ride the cutting edge
and risk bugs in order to get new features. This tactic is not yet
systematically imitated by most Linux hackers, but perhaps it should be; the
fact that either choice is available makes both more attractive. [HBS]

1~ How Many Eyeballs Tame Complexity

It's one thing to observe in the large that the bazaar style greatly
accelerates debugging and code evolution. It's another to understand exactly
how and why it does so at the micro-level of day-to-day developer and tester
behavior. In this section (written three years after the original paper, using
insights by developers who read it and re-examined their own behavior) we'll
take a hard look at the actual mechanisms. Non-technically inclined readers can
safely skip to the next section.

One key to understanding is to realize exactly why it is that the kind of bug
report non–source-aware users normally turn in tends not to be very useful.
Non–source-aware users tend to report only surface symptoms; they take their
environment for granted, so they (a) omit critical background data, and (b)
seldom include a reliable recipe for reproducing the bug.

The underlying problem here is a mismatch between the tester's and the
developer's mental models of the program; the tester, on the outside looking
in, and the developer on the inside looking out. In closed-source development
they're both stuck in these roles, and tend to talk past each other and find
each other deeply frustrating.

Open-source development breaks this bind, making it far easier for tester and
developer to develop a shared representation grounded in the actual source code
and to communicate effectively about it. Practically, there is a huge
difference in leverage for the developer between the kind of bug report that
just reports externally-visible symptoms and the kind that hooks directly to
the developer's source-code–based mental representation of the program.

Most bugs, most of the time, are easily nailed given even an incomplete but
suggestive characterization of their error conditions at source-code level.
When someone among your beta-testers can point out, "there's a boundary problem
in line nnn", or even just "under conditions X, Y, and Z, this variable rolls
over", a quick look at the offending code often suffices to pin down the exact
mode of failure and generate a fix.

Thus, source-code awareness by both parties greatly enhances both good
communication and the synergy between what a beta-tester reports and what the
core developer(s) know. In turn, this means that the core developers' time
tends to be well conserved, even with many collaborators.

Another characteristic of the open-source method that conserves developer time
is the communication structure of typical open-source projects. Above I used
the term "core developer"; this reflects a distinction between the project core
(typically quite small; a single core developer is common, and one to three is
typical) and the project halo of beta-testers and available contributors (which
often numbers in the hundreds).

The fundamental problem that traditional software-development organization
addresses is Brook's Law: "Adding more programmers to a late project makes it
later." More generally, Brooks's Law predicts that the complexity and
communication costs of a project rise with the square of the number of
developers, while work done only rises linearly.

Brooks's Law is founded on experience that bugs tend strongly to cluster at the
interfaces between code written by different people, and that
communications/coordination overhead on a project tends to rise with the number
of interfaces between human beings. Thus, problems scale with the number of
communications paths between developers, which scales as the square of the
humber of developers (more precisely, according to the formula N*(N - 1)/2
where N is the number of developers).

The Brooks's Law analysis (and the resulting fear of large numbers in
development groups) rests on a hidden assummption: that the communications
structure of the project is necessarily a complete graph, that everybody talks
to everybody else. But on open-source projects, the halo developers work on
what are in effect separable parallel subtasks and interact with each other
very little; code changes and bug reports stream through the core group, and
only within that small core group do we pay the full Brooksian overhead. [SU]

There are are still more reasons that source-code–level bug reporting tends to
be very efficient. They center around the fact that a single error can often
have multiple possible symptoms, manifesting differently depending on details
of the user's usage pattern and environment. Such errors tend to be exactly the
sort of complex and subtle bugs (such as dynamic-memory-management errors or
nondeterministic interrupt-window artifacts) that are hardest to reproduce at
will or to pin down by static analysis, and which do the most to create
long-term problems in software.

A tester who sends in a tentative source-code–level characterization of such a
multi-symptom bug (e.g. "It looks to me like there's a window in the signal
handling near line 1250" or "Where are you zeroing that buffer?") may give a
developer, otherwise too close to the code to see it, the critical clue to a
half-dozen disparate symptoms. In cases like this, it may be hard or even
impossible to know which externally-visible misbehaviour was caused by
precisely which bug—but with frequent releases, it's unnecessary to know. Other
collaborators will be likely to find out quickly whether their bug has been
fixed or not. In many cases, source-level bug reports will cause misbehaviours
to drop out without ever having been attributed to any specific fix.

Complex multi-symptom errors also tend to have multiple trace paths from
surface symptoms back to the actual bug. Which of the trace paths a given
developer or tester can chase may depend on subtleties of that person's
environment, and may well change in a not obviously deterministic way over
time. In effect, each developer and tester samples a semi-random set of the
program's state space when looking for the etiology of a symptom. The more
subtle and complex the bug, the less likely that skill will be able to
guarantee the relevance of that sample.

For simple and easily reproducible bugs, then, the accent will be on the "semi"
rather than the "random"; debugging skill and intimacy with the code and its
architecture will matter a lot. But for complex bugs, the accent will be on the
"random". Under these circumstances many people running traces will be much
more effective than a few people running traces sequentially—even if the few
have a much higher average skill level.

This effect will be greatly amplified if the difficulty of following trace
paths from different surface symptoms back to a bug varies significantly in a
way that can't be predicted by looking at the symptoms. A single developer
sampling those paths sequentially will be as likely to pick a difficult trace
path on the first try as an easy one. On the other hand, suppose many people
are trying trace paths in parallel while doing rapid releases. Then it is
likely one of them will find the easiest path immediately, and nail the bug in
a much shorter time. The project maintainer will see that, ship a new release,
and the other people running traces on the same bug will be able to stop before
having spent too much time on their more difficult traces [RJ].

1~ When Is a Rose Not a Rose?

Having studied Linus's behavior and formed a theory about why it was
successful, I made a conscious decision to test this theory on my new
(admittedly much less complex and ambitious) project.

But the first thing I did was reorganize and simplify popclient a lot. Carl
Harris's implementation was very sound, but exhibited a kind of unnecessary
complexity common to many C programmers. He treated the code as central and the
data structures as support for the code. As a result, the code was beautiful
but the data structure design ad-hoc and rather ugly (at least by the high
standards of this veteran LISP hacker).

I had another purpose for rewriting besides improving the code and the data
structure design, however. That was to evolve it into something I understood
completely. It's no fun to be responsible for fixing bugs in a program you
don't understand.

For the first month or so, then, I was simply following out the implications of
Carl's basic design. The first serious change I made was to add IMAP support. I
did this by reorganizing the protocol machines into a generic driver and three
method tables (for POP2, POP3, and IMAP). This and the previous changes
illustrate a general principle that's good for programmers to keep in mind,
especially in languages like C that don't naturally do dynamic typing:

_1 9. Smart data structures and dumb code works a lot better than the other way
around.

Brooks, Chapter 9: "Show me your flowchart and conceal your tables, and I shall
continue to be mystified. Show me your tables, and I won't usually need your
flowchart; it'll be obvious." Allowing for thirty years of
terminological/cultural shift, it's the same point.

At this point (early September 1996, about six weeks from zero) I started
thinking that a name change might be in order—after all, it wasn't just a POP
client any more. But I hesitated, because there was as yet nothing genuinely
new in the design. My version of popclient had yet to develop an identity of
its own.

That changed, radically, when popclient learned how to forward fetched mail to
the SMTP port. I'll get to that in a moment. But first: I said earlier that I'd
decided to use this project to test my theory about what Linus Torvalds had
done right. How (you may well ask) did I do that? In these ways:

_* I released early and often (almost never less often than every ten days;
during periods of intense development, once a day).

_* I grew my beta list by adding to it everyone who contacted me about
fetchmail.

_* I sent chatty announcements to the beta list whenever I released,
encouraging people to participate.

_* And I listened to my beta-testers, polling them about design decisions and
stroking them whenever they sent in patches and feedback.

The payoff from these simple measures was immediate. From the beginning of the
project, I got bug reports of a quality most developers would kill for, often
with good fixes attached. I got thoughtful criticism, I got fan mail, I got
intelligent feature suggestions. Which leads to:

_1 10. If you treat your beta-testers as if they're your most valuable
resource, they will respond by becoming your most valuable resource.

One interesting measure of fetchmail's success is the sheer size of the project
beta list, fetchmail-friends. At the time of latest revision of this paper
(November 2000) it has 287 members and is adding two or three a week.

Actually, when I revised in late May 1997 I found the list was beginning to
lose members from its high of close to 300 for an interesting reason. Several
people have asked me to unsubscribe them because fetchmail is working so well
for them that they no longer need to see the list traffic! Perhaps this is part
of the normal life-cycle of a mature bazaar-style project.

1~ Popclient becomes Fetchmail

The real turning point in the project was when Harry Hochheiser sent me his
scratch code for forwarding mail to the client machine's SMTP port. I realized
almost immediately that a reliable implementation of this feature would make
all the other mail delivery modes next to obsolete.

For many weeks I had been tweaking fetchmail rather incrementally while feeling
like the interface design was serviceable but grubby—inelegant and with too
many exiguous options hanging out all over. The options to dump fetched mail to
a mailbox file or standard output particularly bothered me, but I couldn't
figure out why.

(If you don't care about the technicalia of Internet mail, the next two
paragraphs can be safely skipped.)

What I saw when I thought about SMTP forwarding was that popclient had been
trying to do too many things. It had been designed to be both a mail transport
agent (MTA) and a local delivery agent (MDA). With SMTP forwarding, it could
get out of the MDA business and be a pure MTA, handing off mail to other
programs for local delivery just as sendmail does.

Why mess with all the complexity of configuring a mail delivery agent or
setting up lock-and-append on a mailbox when port 25 is almost guaranteed to be
there on any platform with TCP/IP support in the first place? Especially when
this means retrieved mail is guaranteed to look like normal sender-initiated
SMTP mail, which is really what we want anyway.

(Back to a higher level....)

Even if you didn't follow the preceding technical jargon, there are several
important lessons here. First, this SMTP-forwarding concept was the biggest
single payoff I got from consciously trying to emulate Linus's methods. A user
gave me this terrific idea—all I had to do was understand the implications.

_1 11. The next best thing to having good ideas is recognizing good ideas from
your users. Sometimes the latter is better.

Interestingly enough, you will quickly find that if you are completely and
self-deprecatingly truthful about how much you owe other people, the world at
large will treat you as though you did every bit of the invention yourself and
are just being becomingly modest about your innate genius. We can all see how
well this worked for Linus!

(When I gave my talk at the first Perl Conference in August 1997, hacker
extraordinaire Larry Wall was in the front row. As I got to the last line above
he called out, religious-revival style, "Tell it, tell it, brother!". The whole
audience laughed, because they knew this had worked for the inventor of Perl,
too.)

After a very few weeks of running the project in the same spirit, I began to
get similar praise not just from my users but from other people to whom the
word leaked out. I stashed away some of that email; I'll look at it again
sometime if I ever start wondering whether my life has been worthwhile :-).

But there are two more fundamental, non-political lessons here that are general
to all kinds of design.

_1 12. Often, the most striking and innovative solutions come from realizing
that your concept of the problem was wrong.

I had been trying to solve the wrong problem by continuing to develop popclient
as a combined MTA/MDA with all kinds of funky local delivery modes. Fetchmail's
design needed to be rethought from the ground up as a pure MTA, a part of the
normal SMTP-speaking Internet mail path.

When you hit a wall in development—when you find yourself hard put to think
past the next patch—it's often time to ask not whether you've got the right
answer, but whether you're asking the right question. Perhaps the problem needs
to be reframed.

Well, I had reframed my problem. Clearly, the right thing to do was (1) hack
SMTP forwarding support into the generic driver, (2) make it the default mode,
and (3) eventually throw out all the other delivery modes, especially the
deliver-to-file and deliver-to-standard-output options.

I hesitated over step 3 for some time, fearing to upset long-time popclient
users dependent on the alternate delivery mechanisms. In theory, they could
immediately switch to .forward files or their non-sendmail equivalents to get
the same effects. In practice the transition might have been messy.

But when I did it, the benefits proved huge. The cruftiest parts of the driver
code vanished. Configuration got radically simpler—no more grovelling around
for the system MDA and user's mailbox, no more worries about whether the
underlying OS supports file locking.

Also, the only way to lose mail vanished. If you specified delivery to a file
and the disk got full, your mail got lost. This can't happen with SMTP
forwarding because your SMTP listener won't return OK unless the message can be
delivered or at least spooled for later delivery.

Also, performance improved (though not so you'd notice it in a single run).
Another not insignificant benefit of this change was that the manual page got a
lot simpler.

Later, I had to bring delivery via a user-specified local MDA back in order to
allow handling of some obscure situations involving dynamic SLIP. But I found a
much simpler way to do it.

The moral? Don't hesitate to throw away superannuated features when you can do
it without loss of effectiveness. Antoine de Saint-Exupéry (who was an aviator
and aircraft designer when he wasn't authoring classic children's books) said:

_1 13. "Perfection (in design) is achieved not when there is nothing more to
add, but rather when there is nothing more to take away."

When your code is getting both better and simpler, that is when you know it's
right. And in the process, the fetchmail design acquired an identity of its
own, different from the ancestral popclient.

It was time for the name change. The new design looked much more like a dual of
sendmail than the old popclient had; both are MTAs, but where sendmail pushes
then delivers, the new popclient pulls then delivers. So, two months off the
blocks, I renamed it fetchmail.

There is a more general lesson in this story about how SMTP delivery came to
fetchmail. It is not only debugging that is parallelizable; development and (to
a perhaps surprising extent) exploration of design space is, too. When your
development mode is rapidly iterative, development and enhancement may become
special cases of debugging—fixing `bugs of omission' in the original
capabilities or concept of the software.

Even at a higher level of design, it can be very valuable to have lots of
co-developers random-walking through the design space near your product.
Consider the way a puddle of water finds a drain, or better yet how ants find
food: exploration essentially by diffusion, followed by exploitation mediated
by a scalable communication mechanism. This works very well; as with Harry
Hochheiser and me, one of your outriders may well find a huge win nearby that
you were just a little too close-focused to see.

1~ 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 that 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.

Andy Tanenbaum had the original idea to build a simple native Unix for IBM PCs,
for use as a teaching tool (he called it Minix). 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 RFC 822 address 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:

_1 14. Any tool should be useful in the expected way, but a truly great tool
lends itself to uses you never expected.

The unexpected use for multidrop fetchmail is to run mailing lists with the
list kept, and alias expansion done, on the client side of the Internet
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
(Multipurpose Internet Mail Extensions) operation. This was pretty easy to do,
because I had been careful to keep the code 8-bit clean (that is, to not press
the 8th bit, unused in the ASCII character set, into service to carry
information within the program). Not because I anticipated the demand for this
feature, but rather in obedience to another rule:

_1 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 the MIME standard (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.

1~ 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. Nontechnical
readers can safely skip this section.

The rc (control) 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 normally avoiding 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 remain, 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 bad effect in a lot of so-called "fourth generation"
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 broader lesson here:

_1 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:

_1 17. A security system is only as secure as its secret. Beware of
pseudo-secrets.

1~ Necessary Preconditions for the Bazaar Style

Early reviewers and test audiences for this essay 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 [IN].
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 (a) run, and (b) 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 that 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
popclient (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 through
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 the coordinator 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 essay 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 to avoid this 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 open-source 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.

1~ The Social Context of Open-Source 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:

_1 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. As we've
seen previously, 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. Brooks's Law has been widely regarded as a truism. But we've
examined in this essay an number of ways in which the process of open-source
development falsifies the assumptionms behind it—and, empirically, if Brooks's
Law were the whole picture Linux would be impossible.

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. (Recently, Kent Beck's `extreme programming' technique of deploying
coders in pairs looking over one anothers' shoulders might be seen as an
attempt to force this effect.)

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 bazaar method, by harnessing the full power of the "egoless programming"
effect, strongly mitigates the effect of Brooks's Law. The principle behind
Brooks's Law is not repealed, but given a large developer population and cheap
communications its effects can be swamped by competing nonlinearities that are
not otherwise visible. This resembles the relationship between Newtonian and
Einsteinian physics—the older system is still valid at low energies, but if you
push mass and velocity high enough you get surprises like nuclear explosions or
Linux.

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 [EGCS]). That is, 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 feedback exploring the
design space, code contributions, bug-spotting, and other improvements come
from from hundreds (perhaps thousands) 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 and LCS labs, UC Berkeley—these became the home of innovations that are
legendary and still potent.

Linux was the first project for which a conscious and successful effort to use
the entire world as its talent pool was made. 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 access 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 Pyotr Alexeyvich Kropotkin's Memoirs of a
Revolutionist to good effect on this subject:

_1 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.[SP]

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
have achieved. 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 has long explicitly recognized "egoboo" (ego-boosting, or 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 a 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 documentation? 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:

_1 19: Provided the development coordinator has a communications 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 open-source 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 open-source
software will belong to people who start from individual vision and brilliance,
then amplify it through the effective construction of voluntary communities of
interest.

Perhaps this is not only the future of open-source software. No closed-source
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 200 (1999: 600,
2000: 800) people who have contributed to fetchmail!

Perhaps in the end the open-source 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 closed-source
world cannot win an evolutionary arms race with open-source communities that
can put orders of magnitude more skilled time into a problem.

1~ On Management and the Maginot Line

The original Cathedral and Bazaar paper of 1997 ended with the vision
above—that of happy networked hordes of programmer/anarchists outcompeting and
overwhelming the hierarchical world of conventional closed software.

A good many skeptics weren't convinced, however; and the questions they raise
deserve a fair engagement. Most of the objections to the bazaar argument come
down to the claim that its proponents have underestimated the
productivity-multiplying effect of conventional management.

Traditionally-minded software-development managers often object that the
casualness with which project groups form and change and dissolve in the
open-source world negates a significant part of the apparent advantage of
numbers that the open-source community has over any single closed-source
developer. They would observe that in software development it is really
sustained effort over time and the degree to which customers can expect
continuing investment in the product that matters, not just how many people
have thrown a bone in the pot and left it to simmer.

There is something to this argument, to be sure; in fact, I have developed the
idea that expected future service value is the key to the economics of software
production in the essay The Magic Cauldron.

But this argument also has a major hidden problem; its implicit assumption that
open-source development cannot deliver such sustained effort. In fact, there
have been open-source projects that maintained a coherent direction and an
effective maintainer community over quite long periods of time without the
kinds of incentive structures or institutional controls that conventional
management finds essential. The development of the GNU Emacs editor is an
extreme and instructive example; it has absorbed the efforts of hundreds of
contributors over 15 years into a unified architectural vision, despite high
turnover and the fact that only one person (its author) has been continuously
active during all that time. No closed-source editor has ever matched this
longevity record.

This suggests a reason for questioning the advantages of conventionally-managed
software development that is independent of the rest of the arguments over
cathedral vs. bazaar mode. If it's possible for GNU Emacs to express a
consistent architectural vision over 15 years, or for an operating system like
Linux to do the same over 8 years of rapidly changing hardware and platform
technology; and if (as is indeed the case) there have been many
well-architected open-source projects of more than 5 years duration -- then we
are entitled to wonder what, if anything, the tremendous overhead of
conventionally-managed development is actually buying us.

Whatever it is certainly doesn't include reliable execution by deadline, or on
budget, or to all features of the specification; it's a rare `managed' project
that meets even one of these goals, let alone all three. It also does not
appear to be ability to adapt to changes in technology and economic context
during the project lifetime, either; the open-source community has proven far
more effective on that score (as one can readily verify, for example, by
comparing the 30-year history of the Internet with the short half-lives of
proprietary networking technologies—or the cost of the 16-bit to 32-bit
transition in Microsoft Windows with the nearly effortless upward migration of
Linux during the same period, not only along the Intel line of development but
to more than a dozen other hardware platforms, including the 64-bit Alpha as
well).

One thing many people think the traditional mode buys you is somebody to hold
legally liable and potentially recover compensation from if the project goes
wrong. But this is an illusion; most software licenses are written to disclaim
even warranty of merchantability, let alone performance—and cases of successful
recovery for software nonperformance are vanishingly rare. Even if they were
common, feeling comforted by having somebody to sue would be missing the point.
You didn't want to be in a lawsuit; you wanted working software.

So what is all that management overhead buying?

In order to understand that, we need to understand what software development
managers believe they do. A woman I know who seems to be very good at this job
says software project management has five functions:

_* To define goals and keep everybody pointed in the same direction

_* To monitor and make sure crucial details don't get skipped

_* To motivate people to do boring but necessary drudgework

_* To organize the deployment of people for best productivity

_* To marshal resources needed to sustain the project

Apparently worthy goals, all of these; but under the open-source model, and in
its surrounding social context, they can begin to seem strangely irrelevant.
We'll take them in reverse order.

My friend reports that a lot of resource marshalling is basically defensive;
once you have your people and machines and office space, you have to defend
them from peer managers competing for the same resources, and from higher-ups
trying to allocate the most efficient use of a limited pool.

But open-source developers are volunteers, self-selected for both interest and
ability to contribute to the projects they work on (and this remains generally
true even when they are being paid a salary to hack open source.) The volunteer
ethos tends to take care of the `attack' side of resource-marshalling
automatically; people bring their own resources to the table. And there is
little or no need for a manager to `play defense' in the conventional sense.

Anyway, in a world of cheap PCs and fast Internet links, we find pretty
consistently that the only really limiting resource is skilled attention.
Open-source projects, when they founder, essentially never do so for want of
machines or links or office space; they die only when the developers themselves
lose interest.

That being the case, it's doubly important that open-source hackers organize
themselves for maximum productivity by self-selection—and the social milieu
selects ruthlessly for competence. My friend, familiar with both the
open-source world and large closed projects, believes that open source has been
successful partly because its culture only accepts the most talented 5% or so
of the programming population. She spends most of her time organizing the
deployment of the other 95%, and has thus observed first-hand the well-known
variance of a factor of one hundred in productivity between the most able
programmers and the merely competent.

The size of that variance has always raised an awkward question: would
individual projects, and the field as a whole, be better off without more than
50% of the least able in it? Thoughtful managers have understood for a long
time that if conventional software management's only function were to convert
the least able from a net loss to a marginal win, the game might not be worth
the candle.

The success of the open-source community sharpens this question considerably,
by providing hard evidence that it is often cheaper and more effective to
recruit self-selected volunteers from the Internet than it is to manage
buildings full of people who would rather be doing something else.

Which brings us neatly to the question of motivation. An equivalent and
often-heard way to state my friend's point is that traditional development
management is a necessary compensation for poorly motivated programmers who
would not otherwise turn out good work.

This answer usually travels with a claim that the open-source community can
only be relied on only to do work that is `sexy' or technically sweet; anything
else will be left undone (or done only poorly) unless it's churned out by
money-motivated cubicle peons with managers cracking whips over them. I address
the psychological and social reasons for being skeptical of this claim in
Homesteading the Noosphere. For present purposes, however, I think it's more
interesting to point out the implications of accepting it as true.

If the conventional, closed-source, heavily-managed style of software
development is really defended only by a sort of Maginot Line of problems
conducive to boredom, then it's going to remain viable in each individual
application area for only so long as nobody finds those problems really
interesting and nobody else finds any way to route around them. Because the
moment there is open-source competition for a `boring' piece of software,
customers are going to know that it was finally tackled by someone who chose
that problem to solve because of a fascination with the problem itself—which,
in software as in other kinds of creative work, is a far more effective
motivator than money alone.

Having a conventional management structure solely in order to motivate, then,
is probably good tactics but bad strategy; a short-term win, but in the longer
term a surer loss.

So far, conventional development management looks like a bad bet now against
open source on two points (resource marshalling, organization), and like it's
living on borrowed time with respect to a third (motivation). And the poor
beleaguered conventional manager is not going to get any succour from the
monitoring issue; the strongest argument the open-source community has is that
decentralized peer review trumps all the conventional methods for trying to
ensure that details don't get slipped.

Can we save defining goals as a justification for the overhead of conventional
software project management? Perhaps; but to do so, we'll need good reason to
believe that management committees and corporate roadmaps are more successful
at defining worthy and widely shared goals than the project leaders and tribal
elders who fill the analogous role in the open-source world.

That is on the face of it a pretty hard case to make. And it's not so much the
open-source side of the balance (the longevity of Emacs, or Linus Torvalds's
ability to mobilize hordes of developers with talk of "world domination") that
makes it tough. Rather, it's the demonstrated awfulness of conventional
mechanisms for defining the goals of software projects.

One of the best-known folk theorems of software engineering is that 60% to 75%
of conventional software projects either are never completed or are rejected by
their intended users. If that range is anywhere near true (and I've never met a
manager of any experience who disputes it) then more projects than not are
being aimed at goals that are either (a) not realistically attainable, or (b)
just plain wrong.

This, more than any other problem, is the reason that in today's software
engineering world the very phrase "management committee" is likely to send
chills down the hearer's spine—even (or perhaps especially) if the hearer is a
manager. The days when only programmers griped about this pattern are long
past; Dilbert cartoons hang over executives' desks now.

Our reply, then, to the traditional software development manager, is simple—if
the open-source community has really underestimated the value of conventional
management, why do so many of you display contempt for your own process?

Once again the example of the open-source community sharpens this question
considerably—because we have fun doing what we do. Our creative play has been
racking up technical, market-share, and mind-share successes at an astounding
rate. We're proving not only that we can do better software, but that joy is an
asset.

Two and a half years after the first version of this essay, the most radical
thought I can offer to close with is no longer a vision of an
open-source–dominated software world; that, after all, looks plausible to a lot
of sober people in suits these days.

Rather, I want to suggest what may be a wider lesson about software, (and
probably about every kind of creative or professional work). Human beings
generally take pleasure in a task when it falls in a sort of optimal-challenge
zone; not so easy as to be boring, not too hard to achieve. A happy programmer
is one who is neither underutilized nor weighed down with ill-formulated goals
and stressful process friction. Enjoyment predicts efficiency.

Relating to your own work process with fear and loathing (even in the
displaced, ironic way suggested by hanging up Dilbert cartoons) should
therefore be regarded in itself as a sign that the process has failed. Joy,
humor, and playfulness are indeed assets; it was not mainly for the
alliteration that I wrote of "happy hordes" above, and it is no mere joke that
the Linux mascot is a cuddly, neotenous penguin.

It may well turn out that one of the most important effects of open source's
success will be to teach us that play is the most economically efficient mode
of creative work.

1~ Epilog: Netscape Embraces the Bazaar

It's a strange feeling to realize you're helping make history....

On January 22 1998, approximately seven months after I first published The
Cathedral and the Bazaar, Netscape Communications, Inc. announced plans to give
away the source for Netscape Communicator. I had had no clue this was going to
happen before the day of the announcement.

Eric Hahn, executive vice president and chief technology officer at Netscape,
emailed me shortly afterwards as follows: "On behalf of everyone at Netscape, I
want to thank you for helping us get to this point in the first place. Your
thinking and writings were fundamental inspirations to our decision."

The following week I flew out to Silicon Valley at Netscape's invitation for a
day-long strategy conference (on 4 Feb 1998) with some of their top executives
and technical people. We designed Netscape's source-release strategy and
license together.

A few days later I wrote the following:

_1 Netscape is about to provide us with a large-scale, real-world test of the
bazaar model in the commercial world. The open-source culture now faces a
danger; if Netscape's execution doesn't work, the open-source concept may be so
discredited that the commercial world won't touch it again for another decade.

_1 On the other hand, this is also a spectacular opportunity. Initial reaction
to the move on Wall Street and elsewhere has been cautiously positive. We're
being given a chance to prove ourselves, too. If Netscape regains substantial
market share through this move, it just may set off a long-overdue revolution
in the software industry.

_1 The next year should be a very instructive and interesting time.

And indeed it was. As I write in mid-2000, the development of what was later
named Mozilla has been only a qualified success. It achieved Netscape's
original goal, which was to deny Microsoft a monopoly lock on the browser
market. It has also achieved some dramatic successes (notably the release of
the next-generation Gecko rendering engine).

However, it has not yet garnered the massive development effort from outside
Netscape that the Mozilla founders had originally hoped for. The problem here
seems to be that for a long time the Mozilla distribution actually broke one of
the basic rules of the bazaar model; it didn't ship with something potential
contributors could easily run and see working. (Until more than a year after
release, building Mozilla from source required a license for the proprietary
Motif library.)

Most negatively (from the point of view of the outside world) the Mozilla group
didn't ship a production-quality browser for two and a half years after the
project launch—and in 1999 one of the project's principals caused a bit of a
sensation by resigning, complaining of poor management and missed
opportunities. "Open source," he correctly observed, "is not magic pixie dust."

And indeed it is not. The long-term prognosis for Mozilla looks dramatically
better now (in November 2000) than it did at the time of Jamie Zawinski's
resignation letter—in the last few weeks the nightly releases have finally
passed the critical threshold to production usability. But Jamie was right to
point out that going open will not necessarily save an existing project that
suffers from ill-defined goals or spaghetti code or any of the software
engineering's other chronic ills. Mozilla has managed to provide an example
simultaneously of how open source can succeed and how it could fail.

In the mean time, however, the open-source idea has scored successes and found
backers elsewhere. Since the Netscape release we've seen a tremendous explosion
of interest in the open-source development model, a trend both driven by and
driving the continuing success of the Linux operating system. The trend Mozilla
touched off is continuing at an accelerating rate.

% Thyrsus Enterprises <esr@thyrsus.com>

% http://www.catb.org/~esr/writings/cathedral-bazaar/

% This is version 3.0

% $Date: 2008/12/10 18:25:30 $
% Revision History
% Revision 1.57	11 September 2000	esr
% New major section ``How Many Eyeballs Tame Complexity".
% Revision 1.52	28 August 2000	esr
% MATLAB is a reinforcing parallel to Emacs. Corbatoó & Vyssotsky got it in 1965.
% Revision 1.51	24 August 2000	esr
% First DocBook version. Minor updates to Fall 2000 on the time-sensitive material.
% Revision 1.49	5 May 2000	esr
% Added the HBS note on deadlines and scheduling.
% Revision 1.51	31 August 1999	esr
% This the version that O'Reilly printed in the first edition of the book.
% Revision 1.45	8 August 1999	esr
% Added the endnotes on the Snafu Principle, (pre)historical examples of bazaar development, and originality in the bazaar.
% Revision 1.44	29 July 1999	esr
% Added the ``On Management and the Maginot Line" section, some insights about the usefulness of bazaars for exploring design space, and substantially improved the Epilog.
% Revision 1.40	20 Nov 1998	esr
% Added a correction of Brooks based on the Halloween Documents.
% Revision 1.39	28 July 1998	esr
% I removed Paul Eggert's 'graph on GPL vs. bazaar in response to cogent aguments from RMS on
% Revision 1.31	February 10 1998 	esr
% Added ``Epilog: Netscape Embraces the Bazaar!"
% Revision 1.29	February 9 1998	esr
% Changed ``free software" to ``open source".
% Revision 1.27	18 November 1997	esr
% Added the Perl Conference anecdote.
% Revision 1.20	7 July 1997	esr
% Added the bibliography.
% Revision 1.16	21 May 1997	esr

% First official presentation at the Linux Kongress.